Breeding for Cold Hardiness: Searching for Genes to Improve Fruit Quality in Cold-hardy Peach Germplasm

Abstract

STRATEGY FOR IMPROVING PEACH GERMPLASM The generation of cold-hardy cultivars with high-quality fruit has long been a goal of peach breeding programs. While progress has been made, these traits have been difficult to combine by traditional breeding methods. Both cold hardiness and fruit quality are general terms that encompass various specific traits, many of which may be quantitatively inherited. Thus, many generations of hybridization and selection are required to combine several favorable alleles for both of these characteristics. Moreover, certain aspects of cold har-diness may be physiologically or morphologically incompatible with certain aspects of fruit quality, and/or major genes responsible for certain aspects of cold hardiness may be closely linked with partic-ular genes influencing fruit quality. Advances in plant regeneration, molecular biology, and gene transfer (Broglie et al., 1984; DeBlock et al., 1984; Fillatti et al., 1987; McGranahan et al., 1988; Murai et al., 1983; Parsons et al.. 522 1986) suggest a novel strategy for the development of cold-hardy, high fruit quality cultivars: the manipulation of specific traits through genetic engineering. Such a strategy would allow breeders to ma-nipulate selectively genes that affect cold hardiness or fruit quality through gene transfer without the necessity of the sexual cycle and the recombination of genes that results from this process. We have chosen not to attempt manipulation of cold-hardiness traits for the following reasons: a) Little is understood about the enzymology of cold hardiness. Without this knowledge, the cor-relation of gene expression with cold hardiness is difficult, at best. b) Cold hardiness encompasses various tolerance or avoidance mechanisms, including early dormancy in the fall, low-temperature resistance in midwinter, delayed response to warming temperatures, and late blooming. The physiological and genetic relationships of these factors are not known. In any particular climatic situation, one of these factors may have an overriding effect on hardiness not evident under a different set of cold stress conditions. c) Cold har-HORTSCIENCE, VOL. 26(5), MAY 1991