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Average disease score for Sclerotium oryzae (a) and Rhizoctonia oryzae-sativae (b) in five inoculation methods evaluated for six genotypes, and Pearson correlations among methods. Pairs of genotypic means with different letters were statistically different with a Tukey’s HSD test ( =0.05) for each inoculation method.
Source publication
Stem and sheath diseases caused by Sclerotium oryzae Cattaneo (SCL) and Rhizoctonia
oryzae-sativae Sawada Mordue (ROS) can severely reduce rice (Oryza sativa L.) yield
and grain quality. Genetic resistance is the best strategy to control them. Phenotypic
selection for resistance is hampered due to a heterogeneous distribution of the inoculum
in the...
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Rhizoctonia cerealis and Rhizoctonia solani are considered to be among the most harmful soil-borne pathogens for crop plants globally. The lack of effective protection and the requirement to minimize the use of chemical pesticides necessitate the need to develop alternative protective methods. One such method is resistance breeding against biotic a...
Citations
... Sclerotia then float on the water, germinate, and infect rice stems via mycelia (Cartwright et al. 2018;Ou 1985). Stem rot is the most important yield-reducing rice disease in Uruguay when blast-resistant cultivars are seeded (Cartwright et al. 2018;Rosas et al. 2016). Sheath spot and aggregate sheath spot of rice are considered minor diseases worldwide, but they are of increasing importance and are drawing attention in temperate rice-producing areas (Cartwright et al. 2018;Lanoiselet et al. 2007;Martínez et al. 2018). ...
Rice cultivation in South America is undergoing several intensification processes for economic reasons that cause more rice to be planted continuously on the same soils. This intensification makes the long-term biological and economic sustainability of systems questionable. Among the most common problems that threaten sustainability in intensified systems is pest and disease pressure. In this context, the primary rice diseases were studied during a 6-year period in a long-term experiment of rice rotations established in 2012 in Uruguay. The experiment consisted of six rice rotations with other crops with different duration and intensification levels. The main disease found was stem rot and, to a lesser extent, aggregate sheath spot and sheath spot of rice. These diseases are of importance in intensified rice systems because they produce sclerotia that accumulate in soils. Disease occurrence was variable among years and rotations. Stem rot incidence increased rapidly in the experiment, reaching values close to 85% in the third year, while the severity varied each year. Sheath spot incidence and severity were low and varied with the year. Continuous rice (CR) reached the highest occurrence values for stem rot, but other systems with short pastures in rotation did not differ. Aggregate sheath spot and sheath spot were of importance only in CR and in some years. When levels of intensification were compared, systems with less time (25 to 60%) occupied with rice showed lower disease severity and higher yields. Comparing CR with rice rotation with pastures of different lengths (1 to 3 years), disease occurrence was higher in 2 of the 4 years analyzed. However, yields were consistently lower, denoting that other factors are influencing productivity. Stem and sheath diseases appear not to be a limiting factor in the medium term in intensified rice systems. Also, there are several alternatives of rice intensification incorporating crops and pastures in the rotation.
... Further, the unwise usage and underdose applications of chemicals have the risk of resistance development in the target fungal pathogens (Deising et al. 2008). Development of resistant varieties against these 2 diseases is still a distant dream because of the non-availability of resistant genes in the host due to the saprophytic and opportunistic nature of the pathogens with a wide host base and nonspecific pathogenesis that can trigger pathogen-specific resistant reactions by the host (Rosas et al. 2016). Under these circumstances, biological control offers a suitable and potential alternative for the management of these two pathogens. ...
... Rhizoctonia solani and S. oryzae are ubiquitous fungi, opportunistic in nature, that infect a wide variety of plants, and the host plants do not in general possess inherent resistance against them(Rosas et al. 2016). Dual culture screening of isolates of Trichoderma against R. solani and S. oryzae indicated their suppression byFig. ...
Background
Species belonging to the genus Trichoderma are considered as one of the most potential biocontrol agents which can be readily collected from soil and found effective against various fungal and bacterial diseases. In rice-growing areas, the major fungal pathogens affecting rice production include Rhizoctonia solani causing sheath blight and Sclerotium oryzae causing stem rot disease of rice. Due to the lack of resistant varieties and detrimental effects of chemicals, biocontrol gives a good opportunity to manage the diseases efficiently in a sustainable manner.
