Wednesday, August 1, 2012
Grand Ballroom
The USDA–ARS Tropical Agriculture Research Station is responsible for conserving germplasm of a number of important agricultural crop species. Among these, a Musa spp. collection has been established and is comprised of diploid, triploid, and tetraploid accessions of cultivated, ornamental, wild and hybrid accessions. The collection is maintained in the field for characterization purposes and in tissue culture as a backup and for distributions. As a crop that needs to be vegetatively-propagated frequently, as in vitro plants are established and as accessions are added to the collection, care must be taken to avoid propagation mistakes. In an effort to estimate genetic diversity, to develop reference DNA profiles for clonal accessions and in order to identify any potential propagation mistakes, a set of 22 CIRAD-developed and Global Musa Genomics Consortium (GMGC) recommended SSR markers were screened on a total of 893 Musa spp. DNA samples. DNA samples for each accession were collected from four replicate field-grown plants and from a single individual replicate tissue culture plantlet and analyzed with representative DNA reference samples from the GMGC. Twenty-one out of the 22 SSR markers amplified well and generated an average number of 14.8 alleles per locus. The SSR locus, mMaCIR01 produced 26 alleles with 5 alleles being produced for mMaCIR307. Profiles for clonal plants from the field, tissue culture and from reference samples matched well across all 21 loci showing the technique’s reproducibility. The average number of alleles, gene diversity estimates and representative accessions within subgroups indicate good genetic diversity for cultivated Musa spp. Cluster analysis showed that the accessions in the collection grouped according to their ploidy level and genomic compositions. The SSR markers used in the study were useful in distinguishing among most accessions to the subgroup level. However, observed phenotypic differences among accessions within particular subgroups, could not be resolved with genotypes generated. Field-observed phenotypic differences within subgroups (i.e., ‘Cavendish’) are thought to be due to point mutations and the SSR markers would not be expected to resolve these differences. The SSR markers were useful in identification of several mistakes in propagation, especially in the tissue culture collection, were phenotypic differences are difficult to observe. SSR fingerprint profiles and accessions are available through the USDA, National Plant Germplasm System, Germplasm Resource Information Network (GRIN-Global) database http://www.ars-grin.gov/.