1981 Volume 47 Issue 4 Pages 501-509
It is generally known that Kogyoku is moderately susceptible at seedling stage, and highly resistant at adult stage to bacterial group I of Xanthomonas campestris pv. oryzae. IR 28 and Te-tep, however, show a high level of resistance at both seedling and adult stages to bacterial group I. Hence, the purpose of the present study was to determine the ultrastructures in the resistance expression of Kogyoku, IR 28 and Te-tep varieties to bacterial group I at seedling stage. Inoculation was made at the fourth leaf stage by double needle-pricking method. Leaf samples were collected 3days after inoculation and ultrathin sections of them were observed under electron microscope. Bacterial cells were found normal and multipling in the xylem vessels of variety Kogyoku. The vascular parenchyma cells adjacent to vessels, cell organelles and cell wall appeared to be intact, similar to the healthy leaves. In the vessels of IR 28 and Te-tep, however, bacterial cells were irregular in shape and enveloped by abundant fibrillar material (FM) which was not observed in the vessels of Kogyoku and healthy leaves. Although little is known about the chemical composition of FM, it appears to be derived from the inner vessel wall layer of about 100 nm in thickness. On IR 28 and Te-tep leaves, the disruption of cellular organelles was also observed. The size of the bacterium in the vessels of Kogyoku, IR 28 and Te-tep was 1.25×0.50μm, 1.03×0.42μm, and 1.05×0.41μm, respectively and the bacterial cells which were not enveloped by FM were significantly larger than those enveloped by FM. From these findings, it is concluded that development of fibrillar material may be associated with the resistance expression of a variety to bacterial leaf blight.