A Study of Chilling Factors on Taxa of Red Maple (Acer Rubrum L. and Acer X Freemanii E. Murray)

Abstract

The objectives of this research were to (1) determine the response on budbreak of red maples to natural (ambient) chilling versus constant (forced) chilling; (2) determine the response on budbreak of red maples of forced chilling of red maple at various refrigeration unit settings; and (3) determine the response on budbreak of red maples of incremental chilling totals at various refrigeration unit settings. In the first study, the rate of percent budbreak in container-grown red maple (Acer rubrum L.) trees that were chilled in a 7E C (45° F) cooler was compared to red maple trees that were chilled naturally outdoors. The experiment was carried out during the fall of 2002 and the winter and spring of 2003. The red maple trees were placed in a 22E C (72E F) greenhouse after accumulating 600, 800 and 1000 total chilling hours. In January of 2003 percent

budbreak was visually determined and recorded every four days until all trees reached 100 percent budbreak. The trees were moved out of the greenhouse and placed outdoors under irrigation as they reached 100 percent budbreak. Statistical analysis of these data showed no difference between the rate of budbreak in the red maples receiving 600 hours of chilling in a 7E C (45E F) cooler and those that received 600 chilling hours outdoors. The same results held true at the 800 chill hour level and the 1000 chill hour level. Comparison between the three levels of cooler chilling (600, 800, 1000 hours) showed no difference in percent budbreak over time. Comparison between the three levels of natural chilling (600, 800, 1000 hours) showed no difference in percent budbreak over time. In the second study the rate of percent budbreak in container-grown red maple (Acer rubrum L.) trees chilled in three coolers with temperature set points of 1.7° C, 4.4° C and 7° C (35, 40 and 45° F) respectively was calculated. The experiment was carried out during the fall of 2002 and the winter, and spring of 2003. Trees were placed in a 22E C (72E F) greenhouse after accumulating 500 to 1000 chilling hours in 100 hour increments. In January of 2003 percent budbreak was visually determined and recorded every four days until all trees reached 100 percent budbreak. The trees were moved out of the greenhouse and placed outdoors under irrigation as they reached 100 percent budbreak. Statistical analysis of these data showed no significant difference between the 3 levels of forced chilling 1.7° C, 4.4° C and 7° C (35, 40 and 45° F) for percent budbreak over time.