The expression of components of seedling resistance to Erysiphe graminis f. sp. tritici in Triticum timopheevii and a hexaploid derivative

The expression of components of resistance to three isolates of Erysiphe graminis f.sp. tritici was investigated on the primary seedling leaves of nine lines of Triticum timopheevii, one line of the wild ancestor T. araraticum, and a hexaploid derivative from T. timopheevii, CI12633. Wheat cv. Nord Desprez was used as a susceptible control with no known major gene for powdery mildew resistance. The expression of resistance was studied 72 h after inoculation to investigate the efficiency of a sequence of barriers to fungal penetration and development: cuticle; papilla; epidermal cell hypersensitivity; and the hypersensitive necrotic reaction of mesophyll cells underlying the infection area. Production of conidia was assessed after 10 days. Neither the profuse epidermal hairs nor the leaf cuticle contributed directly to resistance in T. timopheevii. However, both T. araraticum and T. timopheevii exhibited papilla-mediated resistance and, in addition, T. araraticum showed epidermal hypersensitivity. T. timopheevii may possess a gene or genes for resistance additional to those already transferred to, and expressed in, the hexaploid derivative CI12633, particularly those which condition the hypersensitive necrotic reaction of the mesophyll cells surrounding the infection area.