Regional and Yearly Differences in Brown Rice Quality, and their Factors in Brewer’s Rice Cultivar “Ginnoyume” in Kochi Prefecture

Abstract

Using brown rice of the brewer’s rice cultivar “Ginnoyume” produced in 11 regions of Kochi Prefecture during the five-year period from 2016 to 2020 and its production log, We investigated the actual situation of the regional and yearly differences in brown rice quality in“Ginnoyume” and the causal factors. Between regions, significant differences were observed in 1000-grain weight, percentage of whole grains, white-core grains,inspection grade and alkali solubility; and the coefficients of variation were relatively large (more than 10) for percentage of whole grains, white-core grains,inspection grade and alkali solubility.Between years, significant differences were observed in 1000-grain weight, percentage of whole grains, protein content and alkali solubility, and the coefficients of variation for percentage of whole grains and alkali solubility were greater than 10. The maximum and minimum differences in brown rice quality traits found to be significantly different between regions and between years, respectively, were 1.5g and 1.2g for 1000-grain weight, 32.5% and 15.4% for percentage of whole grains, and 0.49 and 0.24 for alkali solubility.Similarly, the coefficients of variation were 1.9 and 2.2 for 1000-grain weight, 14.5 and 10.1 for percentage of whole grains, and 19.7 and 11.7 for alkali solubility, between regions and between years, respectively.Therefore, the differences in 1000-grain weight between regions and between years were similar, and the differences in percentage of whole grains and alkali solubility between regions were larger than those between years. Between regions,the significant correlations were as follows.The percentage of whole grains was positively correlated with elevation; and, negatively correlated with average temperature and solar radiation during the ripening period. The percentage of white-core grains was positively correlated with average solar radiation during the ripening period; and, negatively correlated with maturity time. The inspection grade was positively correlated with average temperature and solar radiation during the ripening period; and, negatively correlated with elevation. The alkali solubility was positively correlated with elevation and maturity time; and, negatively correlated with average temperature and solar radiation during the ripening period. Therefore, the regional differences in the percentage of whole and white-core grains,the inspection grade and the alkali solubility need to be reduced in order to achieve a high brown rice quality in “Ginnoyume”.The regional differences in the percentage of whole and white-core grains, the inspection grade and the alkali solubility were affected by the average temperature and solar radiation during the ripening period through elevation and maturity time. Therefore it is important to develop a cultivation method that provides appropriate meteorological conditions for the ripening period in each production region.