First report of Xanthomonas citri subsp. Citri pathotype a causing citrus canker on nanfeng tangerine in Guangxi Province, China

Abstract

In September 2010, erumpent, callus-like lesions with water- soaked margins, the typical citrus canker (CC) symptoms, were observed on leaves of Nanfeng tangerine [Citrus reticulata Blanco var. kinokuni (Tanaka) H.H. Hu] in Guangxi Province (China). Seven leaf samples of Nanfeng tangerine showing symptoms of CC were collected from three different groves. Pathogen isolations were done using Luria-Bertani medium, and yellow mucoid, Xanthomonas-like isolates were selected. Pathogenicity tests were carried out on Nanfeng tangerine, navel orange (C. sinensis), Mexican lime (C. aurantifolia), and Eureka lemon (C. limon). Four attached leaves of each one-year-old citrus cultivar were inoculated with each of seven isolated Xanthomonas-like strains and two previously identified X. citri subsp. citri pathotype A (Xcc-A) strains at 1 × 107 CFU/ml. After 21 days, all inoculated bacterial isolates induced clear-cut CC symptoms on each of the four tested citrus species and were successfully re-isolated from the symptomatic leaves of inoculated plants. The 16S rDNA and 16S/23S intergenic transcribed spacer (ITS) of the seven isolates were amplified with primer sets fD1/rP1 (1) and 1493f/23r (2), respectively, cloned and sequenced. Consensus sequences of 1469 bp 16S rDNA (accession No. KC820706) and 545 bp 16S/23S ITS (KC820707) were obtained. BLAST analysis showed both 16S rDNA and 16S/23S ITS from this study had the highest sequence identity (99.9% and 100%, respectively) with those of Xcc strain 306 (AE008923). These results confirmed that the pathogen inducing typical CC symptoms on Nanfeng tangerine was Xcc-A. To our knowledge, this is the first formal report of Xcc-A on Nanfeng tangerine in China.