Submitted to: Cucurbitaceae Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 11/15/1998
Publication Date: N/A
Citation: Interpretive Summary: Plant accessions (seed or plant parts) are received by the U. S. Department of Agriculture as a result of collection trips and gifts from worldwide sources. Such accessions form a seed bank known as the National Plant Germplasm System collection (NPGS) from which public and private plant breeders drawn from to create new varieties with improved disease resistance, yield and quality. Accessions in the NPGS are managed and propagated (increased or duplicated) by regional plant introduction stations. These stations (germplasm banks) have very restricted budgets, and often managerial resources (labor, space and budget) in germplasm banks are such that propagation of accessions are made using relatively few plants (5 to 50). This type of management of genetic resources can render accessions susceptible to genetic changes which in turn can change their relative usefulness to plant breeders. Two important factors which can complicate the management of gene banks and mutation [change in the genetic (DNA) structure of the accessions] and selection of individuals due to changing environmental conditions during propagation. The potential adverse affect of mutation and selection over 20 generations of propagation were simulated by a computer program. Results suggest that while mutation does not play an important role in changing the genetic nature of accessions, selection can be important. These results clarify the role of selection and mutation for propagation of accessions in the NPGS. Curators collections will be able to use this information to increase their effectiveness during the propagation of accessions to ensure maximum genetic diversity.
Technical Abstract: Often managerial resources (labor, space and budget) in germplasm banks are such that increases of accessions are made using relatively few plants (5 to 50). This type of management of genetic resources can render accessions susceptible to allelic frequency changes which in turn can change the relative fitness of individuals in the population. Mutation and environmental fluctuations are two factors that can cause allelic frequency changes. Simplistic computer simulations (one locus, 2 alleles, p and q) were conducted in order to investigate the possible role of these factors on changes in allelic frequency and fitness in germplasm collections over 20 generations. Simulations evaluated the role of forward and reverse mutation, relative fitness with and without dominance in changing the population structure of small populations (n = 1000). A predictable decrease in the frequency of p was observed with increasing forward mutation rates of p. However, even with recurrent mutation the frequency of p was not dramatically altered by high mutation rates (10 -3), suggesting that population size must be extremely low and/or mutation rate must be extremely high to have a demonstrable effect on allele frequency over short time periods. Frequency changes in p are most dramatic in the first 10 generations when fitness values range between 0.4 to 1.0. Partial dominance affects the rate of change in allele frequency over 20 generations, and dependent on the relative fitness of p. Moreover, dramatic changes in allele frequency can occur regardless of dominance level between generations 1 to 10, especially if fitness values are high (greater than 0.4).