Studies On Genetic Diversity Of Phytophthora Melonis In Hunan Province

Cucumber blight is one of the important disease in the cucumber production, and a kind of destructive soil-borne disease which caused by Phytophthora melonis. The research focus on the genetic diversity of the P. melonis strains which were isolated from the plant with classical symptom of Cucumber Blight collected from different areas in Hunan.1、22strains of the P. melonis were obtained in5different areas of Hunan province by morphology and molecular identification of the strains, and they were stored by the method of slant preservation and paper disk preservation.2、22isolates of P. melonis were tested with the toxicities of metalazyl,the results showed that all isolates were sensitive and the minimum EC50value being0.09μg/ml,the maxium EC50value was0.15μg/ml, respectively, the average EC50value was0.13μg/ml; Metalazyl has a good inhibition to P. melonis.3、It was found that HJ-2had the highest pathogenicity which was isolated from Hongjiang of Hunan, and the lowest one was CS-3which was isolated from Yuelu area of Changsha through the Pathogenecity test by inoculation22P. melonis strain on3different cucumber varieties in vitro.4、ITS and β-tubulin of the22strains was amplified and sequenced, the length of ITS sequence is770bp and (3-tubulin is800bp. The sequenced ITS and β-tubulin from22strains were aligned with related sequences downloaded from Genbank respectively with bioinformatics softwares. Phylogenetic tree shows that P. melonis and P. drechsleri are located in different branch, but the P. drechsleri and P. capsici are located in the same branch. Phylogenetic tree prove that the affinity of different phytophthora, it concluded that different P. melonis was genetic diversity, but the trend is that the same source isolates have close genetic relationships...