Genetic Diversity Analysis and Fungicides Screening of the Pathogen Causing Cigar Tobacco Black Shank in Shifang

In order to effectively control tobacco black shank of cigars caused by Phytophthora parasitica in Shifang, 27 strains of P. parasitica were analyzed for mating type, population genetic diversity and effective fungicides screening. The results showed that 27 strains were A2 mating type indicating no sexual recombination of P. parasitica in Shifang. Corrected Simpson index and genotypic evenness were 0.776 and 0.643, suggesting the genetic diversity for P. parasitica strains was relatively high. Analysis of molecular variance and a principal coordinate analysis showed that the pathogen population in Shifang was different between strains from other areas and the major (92%) of the genetic divergence was within populations. Overal, metalaxyl, dimethomorph and cyazofamid had the best inhibitory effect on 27 strains, and the average EC₅₀ value was 0.491, 0.574 and 0.730 mg/L, respectively. The results can provide guidance for the scientific and effective control of tobacco black shank of cigars in Shifang.