Hugo Perales

Buried seeds avoid predation, thereby ensuring their survival until conditions are suitable for germination. The ability of seedlings to emerge from the soil depends on soil characteristics, burial depth, and the skotomorphogenic program of each species. This process is of interest to agriculture, as deep planting is practiced in wheat, sorghum, oats, and maize crops in certain arid and semi-arid regions of the world. In maize (Zea mays), deep planting can range from 10–40 cm, and only certain landraces are competent for this practice. It is known that varieties resistant to deep-planting exhibit exaggerated mesocotyl elongation, but it is unclear whether resistance to deep planting has selected positively or negatively the growth capacity and/or development of other seedling organs, and whether deep-planting resistance is an ancestral trait in Zea or has evolved after maize domestication. To determine the skotomorphogenic patterns in the subtribe Tripsacinae, deep-planting trials were conducted with representatives belonging to the genera Zea and Tripsacum and the length or number of seedling organs were measured. The majority of maize seedlings grown in darkness exhibited features that we refer to as quasi-photomorphogenic, namely rupture of the coleoptile tip by the first plumular leaf and development of adventitious roots at the coleoptilar node (ARCN), unlike teosintes that displayed a small proportion of individuals with the quasi-photomorphogenic phenotype or species of Tripsacum that maintained a strict skotomorphogenic phenotype prior to emergence. Moreover, ARCN were absent in Tripsacum and rare in teosintes, while seminal roots were uncommon in both Tripsacum and teosintes. In Tripsacinae, relative deep-sowing depth (RDSD) for seedling emergence correlated positively with mesocotyl and stem lengths. Moreover, RDSD correlated negatively with the number of ARCN and seminal roots and the length of the primary root and, to a lesser extent, of the coleoptile. In maize, seminal root primordia development proceeded both embryonically and post-embryonically. These findings indicated that emergence from deeper soil depths influenced the growth and development of all seedling organs, not just the mesocotyl, and that deep-planting resistance is a characteristic that appeared within the Zea genus prior to maize domestication. In addition, we report that Tripsacum caryopses are dispersed by myrmecochory and teosinte caryopses by seed-caching rodents. The ecological significance of skotomorphogenic development programs that aid in the escaping of wild Tripsacinae seedlings from underground caches made by their animal dispersers is discussed.

Understanding how genetic diversity is distributed within maize races is critical for conserving maize genetic diversity. While maize races are traditionally treated as homogeneous units to be targeted by conservation, each race may encompass genetically distinct populations of landraces, shaped by environmental conditions and farmer selection. In this study, the genetic diversity and population structure of the Olotillo race were examined using 89,810 SNPs from 158 samples collected across local, regional, and national scales in Mexico. Additional samples from other races Dzit-bacal , Tuxpeño , and a Mix , group combining Olotillo with other varieties, brought the total to 171 individuals. Population structure analyses (ADMIXTURE, PCA) revealed that genetic clusters do not align with race identity, but instead reflect geographic origin. Inbreeding depression was evident within Olotillo populations, with mean F _IS = 0.746 ± 0.066. A heterozygote deficiency was observed: mean H _e OB = 0.075 ± 0.020, compared to a higher expected heterozygosity ( H _e EX = 0.295 ± 0.002). Expected homozygosity ( H _O EX) of 0.705± 0.002 was observed, reflecting reduced effective genetic variation. The above is reflected in the population contraction signal (e.g., positive Tajima’s D), and no significant differences between scales in H _e EX, H _O EX, and nucleotide diversity (π), suggesting that similar evolutionary forces act across regions with a strong directional selection. These findings underscore the need to ascertain the genetic background among races and to recognize meaningful within-race differentiation. Conservation actions should reflect this structure, promoting targeted seed exchange to counteract genetic erosion while respecting farmer preferences. Olotillo exemplifies how maize diversity is structured not only by genetics, but by cultural and management systems that shape evolution in situ .

Polyculture, or intercropping, is the practice of growing two or more crops simultaneously in time and space. The milpa is a systematic polyculture involving the simultaneous cultivation of maize (Zea mays), beans (Phaseolus spp.), squash (Cucurbita spp.), and other crops. Milpa polyculture initially emerged in the Mesoamerican region (Mexico and Central America) through the concurrent processes of managing, utilizing, and domesticating its constituent crops. It subsequently spread throughout the Americas via the diffusion of maize and the convergence of its domestication with that of its companion crops and other domesticated plants in the continent. Mesoamerican farmers made an outstanding contribution by domesticating and bringing together crops with contrasting morphological and physiological traits that are ecologically, agronomically, and nutritionally complementary. Despite its importance, few quantitative evaluations of this polyculture exist. However, these evaluations indicate that its productivity and land efficiency use (Land equivalent ratio = 1.34) are comparable to those of other intercrops studied on a global scale. We emphasize the importance of transdisciplinary efforts to study this polyculture and highlight its potential applications related to ecological interactions, plant microbiomes and breeding in order to reach sustainable production goals.

