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Arbuscular Mycorrhizal Fungi Role in Bioremediation in Rice in the Context of Climate Change
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Arable lands getting contaminated with heavy metals have a very high negative impact on crop plants. The establishment of the mycorrhizal association with crop plants is a sustainable strategy to overcome metal toxicity. The major aim of this study was to analyze mycorrhizae-mediated alterations on the physiology and metabolism of Oryza sativa, as well as the impact of these alterations in the metal tolerance potential of the host on exposure to cadmium (Cd) and zinc (Zn) stresses. For this, 45 d old O. sativa (var. Varsha) plants inoculated with Claroideoglomus claroideum were exposed to 1.95 g Zn kg⁻¹ soil and 0.45 g Cd kg⁻¹ soil. Mycorrhization significantly increased shoot weight, root weight, moisture content, and chlorophyll biosynthesis under Cd and Zn stresses. Mycorrhization mitigated the oxidative stress elicited in O. sativa by the elevated Cd and Zn content, and it aided in maintaining the metabolite’s level and rate of photosynthesis as compared to non-mycorrhizal plants. The circular-shaped unique structures seen as opening on the leaf surface of non-mycorrhizal plants under Zn stress, possibly for the emission of volatile compounds synthesized as a result of Zn stress, have a great chance of leaf tissue destruction. This structural modification was characterized in the case of Zn stress and not in Cd stress and can lead to the reduction of photosynthesis in O. sativa exposed to Zn stress. The reduction in oxidative stress could be correlated to the reduced uptake and transport of Cd and Zn ions in mycorrhizal plants. The exudation of tributyl acetyl citrate, 3-beta-acetoxystigmasta-4,6,22-triene, and linoleic acid from the mycorrhizal roots of rice plants has a crucial role in the stabilization of metal ions. This study proposes mycorrhization as a strategy to strengthen the Cd and Zn stress tolerance level of rice plants by regulating the physiology and metabolomics of the host plant.
Microbial inoculants containing arbuscular mycorrhizal (AM) fungi are potential tools in increasing the sustainability of our food production systems. Given the demand for sustainable agriculture, the production of such inoculants has potential economic value and has resulted in a variety of commercial inoculants currently being advertised. However, their use is limited by inconsistent product efficacy and lack of consumer confidence. Here, we propose a framework that can be used to assess the quality and reliability of AM inoculants. First, we set out a range of basic quality criteria which are required to achieve reliable inoculants. This is followed by a standardized bioassay which can be used to test inoculum viability and efficacy under controlled conditions. Implementation of these measurements would contribute to the adoption of AM inoculants by producers with the potential to increase sustainability in food production systems.
Plant-microorganism interactions at the rhizosphere level have a major impact on plant growth and plant tolerance and/or resistance to biotic and abiotic stresses. Of particular importance for forestry and agricultural systems is the cooperative and mutualistic interaction between plant roots and arbuscular mycorrhizal (AM) fungi from the phylum Glomeromycotina, since about 80% of terrestrial plant species can form AM symbiosis. The interaction is tightly regulated by both partners at the cellular, molecular and genetic levels, and it is highly dependent on environmental and biological variables. Recent studies have shown how fungal signals and their corresponding host plant receptor-mediated signalling regulate AM symbiosis. Host-generated symbiotic responses have been characterized and the molecular mechanisms enabling the regulation of fungal colonization and symbiosis functionality have been investigated. This review summarizes these and other recent relevant findings focusing on the molecular players and the signalling that regulate AM symbiosis. Future progress and knowledge about the underlying mechanisms for AM symbiosis regulation will be useful to facilitate agro-biotechnological procedures to improve AM colonization and/or efficiency.
Rice (Oryza sativa L.) is the most widely consumed staple crop for approximately half of the world’s population. Many interactions take place in paddy soil, particularly in the rice mycorrhizosphere region. Arbuscular mycorrhizal fungi (AMF) and soil microbe interactions are among the most important and influential processes that occur, as they significantly influence the plant growth and soil structure properties. Their interactions may be of crucial importance to the sustainable, low-input productivity of paddy ecosystems. In this study, we summarize the major groups of microbial communities interacting with arbuscular mycorrhizal fungi in the rice mycorrhizosphere, and discuss the mechanisms involved in these arbuscular mycorrhizal fungi and microbe interactions. We further highlight the potential application of arbuscular mycorrhizal mutualism in paddy fields, which will be helpful for the production of bioinoculants in the future.
Rice production is affected by important pathogens such as Magnaporthe oryzae, Cochliobolus miyabeanus, Monographella albescens and Sarocladium oryzae, and orchid mycorrhizal fungi can contribute to the biocontrol of these diseases. The aim of this study was to characterize the antagonism mechanisms of W. circinata against rice pathogens. The indoleacetic acid (IAA) and lytic enzymes of W. circinata were quantified. The effectiveness of the bioagent and its metabolites was assessed in vitro. Antagonism in vivo against rice blast was also investigated. Waitea circinata produced IAA (2.3 µg ml-1), cellulase and polyphenol oxidase in a qualitative test. Glucanase, chitinase and protease were also produced in culture with cell walls and in co-culture with pathogens to explain antibiosis. W. circinata acts on direct antagonism by antibiosis and volatile metabolites. Mycelial suspension reduced M. oryzae conidial germination, appressorium formation, and rice blast by 61, 82 and 84%, respectively. W. circinata, a unique bioagent, controls four rice pathogens from mechanisms of parasitism and antibiosis. The results could contribute to new formulations containing this fungus, enzymes as well as its volatile metabolites.
Main Conclusion
Rice is attacked by an armada of pathogens. Present review provides a critical evaluation of the potential of different biotic agents used to protect rice yield drop from pathogenicity and an account of unexplored areas, which might be taken into consideration to manage rice diseases.
Abstract
Rice (Oryza sativa L.), is the most important staple food of Asian countries. Rice production is significantly limited by a diversity of pathogens, leading to yield loss and deficit in current rice supply. Application of agrochemicals of diverse types has been considered as the only option to control pathogens and enhance rice production, thereby causing environmental concerns and making the pathogens resistant to the active ingredients. Increase in population and resistance of pathogen towards agrochemicals put pressure on the agronomists to search for safe, novel, eco-friendly alternative ways to manage rice pathogens. Inducing resistance in rice by using different biotic/abiotic agents provides an environmental friendly alternative way to effectively manage bacterial, fungal, and viral rice pathogens. In recent years, a number of protocols have been developed for inducing pathogen resistance by bio-priming of rice. However, a comprehensive evaluation of the potential of different biotic agents to protect rice crop loss from pathogens is hitherto lacking due to which the research on induction of defense against pathogens in rice is discontinuous. This review deals with the detailed analysis of the bacterial and fungal agents used to induce defense against rice pathogens, their mode of application, mechanism (physiological, biochemical, and molecular) of defense induction, and effect of defense induction on the yield of rice. It also provides an account of gaps in the research and the unexplored areas, which might be taken into consideration to effectively manage rice pathogens.
