Quality traits

The absence of seeds is a desirable trait in a number of fruit crops including eggplant. Parthenocarpic mutants have been identified in several plant species, but their use for generating parthenocarpic varieties is limited by the reduction of fruit set and fruit size. The parthenocarpic trait is polygenic and it proves cumbersome in breeding programmes.⁷⁹ For these reasons biotechnology may prove to be an interesting alternative method. Transgenic eggplants expressing the coding region of the iaaM gene from Pseudomonas syringae driven by an ovule-specific promoter show parthenocarpic development.⁸⁰ The iaaM gene codes for an indolacetamide monoxygenase that converts tryptophan to indolacetamide, a precursor of the plant hormone auxin.⁸¹ Transgenic plants produced seedless fruit of marketable size when the flowers were emasculated or in adverse conditions when untransformed lines where unable to set fruit. The comparison of three hybrids, transgenic for the iaaM gene, with untransformed hybrids and a commercial parthenocarpic cultivar in winter in an unheated greenhouse showed that the yield of the transgenic hybrids was increased by ca. 25%even in the absence of fruit set hormonetreatment.⁷⁹ A 10%reduction in the cultivation costs was also observed. It is concluded that the iaaM gene is a powerful biotechnological tool for generating parthenocarpic eggplants that proves to be superior to the use of both agricultural practices and traditional genetic methods.