Cotton photosynthesis and carbon partitioning in response to floral bud loss due to insect damage

To understand better cotton (Gossypium hirsutum L.) plant compensation for early-season floral bud (square) loss due to insect damage, a field study was conducted in 1994 and 1995 at Marianna, AR. The control treatment was protected by insecticide applications, while tarnished plant bugs (Lygus lineolaris Palisot de Beauvois) and bollworms (Helicoverpa tea Boddie) were released in the plots of the other treatment three times before flowering. Square abscission at the first sympodial fruiting position was 5 and 33% for the control and infested plants, respectively, and yield was reduced 21% by insert infestation. Insect treatment resulted in 4% more light penetration through the canopy, which may have contributed to the 17% increase in photosynthesis of the eighth main-stem leaf from the terminal leaf as compared with the control plants. Canopy photosynthesis recorded 4 wk after the initiation of flowering was 21% higher in the infested plants. CO2 labeling showed infestation also resulted in more C-14 recovered in the terminal node (terminal leaf plus main stem above the terminal leaf) and less remaining in the branch at the same node as the source leaf, which corresponded to an increase in plant height, although node number was not affected. Since our insert-induced abscission treatments had similar effects as manual fruit removal treatments reported by others, future studies seem justified in using either approach. Early fruit loss in the U.S. Mid-south results in changes in carbon exchange and allocation, but poor late-season growing conditions often prevent yield compensation.