Optimization of row-ratios in mechanized hybrid rice seed production: a study on pollen dispersal and seed-setting characteristics at two ecological sites

Ziyu Li¹Guangyi Chen¹Wei Li¹Hong Yang²Pengwang Guo³Conghua Zhu¹Li Zhang¹Yao Zhang⁴Junqi Yu¹Xi Luo¹Tian Li⁴Ouyang Yuyuan^1*Xuyi Li^1*

• ¹Institute of Crop Sciences, Sichuan Academy of Agricultural Sciences, Chengdu, Sichuan, China
• ²South China Agricultural University College of Agronomy, Guangzhou, China
• ³Sichuan Agricultural University Rice Research Institute, Chengdu, China
• ⁴Sichuan Agricultural University College of Agronomy, Chengdu, China

To explore the optimal row-ratio in mechanized hybrid rice seed production, a field experiment was conducted in 2024 at Qionglai and Mianzhu using ‘Tiantai A’ × ‘Taihui 808’. Three row-ratio treatments (H1: 18:6, H2: 24:6, H3: 30:6) were tested using agricultural unmanned aerial vehicles (AUAVs) for pollination assistance. Results showed that row-ratio had little effect on sterile line flowering dynamics. The index of flowers meeting (IFM) was 0.71-0.72 at Qionglai and 0.81–0.86 at Mianzhu, with 11-12 days of flowering duration. As the row-ratio increased, total pollen quantity in the panicle layer and grain filling rate (GFR) decreased, while grain infection rate (GIR) increased. Responses of grain blighted rate (GBR), grain empty rate (GER), and fertilization success rate (FSR) to row-ratio varied between sites. Pollen density and GFR followed the pattern of near region (NR) > central region (CR) > far region (FR). Within the panicle, pollen density was generally highest in the upper panicle layer (UPL), followed by the middle (MPL) and lower (LPL) layers, with partial exceptions observed in the H2 and H3 treatments at Mianzhu. The vertical distribution of GFR varied by site: at Qionglai, it was apical parts of panicle (APP) > median parts (MPP) > basal parts (BPP), whereas at Mianzhu, the order was MPP > APP > BPP. With wider row-ratios, yield per unit area (YUA) and GFR declined (H1 > H2 > H3), while 1000-grain weight increased or decreased then increased. Under H1, yields reached 2107.50 kg ha⁻¹ at Qionglai and 2201.62 kg ha⁻¹ at Mianzhu, 4.18% and 3.18% higher than H2, and 6.74% and 5.77% higher than H3. However, the equivalent monoculture yield per hectare (EMYH) increased with wider row-ratios (H3 > H2 > H1). Under H3, equivalent yields were 1645.43 kg ha⁻¹ at Qionglai and 1734.59 kg ha⁻¹ at Mianzhu, increasing by 4.10% and 1.68% over H1, and 5.05% and 1.62% over H2. In summary, although wider row-ratios reduced pollen supply and GFR per sterile row, the increased number of sterile rows compensated, enhancing total seed production. Thus, the 30:6 row-ratio (H3) is recommended for optimal yield.