かんきつかいよう病菌の感染ならびに発病過程における行動　１　けっ刺接種後の増殖と組織の変化

Bacterial population in and histological changes of leaf tissues of Citrus natsudaidai, a plant susceptible to citrus canker, were studied after needle-prick inoculation with Xanthomonas citri. Bacteria multiplied soon after inoculation in wounded tissues and intercellular spaces when detached leaves were incubated at 6, 10, 15, 20, and 25C, but not at 40C. When inoculated attached leaves were held in a greenhouse, much of the inoculated bacteria died due to withering of wound tissues in the first 24hr, and then bacterial number increased. During the period of bacterial multiplication, however, intercellular spaces of the parenchyma tissues were not occupied by bacterial masses. After the disappearance of chloroplasts, parenchyma cells hypertrophied 10-11, 4-5, and 2.5 days after inoculation in the leaves incubated at 15, 20, and 25C, respectively. These changes have never been observed at 10C or lower until 72 days and 40C until 6 days. In non-inoculated leaves, enlargement of parenchyma cells also occurred with the same time sequence as that observed in the inoculated leaves, but the extent was much smaller. These hypertrophied cells became to form meristematic tissues. These facts suggest that bacteria prevent the host cell division as wound healing reactions. Bacteria multiplied abundantly after the development of hypertrophy in the infected tissues, and came to fill the space between enlarged cells and to ooze out. A period from inoculation to the bacterial multiplication was influenced only by temperature, but not by inoculum size or host resistance. In more resistant C. junos and C. madurensis, the multiplication after the development of hypertrophy was less than that in moderately resistant plants. In the detached leaves, water -soaked lesions appeared at the same time as the hypertrophic changes occurred. On the contrary, in the attached leaves lesion development delayed 2 or more days and diseased tissues were smaller and less hypertrophied comparing with those of the detached leaves.