Chilling and heat requirement for dormancy breaking and flowering of the plum accessions belonging to the living collection of Morocco

Abstract

The date of endodormancy release and chill requirements of twenty-eight plum cultivars (Prunus domestica L. and Prunus salicina Lindl) growing in a collection at the experimental station of the National Institute of Agricultural Research of Meknes (Morocco) were determined according to three models namely the Chilling Hours model (in Chilling Hours, CH), the Utah model (in Chill Units, CU) and the Dynamic model (in Chill Portions, CP). In this regard, the forcing tests were conducted out on floral buds of all plum cultivars in order to follow the weight of buds in field and under controlled climate conditions. The heat requirements calculation was based on counting the Growing Hours Degree between the endodormancy release date determined by forcing tests and the flowering dates observed in field for each cultivar. Significant differences were revealed in chill and heat requirements between the plum cultivars studied, ranging from 336 to 522 CH, 645 to 1,046 CU, 37.5 to 55.93 CP and 6,618 to 9,673 GDH according to Chilling Hours, Utah, Dynamic and GDH models, respectively. In addition, the results showed great variability between cultivars according to their dormancy levels, ranging from low chill and heat cultivars (INRA-PR38, INRA-PR40 and Santa Rosa) to highest ones (Stanley, Prune d’Ente, Monglobe and Fortune), which generated differences in the dates of endodormancy release and flowering process. Correlations between chill requirements, heat requirements and flowering dates have been established since cultivars with low chill requirements (also low heat requirements) have earlier endodormancy release and flowering dates in comparison to those showed high chill requirements. The results obtained in this investigation constitute a basis to improve knowledge of the plum species cultivated under Moroccan climate conditions and make it possible to determine the most appropriate cultivation areas for these cultivars, given the current and future climate change.