INTEGRATION OF ENVIRONMENT, PHYSIOLOGY AND FRUIT ABSCISSION VIA CARBON BALANCE MODELING - IMPLICATIONS FOR UNDERSTANDING GROWTH REGULATOR RESPONSES

Many studies and observations on chemical thinning of apples have suggested that variations in the environment and carbohydrate supply and demand are likely components of variations in responses to chemical thinners. To address the carbohydrate component, we have developed a simplified apple tree carbon balance model that takes into account the environment, leaf area development and light interception, photosynthesis, respiration, growth demands of competing organs and fruit growth/abscission. The integration of many environmental and tree physiological factors has allowed quantitative estimates of effects of various environmental and cultural factors to be evaluated over the season, and in this report focusing on the early post-bloom thinning period. In relation to apple thinning with chemical thinners, the model suggests that there are carbon-based variations in the tree baseline sensitivity that may help explain some of the great variation in thinner response. Comparison of the patterns of post-bloom carbohydrate supply-to-demand balance and responses to chemical thinning timing trials have generally shown to be similar to thinner responses, especially during periods of particularly good or poor carbohydrate supply-to-demand balance. This suggests that carbohydrate supply-demand balance may be a baseline for thinner responses, and that integrative modeling of these balances can be useful in understanding variation in thinning responses.