Estimating the Degree of the High-Temperature Damage in Rice Grain Ripening by Proximity Remote Sensing during the Heading Period

The high temperature from the heading period to the ripening period caused by global warming hinders rice grain ripening in rice cultivation sites in Japan. In this study, we aimed to predict during the heading period, the degree of high-temperature damage in rice grain ripening at harvest, and examined whether the rates of perfect grain and immature grain at harvest could be estimated by the proximity remote sensing during the heading period. Two varieties, Akitakomachi and Fusaotome, which have different degrees of resistance to the high-temperature during rice grain ripening, were cultivated in pots and subjected to different temperature treatments from the heading period to the ripening period. The data obtained by proximity remote sensing during the heading period were compared with the rates of perfect grain and immature grain at harvest. By using the spectral reflectances of two wavelengths, 462.4 nm and 469 nm, at the heading stage, a significant correlation was obtained with the rate of perfect grain at harvest by multiple regression analysis. The relationship between the normalized sufferance spectral index （NDSI）and the rate of perfect grain was also the most significant in the NDSI462.4 nm, 495.4 nm calculated using the spectral reflectances of 488.8 nm and 532.8 nm. A significant correlation with the rate of immature grain at harvest was obtained by multiple regression analysis using the spectral reflectances of the five wavelengths of 462.4 nm, 464.6 nm, 730.8 nm, 735.2 nm, and 737.4 nm during the heading period. Regarding the relationship between NDSI and immature grain ratio, the most significant correlation was obtained at NDSI462.4 nm, 495.4 nm calculated using the spectral reflectances of 462.4 nm and 495.4 nm. These results showed that it is possible to predict the degree of the high-temperature damage to rice grain ripening at harvest from the spectral reflectance data obtained by proximity remote sensing at the heading stage.