Study On Phenotype And Genotype Of Phytophthora Infestans

A total of 130 Phytophthora infestans isolates collected from Heilongjiang and Jilin provinces in 2006~2008 were determined for mating type and sensitivity to metalaxyl, dimethomorph, ethaboxam and fluazinam in vitro. All isolates of P. infestans collected from Heilongjiang and Jilin provinces showed A1 mating type. The results of sensitivity to metalaxyl showed that 94.4% isolates were resistant to metalaxyl; 5.6% isolates were moderate resistant to metalaxyl among the all isolates collected from 2006; 45.9% isolates were resistant to metalaxyl, 33.3% isolates were moderate resistant to metalaxyl, 20.8% isolates were sensitivity to metalaxyl among the all isolates ceollected from 2007; 81.4% isolates were resistant to metalaxyl, 2.9% isolates were moderate resistant to metalaxyl, 15.7% isolates were sensitivity to metalaxyl. The results suggested that P. infestans isolates occur in Heilongjiang and Jilin provinces have been produced metalaxyl resistance. As for results of dimethomorph sensitivity, most isolates could be grown at 0.5μg/mL, but two isolates could be grown at 1.0μg/mL. Based on these results, the MIC of dimethomorph for P. infestants should be 0.5-1.0μg/mL. The results showed that resistance development against to dimethomorph by P. infestans is not likely to occur in the natural condition. As for ethaboxam sensitivity, no isolates was able to grow at 1.0μg/mL, but only 1 isolate could be grown at 0.5μg/mL. Based on these results, the minimum inhibitory concentration (MIC) of ethaboxam for P. infestants should be 0.2-0.5μg/mL.The results of sensitivity to fluazinam indicated that there were no significant differences of sensitivity to fluazinam between P. infestans isolates collected from different location and various years. Their sensitivities distributed as a unimodal curve, EC50 values ranged from 0.2033 to 0.7837μg/mL, the most insensitive was 3.85 folds of the most sensitive, with a mean of 0.4781±0.0163μg/mL, so it can be used as baseline-sensitivity of P. infestans to fluazinam. The paper was tested for the control efficacy of fungicides to potato late blight. The results of pot culture control experiments indicated that fluazinam (WP), fluazinam (SC) and dimethomorph were effective for the control of late blight, and their control effects were 85.7%, 87.1% and 82.2%, respectively. However, control efficacy of metalaxyl was 23.9%. The results of field trial indicated that fluazinam (WP), fluazinam (SC) and dimethomorph were effective for the control of late blight, and their control effects were 75.9%, 79.9% and 74.6%, respectively. However, control efficacy of metalaxyl was 41.0%. In addition, no cross resistance was found between metalaxyl and three fungicides. To examine the genetic diversity of P. infestans isolates collected from Heilongjiang and Jilin provinces, the studies were performed the genotypic characteristics by using allozyme genotypes, random amplified polymorphic DNA (RAPD) and mitochondrial DNA haplotype patterns. The results for the allozyme genotype showed that three different allozyme genotypes found in isolates collected from Heilongjiang and Jilin provinces,.The frequency of three different allozyme genotypes with Gpi100/100 Pep 96/96, Gpi 100/100 Pep 96/100 and Gpi 100/100 Pep 100/100 were 2.4%, 0.8% and 96.8%. Of which, allozyme genotypes Gpi 100/100 Pep 100/100 dominated the population of P. infestans tested. The mtDNA haplotype of all isolates collected from Heilongjiang and Jilin provinces were determined as two genotypes (Ⅰa andⅡa). Of which, 8.1% isolates wereⅠa, 91.9% isolates wereⅡa.In PCR amplification of the genomic DNAs extracted from 17 phenotypic isolates with the selected six primers, total of 129 DNA bands were produced, and among these, 90 bands were polymorphic. The result was similar to the similarity coefficients of the RAPD group for P. infestans, ranging from 0.740 to 1.000. According to the RAPD analysis by using OPD-20 primer, 104 isolates contains standard isolates were separated into two major RAPD groups and eight minor groups at similarity level of 90.8%. The results of RAPD analysis suggested that RAPD groups were not correlated with the allozyme genotypes, metalaxyl resistance and mtDNA genotypes.According to mating types, sensitivity to metalaxyl, allozyme genotypes, RAPD groups and mtDNA haplotype, 104 isolates were separated into 18 multi-locus genotypes. Of which, isolation frequencies of MG2, MG16 and MG18 multi-locus genotypes were more than 10.0%. Although some new genotypes have emerged in the population.