The genetic evaluation of plant genetic resources

Abstract

The characterization of the nature and extent of the genetic diversity preserved in plant genetic resources collections has received much less attention than other aspects of the discipline such as collecting and storage techniques. The workshop was designed to focus on three aspects of genetic evaluation: what is the utility and significance of genetic evaluation, what do we know about the genetic diversity preserved in current collections of plant genetic resources, and what techniques are available for the analysis of genetic diversity. Each of these themes was the subject of an invited presentation, followed by discussion. The workshop was attended by about 50 geneticists. Gkrard Second (ORSTOM, France) addressed the first theme. Genetic evaluation wits defined as the characterization of the amount and structure of genetic polymorphism and of the phylogenetic relationships within and between germ plasm accessions. This was contrasted with agronomic evaluation, which deals with characters involved in the economic sustainability of crops. It was stated that genetic markers used for genetic evaluation may be linked to agronomic traits, but are unlikely to be of direct economic interest. Determining the genetic structure of germ plasm collections provides breeders with a useful framework to take advantage of transgression. Genetic evaluation can be used to predict the likelihood of a successful genetic transfer or to indicate the best strategy for such a transfer. This is complemented by information on the history of the domestication of a crop, obtained by studying the genetic interrelationships between landraces and wild relatives from evolutionary and biogeographical points of view. A sound classification of genetic resources provides the basis for efficient communication between breeders. Genetic evaluation contributes to genetic resources management by orienting collecting trips, determining localities and strategies of conservation, detecting duplication in germ plasm collections, and forming the basis for the choice of accessions for working collections destined for agronomic evaluation. Three examples illustrated these points. Isoenzyme analysis of diploid coffee (CofSea canephorn), a recent domesticate, revealed the existence of two main genetic groups in the wild species: Guinean and Congolese, corresponding to the ecogeographic distribution in West and Central Africa. The majority of the best commercial clones proved to be hybrids between the two groups, thus indicating a strategy for improvement of this crop. Likewise, oil palm (Elaeis guineensis) stocks were traced to Guinean and Congolese origins. The situation is more complex when ancient domesticates such as the rice complex are considered. Separate analyses using morphophysiological, isoenzyme, and nuclear and