For centuries, rice has been the one of the most important crops worldwide; over 3.5 billion of the population relies on rice as one of the most essential staple foods. However, rice diseases are responsible for enormous global economic losses due to the damage they cause to rice crops. Major rice diseases such as bacterial leaf blight (BLB), rice blast, sheath blight (SB), bacterial panicle blight (BPB), and the rice tungro disease can contribute to a great reduction in rice yield annually. Therefore, the availability of sensitive and accurate diagnostic tools in plant disease detection is necessary to facilitate effective management practices. Traditional methods are not the best to deploy in plant disease detection, as they can be time-consuming and unreliable. Hence, the development of serological, molecular, image processing, and biosensor techniques provide important tools for accurate disease diagnosis and precise identification of plant pathogens. This review summarizes BLB, rice blast, SB, BPB, and rice tungro disease, and discusses valuable diagnostic approaches by outlining the advantages and disadvantages of each tool based on previous studies.
Many of the world's soils are experiencing degradation at an alarming rate. Climate change and some agricultural management practices, such as tillage and excessive use of chemicals, have all contributed to the degradation of soil fertility. Arbuscular Mycorrhizal Fungi (AMFs) contribute to the improvement of soil fertility. Here, a short review focusing on the role of AMF in improving soil fertility is presented. The aim of this review was to explore the role of AMF in improving the chemical, physical, and biological properties of the soil. We highlight some beneficial effects of AMF on soil carbon sequestration, nutrient contents, microbial activities, and soil structure. AMF has a positive impact on the soil by producing organic acids and glomalin, which protect from soil erosion, chelate heavy metals, improve carbon sequestration, and stabilize soil macro-aggregation. AMF also recruits bacteria that produce alkaline phosphatase, a mineralization soil enzyme associated with organic phosphorus availability. Moreover, AMFs influence the composition, diversity, and activity of microbial communities in the soil through mechanisms of antagonism or cooperation. All of these AMF activities contribute to improve soil fertility. Knowledge gaps are identified and discussed in the context of future research in this review. This will help us better understand AMF, stimulate further research, and help in sustaining the soil fertility.
Soil-related problems have grown up to be a major threat to human society. Scientific evaluation is helpful to understand the status of soil pollution and provide reference to further work. In this situation, Liaoning Province, a typical industrial and agricultural province in Northeast China, was selected as a case study region. It reviewed 200 studies published between 2010 and 2020 and recorded related data of soil heavy metal. It used model method and index method to evaluate the agricultural region. The comprehensive assessment score of Liaoning pollution level was 0.8998. Dalian was 0.9536, ranking first among the 14 cities. Huludao and Jinzhou were 0.7594 respectively, ranked the last. Heavy metal accumulation in different cities stemmed from different sources, including weathering of parent materials, industrial wastes, sewage irrigation, and mining activities. In general, the pollution level of heavy metal in Liaoning was at low risk level, but it still needs to pay attention to the health risk of heavy metal and the input of heavy metal into the soil, especially cadmium (Cd). This study provides a comprehensive assessment of soil heavy metal pollution in Liaoning, while identifying policy recommendations for pollution mitigation and environmental management.
Drought is one of the hot topics needing urgent attention in the current era of climate change. It massively disturbs the rice growth and productivity and is becoming a serious threat. The drought avoidance strategies in rice include stomatal closure, cellular adaptation and changes in root development. Moreover, the endogenous plant hormones (abscisic acid and jasmonic acid) and reactive oxygen species have paramount importance in drought tolerance in rice. The drought tolerance induces modification in biochemical, molecular and physiological properties of plants. At the molecular level, expression of several transcription-factors is modulated which further determine the activation of drought responsive gene families. Mitogen activated protein kinases and Ca signaling pathways initiate an array of signaling cascade for mediating the gene expression in rice. Approaches, conventional breeding methods combined with modern emerging techniques such as genetic engineering, to improve rice drought tolerance were discussed. This review provided recent insights into major regulatory factors against drought stress, signaling mechanisms and molecular engineering strategies (including conventional transgenic and recent genome editing approaches) to induce drought tolerance in rice.
Field crops are subjected to drought at different growth stages and cause for substantial yield loss in major crops, thus threaten to global food security. The crop researcher have evaluated numerous physiological, biochemical and molecular strategies to combat drought stresses but these approaches are not enough in present scenario. Therefore, it is argued that plants can be primed by assorted organic and in-organic promoters for excelling fortitude under stress conditions. Hence, seed priming with different agents is an auspicious area of research in stress biology and crop stress management, for conferring tolerance when plants are subjected to drought stress. However, the adaptation and tolerance mechanisms of drought stress are complex and quantitative in nature, which have been explored at physiological, biochemical and molecular levels thoroughly in this review. The concept of stress memory and its implication in future generation has also been discussed. Finally, in this review the challenges and opportunities of seed priming with effective application in crop stress management along with expanding the knowledge on deep understanding of drought stress tolerance to reduce the future yield gap are discussed thoroughly.
Arbuscular mycorrhizal (AM) symbiosis is a mutually beneficial interaction between fungi and land plants and promotes global phosphate cycling in terrestrial ecosystems. AM fungi are recognised as obligate symbionts that require root colonisation to complete a life cycle involving the production of propagules, asexual spores. Recently, it has been shown that Rhizophagus irregularis can produce infection-competent secondary spores asymbiotically by adding a fatty acid, palmitoleic acid. Furthermore, asymbiotic growth can be supported using myristate as a carbon and energy source for their asymbiotic growth to increase fungal biomass. However, the spore production and the ability of these spores to colonise host roots were still limited compared to the co-culture of the fungus with plant roots. Here we show that a combination of two plant hormones, strigolactone and jasmonate, induces the production of a large number of infection-competent spores in asymbiotic cultures of Rhizophagus clarus HR1 in the presence of myristate and organic nitrogen. Inoculation of asymbiotically-generated spores promoted the growth of host plants, as observed for spores produced by symbiotic culture system. Our findings provide a foundation for the elucidation of hormonal control of the fungal life cycle and the development of inoculum production schemes.
Almost all living plants can be simultaneously colonised by arbuscular mycorrhizal fungi in the roots and endophytes in the shoots, while also being attacked by insect herbivores. However, to date, no study has ever examined the multitrophic interactions between these two different fungal groups and insects on any species of forb. Here, we examined the effects of two commercial species mixtures of arbuscular mycorrhizal fungi (AMF) and two foliar endophytes ( Colletotrichum acutatum and Cladosporium oxysporum ) on the growth of an invasive weed, Impatiens glandulifera , and the aphids that attack it. AMF reduced plant biomass, which was most evident when C. oxysporum was inoculated. Mycorrhizal fungi had few effects on aphids, and these depended on the identity of the endophytes present. Meanwhile, endophytes tended to increase aphid numbers, but this depended on the identity of the AMF inoculum. Throughout, there were differences in the responses of the plant to the two mycorrhizal mixtures, demonstrating clear AMF specificity in this plant. These specific effects were also strongly affected by the endophytes, with a greater number of interactions found between the AMF and endophytes than between the endophytes themselves. In particular, AMF reduced infection levels by the endophytes, while some endophyte inoculations reduced mycorrhizal colonisation. We suggest that both AMF and endophytes could play an important part in future biological control programmes of weeds, but further multitrophic experiments are required to unravel the complexity of interactions between spatially separated parts of the plant microbiome.
