Good Fruit Grower

June 1

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D uring his 40 years at Cornell University, Dr. Alan Lakso devised some oddly clever ways to figure out how fruit trees do the things they do. For example, he used laser beams as artificial sunbeams to observe which kinds of leaves in apple trees capture the sunlight. Earlier studies had shown that early fruit growth, around thinning time, was supported by spur leaves, not extension shoot leaves. The work with the laser beams showed that more productive orchards captured much more of the sunlight with spurs, while orchards with poor productivity captured the light with extension shoots. Lakso used full canopy balloon chambers, which involves enclosing trees in clear plastic bubbles with air flowing through. By measuring the carbon dioxide removed from the air, he could measure whole tree photosynthesis that provides carbohydrates for the tree to grow shoots, roots, and fruit. With these chambers he was able to determine how European red mites and sum- mer pruning interacted with other factors to affect fruit sizing. These tools taught him many things about trees and how they function. That information has been shared over the years with other researchers and growers, and it has affected how growers plant their orchards, prune their trees, and thin their fruit. As mentioned, leaves just below the growing shoot tips send all the energy they collect to the tips to make them grow. They're not important contributors to early fruit production until shoots stop growing. Spur leaves, on the other hand, send all their energy to fruit growing on the spurs. From that, he concluded that using the plant growth regulator Apogee (prohexadione calcium) to shorten shoots should allow more carbohydrate to go to early fruit growth, which leads to the need for harder thinning. He also found that shaded leaves not only fail to contribute to the fruit crop once they lose that ability to photosynthesize, but they never get it back even if re-exposed to light. From that, he concluded that summer pruning, while it exposes fruit to light and improves fruit color, may reduce the tree's overall ability to photosynthesize since newly exposed leaves don't help out as much as expected. "Midsummer pruning can reduce tree function and light interception," he said. "This may lead to poor fruit sizing." Dr. Alan Lakso spoke about the work of his career during the Cornell University In-Depth Fruit School in Geneva, New York, in March. He was one of six tree fruit 6 JUNE 2014 GOOD FRUIT GROWER Art to Science 5 "Low light causes fruit drop." —Dr. Alan Lakso EXPERT ON tree form and pruning D r. Alan Lakso, a research and teaching professor at Cornell University for 40 years, retired at the end of 2013. He earned a doctorate in plant physiology at the University of California, Davis, where he worked on wine grapes. After moving to Cornell, he learned pomology, he said, but continued to work with grapes. One area of focus has been on how apple orchards use sunlight, leading to improved understanding of the importance of tree form and pruning. A second area of focus has been on carbohydrate relationships in apples and how trees partition carbon to dif- ferent organs. This led to development of the Cornell Apple Carbohydrate Model (MaluSim), which is available for growers to use online to estimate tree response to chemical thinners. A third area of focus has been on fruit crop water relations. He developed an apple-specific water-use calcula- tion program, available to growers online, to give them real-time information on water use and water balance. The system commonly used uses grass as a model, and those calculations don't work well for apples, he said. Last year, he and colleagues at Cornell developed a microsensor that, when embedded into a tree's trunk, allows it to report its own level of water stress. In March, he received the Outstanding Research Career Award from the Environmental Physiology of Fruit Crops Working Group of the International Society of Horticultural Science. —R. Lehnert Alan Lakso in the field Alan Lakso devoted his career to learning about leaves and photosynthesis. by Richard Lehnert What makes apple trees tick?

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