Genetic Analysis And QTL Mapping Of Resistance To Sclerotinia Sclerotiorum In Rapeseed (Brassica Napus L.)

Sclerotinia (stem rot) disease, caused by necrotrophic pathogen Sclerotinia sclerotiorum (Lib.) de Bary, is a worldwide disease of many crops, and the top one of the three major diseases, including Sclerotinia sclerotiorum, clubroot and virus disease in oilseed rape (Brassica napus). This disease spread seriously in the Yangtze River Area of China, the main rapeseed producing area, causing severe economic losses.Genetic studies have indicated that resistance to Sclerotinia is polygenic, and vulnerable to environmental and other factors. Because of the lack of resistance resources and accurate and reliable inoculation methods, the development of rapeseed resistant breeding has been restricted. Therefore, the search for a reliable inoculation method and the application of molecular biology techniques to locate resistance QTLs play a significant role in revealing the mechanism of resistance to Sclerotinia sclerotiorum and marker-assisted breeding of disease resistant varieties of oilseed rape.In this study, resistant phenotype and Quantitative resistance loci(QTL) to Sclerotinia sclerotiorum was identified at the seedling stage and mature stage in double haploid (DH) populations derived from microspore culture of F1 whose parents were Huashuang No.5 and Jia 7005. The major results were as follows: 1.Comparison of different inoculation methodsThe resistance to Sclerotinia sclerotiorum at seedling stage was valuated with four methods, including placing mycelial plugs on leaves of live plants, detached leaves assay, petiole inoculation technology and cotyledon assay. The resistance to Sclerotinia sclerotiorum at mature stage wase valuated by mycelial plugs inoculation method on stems. All these methods were effective for identifying resistant and susceptible plants. There was no correlation between the detached leaves assay and placing the mycelial plug on the leaves of live plants. There was significant correlation between detached leaves assay and mycelial plugs inoculation methods at mature stage. 2.Genetic analysis of resistance to sclerotinia sclerotiorum in Brassica napusAll of the traits of resistance (i.e. tolerance) to Sclerotinia sclerotiorum in different growth stages and different inoculation methods had shown a normal distribution and the phenotypic differences among genotypes reached a significant level. The correlation of the phenotype with the same inoculation method in different years was significant; the correlation between the resistance (i.e. tolerance) to Sclerotinia sclerotiorum in different growing stage and with different inoculation methods also reached a significant level. 3. Mapping QTLs conferring resistance to sclerotinia sclerotiorum in B.napusWith the data of resistant traits collected from detached leaves assay and mycelial plug inoculation method at mature stage in 2010 and 2011,32 QTLs were detected with a LOD seore more than 2.5 in the two years in DH populations, locating on lakeage group A1,A2,A3,A6,A7,A9,C6,C8. The single QTL accounted for phenotype variation from 3.73% to 41.81%. Among them, nine QTLs were totally detected by detached leaves assay in 2010, accounting for phenotype variation from 3.73% to 13.07%. Fourteen QTLs were totally detected by mycelial plug inocalution method at mature stage in 2010, accounting for phenotype variation from 6.07% to 41.81%. Nine QTLs were totally detected by mycelial plug at mature stage in 2010, accounting for phenotype variation from 2.91% to 41.06%.There was one common loci detected in linkage group C6 by mycelial plug inoculation methods at mature stage in different two years. There was two common loci detected by two different inoculation methods. One was located on linkage group A3, and the other was located on linkage group A9.