Induced resistance provides protection in plants against insect herbivores. Silicon and mycorrhizae often prime plant defenses and thereby enhance plant resistance against herbivores. In rice, Oryza sativa L., insect injury has been shown to induce resistance against future defoliators. However, it is unknown if silicon and mycorrhizae treatments in combination with insect injury result in greater induced resistance. Using the fall armyworm (FAW), Spodoptera frugiperda Smith, two experiments were conducted to investigate whether (1) silicon or mycorrhizae treatment alters resistance in rice and (2) induced systemic resistance in response to insect injury is augmented in silicon- or mycorrhizae- treated plants. In the first experiment, silicon treatment reduced FAW growth by 20% while mycorrhizae increased FAW growth by 8%. In the second experiment, insect injury induced systemic resistance, resulting in a 23% reduction in FAW larval weight gains on injured compared to uninjured plants, irrespective of treatment. Neither silicon nor mycorrhizae enhanced this systemic resistance in insect-injured plants. Furthermore, mycorrhizae resulted in the systemic increase of peroxidase (POD) and polyphenol oxidase (PPO) activities, and injury caused a slight decrease in these enzyme activities in mycorrhizae plants. Silicon treatment did not result in a stronger induction of POD and PPO activity in injured plants. Taken together, these results indicate a lack of silicon and mycorrhizae priming of plant defenses in rice. Regardless of injury, silicon reduced FAW weight gains by 36%. Based on these results, it appears silicon-mediated biomechanical rather than biochemical defenses may play a greater role in increased resistance against FAW in rice.
Many plant species simultaneously interact with multiple symbionts, which can, but do not always, generate synergistic benefits for their host. We ask if plant life history (i.e. annual vs perennial) can play an important role in the outcomes of the tripartite symbiosis of legumes, arbuscular mycorrhizal fungi (AMF), and rhizobia.
We performed a meta‐analysis of 88 studies examining outcomes of legume–AMF–rhizobia interactions on plant and microbial growth.
Perennial legumes associating with AMF and rhizobia grew larger than expected based on their response to either symbiont alone (i.e. their response to co‐inoculation was synergistic). By contrast, annual legume growth with co‐inoculation did not differ from additive expectations. AMF and rhizobia differentially increased phosphorus (P) and nitrogen (N) tissue concentration. Rhizobium nodulation increased with mycorrhizal fungi inoculation, but mycorrhizal fungi colonization did not increase with rhizobium inoculation. Microbial responses to co‐infection were significantly correlated with synergisms in plant growth.
Our work supports a balanced plant stoichiometry mechanism for synergistic benefits. We find that synergisms are in part driven by reinvestment in complementary symbionts, and that time‐lags in realizing benefits of reinvestment may limit synergisms in annuals. Optimization of microbiome composition to maximize synergisms may be critical to productivity, particularly for perennial legumes.
The seed is the most primary requirement of agriculture. Hence, it is crucial to maintain the quality of the seeds through nature-based solutions having multiple benefits. Among the pre-sowing techniques, bio-priming has emerged out to be the most simple, economical, and eco-friendly delivery system of beneficial microorganisms in the agroecosystem. Therefore, comprehension regarding the applicability of bio-priming in restoring soil health, improving plant nutrition, and maintaining crop/seed quality has a major role in achieving the UN-Sustainable Development Goals such as no poverty, zero hunger, good health and well-being, etc. Our efforts to minimize the nonrenewable energy sources and promote the use of microbial resources at the community level need to be re-emphasized. Identification of sustainability indicators like soil enzymes, growth hormones, organic acids, etc. under bio-priming based agroecosystems is imperative for utilizing the potential microbes in the best manner. This review highlights bio-priming as a pragmatic technological option in achieving the tripartite goal of food-nutritional security, environmental stewardship/quality, and agricultural profitability under different agroecosystems.
Plants release various metabolites from roots and root exudates contribute to differences in stress tolerance among plant species. Plant and soil microbes have complex interactions that are affected by biotic and abiotic factors. The purpose of this study was to examine the differences in metabolites in root exudates of rice (Oryza sativa) cultivars and their correlation with bacterial populations in the rhizosphere. Two rice cultivars (O. sativa cv. Akamai and O. sativa cv. Koshihikari) were grown in soils fertilized with 0 g P kg−1 (− P) or 4.8 g P kg−1 (+ P). Root exudates and root-attached soil were collected at 13 and 20 days after transplanting (DAT) and their metabolites and bacterial community structure were determined. The exudation of proline, serine, threonine, valine and 4-coumarate were increased under low P conditions in both cultivars. There was a positive correlation between the concentration of pantothenate in root exudates and the representation of members of the genera Clostridium and Sporosarcina, which were negatively correlated with root dry weight. Gracilibacter, Opitutus, Pelotomaculum, Phenylobacterium and Oxobacter were positively correlated with root dry weight and presence of allantoin, 2-aminobtyrate and GlcNac. This study provides new information about the response of plants and rhizosphere soil bacteria to low P conditions.
The dynamic interactions of plants and arbuscular mycorrhizal fungi (AMF) that facilitate the efficient uptake of minerals from soil and provide protection from various environmental stresses (biotic and abiotic) are now also attributed to a third component of the symbiosis. These are the less investigated mycorrhizae helper bacteria (MHB), which constitute a dense, active bacterial community, tightly associated with AMF, and involved in the development and functioning of AMF. Although AMF spores are known to host several bacteria in their spore walls and cytoplasm, their role in promoting the ecological fitness and establishment of AMF symbiosis by influencing spore germination, mycelial growth, root colonization, metabolic diversity, and biocontrol of soil borne diseases is now being deciphered. MHB also promote the functioning of arbuscular mycorrhizal symbiosis by triggering various plant growth factors, leading to better availability of nutrients in the soil and uptake by plants. In order to develop strategies to promote mycorrhization by AMF, and particularly to stimulate the ability to utilize phosphorus from the soil, there is a need to decipher crucial metabolic signalling pathways of MHB and elucidate their functional significance as mycorrhiza helper bacteria. MHB, also referred to as AMF bioenhancers, also improve agronomic efficiency and formulations using AMF along with enriched population of MHB are a promising option. This review covers the aspects related to the specificity and mechanisms of action of MHB, which positively impact the formation and functioning of AMF in mycorrhizal symbiosis, and the need to advocate MHB as AMF bioenhancers towards their inclusion in integrated nutrient management practices in sustainable agriculture.
Waitea circinata (Warcup & Talbot) is an orchid antagonist mycorrhizal fungus with biocontrol potential against rice pathogens. This study aimed to optimize the extraction method, obtain a new extract and evaluate its efficiency against rice pathogens in vitro and in vivo, as well as to compare it with other extraction methods and W. circinata. The extracts were obtained and screened for in vitro growth inhibition against the pathogens Cochliobolus miyabeanus, Monographella albescens and Sarocladium oryzae, using the following extracts: mycelial, crude, lyophilized and mycelial mass. An additional in vitro assay was performed with the principal rice pathogen (Magnaporthe oryzae), in order to evaluate the conidial germination and appressorium formation. Based on this evaluation, the lyophilized and mycelial mass extracts were tested in vivo against rice blast (M. oryzae) and compared to the W. circinata mycelial suspension, in different application forms (simultaneous and previous). The mycelial mass extract inhibited all the pathogens, and the crude and lyophilized extracts inhibited C. miyabeanus and M. albescens, respectively. The mycelial mass extract inhibited the M. oryzae conidial germination and appressorium formation by 80 %, and the simultaneous and previous applications suppressed the rice blast by 94 %. These results indicate that the new extract can be used to control rice pathogens.
