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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.

Globally, farmers cultivate and maintain crop landraces (i.e., traditional varieties). Landraces contain unique diversity shaped in part by natural and human‐mediated selection and are an indispensable resource for farmers. Since environmental conditions change with elevation, crop landraces grown along elevational gradients have provided ideal locations to explore patterns of local adaptation. To further probe traits underlying this differentiation, transcriptome signatures can help provide a foundation for understanding the ways in which functional genetic diversity may be shaped by environment. In this study, we returned to an elevational gradient in Chiapas, Mexico, to assess transcriptional differentiation of genes underlying UV‐B protection in locally adapted maize landraces from multiple elevations. We collected and planted landraces from three elevational zones (lowland, approximately 600 m; midland, approximately 1,550 m; highland approximately 2,100 m) in a common garden at 1,531 m. Using RNA‐seq data derived from leaf tissue, we performed differential expression analysis between maize from these distinct elevations. Highland and lowland landraces displayed differential expression in phenylpropanoid and flavonoid biosynthesis genes involved in the production of UV‐B protectants and did so at a rate greater than expected based on observed background transcriptional differentiation across the genome. These findings provide evidence for the differentiation of suites of genes involved in complex ecologically relevant pathways. Thus, while neutral evolutionary processes may have played a role in the observed patterns of differentiation, UV‐B may have also acted as a selective pressure to differentiate maize landraces in the region. Studies of the distribution of functional crop genetic diversity across variable landscapes can aid us in understanding the response of diversity to abiotic/biotic change and, ultimately, may facilitate its conservation and utilization.

Hybridization is a common phenomenon in plants and can lead to the introgression of alleles from one population into another, generate new hybrid lineages, or cause species extinction. The environmental conditions and the genetic background of the participating populations may influence these outcomes since they can affect the fitness of hybrids, thereby increasing or decreasing the chances of introgression. Thus, it is important to understand the context‐dependent prospects for introgression of alleles into diverse populations and under multiple ecological environments. Crop‐wild hybridization presents an opportunity to explore these dynamics in agroecosystems. To this end, we used diverse wild and hybrid sunflowers from across the northern United States as a basis for evaluating variation in morphological traits and assessing context‐dependence selection. These crop‐wild hybrids and their wild counterparts were grown under agricultural conditions in the field with and without wheat competition. Interactions between origin and cross type affected expression of early functional traits, while interactions between competition and cross type acted on reproductive traits. A smattering of early and reproductive traits were affected by interactions between cross type and competition that varied by origin (i.e., 3‐way interactions). Seven functional traits, especially number of branches and tertiary head diameter, underwent net and direct directional selection, while six out of these seven traits appear to also be experiencing non‐linear selection dynamics. In general, wild‐like traits were favored under both sets of conditions, while, under wheat competition, some crop‐like traits related to fast growth and primary head diameter became important. These data reaffirm the hypothesis that stressful conditions establish a scenario more suitable for crop introgression and clarify that non‐linear selection dynamics may play a role in this process. Fil: Presotto, Alejandro Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentina. Universidad Nacional del Sur. Departamento de Agronomía; Argentina Fil: Hernández, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentina. Universidad Nacional del Sur. Departamento de Agronomía; Argentina Fil: Mercer, Kristin L.. Ohio State University; Estados Unidos

Limiting agricultural P losses to surface waters is essential to overall ecological sustainability of agroecosystems. Recent studies have suggested that decreasing P fertilization rates decrease organic matter content, adversely impacting other mitigation strategies. Corn–soy cropping systems from three soil regions of Ohio were subjected to 11 yr of P restriction to measure impacts on soil P availability and agronomic performance as well as both physical and biological indicators of soil health. While both soil P availability and plant tissue P contents decreased with P fertilization rate, crops did not exhibit signs of P stress, such as consistent decreases in corn yield. Organic P levels increased in plots with no P fertilization. Both physical and biological indicators of soil health showed mixed responses to P fertilization, although trends suggested greater organic matter stabilization in unfertilized plots relative to the fertilized plots. This study suggests that reductions in P fertilization can result in more efficient nutrient cycling without adverse agronomic impacts, although it is unclear how long this effect would persist before P restriction would consistently impact grain yields.

