Histological evidence for diverse mechanisms of resistance to flax rust, Melampsora lini (Ehrenb.) Lev

Abstract

Quantitative histological studies of the number of haustoria, percentage of necrotic haustoria, number of necrotic host cells and area of necrotic tissue per infection site at regular intervals following inoculation indicate that different mechanisms of resistance to flax rust ( Melampsora lini) are operative in certain monogenic lines of flax ( Linum usitatissimum) which contain different genes for resistance. The L and N genes condition the most rapid, localized response to infection. The M and P genes condition a hypersensitive response which is initiated later and over a larger area of host cells than that conditioned by the L and N genes. The size of lesions associated with the M and P genes suggests more extensive diffusion of a toxic substance than in the resistance conditioned by the L and N genes. The K gene provides a moderate degree of resistance accompanied by extensive necrosis of infected leaves, but with less severe effects on host and pathogen cells at the histological level than that conditioned by the L, M, N or P genes.