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Effect of root-zone flooding on mycorrhizal and non-mycorrhizal peach ( Prunus persica Batsch) seedlings
Abstract
The effect of root-zone flooding on mycorrhizal and non-mycorrhizal peach seedlings growing in a low P medium was examined. Mycorrhizal seedlings showed relatively faster development prior to flooding and recorded significantly higher concentrations of shoot P, K and Zn and biomass yield. Ethanol accumulation was significantly higher in the taproots of non-mycorrhizal as compared to mycorrhizal plants after 3 days of flooding. A more rapid decline in plant health was also observed in non-mycorrhizal as compared to mycorrhizal seedlings. The presence or absence of the fungal partner led to significant difference in the ratio of roots that remained viable after extended flooding. Therefore, it is clear that arbuscular mycorrhizal (AM) infection confers limited tolerance to flooding on peach seedlings. This could be due to improved plant nutrition, the suppression of ethanol accumulation in roots and the extension of the duration of root activity in a flooded environment.
... Inoculating with Glomus intraradices increased the P plant Pterocarpus officinalis (Fougnies et al. 2007). Similar results were reported on the Panicum hemitomon and Leersia hexandra plants (Miller and Sharitz 2000;Ipsilantis and Sylvia 2007), Typha latifolia (Ipsilantis and Sylvia 2007;Dunham et al. 2003), Prunus persica (Ruto et al. 2002), Vallisneria americana (Wigand and Stevenson 1997), Ranunculus sp. (Tanner and Clayton 1985a, b), and Oryza sativa (Secilia and Bagyaraj 1994;Solaiman and Hirata 1996). ...
... (Tanner and Clayton 1985a, b), and Oryza sativa (Secilia and Bagyaraj 1994;Solaiman and Hirata 1996). In addition to P, AMF also increase the N plant Aster tripolium (Neto et al. 2006), T. latifolia (Ipsilantis and Sylvia 2007;Dunham et al. 2003), Prunus persica (Ruto et al. 2002), and Casuarina equisetifolia (Osundina 1998). ...
... Poncirus trifoliata (Zou et al. 2014); and colonization by Gigaspora margarita increased the growth of Carex tribuloides, Phalaris arundinacea, Rumex orbiculatus (Fraser and Feinstein 2005), Casuarina equisetifolia (Osundina 1998), T. latifolia (Dunham et al. 2003), rice Bagyaraj 1992, 1994), and Sclerocarya birrea (Muok and Ishii 2006). Gigaspora margarita too promoted growth and biomass of Prunus persica before 12 weeks of stagnancy (Ruto et al. 2002). There was an increase in plant biomass of inoculated Nyssa sylvatica (Marshal and Pattullo 1981), Phragmites australis (Dolinar and Gaberščk 2010), and rice (Secilia and Bagyaraj 1994). ...
Waterlogging is an environmental factor that negatively affects the survival, growth, and development of plants. The same effect also occurs against the presence of fungi in aquatic ecosystems such as arbuscular mycorrhizal fungi (AMF). AMF has been reported as having a symbiosis with various types of aquatic and wetland plants. The existence of AMF has also been found in various types of both permanent and seasonal wetlands including lake and stream flooding, mangrove, salt marsh, river, riparian and floodplain, peat swamp forest, and other wetlands. Glomeraceae is a family with most types, and some of them are found in all types of wetlands, for example, Funneliformis mosseae, Rhizophagus fasciculatus, and F. geosporus. Colonization, spore density, species richness, and diversity of AMF in a puddle condition are influenced by many factors, including the availability of oxygen, seasonal changes, the availability of P, water depth, type of AMF, and other types of vegetation. The AMF presence can promote the growth and biomass of plants through improved nutritional status and potential adjustment and may accelerate the succession in early pioneer vegetation in some types of aquatic habitat.
... As a result, fruit crops grown in waterlogging have bad root hydraulic conductivity, stomatal aperture, photosynthetic capacity, and nutrient availability (Ashraf, 2012;Yin et al., 2012). Earlier studies indicated that AM citrus and peach plants presented greater plant growth performance and plant biomass than non-AM plants under waterlogging stress (Rutto et al., 2002;Wu et al., 2013;Zou et al., 2014). Rutto et al. (2002) found that AMF (G. ...
... Earlier studies indicated that AM citrus and peach plants presented greater plant growth performance and plant biomass than non-AM plants under waterlogging stress (Rutto et al., 2002;Wu et al., 2013;Zou et al., 2014). Rutto et al. (2002) found that AMF (G. margarita) could significantly reduce ethanol accumulation in peach (P. ...
... An association between AMF and host plants occurs in most fruit trees and may occur naturally in the nursery or when transplanted in the orchard (Calvet et al., 2004). Inoculation with Glomus intraradices (now known as Rhizophagous irregularis (Formey et al., 2012) has increased growth in cherry rootstocks (Rutto et al., 2002). Sweet cherry fruit is sensitive to changes in water uptake, and heavy rainfall late in the summer growing season when the fruit is maturing can result in fruit damage through cracking arising from vascular uptake of water. ...
... The effect of R. irregularis colonization on establishment of sweet cherry from cuttings was explored. It was hypothesized that sweet cherry plants would have greater survival and establish more rapidly from cuttings inoculated with AMF than those not inoculated (Gosling et al., 2006;Rutto et al., 2002). ...
... Dickin and Wright (2008) reported a decrease in total root length, but not in the final depth of the root system in waterlogged Triticum aestivum plants. Also, the effect of continued root-zone flooding on Prunus persica seedlings which, among Prunus species, are quite sensitive to flooding, was examined by Rutto et al. (2002). The visual qualities of plants deteriorated with flooding, with complete defoliation occurring over a period of 3 weeks. ...
... This was expressed as an increase in root FW and a higher percentage of viable root mass after flooding. AMF inoculation further suppressed the accumulation of the toxic products associated with anaerobic respiration, such as ethanol (Rutto et al., 2002). Moreover, Asparagus officinalis plants were reported to exhibit improved tolerance to high temperature stress after AMF infection (Matsubara et al., 2000). ...
An experiment was carried out to assess the influence of two substrates (coconut fiber [CC] and urea formaldehyde foam [UF]) on the agronomical and physiological behavior of potted bay laurel (Laurus nobilis L.) irrigated with saline recycled wastewater (RW). Fresh water (FW) was used as a control. Roots and leaves grew differently in each growing medium. With FW the plants cultivated on UF had higher root growth than those cultivated in CC, while no significant differences were observed in root biomass under RW. The plants grown in UF decreased their leaf area by about 20% compared with those grown in CC regardless of water quality. Water consumption in UF was lower than in CC, while both the leaching fraction and the electrical conductivity (EC) of the leachate were higher in UF with the two types of water; in contrast, the pore EC in UF was lower than in CC. The plants cultivated in CC had a higher photosynthesis rate and higher stomatal conductance than in UF under FW; but under RW the photosynthesis rate was similar in the two substrates, while stomatal conductance was higher in UF. When RW was applied, the leaf Cl-, Na+ and B3+ contents in CC were higher than in UF. Our findings indicate that growth and development response to RW was better in plants grown in CC than in UF. So, RW and UF, together, resulted in a fall in ornamental quality and therefore in the commercial value of the plants.
... Dickin and Wright (2008) reported a decrease in total root length, but not in the final depth of the root system in waterlogged Triticum aestivum plants. Also, the effect of continued root-zone flooding on Prunus persica seedlings which, among Prunus species, are quite sensitive to flooding, was examined by Rutto et al. (2002). The visual qualities of plants deteriorated with flooding, with complete defoliation occurring over a period of 3 weeks. ...
... This was expressed as an increase in root FW and a higher percentage of viable root mass after flooding. AMF inoculation further suppressed the accumulation of the toxic products associated with anaerobic respiration, such as ethanol (Rutto et al., 2002). Moreover, Asparagus officinalis plants were reported to exhibit improved tolerance to high temperature stress after AMF infection (Matsubara et al., 2000). ...
Roots usually suffer greater exposure to multiple abiotic stresses than shoots. Therefore, the root system can be as affected, or even more affected, than the aerial parts of a plant by such stresses. Despite this, the influence of abiotic stresses on root development has been considerably less studied than on shoots because of limited accessibility for root observations.This work reviews the recent scientific literature on root development and the performance of root systems in horticultural plants growing under abiotic stresses such as drought, waterlogging, salinity, extreme temperature, low illumination, nutrient deficiency or excess, heavy metals, elevated atmospheric CO2, and mechanical restrictions. Changes in the shoot:root ratio are often observed when plants are subjected to various stresses. Thus, a redistribution of metabolites from shoots to roots is frequently observed under drought, salt, or sub-optimal temperature stress, as well as during some nutrient deficiencies, or elevated levels
... Mycorrhizal Casuarina equisetifolia seedlings were better adapted to flooding than noninoculated seedlings because the greater development of adventitious roots and lenticels increased oxygen availability and therefore AM colonization of plants (Osundina 1998). Accumulation of acetaldehyde, a highly toxic intermediate in ethanol formation, in roots was suggested as the main factor responsible for flooding injury in flood-sensitive species (Osundina 1998; Rutto et al. 2002). Adventitious roots and lenticels may contribute to root aeration and ethanol removal in flood-tolerant species (Crawford 1982; Liao and Lin 2001). ...
... Adventitious roots and lenticels may contribute to root aeration and ethanol removal in flood-tolerant species (Crawford 1982; Liao and Lin 2001). AM colonization also contributed to suppress ethanol accumulation in the roots of peach seedlings (Rutto et al. 2002). Some studies have also suggested that once AM colonization has taken place, the AM association can endure prolonged exposure to flooding (Miller and Sharitz 2000; Neto et al. 2006). ...
P. officinalis is the dominant wetland tree species of the seasonally flooded swamp forests in Guadeloupe, the Lesser Antilles (Muller et
al., 2006). The establishment and population maintenance of P. officinalis are affected by the variations in salinity and hydrology as well as differences in soil microtopography in swamp forests
(Eusse and Aide, 1999). This tree species forms bradyrhizobial nodules and arbuscular mycorrhizas (AMs) on lateral roots of
buttresses both above and below the water table (Bâ et al., 2004; Saint-Etienne et al., 2006). We hypothesized that nodulation
and AMs could improve the performance of P. officinalis seedlings under flooding. Two questions were addressed. First, are P. officinalis seedlings adapted to flooding? Second, do AMs and N2-fixing nodules increase the performance of P. officinalis seedlings under flooding?
... Dickin and Wright (2008) reported a decrease in total root length, but not in the final depth of the root system in waterlogged Triticum aestivum plants. Also, the effect of continued root-zone flooding on Prunus persica seedlings which, among Prunus species, are quite sensitive to flooding, was examined by Rutto et al. (2002). The visual qualities of plants deteriorated with flooding, with complete defoliation occurring over a period of 3 weeks. ...
... This was expressed as an increase in root FW and a higher percentage of viable root mass after flooding. AMF inoculation further suppressed the accumulation of the toxic products associated with anaerobic respiration, such as ethanol (Rutto et al., 2002). Moreover, Asparagus officinalis plants were reported to exhibit improved tolerance to high temperature stress after AMF infection (Matsubara et al., 2000). ...
In landscaping and xerogardening projects, under semi-arid conditions, appropriate techniques used in the nursery during seedling production are crucial for the establishment, survival and subsequent growth of plants after transplanting (Figure 1). Morphological and anatomical adaptations in seedlings include reductions in shoot height and/or leaf area, rises in root-collar diameter and root growth potential and, often, a reduction in the shoot:root ratio; in addition, there are physiological characteristics of seedlings related to osmotic adjustment and water-use efficiency, such as low stomatal conductance, leaf water potential, leaf turgor potential and relative water content. These occur as a result of hardening and acclimation processes (pre-conditioning) during the nursery period, and are correlated with the ability to withstand the shock of transplantation and to increase survival and plant growth following transplantation in xerogardens and semi-arid landscapes (Franco et al., 2006). Deficit irrigation is the most commonly used pre-conditioning technique to produce high-quality seedlings (Arreola et al., 2006; Franco et al., 2008). In addition, using large-sized containers and appropriate substrates, withholding N nutrition, inoculating arbuscular mycorrhizal fungi, applying plant growth retardants and mechanical conditioning methods are common. Varying microclimatic conditions are also used to control growth to produce high-quality seedlings (Franco et al., 2006).
... Consistently, Lodge (1989) observed AM colonization of Populus and Salix trees over a wide range of soil moisture including flooded soils. Other studies with AM mycorrhizae clearly showed that the trees profit from existing mycorrhizal systems as biomass production is increased and nutrient uptake clearly improved compared with trees without established mycorrhizae (Rutto et al. 2002, Muok and Ishii 2006). Rutto et al. (2002) therefore propose that AM infection confers limited tolerance to flooding. ...
