CO2 exchange rate of apple fruitlets before the abscission

Abstract

Fruit CO₂ exchange at the time of fruit setting period was evaluated on mature cv. 'Jonagold' apple trees after 4 days artificial shading with 90 % photosynthetic photon flux (PPF) reduction and after NAA 15 ppm and BA 50 ppm applied immediately after the end of shading. Light reduction which accelerated fruitlets abscission very quickly had a depressive effect on fruits CO₂ dark respiration rate (Rd) and gross assimilation rate (Ag) 3 days after the end of shading. Similarly, reduced Rd and less negative net CO₂ assimilation rate (A) was recorded on fruitlets 7 days after NAA and BA application what is explained as a diminished metabolism of fruits starting with abscission. The fruitlets from shaded trees, which did not tend to abscission any more, showed an enhanced Rd and more negative A on 7^th or 8^th day after the end of shading. Ethylene evolution from fruits 2^nd and 7^th day after NAA 15 ppm application was enhanced comparing to control fruits. BA 50 ppm enhanced ethylene evolution on 2^nd day after spraying, however on 7^th day the ethylene evolution was lower than in control fruits. Healthy, not to drop inclined fruitlets retained on trees 7 days after shading treatment, showed  stronger fruit ethylene production.