Cardinal temperatures variability within a tropical japonica rice diversity panel

Abstract

Air temperature is one of the most critical climatic factors controlling rice growth, development, and production in current and future climatic scenarii predicting increasingly frequent situations of extreme and/or fluctuating temperatures. With its large spectrum of geographical origins and cropping areas, one can credit tropical japonica rice subspecies of a probable genetic diversity of its response to air temperature, which is of major interest for the breeding of better adapted rice varieties. A panel of 195 rice accessions (175 japonica plus 20 reference cultivars) was studied in controlled environment to estimate cardinal (base, optimum, and maximum) temperatures based on the monitoring of the elongation rate (LERmax) of the sixth leaf on the main stem in response to six fixed thermal treatments ranging from 16 to 35 °C. A dedicated statistical framework was elaborated for estimating LERmax, cardinal temperature and related uncertainties. Developed statistical framework enhanced the precision of cardinal temperatures estimated compared to previously reported methods, especially for base temperature. Maximum temperature was trickier to estimate and will require further studies. A significant genotypic variability for base and optimal temperature was pointed out, suggesting tropical japonica subspecies represents a relevant genetic pool to breed for rice genotypes adapted to various thermal situations. These results also suggested that using genotype-dependent cardinal temperature values should enhance the way crop growth models account for genotype × environment interactions hence their predictive value in current and future climatic conditions.

Responses of Rice Growth to Day and Night Temperature and Relative Air Humidity—Leaf Elongation and Assimilation

“…Daytime LER was closely correlated with daytime temperature, which had a much larger effect on LER than RH. The temperature dependence of LER has been demonstrated by several authors [ 4 , 21 , 22 ]. In pressure chamber experiments using salt-treated barley, only daytime LER could be increased, as a result it has been argued that LER was controlled by the plant’s water status during the day, but not during the night [ 12 ].…”

“…Even though the effect of RH on LER was rather weak, it should not be neglected. Leaf elongation rates have been used to calculate cardinal temperatures of crop genotypes [ 4 , 30 , 31 ], and the causal relationship between leaf elongation and leaf appearance has been discussed [ 32 ]. In our experiment, LER Day linearly increased with temperature in the observed range, while LER Night only slightly increased between 25 °C and 30 °C in the treatments around the same mean temperature and even decreased in the constant temperature treatments.…”

“…While under low evaporative demand at 90% RH, tentative T base is 10.6°C, which is relatively close to the T base of 9.55°C described for IR64 [ 35 ], tentative T base increased with evaporative demand to 17.3 °C and 18.5 °C at 65% and 40% RH, respectively. In a previous estimation of cardinal temperatures based on LER for a large panel of rice accessions at 70% RH day and night, T base was found to be systematically higher than values commonly used in crop models [ 4 ]. It is clearly beyond the scope of this manuscript to provide cardinal temperatures for leaf elongation, but since precise cardinal temperatures are of such prominent importance for crop modeling, we would like to emphasize the possibility that high evaporative demand at the experimental site increases calculated T base .…”

“…Therefore, to describe the rate of growth of individual leaves, leaf elongation (increase in length over time) is used instead of leaf expansion (increase in area over time). Leaf elongation rate (LER) follows a logistic function with a maximum derivative being a function of temperature [ 4 ]. Further factors influencing LER are soil water potential [ 5 ] and evaporative demand, which has been confirmed for maize and sorghum by several authors [ 3 , 6 , 7 ].…”

Dynamic Gene-Based Ecophysiological Models to Predict Phenotype from Genotype and Environment Data

“…These parameters are based on daily mean temperatures and cardinal temperatures. The assumption that all genotypes of a species have the same cardinal temperatures contrasts with reports of genetic variation for cardinal temperatures (Hardegree 2006;Rouan et al 2018;Djanaguiraman et al 2019). Also, computation of mean daily temperatures overlooks the effect of daily thermocycling on biological processes that affect yield (Peng et al 2004;Lobell and Ortiz-Monasterio 2007;Shi et al 2016).…”