Application of Molecular Markers to Genetic Diversity and Identity in Forage Crops

Abstract

Molecular genetic tools have been utilised at a much slower pace for forage crops than for the human food crops. Recently, however, molecular marker systems have been incorporated in forage crop breeding to assist in selecting desirable genotypes, to examine genetic diversity and cultivar stability, and to be used for cultivar identification. Molecular tests range from ploidy determination using flow cytometry to exact DNA sequence identification of specific genes. Isozyme studies have shown that forage crops are complex genetically and not only have multiloci, but have multiallelic genetic systems. The PGI 2 locus, for example, has at least seven different allelic forms. Because of the genetic complexity, cultivars and germplasm should be characterised by allelic frequency differences. The AMOVA is a statistical tool that provides relative measures of within accession, among accession, and among broad groupings of genotypes. Choice of molecular test that can be analysed by AMOVA can be determined by the information desired. RAPDs are easy to implement on an individual plant basis and are relatively inexpensive. AFLPs are more expensive, but much more definitive than RAPDs. SSRs measure rather minute genetic changes that can be correlated to evolutionary or genealogical relatedness. Future implementation of ESTs, or SNPs identified by DNA sequence arrays will be used to separate accessions based on actual gene differences.