Genetic and biosystematic studies on two new sibling species of Lycopersicon from interandean Perú

Abstract

All available accessions of the entity previously named "L. minutum" and described by Chmielewski were investigated biosystematically. All such lines can be unequivocally classified into two elements that are morphologically distinguished, chiefly by differences in flower size and exsertion of the stigma. The stigmas of the large-flowered type are strongly exserted; those of the smaller, slightly or not at all. Both forms are sporadically dispersed in the central and northern Peruvian Andes, east of the continental divide. They are sympatric and often cohabit in the Apurimac-Ayacucho-Cuzco region. Despite this overlap of ranges and intermingling, intermediate types have not been found in nature, although they can be produced experimentally by reciprocal crosses between the two forms. The F1 hybrids are highly fertile, but seeds produced by self-pollination germinate poorly.Variation at the individual, populational, and higher levels was assessed in progeny tests of wild plants by analysis of 14 enzyme loci, of which eight proved to be polymorphic. The two taxa could be entirely distinguished by alternative alleles of Got-3; perfect agreement was also found in the sympatric region for alleles of Prx-3; a variable degree of differentiation exists at the other polymorphic loci. For the small-flowered taxon, all tested individuals were homozygous, and all members of a single population had identical genotype; furthermore, only limited differences at two loci were found in the eight tested accessions. In contrast, the larger-flowered type exhibits considerable variation in terms of intra- and interpopulational polymorphy, heterozygosity, and other evidence of outcrossing. With the aforementioned exception, all allozymes detected in the smaller-flowered form are known in the larger-flowered type. All evidence from flower morphology and measures of variability consistently alludes to appreciable outcrossing in the latter and strict autogamy in the former. Considerations of all lines of evidence lead to the conclusion that the self-pollinated entity is sufficiently differentiated from the outcrosser to deserve specific status. The former is named L. parviflorum, the latter, L. chmielewskii, and Latin diagnoses are presented. It is most likely that L. parviflorum evolved sympatrically from L. chmielewskii by virtue of its acquiring autogamous reproduction - an isolating mechanism that is apparently reinforced by poor reproductivity of the interspecific hybrids.