Population Characteristics Of Phytophthora Infestans From Ningxia Of China In 2010

Potato late blight, which is caused by Phytophthora infestans (Mont.) de Bary, is one of the most devastating diseases in potato production. The phenotype of 94 isolates collected from Ningxia province in 2010 was investigated for mating type and metalaxyl resistance. The genotype was also assessed for mitochondrial DNA haplotypes with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), simple sequence repeats (SSR) and amplified fragment length polymorphism (AFLP). During the experiment, lots of A2 mating type isolates were found. 82 isolates were collected from Heilongjiang, Jilin, Inner Mongolia, Switzerland, The United States and Holland, among which 40 isolates were A1 mating type and 42 isolates were A2 mating type. The characteristics of 82 isolates were investigated for metalaxyl resistance and genotypic analysis. The results were as follows.1 Population characteristics of Phytophthora infestans from Ningxia1.1 Determination of mating type: 94 isolates,which were collected from Ningxia province in 2010, were investigated for mating types. The result showed that 86 isolates were A2 mating type, one was A1 mating type, and 7 isolates were self-fertile.1.2 Determination of metalaxyl sensitivity: 94 isolates, which were collected from Ningxia province in 2010, were investigated for metalaxyl resistance. The result showed that all the tested isolates were metalaxyl-resistant, 89 isolates were metalaxyl-high-resistance and 5 isolates were metalaxyl-moderate -resistance.1.3 Determination of mitochondrial DNA haplotype: The mitochondrial DNA haplotypes of 94 isolates were assessed with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), and the genotype of all the strains tested were Ia.1.4 Analysis of SSR genotype: The SSR genotype of the 94 isolates was tested with six pairs of SSR primer, which was compared with 8 Phytophthora infestans reference isolates. Two SSR genotypes were determined. 93 isolates were type I SSR genotype, which were predominant SSR ones.1.5 Analysis of AFLP genotype: The genomic DNA of 50 isolates was amplified with four selective primer combinations. A total of 201 AFLP bands were obtained, and 173 of them, covering 86.1%, showed low polymorphism. The population genetic analysis indicated that A2 mating type and self-fertile also had a near relationship, population of Phytophthora infestans from Ningxia existed genetic differentiation.2. Population characteristics of Phytophthora infestans of A1, A2 mating type2.1 Determination of metalaxyl sensitivity : 82 isolates were investigated for metalaxyl sensitivity. The resistance ratio of A1 mating type was 55%, and A2 mating type was 97%.2.2 Determination of mitochondrial DNA haplotype: The mitochondrial DNA haplotypes of 82 isolates were assessed with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), the genotype of the A1 mating type strains was testedⅡa andⅡb, and the genotype of all of the A2 mating type strains was tested Ia.2.3 Analysis of SSR genotype: The SSR genotype of the 82 isolates was tested with six pairs of SSR primer. 17 SSR genotypes were determined. In A1 mating type strains, 12 SSR genotypes were identified, andⅩⅡtype was the predominant genotype; In A2 mating type strains, 5 SSR genotypes were identified, and typeⅢwas the predominant genotype.2.4 Analysis of AFLP genotype: The genomic DNA of 82 isolates was amplified with four selective primer combinations. A total of 212 AFLP bands were obtained, and 190 of them, covering 89.6%, showed low polymorphism. The population genetic analysis indicated that the overall A1 mating type strains and the A2 mating type strains together in different branches , the AFLP clades were associated with mating type, but were not associated with geographic origin.