Chilling Requirement Studies in Blueberries

Abstract

SUMMARY Two separate studies were initiated in January 1998 on Tifblue' rabbiteye (Vaccinium ashei Reade) and ‘Magnolia’ southern highbush (V. corymbosum L.) blueberry plants that had received > 500 chilling hours (7°C). In each study, the terminal 2 flower buds from both excised stems and paired stems on plants were forced in a greenhouse (17-23°C and natural daylength) and rated for floral bud development. In ‘Magnolia’, leaf removal from excised stems and intact stems resulted in an increased rate of floral bud development. After 7 days of forcing, excised stems with leaves removed showed no significant differences in floral bud development from intact plants with unabscised leaves. After 40 days of forcing, flower buds from all treatments had reached stage 3, an easily recognizable stage of development. ‘Tifblue’ stems with 5 mm basal sections removed weekly to retard vascular blockage did not differ in floral bud development from stems without basal pruning. Excised stems did not differ from matching intact stems for the first 3.5 weeks of forcing. At this time ‘Tifblue’ flower buds had reached 3.7 on the floral development scale. After >4.5 weeks of forcing in the greenhouse floral bud development ratings on excised stems were significantly lower than those on intact stems. These studies indicate that with sufficient chilling, floral bud development in excised stems without leaves approximate that of intact plants for a period of 3.5 weeks and reach at least stage 3, an easily identifiable floral stage.