Among more than 120 rice-producing countries, over 95% of them cultivate primarily indica varieties (Deng 2008; Fang 2005). Globally, only a few countries, such as China, Japan, South Korea, United States, Australia, and Egypt, produce and export japonica rice (Deng 2008). The japonica varieties occupy 8.8% of the rice farming area and are responsible for 14.2% of total rice production worldwide (Fang 2005). From 2007 to 2015, the total amount of rice traded on international markets increased from 32 million tons to 41.67 million tons, while the proportion of japonica rice trade decreased during the same time from 10.9% to 8.1%. This decrease corresponds to approximately 3.5 million tons, which is less than 5% of the amount of japonica rice consumed in China (Cao et al. 2018). China has the largest planting area and the highest total production of japonica rice in the world. Because the culinary quality of japonica is superior to that of the indica rice, the total production and demand for japonica rice has been increasing continuously in China, especial in Northeast China from 1990 to 2015 (Fig. 1, Fig. 2) (Tang et al. 2017). To meet the growing need, the share of the japonica in overall rice planting has been increasing recently, particularly in south China, the main indica producing area of the country.
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