Physiological Races Of Phytophthora Capsici And Resistance Of Capsicum Annuum

Several P. capsici isolates were got from Guizhou Sichuan Guangdong and Qinghai province, and their physiological races were identified; Different pepper cultivars were inoculated with different P. capsici races, and the change rule of peroxidase, catalase and malondialdehyde content were studied; Molecular identification technology of Capsicum annuum resistance to P. capsici were studied. The results as follow:1. According identification hosts, physiological races of P. capsici were identified by normal identification technology. The result shows: isolate (P10) from Guizhou province is belong to race 1; isolate (P3) from Qinghai province is belong to race 2; isolate (ZLT0566) from Guangdong province is belong to race 3; and isolates (P15, P16) from Sichuan province are belong to the other race.2. Inoculated susceptible cv. EC, resistant cv. AA22, high resistant cv. AA5 with isolate P3 and ZLT0566 respectively. The change rule of peroxidase, catalase and malondialdehyde content was studied. The results showed that activity of peroxidase goes up in 96h after inoculation and gets the peak at 96h, and then declines after the peak. Activity of peroxidase in the plants inoculated with P. capsici isolates is significantly higher than the one inoculated with water (CK). But there is no significant difference between treatments with two physiological races. The activity of peroxidase in resistant cultivars (AA5, AA22) is significant higher than the one in susceptible cultivar (EC).3. The activity of catalase goes up on the whole in 144h after inoculation. But the change trend between resistant cultivar and susceptible cultivar is not all the same. The activity of catalase in the plants inoculated with P. capsici isolates is significantly higher than the one inoculated with water (CK). The activity of catalase in high resistant cultivar is significantly higher than susceptible cultivar at 96h post inoculation.4. The content of malondialdehyde in high resistant cultivar (AA5) and susceptible cultivar (EC) shows a same trend as goes up and then declines. And the content of malondialdehyde in resistant cultivar (AA22) shows a reverse trend.5. In a word, activity of peroxidase (POD) could be used as physiological index in pepper resistance to P. capsici, but the activity of catalase (CAT) and content of malondialdehyde could not. They all could not be use as indirect index to identify physiological races of P. capsici. 6. Primers were designed and one pair of them was chosen to carry out this assay, according to the sequence of ribosomal gene of P. capsici and its internal transcribed spacer (ITS). Inoculated different pepper cultivars with P. capsici and selected different plant tissues as samples at 24 and 48 hours post inoculation, and then extracted the genomic DNA of inoculated plants and P. capsici together, did the polymerase chain reaction (PCR) to detect the later one. Nothing was detected in all leaves, whereas P. capsici can be detected in stems of susceptible pepper cultivar at 24 hours post inoculation and all pepper cultivars at 48 hours post inoculation. The amplification products of P. capsici DNA in the susceptible cultivar is 100ng which is 5 times of the one in resistant cultivar with 20ng. The amplification products of P. capsici DNA in the cv. N3 is 77ng which is between the one in the resistant cultivar and susceptible cultivar, but closes with the susceptible one. Therefore cv. N3 is susceptible according to this assay. This result is similar with the one of normal resistance identification.