Changes in the Grain Yield and Quality of Early Indica Rice from 2000 to 2020 in Southern China

The double-season rice system plays an important role in ensuring food security in China. However, changes in the grain yield and quality of recently released rice varieties are still not fully understood, especially early indica rice (Oryza sativa). In this study, we collected the yield and quality traits of 224 early indica rice varieties released in China's Hunan and Jiangxi provinces from 2000 to 2020. The results showed that rice grain yield, but not quality, was significantly improved in early indica rice from 2000 to 2020, and the improvement in grain yield was mainly the result of an increased spikelet number per panicle. Quality traits such as head rice rate, chalky rice rate, and amylose content remained stable while the milled rice rate and degree of chalkiness showed adverse changes during early indica rice breeding. These results suggested that improving grain yield, but not quality, has been prioritized during early indica rice breeding in the past few decades. Further analysis showed that the degree of chalkiness had the largest coefficient of variation among the studied quality traits in the 224 early indica rice varieties, indicating that there is still great potential to decrease the degree of chalkiness through rice breeding. Interestingly, the results showed that lower degrees of chalkiness were associated with lower amylose contents and chalky rice rates but with a higher length-to-width ratios and a gel consistency. Therefore, focusing on the degree of chalkiness seems a promising strategy to synergistically improve the quality traits of early indica rice. Overall, our results have value for guiding future research on high-yield and high-quality breeding in early indica rice.