| Sheath blight is one of the three major diseases of rice, and become the first major disease of rice in southern china. The disease seriously affects rice yield and quality, resulting in huge economic losses. It is generally acknowledge that the most economical method of control crop diseases is breeding new cultivars of resistance to these diseases. However, rice sheath blight is the quantitative trait controlled by polygene and it is very difficult to breed a cultivar resistant to the disease by means of normal breeding technology. The most effective path for resistance breeding to the disease should be marker-assisted selection.In this study, we chose the indica cultivar Teqing as the donor parent, which possesses a QTL resistant to sheath blight, qSB-9TQ, and another QTL controlling tiller angle, qTAC-9TQ, and chose two japonica cultivars Zhendao88and Wulingjing1as the recurrent parent, which have being cultivated in Jiangsu Province now. The method of successive backcross and marker-assisted selection were conducted.We designed molecular markers to cover a larger chromosome interval of qSB-9TQ for marker-assisted selection. When qSB-9TQ was further mapping, we found another gene, qTAC-9TQ controlling tiller angle, on the original interval, too. The Indel markers, Y74.7and Y79.8, flanking the target gene qTAC-9TQ, and the Indel markers, Y83-2ã€Y90.2and Y93.5, flanking the target gene qSB-9TQ, were developed, respectively. The four genotypes of near-isogenic lines, including with both qSB-9TQ and TAC-9TQ, only the qSB-9TQ or qAC-9TQ, and neither qSB-9TQ nor TAC-9TQ (CK), were constructed by means of marker-assisted selection for genotype and visualized selection for agronomic traits.The near-isogenic lines with different backgrounds were transplanted for an artificial inoculation experiment of sheath blight disease in2011. Results of resistance identification showed that, qSB-9TQ could reduce about1.0of disease rating, while qTAC-9TQ reduced about0.5score, and the two-gene combination could reduce about1.3rating score in a0-9rating scale system. There are significant differences of rating averages between the first three genotypes and CK. Results of yield experiment showed that, under normal level applying fertilizer and water managing, the yield levels between near-isogenic lines with qSB-9TQ and TAC-9TQ had no significant difference.Based on the experimental results, it would be suggested that, in breeding of resistance to sheath blight, selecting both QTLs, qSB-9TQ and TAC-9TQ, was more favorable to improve the resistance to sheath blight.Because there were still some differences of these agronomic traits among the near--isogenic lines constructed by us, above results could only provide a primary conclusion. Further study on influence of qSB-9TQ and TAC-9TQ for yield level of rice will be conducted to answer whether both the two QTLs was favorable for increase of rice yield. |