Global climate change is having a significant effect on agriculture by causing greater precipitation variability and an increased risk of drought. To mitigate these effects, it is important to identify specific traits, adaptations, and germplasm that improve tolerance to soil water deficit. Local varieties, known as landraces, have undergone generations of farmer-mediated selection and can serve as sources of variation, specifically for tolerance to abiotic stress. Landraces can possess local adaptations, where accessions adapted to a particular environment will outperform others grown under the same conditions. We explore adaptations to water deficit in chile pepper landraces from across an environmental gradient in Mexico, a center of crop domestication and diversity, as well in improved varieties bred for the US. In the present study, we evaluated 25 US and Mexico accessions in a greenhouse experiment under well-watered and water deficit conditions and measured morphological, physiological, and agronomic traits. Accession and irrigation regime influenced biomass and height, while branching, CO2 assimilation, and fruit weight were all influenced by an interaction between accession and irrigation. A priori group contrasts revealed possible adaptations to water deficit for primary branching, CO2 assimilation, and plant height associated with geographic origin, domestication level, and pepper species. Additionally, within the Mexican landraces, the number of primary branches had a strong relationship with precipitation from the environment of origin. This work provides insight into chile pepper response to water deficit and adaptation to drought and identifies possibly tolerant germplasm.

Responses to drought within a single species may vary based on plant development stage, drought severity, and the avoidance or tolerance mechanisms employed. Early drought stress can restrict emergence and seedling growth. Thus, in areas where water availability is limited, rapid germination leading to early plant establishment may be beneficial. Alternatively, germination without sufficient water to support the seedling may lead to early senescence, so reduced germination under low moisture conditions may be adaptive at the level of the population. We studied the germination response to osmotic stress of diverse chile pepper germplasm collected in southern Mexico from varied ecozones, cultivation systems, and of named landraces. Drought stress was simulated using polyethylene glycol solutions. Overall, survival time analysis revealed delayed germination at the 20% concentration of PEG across all ecozones. The effect was most pronounced in the genotypes from hotter, drier ecozones. Additionally, accessions from wetter and cooler ecozones had the fastest rate of germination. Moreover, accessions of the landraces Costeño Rojo and Tusta germinated more slowly and incompletely if sourced from a drier ecozone than a wetter one, indicating that slower, reduced germination under drought stress may be an adaptive avoidance mechanism. Significant differences were also observed between named landraces, with more domesticated types from intensive cultivation systems nearly always germinating faster than small-fruited backyard- or wild-types, perhaps due to the fact that the smaller-fruited accessions have generally undergone less selection. Thus, we conclude that there is evidence of local adaptation to both ecozone of origin and source cultivation system in germination characteristics of diverse chile peppers.

What constitutes science? What is the relation between scientific practice and capitalist modernity? What are the responsibilities of scientists in the face of our planetary crisis? In 2016 the Zapatistas of Chiapas organized an event to reflect upon and discuss the practice and politics of science. This paper — based on a script of a presentation at the event — takes up these questions, drawing from radical thought and philosophy of science to consider science in our present conjuncture.

In crop centers of origin and diversity, often biotic and abiotic conditions vary across the landscape creating the possibility for local adaptation of crops, whereby local landraces perform better than non-local ones under local conditions. By studying patterns of local adaptation we can better understand the degree of adaptation of landraces, phenotypic mechanisms driving that adaptation, and the plastic responses of adapted populations to environmental change. Studying these basic processes in crop centers of origin and diversity improves basic understanding of adaptive evolution and provides insight for existing farming systems encountering climate change. Using maize landraces collected and reciprocally transplanted in the field in two years along an elevational gradient in Chiapas, Mexico, we aimed to understand their degree of local adaptation, the distribution of adaptive diversity within elevations, and how landraces compared to improved varieties in their responses to environmental variation. We found some patterns consistent with local adaptation among the landraces, although the degree of adaptation differed across measures of fitness components and years. Flowering time variables showed more variability within elevations than total fitness estimates or fitness components did. Improved varieties, like low elevation landraces, were not well-adapted to conditions at higher elevations, although they did possess some beneficial traits. These data reaffirmed experimentally the local adaptation of landraces and their difficulty in reproducing under novel conditions, and indicated the importance of landraces for high productivity (especially in middle and high elevation systems).

