Differences in Protein Content, Amylose Content and Palatability in Relation to Location of Grains within Rice Panicle

The protein and amylose content of milled rice grains collected from the top and base rachis branches at different positions on the panicle were measured. The palatability of the grains on primary and secondary rachis branches were also investigated. Grains on upper rachis branches had a lower protein content than those on lower rachis branches with a gradual change from the base to the top of both primary and secondary rachis branches. Grains on primary rachis branches also had lower protein content than those on secondary rachis branches at any position within the panicle. Conversely, amylose content on upper rachis branches was higher than that on lower rachis branches, and that on primary rachis branches was higher than that on secondary rachis branches. Protein content and amylose content varied widely within the panicle with 1.2% and 3.3%, respectively, range at maximum. Grain weight was negatively correlated with protein content and positively correlated with amylose content. Grains which originated from early flowering spikelets generally had low protein content and high amylose content. The palatability of the grains on primary rachis branches was superior to grains on secondary rachis branches, both in Koshihikari and Nipponbare. It was concluded that the variations in protein content and amylose content, and differences in palatability within a rice panicle were caused by the differences in the extent of grain filling, which was closely related to the flowering order of spikelets. This leads us to suppose the varieties with high and stable palatability in any growth environment could be raised from genetic resources which have more grains on primary rachis branches in the ear or on the secondry rachis branches in the upper position of the ear.