Seasonal variation in susceptibility of apricot to Pseudomonas syringae pv. syringae (bacterial canker), and site of infection in apricot and cherry

The seasonal variation in susceptibility of buds, stems, leaves and fruit of apricot to Pseudomonas syringae pv. syringae, and sites through which infection occurs in apricot and cherry were studied. Infection of apricot and cherry occurred through buds, flowers, leaves, fruit and stems but not leaf scars through which natural infection can occur. Only stem and bud inoculations consistently led to the establishment of cankers. The proportion of buds showing infection was highest with inoculations made in late autumn and winter (May-July), and lowest with inoculations in summer (December-February). The number of stem inoculations, resulting in extensive cankers, was highest in late winter and spring (August-November) and lowest in summer and early autumn (December- March). Leaves and fruit were susceptible only during spring (September-November), when they were immature. The importance of these findings in relation to epidemiology and control of bacterial canker is discussed.