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the risk and expense and rely on their century-tested, regionally adapted stocks (Figure 41–2). In Peru, for example, as altitude increases, the percentage of native potatoes in the field increases steadily (Brush, 1980). In Thailand, rice farmers plant the modern semidwarf varieties in part of their land during the dry season and sow traditional varieties during the monsoon season. They have thus established a system that allows them to take advantage of the productivity of irrigated modern varieties during dry months and the stability of the traditional varieties in the wet season when pest outbreaks are common (Grigg, 1974).
As the economic crisis deepens in most developing countries, and rural populations become increasingly impoverished, a sizeable portion of the peasantry is renewing use of the traditional varieties and low-input management practices needed for subsistence agriculture (Altieri and Anderson, 1986). Opting for less crop uniformity may mean lower yields for farmers, but it gives them the extra margin of resistance to pests, diseases, and other environmental hazards—an important
FIGURE 41–2 Bean seeds of different colors expressing high genetic diversity. Harvested from a single field in a rain-fed traditional cropping system in Tlaxcala, Mexico. Photo by M.A.Altieri.