Analysis of Injuries of Wheat Spikes infected by Gibberella zeae (Schw.) Petch.

Abstract

When a wheat spike infected by head blight but with a healthy culm is put in 0.5∼1.0 % eosin aqueous solution, it absorbs the eosin solution up to the portion of rachis just beneath the part to which the infected spikelets are attached. By this staining method of spikes, the author observed that the water flow in vascular bundles in the rachis was stopped at the portion of the rachis infected by head blight. According to this fact, the author classified the injuries of spikelets (or grains) on the whest spike infected by head blight into 2 groups as follows: (A) Spikelets (or grains) directly infected by head blights. (B) Spikelets (or grains) withered because function of conducting water and nutrients was lost in the rachis which was infected by head blight. And the author found that the rate of growth of head blight in rachis, especially that of downwand growth from the infected segment of rachis, showed varietal differences. For example, the downward growth from the infeced segment of rachis, showed varietal differencea. For example, the downward growth of the disease within rachis was more rapid in the case of Shinchunaga (a resistant variety) than in the case of Saitama No. 27 (a susceptible variety). From these results, the author arrived at the following conclusion : The sooner the rachis withers by infection of head blight, the more rapidly the spikelets (or grains) attached to the rachis wither. Thus, in case of a variety, such as Shinchunaga, having a rachis which withers soon after being infected by head blight, the infection to surrounding spikelets stops due to lack of moisture in the spike, since head blight requires rather high moisture for its infection and growth. On the contrary, in case of a variety Saitama No. 27, having a rachis which withers rather slowly, the disease gradually spreads from the infected segment of rachis to the unwithered lower portion, and thus, results in severe damage.