Symptoms of Dry Injuries on Leaves of Rice Plant as Related to the Drought Resistance

[摘要] The auther had formerly reported on his studies into the drought resistance of rice plants, most parts of which had been made at the Imperial Agricultural Experiment Station of Japan, and pointed out a close relation existung between development of stereomes in leaf-blades and drought resistance of the plant. Varieties with stereomes somewhat poorly developed in the leaves proved generally resistant to dry conditions of environments, practically classed as the upland group of rice, while these guarded with strong stereome tissues were rather less resistant, and as a rule found among the lowland groups. According to the results of many observations, more recently carriedout by the author in Chosen-Corea-The said relation was found mostly agreeable and even more definite under the climatic circumstances of these parts, where the drought is usually much heavier than in Japan Proper. In some cases, however, when the drought took place with somewhat abnormal severity, in the course of field experiments these, the relation seemed to be disturbed or even become reversed in its direction; namely, the dry injuries on the leaves occurred hesvier in many of upland varieties than in low land ones. The present studies have been performed with the object of obtaining some more detailed data on these complicated correlations between drought resistance and susceptibility to dry injuries in the plant. The experiments consisted in two series, with different methods employed. In the first series, the plants of many varieties were cultivated in pots placed in open air, with their soil moisture controlled constant at various amounts, and were observedved in their growth responses to drought weathers, and symptoms of leaf-injuries. In accordance to the results, thus obtained, most of the upland varieties tested were again recognized poorer in the resisting power compared with the lowland ones against severer dryness. For numerical example, as to the leaf injury, the damaged parts on leaves, when grown on the soil with moisture contents of 15% or less for the air-dried weight bases, wewe estimated at 11% in upland varieties, while in lowland, at 7 to 9.5% only; and as for the damages on yield, the decrements in production attributable to lack of moisture, amounted to 15 to 65% in the upland varieties, while in the lowland only 3 to 46%. As the second series of experiments, young plants of each of these varieties, with their roots immersed in sugar solution of various concentrations between 0.1 and 0.7 Mol. were exposed to "artificial drought" namely, either being placed in large glass vessels, through which highly dessicated air flow was passed continuously, or otherwise put open in direct sun-light. As the results of these observations, it was shown that when dryness was severe but yet before attaining some killing degrees, the leaf injuries were heavier in the upland varieties than in the lowland ones, showing the same tendency of relation as in the first series of the present experiments, but in the case where the drought became extremely intense, the relations were reversed again in its direction, that is, the upland varieties were proved more resistant than the lowland ones, in the formers the leaf injuries estimated not exceding 89%, while in the latters being almost 100%. The intermediate varieties were midway between these two groups, the extent of injuries being 97%. In each plant, the higher in position was a leaf inserted on it, or in other words, the later in the order of development was it, the more resistant it seemed against drying. And this phenomenon might be attributed to some physiological characteristics acquired by each leaf during its development throught repeated wilting, as TUMANOW had pointed out in his researches on sunflower plant. [the rest omitted]

[学科分类] 农业科学（综合）