Analysis Of Genetic Diversity Of Phytophthora Capsici And Its Pathogenic Mechanism

Pepper Phytophthora blight spreaded quickly and has become one of the serious widely distributed diseases that jeopardize the production of pepper in many countries since it's first being reported. This research has collected 13 Phytophthora capsici strain from different regions, analysis of genetic diversity of DNA by SRAP. We identified the host by phytophthora sp standards, and identified their physiological strains. and we studied the infection process in item of peppers with different resistances. we initially established the technology of the rejuvenescence of Phytophthora capsici and the separation of single spores, The results are as follows:1. We analyzed the genetic diversity of the physiological strains from 13 different regions after their single spores have been separated, Among the screened out priming with 143 pairs SRAP primers it was observed that 33 pairs primer has shown promising results regarding repeatability and polymorphism and have cloned 606 DNA bands, among them, 587 of a total of 96.86% bands were depicted polymorphism bands, 75 of a total of 12.38% are special bands, which takes up 12.78% of polymorphism bands, it means that pepper Phytophthora blight have a wealth of genetic diversity. According to the clustering analysis of the SRAP results, the strains we were studying can be divided into three categories, the first class has seven strains, namely as P15 from Shanxi, ph3 from Qinghai, ZLT from Guangzhou, YN -9, YN-10 from Yunnan province, PC from Korea and PG-1 from Beijing; four strains can be classified as second type, namely as PG -3 from Beijing, HX-5, HX-9 from Hebei province, YN-1 from Yunnan province; only two strains can be referred as third category. The similarity coefficients were ranged from 0.24 to 0.66. The isolates from the same area were clustered together and showed close genetic relationships. Some isolates from different areas were also clustered together with similarity. We found that the clustering of the strains has no obvious relationship with the place no matter where they came from.2. Root pouring method to inoculate susceptible and resistant pepper. After the vaccination on the interval of 0, 12, 24, 48, 72, 177h, samples were observed for infectionprocess by Phytophthora capsici in different resistant cultivars of pepper. The results shown that Resistant varieties have shown no symptom either in their appearance and hyphae after being vaccinated, But the susceptible cultivar have shown quite vivid symptoms on the third day of inoculation, Under evaluating transmission electron microscopy, Phytophthora capsici penetrated into cortical cells after 72h, entered secondary xylem after 144h, and made the cell membrane disintegrated and cell plasmolysis, mitochondria and other organelles disappeared. These results indicated that Phytophthora capsici interacted with pepper two days later after the inoculation and subsequently infection occurred. Mycelium first enters into the intercellular space and then enters the cell. Resistant varieties of root can inhibit Phytophthora capsici infection, so that their stems can not be infected.3. We have identified the physiological strains of 13 pepper Phytophthora blights from different regions, experiments indicate that: strain PC from Korea and strain YN-1 from Yunnan are ph1, strains of PG-1 and PG-3 from Beijing and strains of YN-9Y and YN-10 from Yunnan and strain ph3 from Qinghai are ph2, N-1 from Inner Mongolia, P15 from Shannxi, YN-1 from Yunnan, HX-5 and HX-9 from Hebei and ZLT from Guangzhou are ph3. The proportion of 1,2 and 3 of the total population are 15.4%,38.5%,46.2%, respectively, it can be predict that physiological strain 3 is the preponderant strain, and there is no direct relationship between the physical separation and sources of geography.4. By studying the effect of the potato dextrose agar (PDA) and PDA drug-containing selective culture medium (PDAPR) on the separation of individual zoosporangium to obtain the most effective culture for the separation of single Phytophthora capsici sporangium. We compared the pathogenicity of Phytophthora capsici before and after rejuvenation by using conventional techniques with one disease resistant host plant and a susceptible one. The results showed that the best culture for a single sporangium separation is the PDAPR, with a separation rate of 95%, where the pollution rate is only 15.8%.The pathogenicity of Phytophthora capsici after rejuvenation to susceptible plant is significant higher than that of before rejuvenation, The virulence of Phytophthora capsici after rejuvenation increased by 27.2%, which shows that the strain pathogenicity can be restored back through rejuvenation.