James N. Cummins

Breeding Apple Rootstocks

The ancient art of grafting makes it possible to fuse two or more different genetic entities into a single tree. Grafting permits the selection of a scion for its horticultural excellence and its adaptations to the aboveground environment—its capacity to produce high quality fruit ripening at a particular season and to survive the vicissitudes of weather and pests. About 250 years ago, apple growers began to recognize that grafting also permitted the selection of specific rootstocks for their capacities to influence favorably the productivity characteristics of the scion cultivar and for their abilities to survive the edaphic, climatic, and biotic components of the rootstock environment. Thus the 2- or 3- or 4-part tree can more easily possess diverse favorable attributes than can a fruiting cultivar on its own roots.

Pome Fruit Genetic Pool for Production in Warm Climates

Two basic factors determine the adaptation of pome fruit to warm climates: 1. the ability of a given species/cultivar to break bud, bloom, set fruit, and grow satisfactorily, naturally or under proper cultural practices; and 2. the ability to produce quality fruit in temperatures during growth and ripening that are higher than the optimum for most cultivars.

Breeding rootstocks for tree fruit crops

Abstract Identification of problems and prioritising breeding objectives based on those problems are essential first steps in a rootstock improvement program. For all tree fruits, incorporating resistances to critical diseases and pests will facilitate fruit production in a social environment demanding reduction in pesticide usage. Diseases caused by various Phytophthora species are important and can be catastrophic for all major tree fruit crops; breeding for resistance to Phytophthora has generally been successful. Very large initial seedling populations are required to permit suitably rigorous early screening; the breeding team should anticipate odds of l:104to 1:106 that any given seedling will be commercially successful. In preliminary orchard tests, positive selection for dwarfing and precocity induction can be made by the fifth year. More rigorous second tests should be made with a number of commercial varieties in several locations. Although almost all rootstock improvement programs now rely on co...