Studies of genetic diversity among phenotypically distinct crop landraces improve our understanding of fruit evolution and genome structure under domestication. Chile peppers (Capsicum spp. L.) are economically valuable and culturally important species, and extensive phenotypic variation among landraces exists in southern Mexico, a center of C. annuum diversity. We collected 103 chile pepper seed accessions from 22 named landraces across 27 locations in southern Mexico. We genotyped these accessions with genotyping by sequencing (GBS), yielding 32,623 filtered single‐nucleotide polymorphisms. Afterward, we genotyped 32 additional C. annuum accessions from a global collection for comparison to the Mexican collection. Within the Mexican collection, genetic assignment analyses showed clear genetic differentiation between landraces and clarified the unique nature of the Tusta landrace. Further clustering analyses indicated that the largest fresh‐use Chile de Agua and dry‐use Costeño landraces were part of separate clades, indicating that these two landraces likely represent distinct populations. The global accessions showed considerable admixture and limited clustering, which may be due to the collapse of use‐type divisions outside of Central America. The separation of the Mexican landraces in part by fruit morphology related to use highlights the relevance of this use‐type morphological diversity for plant breeders and the utility of fruit development variation for evolutionary biologists.

Aim: To fill critical knowledge gaps with regard to the distributions and conservation status of the wild relatives of chile peppers (Capsicum L.).Location: The study covered the potential native ranges of currently recognized wild Capsicum taxa, throughout the Americas.Methods: We modelled the potential distributions of 37 wild taxa in the genus, characterized their ecogeographic niches, assessed their ex situ and in situ conservationstatus, and performed preliminary threat assessments.Results: We categorize 18 of the taxa as high priority for further conservation action as a consequence of a combination of their ex situ and in situ assessments, 17 as medium priority, and two as low priority. Priorities for resolving gaps in ex situ conservation were determined to be high for 94.6%, and medium or high with regard to increased habitat protection for 64.9% of the taxa. The preliminary threat assessment indicated that six taxa may be critically endangered, three endangered,ten vulnerable, six near threatened and 12 least concern.Main conclusions: Taxonomic richness hot spots, especially along the Atlantic coast of Brazil, in Bolivia and Paraguay, and in the highlands of Colombia, Ecuador, Peru and Venezuela, represent particularly high priority regions for further collecting for ex situ conservation as well as for enhanced habitat conservation. Fil: Khoury, Colin K.. National Laboratory For Genetic Resources Preservation; Estados Unidos Fil: Carver, Daniel. State University of Colorado - Fort Collins; Estados Unidos Fil: Barchenger, Derek W.. World Vegetable Center; China Fil: Barboza, Gloria Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina Fil: Zonneveld, Maarten. World Vegetable Center; China Fil: Jarret, Robert. United States Department of Agriculture. Agriculture Research Service; Estados Unidos Fil: Bohs, Lynn. University Of Utah; Estados Unidos Fil: Kantar, Michael. University of Hawaii at Manoa; Estados Unidos Fil: Uchanski, Mark. State University of Colorado - Fort Collins; Estados Unidos Fil: Mercer, Kristin. Ohio State University; Estados Unidos Fil: Nabhan, Gary Paul. University of Arizona; Estados Unidos Fil: Bosland, Paul W.. New Mexico State University.; Estados Unidos Fil: Greene, Stephanie L.. National Laboratory For Genetic Resources Preservation; Estados Unidos

Summary Restoration is normally conducted with the goal of creating plant populations that establish, survive, successfully reproduce, contribute to ecosystem function and persist in the long term. Restoration often relies on revegetation that, on large scales, requires agronomic increase of native plant materials. During this propagation process, restoration populations are subject to genetic sampling as well as natural and artificial selection that could result in adaptation contrasting sharply with that of native populations. Here we draw on insights from the evolutionary and agricultural literature to illustrate how changes in the amount and type of genetic variation in ex situ repositories (source collections and production farms) could affect plant performance in restoration. The consequences of intentional and/or inadvertent evolutionary modification of restoration materials are discussed with respect to population viability and ecosystem function. Synthesis and applications. We conclude that sampling effects and intentional and unintentional selection during collection, propagation and restoration planting have the potential to diminish restored populations. We describe testing for evolutionary change in plant materials using neutral molecular markers and/or field observations. Six practices, multiple collections through time, multiple collections through space, large effective population size, provenance tracking, promoting gene flow and reducing selection comprise ‘evolutionarily enlightened management’ that decreases the potential for unintentional evolution and maladaptation.

