Milky‐White Rice Prediction Based on Chalky Patterns on the Transverse Section of Premature Grains

Abstract

Climate change increases the occurrence of chalky rice (Oryza sativa L.) through frequent extreme weather conditions, such as high temperature and low radiation. The objective of this study was to examine the possibility of developing prediction methods for estimating the occurrence of a major type of chalky rice, the milky‐white rice. The methods evaluated the chalky patterns on the transverse section of premature grains by visual inspection or by employing a newly developed image analyzer. The predicted grain rates of milky‐white rice using the above‐mentioned method(s) as well as two other methods using a grain scanner, were compared with periodically sampled grains approaching maturity under shade treatments at Kagoshima and Fukuoka, Japan. The grain rates predicted using visual inspection and the developed analyzer at 6 to 7 d before maturity (DBM) and 9 to 10 DBM, were positively correlated with the target grain rates of milky‐white rice obtained at maturity; R2 was 0.906 (p < 0.01) to 0.964 (p < 0.001), and the RMSE value ranged from 2.00 to 6.10, at both the DBMs. In the methods employing the grain scanner, the correlations between the predicted and target grain rates at the same DBMs were lower; R2 was 0.556 (p = 0.054) to 0.777 (p < 0.01), the RMSE value was between 7.86 and 12.03. Thus, the methods using transverse section of premature grains developed in this study could be applied for predicting the occurrence of milky‐white rice a week to 10 DBM. Occurrence of milky‐white rice can be predictable using transverse section of the premature grain. The chalky zone detected inside the transparent area on the transverse section is the indicator. The method is based on the regularity of starch accumulation from center towards peripheral in the grain. This method will contribute to mitigation of grain breakage through postharvest management.