HYBRIDIZATION BETWEEN LYCOPERSICON ESCULENTUM AND SOLANUM PENNELLII: PHYLOGENETIC AND CYTOGENETIC SIGNIFICANCE

Abstract

Lycopersicon esculentum can be hybridized with Solanum pennellii to yield viable hybrids without the use of special aids, although it has been possible to make the cross only with the former as female parent. For nearly half of the many morphological character differences between the 2 species the F1 hybrids are intermediate; for about one-fifth the tomato traits are dominant; for the remainder the night shade traits are dominant. In common with both parents, the hybrids have 12 pairs of chromosomes. Despite their heteromorphy, the chromosomes of both parents pair and otherwise function in meiosis of the hybrids with nearly normal regularity. The net reproductive fertility, as measured by the number of F2 progeny produced after self-pollination of the hybrids, is about 12% of normal. Chromosomes of induced tetraploid hybrids form multivalents, but at a frequency lower than that of autoploid tomatoes. Doubling the chromosome number results in a considerably higher seed yield of hybrids- a fact that implies appreciable chromosomal differentiation between the parental species. The anomalous genetic affinity between the parents, despite their possessing the key taxonomic characters that separate the 2 genera, casts doubt on the validity of the genus Lycopersicon. The discovery of S. pennellii and its compatibility with L. esculentum opens a large field of inquiry into compatibility relations, introgression, and tomato breeding and genetics.