| Sheath blight is one of the three major diseases of rice, and can lead to the most severe losses in rice productivity and grain yield, and become the most destructive rice disease in china. It is generally acknowledged that breeding and growing sheath blight resistant varieties is the most economical path to manage the disease. However, resistance to rice sheath blight is the quantitative trait controlled by polygene and it is very difficult to breed a variety resistant to the disease by normal breeding technology. The most effective approach for resistance breeding to the disease should be marker-assisted selection.In this study, the indica variety Teqing was used as the donor of qSB-9TQ, which carried a QTL resistant to sheath blight, and two japonica varieties Zhendao88and Wulingjing1were used as the recurrent parents. In the case of the initial mapping and its resistance authenticity was confirmed, we used three molecular markers which covered a larger chromosome interval of qSB-9TQ for selection. However, when qSB-9TQ was further mapped, we discovered the presence of a QTL controlling tiller angle, TAC-9TQ, within the original qSB-9TQ region, and added new molecular markers screening for progeny that carried tiller angles similar to the recurrent parent. The four genotypes of near-isogenic lines (BC6lines) were constructed in Zhendao88and Wulingjing1, including with qSB-9TQTAC-9TQ、qsb-9TAC-9TQ、qSB-9TQtac-9、 qsb-9tac-9. In this study, sheath blight inoculation treatments were set to mild, moderate and severe disease onset, separately. It was to examine disease severity, basic agronomic traits and economic traits on each near-isogenic lines under different disease onset conditions, and analyze the impact of qSB-9TQ and TAC-9TQ for sheath blight resistance, economic traits and quality of processing and appearance, and identify use value and utilization strategies of QTL in rice SB resistant breeding. The main results obtained are as follows:1) The tiller angle had significant differences between the lines with TAC-9TQ and the lines without the gene. Other investigated agronomic traits had no significant difference between near-isogenic lines. It indicated that TAC-9TQ had no effect on other agronomic traits, and target gene imported could increase the tiller angle of plants. 2) Results of resistance identification indicated that carrying qSB-9TQ could decrease about0.9of disease rating and the two-gene combination could reduce about1.2rating score, and it showed extremely significant differences between them and CK, while TAC-9TQ reducing about0.45score was significantly resistant to CK, under severe disease onset condition. Results were showed that qSB-9TQ on SB resistance existed, and TAC-9TQ would help reduce disease severity, qSB-9TQ and TAC-9TQ had some negative interaction effect on SB resistance.3) Economic traits study results demonstrated that WPP of qSB-9TQTAC-9TQ lines cut at the least and qsb-9tac-9lines (CK) reduced sharpest, the WPP’s difference was significant between them and its components were not significantly different in near-isogenic lines under heavy onset conditions. With the increase of the disease, the WPP of NILs showed a downward trend and was very significantly different in the three disease conditions.4) Results of quality of processing and appearance demonstrated that head milled rice rate of qsb-9tac-9lines (CK) was significant lower than qSB-9TQTAC-9TQ lines under heavy onset conditions and the other quality of NILs had no significant differences in the same disease conditions. Compared with the mild disease onset, the milled rice rate and head milled rice rate of the lines decreased indicated significantly and the degree of chalkiness and chalkiness performance of lines increasing trend in the heavy disease conditions. Overall, with the increase of disease, the quality of processing and appearance performance declined to a certain extent.Based on the experimental results, it would be suggested that carring both qSB-9TQ and TAC-9TQ was more favorable to improve the crop resistance in breeding of resistance to sheath blight. Currently, it was an elusive goal to breeding highly resistant varieties, and should be breeding moderate resistant varieties as the new target. If the varieties might be achieved in moderate resistance, yield loss could reduce to some extent. The MAS approach to transfer a single large effect QTL or pyramid different resistance QTLs, we can make moderate susceptibility varieties resistant to achieve the level of moderate resistant. |
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