Gene Flow: Farmers Keep Maize Thriving and Changing
What role do farmers play in
the evolution of maize
diversity? To understand the
many factors that affect maize
diversity, researchers are
combining knowledge of the
genetic behavior of plants with
information on human
behavior.
Outside a straw and mud-walled house in rural Hidalgo, Mexico, with chickens walking around and the smell of the cooking fire wafting through the air, CIMMYT researcher Dagoberto Flores drew lines with a stick in the red earth as he explained to the woman farmer how maize seed should be planted for an experiment. Along with CIMMYT researcher Alejandro Ramírez, Flores was distributing improved seed in communities where they had conducted surveys for a study on gene flow.
The movement of genes between populations, or gene flow, happens when individuals from different populations cross with each other. CIMMYT social scientist Mauricio Bellon led a study that aimed to find the impact of farmers’ practices on gene flow and on the genetic structure of landraces. Researchers documented how practices differ across farming systems, analyzed their determinants, figured out to what extent farmers control gene flow, and explored gene flow’s impacts on maize’s fitness and diversity and on farmers’ livelihoods.
CIMMYT researcher Dagoberto Flores delivers |
The farmers visited by Flores and Ramírez in June near San Francisco Huatzalingo and Tlacuapan Huautla, Hidalgo, are from just two of 20 study communities spanning ecologies from Mexico’s highlands down to the lowlands. Six months earlier, when farmers were responding to researchers’ survey questions, they asked some questions of their own, such as: What does CIMMYT do? How can we get seed?
Bringing Back
Diversity
The team made it a priority to give the farmers what they requested for free. They drove around in a pick-up truck with seed they had acquired from CIMMYT scientists. They brought black, white, and yellow varieties that were native to the area but to which had been added weevil and drought resistance. They also brought three CIMMYT varieties that were well adapted to a similar environment in Morelos, Mexico. They explained to the farmers how each variety should be planted in separate squares to facilitate pure seed selection. “It’s a way to thank them, to bring something back to the communities,” says Bellon. Bringing improved varieties for experimentation to interested, small-scale farmers also allows researchers to get feedback in a more systematic way.
Farmers in the survey area of rural Hidalgo grow maize on the poorest, most steeply sloping land and struggle with soil diseases, low soil fertility, leaf diseases, low grain prices, and limited information about the use of chemical herbicides. Strong wind, rain, and hurricanes damage crops. Landslides cause erosion.
Where farming is an uphill climb: hillside maize and bean production as practiced by subsistence farmers in Mexico and Central America is difficult, gives relatively low yields, and can often harm the environment. But such farmers have few alternatives. |
Some farms located far from the communities have no highway
access. The paths to farmers’ fields
can be so narrow that not even cargo animals can maneuver on them with
loads, so farmers must
carry the harvest on their backs. Some walk 10 kilometers up and down
slopes with heavy bags.
Maize Landraces not
Museum Pieces
Many people grew coffee around Huatzalingo until about 10 years ago, when the price plummeted. One effect of the price drop has been increased immigration to Mexico City, to the city of Reynosa near the US border, and to lowland areas where orange cultivation is booming.
Farmers have started diversifying into alternative crops such as vanilla, citrus fruits, bananas, sugarcane, sesame, beans, chayote, chili peppers, and lentils, but the poor soils do not favor more lucrative crops. Maize is still the most important agricultural product in people’s diets, and farmers grow it primarily for family consumption.
In Mexico, maize has such great genetic diversity because farmers’ practices encourage the further evolution of maize landraces.
Maize was domesticated about 6,000 years ago within the current borders of Mexico. Farmers created a variety of races to fit different needs by mixing different maize types, and they still experiment to this day. They save seed between seasons and trade seed with each other, and the wind carries pollen between different cultivars to create new mixtures. “Landraces are not artifacts in a museum,” Bellon says. “They are changing, they are moving.”
Gene Flow Study
By learning about the relationships between farmers’ practices and gene flow, researchers hope to promote more effective policies for conserving diversity in farmers’ fields, promote improved varieties, and manage “transgenes” —gene constructs inserted into plants through genetic engineering. The researchers will develop models to try to predict how a transgene would diffuse and behave after being in a population for 10 or 20 years. Funded by the Rockefeller Foundation, the study combines social science with genetics to connect social and biological factors in maize varieties. Molecular markers will help show how much gene flow has occurred over time between the Mexican highlands and lowlands.
Researchers used geographic information systems to choose varied environments for the survey. Starting in October 2003, they sampled maize populations and talked to the male and female heads of 20 households in each community for a total of 800 intensive interviews in 400 households.
For more information:
m.bellon@cgiar.org
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January, 2005