Electron Microscopical Observation of Rice Leaves Infected with Pyricularia oryzae Cav. in Compatible and Incompatible Combinations

I. Fine Structure of Invaded Hyphae in Host Cells

Abstract

The mode of infection by Pyricularia oryzae Cav. in the rice leaf (the top leaf of the 7.5-leaf-stage seedlings) was compared electronmicroscopically between the compatible combination of race 037 and var. Koshihikari (resistance gene +), and the incompatible combination of race 037 and var. Fukunishiki (resistance gene Pi-z) 5 days after inoculation. In the acute type lesions of the compatible combination, the hyphae rich in lipid granules (0.75μm in diameter), cytoplasmic matrix and normal cell organelles were found densely in the host epidermis, parenchymatous cells and vessels. In the parenchymatous cells, the host cytoplasmic membrane and cell organelles were observed to be destroyed by the blast fungus. In the incompatible combination, invaded hyphae were found in epidermal cells, necrotic parenchymatous cells and stomatal chambers. In the epidermal cells, both host and fungus appeard moribund. In the necrotic parenchymatous cells, the hyphae were transformed at various grades, and mitochondria in the hyphae were swollen, and some of the hyphae seemed to be deceased with granulation of their contents. The hyphae in the necrotic cells were observed to be less in lipid granules and their vacuoles developed more remarkably. Moreover, gathering of lamellae in degenerated chloroplasts and a great number of high electron dense granules (0.05∼0.20μm in diameter) was observed in the necrotic parenchymatous cells. In the substomatal chambers, the hyphae were rich in cytoplasmic matrix, appearing to be vivid. In the parenchymatous cells neighbouring the affected substomatal chambers, invaded hyphae were also found frequently.