JIA-2018-09

Journal of Integrative Agriculture 2018, 17(9): 2024–2030 RESEARCH ARTICLE Available online at www.sciencedirect.com ScienceDirect Germination and appressorium formation of Pyricularia oryzae Cavara can be inhibited by reduced concentration of Blasin ® Flowable with carbon dioxide microbubbles Tamaki Masahiko 1 , Kobayashi Fumiyuki 2 , Suehiro Keisuke 1 , Ohsato Shuichi 1 , Sato Michio 1 1 School of Agriculture, Meiji University, Kawasaki 214-8571, Japan 2 Faculty of Applied Life Science, Nippon Veterinary and Life Science University, Musashino 180-8602, Japan Abstract We investigated the possibility to reduce the usage of Blasin ® Flowable (BF), a disinfectant inhibiting the germination and appressorium formation of Pyricularia oryzae Cavara conidia, by using carbon dioxide microbubbles (CO 2 MB). Germination was significantly inhibited by 10 000-fold diluted BF solution containing CO 2 MB generated by the decompression-type generator compared to CO 2 millibubbles (CO 2 MMB) and CO 2 MB generated by the gas-water circulating-type generator. Appressorium formation in the 10 000-fold diluted BF solution containing both CO 2 MBs was less than that in CO 2 MMB. Scanning electron microscopy showed wrinkles and dents on the surface of conidia treated with 5 000-fold diluted BF solution containing both CO 2 MBs. Via transmission electron microscopy, we observed the expansion of the vacuole and the intracellular space and bloated or absent lipid granules in the conidia treated with BF solution containing both CO 2 MBs. Our results show that inhibition of the conidium germination and appressorium formation of P. oryzae Cavara by 10000-fold diluted BF solution could be achieved by using the decompression-type CO 2 MB. Keywords: appressorium formation, Blasin ® Flowable, germination, Pyricularia oryzae , carbon dioxide microbubble may occur in summer of low temperature and following the outbreak of rice blast. Pyricularia oryzae Cavara is a plant-pathogenic fungus that causes the development of rice blast; it grows steadily at periods with low temperature, poor sunshine and relatively heavy rain. The conidia germinate in the presence of water on the surface of paddy and forms an appressorium, with the elongation of the germ tube and a melanin layer just below the cell wall containing the septum (Bourett and Howard 1990). The hyphae expand in the plant from the stoma or by penetrating the cell wall, and several conidia are produced at the top. Hereby, the conidia on the lesion move to the rice stalk, affecting the stalk and the branch and subsequently causing necrosis in most rice tissues. Consequently, the rice stalk lacks nutrients and turns white, resulting in significant yield loss. To mitigate this problem, the use of chemical pesticides in Japanese Received 31 July, 2017 Accepted 20 April, 2018 Correspondence Tamaki Masahiko, Tel/Fax: +81-44-980-5276, E-mail: mtamaki@meiji.ac.jp © 2018 CAAS. Publishing services by Elsevier B.V. All rights reserved. doi: 10.1016/S2095-3119(18)61962-8 1. Introduction Rice blast is the most important disease in Japanese rice cultivation. With improved rice cultivation techniques, yields per 10 acres exceed 500 kg in Japan, with a steadily increasing surplus (MAFF 2015). However, yield deficits