Identification of novel QTLs conferring sheath blight resistance in two weedy rice mapping populations

Authors: GOAD, DAVID - Washington University; Jia, Yulin; GIBBONS, ANDREW - University Of Arkansas; LIU, YAN - University Of Arkansas; Gealy, David; CALCEDO, ANA - University Of Massachusetts, Amherst; OLSEN, KENNETH - Washington University

Submitted to: Rice
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2020
Publication Date: 3/23/2020
Citation: Goad, D.M., Jia, Y., Gibbons, A., Liu, Y., Gealy, D.R., Calcedo, A.L., Olsen, K.M. 2020. Identification of novel QTLs conferring sheath blight resistance in two weedy rice mapping populations. Rice. https://doi.org/10.1186/s12284-020-00381-9.
DOI: https://doi.org/10.1186/s12284-020-00381-9

Interpretive Summary: Rice sheath blight disease is one of the most devastating diseases of rice and causes significant yield losses worldwide. By identifying genetic markers associated with increased resistance to this disease, new lines can be bred to reduce this loss in yield. We looked for resistant markers in two different types of US weedy rice, which despite appearing to be more sheath blight resistant than crop varieties, have never been investigated. We found nine regions of the rice genome that contain markers associated with sheath blight disease resistance. However, sheath blight studies often inadvertently identify markers that are associated with plant height or heading date rather than sheath blight resistance. By using advanced statistical models, we were able to overcome this potential problem and to reveal that four of our nine regions are associated with actual disease resistance rather than plant height or heading date. Three of these appear to have never been identified before and will be of use to breeders attempting to produce disease resistant rice varieties. Our modeling approach will enable researchers to more accurately find markers in the future.

Technical Abstract: Rice sheath blight disease (ShB), caused by the pathogenic fungus Rhizoctonia solani, is one of the most devastating diseases of cultivated rice worldwide. US weedy rice populations, which are feralized forms of cultivated rice, appear to be more resistant to ShB than cultivated rice. We mapped quantitative trait loci (QTLs) associated with ShB resistance using two F8 recombinant inbred line mapping populations generated from crosses of an indica crop variety, Dee-Geo-Woo-Gen (DGWG), with individuals representing the two major US weed biotypes, straw hull (SH) and black hull awned (BHA). We identified nine ShB resistance QTLs across both mapping populations. Five were attributable to alleles that affect plant height and heading date, two growth traits that are known to be closely correlated with ShB resistance. By utilizing an approach that treated growth traits as covariates in the mapping model, we were able to infer that the remaining four QTLs are involved in physiologically-based ShB resistance. Two of these, qShB1-2 and qShB4, do not overlap previously identified ShB QTLs and represent new candidates for further study. Our findings suggest that ShB resistance can be improved through favorable plant growth traits and the combined effects of small to moderate-effect resistance QTLs.