Schriften zu Genetischen Ressourcen - Genres

B. PICKERSGILL, M.I. CHACÓN SÁNCHEZ and D.G. DEBOUCK
Multiple domestications and their taxonomic consequences: the
example of Phaseolus vulgaris
B. PICKERSGILL 1 , M.I. CHACÓN SÁNCHEZ 1 and D.G. DEBOUCK 2
Abstract
The evolutionary history of Phaseolus vulgaris is important to those working on its
genetic resources, but is not reflected in its infraspecific taxonomy. Genetic isolation
of wild populations between and also within Middle and South America has resulted
in morphological and molecular differentiation. Populations from northern and southern
ends of the range are assigned to different gene pools, though intermediates occur
in intervening areas. Chloroplast haplotypes suggest three distinct lineages of
wild beans and several intercontinental dispersals. The species was domesticated
independently in both Middle and South America, probably several times in Middle
America. This, together with further differentiation under human selection, has produced
distinct races among domesticated beans. The informal categories of wild versus
domesticated, gene pool, and race convey the evolutionary picture more clearly
than the formal categories provided by the Codes of Nomenclature for wild or cultivated
plants.
Introduction
One active debate in taxonomy today concerns whether or to what extent taxonomy
should reflect evolution. Above the species level, cladistic principles currently predominate,
but below the species level, cladistics has had much less impact on classification,
for two reasons. Firstly, at this level there is usually too much parallel evolution
in morphological characters and too little variation in molecular characters to
generate a cladistic classification with which one may feel confident. Secondly, hybridisation
is often important at and below the species level, and cladistics is notoriously
bad at dealing with the consequent reticulations in evolutionary lineages.
1 Department of Agricultural Botany
School of Plant Sciences
The University of Reading, Whiteknights
PO Box 221, Reading RG6 6AS, United Kingdom
2
Genetic Resources Unit
CIAT
Apartado Aereo 6713
Cali, Colombia
71