Genetic basis of crown rust resistance in perennial ryegrass, breeding strategies, and genetic variation among pathogen populations: a review

Crown rust caused by the fungus Puccinia coronata f. sp. lolii is probably the most serious disease of perennial ryegrass (Lolium perenne L.). Breeding for resistance to crown rust is a major component of most perennial ryegrass improvement programs. This paper reviews the genetic basis of resistance to crown rust in perennial ryegrass, existing breeding strategies and their progress, and genetic variation in pathogen populations. Resistance to crown rust in perennial ryegrass appears to be controlled by both major and minor genes. Breeding for resistance to crown rust has traditionally been approached from a quantitative perspective (polygenic system), and phenotypic recurrent selection is by far the most commonly used method of selection. There appears to be considerable variation in the pathogen population which may impact on breeding progress. Owing to the present lack of information on the host-pathogen interaction system of this economically important disease, a basic model to study the L. perenne-P. coronata f. sp. lolii interaction system is presented. Its application in a breeding program is discussed.