Abstract
The occurrence of milky white kernels is induced by high temperature and limited assimilate supply. The ring-type milky white kernels is induced mainly by a limited assimilate supply whereas the center-type milky white kernels is induced by a high temperature. The objective of this study was to select lines with a low percentage of milky white kernels from Koshihikari/Kasalath chromosome segment substitution lines (CSSLs) and to determine whether they show a low percentage of milky white kernels under conditions of high temperature and limited assimilate supply. In 2006 and 2007, 36 CSSLs were grown in the field and the percentage of milky white kernels was compared with that in Koshihikari. SL204 and SL236 had a lower percentage of milky white kernels and were selected for the experiments. In 2008 and 2010, these lines and Koshihikari were grown in the field, and in 2008, leaf clipping treatment and thinning treatment were given to change assimilate supply. In 2009, high temperature treatments were given to the pot-grown plants using a temperature gradient chamber. We examined the percentage of milky white kernels in each year, grain yield in 2008 and 2010 and assimilate availability in 2008. SL204 and SL236 had a lower percentage of milky white kernels than Koshihikari under a high temperature and limited assimilate supply conditions. Under high temperature condition, the percentage of center-type, and under a limited assimilate supply, the percentage of ring-type milky white kernels were low. The lower percentage of ring-type milky white kernels was attributed to the higher assimilate supply in SL204 and the lower supply of assimilate required to prevent the occurrence of ring-type milky white kernels in SL236.
