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Allozyme variation in a rare plant species, Pediomelum piedmontanum (Fabaceae), from the lower Piedmont Plateau of Georgia.

Article Excerpt
ABSTRACT

A single population of Pediomelum piedmontanum (Fabaceae) occurs in Columbia County, Georgia. We examined allozyme variation in this population for 20 loci in eleven enzyme systems. Genetic diversity was low (P = 20.0%; A = 1.20; overall average HO = 0.038). Allelic frequencies in a large sample from one of two subpopulations predicted a significant deficiency of heterozygotes for all polymorphic loci (P < 0.001), inconsistent with Hardy-Weinberg expectations. Allelic frequencies for a smaller sample from the other subpopulation predicted a significant deficiency of heterozygotes for one polymorphic locus (P < 0.025) and non-significant excesses of heterozygotes for two others. Genetic differentiation among subpopulations was low ([F.sub.ST] = 0.0142). Factors responsible for the extreme rarity of P. piedmontanum are unknown, but low genetic variation in the small, isolated Georgia population is most likely due to historical factors, genetic drift and perhaps inbreeding.

Key words: allozymes, genetic diversity, Pediomelum piedmontanum, Fabaceae

INTRODUCTION

Genetic variation is an important component to the adaptation and potential long-term survival of plant species (1). Breeding system, past and present levels of gene flow among populations, geographic distributions, isolation, historical events, and human disturbance of the habitat all affect genetic diversity within a species and its populations (2,3). Rare species, particularly those distributed in small, isolated populations, may experience genetic drift and/or inbreeding that lead to random fixation of alleles and reduced heterozygosity (4). A significant loss of genetic variation can contribute to the extinction of small populations (5) and the loss may occur before the endangered status of the species is apparent (6).

Pediomelum piedmontanum Allison, Morris & Egan sp. nov. (7) is a newly described species of perennial herbaceous legume apparently endemic to rocky, open areas and adjacent open woodlands in the lower Piedmont Plateau of Georgia and South Carolina. The species is known from only three populations, two in Richland County and Lexington County, South Carolina, and one in Columbia County, Georgia (7). The Columbia County population covers only a...

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