Abstract
Chalky rice (Oryza sativa L.) grains are induced by high temperature during the grain-filling period. Plant nitrogen status also affects the occurrence of basal- and back-white grains (BBWG). The objective of this study was to elucidate the relations between nitrogen availability per spikelet during the grain-filling period (NGF) and each of the percentage of BBWG and grain protein content (GPC). We further compared the effect of the components of NGF determined before heading (NBH) and after heading (NAH) on BBWG and GPC. We grew the rice cultivar ‘Koshihikari’ in pots in 2012 and 2013, and top-dressed nitrogen at the panicle formation and heading stages, under two (2012) or three (2013) temperature regimes during the grain-filling period. GPC was explained well by NGF, but BBWG was not. BBWG was best explained in a multiple-regression equation by mean air temperature after heading and by NBH and NAH. The partial correlation coefficients for NBH were 1.6 and 3.0 times those for NAH in 2012 and 2013, respectively. On the other hand, in a multiple-regression equation for GPC, the partial correlation coefficients for NBH were 0.91 and 0.71 times those for NAH in 2012 and 2013, respectively. These results suggest that rice grains are most sensitive to plant nitrogen status before heading for BBWG but after heading for GPC, and that there is an optimal timing for nitrogen top-dressing that would maximize the reduction in BBWG per unit increment of GPC.
Highlights
High temperature during the grain-filling period decreases rice (Oryza sativa L.) grain quality by increasing the proportion of chalky grains
In a multiple-regression equation for grain protein content (GPC), the partial correlation coefficients for NGF determined before heading (NBH) were 0.91 and 0.71 times those for nitrogen uptake per spikelet after heading (NAH) in 2012 and 2013, respectively. These results suggest that rice grains are most sensitive to plant nitrogen status before heading for basal- and back-white grains (BBWG) but after heading for GPC, and that there is an optimal timing for nitrogen top-dressing that would maximize the reduction in BBWG per unit increment of GPC
Nitrogen top-dressing at the panicle formation stage and at heading significantly reduced BBWG in both years (Tables 2 and 3)
Summary
High temperature during the grain-filling period decreases rice (Oryza sativa L.) grain quality by increasing the proportion of chalky grains. The occurrence of chalky grains can be reduced by improvement of plant nitrogen status (Takata et al, 2010; Tanaka et al, 2010; Wakamatsu et al, 2008). The occurrence of basal-white grains and white-back grains is unaffected by the assimilate supply (Tsukaguchi et al, 2011) These previous studies suggest that plant nitrogen status directly affects the percentage of basal-white grains and back-white grains, the mechanism is not known. Plant nitrogen status during the later growth stages affects the grain protein content (GPC) in rice (Mori et al, 2010; Tsukaguchi et al, 2016). We used nitrogen availability per spikelet during the grain-filling stage (NGF) to describe the plant’s nitrogen status during this period. We performed our experiment under different temperatures and nitrogen application patterns to provide the basis for the development of optimum nitrogen application technique
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