Premise of research. Weedy species that invade new areas may experience shifts in environmental conditions across generations. Since maternal environments can significantly influence embryo development, shifts in maternal environments could alter the ability of offspring to colonize.Methodology. Here, we report the results of a set of field experiments that study adaptive transgenerational plasticity across three generations using the agricultural, annual weed, Raphanus raphanistrum. We grew replicate lineages across a gradient of experimentally manipulated soil moisture conditions (control rain [×2], no rain, double normal precipitation) for two generations (maternal and offspring) and transplanted individuals of each population to manipulated or unmanipulated soil moisture conditions. We then measured the consequences of the maternal and offspring soil moisture manipulations on traits critical for weediness in the second generation of plants and third (grandchild) generation of seeds.Pivotal results. Ma...

Hybridization produces strong evolutionary forces. In hybrid zones, selection can differentially occur on traits and selection intensities may differ among hybrid generations. Understanding these dynamics in crop–wild hybrid zones can clarify crop-like traits likely to introgress into wild populations and the particular hybrid generations through which introgression proceeds. In a field experiment with four crop–wild hybrid Helianthus annuus (sunflower) cross types, we measured growth and life history traits and performed phenotypic selection analysis on early season traits to ascertain the likelihood, and routes, of crop allele introgression into wild sunflower populations. All cross types overwintered, emerged in the spring, and survived until flowering, indicating no early life history barriers to crop allele introgression. While selection indirectly favored earlier seedling emergence and taller early season seedlings, direct selection only favored greater early season leaf length. Further, there was cross type variation in the intensity of selection operating on leaf length. Thus, introgression of multiple early season crop-like traits, due to direct selection for greater early season leaf length, should not be impeded by any cross type and may proceed at different rates among generations. In sum, alleles underlying early season sunflower crop-like traits are likely to introgress into wild sunflower populations.

Following the decline of industrial manufacturing, many US cities have experienced severe population reductions that have resulted in large areas of vacant land. Urban agriculture has emerged as a desirable land use for these spaces, but degraded soils are common. Therefore, we measured soil and plant responses to amendments and management in urban lots where vacant houses had recently been demolished in Youngstown, OH, USA. Soil degradation was observed following demolition activities in the form of compaction (bulk density of 1·5–1·8 Mg m−3) and low soil microbial biomass C (21 mg C kg−1 soil). Our split-plot experiment measured the effects of organic matter (OM) amendments produced from yard wastes and the use of raised beds on soil properties and vegetable crop yields. Two years after their application, OM amendments resulted in significant improvement to a number of soil physical, chemical, and biological properties. Vegetable crop yields were improved by OM amendments in 2011 and by both OM amendments and the use of raised beds in 2012. A soil quality index, developed using factor analysis and the Soil Management Assessment Framework, produced values ranging from 0·60 to 0·85, which are comparable to those reported for rural agricultural soils. All results indicate that urban agriculture can be productive in vacant urban land and that amendments produced from urban yard wastes can improve soil quality at previously degraded sites and increase crop yields for urban agriculture. Copyright © 2014 John Wiley & Sons, Ltd.

This paper examines how a new highway in Belize will change a tropical forest landscape. Since the end of British colonialism (1981), the Maya communities in Belize's Toledo District have struggled with the state for control of the lands they have customarily used to produce a livelihood. We were approached by some Maya leaders, who recognize that the paving of a new highway through their villages could transform Maya agricultural practices and thus land use and cover change (LUCC), and asked to produce an analysis that could assist them in managing their lands. We braid together historical, social, political, economic, and satellite data to answer two questions: (1) How has land cover changed since 1975 in areas with Maya customary versus noncustomary land-use practices? (2) What will be the consequences of paving the new highway through this region for the landscape and the Maya communities? Using a multifaceted LUCC/political ecology analysis we found that forest clearing is greatest where noncustomary farming practices are employed. Noncustomary practices are spatially concentrated along the Belize-Guatemala border; the shift to noncustomary practices resulted from inmigration by war refugees who maintained close ties to Guatemalan markets. The paving of the highway promises to reduce the functional distance to Guatemala's markets, which could change land use in other villages to the detriment of the forests because of the likely diffusion of noncustomary farm practices. Forest change will be shaped by the region's complex political geography.

