Isolation and Identification of a Pathogen Causing Guava Black Spot

Objective: In order to provide scientific basis for further clarifying the species and characteristics of dominant pathogens causing guava black spot. Method: A dominant pathogen, named S1, was isolated and purified from the guava fruit infected with black spot disease, and subjected to morphology observation, pathogenicity determination, growth characteristics study and polymerase chain reaction (PCR) sequencing comparison analysis were conducted for comprehensive identification of the dominant pathogen S1. Results: According to the morphological observation, the aerial hyphae of the S1 colony were fluffy and dense, and the color was dark green or black. The spore morphology was monospore and transparent, and the size was uniform, about (6~10) μm×(6~7) μm, round or elliptical, compared with the "Fungus Identification Manual", it was preliminarily determined to belong to Phyllanthus spp., and once again inoculated to healthy guava fruits for pathogenicity determination. The results showed that S1 was the dominant pathogen causing guava black spot disease. Research on growth characteristics showed that S1 was more suitable for growth under alkaline, dark and normal temperature conditions. Moreover, S1 was identified as Phyllosticta capitalensis by the comparison of the PCR sequencing results. Conclusion: The dominant pathogen causing guava black spot disease was Phyllosticta capitalensis.