Analysis of Yield-Determining Process and Its Application to Yield-Prediction and Culture Improvement of Lowland Rice : C. Diagnosis of rice culture by morphological observation of adult panicles.(3) The number of differentiated spikelets on the primary and secondary rachis-branches, the length of panicles, the substantial length of panicles and the density of spikelets per unit panicle length

摘要

With the same purpose as in the previous paper (XCIX), the authors examined the usefulness of diagnosing the rice cultivation by the number of spikelets per primary and secondary rachis-branch, the panicle length (from the neck-node to the uppermost grain), the substantial panicle length (from the lowermost grain to the uppermost grain) and the density of spikelets per unit panicle length, obtaining the following results. 1. From the present investigation it has been elucidated that in the general rice cultivation in Japan the number of spikelets per primary rachis-branch, excluding the spikelets on secondary rachis-branches, is 5 to 6 and 5.5 in average, and that per secondary rachis-branch is 2 to 4 and 3 in average. Accordingly, if only the number of primary and secondary rachis-branches is known, the total number of spikelets on a panicle or a hill can easily be estimated. 2. The percentage in occurrence of primary rachis-branches which have 5 and less spikelets or 6 and more spikelets varies with cultivating conditions or environmental conditions, and the percentage of primary rachid-branches which have 6 and more spikelets can be considered as an index of the amount of nutriment per panicle or the goodness of environmental conditions at the spikelet differentiation stage, indicating that the higher the percentage, the better in nutrition or in environmental conditions. 3. The number of spikelets per secondary rachis-branches can also be used for diagnosing the rice cultivation as above, but sometimes secondary rachis-branches are liable to degenerate and therefore it is less important than that per primary rachis-branches, and it is best used as a supplementary means. 4. The length of panicles or the substantial length of panicles can also be considered as an index of the amount of nutriment per panicle or the goodness of environmental conditions during the period from the stage of first bract differentiation to the final stage of reduction division, indicating that the longer the panicle, the better in nutrition or in environmental conditions. 5. The rice variety has its own characteristic density of spikelets per unit panicle length. However, even if an identical variety is used, the density varies markedly with nutrimental or environmental conditions during the period from the final stage of vegetative growth to the final stage of reduction division. 6. However, the density varies also with the interrelation between the length of panicles and the number of spikelets per panicle as shown in Table 7. Therefore, when a given variety has not its own characteristic density, an examination of the interrelationship shown in Table 7 will give further information about the diagnosis of rice cultivation. 7. From the actual instances obtained from the weather-response experiments in various prefectures it has been confirmed again that the morphological characterlistics on adult panicles above mentioned can effectively be used for the diagnosis of rice cultivation.