Background Landrace farmers are the keepers of crops locally adapted to the environments where they are cultivated. Patterns of diversity across the genome can provide signals of past evolution in the face of abiotic and biotic change. Understanding this rich genetic resource is imperative especially since diversity can provide agricultural security as climate continues to shift. Results Here we employ RNA sequencing (RNA-seq) to understand the role that conditions that vary across a landscape may have played in shaping genetic diversity in the maize landraces of Chiapas, Mexico. We collected landraces from three distinct elevational zones and planted them in a midland common garden. Early season leaf tissue was collected for RNA-seq and we performed weighted gene co-expression network analysis (WGCNA). We then used association analysis between landrace co-expression module expression values and environmental parameters of landrace origin to elucidate genes and gene networks potentially shaped by environmental factors along our study gradient. Elevation of landrace origin affected the transcriptome profiles. Two co-expression modules were highly correlated with temperature parameters of landrace origin and queries into their ‘hub’ genes suggested that temperature may have led to differentiation among landraces in hormone biosynthesis/signaling and abiotic and biotic stress responses. We identified several ‘hub’ transcription factors and kinases as candidates for the regulation of these responses. Conclusions These findings indicate that natural selection may influence the transcriptomes of crop landraces along an elevational gradient in a major diversity center, and provide a foundation for exploring the genetic basis of local adaptation. While we cannot rule out the role of neutral evolutionary forces in the patterns we have identified, combining whole transcriptome sequencing technologies, established bioinformatics techniques, and common garden experimentation can powerfully elucidate structure of adaptive diversity across a varied landscape. Ultimately, gaining such understanding can facilitate the conservation and strategic utilization of crop genetic diversity in a time of climate change. Electronic supplementary material The online version of this article (doi:10.1186/s12864-017-4005-y) contains supplementary material, which is available to authorized users.

Abstract The increased incidence of extreme temperature events due to global climate change poses a major challenge for crop production. Ability to increase temperature tolerance through genetic improvement requires understanding of how crops and their wild relatives respond to extreme temperatures. We developed a high-throughput technique to evaluate tolerance to freezing stress (FS) and heat stress (HS) in wild, crop–wild hybrid and cultivated sunflower (Helianthus annuus L.). We also investigated whether trade-offs exist between stress tolerance and growth under benign conditions. Eleven experiments were performed under a combination of growth-chamber and field conditions. In growth-chamber experiments, FS and HS consisted of exposing acclimated plants at the 2–4-leaf stage to temperatures ranging from to –2.5°C to –4°C for 2–4 h and from 52°C to 54°C for 2–3 h. In the field, plants were grown for 32 days during midwinter (FS: average Tmean = 9.9°C and Tmin = 3.8°C) or for 10 days in a heat tent (HS: average Tmean = 30.1°C and Tmax = 43.3°C). We observed large differences in tolerance to FS and HS between wild and cultivated sunflower. Wild sunflower showed higher FS tolerance than cultivated in both growth-chamber and field experiments, whereas cultivated sunflower showed higher HS tolerance in growth-chamber experiments. No differences in HS tolerance were observed in the field. Crop–wild hybrids generally showed intermediate HS and FS tolerance. We found no evidence of a growth-tolerance trade-off, which suggests that tolerance might be introgressed into elite germplasm without growth penalties. The study reveals that wide genetic variation for the tolerance to extreme temperatures exists in the primary gene pool of sunflower.

• Premise of the study: The fitness of an offspring may depend on its nuclear genetic composition (via both parental genotypes) as well as on genetic maternal effects (via only the maternal parent). Understanding the relative importance of these two genetic factors is particularly important for research on crop-wild hybridization, since traits with important genetic maternal effects (e.g., seed size) often differ among crops and their relatives. We hypothesized that the effects of these genetic factors on fitness components would change across the life cycle of hybrids.• Methods: We followed seed, plant size, and reproductive traits in field experiments with wild and four crop-wild hybrids of sunflower (Helianthus annuus), which differed in nuclear genetic composition and maternal parent (wild or F1 hybrid).• Key results: We identified strong genetic maternal effects for early life cycle characteristics, with seeds produced on an F1 mother having premature germination, negligible seed dormancy, and greater seedling size. Increased percentages of crop alleles also increased premature germination and reduced dormancy in seeds produced on a wild mother. For mature plants, nuclear genetic composition dominated: greater percentages of crop alleles reduced height, branching, and fecundity.• Conclusions: Particular backcrosses between hybrids and wilds may differentially facilitate movement of crop alleles into wild populations due to their specific features. For example, backcross seeds produced on wild mothers can persist in the seed bank, illustrating the importance of genetic maternal effects, whereas backcross individuals with either wild or F1 mothers have high fecundity, resulting from their wild-like nuclear genetic composition.

