Abstract
ABSTRACTTemperatures and solar radiation during ripening critically affect grain appearance in rice (Oryza sativa L.). Climatic factors to induce chalky grains were analyzed under the experimental conditions of high-temperature and shading treatment and also under the ambient condition in a high-temperature-prone region of Japan. The frequency of white-back (WB) and basal-white (BW) grains correlated with temperature and solar radiation, whereas that of milky-white (MW) grains was not correlated, suggesting that complicated climatic factors are involved in the formation of MW grains. Further investigation was carried out to identify the parameters that distinguish perfect and MW grains grown in high-temperature versus those grown in low-solar-radiation conditions. As reported previously, the chalk phenotypes in the transverse section of the MW grains were quite different between environments: oval-shaped chalk for MW grains grown in low-solar-radiation condition and center chalk for MW grains grown in high-temperature condition. Grain hardness and amylopectin chain-length distribution did not explain the difference in MW grains between environments. MW grains subjected to high temperatures had a lower protein content without a consistent reduction in the single-grain weight, whereas those from the low-solar-radiation condition had a lower amylose content with a consistent reduction in the single-grain weight, when compared with perfect grains that developed in either environmental condition. Overall, our results suggest that MW grains are formed through different physiological mechanisms with altered starch and protein synthesis under high-temperature and low-solar-radiation conditions.Abbreviations: BW: basal-white; DAH: days after heading; DP: degree of polymerization; MW; milky-white WB: white-back
Highlights
Rice (Oryza sativa L.) grain quality is an extremely important criterion for deciding whether to release a new variety and for determining its market value
Grain quality encompasses a number of parameters including grain shape, amylose content, aroma, and other attributes (Calingacion et al, 2014), but grain chalkiness is commonly used as an indicator of market value since a high frequency of chalky grains degrades grain appearance and affects head rice yield (Lyman et al, 2013; Zhao et al, 2013)
Environmental stresses such as high temperatures and low solar radiation during ripening increase the frequency of chalky grains (Morita et al, 2016)
Summary
Rice (Oryza sativa L.) grain quality is an extremely important criterion for deciding whether to release a new variety and for determining its market value. Grain quality encompasses a number of parameters including grain shape, amylose content, aroma, and other attributes (Calingacion et al, 2014), but grain chalkiness is commonly used as an indicator of market value since a high frequency of chalky grains degrades grain appearance and affects head rice yield (Lyman et al, 2013; Zhao et al, 2013). Environmental stresses such as high temperatures and low solar radiation (shaded) during ripening increase the frequency of chalky grains (Morita et al, 2016). These results suggest that complicated mechanisms underlie the formation of MW grains
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