Abstract
The damping-off of kiwifruit occurs from the latter half of the rainy season to early summer. The trees develop satisfactorily from the time of sprouting to the elongation of new twigs, but suddenly the leaves wilt and the whole tree dies. In almost all these trees, root-rot occurred and the epidermis of crown roots was easily peeled off. In Kumamoto Prefecture, outbreaks have been recorded since 1982, and found in many orchards located in areas which were formerly used as paddy fields and in humid valleys. Although usually the percentage of the affected trees did not exceed 10%, in many areas 30% of the trees were affected by the outbreaks. As a result the destruction of the trees was associated with an economic loss. To analyze the factors involved in the outbreaks, experiments on water tolerance of potted plants of the Hayward variety were carried out. The results showed that almost all the seedlings were healthy when 1/3 of one-foot pot was flooded while 100% of the seedlings died when the whole pot was flooded. After 5 to 7 days of treatment, wilting of the leaves started and after 13 to 15 days the leaves became brown and defoliation was observed. The symptoms of the withered seedlings were nearly the same as those observed in outbreaks of damping-off in the field.
