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28 WINES&VINES September 2017 Viewpoint D eveloping a long-term physiology research pro- gram that has relevance to practical fruit produc- tion requires an integrated approach of studying the physiology of practical problems as well as generating fundamental knowledge of physiologi- cal principles that underpin practice. My program emphasized understanding of the physiological principles of carbon and water physiology, especially integrated with growth and de- velopment, environmental responses and interactions with cultural practices. As such, we have used many different re- search methods, from measuring growth, organ and whole- plant gas exchange, soil and plant water relations, and root growth and development. The emphasis on understanding physiological principles is informed by a quote from Ralph Waldo Emerson: "The value of a principle is in the number of things that it will explain." This can be manifested in not only explaining past results, but also in being able to better predict results under different condi- tions. To help with both of these, I incorporated modeling into my program, integrated with measurements. Modeling has been an extremely valuable research tool for several reasons. Models can help integrate measurements taken only at intervals, evaluate the state of knowledge of our systems, elucidate the key processes regulating system behavior, help understand system dynamics and predict performance under differing conditions. Of course, as great simplifications of complex systems, they are rarely precise. However, the usefulness for specific questions is more im- portant than absolute accuracy. Finally, it is important to understand that models do not produce answers, only quan- titative hypotheses to test. I have addressed many issues in 40 years of research, but three examples indicate how physiology can be useful to practical farming. Apple thinning I developed a simplified, dynamic, daily time-step, carbon supply-demand simulation model with versions for grapes (VitiSim) and apples (MaluSim) to estimate plant photosyn- thesis, respiration and organ growth. This model is used to examine seasonal patterns of carbon supply-demand balances and look for carbon deficits or excesses at critical periods of fruit development. It was found that in one growing season there were major fluctuations in carbon supply versus demand in both grapes and apples, and that they helped explain key growth and development processes. The MaluSim model was developed to integrate occasional measurements of leaf function, shoots and fruit growth and organ respiration through the season, and to see if there were major supply-demand variations related to productivity. Com- pared to measurements, the model has given very good esti- mates of dry matter production and realistic behavior. The model identified a period about one to three weeks after bloom, when an apple tree would be under carbon deficit due to the extreme demand of the excess number of young fruitlets. Weather such as cloudy, warm periods of several days at that time, which can lead to natural fruit drop and strong response to chemical thinners, caused clear carbon deficits. Collaboration with Terence Robinson, a management spe- cialist on apple thinning, demonstrated that the carbon bal- ance of an apple tree could be a useful tool to assess the tree sensitivity to chemical thinners. We currently have an online system for growers to run the model simulation and make adjustments in thinners to obtain more precise crop adjust- ment. This has been very useful as a decision-support tool for apple growers and an example of how understanding physiological pro- cesses of importance to fruit production can lead to useful management tools. Effects of pruning on grapes The Concord juice indus- try in New York has not seen significant increases in price paid per ton of grapes in more than 40 years. This has led to great efforts to reduce production costs, mechanize and increase sus- t a i n a b l e yields. n DR. ALAN LAKSO Perspectives on Applied Physiology in Support of Viticulture S. LAKSO