Plum

Abstract

There are 19-40 species of plum, depending on taxonomist, that have originated in Europe, Asia and America. From this great diversity only two species, the hexaploid European plum (Prunus domestica) and the diploid Japanese plum (P. salicina and hybrids), are of worldwide commercial significance. The European plums were cultivated in Roman times and stone remnants indicate human use 6,000 years ago. Their origin is uncertain but may have involved P. cerasifera and possibly P. spinosa as ancestors. The rich diversity and history of European plums is reflected in the many pomological groups including Prunes, Gages, Mirabelles, Damsons, Bullaces and St Juliens. Today, European plum breeding concentrates on selection for resistance to Sharka disease caused by the Plum Pox Virus which limits production in many countries. Resistant cultivars have been developed using both conventional and genetic transformation techniques. Japanese plums originated in China but were introduced to the west, from Japan, only 150 years ago. Luther Burbank hybridised them with other plum species with the result that most modern cultivars are multi-species amalgams. This heterogeneity, plus the high heterozygosity from outcrossing, means that large seedling populations are required in cultivar development. Efficient cross-pollination and seedling management techniques are required for these large populations. The trend of interspecific hybridisation continues today with four of the top 20 Californian cultivars being interspecifics involving plum and apricot. Fruit quality, functional food value, productivity and adaptation through disease resistance, chilling requirement and phenology are selection criteria in both Japanese and European plum breeding. Molecular markers are used for selection of self-compatibility and nematode resistance and for diversity and taxonomic studies. Most new rootstock releases are clonally propagated and of interspecific origin. The priorities for plum and peach rootstock breeding are similar and rootstocks developed for peach are sometimes also used for plum. American plum species, ancient Oriental cultivars and autochthonous European cultivars represent important germplasm resources that require preservation for use in future breeding.