Location: Forage Seed and Cereal ResearchTitle: QTL for resistance in Lolium perenne to a mixed population of Puccinia graminis subsp. graminicola: use of RAD (restriction site associated DNA) markers to rapidly populate a new linkage map) Author
Submitted to: Theoretical and Applied Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/31/2011
Publication Date: 5/31/2011
Citation: Pfender, W.F., Saha, M.C., Johnson, E.A., Slabaugh, M.B. 2011. QTL for resistance in Lolium perenne to a mixed population of Puccinia graminis subsp. graminicola: use of RAD (restriction site associated DNA) markers to rapidly populate a new linkage map. Theoretical and Applied Genetics. 122:1467-1480. Interpretive Summary: Development of genetic resistance to plant diseases can be greatly facilitated by knowledge of the chromosomal location of the resistance genes. Such information is lacking for stem rust of perennial ryegrass. In this research we produced a genetic map of perennial ryegrass, using standard genetic markers as well as a new type of marker ('RAD' markers) not previously used in disease resistance mapping. The genetic map, created from the offspring of rust-resistant and rust-susceptible parents, is congruent with previous maps of other genetic traits in ryegrass populations using other marker types. We detected chromosomal locations for three genetic resistance sites in ryegrass reacting to inoculation by a mixture of stem rust pathogen strains. The RAD markers allow us to derive the specific DNA sequences for genetic markers located near the resistance sites on the ryegrass chromosomes. Knowledge of the resistance locations, combined with the genetic marker information, will be useful in breeding programs to improve rust resistance in this crop.
Technical Abstract: A mapping population was created to detect quantitative trait loci (QTL) for resistance to stem rust caused by Puccinia graminis subsp. graminicola in Lolium perenne. Susceptible and resistant plants were crossed to produce a pseudo-testcross population. Markers were produced by the Restriction-site Associated DNA (RAD) process, which uses massively parallel and multiplexed sequencing of reduced-representation libraries. Additional simple sequence repeat (SSR) and sequence-tagged site (STS) markers were combined with the RAD markers to produce maps for the female (738 cM) and male (721 cM) parents. Stem rust phenotypes (number of pustules per plant) were determined by inoculation with a field-collected, genetically heterogeneous population of urediniospores. The F1 progeny displayed continuous distribution of phenotypes and transgressive segregation. We detected three resistance QTL. The most prominent QTL (qLpPg1) is located near 41 cM on linkage group (LG) 7 with a 2-LOD interval of 8 cM, and accounts for 30-38% of the stem rust phenotypic variance. QTL were detected also on LG1 (qLpPg2) and LG6 (qLpPg3), each accounting for approximately 10% of phenotypic variance. Alleles of loci closely linked to these QTL originated from the resistant parent for qLpPg1 and from both parents for qLpPg2 and qLpPg3. Observed quantitative nature of the resistance may be due to partial-resistance effects against all pathogen genotypes, or qualitative effects completely preventing infection by only some genotypes in the genetically mixed inoculum. The RAD markers should be useful to derive sequence-based markers for these stem rust resistance QTL.