Abstract
Susceptibility of the new leaves of kiwifruit (cv. Hayward) to bacterial canker increased remarkably when the leaf blades reached ca. 2cm in length. However, it decreased as the leaves matured. The disease development increased rapidly when the mean temperature per 10 days was 15±3°C (April to May). Then, it began to be less serious when the temperature approached 20°C (late May to early June). When the temperature was over 20°C and approached 25°C (June to early July), the disease occurred only under cool and rainy conditions. Over 25°C (after mid.-July) the symptom was not observed. Exudation of bacterial ooze occurred actively on the affected tender canes from April to May. The canes began to wither in early May when the disease developed severely. In case of the disease development remaining in the limited part on the stem, a small amount of oozing was observed from the respectable minority of affected parts until late June (21.8°C). In early July (23.0°C), the number of canes which showed oozing from affected parts decreased remarkably. Moreover, the wound-healing tissue bagan to develop on the affected parts. The wound-healing tissue developed vigorously in mid. to late July (25°C), and oozing stopped. From these results, the suitable mean temperature per 10 days for infection on new canes was concluded to be in the range of 10 to 20°C as optimum at 15±3°C. However, exudation of bacterial ooze occurred again for 20% of the diseased canes in next early spring. It suggested that pathogen over-winters in diseased tissue. Also, the water-soaked spots were produced on the leaves after spray-inoculation at high pressures, and the pathogen was reisolated from those spots. Bacterial canker of kiwifruit is severe in areas where strong wind blow. This phenomenon may be an important factor causing the infection.