KEYWORDS:
Biocontrol; leaf scald; brown spot; sheath rot; rice blast
Arbuscular mycorrhizal fungi (AMF) represent an important group of root symbionts, given the key role they play in the enhancement of plant nutrition, health, and product quality. The services provided by AMF often are facilitated by large and diverse beneficial bacterial communities, closely associated with spores, sporocarps, and extraradical mycelium, showing different functional activities, such as N2 fixation, nutrient mobilization, and plant hormone, antibiotic, and siderophore production and also mycorrhizal establishment promotion, leading to the enhancement of host plant performance. The potential functional complementarity of AMF and associated microbiota poses a key question as to whether members of AMF-associated bacterial communities can colonize the root system after establishment of mycorrhizas, thereby becoming endophytic. Root endophytic bacterial communities are currently studied for the benefits provided to host plants in the form of growth promotion, stress reduction, inhibition of plant pathogens, and plant hormone release. Their quantitative and qualitative composition is influenced by many factors, such as geographical location, soil type, host genotype, and cultivation practices. Recent data suggest that an additional factor affecting bacterial endophyte recruitment could be AMF and their associated bacteria, even though the mechanisms allowing members of AMF-associated bacterial communities to actually establish in the root system, becoming endophytic, remain to be determined. Given the diverse plant growth–promoting properties shown by AMF-associated bacteria, further studies are needed to understand whether AMF may represent suitable tools to introduce beneficial root endophytes in sustainable and organic agriculture where the functioning of such multipartite association may be crucial for crop production.
This study examined the effects of climate change on rice production in 30 Chinese provinces spanning 1998–2017. The study used the pooled mean group technique to capture the long-run and short-run effects of changing climatic conditions on rice production. It further employed the Dumitrescu–Hurlin panel causality test to examine the path of causality between the key variables and rice production. The study found that, in the long run, average temperature negatively influenced rice production, but average rainfall had a positive effect on rice production. The results indicated that the cultivated area and fertilizer usage were positively related to rice production in the long run. The short-run results accentuated that average temperature favourably influenced nationwide rice production, whereas average rainfall had no substantial effect on national rice production. The cultivated area had a significant positive short-term relationship with rice production, although the impact of fertilizer usage on rice production was negligible in the short run. Besides, the results established a bidirectional causality between rice output and the cultivated area, but there was a one-way causality running from fertilizer usage to rice output. Finally, the results indicated that, except for rainfall, a unidirectional causality exists between temperature and rice production. The study, therefore, recommends that in the case of crop failure due to weather conditions, policymakers could implement a new pricing policy to mitigate the deterioration of the farmers’ income. The government must also develop and implement an insurance scheme that compensates farmers for catastrophes induced by rainfall deficiency.
Mycorrhiza is a symbiotic association between the roots of plants with fungi. Among the various types of mycorrhizal fungi, arbuscular mycorrhizal fungi (AMF) are the most prominent as they are obligate symbionts with a wide host range, and they play a major role in shaping ecosystems and associated productivity. Approximately 71% of vascular plant species are able to form symbiotic association with AMF. AMF primarily rely on the host for photosynthates but give much more in return for the well-being of the host plant. Most importantly they are able to improve tolerance of host plants against various biotic stresses, such as—bacterial, fungal, viral, nematode phytopathogens and herbivores. The underlying mechanism includes—competition for nutrients, space, and host photosynthates, rhizosphere alteration and host defense induction. The effectiveness of an AM association in conferring biotic stress tolerance is context dependent, affected by various biotic and abiotic factors. This review describes various mechanisms involved in AMF mediated biotic stress tolerance in plant and the biotic and abiotic factors which influences the performance of AM association.
Stress mitigation strategies present in plants alleviate stress caused by biotic and abiotic factors. In the current era, multi-omics approaches involving genomics, transcriptomics, proteomics, and metabolomics have expanded the horizon of molecular events participating in response to environmental and edaphic mediated stresses. The vigilant amalgamation of these approaches have supported a high level of information generated about root-level mechanisms involved in the alleviation of different plant-stress. Different bioinformatics tools provide a way in which huge amount of data are interpreted in a better form. This combination of multi-omics and bioinformatics approaches increases the genetic knowledge of researchers to improve the plant varieties in respect to their stress tolerance potential. Here, we provide an overview of bioinformatics resources, describing collections from multi-omics approaches, ranging from raw-data to complete databases, particularly highlighting those tools which have been used for answering the long-standing questions in the field of biotic and abiotic stress research.
Purpose
Arbuscular mycorrhizal fungi (AMF) play important roles in agriculture because of their ability to improve plant resilience against abiotic and biotic stresses. AMF as a technology to promote a more sustainable agriculture holds great potential, yet many factors affect the efficiency of this plant-microbe symbiosis leading to inconsistency in performance. The beneficial symbiosis between plants and AM fungi, also-known-as the mycorrhiza is promoted by strigolactones (SLs), carotenoid derivatives active as phytohormones and rhizosphere signals. Natural SLs are effective at extremely low concentrations, however their bioavailability in soil is scarce because their biosynthesis and exudation are plant-regulated, their degradation is fast and their mobility in soil is limited.
Methods
Through a broad synthetic chemistry approach, we explored how structurally diverse SL derivatives could improve hyphal branching of Gigaspora spp AMF under laboratory conditions and thus possibly boost mycorrhization into soil.
Results
We tested twenty-six different derivatives and we could highlight structural enhancements to promote hyphal branching of in vitro germinated AMF spores at equal, and in some cases higher levels compared to natural SLs. A subset of these derivatives was tested for bioavailability, but no clear correlation was found with their activity on hyphal branching.
Conclusion
This study suggests that we could use a targeted, chemical-design approach to synthetize new SL derivatives to enable enhanced promotion of mycorrhization and potentially enhanced bioavailability compared to natural SLs. Due to the roles of AMF in crop production systems, these results highlight new innovative approaches to promote sustainable agriculture.
Rice is a staple food for more than half of the global population. With the increasing population, the yield of rice must correspondingly increase to fulfill the requirement. Rice is cultivated worldwide in four different types of ecosystems, which are limited by the availability of irrigation water. However, water-limiting conditions negatively affect rice production; therefore, to enhance productivity under changing climatic conditions, improved cultivation practices and drought-tolerant cultivars/varieties are required. There are two basic approaches to cultivation: (1) plant based and (2) soil and irrigation based, which can be targeted for improving rice production. Crop plants primarily follow three mechanisms: drought escape, avoidance, and tolerance. Based on these mechanisms, different strategies are followed, which include cultivar selection based on yield stability under drought. Similarly, soil- and irrigation-based strategies consist of decreasing non-beneficial water depletions and water outflows, aerobic rice development, alternate wetting and drying, saturated soil culture, system of rice intensification, and sprinkler irrigation. Further strategies involve developing drought-tolerant cultivars through marker-assisted selection/pyramiding, genomic selection, QTL mapping, and other breeding and cultivation practices such as early planting to follow escape strategies and decreasing stand density to minimize competition with weeds. Similarly, the identification of drought-responsive genes and their manipulation will provide a technological solution to overcome drought stress. However, it was the Green Revolution that increased crop production. To maintain the balance, there is a need for another revolution to cope with the increasing demand.
