Abstract
There are two distinctive varieties of rice plant in the view of cultivation since long time. The one is lowland rice and the other up-land rice. But the functional characters of drought resistance in rice plant has not yet been studied scientifically. The author has studied the drought resistance from the standpoints of rice cultivation and breeding. More than one hundred varieties were treated in low-land and up-land conditions for four years since 1923, and, in the glass house, nine varieties, planted in porcelain pots with various ;moisture contents of soil, were examined. Characters investigated in this study were, the height of culm, mean weight of panicles, the development of the stereome or mechanical tissue in leaves, the osmotic pressure of cell-sap, and the transpiration coefficient or water requirement. In addition to these characters, variations of yield and correlations of the rations of yield, in up-land and low-land conditions, and those of the height of culms, in both conditions. The results are summarized as follows:- (1) The up-land rice was not so much influenced by scanty water supply as low-land rice. The rations of height of culm were larger in up-land rice than in low-land rice. The mean value of the former was 82.30±0.8728% the latter 65.76±0.7588%. (2) In pot cultures, with one variety in each case, the similar result was gained. (3) The mean weight of panicles of the plants grown with soil-moisture of 5, 10, 15, and 20 weight % showed distinct difference between up-land and low-land varieties. The decrease of mean weight of panicles owing to the droughty conditions was not so much in up-land rice as in low-land rice. (4) The difference of development of the stereomes in leaf-blades is very distinctive. The less the soil-moisture contents were, the more the stereomes developed as well as in other plants. (5) In physiological investigations, changes of osmotic pressure of cell-sap as well as pressed plant-juice were seemed to be characterized by two varieties. Up-land rice was not so sensible for slight decrease of soil moisture in moistend state, but in the limiting dryness showed remarkable elevation. Low-land rice, however, was more sensible for little decreasing of soil-moisture in moistened state, but by the limiting dryness did not show any remarkable elevation. (6) Varietal variations in osmotic pressure of pressed cell-sap was compared by cryoscopic method. No relation between osmotic pressure of cell-sap and drought resistance was found. (7) The difference of transpiration coefficients of water requirements between two varieties was not distinct as comprehended from probable errors, while the water requirement of up-land rice was 217.1±10.1 and of low-land rice 241.7±5.4. The water requirement of both varieties was increased according to the decrease of soil-moisture. (8) Ratios of yields per plant in up-land and low-land conditions, was very different with two varies. The yields of up-land rice were not so ouch influenced by soil-moisture as these of low-land rice, just as in height of culm. The ratios of yields of up-land varieties ware larger than those of low-land varieties. The mean value was 180.87±28.073% for up-land varieties and 81.94±4.875% for low-land varieties In regard to this result, the reason why the mean value of the ratios for up-land varieties was more than 100% is that the plant-distances in up-land condition are wider than in low-land condition in accordance with the common method of cultivation for up-land culture. (9) The correlation between ratios of yields in the two different conditions and ratios of culm in the two different conditions, was vary distinctive. Correlation coefficient γ was +0.7313±0.03576 and this value indicates that there is close relation. The influence of drought for plants may be measured by various methods. [the rest omitted]
