Weather and inoculum factors associated with kiwifruit bud rot

Pseudomonas syringae pv. actinidiae biovar 3 (Psa) causes kiwifruit bacterial canker and also bud rot, which destroys developing flower buds and can become a severe problem, particularly in green-fleshed cultivars. The effects of weather and inoculum factors on bud-rot development were investigated. Experiments were conducted on two green kiwifruit cultivars: Actinidia chinensis var. deliciosa ‘Hayward’ and A. chinensis var. chinensis A— A. chinensis var. deliciosa ‘Zesh004’ (known as Green14), at four sites for two consecutive years. Temperature and rainfall were recorded from bud burst to flowering and bud-rot incidence was monitored from approximately two weeks after flower bud appearance until flowering. Correlations between weather parameters and final bud-rot incidence, and between initial bud-rot and final bud-rot incidence were investigated. There was no significant association between temperature and final bud-rot incidence, but total rainfall and number of days of rain were positively correlated with final bud-rot incidence. Initial bud-rot incidence showed the strongest correlation with final bud-rot incidence and appeared to be the main factor that contributed to bud-rot.