Societal Impact Statement: The problem of genetically modified maize contamination in Mexico is the result of both planned and unplanned consequences of scientific and political choices. We show how a risk management strategy based on the modernist dichotomy between “modern” and “native” has failed to protect Mexican landraces and has marginalized other forms of knowledge that are urgently needed to understand and support the fluidity of Mexican biocultural landscapes. Farmers' seed systems are a fundamental source of crop resilience and evolution. They can constitute safe pathways for creating new maize varieties able to withstand climate and societal changes.Summary: In 2001, an alert on the contamination of Mexican maize landraces by genetically modified (GM) maize spurred new actions to conserve the world's biggest reservoir of maize genetic diversity. We analyze how the largest maize collection effort in Mexican history, and the definition of the conservation procedures employed in it, either involved or marginalized different approaches to this environmental problem. The article is grounded in the sociohistorical analysis of the controversy of GM maize contamination and brings together new historiographical perspectives on Mexican scientific and political interest in native maize. It also draws on ethnographic approaches, extended fieldwork, and analysis of data from Mexican government agencies. We show how different epistemological traditions have made the risk of GM maize contamination (in)visible and thereby generated normative choices. We illustrate how the GMO controversy brought the theme of native maize back onto the Mexican political and scientific agenda. The normativity that shaped the controversy in the 2000s influenced current knowledge and how the problem of GM maize introgression is still addressed today. The entanglements between biotechnology, native landraces, and farmers' practices are too dense to be “scientized” and kept separate to be made manageable as areas of purely technical “risk.” The result is a geography of maize infused with all sorts of temporalities and materiality, which escapes the bounds of technoscientific framings. This intricate environment‐making process calls for new collaborations among epistemic cultures to tackle the possible consequences of GMOs for agrobiodiversity, seed systems, and their resilience.

Objetivo: caracterizar el patrón alimentario de las familias campesinas y determinar la influencia de los factores socioeconómicos en el origen y consumo de los alimentos en el Totonacapan poblano (México). Metodología: con la técnica de recordatorio de 24 horas, se aplicó una encuesta a 270 familias sobre su dieta y se documentó la información socioeconómica. Resultados: se registraron 159 alimentos, de los cuales 57.6% tiene procedencia externa e incluyen grasas, lácteos, huevo, pan, pasta de trigo, sal y alimentos y bebidas altas en azúcares. El maíz, algunos frijoles y chiles, las hojas verdes “quelites”, las frutas, la carne de pollo y el puerco proceden en gran medida de la producción propia, local y regional. Valor: se aportan datos sobre la dieta campesina actual y sus implicaciones para la agrodiversidad y la salud. Conclusiones: la dieta campesina se está desligando de la producción de autoconsumo debido a la migración asociada con bajos ingresos.

Seed exchange networks among farmers favor circulation of crop varieties and have been discussed as an effective means of crop diversity conservation. This study aims to document the processes and structure of seed exchange networks of native maize, beans, and squash among farmers and other participating sectors (local market or seed banks), analyzing their influence on agrobiodiversity conservation in the municipalities of Ixtenco and Huamantla, in the Mexican state of Tlaxcala. Through interviews, questionnaires, and social network analysis, nodal farmers were identified. In the maize network, five nodal farmers were detected, the blanco maize being the most commonly exchanged seed. In the bean network, three nodal farmers were identified, with amarillo beans as the most exchanged seed. In the squash network, no nodal farmer was identified. For maize and beans, the greater the number of exchanges, the greater the varieties exchanged. The local market of Huamantla and the Vicente Guerrero seed bank are relevant seed sources. The nodal farmers propitiate circulation of a large number of seed varieties in the exchange networks and contribute to maintenance and conservation of agrobiodiversity.

Summary: Crop diversity underpins the productivity, resilience and adaptive capacity of agriculture. Loss of this diversity, termed crop genetic erosion, is therefore concerning. While alarms regarding evident declines in crop diversity have been raised for over a century, the magnitude, trajectory, drivers and significance of these losses remain insufficiently understood. We outline the various definitions, measurements, scales and sources of information on crop genetic erosion. We then provide a synthesis of evidence regarding changes in the diversity of traditional crop landraces on farms, modern crop cultivars in agriculture, crop wild relatives in their natural habitats and crop genetic resources held in conservation repositories. This evidence indicates that marked losses, but also maintenance and increases in diversity, have occurred in all these contexts, the extent depending on species, taxonomic and geographic scale, and region, as well as analytical approach. We discuss steps needed to further advance knowledge around the agricultural and societal significance, as well as conservation implications, of crop genetic erosion. Finally, we propose actions to mitigate, stem and reverse further losses of crop diversity.