Assessing the vulnerability of traditional maize seed systems in Mexico to climate change

Crop genetic diversity is an indispensable resource for farmers and professional breeders responding to changing climate, pests, and diseases. Anecdotal appraisals in centers of crop origin have suggested serious threats to this diversity for over half a century. However, a nationwide inventory recently found all maize races previously described for Mexico, including some formerly considered nearly extinct. A flurry of social studies seems to confirm that farmers maintain considerable diversity. Here, we compare estimates of maize diversity from case studies over the past 15 y with nationally and regionally representative matched longitudinal data from farmers across rural Mexico. Our findings reveal an increasing bias in inferences based on case study results and widespread loss of diversity. Cross-sectional, case study data suggest that farm-level richness has increased by 0.04 y −1 nationwide; however, direct estimates using matched longitudinal data reveal that richness dropped −0.04 y −1 between 2002 and 2007, from 1.43 to 1.22 varieties per farm. Varietal losses occurred across regions and altitudinal zones, and regardless of farm turnover within the sector. Extinction of local maize populations may not have resulted in an immediate loss of alleles, but low varietal richness and changes in maize's metapopulation dynamics may prevent farmers from accessing germplasm suitable to a rapidly changing climate. Declining yields could then lead farmers to leave the sector and result in a further loss of diversity. Similarities in research approaches across crops suggest that methodological biases could conceal a loss of diversity at other centers of crop origin.in situ conservation | crop evolution | climate change | corn

Section: Discussionmentioning

confidence: 93%

Section: Discussionmentioning

confidence: 99%

Genetic erosion in maize’s center of origin

Dyer

López‐Feldman

Yunez-Naude

et al. 2014

“…Insights from the literature on seed systems elucidate this two-sided reason for the low adoption. On the one hand, informal seed systems are important local safety nets (22,26,33); on the other hand, introduction of modern varieties in an ad hoc manner can increase vulnerability in the affected communities (35). These insights provide important background for considering the sustainability of development assistance initiatives aimed at modernizing the seed sector and introducing new sorghum varieties in Africa.…”

Section: Resultsmentioning

confidence: 99%

“…Impact studies project that anthropogenic climate change will negatively affect sorghum yields in Sub-Saharan Africa (31,32). Such projections pose questions about the availability of appropriate genetic resources and the ability of both breeding programs and local seed systems to develop the required adaptations in a timely manner (33,34). Insight in local seed systems can contribute to more sustainable development assistance efforts aimed at building resilience in African agriculture in the face of climate change and human insecurity (25,35).…”

mentioning

confidence: 99%

Ethnolinguistic structuring of sorghum genetic diversity in Africa and the role of local seed systems

Westengen

Okongo²,

Onek

et al. 2014

Significance This paper shows that cultural factors play a key role in shaping the genetic structure in sorghum. We present molecular evidence of close associations between sorghum population structure and the distribution of ethnolinguistic groups in Africa. We show that traditional seed-management practices, which have played an important role for survival and expansion of agropastoral groups in the past, still are remarkably resilient to threats to human security. We argue that efforts to strengthen African sorghum seed systems are more likely to be successful when building on, rather than seeking to replace, existing traditional seed systems and landraces.

“…Several studies have highlighted the importance of informal seed exchange networks as an essential component of the resilience of local farming systems (1, 2), e.g., in potato (3), maize (4,5), and manioc (6)(7)(8). Exchanging seeds not only allows farmers to obtain new landraces but also to recover lost types or to renew their stock of seeds (1).…”

mentioning

confidence: 99%

Marriage exchanges, seed exchanges, and the dynamics of manioc diversity

Delêtre

McKey

Hodkinson

2011

The conservation of crop genetic resources requires understanding the different variables-cultural, social, and economic-that impinge on crop diversity. In small-scale farming systems, seed exchanges represent a key mechanism in the dynamics of crop genetic diversity, and analyzing the rules that structure social networks of seed exchange between farmer communities can help decipher patterns of crop genetic diversity. Using a combination of ethnobotanical and molecular genetic approaches, we investigated the relationships between regional patterns of manioc genetic diversity in Gabon and local networks of seed exchange. Spatially explicit Bayesian clustering methods showed that geographical discontinuities of manioc genetic diversity mirror major ethnolinguistic boundaries, with a southern matrilineal domain characterized by high levels of varietal diversity and a northern patrilineal domain characterized by low varietal diversity. Borrowing concepts from anthropology-kinship, bridewealth, and filiation-we analyzed the relationships between marriage exchanges and seed exchange networks in patrilineal and matrilineal societies. We demonstrate that, by defining marriage prohibitions, kinship systems structure social networks of exchange between farmer communities and influence the movement of seeds in metapopulations, shaping crop diversity at local and regional levels.seed transmission | social reproduction | traditional economic systems I n smallholder farming systems, farmers maintain a large diversity of cultivated species and recognize many different types (landraces) within each of their crops. Farmers dynamically manage this agricultural biodiversity by continually collecting, testing, and selecting new strains with unusual and interesting traits, sourcing "seeds" (here understood as propagules, i.e., true seeds, tubers, rhizomes, or stem cuttings) through different networks, most of which involve exchanging germplasm with other farmers.Several studies have highlighted the importance of informal seed exchange networks as an essential component of the resilience of local farming systems (1, 2), e.g., in potato (3), maize (4, 5), and manioc (6-8). Exchanging seeds not only allows farmers to obtain new landraces but also to recover lost types or to renew their stock of seeds (1). Through these exchange networks, farmers compile highly diversified portfolios of landraces capable of buffering the effects of unpredictable environmental changes (2). Seed exchange represents a key mechanism in the dynamics of crop genetic diversity (9-11). However, the rules that channel the movement of seeds within and among farming communities have received little attention from geneticists and ethnobotanists alike (12).In small-scale farming communities, circulation of crop landraces is often channeled by marriage networks (7,8,13,14). By defining marriage prohibitions, kinship systems structure social networks of exchange between kin (related by descent) and affines (related by marriage). Kinship systems thus determine the conn...