Identification Of Physiological Race And The Population Genetic Structure Of Phytophthora Capsici In Guizhou

Phytophthora blight induced by Phytophthora capsici is an important soil-bornedisease and causes significant yield loss in China along with the rapidcommercializing development of pepper production, improvement of culturalpractices and popularization of new pepper varieties. Therefore, understanding thecomposition and distribution of mating type, physiological race and the populationgenetic diversity of Phytophthora capsici isolates, has important significance to selectresistant varieties, and the rational distribution and rotation of resistant varieties.In order to master the composition and distribution of mating type, physiologicalrace and the population genetic diversity of Phytophthora capsici isolates, a collectionof P. capsici isolates isolated from different regions in Guizhou Province werecharacterized in this study. Of the72isolates tested,44were isolated from standardsamples in2012and28were got from Guizhou Institute of Plant Protection whichwere isolated from2004,2007and2009, respectively. We analyzed the mating typecomposition by matching pairs with standard isolates, and population diversity byRAPD-PCR method, and49representative strains were selected to identifyphysiological race according to a subset of identification hosts of pepper. The mainresults are as follows:1. Total72isolates throughout the province were divided into A1mating type6isolates, A2mating type64isolates and A1,A2mating type2isolates. A2was thedominant mating type and distributed in all sampling regions which accounted for88.9%. Both mating types were found in the same fields of Qiannan or the sameinfected plant of Guiyang. Their composition differed significantly as the year goingon: Before2012each isolate was A2mating type, but increased to three mating typesin2012. Both A1and A2mating types were found in the same pepper field or peppercultivars, which indicated that the genetic variation probability of Phytophthoracapsici isolates had increased.2. RAPD analysis using31random primers resulted in329reproducible bands, of which317(96.35%) were polymorphic. This shows that abundant genetic diversityexisted among different isolates. The sequence of Shannon’s Diversity indices was“Guiyang (0.4244)> Zunyi (0.2995)> Bijie (0.1926)> Qiannan (0.1822)> Anshun(0.1206)> Liu Panshui (0.1142)”. Seven clusters were obtained by using UPGMAanalysis at level of0.78similarity, clusters have certain relevance with geographicregion and host varieties, respectively.3. Based on factors of population genetic structure, geographic origin and matingtype, forty-nine representative strains of Phytophthora capsici were selected toidentify physiological race according to a subset of identification hosts of pepper. Theresults show that: there were four races, which were Race1, Race2, Race3and Race4.The ratio of each Race was20.41%,20.41%,50.02%,8.16%, of which Race3wasdominant, there had been a palpable shift in physiological races in different years.