... lus and Salix trees over a wide range of soil moisture including flooded soils. Other studies with AM mycorrhizae clearly showed that the trees profit from existing mycorrhizal systems as biomass production is increased and nutrient uptake clearly improved compared with trees without established mycorrhizae (Rutto et al. 2002, Muok and Ishii 2006). Rutto et al. (2002) therefore propose that AM infection confers limited tolerance to flooding. In contrast to AM mycorrhizae , ectomycorrhizae seem to react more sensitively to high soil moisture or flooding (Lodge 1989 ). The few existing studies indicate that this type of symbiosis is rare in waterlogged soils (Theodorou 1978, Lodge 1989) and that the vi ...
The effects of global climate change will regionally be very different, mainly causing considerable changes in temperature and water availability. For Central Europe, for example, increased temperatures are predicted, which will cause increased frequencies and durations of summer drought events. On the other hand, the predicted changes in precipitation patterns will lead to enhanced rainfall during winter and spring, thereby increasing the risk of flooding in Central and Northern Europe. Depending on the sensitivity to reduced water availability on the one hand and oxygen depletion due to waterlogging on the other, physiological performance, growth and competitive ability of trees may be adversely affected. Both drought and excess water availability impair the mineral nutrition of trees by influencing on the one hand the nutrient availability in the soil and on the other hand the physiology of the uptake systems mainly of the mycorrhizal tree roots. Extreme water regimes also change interaction patterns among plants and between plants and microorganisms, and alter the carbon balance of trees and ecosystems. Here we summarize and discuss the present knowledge on tree nutrition under altered water availability as expected to be more common in the future. The focus is on tree mineral nutrient uptake and metabolism as well as on the interaction between carbon allocation and the mineral nutrient balance as affected by reduced and excess water availability.
... Mycorrhizal Casuarina equisetifolia seedlings were better adapted to flooding than noninoculated seedlings because the greater development of adventitious roots and lenticels increased oxygen availability and therefore AM colonization of plants (Osundina 1998). Accumulation of acetaldehyde, a highly toxic intermediate in ethanol formation, in roots was suggested as the main factor responsible for flooding injury in flood-sensitive species (Osundina 1998; Rutto et al. 2002). Adventitious roots and lenticels may contribute to root aeration and ethanol removal in flood-tolerant species (Crawford 1982; Liao and Lin 2001). ...
... Adventitious roots and lenticels may contribute to root aeration and ethanol removal in flood-tolerant species (Crawford 1982; Liao and Lin 2001). AM colonization also contributed to suppress ethanol accumulation in the roots of peach seedlings (Rutto et al. 2002). Some studies have also suggested that once AM colonization has taken place, the AM association can endure prolonged exposure to flooding (Miller and Sharitz 2000; Neto et al. 2006). ...
Pterocarpus officinalis (Jacq.) seedlings inoculated with the arbuscular mycorrhizal fungus, Glomus intraradices, and the strain of Bradyrhizobium sp. (UAG 11A) were grown under stem-flooded or nonflooded conditions for 13 weeks after 4 weeks of nonflooded pretreatment under greenhouse conditions. Flooding of P. officinalis seedlings induced several morphological and physiological adaptive mechanisms, including formation of hypertrophied lenticels and aerenchyma tissue and production of adventitious roots on submerged portions of the stem. Flooding also resulted in an increase in collar diameter and leaf, stem, root, and total dry weights, regardless of inoculation. Under flooding, arbuscular mycorrhizas were well developed on root systems and adventitious roots compared with inoculated root systems under nonflooding condition. Arbuscular mycorrhizas made noteworthy contributions to the flood tolerance of P. officinalis seedlings by improving plant growth and P acquisition in leaves. We report in this study the novel occurrence of nodules connected vascularly to the stem and nodule and arbuscular mycorrhizas on adventitious roots of P. officinalis seedlings. Root nodules appeared more efficient fixing N(2) than stem nodules were. Beneficial effect of nodulation in terms of total dry weight and N acquisition in leaves was particularly noted in seedlings growing under flooding conditions. There was no additive effect of arbuscular mycorrhizas and nodulation on plant growth and nutrition in either flooding treatment. The results suggest that the development of adventitious roots, aerenchyma tissue, and hypertrophied lenticels may play a major role in flooded tolerance of P. officinalis symbiosis by increasing oxygen diffusion to the submerged part of the stem and root zone, and therefore contribute to plant growth and nutrition.
... Different types of mechanism signaling to ameliorate the stresses via bioagents.FloodDevelopment of adv. roots, aerenchyma and hypertrophied lenticelsRutto et al., (2002) ...
Sessile plants confront the fluctuating harsh environmental conditions and react to alterations in biotic and abiotic components of environments by symbiotic association between plant and biosphere. The origins of stresses are the vicinal environment, which is composed of biotic and abiotic agents. A wide range of molecular mechanisms are opted by the plants for their self-defense. The plant faces harsh conditions due to its molecular battery. Signaling molecules engineer the plants to tolerate the stresses. Transposable elements become active due to living and nonliving agents. Physical and chemical agents cause induction in mutation. These changes are the first driving step in the evolution of plants. During evolution, environmental changes force the plants to adapt or succumb to stress. The plants respond to the ecological conditions by modulating the gene programmer.
... The severe energy deficit of roots due to O 2 deficiency induces an irregular functioning of these organs, resulting in deficient absorption and transport and an insufficient supply of the plant with nutrients and water (Zeng et al., 2014;Lambers & Oliveira, 2019). Suppression of the root colonization by mycorrhizal fungi in waterlogged soils contributes to reduced nutrient uptake (Kozlowski & Pallardy, 1997), but in peach seedlings an arbuscular mycorrhizal (AM) infection provides limited tolerance to waterlogging and flooding, possibly due to increased plant nutrition (Rutto et al., 2002). However, waterlogging favors the risk of nutrients leaching to deeper layers of the soil (Friedrich & Fischer, 2000). ...
RESUMEN Incidents of flooding in tropical and subtropical fruit trees have increased as a result of climate change. Because of flooding, the anaerobic conditions of the rhizosphere increase the conditions for phytotoxicity and infection by pathogenic fungi and bacteria. Due to oxygen depletion in waterlogged soils, growth, functions of the roots and of the entire plant are impaired. The decrease in the photosynthetic rate is considerable because of the reduced functional leaf area because of chlorosis, necrosis, leaf drop and stomatal closure, as well as chlorophyll degradation. Plants have developed different morphological, physiological, and biochemical adaptations to survive hypoxic stress. Some fruit trees form an aerenchyma in roots for the diffusion of oxygen from the aerial parts, create aerenchyma-containing adventi-tious roots, rapidly elongate stems into deeply flooded soils; or they form hypertrophied lenticels, like some mango varieties. Measures for better adaptations and tolerance of tropical fruit trees to climatic impact include the following: adaptations of the cultivated terrain, selection of varieties, rootstocks more tolerant to hypoxic stress, pruning to reestablish the balance of the aerial part/roots, and foliar applications (e.g., of glycine betaine or hydrogen peroxide (H 2 O 2)). Mycorrhizal coloniza-tion of roots can increase tolerance to waterlogging, while the application of fertilizers, such as CaO or MgO, can improve the redox potential of flooded soils. We present results of studies on this problem for the following fruits: yellow passion fruit (Pas-siflora edulis f. flavicarpa) and purple passion fruit (P. edulis f. edulis), cape gooseberry (Physalis peruviana), lulo or naranjilla (Solanum quitoense), tree tomato (Solanum betaceum), citrus (Citrus spp.), guava (Psidium guajava), papaya (Carica papaya), and mango (Mangifera indica). Los incidentes por inundaciones en los frutales tropicales y subtropicales han aumentado como resultado del cambio climático. En consecuencia, las condiciones anaeróbicas de la rizosfera aumentan las condiciones de fitotoxicidad y contagio por hongos y bacterias patógenos. Debido al agotamiento del oxígeno en suelos anegados, el crecimiento, las funciones de las raíces y finalmente de toda la planta resultan perjudicados. Se presenta disminución de la tasa fotosintética, debido a la reducida área foliar efectiva como consecuencia de la clorosis, necrosis y caída foliar, además del cierre estomático y la degra-dación de la clorofila. Las plantas han desarrollado diferentes adaptaciones de tipo morfológico, fisiológico y bioquímico para sobrevivir al estrés por hipoxia. Algunos frutales forman un aerénquima en raíces para facilitar el transporte del oxígeno desde las partes aéreas, inducen raíces adventicias que contienen aerénquima, alargan rápidamente los tallos hacia suelos inun-dados más profundos o forman lenticelas hipertrofiadas, como en las variedades de mango. Dentro de las medidas para una mejor adaptación y tolerancia de los frutales tropicales a esta adversidad climática se recomiendan una adecuada preparación del suelo, la selección de variedades y patrones más tolerantes al estrés por hipoxia, podas, para reestablecer el equilibrio de la relación parte aérea/raíz en los árboles, aplicaciones foliares como por ejemplo de glicina betaína o peróxido de hidrogeno (H 2 O 2). La colonización micorrícica en las raíces puede aumen-tar la tolerancia al anegamiento y el potencial redox en suelos inundados puede mejorarse con la aplicación de enmiendas como CaO o MgO. Se presentan resultados de estudios sobre esta adversidad en maracuyá (Passiflora edulis f. flavicarpa), gulupa (P. edulis f. edulis), uchuva (Physalis peruviana), lulo o naranjilla (Solanum quitoense), tomate de árbol (Solanum betaceum), cítricos (Citrus spp.), guayaba (Psidium guajava), papaya (Carica papaya) y mango (Mangifera indica). Impact of waterlogging on fruit crops in the era of climate change, with emphasis on tropical and subtropical species: A review Impacto del anegamiento sobre los frutales en la era del cambio climático, con énfasis en especies tropicales y subtropicales: una revisión
... The severe energy deficit of roots due to O 2 deficiency induces an irregular functioning of these organs, resulting in deficient absorption and transport and an insufficient supply of the plant with nutrients and water (Zeng et al., 2014;Lambers & Oliveira, 2019). Suppression of the root colonization by mycorrhizal fungi in waterlogged soils contributes to reduced nutrient uptake (Kozlowski & Pallardy, 1997), but in peach seedlings an arbuscular mycorrhizal (AM) infection provides limited tolerance to waterlogging and flooding, possibly due to increased plant nutrition (Rutto et al., 2002). However, waterlogging favors the risk of nutrients leaching to deeper layers of the soil (Friedrich & Fischer, 2000). ...
Incidents of flooding in tropical and subtropical fruit trees have increased as a result of climate change. Because of flooding, the anaerobic conditions of the rhizosphere increase the conditions for phytotoxicity and infection by pathogenic fungi and bacteria. Due to oxygen depletion in waterlogged soils, growth, functions of the roots and of the entire plant are impaired. The decrease in the photosynthetic rate is considerable because of the reduced functional leaf area because of chlorosis, necrosis, leaf drop and stomatal closure, as well as chlorophyll degradation. Plants have developed different morphological, physiological, and biochemical adaptations to survive hypoxic stress. Some fruit trees form an aerenchyma in roots for the diffusion of oxygen from the aerial parts. Induced aerenchyma-containing adventitious roots, rapidly elongate stems into deeply flooded soils; or they form hypertrophied lenticels, like some mango varieties. Measures for better adaptations and tolerance of tropical fruit trees to climatic impact include the following: adaptations of the cultivated terrain, selection of varieties, rootstocks more tolerant to hypoxic stress, pruning to reestablish the balance of the aerial part/roots, and foliar applications (e.g., of glycine betaine or hydrogen peroxide (H2O2)). Mycorrhizal colonization of roots can increase tolerance to waterlogging, while the application of fertilizers, such as CaO or MgO, can improve the redox potential of flooded soils. We present results of studies on this problem for the following fruits: yellow passion fruit (Passiflora edulis f. flavicarpa) and purple passion fruit (P. edulis f. edulis), cape gooseberry (Physalis peruviana), lulo or naranjilla (Solanum quitoense), tree tomato (Solanum betaceum), citrus (Citrus spp.), guava (Psidium guajava), papaya (Carica papaya), and mango (Mangifera indica).
... Soil flooding, either with fresh water or seawater, represents another common environmental factor in low-lying coastal grasslands. A number of practically oriented studies on flooding tolerance of mycorrhizal plants have been performed, including seedlings of Citrus sinensis [79], Prunus persica [80,81], Pterocarpus officinalis [82], and showing the overall beneficial effect of mycorrhization on flooding tolerance. Improved mineral nutrition, proline production, and suppression of ethanol production in roots during anoxic conditions were among the mechanisms responsible for growth improvement due to mycorrhizal symbiosis in flooded conditions. ...
