Comparison of the Early Infection Process of Pyricularia oryzae Cav. in Rice Leaves of Compatible and Incompatible Combinations

Abstract

Early infection process of Pyricularia oryzae Cav. in the rice leaves of the compatible combination of race 037 and var. Koshihikari, and the incompatible combination of race 037 and var. Fukunishiki was compared under microscope with an aid of the whole-leaf clearing and staining technique. The difference became apparent at the stages of fungal penetration and mycelial growth. The host reactions in the epidermal cells at the early stage of penetration were grouped into two types, i.e. no-reaction and granulation of host cellular contents. The rate of no-reaction at the penetration sites in the incompatible combination was almost at same as that in the compatible one. Therefore, it seemed that unsuccessful penetration without any host reaction was independent of the specific resistance controlled by the major gene (Pi-z) for resistance to rice blast. On the other hand, the rate of unsuccessful penetration sites with the host cytoplasmic granulation in the incompatible combination was distinctly higher than that in the compatible one, and the time when the granulation of the host cellular contents appeared was coincident with the time when the difference of the penetration percentage between two combinations became apparent. Hence it was suggested that the granulation of the host cellular contents closely correlated with the expression of the specific resistance. Moreover, cessation of mycelial growth in the incompatible combination also closely correlated with occurrence of the granulation of the host cellular contents. It was unlikely that occurrence of the deep-browning of infected host cells was the primary determinants of the specific resistance, because the rate of the infection sites with the deep-browning was very few in the incompatible combination, and the occurrence of the deep-browning was also observed in the compatible combination as in the incompatible one.