Summary 1. Three common goals for restoration are (i) rapid plant establishment, (ii) long-term plant persistence and (iii) restoration of functioning ecosystems. Restoration practitioners often use cultivars optimized for rapid plant establishment under highly disturbed conditions to achieve the first goal; locally adapted genotypes are championed for the second because they can be well suited for local environmental conditions. Restoring functioning ecosystems is considered a loftier goal that practitioners struggle to achieve because we lack proven techniques. 2. Similar to the demonstrated benefits of species, functional and phylogenetic diversity for ecosystem functions (EFs), recent genetic diversity (GD)–ecosystem function (EF) experiments have shown that increases in plant GD can positively influence many different EFs. Would the introduction of diverse plant genotypes of a given species into a restoration enhance ecosystem functioning and the evolutionary potential of restored populations? 3. In this review, we first examine three propagule-sourcing approaches: cultivar, local adaptation and GD. Next, we raise questions that if addressed, could help practitioners implement a GD approach in restoration: (i) How might the selection, relatedness and arrangement of genotypes be optimized to restore functioning ecosystems, (ii) How do traits that affect an EF relate to neutral or adaptive diversity, more common measures of GD and (iii) at which spatial and temporal scales does GD influence EFs in restorations? 4. Synthesis and applications. Although each propagule-sourcing approach may be best suited for a particular restoration goal, each approach may simultaneously benefit other goals. Yet cultivars and locally adapted populations that have experienced artificial and/or natural selection may not possess the levels of diversity that will confer expected benefits to different ecosystem functions. Future research should determine the relative value of each approach (or a combination of approaches) for simultaneously achieving multiple restoration goals. Restoration experiments, where plant genetic diversity (GD) is manipulated and monitored over scales relevant to restoration, could reveal the true promise of a GD approach to restoration.

Gene flow between agricultural crops and related wild plant populations can produce hybrids which differ significantly from their wild counterparts in many life history traits, including seed traits. Seeds from wild annuals often possess significant dormancy, while cultivated varieties have been selected to germinate immediately under favourable conditions. Consequently, the dormancy characteristics of crop–wild hybrids could influence their survival, seed-bank dynamics and, ultimately, the extent to which crop genes persist in wild populations. Dormancy characteristics can be influenced by both maternal effects, as well as the genetics of a seed's embryo, which are the result of contributions from both parents. Here we focus on how maternal effects and embryo genetics affect seed dormancy in crop–wild hybrid sunflowers (Helianthus annuus). Using three laboratory experiments, we quantified the germination and dormancy of 15 crop–wild hybrid sunflower cross types, while also identifying achene characteristics that may influence the differential germination observed. We found that increased frequencies of crop alleles and the maternal effects imparted by hybridization can reduce dormancy, though the effect of increased frequencies of crop alleles was more pronounced in wild- and F1-produced than in the crop-produced achenes. The more open pericarp of the crop-produced achenes and the shorter relative distance that their radicles had to travel to germinate may explain some of the observed maternal effects. Finally, we generated hypotheses about how these results could affect survival and crop gene introgression in the field.

Since plant mating choices are flexible and responsive to the environment, rates of spontaneous hybridization may vary across ecological clines. Developing a robust and predictive framework for rates of plant gene flow requires assessing the role of environmental sensitivity on plant reproductive traits, relative abundance, and pollen vectors. Therefore, across a soil moisture gradient, we quantified pollinator movement, life-history trait variation, and unidirectional hybridization rates from crop (Raphanus sativus) to wild (Raphanus raphanistrum) radish populations. Both radish species were grown together in relatively dry (no rain), relatively wet (double rain), or control soil moisture conditions in Ohio, USA. We measured wild and crop radish life-history, phenology and pollinator visitation patterns. To quantify hybridization rates from crop-to-wild species, we used a simply inherited morphological marker to detect F1 hybrid progeny. Although crop-to-wild hybridization did not respond to watering treatments, the abundance of hybrid offspring was higher in fruits produced late in the period of phenological overlap, when both species had roughly equal numbers of open flowers. Therefore, the timing of fruit production and its relationship to flowering overlap may be more important to hybrid zone formation in Raphanus spp. than soil moisture or pollen vector movements.

