First Report of Bacterial Canker of Kiwifruit Caused by Pseudomonas syringae pv. actinidiae in Georgia

Since its introduction in the mid 20th century, Kiwifruit (Actinidia deliciosa and A. chinensis) has been an important crop in Georgia. In the fall of 2013, symptoms of a disease previously unrecognized in Georgia were observed on kiwifruit (A. deliciosa cv. Hayward) plants growing on a 30-ha plantation in the Lanchkhuti Municipality of western Georgia. Disease incidence was approximately 10%. Symptoms on leaves included brown angular spots surrounded by chlorotic margins that later became dark brown, and occasionally a reddish exudate was observed on the trunk. Seven bacterial cultures isolated from leaves and stems of symptomatic plants on King's B medium were identified as Pseudomonas syringae pv. actinidiae. Bacterial isolates were gram negative, nonfluorescent, positive for levan production, and caused a hypersensitive response on Nicotiana tabacum(cv. Samsun) plants (Lelliot and Stead 1988). Pathogenicity tests for each strain were conducted by injecting leaves of five two-year-old plants of cv. Hayward with bacterial suspension (10 super(8) CFU/ml). Inoculated plants were incubated at 23 + or - 3[degrees]C and 90% relative humidity. Necrotic spots appeared on leaves within 7 days after inoculation. No symptoms developed on control plants treated with sterile water. Five plants were inoculated per treatment. Koch's postulates were established by reisolating bacteria from the inoculated plants (cv. Hayward). Morphological and biochemical characteristics of reisolated bacteria were identical to those of the original isolates described above. PCR with primer pairs KN-F/KN-R (Koh and Nou 2002) and PsaF1/PsaR2 (Rees-George et al. 2010) specific for 16S-23S rDNA ITS region was performed to identify P. syringae pv. actinidiae. The obtained amplicons were 492 bp and 280 bp in size, respectively. P. syringae pv. actinidiae reference strain NCPPB 3738 was used as a positive control for the PCR. This study confirmed for the first time the presence of P. syringae pv. actinidiae associated with kiwifruit bacterial canker in Georgia.