The new USDA-ARS/Cornell University apple rootstock breeding and evaluation program.

摘要

Apple rootstock breeding at Geneva began in 1968, and with the adoption of high-density orchard systems in North America, the programme changed the primary emphasis to developing dwarfing rootstocks with resistance to the pathogens of the northeastern United States. In 1997, the programme was reorganized through a cooperative agreement with the United States Department of Agriculture-Agricultural Research Service (USDA-ARS) with a mandate to breed and evaluate new apple rootstocks for all US production regions. The Geneva rootstock programme has developed several promising new genotypes, and the current focus of the conventional portion of the breeding programme is to produce new rootstock genotypes that retain the disease resistance of the firstgeneration of Geneva rootstocks but with improved horticultural properties. Genetic transformation of popular Malling series apple rootstocks to improve disease resistance is a new major component, and evaluations of Malling 26 with transgenes for improved resistance to the fire blight bacteria (Erwinia amylovora) are ongoing. The conventional breeding of new rootstocks occurs in stages, beginning with strong selection for disease resistance at the seedling stage. Genotypes with tolerance to fire blight, Phytophthora spp.-induced root rots, and acceptable horticultural characteristics are evaluated in orchard trials. Selections from the initial orchard trials are further evaluated in orchard trials replicated in New York, Michigan, and Washington, USA.These selections, and rootstocks from other breeding programmes, are simultaneously evaluated in controlled experiments to determine their reactions to biotic and abiotic stresses. The best selections are distributed to cooperating nurseries for stoolbed evaluations, where trees are produced for replicated trials that are planted throughout North America. Commercialization of the best new rootstock genotypes from the Geneva programme may occur as soon as 30 years from initial hybridizations.