Effects of weed-hosts of Pyricularia on incidence of rice blast diseases.
Pyricularia [Magnaporthe grisea] isolates were collected from 11 plant species, including rice and common weeds in paddy fields in China. They were inoculated to all the plants by smearing leaves with spore suspensions. The Pyricularia isolates from Eleusine indica, Setaria viridis, S. faberi, Leersia hexandra, Digitaria sanguinalis, Rottboellia cochinchinensis, Panicum repens and Echinochloa crus-galli were able to infect rice plants, and the rice isolates were able to infect these weeds. The fungi isolated from Zizania caduciflora and Cyperus iria did not infect rice plants and the rice isolates did not infect these 2 plants. In the natural disease nursery, the isolates from E. indica or S. viridis were able to infect rice plants and the rice isolates were able to infect both plants. All of the isolates from weeds were mildly pathogenic to rice, but their virulence could be improved by inoculating a blast-susceptible rice cultivar and re-isolating the pathogen from the lesions. However, the re-isolates showed the original levels of virulence on their former host plants. It is suggested that the weed hosts of the blast pathogen might be epidemiologically important and have a direct bearing on the disease cycle of rice blast.