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6 September 2010
Modern cactus traced to living ancestor in Mexico

In an article published in the Annals of Botany, a team from the Universidad Nacional Autónoma de México (UNAM) describes the domestication of the Gray Ghost Organ Pipe Cactus. Villagers in the Tehuacán Valley (Mexico) cultivate the cactus in their gardens while a more primitve ancestor of the plant grows wild in nearby forests. The cactus produces a fruit called pitaya.
     According to Dr. Alejandro Casas, an ethnobotanist with the project, "What we found is that the people of the Tehuacán Valley are carefully selecting and cultivating cacti to produce the pitaya they want. They're not attempting to produce one type of pitaya. They have a rich understanding of the cacti and are able to produce fruits with a variety of colours and tastes. We found that the forest cacti showed more diversity in their genes than expected. It is not a case of finding a simple transition from wild to domesticated plants. The methods of propagation of cacti by the traditional farmers, including the production of a variety of fruits, help increase the genetic diversity of the cacti. This is a crucial strategy in conserving the genetic resources of Mesoamerica. In contrast agriculture in the industrialised world aims for mass-produced conformity in fruit."
     Domestication has modified the genes of the cultivated plants. Their chromosomes carry more duplicate alleles than are found in the wild cactus. This would be expected when pollination is restricted to a selected population.
     The implications for the findings are explained by Dr. Mark Olson, a biologist at UNAM who was not a part of the research project. "Mesoamerica is a real laboratory for the study of evolution and domestication is one of the most important ways available for studying the evolutionary process. It is a rare luxury to be able to study not only the descendants of selection but also to be able to examine a true living ancestor. Perhaps more than any other region on earth, Mesoamerica has a range of grades of domestication, from the highly modified, such as maize, to plants only casually managed and in stages of 'incipient domestication'. Understanding this process will be important as Mexico becomes inundated with commercial varieties of corn, beans and other plants, all growing next to their wild ancestors."

Source: Science Daily (25 August 2010)

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