Identification, Genetic Diversity, and Chemical Control of pv. in China.

Peach bacterial spot caused by pv. has become widespread in most peach-producing areas of China and has caused devastating losses to the peach industry. However, little is known about the population biology and epidemiology of pv. in China, thus no effective management strategy is available. Altogether, 321 symptomatic samples of peach bacterial spot from 12 provinces in China were collected from which 612 bacterial isolates were obtained. Based on 16S rDNA sequence comparison in GenBank, the obtained isolates were identified as spp. (514) and spp. (98). The pathogenicity test demonstrated that the causal agent of the peach bacterial spot was the spp. instead of the spp. Based on morphological observation, physiological and biochemical characterization, and molecular identification, the spp. were further identified to be pv. . Then, 41 pv. isolates representing different populations were selected and analyzed with repetitive element sequence based-PCR and intersimple sequence repeat markers to understand the genetic diversity and population structure along with four pv. isolates from plum and three isolates of pv. as comparison. A total of 98 polymorphic alleles were identified, with a mean value of percentage of polymorphic loci of 14. Genetic diversity and phylogenetic analysis revealed the profound heterogeneity between pv. and pv. , moderate genetic differentiation within pv. , and obvious host specificity but weak geographical differentiation in population. Finally, the efficiency of bactericides on pv. was evaluated in vitro and in vivo. The parallel repeated field trials in two orchards demonstrated that 80% Mancozeb (1:800) and 47% Kocide (1:800, 1:1,500, and 1:2,000) had excellent control efficacies for pv. , especially as the control efficacy of Kocide could even reach 90%. This study conducted a systematic investigation for the occurrence, population variance, and chemical control of pv. . It improved the understanding of the pathogen populations of peach bacterial spot in China and provided solid theoretical and practical guidance for pv. control.