Chill unit models for predicting dormancy completion of floral buds in apple and sweet cherry.

Guak, S. and Neilsen, D. (2013). "Chill unit models for predicting dormancy completion of floral buds in apple and sweet cherry.", Horticulture, Environment and Biotechnology, 54(1), pp. 29-36. doi : 10.1007/s13580-013-0140-9  Access to full text

Abstract

Temperature-controlled experiments were conducted to determine the relative contribution of temperatures to dormancy completion of floral buds in ‘Gala’ apple (Malus domestica Borkh.) and ‘Sweetheart’ sweet cherry (Prunus avium L.). Shoots were collected right before chill inception, and exposed continuously to seven different temperatures in the range of −2°C and 16.8°C for 1320 hours. Chilling requirements were determined on sequential field samples from plots of days to bud break against sampling date. Temperature-response curves, which were best fit in a four parameter logistic nonlinear regression, indicated that optimum chilling temperatures were between −2°C and 5.5°C for ‘Gala’ and between −2°C and 7°C for ‘Sweetheart’, with no chilling effect above 13°C in both species. The derived chill unit models predicted that chill unit accumulations required for dormancy completion averaged 921 for ‘Gala’ and 740 for ‘Sweetheart’ over the three year period. The year-to-year variation in ‘Gala’ apple was smaller with our ‘Gala’ model than with the ‘Utah’ model (14% vs 23.5% coefficients of variation), while similar to each other in ‘Sweetheart’ sweet cherry.

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