キウイフルーツかいよう病の発生生態 １． 新梢への感染方法および病原細菌の組織内移行

Abstract

Infection of the disease and bacterial movement in the tissue of new canes were examined using 3-year-old grafted potted vines of kiwifruit (cv. Hayward) and 3-year-old potted seedlings grown from seeds of Hayward. Pseudomonas syringae pv. actinidiae was used as inoculum. Lesions in the field developed on the leaf surface and leaf margin of Hayward after would and spray-inoculation. Since a lot of water droplets were observed on the leaf margin during high humidity, it was thought that the pathogen invaded through hydathode, in addition to the stomata and wounded parts. Lesions were formed when the bacterial suspensions at more than 10(2) CFU/ml were inoculated with or without wounding onto the leaves. In the case of spray-inoculation at 10(2) CFU/ml, however, the lesions appeared 20 days after the inoculation compared to 5 to 8 days for lesion formation using the suspensions at more than 10(3) CFU/ml. Therefore, this may be due to the pathogen surviving on lower surface of the leaves, and the infection occurring after growing of the pathogen during high humidity. The water-soaked lesion without a yellow halo appeared as a mosaic 4 days after inoculation and these lesions expanded rapidly when rain continued after inoculation. It indicates that the latent period is remarkably influenced by relative humidity. When the lesions reached the midrib, the bacterium was isolated from their sections before the appearance of disease symptom. The bacterial population in the sections decreased as the distance apart from border of lesions grew. When they reached the base of leaf blades, the bacterium was isolated similarly from each section of the petioles. Also, when the tender stem was affected severely with the disease, the bacterium was isolated from each section of the petioles and midribs in the process of disease development. This action was remarkable for the seedlings in comparison with the grafted vines of Hayward