Grasslands represent an essential part of terrestrial ecosystems. In particular, coastal grasslands are dominated by the influence of environmental factors resulting from sea-land interaction. Therefore, coastal grasslands are extremely heterogeneous both spatially and temporally. In this review, recent knowledge in the field of biotic interactions in coastal grassland soil is summarized. A detailed analysis of arbuscular mycorrhiza symbiosis, rhizobial symbiosis, plant-parasitic plant interactions, and plant-plant interactions is performed. The role of particular biotic interactions in the functioning of a coastal grassland ecosystem is characterized. Special emphasis is placed on future directions and development of practical applications for sustainable agriculture and environmental restoration. It is concluded that plant biotic interactions in soil are omnipresent and important constituents in different ecosystem services provided by coastal grasslands.
... Our findings from TEM observations of leaves and roots suggested a possible correlation between mycorrhizal fungi infection and waterlogging tolerance of peach rootstocks. It is traditionally believed that mycorrhizal symbiosis participates in proline metabolism and improves root morphology, which can improve the tolerance of plants to various abiotic stresses [4, 31,54,55]. This effect is more pronounced in juvenile seedlings [32]. ...
Peach (Prunus persica (L.) Batsch) is a typical shallow-rooted fruit plant with a high respiratory intensity and oxygen demand, which makes it highly susceptible to oxygen-deficient soil conditions resulting from waterlogging. Rootstock waterlogging resistance is essential to the performance of cultivated peaches under waterlogging stress. In comparison to Prunus persica var. persica (‘Maotao’, M) and Prunus davidiana (Carr.) C. de Vos (‘Shantao’, S), Prunus persica f. Hossu (‘Hossu’, H) exhibited superior leaf photosynthetic electron transfer efficiency, a higher rate of mycorrhizal fungi infection in both fine roots and mesophyll palisade cells, as well as earlier air cavity formation in both leaf midvein and fine roots under waterlogging stress. Furthermore, under non-waterlogging conditions, Hossu had greater leaf superoxide dismutase (SOD) activity, higher proline content, and a greater content of starch granules in the pith and xylem ray cells of stems and roots than rootstocks M and S. As a result, Hossu’s tolerance to waterlogging may be due to its higher photosynthetic efficiency, improved tissue oxygen permeability, higher energy metabolism, and increased intracellular mycorrhizal fungus infection rates in both root parenchyma cells and mesophyll palisade cells.
... Flooding induced nodules both on adventitious roots and submerged parts of the stem (Fougnies et al., 2007). Casuarina equiseti and folia seedlings might be better adapted to flooding than and noninoculated seedlings because of the increased O 2 diffusion and removal of ethanol through adventitious roots (Rutto et al., 2002). ...
Extreme events of abiotic stress conditions such as high temperatures, prolonged drought, salinity, metal toxicity, intense rains, flooding, frost, and low temperatures affect the productivity of crops as well as significantly affect plants and soil microorganisms. The composite and active connections between microorganisms and plant roots during abiotic stress disturb not only the plants but also the physical, chemical, and structural properties of soil. While several studies have found that numerous species of microorganisms, particularly rhizospheric microorganisms generate diverse mechanisms to enhance both plants and their survival ability against abiotic stresses. Among the microorganisms, plant growth-promoting rhizobacteria (PGPR) and Arbuscular mycorrhiza fungi (AMF) were found to be the most important species that enhance plant to mitigate the adverse events of abiotic stress through the production of exopolysaccharides, cytokinins, antioxidants, and enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase and also the formation of biofilm. Besides theses production of organic compounds, dual symbiotic systems of PGPR and AMF (endophytic rhizospheric bacteria and symbiotic fungi) also stimulate to alleviate the adverse effect of abiotic stress in plants. The current book chapter discusses the role of soil microorganisms in plant adaptation to abiotic stresses and also highlights the current scenario, future perspectives, and challenges to use for the sustainability of crop production under the future extreme events of climate change.
... Mycorrhizal Casuarina equisetifolia plants could be better adapted to floods compared to uninoculated plants. This may be due to a higher diffusion of oxygen and ethanol removal from increased development of random roots, hypertrophies, lenticels, and aerenchymatous tissue at the root zone and the submerged portion of the stem (Rutto et al. 2002;Toro et al. 2018). Trifolium plants with AM fungi displayed improved tolerance against flooding, as evidenced by osmotic adaptation and proline improvement in the tissues of plant (Neto et al. 2006). ...
Pollution with petroleum hydrocarbons is far-reaching and thus, a problem for the environment as well as human health. The pristine environment has continuously been influenced by anthropogenic activities. Due to the globalization of various industries; their waste materials are being discharged untreated or partially treated into the ecosystem and having adverse impact on different life forms. Petroleum despite being a priceless resource and central to human life on Earth today, extraction and transportation of petroleum products has a number of ecological repercussions. The most consequential effect of petroleum use leads to the environmental pollution, adversely affecting air, soil and water quality. Petroleum product’s spill and leakage are also a major threat to the environment because petroleum products can rigorously destroy the surrounding ecosystem. So, the removal of petroleum products is imperative using eco-friendly methods, and microorganisms are the cheaply available option for doing so. Biosurfactants are extracellular amphiphilic, surface-active compounds produced by microorganisms. These microbially produced multifunctional biomolecules are versatile products having vast applications in various aspects related to clean up of environmental contaminants inclusive of enhanced oil recovery (EOR), controlling oil spills, detoxification and biodegradation of oil contaminated wastewater, soil or sediments. Biosurfactant works by reducing interfacial and surface tension by collecting at the interface of immiscible liquids and thus improve the bioavailability, solubility and subsequent biodegradation of the insoluble or hydrophobic organic compounds. This chapter summarizes the role of biosurfactant-producing bacteria in the bioremediation of petroleum hydrocarbons polluted environment.
... It is essential for plants to maintain a normal or at least minimum energy supply under flooded conditions, whilst the energy metabolism depends on glycolysis to produce ATP, in which ethanol or lactic acid fermentation is mandatory (Hu and Kang 2005). In peach seedlings, a three-day root-zone flooding was applied to Gigaspora margarita-inoculated and non-inoculated seedlings (Rutto et al. 2002). The study revealed that ethanol concentration was comparatively higher in flooded non-mycorrhizal seedlings than flooded mycorrhizal seedlings. ...
Presence and functional roles of arbuscular mycorrhizal (AM) fungi in wetland environment have gained a global importance in recent past. Wetlands build a low-oxygen atmosphere, forming a completely different ecological environment for AM fungi, known more to occur in terrestrial environment. Nevertheless, as many 101 of AM fungi species, belonging to 19 genera and 9 families have been observed in the rhizosphere of wetland plants. In order to obtain oxygen, AM fungi expand the aeration system of wetland plants, store oxygen through their own vesicles, or change the structure of AM to survive. Human activities negatively affect the wetland environment, thus, reducing the population of AM fungi, while certain AM fungi species still improved the survival and development of wetland plants. AM fungi regulate different physiological activities of wetland plants in response to waterlogging stress, including an enhancement of antioxidant defense system, increased proline accumulation, improved plant growth and root morphology, responses of nutrients and aquaporins, and suppression in ethanol accumulation. The current review briefly summarized different species of wetland plants forming AM structures, the population of AM fungi inhabiting the rhizosphere of wetland plant, AM fungi-colonization of wetland plants, and the effect of AM fungi on physiological functions of wetland plants to neutralize the negative impact of waterlogging in addition to outlook of researchable issues. This review also highlighted human impacts on AM fungi of wetland plants and the impact of AM fungi on wetland environments and wetland plants.
... (Larcher, 2003) menciona que plantas que crecen en suelos compactos y pobremente aireados pueden desarrollar un sistema de raíces laterales cerca de la superficie del suelo para obtener más oxígeno. La formación de una capa de células lignificadas al interior de la hipodermis y una hipodermis suberizada son adaptaciones con que las plantas consiguen minimizar la pérdida de oxígeno, además de los daños que les puede ocasionar (Rutto et al. 2001) observaron en plántulas de duraznero anegadas que la inoculación de micorriza Gigaspora margarita favoreció un mayor porcentaje de raíces viables, concentraciones del tallo más altas de P, K y Zn y biomasa, mientras que las plántulas no inoculadas acumularon un contenido más alto de etanol en las raíces. En citrus (Citrus junos) la colonización con la micorriza, Diversispora spurca, aumentó el crecimiento (altura de la planta, biomasa, longitud y volumen de raíces) comparado con plántulas no inoculadas, por lo cual sugirieron que D. spurca alivia los efectos del anegamiento por su acción sobre la arquitectura radicular y las actividades de enzimas antioxidantes. ...
La resistencia mecánica que opone un suelo y los efectos de diferentes usos sobre propiedades físicas relacionadas con la compactación y humedad del suelo, provoca un empaquetamiento denso de las partículas, lo que aumenta la densidad aparente en detrimento de la porosidad, en especial la macro porosidad impidiendo la entrada de humedad, en donde los insumos agrícolas, la disturbación del perfil del suelo por el uso de herramienta agrícola, el transito rutinario de personal y de animales, permiten a que se incremente esa resistencia y que a su vez reduzca la asimilación de fertilizantes, la efectividad del ingrediente activo de los productos químicos y la actividad microbiológica del suelo; limitando el crecimiento de la raíz de la planta, que en algunos casos, las pérdidas de la cosecha pueden llegar a un 30% a causa de la compactación. Una variable importante para describir la condición física del suelo es la resistencia mecánica y la calidad física del suelo, puede evaluarse a través de la resistencia y resiliencia de los poros del suelo, lo que corresponde a la capacidad de un suelo de mantener sus funciones sin variaciones significativas luego de ser expuesto a un estrés, este problema se puede mitigar midiendo las variables de densidad aparente y de agregados del suelo, precisar la porosidad de un suelo, medir la humedad antes de sembrar (Seybold, C.; et, al 1999).La distribución excesiva de la humedad del suelo, un inadecuado sistema de drenaje y compactado son causales de anegamiento que pueden reducir el crecimiento vegetal, cambios en el metabolismo de las plantas, menor absorción de agua y nutrientes, baja producción y muerte de la planta. El anegamiento en las plantas estará determinada por el tiempo de exposición a este estrés y la tolerancia de éstas, siendo un motivo por el que las plantas pueden presentar modificaciones defensivas como vías alternas de respiración, mayor producción de antioxidantes y etileno, inducción de la epinastia y el cierre de estomas, además la formación de nuevas estructuras como el aerénquima, lenticelas hipertrofiadas y raíces adventicias. No obstante, la falta de oxígeno puede llevar a las plantas a la muerte
... Colonization of Gigaspora margarita promotes stomatal conductance as well as improves dual stress survival in sorghum when exposed to drought stress in salinized soils. Glomus intraradices and Casuarina equisetifolia was found to enhance abiotic stress tolerance and improve plant growth under flooding conditions (Rutto, Mizutani, & Kadoya, 2002;Porras-Alfaro et al., 2008;Sheramati, Tripathi, Varma, & Oelmuller, 2008). Further, several fungi are also known to harbor abiotic stress tolerance and helped the other plants in the same (Neto, Carvalho, Cruz, & Martin-Loucao, 2006;Fougnies et al., 2007;McLellan et al., 2007). ...
Plants are confronted with several biotic and abiotic stresses viz. nutrient starvation, salt stress, drought, flooding, xenobiotic contamination, etc. in order to sustain in an ecosystem. Simultaneously, they shape the microbial composition in their vicinity by modulating their secretions. In the whole process, a plant-microbe interaction is established which help the plants to alleviate the stressful conditions. In view of the agriculture intensification and sustainability issues, there is a pressing demand for a novel and potential microorganism which can support an environmentally friendly and cost-effective way for stress management in the plants. In this perspective, this chapter is an effort to summarize the processes and mechanisms involved in microbe assisted plant stress management which will definitely enhance our knowledge in the scenario.
... 4-020-10116 -1) contains supplementary material, which is available to authorized users. stimulated rate of photosynthesis (Kaschuk et al. 2009), enhanced nutrient status of plants (Aka-Kaçar et al. 2010), increased growth (Berta et al. 1995), reduced impact of soil-borne pathogens (Azcón-Aguilar and Barea 1996), and improved the viability of peach (Prunus persica L. Batsch) seedlings affected by flooding (Rutto et al. 2002) and replant disease (Gao et al. 2020). However, the studies revealed also the genotype dependence in AM and negative effect of AMF on host plants in several combinations (Aguin et al. 2004;Matysiak and Falkowski 2010;Andrade et al. 2015;Leiser et al. 2016;Jin et al 2017). ...
