Abstract
Bakanae disease, caused by Fusarium fujikuroi, is an economically important seed-borne disease of rice. F. fujikuroi is horizontally transmitted to rice flowers and vertically transmitted to the next generation via seeds. The fungus induces typical symptoms such as abnormal tissue elongation and etiolation. Sanitation of seed farms and seed disinfection are the only effective means to control bakanae disease at present; however, the efficacy of these methods is often insufficient. Therefore, alternative and innovative control methods are necessary. We developed a novel method for applying nonpathogenic fusaria as biocontrol agents by spraying spore suspensions onto rice flowers to reduce the incidence of seed-borne bakanae. We visualized the interaction between Fusarium commune W5, a nonpathogenic fusarium, and Fusarium fujikuroi using transformants expressing two different fluorescent proteins on/in rice plants. W5 inhibited hyphal extension of F. fujikuroi on/in rice flowers and seedlings, possibly by competing with the pathogen, and survived on/in rice seeds for at least 6 months.IMPORTANCE We demonstrated that a spray treatment of rice flowers with the spores of nonpathogenic fusaria mimicked the disease cycle of the seed-borne bakanae pathogen Fusarium fujikuroi and effectively suppressed the disease. Spray treatment of nonpathogenic fusaria reduced the degree of pathogen invasion of rice flowers and vertical transmission of the pathogen to the next plant generation via seeds, thereby controlling the bakanae disease. The most promising isolate, F. commune W5, colonized seeds and seedlings via treated flowers and successfully inhibited pathogen invasion, suggesting that competition with the pathogen was the mode of action. Seed-borne diseases are often controlled by seed treatment with chemical fungicides. Establishing an alternative method is a pressing issue from the perspectives of limiting fungicide resistance and increasing food security. This work provides a potential solution to these issues using a novel application technique to treat rice flowers with biocontrol agents.
Highlights
Bakanae disease, caused by Fusarium fujikuroi, is an economically important seed-borne disease of rice
We focused on using nonpathogenic Fusarium spp. (NPFs) that are frequently isolated from rice plant tissues [31] to develop a method for using them as biocontrol agents for bakanae disease
All four selected isolates repeatedly and efficiently controlled bakanae disease in which seeds were treated with a bud-cell suspension in pot tests (Fig. 1)
Summary
Bakanae disease, caused by Fusarium fujikuroi, is an economically important seed-borne disease of rice. IMPORTANCE We demonstrated that a spray treatment of rice flowers with the spores of nonpathogenic fusaria mimicked the disease cycle of the seed-borne bakanae pathogen Fusarium fujikuroi and effectively suppressed the disease. Spray treatment of nonpathogenic fusaria reduced the degree of pathogen invasion of rice flowers and vertical transmission of the pathogen to the plant generation via seeds, thereby controlling the bakanae disease. At present, seed-borne diseases, including bakanae disease, are effectively controlled by the application of chemical fungicides (e.g., ipconazole) onto rice seeds [13] Such application often leads to the emergence of fungicideresistant strains of the pathogens, an issue of great concern. Ipconazole can effectively control bakanae disease at present, in consideration of the possible future emergence of resistant strains and a trend of reducing the use of chemical fungicides, alternative methods are needed
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