Recent Advances in the Characterisation and Control of Pseudomonas syringae pv. actinidiae, the Causal Agent of Bacterial Canker on Kiwifruit

Bacterial canker of kiwifruit is caused by Pseudomonas syringae pv. actinidiae (Psa) and affects Actinidia deliciosa (green-fleshed kiwifruit) as well as A. chinensis (yellow-fleshed kiwifruit). Psa was first isolated in Japan in 1984 and was found in 1992 in Korea and in Italy. The most visible symptoms include production in spring of a red exudate from cankers, which can be followed by wilting and death of canes, leaders or affected vines. Production of a white exudate that helps the dissemination of the pathogen can also be detected during spring and summer. Infection seems to take place preferentially during spring and autumn when the average temperatures are between 10 and 20 degrees C. Infection and dispersal of the pathogen is favoured by rain events and wind. Detection and identification of the pathogen is mostly based on polymerase chain reaction protocols even though today's protocols are not fully specific for Psa. A new outbreak of Psa occurred in Latina (Italy) in 2009. This new outbreak is more destructive than the previous ones in Italy. Analysis of the DNA sequence of the housekeeping gene cts, led to the classification of strains of Psa isolated so far in two groups or two cts haplotypes. The Japanese, the Korean and the strains isolated in Italy in 1992 shared the same haplotype, while all the strains isolated in Italy since 2008 shared the other haplotype. The same grouping was obtained while analysing the BOX-PCR patterns. The methods of control are very limited and consist of removing the inoculum (by cutting and then burning or burying the affected plants) and protecting the plant during the main infection periods in spring and fall by spraying copper formulations.