Breeding strategies for developing temperate fruits for the subtropics, with particular reference to Prunus

A strategy for breeding low-chill temperate fruits should contain elements that are common to all successful fruit breeding programs. In addition it will contain elements that are uniquely required because of the particular climatic conditions in the subtropics. The longer growing season and higher temperatures in subtropical compared to temperate locations may influence breaking of dormancy, tree vigour, flower bud formation, pollination, flowering, fruit setting, fruit maturation and fruit quality. There are many fruit and tree traits that need to be incorporated in the breeding population in order to produce well adapted and well accepted fruits. Location of a suitable source of the low-chill characteristic from within or outside the species is the first requirement in developing adapted cultivars. Studies in many temperate fruit crops report that chilling requirement is a moderate to highly heritable characteristic indicating that breeders will make rapid genetic gain for lower chilling through selection of parents based on phenotype and recurrent mass selection. Blind nodes of peach causes low yields in the subtropics but can be reduced through breeding and selection. Self-fertility is another trait that may be useful in subtropical temperate fruits as there can be difficulty in selecting pollenizers that will overlap in bloom in all locations and years. Fruit quality traits must also be considered in relation to consumer, grower and agent requirements. These traits must be prioritised so that selection intensity can be focussed on the most important traits. Selection is best practised at the location where adaptation is required.