QTL Mapping For Resistance To Sclerotinia Stem Rot In Brassica Napus

S. sclerotiorum is one of the most serious disease in our country. Average loss caused by the disease ranged from30%-50%annually. To increase resistance to S. sclerotiorum in Brassica napus is one of our aims. But now we still know little about the genetic and resistance mechanisms of Brassica napus. Early-maturing varieties were much more easily infected. To analyze the genetic and resistance mechanisms between Brassica napus and the disease, to find correlation between resistance and flower time, and to find the genetic mechanism beween resistance and early-maturing varieties, H100and D126were chosen as two parents, which were significantly different in resistance and days to flowering in this study. DH population was constructed through microspore culture from an F1between H100and D126, where163-DH lines were chosen to construct a genetic linkage map. Stem resistance at the mature plant stage and days to flowering were measured, and then QTLs were located.Results were as follows:1. A total of467molecular markers including SSRs and InDels, which have been screened in their corresponding parents, were employed to construct a genetic linkage map with19linkage groups covering2243.4cM with an average space of4.86cM between adjacent markers.168segregation distortion locus were found in the genetic linkage map(p<0.01), accounting for36%of total markers. In general,92segregation distortion markers bias toward H100, accounting for54.8%; while76markers bias towards D126, accounting for45.2%.2. Resistance was assessed with stem inoculation at the mature plant stage (SR) and Days to flowering was counted in2014. SR was measured7days after inoculation. The average lesion length of H100was3.1cm, while D126was6.85cm. The average lesion length of the DH population was5.48cm, ranging from0.59to13.06cm. Days to Flowering ranged from120-167.5days.7lines were blow125days, while8lines were above165days. A significant negative correlation (R=-0.53) between SR and Days to flowering indicated that compared to early-maturing varieties, late maturing varieties were more tolerant to disease.3. In this study,9QTLs were located. Four QTLs were for stem resistance (SR) at the mature plant stage, named SRA2, SRA3, SRC2a, SRC2b, located on A2, A3, C2and C2respectively. Collectively accounted for39.0%of the total phenotypic variation, each accounting for13.80%、8.50%、8.70%、8.00%, respectively. LOD value was6.22,3.76,3.61,3.82, respectively. Five QTLs for Days to flowering were mapped, located on A2, A3, A6and C8. Phenotypic variation ranged from5.6-25.8%. One QTL FTA2, which was on LG A2and explained25.80%of the phenotypic variations, was considered as a major QTL. SRA3and FTA3a had one overlapping confidence interval, which partly explained why negative correlation occurred between resistence and flower time.4. There were two obvious advantages using InDel markers, which could locate LGs on Chromosomes accurately. Besides, physical position of located QTLs could be confirmed and candidate genes could be identified quickly by using InDel markers. An error was detected that previously defined A4and C4were reversed,after using InDel markers to make LGs densely. Physical position of FTA2was confirmed based on physical position of relevant InDel markers and candidate gene BnFLC was detected in the corresponding physical position.