First successful backcrossing towards eggplant (Solanum melongena) of a New World species, the silverleaf nightshade (S. elaeagnifolium), and characterization of interspecific hybrids and backcrosses.
Silverleaf nightshade (Solanum elaeagnifolium Cav.) is a drought tolerant invasive weed native to the New World. Despite its interest for common eggplant (S. melongena L.) breeding, up to now no success has been obtained in introgression breeding of eggplant with American Solanum species. Using an interspecific hybrid between common eggplant and S. elaeagnifolium as maternal parent we were able to obtain several fruits with viable seed after pollination with S. melongena pollen. Twenty individuals of the first backcross (BC1) generation were crossed again to the S. melongena parent and second backcross (BC2) seed was obtained for 17 of them, suggesting that most of the genome of S. elaeagnifolium is likely to be represented in the set of BC2 families. Five plants of each of the two parents, interspecific hybrid and BC1 generation were characterized with morphological descriptors and for pollen viability. The interspecific hybrid was intermediate among parents, although in overall morphological characteristics more similar to the S. elaeagnifolium parent. However, pollen viability of the hybrid was very low (2.6%). The BC1 generation was intermediate in characteristics between the hybrid and the S. melongena parent, with pollen viability increasing to an average of 19.4%. The root system of the interspecific hybrid indicated that it is able to explore larger areas of the soil than the S. melongena parent. The phenolics profile of the fruit of the two parents and hybrid revealed a higher diversity in phenolic constituents in S. elaeagnifolium compared to S. melongena, where the major phenolic compound was chlorogenic acid, while the interspecific hybrid was intermediate. By using flow cytometry it was found that S. elaeagnifolium, S. melongena, and their interspecific hybrid were diploid, although the genome size of S. elaeagnifolium was slightly smaller than that of S. melongena. Our results represent the first report of successful development of backcross generations of common eggplant with a New World Solanum species. This makes available a relatively unexplored, phylogenetically distant genepool for eggplant breeding. The backcross materials obtained can make a relevant contribution to developing new eggplant cultivars with new nutritional and environmental properties.