Inheritance Of Resistance To Sheath Blight And Mapping Of Relative QTLs For Resistance In Two New Rice Cultivars

Sheath blight, caused by Rhizoctonia solani, is one of major rice diseases. In this study, 158 F2 clones were used. The clonal population and their parents, 91SP068 and Qimiaoxiang, was inoculated with inserted method. The investigation of the sheath blight resistance conformed to the standard of Yangzhou university rice genetic and breeding term's 1997 version. In 2002 and 2003, field experiments were implemented in the farm of agriculture colleges of Yangzhou University. Each F2 clone was planted into three plots in different blocks, respectively. Two blocks were for the investigation of the sheath blight resistance and the other was for the investigation of agronomic traits. The statistical results of the sheath blight resistance suggested that highly significant correlation exist between two years and between the blocks, and highly significant differentia exist among F2 clones. The method of partial correlation analysis was used to study the relationship between the agronomic traits and sheath blight resistance. The result shows that: highly significant partial correlation existed between the plant height / growth stage and sheath blight resistance. SSR (simple sequence repeats) markers distributed in rice genome were used to construct the molecular linkage map of this population. QTLs of resistance were detected with BSA (bulked segregation analysis) method. A total of three sheath blight resistant QTLs (qSB-5, qSB-7 and qSB-8) was identified and located on chromosome 5, 7 and 8, respectively. Resistant alleles of qSB-5 and qSB-7 were derived form the parent Qimiaoxiang and qSB-8 was from parent 91SP068. The qSB-7 and qSB-8 were detected both two years, whereas qSB-5 was detected only in one year. QTLs of the agronomic traits were detected in relative chromosome. A total of seven QTLs contributing to six agronomic traits was identified and located on chromosome 5, 7, 8 and 9, respectively. Among all QTLs of agronomic traits, qHD-8 was in the next region of qSB-8 on the chromosome 8 and qHD-7 was in the next region of qSB-7 on the chromosome 7. There were no other QTLs ofagronomic traits linked to qSB-5. Compared the result of partial correlation analysis with the result of QTLs mapping, we found four kinds of relationship existed between resistance of sheath blight and agronomic traits. 1 : QTLs contributing to resistance and agronomic traits were not linked and the partial correlation between the two kinds of traits was not significant. 2: The QTLs were linked and the partial correlation was significant. 3: The QTLs were linked but the partial correlation was not significant. 4: The QTLs were not linked but the partial correlation was significant. The resistant QTLs of the first class not related to genes of agronomic traits and can be used in breeding directly. The resistant QTLs belonged to the second and the third class should be electively used in breeding. The last one, according to the viewpoint of inheritance, resistant QTLs and agronomic traits were independent of each other, but their partial correlation was significant in some years. The causation was complex and should be studied further.