Sour cherry ‘Latvijas Zemais’ (Prunus cerasus) is a promising dwarfing rootstock for sweet cherries in Latvia, but low growing rate of newly propagated sour cherry plants limits their use. Plum rootstock PU 20651 was selected from hybrids of P. cerasifera and P. salicina ssp. usuriensis recently. The aim of our study was to estimate the effect of arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis MUCL 41833 (Ri) on the growth and P content of rooted green cuttings of sour cherry ‘Latvijas Zemais’ 52, cherry rootstock Gisela 5 (P. cerasus x P. canescens), and plum rootstock PU 20651. The cuttings were planted in peat substrate and grown in plastic tunnel equipped with automatic air moistening system and controllable floor heating. We determined growth parameters and P content in shoots and roots, intensity of mycorrhizal colonization, and frequency of mycorrhiza in root system. In all three Prunus sp. genotypes, the inoculation with Ri resulted in the root colonization. PU 20651 had highest level of colonization at all arbuscular mycorrhiza (AM) estimation parameters. A common effect of colonization was increased diameter of root collar and positive correlation between the leaf number and AM parameters. The effect of Ri on plant biomass and P content depended on the genotype. Beneficial effect of AM on root mass and root P content was detected in ‘Latvijas Zemais’ 52. However, no AM effects on P content were found in Gisela 5, but little negative impact of AM on shoot mass and shoot P content—in PU 20651.
... Flooding induced nodules both on adventitious roots and submerged parts of the stem (Fougnies et al., 2007). Casuarina equisetifolia seedlings might be better adapted to flooding than non-inoculated seedlings because of the increased O 2 diffusion and removal of ethanol through adventitious roots (Rutto et al., 2002). A better adaptation of inoculated Casuarina equisetifolia seedlings to flooding than non-inoculated seedlings was due to better development of adventitious roots and lenticels, which increased oxygen availability and consequently AM colonization of plants (Osundina, 1998). ...
... Mientras que el ácido láctico es el primer producto formado debido a la acidificación citológica (Jiménez et al., 2012), el cambio resultante en el pH de las células favorece rápidamente la formación de acetaldehído, que puede ser muy tóxico, y el cual es convertido en etanol por medio de la actividad de la deshidrogenasa alcohólica (Mittler, 2002). El etanol, producido por la respiración anaeróbica en condiciones de anegamiento puede causar daños importantes, aunque pueden ser contrarrestados con la aplicación de micorrizas (Rutto et al., 2001). ...
Waterlogging and flooding stress have become major abiotic stress factors for the growth, development and productivity of crops. To study the effect of waterlogging on the chonto tomato long-life Roble F1 hybrid, an experiment was conducted in a plastic greenhouse, with and without black shade netting (with the 56.4% light reduction on a sunny day). Plastic pots (1 L capacity) were used with blond peat mixed with organic soil at a 1:1 proportion, which were waterlogged up to 4 cm above the substrate for 4, 8 and 12 days. The assessed variables included plant height, number of leaves and fruits, and dry biomass of the organs. The study showed that 4, 8, and 12 days of waterlogging reduced the plant height and number of leaves after 12 and 16 days from waterlogging initiation, respectively; while the number of fruits was significantly lower at 40 dwi, when the evaluation period finished. The root hypoxia in the plants waterlogged for 8 and 12 days reduced plant dry biomass production, especially in the fruits and roots; while the 12-days-waterlogging x shading interaction impaired the total plant dry mass. In general, the tomato plant seems to be adapted to the effect of this type of shading. Increased periods of waterlogging were accompanied by symptoms such as chlorosis, abscission of basal leaves, leaf epinasty, reddish coloring, and formation of adventitious roots.
... As reported by Tuo et al. (2015), AMF peach plants recorded more proline accumulation in leaves, in company with an increase of (Δ 1 -pyrroline-5-carboxylate synthase and a decrease of orn-δ-aminotransferase and proline dehydrogenase activity. Gigaspora margarita-colonized peach and Casuarina equisetifolia plants under flooding condition represented lower ethanol level (Osundina 1998, Ruto et al. 2002 ...
Citrus, one of the important fruit trees grown in tropical and subtropical regions of the world, has less and shorter root hairs in the field, thus, highly dependent on arbuscular mycorrhizas. Citrus rhizosphere inhabits 45 species of arbuscular mycorrhizal fungi (AMF), belonging to seven genera like Acaulospora, Entrophospora, Gigaspora, Glomus, Pacispora, Sclerocystis and Scutellospora. These AMF can be associated with the roots for the formation of arbuscular mycorrhizal symbiosis, who would enlarge the contacted areas of roots to soil and be regarded as a potential soil biofertilizer, thereby promoting citrus nutrients. In addition to the vital function, mycorrhizas in citrus display other roles in soils and plants. Most AMF species usually significantly increase plant growth and fruit quality of citrus plants, but occasionally inhibit or did not impact plant growth. The inoculation with AMF obviously improved root system architecture of citrus, thereby conferring greater ability of the host plant to obtain soil resources. Mycorrhizas can develop an extensive common mycorrhizal network to colonize neighbouring citrus or other plants for underground communication. AMF release a special glycoprotein, glomalin, into the soils, which can improve soil structure and contribute soil carbon pools, thus, providing better soil fertility and soil physical-chemical traits. Mycorrhizas enhance tolerance of citrus plants to drought stress, salt stress, high temperature but not low temperature, flooding, elevated [CO 2 ], diseases, and insect pests in terms of various physiological and molecular approaches. Based on the mycorrhizal functionings, citrus production will consider mycorrhizal management of citrus orchard and new perspectives are also outlined.
... As reported by Tuo et al. (2015), AMF peach plants recorded more proline accumulation in leaves, in company with an increase of (Δ 1 -pyrroline-5-carboxylate synthase and a decrease of orn-δ-aminotransferase and proline dehydrogenase activity. Gigaspora margarita-colonized peach and Casuarina equisetifolia plants under flooding condition represented lower ethanol level (Osundina 1998, Ruto et al. 2002 ...
Citrus, one of the important fruit trees grown in tropical and subtropical regions of the world, has less and shorter root hairs in the field, thus, highly dependent on arbuscular mycorrhizas. Citrus rhizosphere inhabits 45 species of arbuscular mycorrhizal fungi (AMF), belonging to seven genera like Acaulospora, Entrophospora, Gigaspora, Glomus, Pacispora, Sclerocystis, and Scutellospora. These AMF can be associated with the roots for the formation of arbuscular mycorrhizal symbiosis, who would enlarge the contacted areas of roots to soil and be regarded as a potential soil biofertilizer, thereby promoting citrus nutrients. In addition to the vital function, mycorrhizas in citrus display other roles in soils and plants. Most AMF species usually significantly increase plant growth and fruit quality of citrus plants, but occasionally inhibit or did not impact plant growth. The inoculation with AMF obviously improved root system architecture of citrus, thereby conferring greater ability of the host plant to obtain soil resources. Mycorrhizas can develop an extensive common mycorrhizal network to colonize neighbouring citrus or other plants for underground communication. AMF release a special glycoprotein, glomalin, into the soils, which can improve soil structure and contribute soil carbon pools, thus, providing better soil fertility and soil physical-chemical traits. Mycorrhizas enhance tolerance of citrus plants to drought stress, salt stress, high temperature but not low temperature, flooding, elevated [CO2], diseases, and insect pests in terms of various physiological and molecular approaches. Based on the mycorrhizal functioning, citrus production will consider mycorrhizal management of citrus orchard and new perspectives are also outlined.
... It has been observed that mycorrhizal (Casuarina equisetifolia) seedlings could better adapt to flooding than noninoculated or control seedlings. The reason behind this could be due to increased O 2 diffusion and the removal of ethanol through greater development of adventitious roots, aerenchymatous tissue, and hypertrophies lenticels on the root area and sunken part of the stem (Rutto et al., 2002). The AM inoculated Aster tripolium plants showed increased tolerance to flooding by enhanced osmotic adjustment and accumulation of proline in plant tissues (Neto et al., 2006). ...
Soybean (Glycine max (L.)) is one of the most important oilseed crop grown worldwide. The Seed sowing of this crop intersects with the rainy period in major portions of the world and hence it faces water logged or flooding stress conditions. Flooding causes various physical injuries in soybean crop along with some anaerobic stress conditions. These deleterious effects result in poor vegetative growth of the crop along with reduced photosynthetic activities and diminished nodulation resulting in significant yield loss. Flooding not only disrupts anatomical and physiological features of soybean crop but also down regulates important genes and proteins that assist in flood tolerance. Development of flood tolerant soy crop using different cultivars is not any easy or feasible approach. However, amelioration of flooding stress in soy crop and enhancing production utilizing biological methods (i.e. using plant growth promoting rhizobacteria) could be economical, viable and more practical approach for sustainable agriculture.
... However, the associated AMF and Fe-EDDHA significantly enhanced the shoot length by 18% (p<0.05). These result confirms those showing the imperative effect of AMF and iron chelate in increasing the vegetative growth and the mineral nutrition of plants ( Karaginnidis et al. 2008;Rutto et al. 2002;Traquair and Berch 1988). ...
Peach trees are highly susceptible to lime induced chlorosis which can strongly affect fruit quality and yield resulting on an unbalance of nutrients uptake. The present study was assessed in order to evaluate the impact of arbuscular mycorrhizal fungi (AMF) inoculation and the Fe-ethylenediamine-di (O-hydroxy-phenylacetic-acid) (Fe-EDDHA) on the 'Rich Lady' peach variety behavior, under iron deficiency conditions. At 30 days after full bloom (DAFB), a mixture of six commercial strains of AMF Glomus sp. (T1), a synthetic Fe-EDDHA (T2) and a combination of both treatments (T3) were supplied and compared to a non inoculated and non fertilized peach trees (Tc). The shoots length, the peaches size and the leaves mineral contents were evaluated at 60 and 120 DAFB. The fruit quality was performed at ripening.Results showed greatest effects of the overall applied treatments, compared to the control, in improving the shoots growth, the mineral uptake and equilibrium and the fruit quality. At 60 DAFB, T1, T2 and T3 treatments, significantly improved the foliar total nitrogen and magnesium levels (29%, 34%, 52% and 10%, 16%, 20% respectively) (at P<0.05%). They also significantly decreased the foliar potassium and calcium leaves contents (-22%,-18%,-17% and-21%,-21%,-29% respectively) (at P<0.05%). At 120 DAFB, the T1, T2 and T3 treatments significantly increased the leaves phosphorus levels and leaded to the equilibrium of the iron and magnesium leaves levels. Nevertheless, the T3 treatment was the most effective in decreasing the potassium leaves contents as response to iron chlorosis correction. In addition, it significantly enhanced the peaches size, weight (32.5%) and firmness (15%) and the juice weight (40%), volume (28.9%), pH (4.8%), soluble solids contents (13.3%). Else, it significantly decreased the titratable acidity of peaches by 14.2%. The approach offers challenge of use of AMF for iron chlorosis correction in sustainable agriculture.
... Peach, one of the important deciduous fruit trees, originated from the northwest region of China and is widely planted all over the world (Faust and Timon, 2010). In general, peach plants are highly susceptible to soil waterlogging (Rutto et al., 2002). Prunus persica (L.) Batsch is a rootstock used in China for peach cultivation and production. ...
... Peach is a delicious fruit with lots of nutrition values and is widely distributed and cultivated all around the world, including China. Although mycorrhizal symbiosis could help peach seedlings to overcome soil-fumigation nutrient-deficiency effects in nursery and alleviate flooded stress, but not overcome peach replant problem (Rutto et al, 2002;Rutto and Mizutani, 2006), there is no information about the role of AMF on RSA of peach. Here, it has Extracts for the determinations of glucose and sucrose were followed by Wu et al. (2010). ...
Root system architecture (RSA) is used to describe the spatial configuration of a root system in the soil, which substantially determines the capacity of a plant to take up nutrients and water. The present study was to assess if arbuscular mycorrhizal fungi (AMF), Glomus mosseae, G. versiforme, and Paraglomus occultum would alter RSA of peach (Prunus persica L. Batsch) seedlings, and the alteration due to mycorrhization was related to allocation of glucose/sucrose to root (Aglucose/sucrose). Inoculation with G. mosseae and G. versiforme significantly increased leaf, stem, root and total fresh weights, compared with non-AMF treatment. Mycorrhizal alterations of RSA in peach plants were dependent on AMF species, because only G. mosseae and G. versiforme but not P. occultum markedly increased root length, root projected area, root surface area and root volume. For the distribution of root length classes, AMF mainly increased 0-1 and 3-4 cm root length classes, which is AMF species dependent. Inoculated seedlings with Glomus species recorded significantly higher root sucrose and leaf and root glucose concentrations and lower root sucrose concentrations than un-inoculated control. Compared with the non-AMF treatment, G. mosseae and G. versiforme generally increased the Aglucose and Asucrose, but P. occultum significantly decreased the Aglucose and Asucrose. Asucrose or Aglucose was significantly positive correlated with root length, root projected area and root surface area. The results suggest that AMF modified variables of RSA in peach, which is AMF species dependent and related to Aglucose and Asucrose.
