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Viscosity, a crucial characteristic for rice palatability, is affected by endosperm characters. We compared correlations between differences in viscosity of japonica rice with various palatability and endosperm characters. Changes in apparent amylose and protein contents (AAC% and PC%, respectively) and amylopectin side-chain distribution and the relationship of these traits with palatability were investigated in superior and inferior spikelets of good cultivars with low amylose content from Hokkaido and common cultivars from northeastern Japan, using rapid visco analyzer characteristics and rice-grain microstructures. Significant differences occurred in PC%, AAC%, breakdown, setback, peak time, and pasting temperature of different cultivars and grain positions. Amylopectin components showed remarkable differences in grain surfaces, surface layers, and section structure between the grain varieties. Hokkaido cultivars showed better viscosity than northeastern cultivars, particularly initial stage grains. Correlation analysis indicated viscosity was mainly AAC%-dependent, whereas differences in endosperm characteristics between spikelet positions were mainly due to grain-filling temperature.

Effects of organic (Italian ryegrass and Bokashi) and chemical fertilizer on growth, yield, and grain quality of rice (Oryza sativa L.) were compared under different planting densities in 2013/2014 and 2014/2015. Italian ryegrass was incorporated into the soil as green manure. Bokashi (a mixture of organic materials) was applied as basal dressing. To measure yield and its components, 30 hills were chosen for each treatment. Rice grains were harvested from each treatment to assess the grain quality and to evaluate accumulation structures using a scanning electron microscope. Bokashi treatment increased panicle number per hill, ripened grain percentage, panicle number per m 2 , and grain yield compared to no fertilizer treatment at normal planting density. Chemical fertilizer treatment increased plant length at high planting density. Italian ryegrass and Bokashi treatments promoted the taste point (taste score as reference) by reduction of amylose and protein contents at normal planting density in contrast to chemical fertilizer. 1000-grain weight, panicle number per m 2 , and grain yield were higher at high planting density than at normal planting density. However, high planting density decreased panicle number per hill and spikelet number per panicle. It also enhanced the amylose content of rice grain. Scanning electron microscopic observation revealed that chemical fertilizer treatment marked up protein bodies and their traces on amyloplasts. However, Bokashi treatment produced large amyloplasts, which included many starch granules. These results show that Italian ryegrass and Bokashi can offset reductions of chemical fertilizer and can lead to sufficient starch accumulation structures in rice grains.

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Global warming has already affected agricultural production worldwide. In Japan, the occurrence of chalky rice grains CRGs , which are low quality grains whose occurrence is exacerbated by high air temperature, has become a major issue. There is concern that this occurrence will become more frequent with increasing global warming; therefore, it is necessary to develop a model that can accurately estimate the impact of global warming on the occurrence of CRGs. In this study, such a model was developed for Japan's main cultivars, "Koshihikari" and "Akitakomachi". This model is a non-linear model and was also used to investigate the differences in the responses of these cultivars to temperature and radiation; the occurrence of CRGs was explained as a function of air temperature and solar radiation in this model. The results showed that the occurrence of CRGs could be reproduced more accurately when both air temperature and solar radiation were considered compared to when only air temperature was considered; the latter is the case with existing models. The air temperature at which CRGs begin to appear is lower for "Koshihikari" than "Akitakomachi", when the average solar radiation is small less than 16.4 MJ m-2 d-1. The proposed model will hopefully be applied to impact assessments of global warming and the quantification of varietal characteristics with respect to the occurrence of CRGs.