The Study To Improve Resistance To Sheath Blight Of Japonica Varieties By Polymerizing Different QTL

Sheath blight is one of the three major diseases of rice, and become the most severe disease of rice in southern china. The disease affects rice yield and quality seriously, resulting in huge economic losses. It is generally acknowledge that the most economical method of control crop diseases is to breed new cultivars resistant to these diseases. However, resistance to rice sheath blight is the quantitative trait controlled by polygene and it is very difficult to breed a cultivar resistant to the disease by normal breeding technology. The most effective path for resistance breeding to the disease should be marker-assisted selection.In this study, we choose the Indica cultivar Teqing as the donor parent which carries with the favorable alleles from two QTL controlling the resistance to sheath blight, and choose japonica cultivars Zhendao88, Huajing6#and Wulingjing1#as the recurrent parent which are main commercial cultivars in Jiangsu Province now. We had constructed the near-isogenic lines of qSB-7in Huajing6#and Wulingjing1#background, qSB-9in Zhendao88and Wulingjing1#background, and the lines polymerized qSB-7and qSB-9in Wulingjing1#background by means of the method of backcross combined to marker-assisted selection.The artificial inoculation experiments have been done with the backcross segregation population and the near-isogenic lines, respectively. The results showed that, when carried one of favorable alleles of the two QTL or pyramided them together, the disease scales of the plants or lines were significantly reduced than current parent. The resistant effects of qSB-7under the backcross of Huajing6#and Wulingjing1#were respectively about0.43and0.80disease scales when evaluated by average effect of homozygously resistant plants from BC2F2segregation population, meanwhile respectively about0.85and0.91when evaluated by near-isogenic lines. The resistant effects of qSB-9under background of Zhendao88and Wulingjing1were respectively about1.84and2.10at BC2F2backcross segregation population, meanwhile respectively about1.02and1.10at the near-isogenic lines. The resistant effect of qSB-7and qSB-9under Wulingjing1#background were respectively about0.82and0.89, meanwhile the polymerized effect of the two favorable alleles were1.70, with the interaction effect of about-0.33. In addition, according to the result of investigation of agronomic traits, we found that there were significant differences of plant height and heading date in the near-isogenic lines carried qSB-7, while other agronomic traits were basically uniform among all near-isogenic lines.Based on the experiment results, we believe that polymerizing favorable alleles of the two QTL must be more favorable to improve the resistance to rice sheath blight significantly, which provides a logical proof for breeding of resistance to the disease.