Abstract: To clarify the differences in yield formation and its key influencing factors of direct-seeded rice under different altitudes in the Wuling Mountains, three experimental sites at altitudes of 430 m (Enshi City), 790 m (Xianfeng County) and 1 100 m (Lichuan City) were selected. Three hybrid indica rice varieties and three conventional indica rice varieties were used as test materials. The effects of altitude on growth duration, population tillering, dry-matter accumulation, yield-component traits and harvest index of direct-seeded rice were systematically evaluated. The results showed that with the increase of altitude, the average whole-growth duration of direct-seeded rice extended from 110 d to 136 d, and the average plant height decreased from 117.8 cm to 98.6 cm. The maximum tiller number and total above-ground biomass increased obviously, while the panicle-bearing rate and seed-setting rate decreased significantly. Analysis of variance showed that the main effects of altitude and variety were extremely significant for effective panicle number, total spikelet number, spikelet number per panicle, seed-setting rate, 1 000-grain weight and grain yield of direct-seeded rice (P<0.01). The interaction effect between altitude and variety was extremely significant for spikelet number per panicle and 1 000-grain weight (P<0.01), and significant for grain yield (P<0.05). The average grain yield at 1 100 m altitude (8.69 t/hm²) was significantly higher than that at 430 m (7.73 t/hm²) and 790 m (7.59 t/hm²). Correlation analysis indicated that altitude was significantly positively correlated with maximum tiller number, total biomass, effective panicle number, total spikelet number and 1 000-grain weight, whereas it was significantly negatively correlated with seed-setting rate. Varieties differed in their responses to altitude. Hybrid indica rice exhibited obvious overall advantages, among which Anliangyou 2 showed high and stable yield across the three altitude sites. In conclusion, high-yield potential of direct-seeded indica rice at high altitudes in the Wuling Mountains could be realized by enlarging sink size and increasing grain weight. In production, hybrid rice varieties with coordinated panicle-grain traits and strong cold tolerance should be prioritized, combined with early sowing at appropriate time and optimized water-fertilizer management.

Key words: direct-seeded rice, altitude, yield components, correlation analysis, Wuling Mountains