Cotton seedlings are highly susceptible to damping off (Fusarium spp.) at the beginning of the development of lateral roots. Cotton seedlings affected at this stage, 8 to 15 days old (H-K in Fig. 1) are hardly able to recover and killed easily. At these critical stages, especially 10 to 12 days old (I and J in Fig. 1) cotton seedlings show little or no carbon assimilation, maximum respiration rate, minimum transpiration rate, and exhaustion of stored-up food. The infection by damping off fungi often causes over-increase of respiration and over-decrease of transpiration in cotton seedlings.
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.
In the studies on the influence of cephalothecin upon the secretion of carbohydrases and the absorption of NH4-N by the blast fungus, it was pointed out by the writer that S:N, i. e., Relative Secretion Value (Yoshii 1953), and N:H, i. e., Reiative Absorption Value (Yoshii 1953), of the culture on media supplied with cephalothecin were far larger that of check. These figures show that the increase in dry weight of the mycelium per unit amount of carbohydrates and NH4-N consumed in cultures supplied with cephalothecin is much less than that of check. The poorer the development of the fungus in the tissue of the host is, the smaller the spot on the plant is. The spread of the fungus in the host tissue hasa certain connection with the resistance of the plant. In view of this, the sheath inoculation method (Sakamoto 1951) was applied to the earneck tissue presoaked with cephalothecin in order to determine if cephalothecin impedes the invasion processes of the blast fungus in the cells of rice plant. The results of the observations showed that the inhibitory effects of cephalothecin on the development of the fungus were also remarkably recognized in the cells of the tissues treated with cephalothecin. So it may safely be concluded that the resistance of the treated rice plant to the blast disease is chiefly due to cephalothecin sucked in the tissue.
1. 29 strains of mold were isolated from samples of stored rice grain, of which moisture content had been contro led in several grades. Of the molds Pencillium and Aspergillus were most prevalent (table 2). 2. The most vigorous development of molds was observed at 20°C during incubation and poor at 10°C and 30°C. 3. The largest number of strains were isolated from grains with 18% moisture, the next was from grains of 20% and 16% moisture. 4. Osmotic pressure of spore of the isolated molds exists between 19.6 and 134.8 atmospheric pressure, being the maximum value 6.9 times of the minimum value. 5. It was observed that osmotic pressure of the molds isolated from rice grains lowest moisture content gave the highest value. According as moisture of rice increased, osmotic pressure of the associated molds decreased. So the strain of mold grown on the rice is mainly decided by the actual moisture content of the rice. 6. The osmotic pressure of the rice grain determined on embryo and aleurone layer came to be lower in inverse proportion to the rice moisture content. 7. It seems necessary for molds to grow on the rice grain that their osmotic pressure should be more than about 5 times higher than that of rice. The osomtic pressure of molds does not reach to 5 times of that of rice with 14.5% moisture on which, the molds can scarcely grow. 8. As the conclusion, it is necessary to dry rice grain to a moisture content below 14.5%, in order to prevent mold growth.