2013 Volume 82 Issue 1 Pages 18-27
The essential points for controlling the digestible protein content (DP) of rice grain at low levels in seed-protein mutant rice cultivars (SPMR) were investigated. A low-glutelin cultivar ‘LGCsoft’, a 26-kDa globulin-deficient low-glutelin cultivar ‘LGC-Jun’, and a normal-type cultivar ‘Nihonmasari’, were cultivated for 8–9 cropping seasons over a period of 4 years. Factors affecting seed protein composition and protein content in rice grain were analyzed. DP was affected by both the total protein content (TP) and the ratio of DP to TP in all cultivars. However, the effect of DP/TP on DP was greater in ‘LGCsoft’ and ‘LGC-Jun’ than in ‘Nihonmasari’. A positive correlation between DP/TP and air temperature from 0 to 15 days after heading was observed in all cultivars. The highest correlation coefficient was observed from 0 to 10 days after heading in ‘LGCsoft’ and ‘LGC-Jun’, which was slightly earlier than in ‘Nihonmasari’. Therefore, it is important to adjust the planting season to avoid high temperatures during the early ripening period for the cultivation of SPMR. TP affected DP more than DP/TP not only in ‘Nihonmasari’ but also in SPMR. A positive correlation was observed between TP and the nitrogen content of shoots at the heading stage, and a negative correlation was observed between TP and the percentage of ripened grains. These results indicate that shoot nitrogen status and percentage of ripened grains should be taken into account in planting and cultivation management plans.
