Multivariate analysis of morphological diversity among closely related Daucus species and subspecies in Tunisia

Abstract

The genus Daucus includes about 20–25 species worldwide. Northern Africa represents a major center of diversity of Daucus, with Tunisia thought to contain 11 species and seven subspecies. The greatest taxonomic problems, however, and the greatest economic importance relative to immediate use in breeding, is in a group of species and subspecies in the Daucus carota L. clade, all containing 2n = 18 chromosomes. We assessed morphological diversity from a Daucus L. germplasm collection of nine individuals each from 45 accessions (405 individuals in total), at the National Gene Bank of Tunisia, of the following wild and one cultivated members of this clade: D. carota subsp. capillifolius (Gilli) Arbizu, D. carota subsp. carota, D. carota subsp. gummifer (Syme) Hook. f., D. carota subsp. sativus (Hoffm.) Arcangeli (cultivated), D. sahariensis Murb., and putative hybrids of D. carota subsp. carota and subsp. capillifolius. A prior study showed the effectiveness of fruit characters to identify several species and subspecies in the collection, but distinction between some closely related D. carota subspecies was difficult. In order to resolve the taxonomic classification, we tested 32 quantitative and qualitative morphological characters from leaves, stems and flowers on a field collection of 45 accessions corresponding to the different species/subspecies. The Shannon–Weaver diversity (H’) index was used to study the phenotypic diversity. The estimated H’ ranged from monomorphic for umbel type, position of involucral bracts on primary umbel, anther color, and symmetry of peripheral flowers to highly polymorphic for other traits. The highest (0.98) and the lowest (0.26) H’ values were recorded for flowering pattern within plants and foliage coverage. Multivariate analyses of principal components and dendrograms of all data and canonical discriminate analysis of the quantitative data supported the subdivision of the Daucus collection into five groups with various degrees of distinctness: (1) D. sahariensis, (2) D. carota subsp. capillifolius, (3) D. carota subsp. carota, very similar to (4) D. carota subsp. gummifer, and (5) D. carota subsp. sativus intergrading with putative hybrids between D. carota subsp. capillifolius and D. carota subsp. carota. Individual character state distribution plots provide useful characters and insights into taxonomic problems in the D. carota clade that we here discuss in reference to ongoing molecular studies in Daucus.