CHANG Xiaoxi, ZHANG Lei, CHEN Yunhe, FU Min, ZHANG Lixin
The bacterial canker disease of kiwifruit caused by Pseudomonas syringae pv. actinidiae (Psa) has developed into an important limiting factor for kiwifruit production in Anhui province. Samples with typical bacterial canker symptoms were collected in the main kiwifruit orchards from five counties in Anhui province in 2022-2023. A total of 124 Psa isolates were obtained using the dilution plate methods, and subjected to further analysis via repetitive-element PCR genomic fingerprinting (rep-PCR) techniques. The results revealed that three rep-PCR primer pairs amplified 34 clear bands, among which 26 exhibited polymorphism. Based on sampling location, the isolates were divided into five groups, with effective allele numbers, Nei’s gene diversity index, and Shannon index at the species level being 1.19, 0.13, and 0.21, respectively. The highest genetic diversity was observed among the Psa isolates from Jinzhai, while the lowest was found from Huoqiu. UPGMA cluster analysis indicated that the 124 Psa isolates could be classified into three major groups at a genetic similarity coefficient of 0.80, with no significant correlation between group classification and geographical origin of strains. Pathogenicity tests showed that 72 isolates were classified as highly virulent, intermediately virulent,weekly virulent and avirulent strains, accounting for 59.72%, 25%, 5.56%, and 9.72% of the total, respectively. Virulence differentiation was observed among isolates from the same geographical location, host species, or organ, but no significant correlation was found between virulence differentiation and strain origin. Additionally, the insertion of ISPsy36 into the hrpS gene was detected in four avirulent strains, suggesting that the disruption of the type III secretion system (T3SS) function by transposon insertion is one of the primary reasons for the loss of virulence in Psa strains in the field.
