QTL mapping in Lolium perenne

A perennial ryegrass F2 family, comprising 194 individuals was used to develop a linkage map of RFLPs, AFLPs, SSRs, and isozymes. Seven linkage groups were identified and aligned with the ILGI reference map and other maps investigating feed value and nitrogen use efficiency (NUE) in the EC project NIMGRASS. Traits mapped in the family include water-soluble carbohydrate content (WSC), neutral detergent fibre (NDF), plant size, leaf extension rate and regrowth rate. QTL for morphological and growth traits that explained between 23-40% of the phenotypic variation in the trait were found on all seven linkage groups. QTL for nutritive quality traits (total WSC, crude protein and NDF) were found on four linkage groups and explained around 20-25% of trait variation. QTL for individual WSC components were found on six linkage groups. Leaf carbohydrate QTL did not coincide with tiller base carbohydrate QTL. Total WSC QTL usually coincided with high molecular weight fructan QTL, and NDF QTL coincided with QTL for WSC on LG 1 and 2. Initial work on marker-assisted selections for WSC generally produced responses in the directions expected but differences were small. Selection for homozygosity in QTL regions could result in some inbreeding depression in this outbreeding species and future comparisons will include homozygous and heterozygous marker selections. Assessment of individual QTL effects may be difficult against a background of segregation at other loci. Co-selection at two or more QTL may prove to be more effective