The supernatant of a conidial suspension of magnaporthe oryzae contains a factor that promotes the infection of rice plants

Many factors produced by the pathogen Magnaporthe oryzae enhance its ability to infect rice. We found a novel infection-promoting activity in the supernatant of a conidia suspension (SCS) of M. oryzae. The addition of SCS promoted the invasion of excised rice leaf sheaths by infectious hyphae. The activity was heat-stable and was found in SCSs from five virulent and three avirulent isolates of M. oryzae on the rice cv. Nipponbare (Pia). The effect was exclusively detected in compatible interactions. The infection of rice plants by non-rice blast fungi was not enhanced by SCS. These results suggest that SCS includes a heat-stable factor(s) that promotes M. oryzae infection during compatible interactions.