Glucosinolates, flea beetle resistance, and leaf pubescence as taxonomic characters in the genus Barbarea (Brassicaceae)

Abstract

Glucosinolate content of leaves and roots, diversity in leaf pubescence, and resistance to two near-isogenic lines of the flea beetle Phyllotreta nemorum with or without an R-gene, were determined for 27 accessions of 7 Barbarea taxa, i.e. B. stricta, B. orthoceras, B. intermedia, B. verna, B. vulgaris var. vulgaris, the G-type of B. vulgaris var. arcuata and the P-type of B. vulgaris var. arcuata. Four variable glucosinolate biosynthetic characters were deduced. For (formally) homophenylalanine-derived glucosinolates: (1) Presence or absence of 2-hydroxylation, and if present, R- or S-configuration of 2-hydroxylation; (2) presence or absence of p-hydroxylation; and for tryptophan-derived glucosinolates: (3) presence or absence of N-methoxyglucobrassicin; and (4) presence or absence of 1,4-dimethoxyglucobrassicin. Three phenotypes of leaf-pubescence were observed; (1) glabrous to glabrate leaves; (2) glabrous to glabrate leaves with hairs along the edge; (3) pubescent leaves. The hairs were characterized as simple by scanning electron microscopy. Full resistance to a flea beetle line (ST) was found in B. vulgaris var. vulgaris and in the G-type of var. arcuata; partial resistance was found in B. verna and B. intermedia, while the remaining taxa were fully susceptible to the ST line. All investigated Barbarea taxa were susceptible to larvae from another line containing an R-gene, indicating a similar flea beetle resistance mechanism in the three resistant species. Most Barbarea taxa could be characterized by a particular combination of the investigated characters. The most aberrant was the P-type of B. vulgaris var. arcuata, and the taxonomic status of this type should be reconsidered.