Evaluation of various cultivars of Actinidia species and breeding source Actinidia rufa for resistance to Pseudomonas syringae pv. actinidiae biovar 3

Pseudomonas syringae pv. actinidiae causes kiwifruit bacterial canker, which seriously harms or kills plants, in many countries. After the first appearance of P. syringae pv. actinidiae biovar 3, having the strongest virulence among all biovars of this pathogen, in Japanese orchards in 2014, the disease spread widely and damaged plants across the nation within a few years. Since introduction of resistant cultivars is the best approach to control the disease, we examined the responses of nine kiwifruit cultivars and six collection lines used as genetic resources for breeding after infiltration of detached leaves with P. syringae pv. actinidiae biovar 3. All cultivars had different degrees of resistance to the pathogen, and collection lines of Actinidia rufa and cultivar Kosui crossed with A. rufa and A. chinensis showed significant resistance. Our investigation revealed that A. rufa is an excellent genetic source for kiwifruit breeding.