Mapping Sheath Blight Resistance Quantitative Trait Loci In Rice

Sheath blight caused by Rhizoctonia solani Kühn and is one of the three major rice(Oryza sativa L.)diseases in China,and its also causes yield loss in many rice producing areas around the world.Breeding and promoting resistance varieties is the most economical,environmentally friendly and effective way to control sheath blight.However,the mining and application of the resistance gene of sheath blight is the basis of resistance breeding of sheath blight.Rice sheath blight resistance is a typical quantitative trait controlled by multiple genes,Therefore,its resistance is susceptible to environmental influences.Lemont,a sheath blight susceptible japonica cultivar,was crossed with Yangdao4,a relatively sheath blight resistant indica cultivar,to develop a recombinant inbred line(RIL)mapping population consisting of 219 lines.We used this mapping population to detect stable resistance to sheath blight resistance in six different mapping environments in Hangzhou from 2013 to 2018.The main results of this study were as follows:1.Polymorphic makers between Lemont and Yangdao4 were screened using 1047 insertion-deletion markers and 548 simple sequence repeat markers.A total of 208 polymorphic markers covering 12 rice chromosomes were used to construct a genetic linkage map.A genetic linkage map of polymorphic markers with a total length of 2228.0 cM was constructed,and the average distance of adjacent polymorphic markers was 11.4 cM.2.Two traits related to sheath blight resistance(disease rating and lesion length)were assayed in six different QTL mapping environments.Combining genetic linkage maps and phenotypic traits data,multiple interval mapping(MIM)was used to locate the QTL in RIL population.A total of 55 QTLs related to resistance to sheath blight were detected,and the contribution rate of a single QTL ranged from 2.5% to 12.0%.Among them,there are 29 QTLs related to the disease rating,2 QTLs with a contribution rate greater than 10%(qDR9.2 and qDR11.2).26 QTLs related to the lesion length,and a QTL with a contribution rate greater than 10% is qLL11.2.In addition to chromosomes 6 and 10,QTL for resistance to sheath blight was detected on other chromosomes.3.Analysis of resistance to sheath blight detected in different localization environments QTL.41 QTLs were clustered in 11 QTL-rich regions/putative loci(qSBR1.1,qSBR1.2,qSBR2.1,qSBR3.1,qSBR5.1,qSBR7.1,qSBR9.1,qSBR11.1,qSBR11.2,qSBR12.1and qSBR12.2).The resistance QTLs in which 4 clusters(qSBR1.2,qSBR3.1,qSBR5.1and qSBR12.1)were clustered were detected only in the same environment,and the other 7 clusters were resistant to QTLs from multiple environments.The resistant QTLs clustered on qSBR9.1 were derived from all six environments.Secondly,the resistant QTLs clustered on the 4 clusters qSBR2.1,qSBR7.1,qSBR11.1 and qSBR11.2 were derived from three environments.The resistance QTLs clustered on the two clusters qSBR1.1 and qSBR12.2 were derived from two environments.4.In order to test whether the QTLs for sheath blight resistance on the above 11 QTL clusters were stable under different environments,two-way ANOVA analysis was used to detect QTL by environment at the 11 putative loci.Significant QTL by environment interactions(P< 0.05)were detected at two putative loci(qSBR11.1 and qSBR11.2),indicating that these 2 loci were not stable.No significant QTL interactions with the environment were detected at the other 9 putative loci,indicating that the QTLs at these 9 loci are stable resistance QTLs.5.In order to analyze the relationship between plant type traits and resistance to sheath blight,this study also analyzed the correlation between plant type traits(plant height and tiller angle)and resistance to sheath blight,and QTL mapping of plant type traits in three environments.It was found that only the disease rating and plant height were significantly negatively correlated in all three environments.In the three environments,there were 3 plant height QTLs and 4 tiller angle QTLs that could be replicated between different environments.There were only one tiller angle QTL qTA9.1 located on the same region with a stable sheath blight resistance QTL qSBR9.1.