2023 Volume 92 Issue 1 Pages 19-27
For barley pearling in Japan, glassy grain rate is an important quality factor. However, the relationship between glassy grain rate and temperature has not been clarified. We investigated the effects of moderately high daytime and nighttime temperatures during the ripening period on the glassy grain rate of barley using phytotrons. The barley variety ‘Shunrai’ was tested under three conditions: high daytime temperature (HD: 25°C / 9°C), high nighttime temperature (HN: 20°C / 14°C), and control (CT: 20°C / 9°C) in 2016/2017 and 2017/2018. The HD group showed an increase in the glassy grain rate. This was possibly due to the decrease in grain weight and increase in grain protein content. The HN group did not show any decrease in grain weight or increase in grain protein content, and the glassy grain rate was similar to that in the CT group. Based on these results, we investigated the trends of starch, soluble sugars, N, and C content in the seed during the ripening process in the HD and CT groups in 2019/2020. Accumulation of starch and N was accelerated during the first half of ripening in the HD group, but the final starch synthesis per individual plant was reduced because the ripening period was shortened. The ratio of change in N content to C content (ΔN/ΔC) from flowering to physiological maturity increased. Protein content per grain increased in the HD group. Furthermore, electron microscopic observation of the endosperm in the HD group revealed that large starch granules became larger while small starch granules became smaller. These results suggest that the increase in glassy grain rate due to high daytime temperatures is mainly due to changes in the accumulation pattern of starch and cytoplasmic proteins in the endosperm and the accumulation of more cytoplasmic proteins. This study may serve as a stepping stone to understanding the factors that increase the glassy grain rate in barley production sites.
