The Composition And Distribution Of Physiological Races Of Phytophthora Infestans In Southwest Hubei And Their Resistance To Metalaxyl

Late blight is regarded as the world’s most serious crop disease, which is a severe threat to the growth and industrial development of the potato. An effective method of solving this problem is to cultivate varieties of the crop that are resistant to late blight. In order to make potato late blight resistant and breeding more targeted, it is required to investigate the composition and distribution of physiological races of Phytophthora infestans, which will provide theoretical basis for the potato breeding and scientific introduction.This paper aims to identify the physiological races of Phytophthora infestans, isolates which came from different host of potatoes, collected in different regions in southwest Hubei in 2009. Frequency of different virulence genes, the distribution of different physiological races in different ecological regions, analysis of metalaxyl-resistance was tested. It can systematically reveal the genetic structure of phenotype of Phytophthora infestans population in southwest Hubei, making the varieties selection to late blight resistant of different areas in southwest Hubei and the comprehensive prevention to late blight more targeted. The main research results are as follows:1. Isolates collected from four ecological regions, low lountain area in Changyang and Enshi (≤800m asl), sub-high mountain area (800m-1200m asl) in Enshi, high mountain area in Enshi (> 1200m asl) respectively, from five different varieties of potato in southwest Hubei province in 2009, fifty-five isolates obtained after isolation procedure.2. Fifty-five isolates were tested with monogene R1-R11 potato clones of potato late blight differential host. Tewenty-nine physiological races had been identified, and also supervirulence structure was identified, eleven virulence genes were identified from collections. Results showed that high frequency virulence genes are Vir3, Vir4, Vir7, higher than 90%. It showed that R3, R4, R7 lost their resistance in southwest Hubei.3. Frequency of different virulence genes in different regions is almost same as all of the regions in total. On the other hand, frequency of different virulence genes has bigger difference among different ecological regions. Accordingly, it showed that in order to make potato late blight resistant and breeding more targeted, varieties which contain different major resistant genes should be planted in different ecological regions.4. The results showed that Isolates of P. infestans collected from different ecological regions in Hubei province have been becoming higher diversity and more complex virulence structure, both of number of physiological race and types of physiological race are high. Frequency of virulence genes on different varieties of host is different.5. Twenty-seven isolates which selected from fifty-five isolates according to different resources and different types of physiolocal race were tested to sensitivity to metalaxyl, and only one sensitive isolate was discovered, others were intermediate resistance and highy resistance respectively. It showed that it will be not useful any more to late blight by applying metalaxyl fungicide.