On the influence of cephalothecin upon the nutritional absorption of ammonium nitrogen by the blast fungus

Abstract

In order to research the influence of cephalothecin upon the nutritional absorption of NH₄-N by the blast fungus, cultural experiments were carried out by using the modified Tochinai and Nakano's synthetic nutrient solution with addition of Biotin or decoction of rice-culm. Cephalothecin was tested at dilutions of 1:5∼160. The amount of ammonium absorbed during the development of the fungus in the culture solution was determined by the ordinary distillation method every other day. The growth of the fungus and its absorption of NH₄ was more or less inhibited by supply of cephalothecin (table 3). The dry weight of the mycelial mat, and amount of ammonium absorbed in cultures supplied with ammonium salt, were larger than in cultures than in cultures without any ammonium salt. The differences are indicated by symbols of H and N respectively.
After 4 and 6 days' incubation, it was shown that N:H was far larger in cultured containing cephalothecin at strengths of 1:2∼20 than either in 1:40∼160 or in the check. Even after 10 days, it was rather larger in 1:5∼10 solution than in others. The relative absorption value (N:H) shows the amount of the ammonium consumed by the fungus to increase 1mg of the mycelium in dry weight. Accordingly, for consumption of 1mg of ammonium, the increase in dry weight of the mycelium should be far less in 1:5∼20 solution of cephalothecin than either in 1:40∼160 or in the standard solution.
On the other hand, the analyses of the leaf-blades and sheathes of the rice plants showed that the contents of the nitrogenous compounds in the nontreated plants, and that especially the contents of NH₄-N decrease considerably in the former. Thus, the phases of N:H suggests certain connection between the fungu's absorption of NH₄-N under the influence of cephalothecin and the resistance to blast disease of the rice plant treated with cephalothecin.