AFLP fingerprinting in Medicago spp.: Its development and application in linkage mapping

Cultivated alfalfa (Medicago sativa L., 2n = 4x = 32) is one of the most im portant forage crops in temperate climates. The genus Medicago includes dip loid species that are a valuable source of wild germplasm for studying the reproductive system of alfalfa and its abnormalities. A linkage map of an a pomeiotic mutant of Medicago falcata (L.) Arcang. (2n = 2x = 16) that spann ed 368.6 cM and included 29 amplified fragment length polymorphism (AFLP), 35 random amplified polymorphic DNA (RAPD) and three restriction fragment l ength polymorphism (RFLP) loci was constructed using a one-way pseudo-testc ross mapping strategy. The success of such a strategy depends on the presen ce of sufficiently high levels of heterozygosity in the individual plant wh ich is being mapped and on the informativeness of the marker system that is used. In general: (1) highly informative and reproducible RAPD and AFLP fi ngerprints were generated and several genome-specific primers selected; (2) of 67 marker loci mapped, 51 were arranged in 11 main linkage groups and e ight additional couples of linked marker loci were detected; (3) mapping of an F-1 population theoretically allowed a better estimation of linkage dis tances since it avoided segregation distortion (chi(2) analyses revealed se gregation distortion in only 5.2% of marker loci); (4) the high frequency o f unlinked marker loci obtained suggests that, in this alfalfa genotype, DN A markers are distributed throughout the genome. This type of genetic map s hould find application and prove useful in marker-assisted selection and ma p-based breeding programmes in meiotic mutants of alfalfa for which there i s a lack of suitable genetic markers.