Global warming is threatening rice industry

The demand for food production and quality has tremendously increased with world population expansion and economic development. Rice (Oryza sativa L), which is consumed by more than half of the global population, serves as a crucial food resource to fulfill caloric and nutritional demands. The satisfaction of rice production mostly comes from greater yields on existing cropland to avoid environmental degradation, destruction of natural ecosystems, and loss of biodiversity. Achieving greater rice yields depends on normal development of floral organs, adequate growth time for caryopsis formation and the functioning of the photosynthetic apparatus.

The quality of cooked rice is greatly affected by starch, which accounts for >85% of rice grain weight and provides the main source of energy in the human diet [1]. Factors such as amylose content, granule size distribution, crystallinity, and pasting temperature have been used as indices for this effect [2]. The amylose content greatly affects physicochemical properties and applications of starch. The shape, structure and size distribution of granule are important factors that influence starch quality and end-use application of rice consumption. The crystallinity is a way to elucidate the crystal structures of the crystallites of the starch granules. Pasting behavior indicates retrogradation tendency of a given starch.

Global warming is a challenge for food security (Image Source: Inc. Magazine)

In spite of the growing demand for rice yield and starch quality, global warming is predicted to challenge rice industry [3]. Global air temperature is predicted to increase by 2.0 °C to 4.5 °C during the 21st century [4]. High temperatures due to global warming inhibit rice development and specifically affect floral organs, fruit formation, and the functioning of the photosynthetic apparatus, thereby decreasing total above-ground biomass, grain yield, and starch quality [5].

Regarding the effect of high temperature on rice development and starch physicochemical properties, high temperature-stressed rice showed a decreased grain filling period from 32 to 26 days, and a reduction in total starch (3.1%) and amylose content (22%) [6]. High temperature was also proved to increase the average diameter of starch granules and alter the granule size distribution of rice starch [7]. Above all, rice grain yield was reported to vary from 354 to 736 g/m² due to different environment temperature exposure [8]. However, these previous findings mostly came from studies concentrating on the influence of high temperature during only flowering and grain filling stages. PD and PF stages, which are involved in the early development of rice spikelet and branch, play a fundamental role in the growth of caryopsis and formation of starch physicochemical properties. Nevertheless, to the best of our knowledge, studies in these areas are limited, especially comparative studies between the two stages. Therefore, there is an unmet need for researches on the effects of high temperature during PD and PF stages on the caryopsis development and starch physicochemical properties of rice. 

Reference

[1] J.A. Patindol, T.J. Siebenmorgen, Y.J. Wang. Impact of environmental factors on rice starch structure: a review. Starch, 67 (1–2) (2015), pp. 42-54

[2] D. Zhu, H. Zhang, B. Guo, K. Xu, Q. Dai, C. Wei, H. Wei, H. Gao, Z. Huo, Y. Hu. Effect of nitrogen management on the structure and physicochemical properties of rice starch. J. Agric. Food Chem., 64 (42) (2016)

[3] P. Shaobing, H. Jianliang, J.E. Sheehy, R.C. Laza, R.M. Visperas, Z. Xuhua, G.S. Centeno, G.S. Khush, K.G. Cassman. Rice yields decline with higher night temperature from global warming. Proc. Natl. Acad. Sci. U. S. A., 101 (27) (2004), pp. 9971-9975

[4] S. Solomon. Climate change the physical science basis. Agu Fall Meeting, IPCC (2007), p. 2007

[5] D. Egli. Seed Biology and the Yield of Grain Crops Cab International (1998)

[6] N. Ahmed, I.L. Tetlow, S. Nawaz, A. Iqbal, M. Mubin, N.U. Ms, A. Butt, D.A. Lightfoot, M. Maekawa. Effect of high temperature on grain filling period, yield, amylose content and activity of starch biosynthesis enzymes in endosperm of basmati rice.

[7] J. Liu, Z. Qian, L. Zhou, Z. Cao, C. Shi, F. Cheng. Influence of environmental temperature during grain filling period on granule size distribution of rice starch and its relation to gelatinization properties. J. Cereal Sci., 76 (2017), pp. 42-55

[8] T. Kobata, J.A. Palta, T. Tanaka, M. Ohnishi, M. Maeda, M. Koç, C. Barutçula. Responses of grain filling in spring wheat and temperate-zone rice to temperature: similarities and differences. Field Crop Res., 215 (2018), pp. 187-199

[9] X. Yu, H. Yu, Z. Jing, S. Shao, Z. Liang, X. Fei, W. Zhong. Comparison of endosperm starch granule development and physicochemical properties of starches from waxy and non-waxy wheat. Int. J. Food Prop., 18 (11) (2015), p. 13

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