Genetic Analysis Of Rice Sheath Blight Resistance And Rice Germplasm Identification And Evaluation Of Resistance

Rice sheath blight, caused by Rhizoctonia solani, is one of the most prevalent fungal diseases in rice, which leads to a great loss of rice yield and quality worldwide. In the present study, a recombinant inbred lines (RILs) population which consists of 155 individuals was derived from a cross between HuHan 1B and RSB02, and a genetic linkage map was constructed based on the RILs and 163 SSR markers, which covered a total of 2588.8cM with an average interval of 15.88cM between adjacent markers. The QTLs analysis and the effect of environment for 9 traits on resistance to rice sheath blight, including disease rate (DR), lesion length (LL), lesion height (LH), relative lesion length (RLL), relative lesion height (RLH), heading date (HD), plant height(PH), spikelet fertility percentage (SF),1000-grain weight (TGW), were conducted according to the phenotypic data across three environments by using the toothpick inoculation method. Cultivars from China rice mini core collection and "global rice molecular breeding program" were identified and evaluated for resistance to rice sheath blight under natural induction or artificial inoculation. Main results are as following:1. Rice sheath blight resistance of parents and RILs population were identified in Shanghai in 2008(E1), Hainan (E2) and Shanghai in 2009 (E3). A total of 22,22 and 20 main QTLs,20,23 and 34 epistatic QTLs were detected across three environments, respectively, for nine traits, DR, LL, LH, RLL, RLH, PH, HD, SF and TGW. Among them, the QTL that influenced DR, PH, RLL and RLH simultaneously locating between RM3442 and RM5501 on chromosome 1 and the QTL for RLL locating at interval of RM1369-RM8121 on chromosome 6 were identified repeatedly in E1 and E2. While, the QTL for RLH flanked by RM3233 andRM8134 on chromosome 1 was identified repeatedly in E1 and E3. The resistance alleles of these QTLs came from resistant parent, RSB02. The QTL that located at interval of RM3442-RM5501 on chromosome 1 enhanced resistance to sheath blight, while greatly increased the plant height.2. Combined QTLs analysis was conducted with the total data in three environments. 35 main QTLs were detected which located on chromosome 1,2,3,4,5,6,7,9. The resistance alleles of most QTLs came from resistant parent RSB02. The QTLs at interval of RM3442-RM5501 and RM3233-RM8134 on chromosome 1 influenced DR, PH, RLL and RLH. And 46 epistatic QTLs were detected for nine traits. All traits had QTLs with significant Q X E interation excepted HD.3. Correlation analysis shoewed that DR had significant positive correlations with LL, LH, RLL, and RLH but negatively correlated with PH, SF and TGW. The average correlation coefficients between DR and RLH, RLL were 0.913 and 0.778, respectively. Among 6 QTLs for DR detected by combined QTLs analysis,5 QTLs were identified to control RLL and RLH and 2 QTLs to influence PH simultaneously. The results showed that plant height had great impact on rice sheath blight resistance. RLH and RLL could be used as important indices indicading sheath blight resistance due to its high correlation with DR and simple, objective measurement.4.159 rice cultivars from China mini core collection and 137 varieties from the "global rice molecular breeding program" were identified and evaluated for resistance to rice sheath blight using naturally induced and artificial inoculation methods in Enshi and Shanghai in 2008. The number of resistant and moderately resistant germplasm were 4 and 68. The percentage of resistant, moderately resistant, moderately susceptible, susceptible and highly susceptible germplasm were 1.4%,23%,33.8%,22%,19.9%, respectively. HD, FLPH, PH, the ratio of FLPH and PH were significant negatively correlated with DR. LL, LH, the ratio of LL and FLPH, the ratio of LL and PH, the ratio of LH and FLPH and the ratio of LH and PH were significant positively correlated with DR.