Main body
Trichoderma spp. from native rice rhizosphere soil were examined for their antagonistic efficiency to supress the two soil-borne rice pathogens, viz., R. solani and S. oryzae . Morphological, biochemical and molecular characterisation of the isolates led to the identification of species as T. asperellum . The isolates of Trichoderma spp. were found to be positive to IAA release and phosphate solubilisation and were screened against R. solani and S. oryzae in vitro and in vivo in pots under glass house conditions. Regression analysis indicated a positive correlation between the amount of chlamydospores produced by T. asperellum and their antagonistic potential against the two pathogens. Exposure to external stimuli, viz., light, injury and nitrogen sources in culture media triggered increased conidiation in Trichoderma isolates. Among the four isolates studied, Trichoderma asperellum IIRRCK1 (TAIK-1) was found to be the most effective in improving plant growth in rice and highly antagonistic against R. solani and S. oryzae . Sorghum grain was found to be the most suitable among different organic substrates studied to provide better growth and viability of TAIK-1 and improved the efficiency of the seed treatment and soil application. External stimuli in the form of near UV blue light, mechanical injury to the colonies and nitrogen source added to the culture media help in faster conidiation of Trichoderma .
Conclusion
Strain TAIK-1 showed strong competitive and antagonistic activities against fungal soil-borne pathogens, in addition with promoting healthy growth and development of rice plants. This can be a suitable and safe alternative to chemical management in the rice fields for long-term scenario.
... The incidence and severity of stem rot in rice were assessed based on a scale modified from the Standard Evaluation System for Rice (IRRI 1981;Martínez 2016;Rosas et al. 2016). Immediately before harvest, around 100 stems in groups of 5-10 tillers were randomly harvested from different points along a W-shaped path in each experimental unit. ...
Stem rot (Nakataea oryzae) limits rice (Oryza sativa) production in Uruguay when there are high inoculum levels in the soil. This disease is particularly damaging in potassium (K) deficient soils that receive excessive nitrogen (N) fertilization. Nevertheless, no data exist for the response to stem rot in modern rice cultivars with respect to the interaction between balanced N and K fertilization. The aim of this work was to evaluate the combined effect of K and N fertilization and a foliar phosphite (Phi) in reducing stem rot severity in rice to prevent significant yield losses. A three-year field study was conducted in a rice-producing region of Uruguay to investigate the effects of 1) K fertilization rate, 0 or based on the Mg:K ratio; 2) N fertilization rate, 0 or 140 kg ha–1 N; 3) Phi treatment, with or without foliar Phi (1.775 kg ha–1 of K Phi, 71%), at growth stages R2-R3. While the experiment was conducted in a soil with sufficient potassium, K fertilization reduced the severity and percentage of rice tillers that were severely affected by stem rot, resulting in a mean yield increment of 2% to 18% depending on the year (mean 7.5%). Nitrogen fertilization increased stem rot severity only in one year, but resulted in a mean yield increment of 10% over the three years of the experiment. Foliar Phi applied at the late boot to panicle exertion stage did not reduce disease incidence or severity, and failed to increase the total rice grain and milling yield.
... Resistance to N. oryzae and R. oryzae-sativae was evaluated in both greenhouse and field trials in Uruguay, whereas resistance to T. cucumeris was evaluated in greenhouse trials in Colombia. Greenhouse experiments for N. oryzae and R. oryzae-sativae have been described elsewhere (Rosas et al., 2016). Briefly, two trials for N. oryzae and three trials for R. oryzae-sativae were conducted from 2012 to 2014 at INIA Treinta y Tres Experimental Station, Treinta y Tres, Uruguay (33°15ʹS, 54°25ʹW). ...