Plant association with arbuscular mycorrhizal fungi (AMF) can increase their ability to overcome multiple stresses, but their impact on plant interactions with herbivorous insects is controversial. Here we show higher mortality of the leaf-chewer Spodoptera exigua when fed on tomato plants colonized by the AMF Funneliformis mosseae, evidencing Mycorrhiza-Induced Resistance (MIR). In search of the underlying mechanisms, an untargeted metabolomic analysis through UPLC-MS was performed. The results showed that the mycorrhizal symbiosis had a very limited impact on the leaf metabolome in the absence of stress, but significantly modulated the response to herbivory in the damaged area. A cluster of overaccumulated metabolites was identified in those leaflets damaged by S. exigua feeding in mycorrhizal plants, while unwounded distal leaflets responded similarly to those from non-mycorrhizal plants. These primed-compounds were mostly related to alkaloids, fatty acid derivatives and phenylpropanoid-polyamine conjugates. The deleterious effect on larval survival of some of these compounds, including the alkaloid physostigmine, the fatty acid derivatives 4-oxododecanedioic acid and azelaic acid, was confirmed. Thus, our results evidence the AM impact on metabolic reprograming upon herbivory that leads to a primed accumulation of defensive compounds.
Microbiological tools, biofertilizers, and biocontrol agents, which are bacteria and fungi capable of providing beneficial outcomes in crop plant growth and health, have been developed for several decades. Currently we have a selection of strains available as products for agriculture, predominantly based on plant-growth-promoting rhizobacteria (PGPR), soil, epiphytic, and mycorrhizal fungi, each having specific challenges in their production and use, with the main one being inconsistency of field performance. With the growing global concern about pollution, greenhouse gas accumulation, and increased need for plant-based foods, the demand for biofertilizers and biocontrol agents is expected to grow. What are the prospects of finding solutions to the challenges on existing tools? The inconsistent field performance could be overcome by using combinations of several different types of microbial strains, consisting various members of the full plant microbiome. However, a thorough understanding of each microbiological tool, microbial communities, and their mechanisms of action must precede the product development. In this review, we offer a brief overview of the available tools and consider various techniques and approaches that can produce information on new beneficial traits in biofertilizer and biocontrol strains. We also discuss innovative ideas on how and where to identify efficient new members for the biofertilizer and biocontrol strain family.
Arbuscular mycorrhizal fungi (AMF) and plant symbiosis is the old, fascinating and beneficial relation that exist on earth for the plants. In this review, we have elaborated that the strigolactones (SLs) are released from the roots and function with root parasite, seeds and symbiotic AMF as contact chemicals. They are transported through the xylem in the plants and can regulate plant architecture, seed germination, nodule formation, increase the primary root length, influence the root hairs and physiological reactions to non-living agents by regulating their metabolism. SLs first evolved in ancient plant lineages as regulators of the basic production processes and then took a new role to maintain the growing biological complexities of terrestrial plant. SLs belongs to a diversified category of butenolide‐bearing plant hormones related to various processes of agricultural concern. SLs also arouses the development of spores, the divergence and enlargement of hyphae of AMF, metabolism of mitochondria, reprogramming of transcription process, and generation of chitin oligosaccharides which further stimulate the early response of symbiosis in the host plant, results from better communication in plant and ability of coexistence with these fungi. The required nutrients are transferred from the roots to the shoots, which affect the physiological, biochemical, and morphological characteristics of the plant. On the other hand, the plant provides organic carbon in the form of sugars and lipids to the fungi, which they use as a source of energy and for carried out different anabolic pathways. SLs also lead to alteration in the dynamic and structure of actin in the root region as well as changes the auxin’s transporter localization in the plasma membrane. Thus, this study reveals the functions that SLs play in the growth of roots, as well as their effect and interaction with AMF that promote plant growth.
Extraradical hyphae (ERH) of arbuscular mycorrhizal fungi (AMF) extend from plant roots into the soil environment and interact with soil microbial communities. Evidence of positive and negative interactions between AMF and soil bacteria point to functionally important ERH-associated communities. To characterize communities associated with ERH and test controls on their establishment and composition, we utilized an in-growth core system containing a live soil–sand mixture that allowed manual extraction of ERH for 16S rRNA gene amplicon profiling. Across experiments and soils, consistent enrichment of members of the Betaproteobacteriales, Myxococcales, Fibrobacterales, Cytophagales, Chloroflexales, and Cellvibrionales was observed on ERH samples, while variation among samples from different soils was observed primarily at lower taxonomic ranks. The ERH-associated community was conserved between two fungal species assayed, Glomus versiforme and Rhizophagus irregularis, though R. irregularis exerted a stronger selection and showed greater enrichment for taxa in the Alphaproteobacteria and Gammaproteobacteria. A distinct community established within 14 days of hyphal access to the soil, while temporal patterns of establishment and turnover varied between taxonomic groups. Identification of a conserved ERH-associated community is consistent with the concept of an AMF microbiome and can aid the characterization of facilitative and antagonistic interactions influencing the plant-fungal symbiosis.
A field experiment was conducted during two consecutive growing seasons
(2017 and 2018) to evaluate the effects of inoculations with arbuscular
mycorrhizal fungi (AMF) (Funneliformis mosseae, Rhizophagus intraradices
and Claroideoglomus etunicatum) and phosphorus (P) fertilization (40 kg P2
O5 ha−1) on the growth, yield and P use efficiency (PUE) of two soybean
(Glycine max L.) cultivars under low soil P (6 mg kg−1) condition. AMF
inoculation promotes the growth of soybean to some level compared to
the P fertilized plot; however, inoculation (~960 spores per 100 g of soil) of
R. intraradices or F. mosseae increased the number of nodules, nodule dry
weight, shoot dry weight, root dry weight, number of pods, 100-seed weight
and seed yield in both TGx 1440–1E and TGx 1448–2E soybean cultivars
compared to C. etunicatum and the control. The P uptake in the shoot and
grain in both cultivars increased with AMF inoculations in the order
R. intraradices > F. mosseae > C. etunicatum. The studies showed that the
highest yield response (44.2– 45.4%) and (44.9– 46.5%) over the control was
revealed by the inoculation with R. intraradices and F. mosseae inoculants,
respectively, in both soybean cultivars. TGx 1448–2E variety was more tolerant to low soil P availability and had higher root nodulation, seed yield and
PUE than TGx 1448–2E variety. The results confirm functional variation
among the three AMF isolates tested, which is crucial in establishing potential formulation of AMF inoculants to enhance soybean productivity in
P-deficient soils.
Arbuscular mycorrhizal fungi (AMF) are widely distributed soil-borne microorganisms, which have a symbiotic relationship with several terrestrial plants. They play a key role in plant growth promotion and development, plant nutrient homeostasis, soil nutrient management, and induction of plant defense mechanisms against pest infestation and disease incidences. This interaction of AMF with rice plants has been studied in great detail, providing distinct perspectives on the natural basis of nutrient transport, stress management, improvement of soil health, and induction of systemic plant resistance. This review highlights the responses of (i) AMF interaction with rice plants, (ii) AMF colonization and sporulation potential in rice rhizosphere, (iii) AMF species as a source of inoculum for rice production, (iv) AMF for rice plant maintenance and durability, and (v) AMF responses to other soil microorganisms. Additionally, a new class of phytohormones known as strigolactone (SLs) has been briefly described covering the various forms of analogs, isomers, and membrane transporters. The role of SLs in pre-symbiotic molecular talks, induction of energy metabolism in mitochondria, spore germination, stimulation of hyphal branches, and the relationships of SLs synthesis with soil nutrient content provides in-depth insights into the mechanisms involved in improving AMF interactions with rice plants.
Arguably, symbiotic arbuscular mycorrhizal (AM) fungi have the broadest host range of all fungi, being able to intracellularly colonise root cells in the vast majority of all land plants. This raises the question how AM fungi effectively deal with the immune systems of such a widely diverse range of plants.
