Abstract
Using 10 rice varieties cultured early in the year (early-season culture) in the warm south-western district of Japan, the type of white immature kernels that lowered husked rice quality in years with a high temperature and abundant sunshine (HTAS) and in years with a high temperature and poor sunshine (HTPS) was investigated. Whether the ripening capability (RC) under HTPS conditions could be evaluated by ripening the rice in a shaded (shading rate 66%) greenhouse was also examined. In the field examination, deterioration of husked rice quality was strongly related with the occurrence of white-back kernels and white-based kernels under the HTAS conditions, and with the occurrence of white-back kernels, white-based kernels and milky-white kernels (MWK) under the HTPS conditions. This suggested that the examination of the percentage of white-back kernels, white-based kernels and MWK was suitable for evaluating the RC of rice under the HTPS conditions. The percentage of MWK in the field in a year with HTPS was significantly correlated with that in the shaded greenhouse in a year with HTAS, which suggested that the RC under the HTPS conditions could be evaluated by ripening the plants in a shaded greenhouse. In addition, it was indicated that Fusaotome, Akitakomachi and Hatsuboshi which are used as standard varieties for “strong”, “middle” and “weak” RC under high temperature conditions, respectively, are also available as standard varieties under the HTPS conditions, Tosapika and Okiniiri in which the percentage of MWK was similar to that in Fusaotome and Hatsuboshi were also judged to be available as standard varieties for “strong” and “weak” RC, respectively, under the HTPS conditions.
