Studies on the mechanism of the formation of yield differences in indica- japonica hybrid rice

Optimizing planting density is crucial for enhancing the yield of indica-japonica hybrid rice by regulating yield components and population characteristics. A two-year field experiment was conducted using four indica-japonica hybrid rice varieties with three planting densities: 15.15×10⁴ hills hm^− 2 (T1), 20.83×10⁴ hills hm^− 2 (T2), and 27.78×10⁴ hills hm^− 2 (T3). Results showed that super-high-yielding varieties had larger sink capacity and stronger source compared with high-yielding varieties, while population characteristics such as top three leaves and panicle patterns varied due to genetic differences among varieties. Increasing planting density enhanced the yield of super-high-yielding varieties, primarily through increased panicle number. However, this also led to higher ineffective tiller numbers, reduced productive tiller percentage, accelerated leaf area reduction in the reproductive stage, lower flag leaf SPAD values, restricted plant growth (shorter plant height and smaller top three leaf length, width, and angle), and restricted panicle development (shorter panicle length, fewer branch pedicels, and reduced seed-setting rate, 1000-grain weight, and spikelets per panicle). Despite these limitations, the higher total spikelet number compensated for the yield gap, achieving higher yields. In conclusion, an appropriate increase in planting density enhances sink capacity and is favorable for increasing the yield of super-high-yielding indica-japonica hybrid rice.