Photosynthetic Carbon Production and Use by Developing Cotton Leaves and Bolls

Understanding the photosynthetic C contribution of leaves to vegetative and reproductive processes is important in defining yield productivity. However, the morphological complexity of the cotton (Gossypium hirsutum L.) canopy has proven a significant barrier to establishing specific yield relationships. Therefore, a 2-yr study examined the developmental sequences of C production and utilization by leaves and bolls within the crop canopy. Photosynthesis of sympodial leaves reached a maximum just prior to anthesis of the subtended flower and tehrafter declined throughout the boll-filling period. Carbon budgets for individual sympodial leaves and their subtended bolls at mainstem Nodes 8, 10, and 12 indicated that C production was seldom synchronized with C utilization. Carbon import requirements for the first three fruiting positions at mainstem Node 10 were 50, 37, and 21%, respectively. Bolls at mainstem Node 8 collectivity required >60% import of C to sustain growth during the season. Only at mainstem Node 12 were leaves capable of supplying the total C needs of their subtended bolls. Carbon deficiencies at mainstem Nodes 8 and 10 suggested that substantial translocation of photosynthate from adjacent leaves and leaves outside the mainstem node was necessary. This was confirmed through short-term studies of 14 C-assimilate movement from leaves to developing cotton bolls. Breeding goals for improved yields through crop genetics. These simulations indicated an advantage of increased leaf longevity in the maintenance of C production