A study of the resistabilities of paddy rice varieties to unseasonable low temperatures and the methods of their determination. : VIII Inter varietal differences in the injury caused by low temperature and the blast disease due to late seeding and transplanting.

Abstract

The occurence of sterile sprkelets as an injury by low temperature due to late seeding and transplanting is insignificant in a year like 1943 when abundant sunshine and high temperature prevailed during the whole growing period, and consequently no inter-varietal difference sbows itself, but in a year like 1942 when the climatic conditions during the growing period were unfavorable with frequent visits of abnormal low temperature at the stage of ear formation and flowering, the per-centage of sterile spikelets increases and inter-varietal differences show themselves somwhat notably. This manifestation of inter-varietal differences in injury to fertilization is chiefly sttributable to the differences in the varietal resistability to low temperature and the degree of decline of the physiological function due to late seeding and transplanting, chance concurrences of the stage of formation of generative cells or the stage of flowering and pollination with abnormal low ternperature, and other relations. By inquiring into such relations, we classified the insensibilities to cold of the varieties used in our experiment. In late seeding and transplanting, inter-varietal differences arise in the injury to fructification due to low temperature, but it is difficult to detect therefrom differences in the resistability to low temperature or in the insensibility to cold of a variety. Inter-varietal differences in the degree of reduction of the number of days from seeding to earing attendant upon late seeding and transplanting is thought to be accompanied with differences in the degree of decline of the physiological function, and therefore is, in this sense, related to the injury by low temperature. Inter-varietal differences in the delay of earing exercise an influence upon the degree of injury by low temperature by causing more or less chances of meeting with an unseasonable low temperature at the stage of ear formation or flowering. Decrease in the number of ears per hill (individual) is, in ordinary cases, not due to injuty dy low temperature. The total number of spikelets per ear generally shows little cbange, and inter-varietal differences in the rate of its decrease are hard to detect. Aa a method of determining the insensibility of a paddy rice variety to cold, late seeding and tra splanting has the advantage that a number of materials can be used in experiment at the same time, but this method can be employed only in cold regions, and that in a year when unseasonable low temperatures attack during the specific growing period. Moriover, it involves much labor and trouble in the conduct of an experiment and judgement of its results, and therefore cannot be considered as appropriate for general purposes. we have also made a classification of the insensibilities to disease of the varieties used in our experiment on the basis of the per-centages of ears affected by blast as the result of late seeding and transplanting, and we can infer that different genetic factors take part in the insensibilities of a paddy rice variety to cold and to disease.the differences in the varietal resistability to low temperature and the degree of decline of the physiological function due to late seeding and transplanting, chance concurrences of the stage of formation of generative cells or the stage of flowering and pollination with abnormal low ternperature, and other relations. By inquiring into such relations, we classified the insensibilities to cold of the varieties used in our experiment. In late seeding and transplanting, inter-varietal differences arise in the injury to fructification due to low temperature, but it is difficult to detect therefrom differences in the resistability to low temperature or in the insensibility to cold of a variety. Inter-varietal differences in the degree of reduction of the number of days from seeding to earing attendant upon late seeding and transplanting is thought to be accompanied with differences in the degree of d