Identification and Genetic Characterization of Pseudomonas syringae pv. actinidiae from Kiwifruit in Sichuan, China

Pseudomonas syringae pv. actinidiae causes kiwifruit bacterial canker and poses a major threat to the kiwifruit industry. This study aimed to investigate the genetic characteristics of the P. syringae pv. actinidiae population from kiwifruit in Sichuan, China. Sixty-seven isolates obtained from diseased plants were characterized using morphological features, multiplex-PCR, and multilocus sequence analysis (MLSA). The isolates exhibited the typical colony morphology of P. syringae pv. actinidiae. Multiplex PCR amplification identified every isolate as P. syringae pv. actinidiae biovar 3. MLSA of the three housekeeping genes gapA, gyrB, and pfk, revealed that the reference strains of the five described biovars were clearly distinguished by a combined phylogenetic tree, and all of the tested isolates clustered with the reference strains of P. syringae pv. actinidiae biovar 3. Through a phylogenetic tree constructed from a single gene, it was found that pkf gene alone could distinguish biovar 3 from the other biovars. Furthermore, all P. syringae pv. actinidiae isolates analyzed by BOX-A1R-based repetitive extragenic palindromic (BOX)-PCR and enterobacterial repetitive intergenic consensus (ERIC)-PCR clustered into four groups. The clustering results of BOX- and ERIC-PCR indicated that group III had the largest number of isolates, accounting for 56.72 and 61.19% of all 67 isolates, respectively, and the two characterization methods were similar and complementary. The results of this study revealed that the genomes of P. syringae pv. actinidiae isolates from Sichuan had rich genetic diversity but no obvious correlation was found between clustering and geographical region. This research provides novel methodologies for rapidly detecting kiwifruit bacterial canker pathogen and a molecular differentiation at genetic level of P. syringae pv. actinidiae biovar diversity in China.