METHOD TO DETERMINE CHILLING REQUIREMENT IN BLUEBERRIES

Abstract

A chilling study was initiated in January 1998 on 'Tifblue' rabbiteye (Vaccinium ashei Reade) and blueberry plants that had received > 500 chilling hours (<7'C). The terminal 2 flower buds from both excised stems and paired stems on plants were forced in a greenhouse and rated for floral bud development. After 23 days of forcing, flower buds from all treatments had reached stage 3, an easily recognizable stage of development. Excised stems did not differ from matching intact stems for the first 3.5 weeks of forcing, but after ?4.5 weeks of forcing in the greenhouse floral bud development ratings on excised stems were significantly lower than those on intact stems. Another study was started in October 1999 to determine the accuracy and efficiency of using cuttings from plants to determine the sufficient accumulation of chilling for bloom. In this study 2 rabbitcyc (Tifblue and Climax) and 3 southern highbush (V. corv,nbosun, x) (Jubilee, Pearl River and Biloxi) cultivars were naturally chilled. At 100 chilling hour (<7 C) intervals, plants and cuttings were placed in a greenhouse and floral development was rated weekly. In this study the rate of floral development generally did not significantly differ between buds on excised stems and stems on intact plants for the first 3 weeks of forcing. We have found that for 3.5 weeks, buds on excised stems develop the same as those on intact plants. We therefore propose that chilling requirements of a plant are satisfied if a floral bud reaches stage 3, an easily identifiable stage of flowering in which the floral apices are visible, within a 3 week period of forcing. Using this method to determine chilling hours required to break dormancy, data indicated that 'Biloxi' required 200 hours 7°C, 'Climax' - 300 hours, 'Tifblue', 'Jubilee', and 'Pearl River' - 400 hours. These data approximate field observations on blooming sequence of these eultivars. These studies indicate that floral bud development in excised stems approximate that of intact plants for a period of 3 1/2 weeks and with sufficient chilling reach a stage of at least 3 within this period of forcing. These studies indicate that cuttings from blueberry plants can be used to determine approximate chill hour requirements.