ISHS Acta Horticulturae 738: International Symposium on Biotechnology of Temperate Fruit Crops and Tropical Species
COMMERCIALIZATION OF GENETICALLY ENGINEERED PAPAYA: BREEDING PERSPECTIVES |
| Author: | R.M. Manshardt |
| Keywords: | papaya, crop improvement, conventional breeding, genetic engineering, papaya ringspot virus, pathogen derived resistance, gene silencing, commercialization |
| Abstract:
Papaya is a “breeder-friendly” plant well suited to improvement by conventional methods. However, breeding failed to produce resistance to papaya ringspot virus (PRSV) due to inadequate genetic variation within the crop and sterility in interspecific hybrids. The transgenic approach succeeded because it provides effective resistance, is genetically simple to transfer (single dominant gene), and requires no change in farming practices. Success was aided by deploying transgenic resistance in a worthy F1 hybrid cultivar (‘Rainbow’) having excellent flavor, high yield, and broad environmental adaptation. An on-going program to improve ‘Rainbow’ for resistance to Phytophthora aerial blight and other highly heritable traits is based on phenotypic recurrent selection. Virus resistance results from post-transcriptional gene silencing of the PRSV coat protein gene and is most effective against PRSV strains with high homology to Hawaiian strains. Resistance in Hawaii has held up very well since the first field tests in 1992, but dependence on a single transgene raises concern about durability. Field tests with transgenic plants suggest that resistance-breaking PRSV strains are less likely to arise by viral recombination with coat protein transgenes than by accidental introduction of heterologous PRSV strains. In the future, complex quantitative traits will continue to be enhanced through conventional breeding, aided by marker-assisted selection. Genetic engineering will be most useful for contributing new single-gene traits when natural variation is lacking within papaya germplasm. Objectives of various on-going transformation projects include extending postharvest shelf life, developing durable PRSV resistance, and creating a phenotypic marker for early sexing of seedlings. | |
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