Schriften zu Genetischen Ressourcen - Genres

B. PICKERSGILL, M.I. CHACÓN SÁNCHEZ and D.G. DEBOUCK
These data support BEEBE et al. (2000) in suggesting that at least three of the four
Mesoamerican races were domesticated independently: Race Jalisco in Jalisco;
Race Guatemala in Guatemala or Chiapas; Races Mesoamerica and Durango in
northern and/or southern Mexico. If there was only a single domestication, as GEPTS
(1990) argued, then it probably occurred in Oaxaca rather than Jalisco, since in Oaxaca
the relevant chloroplast haplotypes all occur and S phaseolin is also present.
Infraspecific taxonomy of Phaseolus vulgaris
Three particularly significant events have occurred in the evolutionary history of P.
vulgaris. Firstly, early intercontinental dispersal resulted in genetic isolation of wild
populations in the two continents, so they differentiated into what have been called
the Mesoamerican and Andean gene pools. Secondly, beans in each of these gene
pools were independently domesticated, probably in more than one location in the
case of Mesoamerica. Thirdly, domesticated beans diverged and diversified under
human selection into different ecogeographic groups (races), different agronomic
groups (e.g., climbing or bush beans) and different use groups (popping beans, black
beans, navy beans, pinto beans, etc.). The question then arises, should any or all of
these events be recognised in the infraspecific classification of P. vulgaris and if so,
how?
Intercontinental dispersal and divergence of gene pools
The many differences between Mexican and Andean wild beans have led to their
being recognised as distinct varieties (see DEBOUCK 1991 for further discussion). This
provides a formal taxonomic rank for the informal category of gene pool.
Wild beans from Ecuador and northern Peru are morphologically intermediate between
those of the Mesoamerican and Andean gene pools (DEBOUCK et al. 1993),
and combine isozyme alleles characteristic of both gene pools (GEPTS 1993). They
are genetically unique in their RAPD and AFLP patterns (FREYRE et al. 1996, TOHME
et al. 1996) and in their mitochondrial DNA (KHAIRALLAH et al. 1992). They also carry
an apparently ancestral type of phaseolin (KAMI et al. 1995). It has been suggested
that these populations are relicts of the ancestral stock from which the Mesoamerican
and Andean gene pools are derived (KAMI et al. 1995, TOHME et al. 1996). Wild
beans from Costa Rica south to Colombia are also morphologically intermediate
(SINGH et al. 1991), while a study of AFLPs showed a genetic continuum between
wild beans from the northern and southern ends of the range (TOHME et al. 1996).
Under the Rules of the International Code of Botanical Nomenclature, populations
that are intermediate between two varieties must be included in one or the other
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