Infection process of Pyricularia oryzae on the leaves of wheat seedlings

The aim of this study was to use scanning electron microscopy (SEM) to elucidate the infection process of Pyricularia oryzae on leaf surfaces of wheat seedlings. Wheat seedlings were inoculated with a conidial suspension of P. oryzae (105 conidia/mL), and leaf samples were collected for observation via SEM. The first blast symptoms appeared 48 h after inoculation (hai) as small water-soaked lesions. From 72 to 96 hai, these lesions expanded, and intense chlorosis occurred around them. At 120 hai, the lesions became necrotic, adopting a grayish coloration, coalesced and the entire leaf showed signs of tissue death. SEM observations indicated that conidia of P. oryzae began to germinate at 6 hai, and appressoria differentiation occurred at 12 hai. From 12 to 24 hai, wax removal occurred on the leaf surface at the appressorial sites examined. From 36 to 72 hai, conidia and accompanying appressoria appeared to be dehydrated and withered. At 96 hai, leaf tissue adjacent to the fungal hyphae showed signs of degradation. At 120 hai, conidiophores bearing numerous conidia were noticed on the leaf surface. Some conidia germinated next to the conidiophores. This study reports novel information regarding the infection process of P. oryzae on the leaf surfaces of wheat seedlings.