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Title: SIMPLE SEQUENCE REPEAT (SSR) DNA MARKERS IN ALFALFA AND PERENNIAL AND ANNUAL MEDICAGO SPECIES

Author
item DIWAN, NOA - UNIVERSITY OF MARYLAND
item Cregan, Perry
item Bauchan, Gary
item BHAGWAT, ARVIND - UNIVERSITY OF MARYLAND

Submitted to: Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: Genetic markers are used to create "road maps" of the chromosomes of plant and animal species. The positions of genes controlling important traits such as disease resistance or forage quality and yield of alfalfa can then be established in reference to the genetic markers or "milestones" on the genetic map. When a marker is situated near a gene controlling a trait of interest, the plant breeder can use the marker to select for the trait and thereby avoid the cost and time required to assess the level of disease resistance, nutritive value of the forage, etc. The purpose of this work was to determine if a new type of genetic marker based on Simple Sequence Repeat (SSR) DNA is present and can be used in alfalfa. If present, SSR markers could be used to create a genetic map of alfalfa and for other purposes as well. The DNA of cultivated alfalfa was searched for the presence of SSR markers and it was estimated that about 19,000 such DNA sequences exist in alfalfa.Four markers were developed and tested in cultivated alfalfa as well as many related species with agricultural potential. This new type of DNA marker should provide an excellent complement to currently available DNA markers and can be used by alfalfa breeders and geneticists for alfalfa improvement and for more basic research in population genetics and in molecular biological studies including the isolation of genes.

Technical Abstract: Simple sequence repeat (SSR) DNA markers are multi-allelic, co-dominant, polymerase chain reaction (PCR) based markers that have been demonstrated to function well in plant species for genetic map construction and genotype identification. It was the objective of the work reported here to assess the presence and frequency of SSR DNA in the alfalfa [Medicago sativa (L.) L.&L] genome, and to examine the function of selected markers in a spectrum of perennial and annual Medicago species. The screening of a small insert alfalfa genomic DNA library followed by the sequencing of clones putatively containing SSRs indicated approximately 19,000 (AT)n + (CT)n + (CA)n + (ATT)n SSRs in the tetraploid genome. Mendelian inheritance at four selected SSR loci was demonstrated. In addition, genotypes from a range of Medicago species including 10 perennial species of the Medicago sativa complex, seven other perennial Medicago species, and nine annual medics were analyzed at each of the four SSR loci to ascertain the presence, number, and size of SSR alleles at each locus in each genotype. With only one exception PCR products were produced by all genotypes at three of the loci derived from the genomic library. These studies indicate that SSR markers should function in alfalfa for the construction of genetic maps and will also be useful in a range of Medicago species for purposes of assessing genetic relatedness and taxonomic relationships, and for genotype identification.