Temporal sequence of cytological events in rice leaves infected with Pyricularia oryzae

Abstract

A time-course investigation was made of early events in leaves of four rice cultivars following inoculation with Pyricularia oryzae Cavara race 131. The pathogen conidia germinated and formed appressoria at a similar frequency in all four cultivars. A difference was found in fungal penetration frequency among the cultivars but it did not appear to be related to race-specific resistance. Growth inhibition of infection hyphae was pronounced in incompatible race–cultivar combinations relative to compatible ones, and a correlation between inhibition of infection hyphae and expression of race-specific resistance was found. The cultivars showed five types of cellular reactions to the pathogen. Light browning and aniline blue staining of the epidermal cell wall (type B reactions) were the first reactions observed in all cultivars and a decrease in their frequency was followed by an increase of other cellular reactions such as cytoplasmic granulation or cell necrosis. This result suggested that cytoplasmic granulation or cell necrosis might be generated from type B reactions. Compared with compatible cultivars, incompatible ones showed type B reactions much more rapidly. The study also revealed the temporal coincidence between inhibition of growth of infection hyphae and occurrence of type B reactions.