HYBRIDIZATION STUDIES ON FOUR HEXAPLOID SOLANUM SPECIES IN SERIES DEMISSA BUK

Abstract

The presence of a polyploid series of species in the tuber-bearing Solanums was first demonstrated by Smith (1927) and confirmed by Rybin (1930). The basic chromosome number was considered to be 12, and in addition to numerous diploid, triploid, tetraploid and pentaploid species these authors found one hexaploid, Solanum demissum Lindl. (2n=72). In point of fact the haploid number of 36 had already been noted by Salaman (I926), though the full significance of S. demissum as a higher polyploid was not at that time realized. Until quite recently S. demissum, which is a wild blight resistant species from the high mountains of Mexico, was the only hexaploid known in this group. In the last two or three years, however, four other hexaploid species have been discovered, namely S. brachycarpum Corr., S. guerreroense Corr., S. spectabile (Corr.) Hawkes and S. moscopanum Hawkes. The first three of these are, moreover, quite closely related to S. demissum in their morphological features. Yet, as we shall attempt to show in the present communication, they behave as good species, forming infertile hybrids with each other and with S. demissum. The taxonomic grouping, together with the geographical distribution and a reference to the first published chromosome counts, is given in Table i.