Submitted to: Genetic Resources and Crop Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2006
Publication Date: 8/3/2007
Citation: Richards, C.M., Antolin, M.F., Reilley, A., Poole, J., Walters, C.T. Capturing genetic diversity of wild populations for ex situ conservation: Texas wild rice (Zizania texana) as a model. Genetic Resources and Crop Evolution 54:837-848.
Interpretive Summary: Efficiently capturing genetic diversity that is extant in the wild for ex situ conservation is an important part of the genebanking process. We have developed techniques to measure and model genetic diversity using an aquatic grass, Zizania texana, as a case study. The extremely restricted population of this endangered species allowed us to thoroughly sample the genetic diversity and to make comparisons among stands and years. We measured genetic diversity by genotyping, using micosatellite markers, 471 plants collected from the river and 36 plants that were growing in an ex situ reserve. There was more genetic diversity in the river population than we expected based on the species' restricted habitat and presumed asexual reproduction. We could efficiently capture this diversity by focusing sampling efforts on the large stands, which harbored all the unique alleles.Combining this study with previous ones, showing that the recalcitrant seeds of this species can be cryopreserved and that flowering can be induced in greenhouse grown plants, provides a comprehensive strategy to preserve genetic diversity of this species in a genebank.
Technical Abstract: In order to develop sampling strategies for ex situ conservation collections, we measured the genetic diversity and population structure of the endangered aquatic grass Zizania texana (Hitchcock)(Texas wildrice). This perennial species grows only in the upper four km of the San Marcos River in south central Texas, USA, in submerged stands that range in size from less than one m2 to greater than 300 m2. Genetic variation was measured within 23 stands by genotyping 471 individuals using six polymorphic microsatellite markers. The population had high heterozygosity and allelic diversity, but few duplicated genotypes. Stands were genetically differentiated, and could be consolidated into eight subpopulations using a Bayesian clustering algorithm that admixed adjoining stands or stands in adjacent segments of the river. Most of the genetic diversity of the river population was concentrated in large stands, and stands smaller than two m2 contributed no new alleles. These findings suggest that Z. texana reproduces predominantly by seed, rather than asexually by adventitious shoots, and that the species tends to outcross. Sampling strategies designed to maximize genetic diversity confirm the importance of large stands as stable reservoirs of genetic diversity. This study integrates demographic and genetic data to design efficient collection strategies for ex situ conservation and to guide in situ conservation.