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 w as conducted in 1994 and 1995 at Marianna, AR. The control treatment was pr otected by insecticide applications, while tarnished plant bugs (Lygus line olaris Palisot de Beauvois) and bollworms (Helicoverpa tea Boddie) were rel eased in the plots of the other treatment three times before flowering. Squ are abscission at the first sympodial fruiting position was 5 and 33% for t he 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 photo synthesis of the eighth main-stem leaf from the terminal leaf as compared w ith the control plants. Canopy photosynthesis recorded 4 wk after the initi ation of flowering was 21% higher in the infested plants. CO2 labeling show ed infestation also resulted in more C-14 recovered in the terminal node (t erminal 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 in crease in plant height, although node number was not affected. Since our in sert-induced abscission treatments had similar effects as manual fruit remo val treatments reported by others, future studies seem justified in using e ither approach. Early fruit loss in the U.S. Mid-south results in changes i n carbon exchange and allocation, but poor late-season growing conditions o ften prevent yield compensation.