Here, we studied the role of a nuclear‐localisation signal‐containing effector from Rhizophagus irregularis, called Nuclear Localised Effector1 (RiNLE1), that is highly and specifically expressed in arbuscules.
We showed that RiNLE1 is able to translocate to the host nucleus where it interacts with the plant core nucleosome protein histone 2B (H2B). RiNLE1 is able to impair the mono‐ubiquitination of H2B, which results in the suppression of defence‐related gene expression and enhanced colonisation levels.
This study highlights a novel mechanism by which AM fungi can effectively control plant epigenetic modifications through direct interaction with a core nucleosome component. Homologues of RiNLE1 are found in a range of fungi that establish intimate interactions with plants, suggesting that this type of effector may be more widely recruited to manipulate host defence responses.
The impact of stress on crop productivity and the ecosystem have been magnified by climate changes and mispractices in the agriculture field. Soil microbiome is a diverse system consisting of various microorganisms. Environmental control techniques like the use of arbuscular mycorrhizal fungi (AMF) are necessary to enhance crop productivity. AMF is known as stress regulating organisms that help plants within the nutrient uptake, biotic and abiotic stress management, plant protection, and consequently enhancement on crop yields. Also, host plants can tolerate many difficult situations such as water problems, salt stress, heavy metals, and temperature changes through AMF inoculation. Arbuscular mycorrhizae (AM) enhance plant growth under stress by mediating a series of complex contact events between the two symbiotic partners resulting in a good photosynthetic and gas exchange amelioration. Plants have several tolerance mechanisms to deal with the constraints of environmental changes. The antioxidant ability is the principal tolerance mechanism; it is assisted by osmolytes accumulation and exacting absorption of ions. In this review, we will discuss the effect of AMF colonization on the host plants at different stages of growth, with comprehensively updated knowledge, their roles, and applications for plant growth enhancement and mycorrhizae role on plant resistance induction and stress management.
Trace metals such as manganese (Mn), copper (Cu), zinc (Zn), and iron (Fe) are essential for many biological processes in plant life cycles. However, in excess, they can be toxic and disrupt plant growth processes, which is economically undesirable for crop production. For this reason, processes such as homeostasis and transport control of these trace metals are of constant interest to scientists studying heavily contaminated habitats. Phytoremediation is a promising cleanup technology for soils polluted with heavy metals. However, this technique has some disadvantages, such as the slow growth rate of metal-accumulating plant species, low bioavailability of heavy metals, and long duration of remediation. Microbial-assisted phytoremediation is a promising strategy for hyperaccumulating, detoxifying, or remediating soil contaminants. Arbuscular mycorrhizal fungi (AMF) are found in association with almost all plants, contributing to their healthy performance and providing resistance against environmental stresses. They colonize plant roots and extend their hyphae to the rhizosphere region, assisting in mineral nutrient uptake and regulation of heavy metal acquisition. Endophytic fungi exist in every healthy plant tissue and provide enormous services to their host plants, including growth enhancement by nutrient acquisition, detoxification of heavy metals, secondary metabolite regulation, and enhancement of abiotic/biotic stress tolerance. The aim of the present work is to review the recent literature regarding the role of AMF and endophytic fungi in plant heavy metal tolerance in terms of its regulation in highly contaminated conditions.
Alterations in the photochemical responses of Zea mays L. and Oryza sativa L. were analyzed to compare the tolerance level of these two crops towards Cd and Zn toxicity. To achieve this, photosynthetic efficiency of maize and rice plants was probed on the 8 days of CdCl2 and ZnSO4 exposure using chlorophyll a fluorescence kinetics, a noninvasive method suitable to examine the impact of different toxic compounds on photochemistrys. Analysis of induction curves and phenomenological energy pipeline models showed that both Cd and Zn reduced the efficiency of electron transport and associated photosystem II (PSII) functionality. A strong negative correlation was found between the accumulation of reactive oxygen species and ascorbate with the photosynthetic efficiency in both crops, but rice was more tolerant than maize towards Cd and Zn toxicity. Further, we found that Cd strongly affected the early photochemical reactions of maize, which can be considered as the reason for the higher vulnerability of this crop towards Cd. Our study suggests that the non-specific toxic effects of Cd and Zn resulted in chlorophyll degradation, reduction in efficiency of PSII and the disturbance in the electron transport process.
Soil salinity often hinders plant productivity in both natural and agricultural settings. Arbuscular mycorrhizal fungal (AMF) symbionts can mediate plant stress responses by enhancing salinity tolerance, but less attention has been devoted to measuring these effects across plant-AMF studies. We performed a meta-analysis of published studies to determine how AMF symbionts influence plant responses under non-stressed vs. salt-stressed conditions. Compared to non-AMF plants, AMF plants had significantly higher shoot and root biomass (p < 0.0001) both under non-stressed conditions and in the presence of varying levels of NaCl salinity in soil, and the differences became more prominent as the salinity stress increased. Categorical analyses revealed that the accumulation of plant shoot and root biomass was influenced by various factors, such as the host life cycle and lifestyle, the fungal group, and the duration of the AMF and salinity treatments. More specifically, the effect of Funneliformis on plant shoot biomass was more prominent as the salinity level increased. Additionally, under stress, AMF increased shoot biomass more on plants that are dicots, plants that have nodulation capacity and plants that use the C3 plant photosynthetic pathway. When plants experienced short-term stress (<2 weeks), the effect of AMF was not apparent, but under longer-term stress (>4 weeks), AMF had a distinct effect on the plant response. For the first time, we observed significant phylogenetic signals in plants and mycorrhizal species in terms of their shoot biomass response to moderate levels of salinity stress, i.e., closely related plants had more similar responses, and closely related mycorrhizal species had similar effects than distantly related species. In contrast, the root biomass accumulation trait was related to fungal phylogeny only under non-stressed conditions and not under stressed conditions. Additionally, the influence of AMF on plant biomass was found to be unrelated to plant phylogeny. In line with the greater biomass accumulation in AMF plants, AMF improved the water status, photosynthetic efficiency and uptake of Ca and K in plants irrespective of salinity stress. The uptake of N and P was higher in AMF plants, and as the salinity increased, the trend showed a decline but had a clear upturn as the salinity stress increased to a high level. The activities of malondialdehyde (MDA), peroxidase (POD), and superoxide dismutase (SOD) as well as the proline content changed due to AMF treatment under salinity stress. The accumulation of proline and catalase (CAT) was observed only when plants experienced moderate salinity stress, but peroxidase (POD) and superoxide dismutase (SOD) were significantly increased in AMF plants irrespective of salinity stress. Taken together, arbuscular mycorrhizal fungi influenced plant growth and physiology, and their effects were more notable when their host plants experienced salinity stress and were influenced by plant and fungal traits.
