| Rice is one of the major grain crops in China and with a plant area of450million mu. The sheath blight disease often occur and leads to a great loss of rice yield and quality. Understanding the genetic mechanism of the disease and cultivation of disease-resistant varieties are possible effective control methods in the future. In this study, phenotypic of sheath blight resistance was identified and genotype of the C418introgression lines were analysed for QTL mapping. A mini-core collection of Chinese germplasm of rice and a core collection of drought-resistant germplasm were also identified and evaluated for resistance to rice sheath blight. The main results of the study were:1. A BC2F3introgression lines consisting of269individuals were developed by crossing and backcrossing, in which a major hybrid restorer lines C418was used as recurrent parent, BR24, Cisanggurang, Dhan4and Diantun502were used as donor parents. The BC2F4, BC2F5,BC2F6population were inoculated using toothpick imbedding method, then plant height (PH), lesion height (LH), relative lesion height (RLH) and disease rate (DR) were record for sheath blight resistance evaluation.2. The evaluation of disease resistance of the introgression lines and parents were carried out at Shanghai in2011(E1), at Hainan in2011(E2), at Shanghai in2012(E3), respectively. The average values of DR for BR24, Cisanggurang, Dhan4, Diantun502and C418were5.3,6.3,6.3,6.0and7.0, respectively. The results indicated that the resistance level of donor parents was higher than that of C418. Other disease related traits have the same phenotypic values.3. A genetic linkage map was constructed based on the introgression lines using163SSR markers covering all12chromosomes, which covered a total of2348.64cM with an average interval of15.65cM between adjacent markers. The donor allelic frequencies in the four introgression lines were9.2%～11.0%, in the scope of theoretical predictions. The replacement rate of the four single segment substitution lines were89.1%-95.9%, making sure that the genetic background of the introgression lines are similar to recurrent parent C418.4. A total of21main-effect QTLs and26epistatic QTLs affecting sheath blight resistance were indentified in three environments and the resistant allele of most QTLs came from donors. The QTLs detected did not overlap, indicating that the four donors contain different favorable alleles. Some QTLs for lesion height, relative lesion height, disease rate were located in the same chromosome regions, forming6multiple QTL-rich regions, they are marker RM5310on chromosome1, marker RM341on chromosome2, marker RM523and marker RM6914on chromosome3, marker RM180on chromosome7and marker RM519on chromosome12. These QTL-rich regions have given a subset of efficient chromosome regions for fine mapping and map-based clone of genes for rice sheath blight resistance.5. From the mini-core collection of Chinese germplasm of rice (181varieties), core collection of drought-resistant germplasm (107varieties), resistant and susceptible materials (56varieties) were identified and evaluated for resistance to rice sheath blight using artificial inoculation methods at Shanghai in2011(E1), at Hainan in2011(E2), at Shanghai in2012(E3), respectively. The numbers of resistant, moderately resistant, moderately susceptible, susceptible and highly susceptible germplasm were4,82,161,54,10, and the percentage were2.9%,23.8%,46.8%,15.7%,10.8%, respectively. According to this study, no highly resistant germplasm have been found while the moderately susceptible germplasm had the highest numbers, almost half of the total. |
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