Heterosis in Upland Cotton. II. Relationship of Leaf Area to Plant Photosynthesis

Abstract

Heterosis results in a generalized increase in plant growth, yet the involvement of photosynthesis in this response is not well understood. We examined the relationship between leaf area (LA) and canopy photosynthesis of F1, cotton (Gossypium hirsutum L.) hybrids and their parents. The effect of heterosis on leaf apparent photosynthesis (AP) was also studied. Three established cultivars and three F1, hybrid progeny were examined in two field environments. Hybrid progeny had significantly greater leaf area index and canopy photosynthesis rates in both environments during the earliest plant growth stages studied. At the same time, the hybrids and their parent showed no differences in single leaf AP efficiency. Total dry matter was significantly correlated with LA (r = 0.85**, significant at the 0.01 probability level). All measurements during early growth found AP per plant to be significantly associated to LA per plant. Later in growth, the association between AP per plant and LA per plant weakened after mutual shading of leaves had developed. The data indicate that hybrids produced generally bigger plants that intercepted more light than their parents, and hence had increased photosynthesis rates on a per plant basis. Factors that affect early plant growth can result in associated changes in AP per plant and accentuate the need for prudent crop management during early development.