Genetic improvement of grain quality traits in indica inbred rice cultivars developed in South China during 1956–2020

Rice is the most staple food consuming in China. During the past six decades, a large number of indica inbred rice cultivars have been developed. However, seldom studies have focused on evaluating the dynamic changes of grain quality improvement among the major cultivars. Our study evaluated the genetic improvement of 12 quality traits in indica inbred rice cultivars developed in rice breeding programs in South China during 1956–2020. The results indicated that significant improvement had been gained for the appearance quality, cooking and eating quality in the breeding program since the 1990s, while slight genetic improvement was attained before 1990. Among all the 12 traits, MGL (Milled Grain Length), LWR (Length Rate Ratio), GC (Gel Consistency), and ASV (Alkali Spreading Value) were significantly increased among these different cultivars; MGW (Milled Grain Width), CGR (Chalky Grain Rate), CA (Chalkiness Area), and AC (Amylase Content) showed a tremendously decreased trend from last thirty years. However, the other four traits, such as BRR (Brown Rice Rate), MRR (Milled Rice Rate), HMRR (Head Milled Rice Rate), and PC (Protein Content) showed little improvement during the breeding processes in these cultivars. The results also suggested that selecting a slender grain shape would be beneficial for breeding high quality indica rice. We also discussed that improving milling quality, especially HMRR of the high-quality cultivars and nutrition quality for special consumer groups as an meaningful direction for rice breeding.