Taxonomy, evolution and domestication of Vicia in relation to aphid resistance

Thirty Vicia species and 28 V. faba cultivars were evaluated for Aphis fabae resistance by measuring rates of aphid population increase (r_m) on the host plants. A subset of these species (22) and cultivars (five) were evaluated for resistance to Acyrthosiphon pisum and Megoura viciae. For the same subset of 22 Vicia species and all three aphid species, positive correlations were observed between the concentration and numbers of leaf and stem non-protein amino acids and the level of aphid resistance. Correlations were also observed between trichome density, on some organs of the host, and both nymphal survival and development time. Aphid resistance, together with these possible physical and chemical resistance mechanisms, showed a pattern which was described in relation to the taxonomy of the genus Vicia and the degree of domestication of the host. The least advanced Vicia species were most resistant whilst the more specialised species and those most closely related to V. faba and V. faba itself were most susceptible. Within each taxonomic group (subgenus or section), the most domesticated species were least resistant. The merits of utilising the resistance found in some V. faba cultivars and in other wild Vicia species were considered.