Submitted to: Cucurbitaceae Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 10/20/2000
Publication Date: N/A
Citation: Interpretive Summary: Genetic diversity is essential for crop improvement and therefore substantial government resources have been directed towards collecting, preserving and evaluating plants (germplasm). It is important for USDA scientists who manage these collections to obtain estimates of the genetic nature of their (curators) collections (genebanks). Such information often enhances a curator's ability to develop management strategies (what needs to be added or removed because of duplication). A DNA biotechnology that allows for the assessment of genetic variation (differences between plants) is called molecular marker technology. Molecular markers identify and characterize the variation of genes in an organism. Genes, the action factors which regulate life in living organisms, are located on chromosomes which are present in every cell of organisms. Knowing the genetic difference between organisms (genetic diversity) allows for a better understanding of the genetic structure of populations. We used molecular markers to survey the genetic diversity of samples in the USDA cucumber germplasm bank. We discovered that cultivars from India and China had the greatest genetic diversity. We recommended that more germplasm be collected from these countries for storage. Curators develop more informed strategies for managing their collection. It also produced information that allows plant breeders to acquire diverse germplasm to enrich their collections such that they can improve the quality of their germplasm by cross- breeding during cultivar development.
Technical Abstract: The most important resource that mankind has, apart from innate intelligence, is germplasm. Because of the decrease in arable land and the projected increases in world population, many crops are being evaluated for their resident genetic diversity in order to formulate strategies for the effective deployment of genetic resources for plant improvement. We assessed 922 of 1345 accessions in the U.S. National Plant Germplasm System (NPGS) cucumber collection using isozymes (14-21 loci) and random amplified polymorphic DNA (RAPD; 71 loci) to determine the population structure of this collection. We compared this population structure with the genetic diversity in an array of 118 diverse commercial accessions used (released or currently in use as experimental lines) between 1846 to 1999. We found that the NPGS accessions are genetically diverse, that they are not in Hardy-Weinberg equilibrium, and that they markedly differ from the commercial germplasm evaluated in their genetic structure. In contrast, the commercial germplasm exhibited a remarkably narrow genetic base, and thus could benefit from the introgression of exotic genes present in NPGS accessions. Backcrossing strategies combined with continued monitoring of genetic diversity vis molecular marker analysis would allow for relatively rapid development of germplasm pools (3 to 5 years) leading to homogeneous, but heterozygous, highly diverse populations for plant improvement.