Abstract
TUMANOV, in his study on the snow killing of wheat plants, said that the wheat plant under snowcovering came to utilize protein as a respiration material after they had consumed the reserved sugars, and the subsequent breakdown of protein by promoted proteolysis caused the weakening of resistance of wheat plant to the attacks of snow blight fungi and might result severe damages.
However, the present writer's experiments showed that, in the older leaves a remarkable proteolysis took place soon after the plants were covered with snow, despite a fairly large amount of carbodydrates remained unconsumed, whereas, in the younger leaves, such consumption of protein was not actually observed even far later in the season. In reality, the infection of older leaves of wheat plants by Typhula Itoana and T. ishikariensis takes place at the beginning of snow covering.
T. ishikariensis developed first in the older leaves attacks readily the younger ones and causes frequently the entire decaying of the whole plant. T. Itoana, on the contrary, can hardly attack the younger leave, wherefore, this fungus scarcely causes the entire decaying of the wheat plant under ordinary condition. The wheat plant affected previously by T. Itoana frequently escape from the attack of T. ishikariensis on account of the antagonistic relationship between two pathogens, and it means that the winter wheat can escape the severe damage caused by T. ishikariensis owing to the previous infection by mild-virulent T. Itoana.
From these results, it is concluded that the leaf age, the resistance of younger leaves of wheat plants to the pathogens, and the relative frequency of occurrence of T. Itoana and T. ishikariensis are important factors affecting the winter-killing of wheat plants under snow covering.
