Conservation of allelic richness in wild crop relatives is aided by assessment of genetic markers.

Abstract

Wild crop relatives are an important source of genetic variation for improving domesticated species. Given limited resources, methods for maximizing the genetic diversity of collections of wild relatives are needed to help spread protection over a larger number of populations and species. Simulations were conducted to investigate the optimal strategy of sampling materials from populations of wild relatives, with the objective of maximizing the number of alleles (allelic richness) in collections of fixed size. Two methods, based on assessing populations for variation at marker loci (e.g., allozymes, restriction fragment length polymorphisms), were developed and compared with several methods that are not dependent on markers. Marker-assisted methods yielded higher overall allelic richness in the simulated collections, and they were particularly effective in conserving geographically localized alleles, the class of alleles that is most subject to loss.Decisions in conservation biology may be based on demographic or genetic criteria or both (1). Demography often takes precedence when populations face immediate threats (2), but the long-term viability of species requires genetic variation (3). In domesticated species the conservation of single-locus variation is of special interest, as disease resistance and other economically important characteristics are often inherited in simple Mendelian fashion (4,5). Genes introduced from the wild relatives of crops constitute an important source of single-locus variation for the improvement of domesticated species (6-8). The diversity of alleles at single loci (allelic richness) in wild relatives is particularly vulnerable to loss due to reduction in population size (9, 10). The problem is compounded by the fact that most crop relatives are found only in nature, and many such species and populations are increasingly threatened by habitat reduction (8). Moreover, there are many potentially useful populations of wild relatives, yet for practical purposes only a fraction of all such material can be afforded protection or maintenance in gene banks or in nature reserves. In addition, wild relatives are often geographically wide ranging, making it costly to collect representative samples of these materials. By maximizing genetic diversity in germ-plasm collections of fixed size, resources available for conservation of crop biodiversity can be allocated to a larger number of species.This paper is concerned with how genetic markers (allozymes, restriction fragment length polymorphisms, etc.), which have been successfully employed in many other applied aspects of biology and medicine, can be used to help construct collections of wild crop relatives having maximal allelic richness. Because of their increasing importance in germ-plasm conservation we focus on the core collection (11, 12 MATERIALS AND METHODSTwo marker-assisted strategies for constructing core collections were developed. Each delineates how accessions are to be selected from a larger collection that has been div...

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