Spray Application of Nonpathogenic Fusaria onto Rice Flowers Controls Bakanae Disease (Caused by Fusarium fujikuroi) in the Next Plant Generation.

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.

Measurement of a new parameter representing the gas transport properties of the catalyst layers of polymer electrolyte fuel cells.

The optimization of the catalyst layers is necessary for obtaining a better fuel cell performance and reducing fuel cell cost. Although the ionomer coverage of the Pt catalyst is said to be a key parameter in this regard, the proportion of Pt either directly or indirectly covered by the ionomer is thought to be an important parameter with regard to gas transport (indirectly covered Pt: its gas transport paths are completely blocked by the ionomer even if it does not directly cover Pt). In this study, a new technique has been developed for evaluating the proportion of Pt covered indirectly or directly by the ionomer, which is defined as the "capped proportion", based on the carbon monoxide (CO) adsorption properties at different temperatures. The validity of the method was thoroughly examined by identifying the CO adsorption properties of the components of the catalyst layers. The capped proportion and oxygen transport resistance in the catalyst layers showed a good correlation, indicating that the capped proportion is a dominant factor of oxygen transport resistance. This technique thus enables the evaluation of the dominant factor of the gas transport properties of the catalyst layers. The method has another significant advantage in that it does not require a membrane electrode assembly, let alone electrochemical measurement, which should be helpful for catalyst layer optimization.