... Inoculation with G. fasciculatus was equally or more effective in overcoming soil-fumigation nutrientdeficiency effects in peach nursery seedlings than the standard nursery practice of side-dressing P and Zn at planting time (Larue et al., 1975). Mycorrhizal symbiosis helped peach seedlings to overcome soil-fumigation nutrient-deficiency effects in nursery, uptake nutrients, and alleviate flooded stress, but not overcome peach replant problem (Rutto et al., 2002;Rutto and Mizutani, 2006). The objective of the present study was to evaluate the potential roles of three AMF species on peach seedlings, in terms of mycorrhizal colonization, plant growth and nutrient acquisition. ...
Arbuscular mycorrhizal fungi (AMF) can form mutualistic symbioses with the roots of 80% of plants, which increase soil water and nutrient uptake for the host plants. However, little information is known on potential roles of different AMF for growth and nutrient acquisition of peach. In a potted experiment, we determined the growth performance, nutrient concentrations and mycorrhizal nutrient efficiency of the peach (Prunus persica L. Batsch) seedlings inoculated with Glomus mosseae, G. versiforme, and Paraglomus occultum, respectively. After 100 days of mycorrhizal inoculations, mycorrhizal colonization of one-year-old seedlings ranged from 23.4% to 54.9%. Generally, the formed mycorrhizal symbiosis significantly improved plant growth performance, such as plant height, stem diameter, shoot, root or total dry weight. Compared with the non-AMF seedlings, a range of 9.450.0% Zn of roots were respectively higher in the mycorrhizal seedlings. The mycorrhizal benefit role on nutrient uptake generally was the best in the G. mosseae treatment. It suggests that arbuscular mycorrhizas could improve growth performance and part nutrient acquisition of peach, which were absolutely dependent on AMF species.
... Mientras que el ácido láctico es el primer producto formado debido a la acidificación citológica (Jiménez et al., 2012), el cambio resultante en el pH de las células favorece rápidamente la formación de acetaldehído, que puede ser muy tóxico, y el cual es convertido en etanol por medio de la actividad de la deshidrogenasa alcohólica (Mittler, 2002). El etanol, producido por la respiración anaeróbica en condiciones de anegamiento puede causar daños importantes, aunque pueden ser contrarrestados con la aplicación de micorrizas (Rutto et al., 2001). ...
El estrés por anegamiento e inundación de las plantaciones se ha convertido en un factor abiótico limitante del crecimiento, el desarrollo y la productividad de los cultivos. Para estudiar el efecto del anegamiento sobre el tomate tipo chonto, híbrido larga vida Roble F1, se realizó un experimento en condiciones de invernadero de plástico, con y sin sombrío (una polisombra negra con 56,4% de reducción lumínica en un día soleado) de plantas anegadas. Se utilizaron materas plásticas de 1 L de capacidad, con turba rubia como sustrato en mezcla con suelo orgánico en proporción 1:1, las cuales fueron anegadas con una lámina de agua hasta 4 cm por encima del sustrato durante 4, 8 y 12 días. Las variables evaluadas incluyeron altura de planta, número de hojas y frutos, y biomasa seca de los órganos. El estudio mostró que los periodos de 4, 8 y 12 días de anegamiento redujeron significativamente la altura de la planta y el número de hojas, después de 12 y 16 días de iniciado el anegamiento, respectivamente, mientras el número de frutos en las plantas anegadas fue significativamente menor a los 40 dda cuando terminó la evaluación. La hipoxia radical en las plantas anegadas durante 8 y 12 días, redujo la producción de biomasa seca, especialmente en frutos y raíces, mientras la interacción 12-días-anegamiento y sombrío disminuyó la masa seca total de la planta. La planta de tomate, en general, parece estar adaptada al efecto de este tipo de sombrío. Con el aumento de la duración del anegamiento aparecieron síntomas como clorosis y caída de hojas basales, además de la epinastia y coloración roja foliar, así mismo la formación de raíces adventicias.
... Although the set of adaptive responses was quite complex, the authors suggested that the higher tolerance of Myrobalan plums to flooding cannot be ascribed to these enzyme activities (Amador et al., 2012). Peach seedlings used as rootstock have been reported to be intolerant of flooding, as indicated by slow growth, plant decline, or both, on poorly drained soils (Rutto et al., 2002). Grafting peach cultivar onto an appropriate rootstock could generate a more adaptable tree by combining the high quality production of the cultivar (scion) with a flood-tolerant rootstock. ...
Plants are aerobic organisms that require the availability of O2 for nutrient uptake, so excess water surrounding roots can generate lethal conditions. Therefore a new flood-tolerant stone-fruit rootstock was used in a grafted combination with peach cv Suncrest (Prunus persica (L.) Batsch.) used as scion, to test its tolerance strength during a twenty-one day flooding period. Potted plants, from graft combination of cv Suncrest with rootstock Mr.S 2/5 wild type (Prunus cerasifera Erhr) and its clone variant (S.4), were submitted to normoxic and flooded stress for 21 days, under open conditions. Suncrest/S.4 plants had the highest plant growth under normoxic condition and the highest plant survival under flooded conditions. Under flooded conditions a halt in plant growth and the appearance of severe damage were detected in the Suncrest/wt plants. In the latter, symptoms of flooding were desiccation of the shoot apex, strong reddening of leaves followed by appearance of necrotic areas and senescence of almost all leaves.The responses observed in all organs of the grafted plant could be linked to relevant morpho-physiological adaptations to flooding that would ensure survival during short periods of anoxia. Results also provided evidence that flooding tolerance was conferred by the S.4 clone to the scion. The availability of a novel rootstock tolerant to short-term waterlogging conditions will offer new possibilities to the stone-fruit industry located in various adverse environments.
... For other nutrients such as N, K, or Mg, AM fungi were reported both to have and not to have an effect on the uptake these nutrients up to host plants. It depended on the species of AM fungi and the soil conditions [20][21][22][23] . In the pot experiment, root colonization by AM fungi and rhizosphere spore density in tangerine also showed a response to N and P treatments (Table 4). ...
There are many tangerine (Citrus reticulata) orchards in northern Thailand. These orchards are supplied with different levels of fertilizers. The objective of this study is to investigate arbuscular mycorrhizal (AM) fungi associated with tangerine in Chiang Mai province, northern Thailand, and the effect of AM fungi on the growth of the air layered tangerine variety 'Sai Num Phung' with different levels of nitrogen (N) and phosphorus (P) fertilizers in a pot experiment. Percentage of AM colonization in the tangerine roots and spore density in the rhizosphere varied significantly with the available P levels in the orchard soil. Means of root colonization and spore density were significantly depressed at >500 mg P/kg soil. Twenty-two species of AM fungi were found to be associated with tangerine in orchards of the Chiang Mai province. The effects of AM fungi, and N and P fertilizers on air layered tangerine plants were investigated in pots for ten months. AM fungi increased growth of the host plant especially in pots with N but without P fertilizers. AM fungi increased concentrations of P and Mg in leaves of tangerine. Application of N and P fertilizers depressed root colonization of AM fungi in the pot experiment. This study has shown that a wide range of AM fungi is associated with tangerine in commercial orchards, but with high levels of N and P fertilizers the increase in growth of tangerine trees due to the association with AM fungi may be limited.
... This mechanism is based on a range of biochemical and physiological responses such as a lower permeability of plasma membrane induced by the AMF, and high soluble sugar and P content in the aerial parts of the plant. AMF also confer resistance to flooding (Rutto et al., 2002). C. equisetifolia mycorrhized seedlings were shown to be better adapted to flooding conditions than noninoculated seedlings (Osundina, 1997). ...
... Mycorrhizal Casuarina equisetifolia seedlings could better adapt to flooding than noninoculated seedlings. This could be due to increased O 2 diffusion and removal of ethanol through greater development of adventitious roots, aerenchymatous tissue and hypertrophies lenticels on the root zone and submerged part of the stem (Rutto et al. 2002). The better tolerance of AM inoculated A. trifolium plants to flooding was mediated through an improvement of osmotic adjustment and proline in plant tissue (Neto et al. 2006). ...
Increased incidences of abiotic and biotic stresses impacting productivity in principal crops are being witnessed all over
the world. Extreme events like prolonged droughts, intense rains and flooding, heat waves and frost damages are likely to
further increase in future due to climate change. A wide range of adaptations and mitigation strategies are required to cope
with such impacts. Efficient resource management and crop/livestock improvement for evolving better breeds can help to overcome
abiotic stresses to some extent. However, such strategies being long drawn and cost intensive, there is a need to develop
simple and low cost biological methods for the management of abiotic stress, which can be used on short term basis. Microorganisms
could play a significant role in this respect, if we can exploit their unique properties of tolerance to extremities, their
ubiquity, genetic diversity, their interaction with crop plants and develop methods for their successful deployment in agriculture
production. Besides influencing the physico-chemical properties of rhizospheric soil through production of exopolysaccharides
and formation of biofilm, microorganisms can also influence higher plants response to abiotic stresses like drought, chilling
injury, salinity, metal toxicity and high temperature, through different mechanisms like induction of osmo-protectants and
heat shock proteins etc. in plant cells. Use of these microorganisms per se can alleviate stresses in crop plants thus opening
a new and emerging application in agriculture. These microbes also provide excellent models for understanding the stress tolerance,
adaptation and response mechanisms that can be subsequently engineered into crop plants to cope with climate change induced
stresses.
KeywordsAbiotic stress tolerance–Microorganisms–Crop production–Climate change
... Interestingly, it has been shown that mycorrhiza increases flood tolerance of plants, mainly through suppression of toxic products of anaerobic respiration including ethanol (Osundina 1998;Rutto et al. 2002). Although these observations were made on endomycorrhiza using Glomus clarum and Gigaspora margarita, the same role in ectomycorrhiza is suggested, considering many other shared physiological roles between these mycorrhizal types. ...
We report the first mycorrhizal fungal aldehyde dehydrogenase gene, ald1, which was isolated from the basidiomycete Tricholoma vaccinum. The gene, encoding a protein Ald1 of 502 amino acids, is up-regulated in ectomycorrhiza. Phylogenetic analyses using 53 specific fungal aldehyde dehydrogenases from all major phyla in the kingdom of fungi including Ald1 and two partial sequences of T. vaccinum were performed to get an insight in the evolution of the aldehyde dehydrogenase family. By using competitive and real-time RT-PCR, ald1 is up-regulated in response to alcohol and aldehyde-related stress. Furthermore, heterologous expression of ald1 in Escherichia coli and subsequent in vitro enzyme activity assay demonstrated the oxidation of propionaldehyde and butyraldehyde with different kinetics using either NAD(+) or NADP(+) as cofactors. In addition, overexpression of ald1 in T. vaccinum after Agrobacterium tumefaciens-mediated transformation increased ethanol stress tolerance. These results demonstrate the ability of Ald1 to circumvent ethanol stress, a critical function in mycorrhizal habitats.
... Many experiments reported that AM fungi increased P contents of the host plants. But AM fungi may or may not increase uptake of these N, K and Mg, depending on host plants, species of AM fungi and soil conditions (Marschner and Dell, 1994; Taylor and Harrier, 2001; Rutto et al., 2002). Wu and Xia (2006) reported that level of Mg in leaves of tangerine inoculated with AM fungi was higher in AM seedlings than those in non-AM seedlings under well-watered and water stress conditions. ...
Thailand is part of Southeast Asia that covers the center of diversity of citrus species, where various species of thegenus are widely grown. One of the most common is tangerine (Citrus reticulata), which is commonly grown bygrafting on rootstocks of different tangerine varieties or other citrus species. The objective of this study is to investigateresponses of some Citrus spp. seedlings to arbuscular mycorrhizal (AM) fungi, and thus their potential as rootstocks.The experiment was done with four tangerine varieties, Cleopatra, Fremont, Ocean and Sainamphung; and four othercitrus species, lime (C. aurantifolia), pomelo (C. maxima), sweet orange (C. sinensis) and Troyer citrange (Citrussinensis????Poncirus trifoliata), in pots for five months. Roots of non-inoculated plants were not infected with AM fungi,while inoculated plants were heavily infected with AM fungi, and contained 14-28 AM spores per 10????g of rhizospheresoil. Most of the citrus responded positively to AM fungi, but with different magnitudes among the varieties and species.Lime and pomelo seedlings were fast growing compared to other citrus species. Total dry weight and N, P, K and Mgcontents were increased most strongly by AM fungi in lime, pomelo and tangerine varieties Ocean, Fremont andSainamphung, but little or none in Cleopatra, Troyer and sweet orange. Lime was the most outstanding in the responseto AM fungi, followed by Ocean tangerine and pomelo. The potential of lime, pomelo and Ocean tangerine as rootstockfor tangerine should be further investigated.
