Effect Of Genotype And Nitrogen On Grain Milling Quality Of Japonica Rice

Improving rice quality has been one of the major objectives for rice production in China, as the increasing living standard of the whole population. Milling quality has gained more attention as the deleterious effect on it of the high-yielding technology in rice production and the selection for slender grain aiming for lower chalky grains in rice breeding. However, little is known concerning the genotypic variations in milling quality, as well as the influence of nitrogen fertilizer. In this study, two japonica rice cultivars, Wuyunjing7and Wuyujing3, and the mutants of Wuyujing3induced by EMS were used, and field experiments with treatment of nitrogen rate and timing were conducted, with the aims of elucidating the effect of genotype and nitrogen fertilizer on milling quality as measured by head rice rate. We hope the results obtained should be helpful for both rice breeding and agronomical practices aiming at high milling quality. The main findings are shown as follows.1. Genotypic variations in parameters of milling quality for japonica rice were detected using177mutants of Wuyujing3. Brown rice rate (BRR), milled rice rate (MRR), and head rice rate (HRR) showed large differences, with BRR having a range of69.5%-86.2%and an average of81.7%, MRR a range of52.0%-76.3%and an average of71.4%, HRR a range of29.4%-73.9%and an average of68.3%. Twenty elite germplasm with low or high HRR were identified, which should be used for rice improvement. Correlation coefficient analysis revealed significantly negative correlations between HRR and chalky grain rate (r=-0.291**) and total protein content (r=-0.369**), and positive correlations between HRR and grain length (r=0.209*) and grain weight (r=0.400**). This results help to understand the physicochemical causes underlying milling quality.2. To investigate the influence of nitrogen fertilization mode on grain milling quality,12mutants with contrasting agronomic traits were used and two treatments on ratios of basal to topdressing (N5:5and N10:0) were performed. Results showed significant effect of nitrogen fertilization mode on parameters of milling quality, with fertilization shifting from basal to topdressing exhibiting promoting effect. For HRR, N5:5had larger value of70.0%than that of69.1%. Correlation coefficient analysis revealed significant negative correlations between HRR and chalky grain rate and starch content, indicating that the reduction of chalky grain rate by nitrogen should be the possible reason for the increase in HRR.3. To measure the influence of nitrogen panicle fertilization on grain milling quality, two japonica rice cultivars (Wuyunjing7and Wuyujing3) were used and two treatments on nitrogen rate and timing treatments were performed. Results showed significant effect of nitrogen panicle fertilization mode parameters of milling quality, with fertilization at stage of latter half of4nd leaf in reverse order having beneficial effect. Chalky grain rate decreases with nitrogen rate, which can explain the increase in HRR as nitrogen fertilization at panicle development stage. This study further suggests the possibility of improving milling quality by nitrogen panicle fertilization.