Rice Responds to Different Light Conditions by Adjusting Leaf Phenotypic and Panicle Traits to Optimize Shade Tolerance Stability and Yield

Prolonged low-light stress during growth significantly reduces rice yield in southwest China. In order to systematically study the dynamic response of rice to long-term shading, field experiments were conducted in Chongqing, China, from 2021 to 2022, investigating the effects of 50% and 75% shading from the seedling to heading stage on morphological characteristics, physiological traits, and yield formation in 12 rice cultivars. The results showed that shading reduced tiller number, leaf mass per area, total dry mass, leaf area index, panicle number, seed-setting rate, and yield. Meanwhile, rice acclimated to low light by increasing plant height, leaf chlorophyll content, and leaf-total mass ratio. In particular, leaf width in low-light treatments was narrower under short-term shading but became wider under long-term shading compared to natural light. Moreover, under 50% shading condition, rice optimized panicle structure by increasing grain number per panicle and primary and secondary branch numbers to compensate for adverse effects. Cultivars, including Le you 918 and Shen 9 you 28, exhibited high yield and strong shade tolerance. Overall, rice acclimates to low light through the synergistic interactions of various traits, with leaf phenotypic adjustments and panicle structure optimization being crucial for improving yield under low light.