Both biotic and abiotic stresses are major limits to agricultural production. Under stress conditions, plant growth is affected by a number of factors such as hormonal and nutritional imbalance, ion toxicity, physiological disorders, susceptibility to diseases, etc. Plant growth under stress conditions may be enhanced by the application of microbial inoculation including plant growth promoting rhizobacteria (PGPR) and mycorrhizal fungi. These microbes can promote plant growth by regulating nutritional and hormonal balance, phytohormones and synthesizing some compounds or enzymes that can develop plant growth, solubilizing minerals such as phosphorus and inducing resistance against stresses. This environmentally friendly bacterial population is effective in promoting crops productivity under stress conditions. The present review comprehensively discusses recent developments on the effectiveness of PGPR for enhancing plant growth under stressful environments. The key mechanisms involved in plant stress tolerance and the effectiveness of microbial inoculation for enhancing plant growth under stress conditions have been discussed at length in this review.
Plant beneficial microorganisms (PBMs) have a tendency to colonize soil and various parts of plant (especially in root) for augmenting the nutrients in soil as well as secretion of other biomolecules. In either ways PBMs help to improve plant productivity and immunity for increasing tolerance capability or adaptation towards diverse climatic conditions. Although earlier reports have exhibited significant contribution of PBMs for the development of induced systemic resistance against abiotic stresses like low/high temperature, salinity, moisture deficit and acidic conditions. PBMs play crucial role in nutrients transportation from soil to plant that leads to the reduction in application of chemical fertilizers and low accumulation of toxic elements in agricultural lands. Reducing or minimizing the use of chemical fertilizers may also help to decrease the occurrence of contamination by fertilizers and maintains ion balance in soil, as a result soil health will be improved. In addition, exopolysaccharide secretion and biofilm formation by PBMs alter the physico-chemical properties of rhizospheric soil that also impact higher plant response to abiotic stress, such as moisture deficit, metal toxicity, chilling injury, saline, and low/high temperature. PBMs mediated adaptation or tolerance in plants towards different climatic conditions might be accompanied through different mechanisms like induction of cold/heat shock proteins and osmoprotectants. Application of these microorganisms might be effective for alleviation of climate change in various crops, thus developing an emerging approach towards sustainable agriculture. These microorganisms might also be utilized as model to decipher stress tolerance mitigation and responding processes that can be established for crop plants to cope with the stress caused by climate change.
Agriculture is considered to be one of the most vulnerable sectors to climate change. Crop production, particularly in tropical regions is facing increasing stresses caused due to natural and anthropogenic factors. Stress in plants refers to external conditions that adversely affect growth, development, or productivity of plants. Stresses trigger a wide range of plant responses like altered gene expression, cellular metabolism, changes in growth rates, crop yields, etc. A plant stress usually reflects some sudden changes in environmental condition. Plant stress can be divided into two primary categories namely abiotic stress and biotic stress. Abiotic stress imposed on plants by environment may be either physical or chemical, while biotic stress exposed to the crop plants is a biological unit like diseases and insects. Plants in natural systems and crop lands are simultaneously exposed to both biotic and abiotic stresses. Abiotic stresses such as drought (water stress), excessive watering (water logging), extreme temperatures (cold, frost, and heat), salinity, and mineral toxicity negatively impact growth, development, yield, and seed quality of crops and other plants. Abiotic stress tolerance plays a vital role in determining crop productivity and distribution of plant species across the environment. These factors are likely to cause serious negative impacts on crop growth and yields and impose severe pressure on our land and water resources. The plant provides nutrition to the endophytes, while in return endophytes help in adaption to abiotic conditions like nutrients limitation, salination, and extreme pH, drought, temperature variation, and protection from pathogens, insects, and nematodes.
Key message
This article describes the composition of root exudates, how these metabolites are released to the rhizosphere and their importance in the recruitment of beneficial microbiota that alleviate plant stress.
Abstract
Metabolites secreted to the rhizosphere by roots are involved in several processes. By modulating the composition of the root exudates, plants can modify soil properties to adapt and ensure their survival under adverse conditions. They use several strategies such as (1) changing soil pH to solubilize nutrients into assimilable forms, (2) chelating toxic compounds, (3) attracting beneficial microbiota, or (4) releasing toxic substances for pathogens, etc. In this work, the composition of root exudates as well as the different mechanisms of root exudation have been reviewed. Existing methodologies to collect root exudates, indicating their advantages and disadvantages, are also described. Factors affecting root exudation have been exposed, including physical, chemical, and biological agents which can produce qualitative and quantitative changes in exudate composition. Finally, since root exudates play an important role in the recruitment of mycorrhizal fungi and plant growth-promoting rhizobacteria (PGPR), the mechanisms of interaction between plants and the beneficial microbiota have been highlighted.
Crop plants are subjected to different kinds of stresses, and as a result, their growth is adversely affected. Different mechanisms may be used by crop plants to tolerate the stress including the morphological and physiological ones. However, the efficiency of such mechanisms differs in sensitive and tolerant crop species, and the tolerant species can utilize such mechanisms more efficiently. The other important aspect of stress tolerance in crop plants is related to their interactions with the soil microbes. A wide range of soil microbes including arbuscular mycorrhizal (AM) fungi, plant growth-promoting rhizobacteria (PGPR), and endophytic bacteria as well as their interactions can affect stress tolerance in crop plants. Such a topic is among the most important research subjects and can greatly affect the efficiency of crop plants under stress. Mycorrhizal fungi are soil fungi, developing a symbiotic association with their nonspecific host plants, and increase their growth by enhancing the uptake of water and nutrients. PGPR are soil bacteria, which can enhance the growth of their host plant by different mechanisms through developing a nonsymbiotic association. The endophytic microbes are able to colonize the inner parts of their host plant and affect its growth under different conditions including stress. The interactions of soil microbes in most cases can positively affect the growth of the host plant under different conditions including stress. The important point, which deserves investigation, is the interaction of mycorrhizal fungi, PGPR, and the endophytic bacteria, which reside in plant roots affecting plant growth and yield production. Such details will be useful for the production of more tolerant microbial inoculums, which are more efficient under different conditions including stress. Some of the most important and recent findings related to the growth of crop plants under stress, as affected by the interactions of soil microbes, along with the future perspectives are presented, reviewed, and analyzed.
The effect of arbuscular mycorrhiza (AM) fungi on growth, nutrient uptake and root infectivity was determined in passion fruit (Passiflora edulis var. edulis), rough lemon (Citrus limon) and papaya (Carica papaya var. solo) seedlings raised under four phosphorus regimes (0, 0.44, 0.88 and 1.68 mg/ml) in sand culture and also in sand/nitrosol sterile and unsterile conditions. Inoculation with AM fungi increased the plant height, leaf number and stem girth in relation to un-inoculated seedlings grown under equivalent P concentrations. An increase in plant height, leaf number and stem girth also occurred in both inoculated sterile and un-sterile sand/nitrosol media in relation to un-inoculated sterile and unsterile media. AM also increased the leaf area and the root, leaf and stem fresh and dry weights and also caused an increase in the uptake of phosphorus in the leaf tissues. It also favored mycorrhizal infectivity of roots and increased the root absorptive surface area. This study indicates that AM fungi improves tropical fruit seedling performance by increasing the capacity of roots to absorb and utilize plant nutrients and also by increasing the effective root surface area from which available form of nutrients are absorbed.
For re-forestation of metal-contaminated land, ectomycorrhizal trees may provide a solution. Hence, the study of the interaction is necessary to allow for comprehensive understanding of the mutually symbiotic features. On a structural level, hyphal mantle and the Hartig' net formed in the root apoplast are essential for plant protection and mycorrhizal functioning. As a model, we used the basidiomycete Tricholoma vaccinum and its host spruce (Picea abies). Using an optimized hydroponic cultivation system, both features could be visualized and lower stress response of the tree was obtained in non-challenged cultivation. Larger spaces in the apoplasts could be shown with high statistical significance. The easy accessibility will allow to address metal stress or molecular responses in both partners. Additionally, the proposed cultivation system will enable for other experimental applications like addressing flooding, biological interactions with helper bacteria, chemical signaling, or other biotic or abiotic challenges relevant in the natural habitat.
The present investigation was conducted during 2006 and 2007 growing seasons in order to study the effects of different salinity levels on the growth and chemical composition of sour orange and Volkamer lemon rootstocks. Besides, this research was also undertaken to elucidate the efficiency of mycorrhizal colonization on controlling the various hazards accompanying salinity stress. One-year-old sour orange and Volkamer lemon rootstocks were kept in a glasshouse and irrigated with control (non-saline), 1500ppm, 3000ppm and 4500ppm of salinity levels. Salinity decreased arbuscular mycorrhizal (AM) colonization. In both the AM and non AM, leaf area, trunk cross-sectional area, total, top, leaf and root dry weights were decreased under salinity. The plants inoculated with the AM fungus had significantly higher growth parameters compared to the non-inoculated plants. Increasing the salinity level tended to increase the concentrations of leaf Na, N, Ca and Cl while P, K, Mg, Fe, Mn, Zn and Cu decreased. On the contrary, inoculating the seedlings with AM tended to increase the levels of P, K, Mg and Zn. Whereas leaf N, Ca and Na of inoculated seedlings was significantly lower than that of un-inoculated ones. Leaf Cl, Fe, Mn and Cu contents did not statistically vary in this concern.
A greenhouse experiment was conducted to determine the influence of arbuscular mycorrhizal (AM) fungus inoculation on water stress, salt stress and flooding tolerance of three subspecies of Scleocarya birrea (A. Rich.) Hochst. Gigaspora margarita Baker and Hall was used for the inoculation. All the three subspecies of S. birrea had high tolerance both to water stress and flooding even without G. margarita inoculation. All flooded seedlings developed lenticels and survived three months of flooding. Non-mycorrhizal seedlings of S. birrea subsp. multifoliolata survived even under electric conductivity of up to 7.1 dS.m(-1). Root colonization by G. margarita markedly improved tolerance of S. birrea seedlings to water stress, salt stress and flooding. In particular, S. birrea subsp. caffra under water stress and flooding conditions showed the highest response to inoculation. Mycorrhizal S. birrea subsp. multifoliolata recorded enhanced uptake of N, P, Ca and Mg at 7.1 dS.m(-1). These results demonstrate that even though S. birrea has natural tolerance to water stress, salt stress and flooding, AM fungus is very effective in strengthening the tolerance of S. birrea grown in and and semi arid areas.
The effect of arbuscular mycorrhizal (AM) inoculation and activated charcoal on growth and nutrition in peach seedlings treated with peach root-bark extracts was studied under greenhouse conditions. Peach root-bark extracts significantly inhibited growth in both mycorrhizal and non-mycorrhizal seedlings, although mycorrhizal seedlings demonstrated better growth and biomass yield. Activated charcoal slightly alleviated the negative effects of root-bark extract treatment but reduced the benefits derived from mycorrhizal symbiosis. The initiation of mycorrhizal symbiosis may be delayed by activated charcoal through the adsorption of signal chemicals from host plants. Generally, mycorrhizal seedlings had better P and Ca nutrition. There were no differences in mycorrhizal infection among the inoculated plants, but there was increased sporulation in root-bark extract treatments without activated charcoal. These results suggest that activated charcoal should be applied after mycorrhizal symbiosis has been established.
The effect of pre-inoculation with arbuscular mycorrhizal fungi (AMF) on post-transplant growth of peach seedlings in replant and non-replant soils was studied for two successive seasons. Seedlings raised in sterile media and pre-inoculated with soil-based Gigaspora margarita inoculum were transplanted in replant and non-replant field soils alongside non-inoculated controls. Pre-inoculated seedlings transplanted in non-replant soils showed greater initial growth in the first year. Plant height, and lateral shoot length and number was highest in non-replant soils irrespective of mycorrhizal pre-inoculation. Similarly, biomass yield was significantly higher in seedlings in non-replant soils, though there were no significant differences in shoot/root ratios, and in tissue mineral content between and within treatments. Seedling infection by indigenous AMF was high in both replant and non-replant soils, and even non-inoculated seedlings recorded high infection levels after the first season. Generally, mycorrhizal activity was lower, and spore populations higher in replant soils, while the opposite was true in non-replant soils. It seems that soil sickness has a negative impact on plant metabolism and limits the capacity of the plant host to support the mycorrhizal symbiosis.
A study of peach ( Prunus persica (L.) Batsch) seedlings which became stunted in soil fumigated with methyl bromide-chloropicrin indicated that poor growth was associated with a major deficiency of P aggravated by marginal levels of Cu and Zn. The concentrations of K, Ca, and Mg were also lower in stunted plants. Where stunting occurred, mycorrhizal root colonization was very poor and viable inoculum was low. These results indicate that elimination of mycorrhizal fungi is the primary factor in fumigation-induced stunting of peach, and also suggest that a reduction in Cu uptake in combination with previously recognized P and Zn deficiencies may contribute to poor growth.
Peach seedlings had severe Zn-deficiency symptoms and grew poorly in pots of steamed Yolo loam with or without sand admixed. Growth was greatly improved in pots by inoculating with one of a number of Endogone (Phycomycetes) cultures, which formed vesicular-arbuscular mycorrhizae with the seedlings. Plants with inocula disinfested of associated field organisms by treatment with Chloramine Τ were larger than those with untreated spores. All 6 inocula tested were beneficial, although only 2 completely prevented appearance of Zn-deficiency symptoms. Peach seedlings grown with one of these two had foliar Zn levels 2-3 times those of the controls.
