Assessment of rice sheath blight resistance including associations with plant architecture, as revealed by genome-wide association studies

Authors: LI, DANTING - Guangxi Academy Of Agricultural Sciences; ZHANG, FANTAO - Jiangxi Normal University; Pinson, Shannon; Edwards, Jeremy; Jackson, Aaron; XIA, XIUZHONG - Guangxi Academy Of Agricultural Sciences; Eizenga, Georgia

Submitted to: Rice
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2022
Publication Date: 6/18/2022
Citation: Li, D., Zhang, F., Pinson, S.R., Edwards, J., Jackson, A.K., Xia, X., Eizenga, G.C. 2022. Assessment of rice sheath blight resistance including associations with plant architecture, as revealed by genome-wide association studies. Rice. https://doi.org/10.1186/s12284-022-00574-4.
DOI: https://doi.org/10.1186/s12284-022-00574-4

Interpretive Summary: Sheath blight disease is one of the most economically damaging rice diseases worldwide. It occurs in all areas where rice is grown, reducing grain yields up to 50%. Sheath blight is caused by a soil-borne fungus, Rhizoctonia solani, that spreads by filaments (“hairs” produced by the fungus, R. solani) creating new lesions along the plant stems that results in a loss of grain development. Recently R. solani fungal isolates were discovered that were tolerant to one of the main fungicides in the USA currently used to control sheath blight. This is a problem because there are no known major resistance genes, thus there is a need to discover additional genes that can be incorporated into modern rice cultivars to improve natural resistance to sheath blight disease. Unfortunately, many of the sheath blight resistance genes currently reported are associated with traits detrimental to grain yields such as tall plant height, late maturity, spreading tillers, or reduced tiller number. In this study we discovered ten potential genes for sheath blight resistance that were not associated with tall height or late maturity. As part of this study, four cultivars, not adapted to the US growing conditions, were identified that had four or more of the ten genes for sheath blight resistance identified here, and the cultivars were highly tolerant to sheath blight. This illustrates the need to have several resistance genes to achieve useful levels of sheath blight resistance. Rice breeders can potentially incorporate these genes for sheath blight resistance into US adapted cultivars, thus reducing the need for fungicide applications. We also noted that one sheath blight resistance gene was near a gene for producing more panicles, thus this gene could potentially also be used to improve grain yield.

Technical Abstract: Sheath blight (ShB) disease is one of the most economically damaging rice diseases worldwide. It occurs in all areas where rice is grown, reducing grain yields up to 50%. The causal agent, Rhizoctonia solani, a soil-borne fungus, spreads by runner hyphae creating new lesions along a stem or onto other plants and tillers via physical contact, not by spores. There are no known major resistance genes, leaving only partial resistance QTLs available for cultivar improvement. Many reported ShB-QTL are associated with plant architectural traits detrimental to grain yields such as tall height, late maturity, wide culm angle, or reduced tiller number. To identify germplasm and QTLs providing physiological defense rather than morphological avoidance mechanisms, the Rice Diversity Panel 1 was evaluated in Arkansas, USA and Nanning, China for ShB resistance, height and days to heading in inoculated field plots, and at the seedling stage using a microchamber method which minimizes confounding by plant architecture. Tiller (TN) and panicle number (PN) per plant were evaluated in the greenhouse. Genome-wide association mapping identified 10 ShB QTL not confounded by plant architecture. Two ShB QTL (qShB4 and qShB12) were associated with TN and PN, but in a desirably coupled way, with TN and PN increasing resistance. Among the annotated genes in the qShB4 and qShB12 regions, pleiotropic effect on ShB and tillering was not evident among the chromosome 4 gene functions, but was evident for two chromosome 12 candidate genes, OsNAM/OsNAC139 and Osdec-1, which reportedly impact tolerance to biotic and abiotic stress, and affect tiller and panicle number by affecting meristem development.