SRAP Analysis Of Marginal Scorch And Downy Mildew Resistant Genes In Brassica Rapa L. Ssp. Pekinensis

Chinese cabbage (Brassica rapa L. ssp. pekinensis) is an important vegetable crop in China. Many diseases cause extensive losses in yield and quality during the Chinese cabbage planting. A novel disease, Marginal Scorch, was found in Chinese cabbage. It happened on leaves and can deeply damage the Chinese cabbage crops. Downy Mildew has been one of three most important diseases in Chinese cabbage. The breeding objective is high resistance, high yield and high quality for many years and it is an urgent demand to select and breed the improved varieties with Marginal Scorch resistant and Downy Mildew resistant.In this study, genetic analysis of Marginal Scorch and Downy Mildew by using field identification and lab artificial inoculation was conducted. One Sequence related amplified polymorphism (SRAP) marker was found to link Marginal Scorch resistant gene. Two SRAP markers were linked to Downy Mildew resisitant gene, and this gene was mapped on A1 linkage group. The main results are as follows:(1) Six Marginal Scorch and Downy Mildew resistant lines (Shan xi xin zhong zi331, Shan xi xin zhong zi 338, Shan xi xin zhong zi 339) and 4 sensitive lines (Shan xi xin zhong zi332, Shan xi xin zhong zi 340) were found in 20 selfing lines. Three F2 populations were constructed by the crosses between 331 and 332, 339 and 332, 338 and 340.(2) In the three F2 populations, the segregation ratios of Marginal Scorch resisitance were following 3:1. SRAP analysis and bulked segregation analysis (BSA) were used to screen markers linked to the disease resistant gene in F2 population of 339×332 . Among 672 primer pairs, BMe10Co11 showed polymorphism, and the distance was 11.4 cM.(3)Genetic analysis of Downy Mildew resistance in three F2 populations was conducted. The segregation ratios of two F2 populations (331×332, 339×332) were following 3:1. SRAP technique and BSA were used to screen markers linked to the Downy Mildew resistant gene in F2 population of 331×332. Among the 712 SRAP primers, only Me1E40 and Me3E33 showed polymorphism. The distance of markers and resistant gene was 8.1 cM and 10.3 cM respectively. Cloned and sequenced the two SRAP markers, the length of Me1E40 was 159 bp, and the length of Me3E33 was 121 bp. According to the alignments with the whole genome sequence of Brassica rapa, Me1E40 and Me3E33 were mapped on scaffold61 and scaffold151 respectively. These two scaffolds were on linkage group A1 (Chr 3) in Chinese cabbage.