Effects of Paclobutrazol Seed Soaking on Non-Structural Carbohydrate and Grain Enrichment in Direct-Seeded Rice

The yield of direct-seeded rice (DSR) was constrained by inadequate grain filling. Recent studies have indicated that paclobutrazol application plays a significant role in enhancing crop agronomic traits and increasing yield. This study aimed to examine the effects of paclobutrazol seed soaking (PSS) on non-structural carbohydrate accumulation and grain enrichment in DSR, potentially providing a theoretical foundation for achieving high-yield DSR cultivation. The experiment utilized two rice varieties, Jiyujing (JYJ) and Jijing305 (JJ305), with seeds soaked in paclobutrazol concentrations of 0 mg L⁻¹ and 100 mg L⁻¹. PSS demonstrated increased chlorophyll content, net photosynthetic rate, and leaf area, as well as an extended photosynthetic function period during the filling stage. It also elevated soluble sugar and starch contents in the flag leaf (during the filling stage) and stem sheath (after heading), decreased starch content in the top panicle while increasing it in the middle and lower panicle during the filling stage, and enhanced spikelet per unit area and seed setting rate, thereby improving DSR yield. In conclusion, PSS enhanced the photosynthetic capacity of DSR during the filling stage, coordinated the filling process of superior and inferior grains, maintained source-sink balance, and facilitated stable and orderly filling, ultimately resulting in improved yield.