The 140 antifungal actinomycetes, which had been selected from 7243 strains in Tokyo University, were tested in our laboratory in relation to their antifungal activity against seven plant pathogens; Piricularia oryzae Bri. et Cav., Ophiobolus miyabeanus Ito et Kuribayashi, Gibberella saubinetii (Mont.) Sacc., Ceratostomella fimbriata (E. et H.)Ell., Alternaria kikuchiana Tanaka, Glomerella cingulata Spauld. et Schr., and Fusarium lini Bolley. As shown in Tabe I, many actinomycetes showed strong inhibitory action against one or more of the seven test plant pathogens in of 12 strains agar disc diffusion tests. The antifungal spectra of actinomycetes, which were found to be highly effective on P. oryzae, are given in Table 2.
The 40 strains of actinomycetes, which showed high antifungal activity on P. oryzae, were cultivated in shaken liquid modified Waksman media at 28°C. The antifungal activities of culture fiitrates at three and five days were tested by cup method. Data obtained are given in Table 3. Twelve strains were selected on the basis of the size and clearnesss of the inhibition zone around the cup.
The effect in vivo of 12 strains, which were found to be effective in vitro on rice blast fungus, were studied in greenhouse tests. As shown in Table 4, the culture filtrates were found by slidetests to be capable of inhibiting the germination of conidia. Rice plants showed an increase in resistance to the rice blast when cultured in water added with filtrates of actinomycetes culture at two to seven days or sprayed with diluted filtrates. The number of leaf-spots were remarkably less than in the untreated plants, as shown in Table 5 and 6.
As the result of these tests, two active strains were selected as the most promising anti-blast actinomycetes among the 140 strains.
