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United States Department of Agriculture

Agricultural Research Service

Title: Interaction of chill and heat in peach flower bud dormancy

Authors
item Okie, William
item BLACKBURN, BRYAN

Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: June 20, 2008
Publication Date: July 15, 2008
Citation: Okie, W.R., Blackburn, B. 2008. Interaction of chill and heat in peach flower bud dormancy [abstract]. American Society of Horticultural Science Annual Meeting, July 21-24, 2008, Orlando, Florida. HortScience. 43(4):1161.

Interpretive Summary: Time of bloom in peaches is determined by the chilling requirement of the variety, as well as the weather during the winter. Growers must choose a variety with a chilling requirement that matches the typical weather where it will be grown, so it will bloom at an appropriate time. Observations over 5 years on orchard shoots (using varieties 'Flordaprince', 'Flordadawn', 'Flordaking', 'Juneprince', 'Sunland', 'Redglobe', 'Cresthaven', and 'Contender') cut at weekly intervals consistently showed that as the field chilling increased, percentage of flower buds able to break increased while time to bud break (days at 18 °C) decreased. No bud break occurred if shoots were more than about 150 chill units below their standard chill requirement. It appeared that artificially supplied, incremental chilling dramatically reduced heat unit requirement to bud break when the shoots were under-chilled, but the effect diminished as buds received more chilling. As with naturally-chilled shoots, the percentage of bud break increased as chill increased, suggesting that the buds on a single shoot have a wide range of chill requirements. This response curve may be useful in developing a peach chilling model that better accounts for the transition between chilling accumulation and heat accumulation.

Technical Abstract: Peach bud dormancy requirement is a critical factor in selecting adapted cultivars, but the dormancy process is not well-understood. The Utah model proposes bloom occurs after a cultivar-specific amount of chilling followed by 5000 heat units above 4 °C. This model works well in colder climates, but is difficult to apply in moderate climates where chilling is interspersed with extended warm spells. Observations over 5 years on orchard shoots ('Flordaprince', 'Flordadawn', 'Flordaking', 'Juneprince', 'Sunland', 'Redglobe', 'Cresthaven', and 'Contender') cut at weekly intervals consistently showed that as the field chilling increased, percentage of flower buds able to break increased while time to bud break (days at 18 °C) decreased. No bud break occurred if shoots were more than about 150 chill units below their standard chill requirement. However these results are confounded by the effects of heat during the chilling process and vice versa. We studied the response (18 °C days to greeneye stage) of 40 cm long excised shoots ('Juneprince', 'Goldprince', 'Redglobe', and 'Blazeprince') cut early in the chilling process and stored at 4 °C to provide additional chilling. The response curve was hyperbolic, with time to initial bud break declining from 4-5 weeks for minimally chilled buds, down to 7-10 days for buds with extended chilling. It appeared that incremental chilling dramatically reduced heat unit requirement to bud break when the shoots were under-chilled, but the effect diminished as buds received more chilling. As with naturally-chilled shoots, the percentage of bud break increased as chill increased, suggesting that the buds on a single shoot have a wide range of chill requirements. This response curve may be useful in developing a peach chilling model that better accounts for the transition between chilling accumulation and heat accumulation.

Last Modified: 9/10/2014
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