Evolutionary-genetical studie of modern and archaeological samples of maize (Zea mays mays, L.) and beans (Phaseolus vulgaris, L.). / Estudo genético-evolutivo de amostras modernas e arqueológicas de milho (Zea mays mays, L.) e feijão (Phaseolus vulgaris, L.).

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

Seven archaeological samples of maize (Zea mays mays, Lineu), 620±60 to 990±60 years old and one sample of bean (Phaseolus vulgaris, Lineu), 301 ± 39 years old (based on C14 datation), were studied by biomolecular techniques to understand their historical origin. They were found in indigenous subterranean silos, from archaeological sites at Januária (Peruaçu Valley), state of Minas Gerais, Brazil. A segment of the nuclear gene encoding alcohol dehydrogenase 2 (Adh2) was amplified and sequenced from extracts of the maize specimens. In the bean sample, two portions of the nuclear gene encoding the protein Phaseolin were used. In maize, 3 main alele groups were observed for the Adh 2 previously know in the maize origin center in the Central America. In the South America, these groups have also been founded but presenting a characteristic geographical distribution. One of the aleles, considered the most primitive, occurs in the Andean highlands. The other two are present mainly in lowlands, one of them restrict to São Francisco and Paraná-Paraguai rivers basin, along the Atlantic coast. These dates suggest that, historically, different maize varieties were introduced in South America, perhaps in two different periods and spread to distinct regions by migrating or trading human populations. The first introduction is estimated to have occurred about 5,000 years ago, and the second and possibly a third, about 3,000 years later. These introductions must be responsible for the high-/lowland distribution pattern, which maintains up to today. The European colonisation of the South America in the 15-16th century kept this pattern. Portugal conquered the lowlands and Spain the highlands and they maintained a cultural and trade barrier for long time. However in the Southern part of South America there must have been some exchange, since aleles from lowlands were found in archaeological sites in highlands of Chile, and conversely, highland aleles were present in one modern indigenous sample from Paraguay. It should be mentioned that archaeological and modern aleles found in Peru are remarkably different from those of Brazil. This would mean that Brazilian indigenous populations must have been more influenced by Central America culture, rather than from that of Andean highlands. In the case of Januária bean sample, identified as Phaseolus vulgaris, presents the basic genetic type of the Phaseolin of type a. The alleles from modern samples from Mexico to Argentina, indicate a geographical distribution pattern. The alleles originated from Mexico to the Northern region of South America (Colombia, Ecuador and North of Peru) fall in the same group, what we called Northern alleles group, while those from Southern Peru to Argentina fall in another group, that we called Southern alleles group. Apparently Northern group of alleles are older, pointing the corresponding region as the centre of the origin for Phaseolus vulgaris. Southern group of alleles must have been derived from those from the North. This confronts some theories suggesting that bean might have had more than one centre of origin, independently. The Januária sample had six different alleles, two identical to the Northern group. Of the remaining four, two are very close to the Northern group, while the other two may be considered intermediary. No allele similar to the Southern group was found. The conclusion is that the bean sample from Januária is genetically closer to the Northern populations but has vestiges of contacts with populations from Centre and Southern Andes. All put together, maize and beans populations from Januária seem to had a lager relation or influence of materials originating with those from Central Andes, as Peru. Also, a higher genetic diversity was observed within bean genes than maize. Finally, this research demonstrated that plant archaeological samples from the Tropics may contain well preserved genetic material suitable for evolutionary studies and provide data to understand the life history of the Humanity in the Americas.

ASSUNTO(S)

archaeological agriculture feijão fóssil milho fóssil genética vegetal plant evolution archaeological bean plant genetics agricultura pré-história archeological maize evolução vegetal

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