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United States Department of Agriculture

Agricultural Research Service

Title: Sub-Freezing Temperatures Affect Chilling Accumulation in Peach

Authors
item Okie, William
item Blackburn, Bryan
item Taylor, Kathy - UGA

Submitted to: HortScience
Publication Type: Abstract Only
Publication Acceptance Date: May 1, 2003
Publication Date: August 1, 2003
Citation: Okie, W.R., Blackburn, B., Taylor, K. 2003. Sub-freezing temperatures affect chilling accumulation in peach [abstract]. Hortscience. 38(5):778-779.

Interpretive Summary: Peach trees and other temperate zone fruit crops require chilling during the winter in order to develop and bloom properly in the spring. Current chilling models assume sub-freeezing temperatures are ineffective for chilling accumulation. We tested this using twigs 12-15 inches long, cut from bearing trees and stored in plastic bags in temperature-controlled chambers. After treatment they were placed in Flora-Life in individual polystyrene vials in a room held at 15, 20 or 25C. Cuttings were rated daily for flower buds that had reached "green bud" which were then rubbed off. Lateral and terminal budbreak was noted when the shoots were visible, but not removed. In Test 1 'Juneprince' (600 hr chill rating), and 'Redglobe' (850) were cut after 130 field units of chill and stored at 4C. Weekly a set of 8 of each was moved to 15C or to 0C (for 2 wks, then to 15C). Two wks at 0C resulted in budbreak similar to those held at 4C for those 2 wks, suggesting 0C was "effective" in chilling. In Test 2 'Redglobe', 'Cresthaven' (950), and 'Contender' (1050) cuttings (field chill=615 units; 8 per treatment) were placed at -4, 0, or 5C . At 4-d increments for 20d (~100 hours of additional chilling each date), a set of cuttings was moved to the 15C room. Exposure to -4 also enhanced budbreak, although less so than to 0 or 5C. In Tests 3/4, 'Redglobe' (field chill=230 or 410 units) was stored at -16, -5, -1, or 6C; and -16, -9, -5, -4, -1, or 6C for 24/32 or 21/50/80 d. Budbreak speed and frequency was less as temperature went down. Budbreak was minimal after 24 d and 21 d treatments, but there was substantial break after the 50 d treatment, even for -5C. These results indicate temperatures well below 1C can have a beneficial effect in satisfying the chilling requirement in peach.

Technical Abstract: Current chilling models assume sub-freeezing temperatures are ineffective for chilling accumulation. We tested this using terminal twigs 16-20 cm long, cut from bearing trees and stored in plastic bags in temperature-controlled chambers. After treatment they were placed in Flora-Life in individual polystyrene vials in a room held at 15, 20 or 25C. Cuttings were rated daily for flower buds that had reached "green calyx" which were then rubbed off. Lateral and terminal budbreak was noted when the shoots were visible, but not removed. In Test 1 'Juneprince' (600 hr chill rating), and 'Redglobe' (850) were cut after 130 field units of chill and stored at 4C. Weekly a set of 8 of each was moved to 15C or to 0C (for 2 wks, then to 15C). Two wks at 0C resulted in budbreak similar to those held at 4C for those 2 wks, suggesting 0C was "effective" in chilling. In Test 2 'Redglobe', 'Cresthaven' (950), and 'Contender' (1050) cuttings (field chill=615 units; 8 per treatment) were placed at -4, 0, or 5C. At 4-d increments for 20d (~100 hours of additional chilling each date), a set of cuttings was moved to the 15C room. Exposure to -4 also enhanced budbreak, although less so than to 0 or 5C. In Tests 3/4, 'Redglobe' (field chill=230 or 410 units) was stored at -16, -5, -1, or 6C; and -16, -9, -5, -4, -1, or 6C for 24/32 or 21/50/80 d. Budbreak speed and frequency was inversely proportional to chilling temperature and duration. Budbreak was minimal after 24 d and 21 d treatments, but there was substantial break after the 50 d treatment, even for -5C. These results indicate temperatures well below 1C can have a beneficial effect in satisfying the chilling requirement in peach.

Last Modified: 10/23/2014
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