Basic Study on Super Panicle Weight Type Varieties in Rice

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This study was carried out to clarify the characteristics of determining processes of number of spikelets, sink capacity and grain-filling in super panicle weight type (SPWT) varieties in rice. The results obtained were summarized as follows ;1. The high yielding semidwarf and intermediate culmed indica SPWT varieties had higher sink capacity due to higher both components, i.e., number of spikelets per m^2 and 1 grain volume (weight) and good transportation system of carbohydrates from the vegetative organs to the panicle.2. The final grain weight at the different positions in a panicle was mainly determined by the grain-filling rate compared with the grain filling period, irrespective of large differences in grain size among varieties including SPWT.3. With increasing amount of nitrogen application at various stage from transplanting to heading decreased the hull size of SPWT varieties and resulted in lighter grain weight. The unhulled grains with heavier specific weight showed heavier grain weight, and the grain weight closely and positively associated with the volume of brown rice which was mainly related to the thickness.4. The percentage of ripened grains and 1000-grain weight of a SPWT variety were strongly and positively correlated with the root activity (α -naphthylamine oxidizing activity) per grain during grain-filling period, and the promotion of these characters with increasing the root activity were greater in the inferior spikelets located on the lower part of a panicle.