Schriften zu Genetischen Ressourcen - Genres

Multiple domestications and their taxonomic consequences: Phaseolus vulgaris
through one parent only, so heterozygosity does not complicate the analyses. Contrary
to early reports, chloroplast DNA, particularly the non-coding regions of the
molecule, often does vary within a species.
Chloroplast DNA and domestication of common bean
We amplified 10 different regions of chloroplast DNA and studied them by sequencing
and/or restriction digestion (for details, see CHACÓN S. 2001). In a sample of 158
accessions of wild common bean from the CIAT gene bank collection, we identified
16 chloroplast haplotypes, each characterised by at least one unique feature, usually
a nucleotide substitution. A network was constructed which linked these haplotypes
by single mutational steps (Fig. 1), often through inferred haplotypes that may now be
extinct, or not yet collected, or simply not represented in our sample.
Only four of the 16 haplotypes present in wild common bean occur in domesticated
beans, illustrating the familiar founder principle or genetic bottleneck associated with
domestication. Table 1 shows that landraces originating in Mesoamerica differ in
chloroplast haplotype from Andean landraces. The three haplotypes present in
Mesoamerican landraces are found only in wild beans from Mesoamerica and Colombia,
while the single haplotype present in Andean landraces occurs only in wild
beans from central and southern Peru. This provides further evidence of independent
domestication of common bean in Mesoamerica and the Andes. It also agrees with
the DNA studies of BEEBE et al. (2000, 2001) in demonstrating greater molecular diversity
in Mesoamerican landraces than in Andean landraces.
To investigate further whether there were more than two domestications of this crop,
it is necessary to look more closely at the frequencies and distributions of haplotypes
in Mesoamerican common beans (Tab. 2 and 3).
Tab. 2: Chloroplast haplotypes in races of domesticated common bean
(figures represent numbers of accessions; * haplotype resulting from interracial
introgression)
Haplotype
Total
C I K L
Mesoamerican 0 7 65 20 92
Race Mesoamerica 0 4 45 5 54
Race Durango 0 0 18 7 25
Race Jalisco 0 0 1* 8 9
Race Guatemala 0 3 0 0 3
Andean 30 0 1* 0 31
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