Molecular analysis of genetic relatedness among alfalfa clones differing in levels of self-incompatibility

The possibility of increasing hybridity in alfalfa (Medicago sativa L.) cul tivars through the use of self-incompatible (SI) parents is being investiga ted. Prior research has demonstrated that self-incompatibility is a heritab le trait and that environmentally stable SI clones can be selected. However , inbreeding depression is very severe in alfalfa, and a potential problem associated with utilizing self-incompatibility to increase hybridity is the purported positive relationship between self-incompatibility and inbreedin g. Fifteen stable, partially to fully self-incompatible clones and 18 stabl e self-compatible (SC) clones were selected from the broad-based population W10-AC3. RAPD, Anchored Microsatellite Priming (AMSP), and Simple Sequence Repeat (SSR) analyses were performed on genomic DNA using 9, 10-mer RAPD p rimers; the AMSP primers (from the 5' end) CAA(CA)(5), CCCC(GA)(5), CCG(GA) (5), and GCC(GA)(5); and eight SSR primer pairs. Based on genetic distance (GD) estimates (computed from RAPD and AMSP markers) and numbers of tri-all elic and tetra-allelic loci from SSR analysis, there is no evidence that SI clones were more closely related than SC clones. Assuming parental GD is p ositively correlated with heterosis, environmentally stable SI clones with acceptable specific combining ability and separated by large GD's would be a good basis for a hybrid alfalfa system, or for use in other breeding sche mes designed to minimize inbreeding while maximizing heterosis.