Arbuscular mycorrhizal fungi (AMF) and plant rhizosphere microbes reportedly enhance plant tolerance to abiotic stresses and promote plant growth in contaminated soils. The co-contamination of soil by heavy metals (e.g., Cd) and rare earth elements (e.g., La) represents a severe environmental problem. Although the influence of AMF in the phytoremediation of contaminated soils is well documented, the underlying interactive mechanisms between AMF and rhizosphere microbes are still unclear. We conducted a greenhouse pot experiment to evaluate the effects of AMF (Claroideoglomus etunicatum) on maize growth, nutrient and metal uptake, rhizosphere microbial community, and functional genes in soils with separate and combined applications of Cd and La. The purpose of this experiment was to explore the mechanism of AMF affecting plant growth and metal uptake via interactions with rhizosphere microbes. We found that C. etunicatum (i) significantly enhanced plant nutritional level and biomass and decreased metal concentration in the co-contaminated soil; (ii) significantly altered the structure of maize rhizosphere bacterial and fungal communities; (iii) strongly enriched the abundance of carbohydrate metabolism genes, ammonia and nitrate production genes, IAA (indole-3-acetic acid) and ACC deaminase (1-aminocyclopropane-1-carboxylate) genes, and slightly altered the abundance of P-related functional genes; (iv) regulated the abundance of microbial quorum sensing system and metal membrane transporter genes, thereby improving the stability and adaptability of the rhizosphere microbial community. This study provides evidence of AMF improving plant growth and resistance to Cd and La stresses by regulating plant rhizosphere microbial communities and aids our understanding of the underlying mechanisms.
There have been a few reports on the impacts of arbuscular mycorrhizal fungi (AMF) on the expression of genes associated with the uptake, transport and detoxification of Cd in upland rice, but there is no study on the impacts of AMF on the transcriptome of upland rice grown in Cd-contaminated soil. In the present work, a pot experiment was conducted to study the influences of the AMF-Glomus versiforme (Gv) on the Cd accumulation, photosynthesis, antioxidant enzymes and transcriptome in upland rice grown in soils supplemented with 10 μg Cd g⁻¹ soil. Gv symbiosis evidently promoted the plant growth, P acquisition and photosynthetic characteristics in upland rice. In addition, 229 differentially expressed genes (DEGs) were identified in upland rice root inoculated with Gv, of which 149 DEGs were upregulated and 80 DEGs were downregulated. More importantly, one Cd transporter gene Nramp5 was significantly downregulated, thus reducing Cd absorption, transfer and accumulation in mycorrhizal upland rice. Moreover, four genes in the Gene Ontology (GO) term of cysteine biosynthesis and two metallothionein genes were upregulated, which could have decreased Cd phytotoxicity in upland rice inoculated with Gv. Meanwhile, one peroxidase gene, two genes in the GO term of peroxisome and one gene in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway of carotenoid biosynthesis were significantly upregulated, and enhanced the activities of catalase (CAT) and peroxidase (POD) in Gv-inoculated upland rice. Our results of transcriptome analysis initially elucidated the molecular mechanism by which AMF decreased the accumulation and toxicity of Cd in upland rice.
Arsenic (As) is a potentially toxic metalloid classified as a group 1 carcinogen, released in the soil environment because of natural as well as different anthropogenic activities. The presence of excess As content in soil and irrigation water enhances the As accumulation in rice grains. Millions of people who consume these contaminated grains are exposed to severe health issues. Increased arsenic uptake causes oxidative stress in plants, which combats by inducing the expression of several genes and signaling the biosynthesis of various antioxidants and phytochelatins. As toxicity reduces crop productivity, so it's critical to improve plant growth in As-contaminated environments while minimizing metal translocation to grains. Arbuscular mycorrhiza fungi (AMF) is considered a sustainable way to tolerate As toxicity. Organic pollutants metabolism by AMF, degradation of these soil contaminants by AMF exudation enzymes, and elimination of the pollutants by plant uptake and accumulation are the principal mechanisms of AMF mediated bioremediation. However, plant responses are established to vary with the host plant and the species of AMF. In our review, we showed that understanding the community composition, diversity, and gene regulation of AMF in the rice ecosystem played a critical role in maximizing As uptake and their potential in sustainable rice and other crops production. It has been reviewed that AMF has the potential to survive in an extremely As toxic condition and it potentially aids to improve the tolerance level of host plants.
Arbuscular mycorrhizal fungi (AMF) are plant symbionts that promote plant growth and provide important plant and ecosystem functions. These abilities have great economical potential which has resulted in an increasing number of commercially available AMF inoculants. Here, we present the results of a global study in which we evaluate the effectiveness of 28 commercial AMF inoculants to colonize host plants under greenhouse and field conditions. This evaluation includes three independent studies across three continents (Australia, Europe, and North America). The Australian and European studies tested 25 different commercial AMF inoculants in non-sterilized and sterilized soils under greenhouse conditions and compared them against laboratory cultures of the AMF Rhizophagus irregularis. This is supplemented by the North American study which evaluated the effects of three commercial inoculants under field conditions. In the greenhouse trials using non-sterilized soil, we observed that the addition of commercial inoculants did not lead to enhanced mycorrhizal colonization and inoculation increased plant biomass in only one out of 25 treatments. In sterilized soil, 84% of the mycorrhizal inoculants did not lead to mycorrhizal root colonization, demonstrating that these products did not contain viable propagules. In contrast, the laboratory cultures of the AM fungus Rhizophagus irregularis resulted in substantial root colonization (48% and 79%) in the Australian and European bioassay. Moreover, only five out of 25 treatments enhanced plant biomass when added to sterilized soil. Metagenomic analysis of field roots in the North American field trial revealed changes in the mycorrhizal community after inoculation. For one inoculant, this was accompanied by increased biomass production. This global evaluation of commercial inoculants raises concerns over unreliable products which do not contain viable propagules and do not result in mycorrhizal root colonization. Under field conditions, effects on plant growth are dependent on changes within the mycorrhizal community. The results of this study highlight the need for standardized quality control of AMF inoculants and further research on their establishment and effects under field conditions.
The chemistry of root cell wall of rice could be changed by inoculation of arbuscular mycorrhizal fungi (AMF). Hydroponic experiments were conducted to investigate the roles of such changes on cadmium (Cd) uptake and distribution in rice. Results showed that inoculation of AM fungus Rhizophagus intraradices (RI) significantly enhanced (p < 0.05) shoot biomass, plant height and root length of rice, and decreased Cd concentration in shoot and root under Cd stress. Moreover, Cd in root was mainly found in pectin and hemicellulose 1 (HC1) components of root cell wall. Inoculation of RI increased the levels of pectin, HC1 and lignin content, accompanied by the increments of L-phenylalanine ammonia-lyase (PAL) and pectin methylesterase (PME) activities. Results of Fourier transform infrared spectroscopy further showed that more hydroxyl and carboxyl groups in root cell wall were observed in mycorrhizal treatment, compared with control. This study demonstrates that cell wall components could be the locations for Cd fixation, which reduced Cd transportation from root to shoot. Inoculation of AMF may remodel root cell wall biosynthesis and affect the characteristics of Cd fixation. The entering and fixing mechanisms should be further studied.
Arbuscular mycorrhizal fungi (AMF) are widely distributed soil-borne microorganisms, which have a symbiotic relationship with several terrestrial plants. They play a key role in plant growth promotion and development, plant nutrient homeostasis, soil nutrient management, and induction of plant defense mechanisms against pest infestation and disease incidences. This interaction of AMF with rice plants has been studied in great detail, providing distinct perspectives on the natural basis of nutrient transport, stress management, improvement of soil health, and induction of systemic plant resistance. This review highlights the responses of (i) AMF interaction with rice plants, (ii) AMF colonization and sporulation potential in rice rhizosphere, (iii) AMF species as a source of inoculum for rice production, (iv) AMF for rice plant maintenance and durability, and (v) AMF responses to other soil microorganisms. Additionally, a new class of phytohormones known as strigolactone (SLs) has been briefly described covering the various forms of analogs, isomers, and membrane transporters. The role of SLs in pre-symbiotic molecular talks, induction of energy metabolism in mitochondria, spore germination, stimulation of hyphal branches, and the relationships of SLs synthesis with soil nutrient content provides in-depth insights into the mechanisms involved in improving AMF interactions with rice plants.
