Infection of rice plants and seeds by Pyricularia oryzae and Ustilaginoidea virens

Rice blast is an important disease of rice worldwide, however false smut of rice is considered to be a rice disease of only occasional importance to localized areas. The biology and disease cycle of rice blast are known, with the exception of the means by which it infects or infests rice seed; the biology and disease cycle of false smut, conversely, is poorly understood. In the first study, rice florets were inoculated with conidial suspensions of P. oryzae during flowering. Inoculated florets developed into seeds displaying symptoms of rice blast. Isolations made from symptomatic seeds resulted in recovery of P. oryzae sul 18/1. Data show that inoculation of florets on rice panicles at 33%, 50%, and 66% of anthesis resulted in the highest mean percentages of symptomatic seed. In the second study, the germinability of spores of U. virens and modes of infection of rice plants by U. virens were investigated in greenhouse and field experiments. Spores remained viable after storage for up to 18-months, germinated successfully in water, 1% sucrose solution, or nutrient broth, and that the fungus can be brought into culture on pH-adjusted PDA. Experiments to produce symptomatic rice plants were unsuccessful, although spores of U. virens infected roots of rice plants.