Endomycorrhizae of aquatic plants may be important in phosphorus uptake and carbon exchange in lakes, but the environmental controls on mycorrhizal distribution are not known. We examined biogeochemical variables that were correlated with aquatic endomycorrhizae of isoetid-type macrophytes in an oligotrophic, softwater lake. En- domycorrhizal infection was greatest in the shallow stations with high sediment redox potential and lowest in the deeper stations where there was low redox potential and high sediment organic content and porewater P levels. There was a significant 0. = +0.93, P < 0.05) positive correlation between percentage of hyphal infection of the roots and a root ergosterol (a specific fungal sterol) index determined per root mass. Fungal vesicle infection was also positively correlated with the root ergosterol index, although not significantly (r = +0.76, P = 0.14). Fur- thermore, the root ergosterol index was significantly correlated with plant rosette density (r = +0.97, P < 0.03. An increase in rosette density of isoetids increases the number of lacunae transporting oxygen to the roots, perhaps increasing fungal infection. The root ergosterol index was also significantly (P < 0.05) correlated with sediment redox status, porewater phosphate, solid phase iron-bound P, exchangeable inorganic P, and inorganic adsorbed P There were no significant correlations between above- or belowground biomass or porewater NH,' with the root ergosterol index, and porewater DOC was weakly correlated (P = 0.08) with the ergosterol index. Isoctid-type plants are common in oligotrophic softwater lakes, and knowledge of environmental variables that are associated with endomycorrhizae will facilitate in management and restoration of these types of submersed vegetation.
Les effets de l'interaction entre #Pratylenchus vulnus$ et le champignon mycorrhizien #Glomus mosseae$ sur les porte-greffe de pêcher "Nemared" ont été étudiés en microparcelles pendant deux saisons de croissance. Le poids frais des pieds, le diamètre de la tige, la longueur des pieds et le poids frais des racines sont significativement plus faibles chez les pieds infestés par le nématode - qu'ils soient ou non colonisés par #G. mosseae$ - que chez les pieds non infestés. Un taux élevé de phosphore augmente la croissance des pêchers dans le cas de témoins non mycorrhizés. Les traitements des pieds infestés par "P. vulnus$ à l'aide de mycorrhizes provoquent une diminution de la population finale du nématode et du nombre de nématodes par gramme de racine par rapport aux pieds infestés par #P. vulnus$ et non traités à l'aide du champignon. La colonisation par les mycorrhizes n'est pas affectée par la présence du nématode. Chez les pieds infestés par le nématode, le Cu est le seul élément déficitaire détecté par analyse foliaire, quoique des taux faibles de fer y aient été observés. Les taux les plus élevés de Ma, Mg, Mn et Zn ont été détectés chez les pieds infestés par #P. vulnus$. Les pieds mycorrhizés recèlent les taux les plus élevés de Cu et d'Al. #G. mosseae$ est bénéfique pour la croissance des pêchers "Nemared" mais ne leur confère aucune protection contre #P. vulnus$. (Résumé d'auteur)
We have examined the hypothesis that cytokinins transported from roots to shoots affects leaf growth, stomatal conductance,
and cytokinin concentration of leaves of Phaseolus and a hybrid poplar (Populus trichocarpa × Populus deltoides) with hypoxic roots. Because cytokinins may interact with other substances, potassium and calcium concentrations were determined
in xylem sap of Populus plants with hypoxic and aerated roots while gibberellin (GA) concentrations were measured in shoot tissues. Root hypoxia
decreased leaf growth and closed stomata in both species. In both species, fluxes of cytokinins out of the roots were reduced,
but no differences in bulk leaf concentrations were measured between the hypoxic and aerated plants. Shoots with aerated roots
contained slightly higher concentrations of GA1 and GA3 than shoots from hypoxic plants. There were no differences in calcium or potassium concentrations in xylem sap between aeration
treatments. Exogenously applied cytokinins did not alleviate the growth or stomatal responses caused by root hypoxia. Information
on the site(s) and mechanism(s) of cytokinin action and the ways in which cytokinins are compartmentalized within plant cells
will be required to understand the physiological significance of cytokinin transport in the transpirational stream.
Carrot (Daucus carota L.) cell cultures show high sensitivity to ethanol since both unorganized cell growth and somatic embryogenesis are strongly inhibited by ethanol at relatively low concentrations (10-20 millimolar). The role of acetaldehyde on ethanol-induced injuries to suspension cultured carrot cells was evaluated. When ethanol oxidation to acetaldehyde is prevented by adding an alcohol-dehydrogenase (EC 1.1.1.1) inhibitor (4-methylpyrazole) to the culture medium, no ethanol toxicity was observed, even if ethanol was present at relatively high concentrations (40-80 millimolar). Data are also presented on the effects of exogenously added acetaldehyde on both carrot cell growth and somatic embryogenesis. We conclude that the observed toxic effects of ethanol cannot be ascribed to ethanol per se but to acetaldehyde.
Stomatal gas exchange and zeatin riboside levels (as determined by ELISA) of flax (Linum usitatissimum L.) were investigated with regard to an observed growth response of these plants to vesicular-arbuscular mycorrhizal infection, which was shown not to be related to increased nitrogen, phosphorus or potassimum contents of plants. Additionally, the stomatal gas exchange responses of non-mycorrhizal plants to zeatin and abscisic acid were studied by xylem application experiments. In comparison to non-mycorrhizal plants highly infected plants revealed increased transpiration and CO2 assimilation rates, while stomatal density was not affected and the shoot water potential (Ψ) was unchanged or even lowered. These findings indicated that enhanced stomatal opening was not primarily caused by an improved water supply of the shoots. Additionally, respiration rates of leaves of mycorrhizal plants were lower when compared with non-mycorrhizal plants at the end of the experiments. During the beginning of the mycorrhizal infection zeatin riboside levels in roots were temporarely decreased when compared to non-mycorrhizal plants, whereas levels where increased in shoots. However, when the symbiosis had established colonized roots revealed significantly higher zeatin riboside than those of non-mycorrhizal plants. Significant growth responses of shoots and roots due to mycorrhizal infection were preceded by higher zeatin riboside levels in the respective organs. Zeatin applied alone into the vascular system of non-mycorrhizal flax did not affect stomatal gas exchange, whereas abscisic acid applied alone decreased transpiration and CO2 assimilation rates. Additional application of zeatin, however, partially reversed abscisic acid-mediated effects and improved transpiration and CO2 assimilation rates showing analogy to the mycorrhizal infection. These results leed to the conclusion, that the enhanced internal Cytokinin levels are involved in the improved photosynthesis and growth of mycorrhizal flax.
Pepper (Capsicum annuum L.) plants with and without VA-mycorrhiza (formed by the fungus Glomus deserticola Trappe, Bloss & Menge), VAM, and NVAM, respectively, were drought acclimated (DA) by four drought cycles or kept well watered (NDA). All plants were then subjected to an additional drought cycle. Similar shoot mass and leaf area were achieved in all treatments by giving more P fertilizer to NVAM than VAM plants. With few exceptions, leaf nutrient concentrations of 12 elements, including P, were either equal or higher in NVAM than VAM plants. During peak drought stress, plants with the combination of VAM-DA treatments had the greatest drought resistance, as indicated by the highest leaf water potential, turgor, relative water content and frequency of non-wilted plants. Some drought resistance, as indicated by intermediate frequency of wilting, occurred when VAM or DA were applied singly. Nutrition and plant size were not associated with this drought resistance. Extraradical hyphae development and soil aggregation of VAM plants were enhanced by drought acclimation, suggesting that these hyphae improved drought resistance by facilitating soil water uptake.
Temperature-stress tolerance through symbiosis with arbuscular mycorrhizal (AM) fungi [Gigaspora margarita (GM) and Glomus sp. R10 (GR)] in seedlings of asparagus (Asparagus officinalis L., cv. Mary Washington 500W) was investigated. Seven weeks after inoculation under a bed soil kept at 25 °C/20 °C (clay/night) under a 16-hr photoperiod, AM fungus-infection levels in a root system reached 63.0% in GM and 20.0% in GR. AM fungus-infected plants were taller, produced more shoots, accumulated more dry matter and attained higher P concentration in both shoots and roots than the noninoculated plants. Under a constant 15 °C bed soil for 4 weeks followed by an elevation to 25 °C/20 °C, shoot elongation was promoted in AM fungus-infected plants, especially after the third emergence; the effect was more pronounced in GR than in GM plots. Eleven weeks after inoculation, AM fungus infection levels reached 48.9% in GM and 58.9% in GR. Plant height, no. of shoots, no. of crowns, dry weight, and phosphorus concentration in shoots and roots became greater in AM fungus-infected plants than in noninoculated ones. When bed soil was heated to 30 °C, shoot growth after the fourth emergence became restricted in noninoculated plants, whereas shoot emergence and elongation were promoted, especially after the fifth and fourth emergences in GM and in GR plots, respectively. Eleven weeks after inoculation, AM fungus infection levels reached 66.3% in GM and 36.7% in GR. All measured parameters in AM fungus-infected plants were larger than in the noninoculated plants; the effect appeared significantly greater in GM than in GR plots. These results reveal that the asparagus seedlings infected with AM fungus tolerated greater temperature stress through symbiosis and that the degree of tolerance differed with the fungal species.
Six-month-old seedling rootstocks of peach cultivars Siberian C, Bailey and Harrow Blood, and mature trees in a 4-yr-old orchard which was planted with rootstock cultivars Siberian C, Bailey, Harrow Blood, Chui Lum Tao, Tzim Pee Tao, Lovell, Halford, H7338013, H7338016 and H7338019 grafted with scion cultivar Redhaven, were rated for colonization by indigenous vesicular-arbuscular mycorrhizal fungi after growth in a local sandy soil. Feeder roots of all the rootstocks were heavily colonized. However, no significant differences between the cultivars were observed with respect to percentage of root lengths colonized under these field conditions. Fungi identified on the basis of spore extraction from soil around colonized roots included G. aggregatum, G. mosseae, G. tortuosum, Scutellospora aurigloba, and S. calospora.Key words: Intraspecific receptivity, endomycorrhizae, Prunus persica
Controversy exists as to whether ethanol ever accumulates to toxic levels in anaerobic tissues of higher plants. In order
to manipulate the internal concentrations of ethanol and relate these to anaerobic injury, seedlings of chickpea (Cicer arietinum L.) were incubated under strict anoxia in vessels in which the anaerobic atmosphere either remained static or else was circulated
with that of a large anaerobic incubator. Incubation with a circulating, as compared with a static, anaerobic atmosphere doubled
the time that the seedlings could be kept under anoxia and emerge in subsequent survival testing in the glasshouse. Circulating
the anaerobic atmosphere gave a 13-fold reduction in the accumulation of ethanol in the seedlings. Parallel experiments which
varied the ratio of head space relative to seedling number confirmed that the dilution of the volatile products of anoxia.increased
survival. These products included carbon dioxide, ethanol and traces of acetaldehyde. While carbon dioxide may play a role
in modifying glycolytic activity under anoxia, it is suggested that it is not directly toxic and that it is the reduction
in ethanol concentration in the seedlings as a result of head space dilution that contributes to their increased longevity
in circulating anaerobic atmospheres.
Cowpea [Vigna unguiculata (L.) Walp.] and soybean [Glycine max (L.) Merr.] plants were grown in pots and either inoculated with the vesicular-arbuscular (VA) mycorrhizal fungi, Glomus intraradices Schenck and Smith (cowpea) and G. mosseae (Nicol & Gerd.) Gerd. and Trappe (soybean), or provided with regular P fertilization (non-VA mycorrhizal plants). When plants were six to ten weeks old, roots were exposed to osmotic stress and stomatal behaviour monitored for several hours. Leaves of VA mycorrhizal cowpea had higher stomatal conductance (gS) than those of non-mycorrhizal cowpea before and after lowering soil water potential (Ψ) to −0.7 MPa with either sorbitol or macronutrient solutions. Pre-stress gs and the initial decline in gs after exposure to − 0.5 MPa sorbitol were similar in mycorrhizal and non-mycorrhizal soybean leaves. Stomatal conductance was higher in the latter after 2 h but higher in the former after 21 h. CO2 exchange rates and leaf water relations were similar in VA mycorrhizal and non-mycorrhizal soybean before and after soil Ψ was lowered. Higher gs at equal soil Ψ suggests that mycorrhizal root systems either scavenged water of low activity more effectively or influenced nonhydraulic root-to-shoot communication differently from that in non-infected root systems.
