Submitted to: In Vitro Culture and Horticulture Breeding Symposium
Publication Type: Abstract only
Publication Acceptance Date: 10/18/2004
Publication Date: 6/4/2005
Citation: Scorza, R., Ravelonandro, M. 2005. The opportunities and challenges of genetic engineering for improvement of perennial tree fruit - plum pox virus resistant plums as a case study. In Vitro Culture and Horticulture Breeding Symposium. In Vitro 41:14A (abstract P-8). Interpretive Summary:
Technical Abstract: Tree fruit breeding is an inherently long-term process. The average generation time can range from 2 to 20 years, depending on the species. While the production of large numbers of progeny favors the appearance of rare but desired recombinants, large tree size limits the number of progeny that can be planted and maintained. Significant genotype x environment interactions require multiple test sites for selections, which in turn, require vegetative propagation and years of tree growth to resume evaluations. Breeding for disease resistance adds unique challenges related to variability in virulence of pathogen genotypes, environmental effects on the pathogen, and pathogen-vector-host interactions. Importantly, disease resistance of a clone has practical, economic value, only if yield and fruit quality, storage, and shipping characteristics are commercially acceptable, if not superior, to currently grown cultivars. In the face of these difficulties, tree fruit breeding for disease resistance has persisted with varying levels of success, depending upon the host and pathogen species. Our research program has, for a number of years, been concerned with the problem of tree fruit virus diseases. While fruit species are affected by a number of viral pathogens, few have affected the fruit industry as significantly as plum pox virus, the causal agent of sharka disease. Plant quarantine and eradication have been the methods of control for this disease, and the effects of sharka have been devastating, particularly for plum and apricot growers. While resistance has been identified in some Prunus germplasm, the effectiveness of resistance and its multigenic nature have slowed progress in the incorporation of such resistance into new varieties. Genetic mapping and marker-assisted selection offer new possibilities for resistance breeding but will not provide a panacea. An important approach to resistance breeding is the use of gene transfer, again, not as a panacea for plant improvement, but as an important tool to be combined with other plant improvement technologies. The potential for genetic transformation and, in particular, the use of gene-silencing technology for the control of plum pox virus in transgenic plums will provide an example of the opportunities and challenges of this technology for virus disease resistance development in woody perennial tree fruit species.