Can a delayed sowing date improve the eating and cooking quality of mechanically transplanted rice in the Sichuan basin?

Adjustment of the sowing date is a widely used measure in rice production to adapt to high-temperature conditions. However, the impact of delayed sowing date (DS) on rice quality may vary by variety and ecological conditions. In this study, we conducted experiments using different sowing dates, that is, conventional sowing date 1 (CS1), CS2 (10 d later than CS1), DS1 (30 d later than CS1), and DS2 (30 d later than CS2), and three rice varieties, i.e., “Yixiangyou 2115,” “Fyou 498,” and “Chuanyou 6203.” This experiment was conducted at four sites in the Sichuan basin in 2018 and 2019 to evaluate the influence of DS on the pasting properties of rice, which are a proxy for eating and cooking quality (ECQ). In DS1 and DS2, rice had a significantly greater amylose content (AC) but a lower protein content (PC), peak viscosity (PKV), cool paste viscosity (CPV), and hot paste viscosity (HPV) than in CS1 and CS2. Moreover, with the exception of CS2 and DS1 in 2018, DS1 and DS2 led to a 2.15–11.19% reduction in breakdown viscosity (BDV) and a 23.46–108.47% increase in setback viscosity (SBV). However, the influence of DS on rice pasting properties varied by study site and rice variety. In 2019, DS1 and DS2 led to a BDV reduction of 2.35–9.33, 2.61–8.61, 10.03–17.78, and 2.06–8.93%, and a SBV increase of 2.32–60.93, 63.74–144.24, 55.46–91.63, and -8.28–65.37% at the Dayi, Anzhou, Nanbu, and Shehong, respectively. DS resulted in a greater decrease in PKV, HPV, CPV, and BDV and a greater increase in the AC and SBV for Yixiangyou 2115 than for Chuanyou 6203 and Fyou 498. Correlation analysis indicated that PKV and HPV were significantly and positively related to the mean, maximum, and minimum temperatures after heading. These temperatures have to be greater than 25.9, 31.2, and 22.3℃ to increase the relative BDV and decrease the relative SBV of rice, thereby enhancing ECQ. In conclusion, DS might contribute to a significant deterioration in ECQ in machine-transplanted rice in the Sichuan basin. A mean temperature above 25.9℃ after heading is required to improve the ECQ of rice.