Abstract
1. The relation of temperature to the growth of the strain of Piricularia Oryzae used in this experiment was first tested by growing the mycelium on potato decoction agar containing 1% sucrose at different temperatures. The most vigorous growth of mycelium seemed to occur at about 28°C. At the temperatures of about 24°C., 20°C., 11°C. and 36°C., the growth of the present fungus decreased gradually in order.
2. At about 28°C., the most favorable temperature to the fungus, the mycelial growth was stimulated by adding CuSo4 to the agar medium in the concentrations between 1/400 and 1/6000mol. The maximum growth occurred in the concentration of 1/1000mol. In the case of the liquid medium the stimulating action of CuSo4 to the mycelial growth of the fungus was more or less recognized. It was, however, not so remarkable as in the case of the agar medium.
3. At the various temperatures, such as 20°C., 24°C. and 32°C., the same experiments were done. However, the stimulating action of CuSo4 to the mycelial growth was not recognized in any concentrations tested. At about 36°C. any conclusive results were neither obtained in the liquid nor on the agar medium.
4. At all the temperatures tested, the conidial formation was retarded in inverse proportion to the amount of CuSo4, when added in higher concentrations than 1/6000mol. On the culture media containing CuSo4 in higher concentrations than 1/400mol., it was almost unrecognizable.
5. The conidial formation tends to decrease gradually with the difference of temperature from the optimum for the mycelial growth. Such retardation was most remarkable at about 36°C.
6. On the culture media containing CuSo4 in higher concentrations than 1/600mol., the chlamydospores were formed at all the temperatures tested. The limitation for the chlamydospore-formation with regard to the concentration of CuSo4 tends to become lower in proportion to the difference of temperature from the optimum for the mycelial growth. Such tendency is quite contrary to that of the conidial formation
7. The development of the aerial mycelium was checked gradually owing to the increment of the concentration of CuSo4 and it was not observed in the concentration of 1/200mol. at any temperatures tested.
8. On the culture media containing CuSo4 in higher concentr tion than 1/6000mol., the color of the colony changed to gradually from grayish white to dark, and the degree of coloring increased remarkably in the concentration of 1/400-1/600mol. In the concentration of 1/200mol., the colony showed yellowish olive and soaked appearance. The hyphae became remarkably slenderer and more winding than those of the controls.
