Chilling and heat requirements of sweet cherry cultivars and the relationship between altitude and the probability of satisfying the chill requirements

Sweet cherry cultivars have different chilling and heat requirements for breaking rest and flowering. The knowledge of these requirements may be valuable in the selection of the appropriate cultivars for producers and to avoid losses caused by an inadequate cultivar selection in a particular area. Determination of chilling and heat requirements is also important within a breeding programme, when choosing parents to obtain early flowering cultivars. Chilling requirements of seven cherry cultivars growing in south-eastern Spain were calculated using different methods (hours below 7 °C, Utah and Dynamic model), which were compared. Recording hourly average temperatures at several locations during 2 years, the Utah and Dynamic models performed better than hours below 7 °C. Different chilling requirements and slight differences in heat requirements were observed in the studied cultivars. 'Cristobalina' and 'Brooks', the earlier-flowering cultivars, were those with the lowest chilling requirements. 'Burlat', 'New Star' and 'Somerset' had medium chilling and heat requirements for flowering, and 'Marvin' showed the highest values and also the latest blooming date. All the studied cultivars may have their chilling requirements satisfied in the region of Murcia, if grown at least 650 m above sea level. Some cultivars, such as 'Cristobalina' and 'Brooks', could successfully break dormancy already when grown at an altitude above 325 m.