S ummary
Assessment of infection is an essential part of many studies involving VA mycorrhiza. A summary is given of the range of techniques that have been used. We calculated the standard error of four methods of assessment based on observations of stained root samples either randomly arranged in a petri dish or mounted on microscope slides. The methods are based on presence or absence of infection at root/grid intersect points, on a visual estimate of percentage cortex occupied by fungus or on estimates of length, or presence or absence of infection in root pieces mounted on slides. The number of replicate observations required for a given standard error % infection can be read from the curves provided. The advantages of the different methods of assessment are discussed and reasons given why they all probably overestimate the true values.
Pepper (Capsicum annuum L.) plants with and without the VA-mycorrhizal fungus Ghmus deserticola Trappe. Bloss and Menge (VAM and NVAM. respectively), were drought acclimated by four drought cycles (DA) or kept well watered (NDA). All plants were then subjected to an additional drought followed by a 3-day irrigation recovery period. Measurements of water relations, gas exchange and carbohydrates were made at selected intervals throughout the drought cycles and recovery. To equalize growth and avoid higher P in VAM plants. NVAM plants received higher P fertilization. Consequently, similar transpirational surface and shoot mass were achieved in all treatments, but NVAM had a higher tissue P concentration than VAM plants. Plants that were either VAM or DA, but especially the VAM-DA plants, tended to be high in net photosynthetic flux (A), A per unit of tissue P concentration (A/P), stomatal conductance (g) or leaf turgor (Ψp) during high environmental stress or recovery from stress. During this time, NVAM-NDA plants had low A. A/P and leaf chlorophyll, but high soluble carbohydrate concentrations in their leaves. All VAM and DA plants had some osmotic adjustment compared to the NVAM-NDA plants, but VAM-DA plants had the most. Osmotic adjustment was not due to accumulation of soluble carbohydrate. The high turgor, A and g in the VAM-DA plants during and following environmental stress indicated superior drought resistance of these plants; however, osmotic adjustment was only apparent during recovery and cannot account for the observed drought resistance during environmental stress. Drought resistance of VAM-DA plants was not attributable to high leaf P concentration or confounded by differences in plant transpirational surface.
1) The range of mycorrhizal types is briefly compared, with respect to structure and nutritional mode of the symbionts. Ectotrophic, vesicular‐arbuscular and erica‐ceous mycorrhizas of autotrophic plants are selected for further consideration, both because the symbionts have nutritional similarities, and because recent experimental work provides a basis for useful comparisons.
(2) A generalized, qualitative model of interactions between the symbionts is presented, with the aim of providing a framework for discussion of the similarities and differences between the mycorrhizas of autotrophic plants. The model describes the distribution of biomass and the flow of carbon and mineral nutrients, together with the effects of distribution of fungal inoculum and environmental conditions.
(3) Experimental work pertaining to the model is discussed with emphasis on experimental problems, growth depressions, changes in root: shoot ratio and nitrogen nutrition, as well as the more frequently discussed increases in growth and improved phosphorus nutrition.
(4) Nitrogen is considered with respect not only to its uptake, but also in relation to the possible involvement of mycorrhizas in pH regulation and the absorption of cations by plants.
(5) The importance of mycorrhizas in forestry and agriculture is briefly discussed.
(6) It is concluded that more research into the physiology and ecology of mycor‐rhizal associations is required, in order to provide a basis for effective management of the symbioses in agricultural and natural ecosystems.
Benzyladenine (BA) and gibberellic acid (GA) were applied together as a foliar spray to young tomato plants growing in pots of well drained soil, waterlogged soil or in nutrient solution supplied with air (aerobic), nitrogen gas (anaerobic), or ethylene (20 or 100 ul 1−1 in air) for up to 6 days.
BA and GA (10 fig ml−1) lessened the inhibitory effects of waterlogging on stem elongation, transpiration and the increase of fresh and dry wt of the shoots. In absolute terms the promotion of shoot growth by BA and GA was greater in plants growing in non-waterlogged than in waterlogged soil. Root growth was inhibited by BA and GA. The effect of waterlogging in promoting adventitious rooting at the base of the stem was reduced by BA and GA.
Epinastic curvature by petioles was promoted by growing plants in waterlogged soil or anaerobic solution culture in association with an increase in the production of ethylene by the petioles. Applications of BA and of GA inhibited this epinastic growth but they did not lower the rate of ethylene production. However BA and GA diminished the effectiveness of ethylene as a stimulator of epinastic curvature.
The application of ethylene to the roots inhibited the accumulation of dry wt by the root system and decreased slightly the growth promoting effects of BA and GA in the shoots.
The inhibiting effect of waterlogging the root system on stem elongation could be offset if adventitious roots maintained in well aerated conditions were previously induced on the main stem above the primary roots. Epinastic curvature and ethylene production were not decreased by the presence of an adventitious root system. The extent to which applications of BA and GA may reflect the activity of endogenous hormones produced by aerobic roots is discussed.
The effects of the interaction between Pratylenchus vulnus and the endomycorrhizal fungus Glomus intraradices on growth and nutrition of Santa Lucia 64 cherry rootstock was studied under microplot conditions during one growing season.
Fresh top weight, and stem diameter of mycorrhizal plants and high P treatments with and without P. vulnus were significantly higher than those of non-mycorrhizal plants. The lowest shoot length and fresh root weights were recorded
in nematode inoculated plants in low P soil. Mycorrhizal infection did not affect the number of nematodes per gram of root
in plants infected with P. vulnus. In the presence of the nematode, internal spore production by G. intraradices was significantly reduced. No nutrient deficiencies were detected through foliar analysis, although low levels of Ca, Mn
and Fe were detected in nematode treatments. Mycorrhizal plants achieved the highest values for N, P, S, Fe, and Zn, whereas
high P treatments increased absorption of Ca and Mn. Early mycorrhizal infection of Santa Lucia 64 cherry rootstock by G. intraradices confers increased growth capacity in the presence of P. vulnus.
Leek, maize, and pigmented soybean roots colonized by vesicular-arbuscular mycorrhizal (VAM) fungi were assessed for succinate dehydrogenase (SDH) activity using the nitro blue tetrazolium chloride (NBT)-succinate method. NBT-succinate-reacted roots, cleared in a 55 C drying oven in 5% (w/v) KOH for 24 h or longer and observed as whole mounts, revealed signs of intraradical VAM fungus colonization more clearly than roots cleared by the standard 20% (w/v) boiling chloral hydrate method. Combined clearing of NBT-succinate-reacted roots using boiling chloral hydrate followed by clearing in 5% KOH at 55 C for prolonged periods also improved the visualization of intraradical fungal structures. Bleaching of NBT-succinate-reacted roots using the standard NH3-H2O2 method removed pigmentation from roots and did not alter the viability indicator, formazan. Pigmented, field-collected soybean roots were successfully cleared and bleached to reveal signs of viable and nonviable intraradical fungal structures. Counterstaining of NBT-succinate-reacted roots with acid fuchsin clearly revealed both viable and nonviable intraradical fungal structures. The NBT-succinate solution infiltrated all intraradical fungal structures after 24 h; formazan products were observed at similar concentrations in viable structures after 24, 36, and 48 h.
The influence of vesicular-arbuscular mycorrhizal (VAM) inoculation on nodulation and growth of flooded Casuarina equisetifolia J.R. and G. First was investigated. Casuarina seedlings were grown in sterile soil inoculated with Glomus clarum Nicolson and Schenick and flooding was imposed for 8 weeks. Mycorrhizal Casuarina seedlings adapted to flooding better than non-inoculated seedlings. This was achieved partly by the greater development of
adventitious roots and hypertrophied lenticels which increased oxygen availability, and therefore VAM infection in the upper
soil zone. The VAM infection led to the suppression of the accumulation of toxic products of anaerobic respiration, such as
ethanol. Mycorrhizal inoculation also prevented the total suppression of nodulation in the flooded plants. Nodulation was
observed only in the upper soil zone, and its occurrence made dinitrogen fixation possible. The results suggest that mycorrhizal
infection is essential for nodulation of Casuarina in flooded soils and is therefore related to the relatively higher dinitrogen accumulation in Casuarina under anoxic conditions.
A low-cost, low-maintenance system for soilless production of vesicular-arbuscular mycorrhizal (VAM) fungus spores and inoculum was developed and adapted for production of acidophilic and basophilic isolates. Corn (Zea mays) plants were grown with Glomus etunicatum, G. mosseae or Gigaspora margarita in sand automatically irrigated with modified Hoagland's solution. Sand particle size, irrigation frequency, P concentration, and buffer constituents were adjusted to maximize spore production. Modified half-strength Hoagland's solution buffered with 4-morpholine ethane-sulfonic acid (MES) automatically applied 5 times/day resulted in production of 235 G. etunicatum spores/g dry wt. of medium (341000 spores/pot) and 44 G. margarita spores/g dry wt. of medium (64800 spores/pot). For six basophilic isolates of G. mosseae, CaCO3 was incorporated into the sand and pots were supplied with the same nutrient solution as for acidophilic isolates. The increased pH from 6.10.2 to 7.20.2 resulted in spore production ranging from 70 to 145 spores/g dry wt. (102000–210000 spores/pot). Spore production by all isolates grown in the soilless sand system at Beltsville has exceeded that of traditional soil mixtures by 32–362% in 8–12 weeks.
In the past few years large areas of the Midwest and Great Plains have been inundated with water and plant P deficiency is often a problem after such events. Soil and plant samples were collected in 1994 in Missouri and Iowa from sites flooded and fallowed in 1993. Plants were P deficient during early vegetative growth in spite of soil tests indicating adequate P availability and typical levels of starter fertilizer. The flood and fallow problem was associated with the loss of root colonizing vesicular-arbuscular mycorrhizal (VAM) fungi that benefit the plant by increasing uptake of P. The VAM fungi are dependent upon the plant for growth and reproduction and loss of host significantly reduces VAM fungal populations in soil. The VAM fungal populations increased with the presence of a crop in the year following the flood. A greenhouse study on the effect of flooding on VAM fungi indicates the number of VAM hyphae or spores producing colonization were not affected by an extended flooding period and therefore are related to the lack of host for an extended period of time in the same manner as "long fallow disorder" in Australia. The research conducted indicates that the Post Flood Syndrome was associated with the loss of VAM fungi. Use of starter fertilizer was beneficial in correcting Post Flood Syndrome but broadcast fertilizer application appeared to have an insignificant effect on reducing the P deficiency. The application of 80 lb P/acre as starter fertilizer produced plants that were not P deficient.
The objective of this research was to study the growth response to drought of arbuscular mycorrhizal and non-mycorrhizal alfalfa (Medicago sativacv. Aragón) in relation to leaf cytokinin levels. In the experiment, four treatments were used: (a) plants inoculated with Clomus fasciculatum (Taxter sensu Gerd.) Gerdemann and Trappe and Rhizobium meliloti 102 F51 strain, (MR); (b) plants inoculated with only Rhizobium (RP); (c) plants inoculated with only mycorrhizae (MN); and (d) plants non-inoculated (NP). Non-mycorrhizal plants were supplemented with phosphorus and nonnodulated ones with nitrogen to achieve similar size in all treatments. Plants were subjected to drought by withholding irrigation in a cyclic way. The effects of drought on growth, number of stems, degree of senescence, and leaf cytokinin levels were measured.
Results of identification of cytokinins showed that dihydrozeatin riboside (dHZR) and ortno-topolin riboside (oTR) were predominant in alfalfa leaves. Nonsymbiotic plants (NP) showed higher total cytokinin concentrations (dHZR and oTR). Under drought, NP plants showed the largest percentage drop in cytokinins and lower number of stems as well as increased degree of senescent leaf tissue relative to control values. By contrast, stressed symbiotic plants (RP, MN and MR) showed higher green leaf weight than nonsymbiotic ones (NP) due to delay of leaf senescence and maintenance (RP) or increase (MN, MR) of stem leaf cytokinin levels during drought.
The relationships between growth and the different cytokinins are discussed, suggesting an important role of mycorrhizal symbiosis in maintaining cytokinin levels under drought.
This study examined the potential role of restricted phloem export, or import of substances from the roots in the leaf growth response to root hypoxia. In addition, the effects of root hypoxia on abscisic acid (ABA) and zeatin riboside (ZR) levels were measured and their effects on in vitro growth determined. Imposition of root hypoxia in the dark when transpirational water flux was minimal delayed the reduction in leaf growth until the following light period. Restriction of phloem transport by stem girdling did not eliminate the hypoxia-induced reduction in leaf growth. In vitro growth of leaf discs was inhibited in the presence of xylem sap collected from hypoxic roots, and also by millimolar ABA. Disc growth was promoted by sap from aerated roots and by 0.1 micromolar ZR. The flux of both ABA and ZR was reduced in xylem sap from hypoxic roots. Leaf ABA transiently increased twofold after 24 hours of hypoxia exposure but there were no changes in leaf cytokinin levels.
Interactions of nematodes and mycorrhizal fungi
- G S Smith
Mycorrhizal fungi and peach nursery nutrition
- Larue