Value and Limitations of QTL in Temperate Forage Breeding Systems.

Despite grasslands covering 70% of the world’s agricultural area, growth and quality of temperate forage is a relatively under-studied aspect of plant improvement.  Enhancement of breeding systems for open-pollinated forage species, including QTL acquisition and utilisation, presents unique challenges and opportunities.  Microsatellite-based QTL discovery in forages has gathered pace over the last decade, providing insight to genetic control of pasture and seed-related traits.  In New Zealand, practical utilisation of QTL has been investigated in white clover and perennial ryegrass breeding systems, wherein QTL are prioritised on the basis of magnitude, consistency, trait value and breeding system efficiency.  Options considered include backcross introgression, forward selection, and confirmation of phenotype-based parental selections.  For seed yield in white clover (Trifolium repens L.), markers at a QTL region are used to establish allele:trait associations in elite populations enabling forward selection in spaced plant trials.  Assays for forage-related morphologic traits including yield, stolon, and root growth are in development.  In perennial ryegrass (Lolium perenne L.) forage yield is a major target.  Confirmation of marker allele composition during parental selection by genotyping critical QTL regions confers a predictable, significant (p<0.05) seasonal and annual yield advantage among progeny of otherwise indistinguishable parents in complex breeding populations.  Future opportunities and constraints for QTL discovery and utilisation in forages are discussed in the context of spatial-temporal analyses, automated phenotyping, genomic selection, and marker systems including Genotyping-by-Sequencing (GBS).  Evaluation of GBS data from white clover and perennial ryegrass breeding populations will be presented.