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Title: MICROSATELLITE (SSR) MARKERS REVEAL GENETIC IDENTITIES, GENETIC DIVERSITY AND RELATIONSHIPS IN A MALUS X DOMESTICA BORKH. CORE SUBSET COLLECTION

Author
item Hokanson, Stan
item SZEWC-MCFADDEN, A - USDA, ARS, GENEVA, NY
item LAMBOY, W - CORNELL UNIV., GENEVA, NY
item MCFERSON, J - WASH. APPLE COMM. WA

Submitted to: Journal of Theoretical and Applied Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/29/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Germplasm collections need to be well characterized in order to be most effectively managed and utilized. Modern molecular tools are allowing germplasm managers the opportunity to do fine-scale genetic characterizations of large collections quickly and efficiently. One of the world's largest apple germplasm collections is housed at the USDA-ARS Plant Genetic Resources Unit (PGRU) in Geneva, New York. Over 2,500 unique apple trees are maintained at the site. As part of an effort to begin the detailed characterization of the collection we used a relatively new class of molecular tools to evaluate 66 domesticated apple types in the collection. The markers revealed extensive genetic variation in the collection. The markers allowed for the establishment of unique genetic fingerprints for nearly all the 66 domesticated apples. In two cases where individual apple trees could not be differentiated with the markers, further investigation revealed that two of the apple trees in the collection were mislabeled. Data generated with the markers confirmed existing information regarding genetic relatedness amongst individual apple cultivars in this study and also shed some new light on long existing questions regarding the origins of some old apple cultivars. This new class of molecular tools shows great promise as a means to quickly and definitively identify existing and new apple cultivars for nurseryman, breeders and germplasm managers, and providing the basis for a highly efficient genetic mapping/marker-assisted breeding scheme.

Technical Abstract: A collection of 66 Malus x domestica Borkh. accessions from the USDA-ARS Plant Genetic Resources Unit's core collection was screened with a set of eight SSR (Simple Sequence Repeat) primers developed at the PGRU in order to determine genetic identities, estimate genetic diversity, and to identify genetic relationships among these accessions. All eight primer pairs generated multiple fragments when used in amplification reactions with DNA from these accessions. High levels of variation were detected with a mean of 12.1 alleles per locus and a mean heterozygosity across all eight loci of 0.693. The eight primer pairs utilized in this study unambiguously differentiated all but seven pairs of accessions in this collection of 66 M. x domestica Borkh. genotypes. The probability of matching any two genotypes in this study at all eight loci was approximately 1 in one billion. The markers detected two misnamed accessions in the collection. Genetic identity data produced a genetic relatedness phenogram which was concordant with geographic origins and/or known pedigree information. These SSR markers show great promise as tools for managing Malus ex situ germplasm collections as well as for collection and preservation strategies concerning wild Malus populations in situ.