Abstract
(XI) On forecast of fruit bearing percentage in rice. In 1951 and 1952, the authors tried to find out methods for forecasting fruit bearing percentage in rice plant, making experiments to ascertain, on the one hand, the period in which fruit bearing percentage is finally determined and, on the other hand, to trace up the process in which the percentage is destined. Various degrees of fruit bearing percentage were obtained by cutting leaf-blades at different growing stages of 3 varieties differing in earliness of maturity. Tracing up the fruiting process of grains was made by measuring specific gravity of developing grains (air dried) at an interval of 5-7 days after heading. Results obtained are summarized as follows: (1) The period in which fruit bearing percentage of medium maturing variety is finally determined, in most cases, is about 33-38-days after heading, and 20 days prior to maturity. But the period varies with varieties and years to a considerable extent. (2) It has been made clear that there exists the period in which the fruit bearing percentage is destined and the period is considerably previous to that in which the percentage is finally determined. And the period has been proved to be at about 17th day after heading for the early maturing variety, and 22-27th day after heading for the medium and late variety used. Moreover, in all cases differing in cultivating conditions or in stages and in degrees subjected to cutting treatment of leaf-blades, fruit bearing percentage of medium variety used has been observed to be destined at about 21st day after heading. (3) As number of days from heading when fruit bearing percentage is destined varies with varietes and with years, it seems to be unavailab1e in forecasting the percentage. Therefore, it is necessary to find out a method by means of which fruit bearing percentage can be forcast in every case differing in vgrieties and years. In consequence of examining the data here obtained, the authors have ascertained that fruit bearing percentage in every case will be able to be forecast by investigating the developing preocess of grains as follows. (4) Taking a given value of specific gravity for a standard, the percentage of grains heavier than the standard specific gravity to total number of sampled grains always increases with maturity. And the period when the rate of increase in the percentage above mentioned reaches a maximum and thereafter the rate begins to decrease remarkably has been proved to be the period in which fruit bearing percentage is destined. (5) At this critical period, the persentage of grains heavier than a standard specific gravity is always highly correlated with final fruit bearing percentage in evry case differing in varieties and in cultivating conditions or in stages and in degrees subjected to cutting treatment of leaf-blades. Accordingly, this present correlation is considered to be utilized as a criterion for forecasting fruit bearing percentage of rice plant. (Whatever value of specific gravity one may take as a standard, one can obtain almost identical results. But, it is recommendable to use the value 1.00 as a standard for getting most exact results.)
