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ISHS Acta Horticulturae 884: XI International Symposium on Plant Bioregulators in Fruit Production

TEMPERATURE BEFORE AND AFTER APPLICATION OF CHEMICAL THINNERS AFFECTS THINNING RESPONSE OF 'EMPIRE' APPLE TREES

Authors:   D. Kviklys, T. Robinson
Keywords:   Malus × domestica, fruit set, sunlight, carbohydrate balance
DOI:   10.17660/ActaHortic.2010.884.67
Abstract:
Seven-year old potted ‘Empire’ apple trees on M.9 rootstock were treated with one of 9 temperature regimes for a 10 day period when fruitlets were between 7 and 16mm at Geneva, NY. When fruit size was 7 mm, trees were placed in one of three glasshouses with different day/night temperature regimes (15/7.5°C; 22/15°C; 29/22.5°C). A second control group of trees was maintained outside. Light intensity in the glasshouses averaged 30-35% of outside light. The trees were maintained in the glasshouses for an initial 5 days and then removed for application of chemical thinners (either 7.5 mg Napthaleneacetic acid (NAA)•L-1 + 1240 mg Carbaryl•L-1 or 100 mg Benzyladenine (BA)•L-1 + 1240 mg Carbaryl•L-1) when fruits were 12 mm in diameter. A third group of trees was untreated. Trees in the field were also sprayed with either NAA + Carbaryl or BA + Carbaryl or left unsprayed. Following the application of chemical treatments, the glasshouse trees were reassigned to one of the three temperature regimes and placed again in the glasshouse rooms for 5 days. At the end of the 5 days treatment period the trees were moved back to the field for the rest of the season. Fruit set was more affected by temperatures after application of chemical thinners than temperatures before application. High temperatures for 5 days post chemical treatment had a large negative effect on fruit set. Cool temperatures for 5 days post chemical treatment had a positive effect on fruit set compared to the set at intermediate temperatures. We also estimated carbohydrate supply to the growing fruitlets by using the temperature and light levels of each glasshouse room and outside values using the Lakso carbohydrate supply/demand model. Carbohydrate balance during the 5 days after application of chemical thinners was positively related to fruit set. The addition of chemical thinners reduced fruit set at all carbohydrate balance levels but for each chemical there was a linear relationship between carbohydrate balance and fruit set.
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