Marker-assisted selection to accelerate forage improvement

Abstract

The use of biotechnology, in the form of gene mapping, marker-assisted selection (MAS), and map-based cloning can increase breeding efficiency and the array of traits amenable to selection. The increased efficiency is achieved by combining conventional glasshouse and field evaluations with DNA marker-based selection for superior genes; thereby maximising genetic gain from selection and/or improving traits with low heritability which are not amenable to improvement by conventional breeding alone. Implementation of MAS also reduces costs by permitting selection of superior plants at an early developmental stage or in the absence of the pathogen or pest. Robust genetic linkage maps are the basic requirement for identifying the genes controlling agronomically significant traits, and subsequent implementation of MAS. Recent advances in biotechnology have developed high-throughput, gene-targeted marker systems that allow rapid development of comprehensive genome maps and MAS programmes. Core linkage maps based on multiple DNA marker technologies are being developed for two of New Zealand's most important forage genomes, white clover (Trifolium repens) and perennial ryegrass (Lolium perenne). Markers from these maps will be used to: a) identify genes controlling simple and complex traits, b) implement targeted MAS strategies, c) transfer novel traits from related species into elite forage cultivars via crosshybridisation, d) clone genes to be inserted directly into elite cultivars, e) provide DNA fingerprints for variety identification, and f) identify putative heterotic groups for hybrid cultivar development. Keywords: DNA markers, EST, gene mapping, linkage, Lolium perenne, marker-assisted selection, Trifolium repens