Abstract
Tartary buckwheat is characterized by its numerous inflorescences; however, the uneven distribution of resources can lead to an overload in certain areas, significantly limiting plant productivity. Plant growth regulators effectively modulate plant growth and development. This study investigated the effects of three concentrations of brassinosteroids (EBR) on the Tartary buckwheat cultivar with high seed-setting rates, specifically Chuanqiao No. 1 (CQ1), and low seed-setting rates, namely Xiqiao No. 1 (XQ1), through field experiments. The goal was to investigate how EBR regulates buckwheat grain-filling, enhancing the seed-setting rates, and to understand the physiological mechanisms behind this improvement. The results indicated that EBR treatment followed the typical "S" type growth curve of crops, resulting in an increase in the Tartary buckwheat grain-filling rate. Varieties with high seed-setting rates demonstrated a greater capacity for grain-filling. EBR was observed to regulate hormone content, enhance the photosynthetic capacity of Tartary buckwheat, and increase yield. This was accomplished by enhancing the accumulation of photosynthetic products during the grain-filling period. Specifically, EBR elevated the activity of several key enzymes, including pre-leaf sucrose phosphate synthase (SPS), seed sucrose synthase (SS), late grain-filling acid invertase (AI), grain-filling leaf SPS, and grain SS. These changes led to an increased accumulation of sucrose and starch from photosynthetic products. In summary, the G2 concentration of EBR (0.1 mg/L) demonstrated the most significant impact on the seed-setting rates and yield enhancement of Tartary buckwheat.