Isolate-specific QTLs of resistance to leaf stripe (Pyrenophora graminea) in the 'Steptoe' × 'Morex' spring barley cross

Abstract

Leaf stripe caused by the fungus Pyrenophora graminea represents a serious threat to grain yield in organically grown barley and in conventional Nordic and Mediterranean districts, for which resistant cultivars are necessary. A medium-density, molecular marker map derived from a 'Steptoe' (partially resistant) x 'Morex' (susceptible) spring barley cross and its derived doubled-haploid mapping population inoculated with the fungus made it possible to identify QTLs of resistance to leaf stripe. In order to investigate isolate-specificity of partial resistance, the 'Steptoe' x 'Morex' segregating population was inoculated with two highly virulent P. graminea isolates, Dg2 and Dg5. The present study demonstrates that partial resistance to leaf stripe of cv 'Steptoe' is governed in part by shared loci and in part by isolate-specific ones. One QTL is common to the resistance for the two isolates, on the long arm of chromosome 2 (2H), two QTLs are linked on chromosome 3 (3H), and the remaining two are isolate-specific, respectively for isolate Dg2 on chromosome 2 (2H) and for isolate Dg5 on chromosome 7 (5H). The QTL in common is that with the major effect on the resistance for each isolate, explaining 18.3% and 30.9% R(2) respectively for Dg2 and Dg5. The isolate-specific QTLs mapped in the 'Steptoe' x 'Morex' barley reference map support the assumption of Parlevliet and Zadoks (1977) that partial resistance may be due to minor gene-for-minor-gene interactions. Map comparisons of the QTLs with the known qualitative resistance genes to leaf stripe, Rdg1 (2H) and Rdg2 (7H), as well as with other QTLs of partial resistance in barley, show that the QTL for resistance to both isolates mapped on the long arm of chromosome 2 (2H) does not coincide with the qualitative Rdg1 gene but is linked to it at about 30 cM. One isolate-specific QTL of resistance to P. graminea, mapped on the short arm of chromosome 2 (2H), is coincident with a QTL for resistance to Pyrenophora teres previously mapped in the 'Steptoe' x 'Morex' cross.

Complex Genetics Control Natural Variation inArabidopsis thalianaResistance toBotrytis cinerea

“…These studies have focused on biotrophic pathogens, where qualitative race-specific resistance conferred by major resistance genes is vulnerable to changes in the genetic composition of the pathogen population. The identification of both broad-spectrum and isolate specific resistance QTL suggests that significant variation for mechanisms of pathogenesis exists within many pathogen species and that qualitative isolate-specific resistance conferred by major resistance genes accounts for only a portion of plant defense against naturally variable pathogen populations (Caranta et al 1997;Arru et al 2003;Calenge et al 2004;Talukder et al 2004;Diener and Ausubel 2005;Jorge et al 2005). Understanding differences and similarities in mechanisms of partial or quantitative resistance to pathogens of different lifestyles, including biotrophs and necrotrophs, is vital to developing long-term strategies for pathogen control in a complex environment.…”

Diallel analysis of barley for resistance to leaf stripe and impact of the disease on genetic variability for yield components

“…During seed germination, its growing mycelium penetrates the coleorhiza and it colonizes the plant systemically starting from the root tip (Haegi et al, 1998). The disease is particularly acute in Mediterranean's winter barley districts, where soil temperatures below 12 • C during seed germination promote the infection of the rootlet (Arru et al, 2003). The typical symptoms, spike sterility and chlorotic stripes on leaves, which gradually extend to the full length of the leaf and finally become necrotic, lead to severe yield reductions when seed infection is high (Delogu et al, 1995).…”

High-resolution genetic mapping of the leaf stripe resistance gene Rdg2a in barley

“…Resistance genes are therefore desirable for controlling leaf stripe disease. Both polygenic partial resistance (Skou and Haar 1987;Pecchioni et al 1996;Arru et al 2002Arru et al , 2003a) and race-specific resistance genes have been identified. Rdg1a, conferring complete resistance to a subset of P. graminea isolates, has been mapped on the long arm of barley chromosome 2 (2H) (Giese et al 1993; Thomsen et al 1997).…”