Study On Phenotype Of Phytophthora Infestans From Heilongjiang Prvince

Potato Late blight, caused by the oomycete pathogen Phytophthora infestans (Mont.) de Bary,is the most damaging disease of potato worldwide and also highly prevalent in the northeast andsouthwest regions of China. The disease frequently causes severe production loss up to50%andhas severely restricted the development of potato industry in China.The dispersal of A2mating type strains of P. infestans in China has resulted in increasingRulence and genetic variation; frequent use of Metalaxyl fungicides has led to the establishment ofresistant strains of P. infestans; long plantation of single and vertically resistant varieties hasresulted in these varieties losing resistance to P. infestans and a rapid change of populationstructure of the pathogen. All these factors are creating new challenges for the management of lateblight.The main goal of this study is to characterize the population structure of P. infestans fromHeilongjiang for mating type, Rulence and metalaxyl sensitivity. The study includes a systematicsurvey of P. infestans isolates collected in Heilongjiang province in2010. The results of our studywill provide important information for evaluation of variety resources and a guide for fungicideapplication.1. A total of95isolates of Phytophthora infestans collected from Harbin, Keshan, Tahe andMohe in2010were tested on11potato R-gene differentials: R1-R11, each possessing a differentpreviously identified R-gene from Solanum demissum, and a plant with no known R genes from S.demissum (r). There were24physiological races identified. Results showed the dominant racescould be ranked as1.3.4.7.8.10.11,1.3.4.7.8, and1.3.4.7.10.11, with the occurrence frequencies of29.5%,9.5%and9.5%, respectively, and the race1.3.4.7.8.10.11was found in all sampling sites.Races1.2.3.4.5.7.8.9.10.11and1.3.4.5.6.7.8.9.10.11carry10Rulence genes, but no “super race”was detected. The Rulence genes R3, R4and R7were most common, each with a frequency of100%, followed by R8, R10and R11with frequencies of67.37%,72.63%and77.89%,respectively. R9had the lowest frequency of3%.2. One hundred and fifty-five isolates of P. infestans collected from Harbin, KeShan, TaHe,MoHe were tested for mating type. All96isolates were of A1mating type.3. One hundred and fifty-five isolates collected from MuDanjiang, Harbin, SuiHua, HaLun,KeShan, NenJiang, TaHe and MoHe were analyzed for their resistance to metalaxyl fungicide. Ofthese,125isolates (80.6%) were resistant to metalaxyl.As our showed, highly complex races of P. infestans were already commonly present inHeilongjiang province, which can overcome R3, R4, R7, R1, R8, R10and R11. Up to now, no A2mating type was reported in Heilongjiang, so it’s critical to block the introduction of the A2matingtype. The overall high frequency of resistance to metalaxyl that we found in Heilongjiangindicated that it would not seem advisable to use phenylamide compounds in this province.