There are few reports on the use of arbuscular mycorrhizal fungi (AMF) to promote growth and stress tolerance of soybean (Glycine max L.) in agricultural soils contaminated with heavy metals. The present study evaluated the role of AMF in promoting tolerance and growth, as well as uptake of heavy metals in shoots of soybean plants. Soybean plants were inoculated with AMF (Funneliformis mosseae) in a pot experiment polluted with different concentrations of heavy metals [copper (Cu), lead (Pb) and zinc (Zn)] as well as their combination. The tested AMF inoculum promoted the soybean growth and seed yield. Increased colonization of the soybean roots improved the soybean growth through increased phosphorus uptake and accumulation in the plant tissues by 68.8%. The results showed that soybean grown in the contaminated soils inoculated with AMF were more tolerant in alleviating the metals toxicity by retaining the heavy metals in the roots, thereby reducing translocation of Cu, Pb and Zn by 21.8, 57.6 and 67.3% respectively in the aerial part of the plant and improving the overall plant productivity by 59.1%. The findings provide evidence of the potential of AMF in phytoremediation of agricultural soils contaminated with toxic metals.
Arbuscular mycorrhizal fungi (AMF) contribute to the sequestration of soil organic carbon (SOC) by glomalin production through their hyphal network which helps to bind soil aggregates and improve other physical and biological properties of soil. The current study was aimed to assess (i) AMF biomass, glomalin related protein (GRP), SOC stocks and soil quality parameters such as microbial biomass carbon (MBC) and β-glucosidase activity, and (ii) to find out whether GRP production and PLFA C16:1ω5 can be used as consistent indicators of soil quality across seven different rhizosphere soil niches such as zero-tillage with Cenchrus ciliaris and minimum-tillage with Chloris barbata; conventional tillage with soybean-wheat system from soybean rhizosphere and raised beds with four mycorrhizal host plants (Fenugreek, maize, marigold and sorghum). Among all the soil niches, AMF biomass, the content of SOC, MBC, soil and root GRP, the activity of β-glucosidase were significantly higher under zero tillage. The AMF biomass, SOC-sequestration and soil quality parameters established a common trend across all the soil management systems and hosts examined. PLFA C16:1ω5 was positively correlated with microscopic estimates of AMF biomass, MBC, β-glucosidase activity and both the fractions of total (T) GRP (the easily extractable and difficulty extractable) in soil and roots. A significant positive correlation of both the fractions of soil-GRP with MBC (r = 0.78**, 0.83**) and β-glucosidase activity (r = 0.86**, 0.76**) was also found. In general, soil T-GRP (r = 0.93**), soil T-GRP stocks (0.94**) and PLFA C16:1ω5 (r = 0.68**) were highly related to SOC stocks. These findings confirm that zero tillage and raised beds favour AMF activity thus improving SOC sequestration potential and soil quality which can be assessed using GRP and PLFA C16:1ω5 as potential indicators.
At present, the levels of cadmium (Cd) and zinc (Zn) in arable land are high and affect the growth and development of important food crops, including rice and maize. However, the application of silicon (Si) in contaminated areas increases the metal tolerance potential of these plants. This work aimed to study the variations in the distribution pattern of endogenous Si in various tissue regions in roots and leaves of rice and maize exposed to cadmium (Cd) and zinc (Zn) stresses. For these experiments, 45 day‐old rice (var. Varsha) and maize (var. CoHM6) seedlings were treated with 1.95 g Zn and 0.45 g Cd kg‐1 soil. Under Cd stress, the distribution of Si was high in the cortical region of the root, but under Zn stress, the highest Si deposition was found in the endodermis. In leaves, Si deposition was high in both the mesodermis and stelar regions of Cd‐treated plants but more Si was deposited in the mesodermis tissue of Zn‐treated plants. Heavy metal (Cd and Zn) accumulation and Si deposition showed a strong negative correlation in the roots of rice and maize plants. Complexation with metal ions and redistribution of Si were considered the major mechanisms in Si‐mediated mitigation of Cd and Zn stress. Cd‐ and Zn‐induced anatomical changes, such as endodermal thickening, deposits in the xylary elements and aerenchyma formation in the roots of rice and maize, were also associated with the Si distribution.
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The appeal of using microbial inoculants to mediate plant traits and productivity in managed ecosystems has increased over the past decade, because microbes represent an alternative to fertilizers, pesticides, and direct genetic modification of plants. Using microbes bypasses many societal and environmental concerns because microbial products are considered a more sustainable and benign technology. In our desire to harness the power of plant–microbial symbioses, are we ignoring the possibility of precipitating microbial invasions, potentially setting ourselves up for a microbial Jurassic Park? Here, we outline potential negative consequences of microbial invasions and describe a set of practices (Testing, Regulation, Engineering, and Eradication, TREE) based on the four stages of invasion to prevent microbial inoculants from becoming invasive. We aim to stimulate discussion about best practices to proactively prevent microbial invasions.
Intercropping of hyperaccumulators with crops is a promising measure to enhance phytoremediation without impeding agricultural production. A Cd-hyperaccumulator, Solanum nigrum L. (S. nigrum), was intercropped with upland rice in a pot and rhizo-box experiment with Cd-contaminated soil to evaluate the combined effects of intercropping and arbuscular mycorrhizal fungi on plant growth and Cd accumulation. The results showed that, compared with monoculture, the combined treatments markedly decreased Cd concentration in rice parts, with the lowest Cd concentration in brown rice (reducing by 64.5%). The spatial distribution of root surface area and DTPA-Cd in the rhizo-box indicated competitive Cd uptake by neighbouring S. nigrum. Moreover, the combined treatments reduced Nramp5 expression but increased HMA3 levels in rice roots, leading to lower bioaccumulation and transfer coefficients. Additionally, fewer secreted organic acids and a higher rhizosphere pH were observed in rice. Conversely, the combined treatments promoted biomass, root length, root surface area, and decreased the rhizosphere pH in S. nigrum, thus increasing the Cd accumulation. Although the intercropping system with AMF inoculation notably reduced rice yield, the land-use efficiency was higher. These results provided insights into the role of AMF in the upland rice/S. nigrum system and demonstrated an alternative system for Cd phytoremediation.
There is relatively little information about root architecture response under various cropping systems. This research concerns the influence of rock phosphate enriched compost and microbial inoculants on root morphology and root colonization through Arbuscular Mychorrhizal fungi under rice crop. In this study, we estimated the root length (RL), root diameter (RD), root biomass (RB), mychorrizal root infection, crop yield and phosphorus uptake in grain and straw. Root samples were collected after harvesting of crop located at Instructional farm of Bihar. Root parameters including root length (18.14 cm) and dry root biomass (0.93 g) were observed to be significantly higher in the treatments inoculated with Arbuscular mycorrhizal fungi over control (statistically at par but numerically higher than 100% RDF) because of the hyphal extensions leading to increased reach and surface area of roots in rice crop. Highest uptake of P by the grain and straw of rice (13.78 and 11.03 kgha-1) was recorded with the combined application of chemical fertilizers with rock phosphate enriched compost in the presence of microbial inoculants like PSB and AMF.