| Rapeseed is one of the most important oil crops in the world, and also the momentous source of edible vegetable oil in China. Sclerotinia sclerotiorum (Lib.) de Bary is a necrotrophic pathogen which has a wide range of host. Stem rot caused by Sclerotinia sclerotiorum is a recurrent disease in rapeseed around the world, which impedes the development of rapeseed planting and production in China. The purpose of this study is to analyze the genetic mechanism of Brassica napus against Sclerotinia sclerotiorum by diallel cross design and artificial inoculation. Meanwhile, we carried out the histological staining to the cotyledon of resistant and susceptible lines after inoculation. It is aimed at providing theoretical and applied research basis for resistance to Sclerotinia in rapeseed breeding. The main results are as follows:1. Combined with the public molecular marker information of B. napus, we conducted cluster analysis among the11parents for diallel analysis by using of SSR molecular markers.284allele loci were amplified from53pairs of SSR primers which were distributed uniformly in19B. napus chromosomes, and175of which were polymorphic, accounting for61.6%of the total alleles. The11parental lines of B. napus were classified into6groups at the threshold of genetic distance as0.68. According to the clustering result, we formulated a5x6incomplete diallel crosses.2. The identification stem resistance of the parental lines and F1of the incomplete diallel crosses (a total of41materials) at the adult stage showed that, the environment impacted the lesion length (the resistance of stem rot) significantly. However, the difference between most of materials was significant. The parental strain of C4-173B performed the best resistance against Sclerotinia in two years. Meanwhile, the F1of Xiangyou15×C4-173B performed the high and stabilized resistance in all experimental environment.3. We analyzed the genetic effects of the resistance against Sclerotinia in B. napus based on the the Minimun Norm Quadrate Unbiased Estimation (MTNQUE). The results revealed that the stem resistance of B. napus was controlled by both additive and dominant effects. Furthermore, the dominant effect accounted for a greater proportion relative to the additive effect. The broad-sense heritability of the stem resistance was accordant in two years, and the score was between68%and69%. In addition, the general combining ability (GCA) of the parental strain C4-173B exhibited significant negative effects in two years. Therefore, C4-173B had good effect on enhancing the resistance against Sclerotinia.4. With the augmented NCⅡ design, we also carried out the genetic analysis of the the resistance against Sclerotinia in B. napus. It indicated that the genetic control of stem resistance of B. napus fit to the additive-dominance model and there was no epistatic effect. The narrow-sense heritability was between47%and60%.5. About two-thirds of combinations showed significant mid-parent heterosis in both years. It demonstrated that the different dominant genes in F1materials had some definite effects on enhancing the resistance. Moreover, the resistance was exhibited dominance against the susception of the Sclerotinia sclerotiorum.6. The results of the histological staining to the cotyledon of resistant and susceptible strains after inoculation showed that cuticle or wax had some definite effects on enhancing the resistance. The hypha was bifurcated frequently in the highly resistant strain (C18-129) after intruding cells, while which was exhibited less bifurcation in highly susceptible strain (C4-43A). Furthermore, the structure of the infection cushion was compact and like dome in C18-129, while which was sparse and like finger in C4-43A. |
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