Low light stress at tasseling threatens high-density maize production by impairing silk emergence

Shading during the maize tasseling stage caused significant yield loss, particularly under high planting densities. Silk emergence was the primary determinant of kernel number under shading stress at tasseling. Shading inhibited silk growth by impairing sugar metabolism and disrupting hormonal balance in the silks. Low light stress during the flowering stage has become a limiting factor in high-density maize production. Understanding the combined effects of shading and planting density on maize yield is essential for improving productivity. A three-year field experiment was conducted using six consecutive days of shading (25% light transmittance) initiated at tasseling, under three planting densities (4.5, 6.75, and 9.0 plants m −2 ; D1, D2, and D3). Grain yield, photosynthetic rate, stem carbohydrate availability, silk growth dynamics, and sucrose metabolism and hormonal changes in silks were measured. Results indicated that shading-induced yield penalties were more severe at higher planting densitiy. Compared with ambient light conditions, shading reduced maize yield by 57.9, 59.0, and 84.2% at D1, D2, and D3, respectively, across the three years. The reduction in kernel number per ear was the primary cause of yield decline. The occurrence of barren ear tips indicated ovary fertilization failure rather than post-fertilization grain abortion. Pollen viability remained unaffected by shading, whereas the number of silks emerging from the husk declined significantly, especially at higher densities. A strong positive linear correlation was observed between kernel number per ear and emerged silk count ( R 2 =0.94). Furthermore, random forest analysis identified the number of emerged silks as the most influential factor affecting kernel set. These findings together indicated that silk growth arrest determined final kernel number under shading at tasseling. Further analysis revealed that shading induced carbon deficiency in maize, reducing sucrose content in silks. This disruption impaired hormone-mediated cell expansion and consequently limited silk growth. The mechanism of yield loss under the synergistic interaction of shading and planting density was thus elucidated, with silk growth arrest governing final kernel number. Paying attention to accelerating silk growth is critical for maize production under low light conditions caused by high planting density, continuous rainfall, or similar stresses.