Schriften zu Genetischen Ressourcen - Genres

Multiple domestications and their taxonomic consequences: Phaseolus vulgaris
(which causes problems in distinguishing between the varieties) or else a third variety
must be created for the intermediates. The advantage of an informal category such
as gene pool is that the situation can be described without every accession having to
be placed in a gene pool. In other words, the Mesoamerican and Andean gene pools
can be recognised, together with the Ecuadorian / north Peruvian relict of the ancestral
gene pool if desired. Wild beans from intervening areas can be treated in whatever
way the available information seems to warrant. For example, they may be left
as intermediates or placed in additional gene pools. Furthermore, gene pools, unlike
taxonomic varieties, do not have to be morphologically distinguishable. Gene pool is
a category used to express genetic differentiation, not necessarily a category that can
be recognised in the field.
The chloroplast haplotypes define three lineages of wild P. vulgaris (Fig. 1). These
agree only partially with the picture based on gene pools. Haplotypes E and F are
found in the putatively ancestral relict populations of Ecuador and northern Peru and
seem to represent early derivatives of a lineage that then spread into Central America
(haplotypes G and H). No elements of this lineage seem to have been domesticated.
A second lineage, bearing haplotypes I to O, contains wild beans of the
Mesoamerican gene pool and some of the intermediates. However, the third lineage
(haplotypes A to D and P) combines morphologically distinct wild beans from both
Mesoamerican and Andean gene pools. These chloroplast data are potentially significant
with regard to both conservation and utilisation of genetic resources of wild
beans. For example, Mesoamerican beans with haplotypes A, B and P appear to
have evolved independently of Mesoamerican beans with haplotypes I to O for a long
time so may carry significantly different diversity. They should therefore be prime
candidates for both conservation and evaluation. However, we consider it premature
to try to represent the chloroplast lineages in either formal or informal classifications,
at least until some nuclear phylogenies are available and the chloroplast lineages
checked for congruence with these.
Domestication
As in many species that include a crop and its conspecific wild progenitor, wild and
domesticated common beans are usually placed in different subspecies, ssp. aborigineus
and ssp. vulgaris respectively (see POLHILL and VAN DER MAESEN 1985 for
discussion of this treatment for grain legumes in general, including Phaseolus). However,
subspecies ranks above variety in the taxonomic hierarchy, so if the
Mesoamerican and Andean gene pools are treated as varieties, they cannot then be
subdivided into subspecies. Moreover, at whatever rank the gene pools are treated,
four (not two) names at a lower rank would be needed to classify the wild and domesticated
beans within each gene pool. The current Code of Nomenclature for Cultivated
Plants (TREHANE et al. 1995) recommends that cultivated plants below the
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