| Phytophthora blight caused by Phytophthora capsici Leonian is one class of devastating diseases that impair seriously the output and quality of crops worldwide, such as vegetables. Changes of genetic structure and resistance to fungicides of P. capsici population are positively associated with disease occurrence and prevailing.In this study,54 P. capsici isolates were collected from six regions (East, North, Southwest, Northwest, Northeast and South) of China, plus one American control isolate. To effectively control the diseases, the population genetic diversity and resistance to dominant fungicides of P. capsici isolates were examined.By using the confrontation culture method, mating types of 55 isolates were determined. The result indicated that two major mating types (A1 and A2) were distributed in all examined regions in China. Each of 6 regions hosts mating type A1 and A2, except South China in which only one isolate was tested (A2 mating type). The ratio of mating type Al and A2 among the isolates was approximately 1 to 1.The genetic diversity of P. capsici population from above regions was analyzed using 7 SSR (Simple Sequence Repeat) primer pairs (Pcapl, Pcap3, Pcap4, Pcap5, Pcap6, Pcap7 and Pcap8). To do so, firstly, an economical method namely TP-M13-SSR based on fluorescent labeling of SSR PCR productsand high throughput sequencing technique was established. Using this method, 21 allelic genes were detected. Three allelic genes for each site on average and at least 2 for any site were detected. Chi-square test showed that allele frequency of five SSR sites (Pcapl, Pcap4, Pcap6, Pcap7 and Pcap8) were significantly different. The gene diversity and polymorphism information from SSR locus Pcap3 were the highest, while those from Pcap8 the lowest. From thepopulations,32 SSR genotypes were identified. Isolates collected from Southwest China possessed 8 genotypes and genotype AB was the dominant one with 34% frequency. Isolates collected from North China had 10 genotypes and DG was dominant with 31% frequency. Twelve genotypes were detected among the isolates from Eastern China and DI had the highest frequency of 21%. Three genotypes (AA, AB and BD) arose two times and the rest arose only once. Among the regional population, genetic diversity in the population of East China was the most abundant. American isolate showed great genetic differentiation from Chinese isolates.The resistance of 55 isolates to Metalaxyl, Dimethomorph and Pyrimorph were testedon medium. The results showed that Dimethomorph possessed the best inhibitory effect on P. capsici with 0.2156-4.5993 μg/mL EC50 value. EC50 value of the least sensitive isolate was 21.33 times that of the most sensitive isolate. The sensitivity of the isolates from different regions to Metalaxyl, Dimethomorph and Pyrimorph varied.Pyrimorph resistant isolates with increased 5.5645-73.7288 fold were obtained by ultraviolet mutagenesis(3) and fungicide taming(3). Resistant isolates subjected to 15 successive transfers on fungicide-free PDA (Potato Dextrose Agar) plates still showed stable fungicide resistance. These six isolates had the same mating type as the parent isolates, indicating that the occurrence of fungicide resistance had no effect on the mating type. The growth rate of resistant isolates on fungicide-free PDA plates was significantly lower than that of parent isolates, which showed that the resistance occurrence affected the growth rate. By analyzing the sensibility of 6 resistant isolates and 12 control isolates to Flumorph and Mandipropamid, it was found that isolates with Pyrimorph resistance had cross-resistance to other CAA pesticides such as Dimethomorph, Flumorph and Mandipropamid.In this study, the genetic structure of P. capsici populations using TP-M13-SSR technology and their resistance to major fungicides were analyzed. The results will provide scientific guide for better control of diseases caused by P. capsici.
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