SSR‐based genetic linkage analysis of resistance to crown rust (Puccinia coronata f. sp. lolii) in perennial ryegrass (Lolium perenne)

Abstract

Crown rust (caused by Puccinia coronata f. sp. lolii ) is a serious foliar disease of the pasture and turfgrass perennial ryegrass ( Lolium perenne ). Previous genetic studies have detected both qualitative and quantitative resistance mechanisms, and interpretation of the genetic system is complicated by variation within the sexually reproducing pathogen. Resistant and susceptible parental genotypes of ryegrass were identified using a composite urediniospore population collected from three geographically distinct locations. A two-way pseudo-testcross mapping population was obtained as the F 1 progeny of the pair-cross between ryegrass parental genotypes Vedette 6 and Victorian 9 . Both parents showed intermediate resistance against a pathogen population collected in a single geographical zone (Hamilton, Victoria), but in the F 1 population, significant variation for a range of resistance-associated characters was detected. Statistical analysis of phenotypic data suggested a major gene effect, hence bulked segregant analysis with map-assigned simple sequence repeat (SSR) markers was used to scan the genome. A marker showing strong association with resistance was assigned to linkage group (LG) 2 of perennial ryegrass. Analysis of 11 LG2 SSR markers defined an interval between loci xlpssrh03f03 and xlpssrk02e02 as containing the gene or genes ( LpPc1 ) conferring crown rust resistance. Resistance gene determinants were inherited from both parents, with up to 80% of the total phenotypic variation explained by markers segregating from Vedette 6 and up to 26% of the variation explained by markers segregating from Victorian 9 . The two contributions together resulted in an additive increase in effect, with fully resistant individuals requiring determinants from both parents. A conserved syntenic relationship was observed with linkage group B of Avena strigosa , which is the location of a cluster of resistance genes to the oat form of crown rust. The implications of this study for marker-assisted selection of disease resistance in perennial ryegrass are discussed.

Four QTLs determine crown rust (Puccinia coronata f. sp. lolii) resistance in a perennial ryegrass (Lolium perenne) population

“…This indicates that QTL1 in our study corresponds to the same region as LpPc1 in the study of Dumsday et al (2003). However, QTL1 does not explain a high proportion of variance (2.6%), in contrast to the high proportion of variance explained in the study of Dumsday et al (2003). In our study, QTL2 is of major importance (420% variance explained).…”

“…QTL pairs were tested for epistatic interactions using GLM analysis (Kover and Caicedo, 2001) but no epistatic effects were identified. Dumsday et al (2003) detected a major QTL for crown rust resistance on LG2. In our study, QTL1 is also located on LG2, in the proximity of Xcdo385 (Figure 3).…”

“…According to Jones et al (2002b), Xcdo385 maps to LG2 in the ILGI mapping population. It is in this genomic region that Dumsday et al (2003) also located SSR markers associated with crown rust resistance. This indicates that QTL1 in our study corresponds to the same region as LpPc1 in the study of Dumsday et al (2003).…”

“…It is in this genomic region that Dumsday et al (2003) also located SSR markers associated with crown rust resistance. This indicates that QTL1 in our study corresponds to the same region as LpPc1 in the study of Dumsday et al (2003). However, QTL1 does not explain a high proportion of variance (2.6%), in contrast to the high proportion of variance explained in the study of Dumsday et al (2003).…”

“…Dumsday et al (2003) detected one major locus (designated LpPc1 by the authors) on linkage group (LG) 2 of the L. perenne genetic map. Muylle et al (2005) detected two clusters of AFLP markers associated with crown rust resistance, explaining 35% of the variance observed in the segregating population investigated.…”