vulnerability of US apple (Malus) genetic resources

Apple (Malus 9 domestica Borkh.) is one of the top three US fruit crops in production and value. Apple production has high costs for land, labor and inputs, and orchards are a long-term commitment. Production is dominated by only a few apple scion and rootstock cultivars, which increases its susceptibility to dynamic external threats. Apple crop wild relatives, including progenitor species Malus sieversii (Ledeb.) M. Roem., Malus orientalis Uglitzk., Malus sylvestris (L.) Mill., and Malus prunifolia (Willd.) Borkh., as well as many other readily hybridized species, have a wide range of biotic and abiotic stress resistances as well as desirable productivity and fruit quality attributes. However, access to wild materials is limited and wild Malus throughout the world is at risk of loss due to human encroachment and changing climatic patterns. The USDA-ARS National Plant Germplasm System (NPGS) Malus collection, maintained by the Plant Genetic Resources Unit in Geneva, NY, US is among the largest collections of cultivated apple and Malus species in the world. The collection currently has 5004 unique accessions in the field and 1603 seed accessions representing M. 9 domestica, 33 Malus species, and 15 hybrid species. Of the trees in the field, 3,070 are grafted and are represented by a core collection of 258 individuals. Many wild species accessions are represented as single seedlings (nongrafted). The crop vulnerability status of apple in the US is moderate because although there are a few breeders developing new commercial cultivars who also access Malus species, threats and challenges include new diseases, pests, and changing climate combined with industry needs and consumer demands, with a limited number of cultivars in production.