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. 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.