A taxonomic study of aphid resistance in the genus Vicia

Birch, Andrew Nicholas Edmund (1983) A taxonomic study of aphid resistance in the genus Vicia. University of Southampton, Doctoral Thesis.

Abstract

This study examined the range, taxonomic patterns and mechanisms of aphid resistance in the genus Vicia. This research was initiated because existing VVffaba cultivars are only partially resistant to aphids; however, one wild species, V. narbonensis, has been shown to be comparatively resistant and contains unusual non-protein amino acids not found in V. faba. Thirty one taxonomically selected Vicia species were screened for antibiotic resistance to Aphis fabae, Acyrthosiphon pisum and Megoura viciae. Resistance was quantified using intrinsic rate of natural increase (r and its components, on leaf and stem feeding sites. A wide range of m aphid resistance was detected within the genus, and clear taxonomic patterns of host susceptibility were evident. Total resistance was found in most perennial species, intermediate levels in annuals from both subgenera, and partial resistance, equivalent to levels reported in resistant V. faba cultivars, in most of the closest relatives of the crop plant.For all 3 species of aphid, nymphal survival rate was found to be the host critically limiting factor on highly resistant hosts; only on partially resistant hosts did development rate and fecundity influence r values. A. pisum was the most successful exploiter of the genus, A.mfabae intermediate and M. viciae most host-restricted; these differences were discussed in relation to each aphid's host range and feeding behaviour. An agronomic and taxonomic field assessment was made of Vicia species in section Faba. Vicia johannis and to a lesser extent V. narbonensis were moderately resistant to A his fabae; time of flowering, plant growth stage and degree of pubescence strongly influenced levels of resistance. A morphometaic analysis revealed that these 2 species were clearly distinct and could be identified by flower colour. Both species were assessed for yield potential, resistance to Botrytis fabae and frost tolerance.The causes of aphid resistance were examined. Thick cuticle of oroboid perennials inhibited stylet penetration of all 3 aphid species. High-ichome densities on preferred feeding sites correlated significantly with resistance to A. fabae and M. viciae but not A. pisum. The amino acid content of host tissue, especially non-protein amino acids, gave significant correlations with the performance of A. fabae and M. viciae and to a lesser extent, A. pisum; inhibition of feeding by non-protein amino acids was implied but requires further study. The usefulness and durability of resistance detected in wild Vicia species was discussed, in relation to future plant breeding programmes.

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