DEVELOPMENT OF EFFICIENT MOLECULAR MARKER SYSTEMS FOR FORAGE CROP SPECIES

Plant Biotechnology Centre, Agriculture Victoria, La Trobe University and CRC for Molecular Plant Breeding, Bundoora, Victoria 3083, Australia

Perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) are the predominant grass and legume species of temperate pasture agriculture. Both species are obligate outbreeders with genetically controlled self-incompatibility systems. The application of molecular marker technology to breeding of these species must take account of the genetic heterogeneity of natural and synthetic populations and the allelic complexity of pair crosses. Efficient PCR-based molecular marker systems are required for forage crop breeding. Although AFLP systems based on EcoRI and PstI rare cutter enzymes have been optimised and implemented for both species, multiallelic codominant markers such as SSRP systems are of higher value. We describe the current status of our SSR discovery programs for perennial ryegrass and white clover. Partial genomic libraries showing greater than 50% enrichment were obtained for both species. Isolation of cryptically simple sequences and truncated SSR clones limit the efficiency of discovery. However, over 1000 SSR positive clones have been isolated from perennial ryegrass, of which at least 40% are accessible to primer design. Over 700 SSR positive clones have been isolated from white clover, of which at least 50% are accessible to primer design. The prevalence and repeat length distributions of different SSR motifs have been analysed for each library. SSR polymorphism has been evaluated within each species and detection of ortholoci in related species has been determined. Loci which are polymorphic in a perennial ryegrass reference genetic mapping population are being used to construct a framework SSR based genetic linkage map.