Delayed Sowing Date Improves Rice Cooking and Taste Quality by Regulating the Quantity and Quality of Grains Located on Secondary Branches

Grains located on different positions of the panicle differed in grain weight and quality performance, however, the comprehensive effect of sowing dates on physiological and quantitative characteristics of grains located on different positions still remains unclear. In this study, a field experiment was conducted with two japonica rice cultivars, Nanjing 9108 and Ningjing 7, under 3 sowing dates (S1, 30th April; S2, 30th May; S3, 30th June). Delayed sowing treatments increased before-heading mean temperature (Tmean), day temperature (Tday), night temperature (Tnight) and mean solar radiation (Smean) for 0.94 degrees C, 0.99 degrees C, 1.23 degrees C, and 1.04 MJ, respectively, while decreased growth duration (GD) for 13.4 days, with 30 days delaying sowing date. Elevated before heading thermal resources and shortened GD contributed to enlarged panicle size via enhancing number of grains on secondary branches (SG) and led to higher ratio of SG per unit area (SG%). Meanwhile, delayed sowing decreased after heading Tmean, Tday, Tnight and Smean by 0.84 degrees C, 1.23 degrees C, 1.13 degrees C, and 2.12 MJ, respectively, with 30 days delaying sowing, and further enhanced rice stickiness (ST), peak viscosity (PKV) and breakdown (BD), but suppressed hardness (HD), amylose content (AC), cold pasting viscosity (CPV), hot pasting viscosity (HPV) and setback (SB) of SG, whilst grains on primary branches (PG) di no significant differences. Elevated taste and cooking quality of SG under delayed sowing was regulated by slower grain filling rate, which is largely regulated by AGPase and GBSS. Compared to PG, SG has better physiochemical, texture properties and RVA profiles due to its slower starch biosynthesis. The above results suggested that physiological (starch biosynthesis of SG) and quantitative parameters (amount of SG) of the rice population should be referred simultaneously to improve rice cooking and taste quality.