Single-Marker Assisted Introgression of Crown Rust Resistance in an Italian Ryegrass Breeding Program

Abstract

Ecotype populations of Italian ryegrass (Lolium multiflorum Lam.) provide a valuable gene pool for further improvement of this important forage grass species. Although they are often characterized by high yield potential and persistence, ecotype populations usually suffer from severe susceptibility to leaf diseases such as crown rust, caused by Puccinia coronata. In this study we tested the potential of single-marker assisted selection to introgress a resistance gene from a bi-parental mapping population into ecotype-based breeding material. A single SSR marker linked to a major QTL for crown rust resistance on LG2 of L. multiflorum was used to generate three breeding populations with contrasting intensities of marker assisted selection (homozygous for the marker allele, heterozygous, absence of the marker allele). In the framework of our breeding program, these populations were continuously genotyped and characterized for crown rust resistance over five generations. Observations on individual plants of the F3 generation showed significant linkage of the marker allele with crown rust resistance but there was no significant difference between individuals homozygous or heterozygous for the marker allele, respectively. In plot trials with Syn2 progeny, crown rust scores ranged from 1.44 to 2.00 (1{\thinspace}={\thinspace}resistant, 9{\thinspace}={\thinspace}susceptible) for populations based on positive selection for the marker allele while populations based on pure phenotypic selection had crown rust scores ranging from 3.11 to 4.56. Thus, our results demonstrate that genotypic selection based on a single marker can complement phenotypic selection and facilitate the introgression of resistance traits in breeding material.