ASHS 2025 Conference

Lack of winter chill accumulation is a major limiting factor for blackberry production in regions with mild or absent winters. For blackberry buds to release endodormancy they must be exposed to a range of temperatures between 0-7°C for a period of time that is genotype-specific. Insufficient chill in blackberries results in incomplete bud development, irregular budbreak, extended flowering periods, nonsynchronous fruit set, and lower fruit yields. The University of Arkansas Division of Agriculture (UADA) Fruit Research Station, located in Clarksville, Arkansas, experiences 1000 hours of annual chill each year, inhibiting the identification of low chill germplasm in the Arkansas Fruit Breeding Program. This study compares two methodologies for determining chilling requirements in six blackberry cultivars (Von, Natchez, Navaho, Ouachita, Sweet-Ark® Ponca, and A-2491T). Long-cane blackberry plants were exposed to controlled artificial chilling in a cooler, with removal at six weekly intervals from 0 to 840 hours, followed by exposure to forcing conditions in a heated greenhouse. Concurrently, field-grown plants of the same cultivars were exposed to naturally occurring chill hours in the field with six stem cuttings per genotype collected biweekly and forced under a mist bed in a heated greenhouse. The number of buds broken, reproductive laterals, and open flowers were recorded on a weekly basis for both methods. Results indicated that both methods effectively differentiated chilling requirements across cultivars, with budbreak and flowering progressing more rapidly and synchronously once plants reached their cultivar-specific chilling requirement. This study aims to identify an effective, repeatable method of evaluating blackberry chilling requirement in Arkansas to inform breeding decisions and identify low chill material in UADA blackberry germplasm.