Genetic and Breeding Aspects of Durable Resistance of Crops to Pathogens

Rapid adaptation of pathogens to introduced resistance is largely restricted to biotrophic or hemibiotrophic pathogens with a narrow host range and an air-borne or splash-borne dispersal, and to resistances of the major genic types that operate on a gene-for-gene basis with a virulence genes in the pathogen, resulting in a hypersensitive reaction, a post-haustorical resistance. Durable resistance against these pathogens rests basically on a different resistance mechanism (pre-haustorial) and not on the number of genes. Selection for durable resistance against such pathogens should consists of removing the most susceptible entries (selection against susceptibility) and of removing the (near-) completely resistance entries (selection against non-durable, major genes). Among the remaining entries selection for agronomic performance can be carried out. Another approach could be the exclusive use in the crossing programme of cultivars with known durable resistance and of cultivars with a high level of residual resistance after the major gene resistance has been overcome