The Resistant Analysis Of Rice Sheath Blight By Developing Chromosome Segment Substitution Lines

Rice is one of the important food crops in the world and is always harmed by many diseases. Rice sheath blight, caused by Rhizoctonia solani, had caused severe yield loss each year. In southern China, sheath blight had become the severest disease in part of the rice region. It was extremely urgent to explore new resistance germplasm and breed disease-resistant cultivars. Most traits of the rice, including resistance to sheath blight are qunatitative traits, which are controlled by polygenes. To study quantitative trait loci (QTL) by dissecting individual QTL into single Mendelian factors is important in understanding the machanism of rice growth and development and improving the yield and stress resistance of rice. An important strategy for dissecting individual QTL is to construct a set of chromosome segment substitution lines (CSSL), which is crucial tool material because each line possesses the genetic background of the recurrent parent with just one segment from the donor. The advantage of using CSSL in QTL mapping is that the "noise" of the genetic background was eliminated. So they are very important experimental materials widely used in mapping and analysis of the quantitative trait loci (QTL).Excellent germplasm is the material base for exploring major disease-resistant QTL and further breeding new cultivars against to rice sheath blight. A new pure line, YSBR1, from a cross of indica/japonica rice, performed excellent resistance to sheath blight in field experiment in many years. Huajingxian74with moderate resistance to the rice sheath blight is a commercial indica cultivars in southern China. In order to explore and utilize noval main effective QTL for resistanse to sheath blight and some important agronomic traits gene, we utilized two sets of CSSL populations. One set was developed by backcross and marker-assisted selection (MAS), in which chromosome segments from excellent resistance germplasm YSBR1(donor parent) were introgressed into an susceptible genetic background of Lemont (recurrent parent). The other was introduced from South China Agricultural University, in which Huajingxian74was used as recurrent parent and Amol3(sona) as donor parent. The main results are as follows:1. A total86CSSLs of YSBR1was preliminarily constructed by maens of continuous backcrosses with marker-assisted selection. In these CSSLs, Chromosome2,7,8,9,10were mainly covered by the substitute sequences of YSBR1, and the coverage ratios of other chromosomes were different. We found that the growth stage and important agronomic traits among most CSSLs seemed consistent with the recurrent parent in field experiment.2. Polymorphism between two parents, YSBR1and Lemont, was poor. A total1600pairs of SSR primers and781pairs of new developed In/Del markers were used to detect the polymorphism between the parents and215pairs of them showed polymorphism with9.03%of polymorphism ratio. The frequency of the polymorphism markers varied from chromosomes with the highest of18.97%on chromosome3and the lowest of1.51%on chromosome11. YSBR1and Lemont did not belong to typical indica or japonica subspecies but was partial indica or partial japonica (Javanica) ecotype, respectively. The results suggested that genetic background of the parents had greater influence on gaining polymorphism marker between the parents.3. A total48CSSLs derived from the backcross of Lemont (current parent) and YSBR1) were uesed to detect the quantitative trait loci contributing to resistance to rice sheath blight. Variance analysis and correlation analysis showed that, the same as the results of the parents, there were highly significant difference of ressitant revel among CSSLs and highly significant correlation between two repeats. Preliminary analysis indicated that there were QTLs for resistance to rice sheath blight existing on chromosome2,8,9,12. Among them, qSB-2Y-and qSB-12Y-were located in the same regions as previous research results and showed better resistance against to sheath blight, which were likely to be real main effect QTL of resistance to sheath blight. Sixty one CSSLs of YSBR1were used to detect the quantitative trait locus (QTL) for agronomic traits and some results were the same as the ones of F2cloning population of Lemont×YSBR1. Considering the fact that most CSSLs actually substituted multiple segments from donor, the authenticity of QTLs and the relationship between QTLs controlling resistance to sheath blight and agronomic traits needed to confirm by multiple repeats of field experiment after further purifying background of CSSLs.4. Among introduced66SSSLs of Huajingxian74(recurrent parent), most traits of SSSLs were the same as recurrent parent from plant type to development process, and a few of SSSLs showed significant difference in growth stage and plant height contrasted to recurrent parent. We detected5QTLs for resistance to sheath blight in a two-year field test, named qSB-1aHJX、qSB-1bHJX、qSB-2HAM、qSB-3AM、qSB-11HJX, respectively. The most effect QTL was qSB-11HJX, the second was qSB-1aHJX.5. One line (P271) from66SSSLs was backcrossed with the recurrent parent to generate a F2segregation population for further mapping qSB-11HJX. Composite Interval Mapping was used to find QTL and the results showed that qSB-11HJX from Huajingxian74was a real main effect QTL against to sheath blight, which was located interval of markers between ZY27.92and ZY27.49(～0.43Mb,2.5cM) on the long arm end of chromosome11and could explain12.08%of the total phenotypic variation with-0.7595of additive effect and0.1872of dominant effect. The results also identified that the hereditary manner of qSB-11HJX was partially recessive. By analyzing near-isogenic lines materials (P272、P274), the confidence interval of qSB-1aHJX was narrowed down to RM490to ZY7.7-1-5markers (～0.93Mb), whose hereditary manner was partially dominant.