Genotypic response to chilling period of apple buds from two Western Cape localities

Abstract

One-year-old, ca. 40 cm long shoots of various apple cultivars were selected from commercial orchards in both the Elgin [34°S, 305 m, ca. 750 Utah Chill Units (CU)] and Koue Bokkeveld (33°S, 945 m, ca. 1300 CU) regions of the Western Cape, South Africa. Shoots were forced at a constant 25°C with continuous illumination after chilling at 4°C. The effect of chilling period on the budburst of each cultivar in both regions was estimated in 1998 and 1999 by determining: 1) % budburst; 2) the % terminal budburst; and 3) the rate of budburst [1/(days to 25% budburst)]. It was found that these indices, in reaction to chilling, differed significantly between cultivars, and within cultivars between areas. The rate of budburst was the most consistent in describing the reaction of buds to chilling and may be more useful for grouping cultivars according to chilling response.