Molecular Markers for Gene Pyramiding and Disease Resistance Breeding in Barley

Abstract

Barley (Hordeum vulgare L.) is one of the oldest crop plants and among the most important cereals worldwide which is cultivated from the polar circle to the tropics. Barley crops can be infected and severely damaged by many fungal, viral and bacterial pathogens as well as insect pests. Therefore, breeding for disease and pest resistance is of special importance in barley in order to prevent or reduce yield losses. Furthermore, genetic resistance allows the reduction of agrochemical applications and thereby greatly contributes to environment and consumer protection. Resistance breeding has already been very successful in the past and provided many resistant or tolerant barley varieties highly adapted to adverse growing conditions. The genetic basis of such resistance depends on the respective pathogen or pest: Many cases of monogenic (major gene) resistance have been described but oligo- or polygenic types of resistance are also widespread and appreciated by breeders and growers due to their superior durability. Today, molecular markers are available for many major resistance genes and resistance QTL (quantitative trait loci) against a wide range of pathogens in barley. Such markers are the basis for an efficient marker assisted selection (MAS) in scientific breeding research and commercial barley breeding. Furthermore, marker assisted backcrossing procedures allow an enhanced incorporation of resistance genes derived from non-adapted germplasm (e.g. H. bulbosum). Beyond this, pyramiding of resistance genes by marker-assisted combination breeding may lead to longer lasting resistance and enable the further use of resistance genes already overcome by single strains or isolates of the respective pathogen. This chapter reviews the present state of the art concerning markers available for major resistance genes and resistance QTL in barley and exemplifies marker assisted backcrossing and pyramiding strategies in the pathosystem barley – barley yellow mosaic virus disease caused by BaYMV and BaMMV.