Antagonistic yeasts and thermotherapy as seed treatments to control Fusarium fujikuroi on rice

Bakanae disease, caused by Fusarium fujikuroi, is the most important seedborne disease of rice. Biological control and physical treatments can be effective tools to control seedborne diseases. Sixty-two isolates of yeasts and yeast-like fungi were obtained from different rice seeds. Four yeast isolates were selected in dual culture assays for mycelial growth inhibition, and in seed tests for reduction of infection rate. The isolates R23 and R26 were identified as Metschnikowia pulcherrima, the isolate R9 as Pichia guilliermondii, and the isolate SB1 as Sporidiobolus pararoseus. Rice seeds treated with P. guilliermondii R9, M. pulcherrima R23 and R26 significantly reduced the infection rate of F. fujikuroi, compared to some commercial biofungicides. The four selected yeasts reduced the bakanae disease severity in rice plants grown in greenhouse trials. Antagonist seed dressing resulted in reduction of the disease index from 93.0% in the untreated control to 20.0% in P. guilliermondii R9 treated seeds, and to 28.5% in M. pulcherrima R23 treated seeds. Selected antagonists were also used in combination with thermotherapy, which contributed to increase their efficacy. Thus, P. guilliermondii R9 and M. pulcherrima R23 combined with thermotherapy at 60 C for 10 min decreased the bakanae disease index below 5%, and improved the seed germination rate compared to the single treatments, showing a seed priming effect. This is the first report about the use of antagonistic yeasts for seed dressing of rice to control F. fujikuroi on rice seeds, and biological treatment may be improved through combination with thermotherapy.