Submitted to: Conservation Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2004
Publication Date: 12/1/2004
Citation: Richards C.M., A. Reilley, D.H. Touchell, M.F. Antolin and C. Walters. Microsatellite primers for Texas wild rice (Zizania texana), and a preliminary test of the impact of cryogenic storage on allele frequency at these loci. Conservation Genetics 5:853-859. Interpretive Summary: We compared the allelic frequencies from 5 microsatellite loci in populations of seed with and without cryogenic exposure and found that the mortality associated with cryogenic exposure is random with respect to genotype. This paper demonstrates that genetic diversity of seed samples is not significantly altered by exposure to cryoprotectants and liquid nitrogen.
Technical Abstract: Collections of seeds stored in gene banks are increasingly used for the conservation of wild collected taxa with conservation importance. In some instances these seeds may not be stored in conventional cold storage (-18°C) but must be pretreated and stored in the vapor phase of liquid nitrogen. Implicit in this approach is the assumption that these added manipulations do not change the genetic diversity of these heterogeneous samples. We developed polymorphic microsatellite markers for the endangered aquatic plant Texas wild rice (Zizania texana) to evaluate the effects of cryogenic preservation of mature embryos on genetic diversity. Seeds were harvested at two times from wild collected maternal lines and genotyped for 5 microsatellite loci that amplified a total of 28 alleles. Samples of seed from each harvest date were subjected to a pre-treatment protocol and exposed to liquid nitrogen. Embryos recovered from the treatment were germinated and genotyped at the same 5 loci. Comparisons of the genotypic data suggest that the 30% mortality associated with cryopreservation does not impose selection among the loci examined. Using several statistical approaches, we show that there were no significant differences in allele frequencies before and after cryopreservation. The retention of the allelic diversity at the 5 loci examined suggests that differential mortality of particular genotypes is not significant and that these protocols may be adequate for ex situ conservation of genetically diverse wild germplasm.