The effect of air temperature and solar radiation on the occurrence of chalky rice grains in rice cultivars “Koshihikari” and “Akitakomachi”

Abstract

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.

Rice grain quality degradation and economic loss due to global warming in Japan

“…However, it should be noted that the statistical relationships can be valid in different environments when models are calibrated using reliable and representative set of data for the conditions to be explored [40]. In the calibration process, the optimal duration after the flowering date for averaging air temperature differs among varieties [13,21]. The calibrated parameters, T crit and k , T represent quantitative characteristic of each variety for the occurrence of CRG [13].…”

“…There are some limitations and challenges in the model. The occurrence of CRG is known to depend on not only air temperature, but also radiation [21,41], wind speed [42], CO 2 concentration [43], and management, including nitrogen application [44] and planting density [45]. Although our simple model was accurate enough for estimating the occurrence of CRG under current conditions, it is an important challenge to develop and use a model that considers the other factors.…”

“…A feature of these simple statistical models is that they can be easily developed for any variety and applied to any area without much loss of accuracy in estimations, if input data, including temperature, CRG occurrence, and flowering date, are available for the varieties and regions. As an improvement of these simple statistical models, Takimoto et al (2019) suggested that the consideration of radiation can improve the accuracy of estimations [21]. As other types, Wakiyama et al (2010) proposed a non-linear regression model between dry matter weight per grain and the occurrence of milky-white grain, which is a type of CRG [20], and Yoshida et al (2016) developed a model combined with a rice growth simulation model [22].…”

Model‐based evaluation of climate change impacts on rice grain quality in the main European rice district

“…Bunyawanichakul et al, 2007;Franco et al, 2020) require engineering and process background, are completely isolated from the outside environment (i.e., do not consider the effect of pedo-climatic conditions) and are too sophisticated to be effectively coupled with rice models (consist of chains of interdependent differential equations that require huge number of input factors-variables and parameters-and measured data for calibration). Lastly, Takimoto, Masutomi, Tamura, Nitta, et al (2019) demonstrated that the simulation of chalky grains is more accurate when both air temperature and solar radiation are considered together and that low radiation levels can exacerbate the sensitivity of rice grains to temperature damage even in cultivars ranked as intermediate heat tolerant. This consideration is even more important in view of the models' application in a climate change impact assessment, since increasing air pollution and aerosol concentration are affecting the amount of solar radiation reaching the Earth's surface (Stanhill & Cohen, 2001;Thakur, 2018), causing the so called "global dimming" phenomenon.…”

Breeding targets for heat-tolerant rice varieties in Japan in a warming climate

“…Rice, one of the world's major cereals, has a high incidence of low quality rice grains, called chalky rice grain (CRG; Fig. 1) as a result of high temperatures during the ripening period (Krishnan et al 2011;Masutomi et al 2015;Morita et al 2016;Takimoto et al 2019;Tashiro & Wardlaw 1991;Xiong et al 2017). CRG is fragile, which increases loss during milling, thus reducing the marketable yield (Bao 2019;Lyman et al 2013;Zhao & Fitzgerald 2013).…”