Conservation and Change: A Comparison of In-situ and Ex-situ Conservation of Jala Maize Germplasm in Mexico
Conservation of agricultural genetic diversity is necessary as a source of variation for breeding and selection efforts. Traditionally, conservation efforts focus on the maintenance of diversity both in genebanks (ex-situ) and on farm (in-situ). This study takes an interdisciplinary approach to understanding in-situ and ex-situ conservation of Jala, a gigantic Mexican variety of maize (Zea mays). To understand the social and policy context of Jala farmers? conservation decisions, a formal, random survey of 79 households was undertaken. In the past, 77% of farmers grew Jala. Today, 19% of farmers plant Jala on only 5% of the cultivated maize area. Jala growers are ?generalists,? older farmers, seed keepers with larger landholdings, diversified in many income-producing activities, with small Jala plots for household consumption and local sale; or ?specialists,? younger farmers, less likely to save seed, with smaller landholdings, heavily (75% of area) committed to Jala. To date, Jala has been effectively conserved in farmers? fields; conservation will likely continue as long as farmers have an economic incentive to do so. To understand the genetic effects of in-situ and ex-situ conservation, a diversity study was performed using 22 microsatellite (SSR) markers. Populations studied included Jala from farmers? fields, genebank Jala, other maize races, and teosinte (Zea spp.). Farmers? Jala populations were highly diverse but not highly differentiated (Fst <0.05), indicating the unit of conservation is likely the valley, not an individual farmer. Older Jala genebank populations were less diverse and more differentiated from recent Jala, perhaps due to genebank collection and regeneration methods. Jala?s allelic profiles remained stable from 1944 to 1999. Therefore, Jala appears to have been well-conserved both in-situ and ex-situ. By resampling the above data (1000 bootstraps), optimal sample size was evaluated. The number of individuals for accurate measurement of allele number (An), gene diversity (He) and population differentiation (Fst) were small. Unexpectedly, population category?whether Jala from the genebank or teosinte?had little effect on optimal sample size. Studying populations derived from advanced generations of the hybrid variety Dekalb 880 showed gene flow in the valley. These populations represent a reservoir of conserved traditional Jala genetic material.
genetics; conservation; Zea mays; agriculture; SSR; genetic diversity; microsatellite
dissertation or thesis