Identification and characterization of the causal agent of bacterial canker of kiwifruit in the Shaanxi province of China

Abstract

Bacterial canker of kiwifruit has become a serious disease problem in many countries, including China, but the causal agent in China has not yet been sufficiently characterized. In this study, the aetiology of bacterial canker was investigated in woody vines and leaves of the kiwifruit species Actinidia chinensis and A. deliciosa in the Chinese province of Shaanxi. Symptoms on woody vines appeared from September to June of the following year, and on leaves during May-July and September-October. More than 300 bacterial isolates were obtained from seven cultivars. Pure cultures were identified as Pseudomonas syringae pv. actinidiae (Psa) based on pathogenicity as well as morphological, physiological, biochemical, and genetic characteristics. In pathogenicity assays, symptoms on branches and leaves similar to those observed in the field on A. chinensis cv. Hongyang and A. deliciosa cv. Xuxiang 15 days post inoculation. The 16S rDNA sequences were 99.9% identical to those of the Psa strains available in GenBank. In addition, PCR analyses with five pairs of pathovar-specific primers provided a further proof of identification. Repetitive-sequence PCR fingerprint patterns of Psa strains isolated in Shaanxi using ERIC and BOX primer sets were consistent with those from New Zealand (2010) and Italy (2009), but slightly different from that of the Psa strain ICMP 9853 (Japan, 1984). The conclusion is that the causal agent of bacterial canker of kiwifruit in Shaanxi was identified as Psa strain identical with those currently spreading in New Zealand and Italy.