STRUCTURAL HYBRIDITY IN A TUBEROUS SOLANUM HYBRID

Abstract

A hybrid between S. morelliforme and S. clarum, both distinct diploid (2n = 2x = 24) Solanum species, is shown to be heterozygous for a chromosome interchange and possibly two inversions. This situation, common in some genera, is extremely rare in Solanum. In an F2 progeny of 13 plants 5 were interchange heterozygotes; all but one of the 13 showed failure of chromosome pairing despite having high chiasma frequencies. In three morphological and five biochemical characters scored, there was segregation in four cases, and of these, leaf index and flower number gave clear indications of transgressive segregation. Apart from flower color and an unidentified phenolic compound in the leaves, – both characters derived from S. clarum – all characters showed a dominant effect of S. morelliforme, the female parent.A single case of structural hybridity does not necessarily mean that chromosomal rearrangements have played a part in the differentiation of the parent species. It does, however, illustrate the point that the chromosomal mechanism necessary to reveal gross structural hybridity can exist in diploid Solanum species suggesting therefore that the regularity of chromosome behavior observed in species and in species hybrids does in fact reflect a true absence of gross structural hybridity.