Determination of Self-Incompatibility Genotypes in Lolium perenne through linked DNA marker genotyping

Self-incompatibility (SI) is a mechanism under genetic control that prevents inbreeding by blocking fertilisation of ovules by like-pollen. Subject to frequency dependent selection, rare alleles, originating through mutation or ingression into populations, are at a selective advantage and theoretically increase in frequency under balancing selection. SI loci are therefore highly poly-allelic. The grass family shares a common two locus SI system controlled gametophytically by two loci, S and Z. Although the genes responsible for SI in grasses have not been identified yet, fine-mapping of S and Z in Lolium perenne has resulted in a number of close flanking markers. For this proof of principle study, we investigate the possibility of using S- and Z-linked marker variation to predict genotypes and their frequencies in plant populations. We used a population of 55 plants derived from a base population of nine genotypes that has been subjected to twelve generations of mixed and half-sib family selection. We screened non- and infrequently-recombinant S and Z DNA markers using high resolution melting curve analysis (HRM) which is highly discriminating, quick and relatively easy to perform. Marker genotypes were then grouped and relative S/Z genotypes were predicted. Marker polymorphisms were confirmed by DNA base sequencing. S/Z genotypes will be confirmed by making selected in-vitro cross-pollinations to demonstrate that the genotype combinations produce the predicted incompatible, half-, three-quarters- and fully-compatible pollinations. The ability to readily determine S/Z genotypes
of grass plants will be of interest to population geneticists investigating properties of SI loci and their evolutionary significance. Being able to genotype large numbers of plants quickly and cheaply will also enhance breeders’ ability to select plants on SI genotype in order to produce highly intra-incompatible, inter-compatible population combinations for the production of heterotic F1 hybrid populations in forage, turf and bio-energy grass crops.