Abstract
We imposed leaf clipping treatment in 2008 and 2010 and thinning treatment in 2008 on field grown Koshihikari plants at full heading. In 2009 and 2010, pot grown Koshihikari plants were placed in a temperature gradient chamber (TGC) during the grain-filling period. In 2010, leaf clipping treatments were conducted in each temperature regime. The pattern of cross sectional chalkiness was investigated using kernels that were classified into milky white and opaque kernels by grain quality inspector (RGQI20A, Satake). Most of the milky white kernels were classified into two types: milky white kernels with chalkiness at the central part of endosperm and those with rings of chalkiness. The percentage of ring-type milky white kernels were significantly increased and decreased by leaf clipping and thinning treatment, respectively and negatively correlated with grain-filling percentage which is considered to reflect assimilate supply. There was no relation between the percentage of the ring-type milky white kernels and mean daily air temperature during 20 days after heading. The percentage of the center-type milky white kernels was not affected by leaf clipping or thinning treatments and was not correlated with grain-filling percentage. The percentage of center-type milky white kernels increased exponentially with the rise in mean daily temperature during 20 days after heading and was associated more closely with the mean temperature of 12:00 to 15:00, suggesting that they are more sensitive to the daily maximum temperature during this period.
