Morphological and molecular diversity of the wild carrot Daucus pusillus: implications for classification and ex situ conservation

Abstract

Daucus pusillus Michx. and Daucus montevidensis Link ex Spreng. are wild carrots from the Americas with unresolved taxonomic status. An investigation was carried out with accessions of D. pusillus and (or) D. montevidensis from Argentina for (i) morphological and molecular (amplified fragments length polymorphism (AFLP) and inter simple sequence repeat (ISSR)) characterization, (ii) analysis of congruence of morphological and molecular variation, and (iii) comparison of diversity for the internal transcribed spacer (ITS) region with that reported for a North American accession of D. pusillus. Twelve accessions of D. pusillus and (or) D. montevidensis — representing their geographical distribution in Argentina — and one accession each of wild Daucus carota L. and Daucus montanus Humb. & Bonpl. ex Schult. — as outgroups — were included. In the multivariate analysis of morphological diversity, two accessions were clearly differentiated; this result is not sustained by multivariate analysis of molecular diversity. Based on multivariate and molecular variance (AMOVA) analyses, D. pusillus and (or) D. montevidensis accessions were separated at the molecular level into two groups, associated with geographical origin. Because this result is not supported by morphology, the segregation into two taxa seems unjustified. In all accessions, ITS and 5.8S rDNA regions had identical sequences, which differ in one nucleotide from the corresponding sequence of the North American accession. According to the combined results, D. pusillus would be a single taxon distributed from North to South America, and D. montevidensis a nomenclatural synonym. Autogamy of D. pusillus and its highly structured genetic diversity (Fst = 0.86) allows the application of a geographically targeted approach for germplasm exploration, conservation and eventual use in pre-breeding.