| Chinese cabbage (Brassica rapa L. ssp. Pekinensis) originated from China, is one of the largest vegetable crops in China, and has gradually become a world wide vegetable crop. According to the statistics of ministry of agriculture, Chinese cabbage production area is about 2.67 million hectares, account for about 15% of the total sown area of the vegetables in China. It plays an important role in vegetable supply and increasing farmers’income in our country. However, in recent years, the verticillium wilt has seriously affected in Chinese cabbage production in Beijing, Hebei Zhangjiakou, Gansu Yongdeng, Yunnan Tonghai and other large-scale planting base, and quickly spread to the surrounding areas. Verticillium wilt has become one of the most important diseases in these areas. Planting resistant varieties is of great significance for the safety of production of Chinese cabbage. Therefore, breeding varieties with resistance to verticillium wilt has become one of the main objectives in Chinese cabbage breeding.Previous studies have been identified the pathogens caused veticillium wilt of Chinese cabbage in Beijing areas as Verticillium dahliae. In order to clarify the types of pathogens, further identification of three pathogenic isolates based on the sequences of group I intron of 18s rDNA, mitochondrial-SSU rDNA and cytochrome b gene has been conducted. Four Chinese cabbage inbred lines with different resistance to verticillium wilt were used, the symptoms of plants after inoculation by vertillium wilt pathogen were investigated. The changes of leaf area, chlorophyll content and leaf fresh weight were evaluated. Based on the real-time PCR technology, we developed an optimized approach to evaluate verticillium wilt resistance. The main results are as follows:1. Based on the analysis of the sequences of group I intron of 18S rDNA, mitochondrial-SSU rDNA and cytochrome gene, three isolates named BCHW10-2, BCHW8-35 and BCHWJ-15 isolated and preserved in our laboratory, were further confirmed to be V. dahlia, the produced spore is considered to be long spore type.2. Four Chinese cabbage inbred lines with different resistance level to verticillium wilt were used as materials, the disease symptoms of plants after inoculation were observed, the physiological indicators such as leaf fresh weight were further investigated. It was observed that the succeptible plants after inoculation showed significant stunting and leaves’ yellowishing. The leaf area, leaf fresh weight and chlorophyll content both of susceptible and resistant cultivars were found to be declined compared with the control, but susceptible varieties decreased more than that in the resistant paints. When leaf of plants after inoculation was stained by basic fuchsine, the colour of basic fuchsine was found to be full of the whole leaf along the vascular bundle in resistant varieties; but not in susceptible cultivars. It is concluded that the degree of vascular damage was greater in susceptible varieties than in the resistant ones.3. Based on the sequence of rDNA-ITS of Verticillium dahliae, specific primers HW1 was designed for amplification of pathogen. By optimizing the reaction system, the content of pathogen of four Chinese cabbage inbred lines with different resistance level to verticillium wilt in different organs and different stages were evaluated with qRT-PCR. The results showed that the content of pathogen in roots, stems and leaves was significantly negative correlated to disease resistance. This method provides the possibility to be used in resistance evaluation with young plants in breeding progam at large scale.4. With qRT-PCR technology system established in this study,254 core breeding lines bred in our laboratory were screened,88 highly resistant (HR) materials,109 resistant (R) materials, and 12 moderately (MR) resistant lines were observed. |
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