... Strain ROS-17 (R. oryzae-sativae) was obtained from soil after cultivation with the tropical japonica rice cultivar INIA Tacuarí in Paso de la Laguna Experimental Unit in 2003. The SO-Samba and ROS-17 strains caused good discrimination among rice genotypes, and are maintained at the Culture Collection of the Plant Pathology Laboratory of INIA Treinta y Tres (Rosas et al., 2016). Strain 1953-1 (T. ...
Stem rot and aggregated sheath spot are the two major stem and sheath diseases affecting rice (Oryza sativa L.) in temperate areas. A third fungal disease, sheath blight, is a major disease in tropical areas. Resistance to these diseases is a key objective in rice breeding programs but phenotyping is challenged by the confounding effects of phenological and morphological traits such as flowering time (FT) and plant height (PH). This study sought to identify quantitative trait loci (QTL) for resistance to these three diseases after removing the confounding effects of FT and PH. Two populations of advanced breeding germplasm, one with 316 tropical japonica and the other with 325 indica genotypes, were evaluated in field and greenhouse trials for resistance to the diseases. Phenotypic means for field and greenhouse disease resistance, adjusted by FT and PH, were analyzed for associations with 29,000 single nucleotide polymorphisms (SNPs) in tropical japonica and 50,000 SNPs in indica. A total of 29 QTL were found for resistance that were not associated with FT or PH. Multilocus models with selected resistance-associated SNPs were fitted for each disease to estimate their effects on the other diseases. A QTL on chromosome 9 accounted for more than 15% of the phenotypic variance for the three diseases. When resistance-associated SNPs at this locus from both the tropical japonica and indica populations were incorporated into the model, resistance was improved for all three diseases with little impact on FT and PH.
The rice crop is affected by diseases throughout its cycle, impacting negatively on grain yield and quality. The control of the disease impact can be accomplished via crop breeding, using highly multiple resistant genotypes. This study aimed to evaluate the efficiency of multiple‐character and specific selection of multiple resistance to major culture‐associated diseases (neck blast, leaf scald and grain discoloration) in rice lines of the Upland Rice Genetic Breeding Program. The experiments were conducted in 35 sites during 12 agricultural years, where 124 lines were evaluated for the severity of fungal diseases, under natural field conditions. Multiple parameters were calculated based on the diseases´ scores: genetic, phenotypic and environmental variances, heritability, selection gain, renewal rate, and genetic and renewal progress. Genetic variance for the disease resistance was identified in the population, and the selection gain for multiple‐character selection was of 3.16 year⁻¹ throughout the breeding process with a renewal rate of over 35%. The programme has showed efficiency in selecting multiple resistant genotypes to the mentioned diseases, highlighting genotypes with high potential for market release.
One of the main current societal challenges is the production of food supplies to feed a constantly growing human population. In the forthcoming years, we will have to increase the global production of staple cereals such as rice to achieve this goal. Several factors compromise this objective, including the variation of raining patterns due to climate change and pathogen infections that drastically reduce crop yields. Wheat and rice are frequently affected by diseases caused by several root‐infecting species of Magnaporthales such as Gaeumannomyces graminis, Magnaporthiopsis rhizophila and Nakatea oryzae (syn. Magnaporthe salvinii). Other economically significant root pathogen of this fungal family is Magnaporthiopsis poae, which causes severe damages in turfs used for sport courts flooring and home lawns. The blast fungus Magnaporthe oryzae, an extremely damaging airborne fungal pathogen of wheat and rice, also infects underground tissues. This is in accordance with the distinct penetration strategies displayed by M. oryzae during aerial and underground plant colonisation.
Key Concepts
• A clade is a phylogenetic group, which comprises a single common ancestor and all the descendants of that ancestor.
• The appressorium in Magnaporthales is a melanised fungal structure required for penetration of aerial plant tissues, and it is formed at the tips of spore germ tubes or hyphae.
• An hyphopodium in Magnaporthales is a specialised structure produced at the tip of the hyphae to penetrate roots. Gaemannomyces sp. can produce simple or lobed hyphopodia. M. oryzae produces simple hyphopodia.
• Disease‐suppressive soils are soils in which little or no disease occurs under favorable conditions for disease development. Generally, this is due to the presence of indigenous soil microbes.
• The immune response in rice roots and leaves against the blast disease differs.