We describe techniques for approximating seed bank dynamics over time using Helianthus annuus as an example study species. Strips of permeable polyester fabric and glue can be folded and glued to construct a strip of compartments that house seeds and identifying information, while allowing contact with soil leachate, water, microorganisms, and ambient temperature. Strips may be constructed with a wide range of compartment numbers and sizes and allow the researcher to house a variety of genotypes within a single species, different species, or seeds that have experienced different treatments. As opposed to individual seed packets, strips are more easily retrieved as a unit. While replicate packets can be included within a strip, different strips can act as blocks or can be retrieved at different times for observation of seed behavior over time. We used a high temperature glue gun to delineate compartments and sealed the strips once the seed and tags identifying block and removal times were inserted. The seed strips were then buried in the field at the desired depth, with the location marked for later removal. Burrowing animal predators were effectively excluded by use of a covering of metal mesh hardware cloth on the soil surface. After the selected time interval for burial, strips were dug up and seeds were assessed for germination, dormancy and mortality. While clearly dead seeds can often be distinguished from ungerminated living ones by eye, dormant seeds were conclusively identified using a standard Tetrazolium chloride colorimetric test for seed viability.

Chile peppers, native to the Americas, have spread around the world and have been integrated into the diets of many cultures. Much like their heat content, nutritional content can vary dramatically between different pepper types. In this study, a diverse set of chile pepper types were examined for nutrient content. Some pepper types were found to have high levels of vitamin A, vitamin C, or folate. Correlations between nutrient content, species, cultivation status, or geographic region were limited. Varietal selection or plant breeding offer tools to augment nutrient content in peppers. Integration of nutrient rich pepper types into diets that already include peppers could help combat nutrient deficiencies by providing a significant portion of recommended daily nutrients.

SUMMARYCurrent agricultural practices rely on crops with developmental phenologies adapted to local climate, photoperiods and soils; however, global climate change will alter some abiotic factors (e.g. temperature and precipitation). Previously adapted varieties may be poorly prepared for these changing conditions, if such conditions induce mismatched phenologies. Crops that depend on cross-pollination and synchronous flowering may be most susceptible, e.g. monoecious plants have separate male and female flowers, and changes in flowering synchrony may alter yield. Using genetically diverse (open-pollinated (OP)) and genetically homogeneous (hybrid) varieties of a monoecious crop, courgette, also known as zuchinni (Cucurbita pepo), phenological responses to experimentally manipulated moisture conditions were explored in an agricultural context. Under drier and wetter conditions, the hybrid courgette plants shifted towards a male-biased floral sex ratio due to the reduced production of female flowers. However, flowering synchrony and fruit production were unaffected by moisture treatment in both varieties. The hybrid and OP varieties differed in many traits related to floral sex ratios, phenology, synchrony and fruit production. Further, the OP variety displayed more phenotypic variation than the hybrid in many traits. Being in a population context rather than relying on self-pollination increased the availability of potential mates for a given female flower in both the hybrid and, particularly, the OP variety. Thus, the increased genetic diversity found in OP v. hybrid varieties may buffer the possible environmental effects on flowering synchrony within a cropping context. Finally, the likelihood of female flowers setting fruit increased with the number of male flowers within a population, and the rate of increase was higher in the hybrid variety. In summary, climate change is predicted to reduce investment in female function in some monoecious crops and genetically diverse varieties may play an important role in maintaining reproductive synchrony in altered environments.

Climate change will affect agricultural production by subsistence farms in crop centers of origin, where landraces are conserved in situ . Various strategies for adaptation to climate change have been proposed. In this paper we examine the prospects of what we call the ‘transgenic adaptation strategy’, i.e. the appeal to use transgenic seeds to adapt to climate change, through the lens of smallholder maize farming in Mexico. Landraces are the bedrock of maize production in Mexico. We consider how maize farmers may respond to climate change and the effects of those responses on crop diversity. In this paper, we argue that the promotion of the transgenic adaptation strategy is problematic for biological and social reasons. Smallholder livelihoods in southern Mexico could suffer a disproportionate negative impact if transgenic technology is privileged as a response to climate change. Agroecological and evolutionary approaches to addressing the effects of climate change on smallholder agriculture provides an alternative adaptive strategy.

 Premise: Variation in seedling emergence timing is considered adaptive over the long term in wild populations, but early emergence can result in a fi tness advantage. To explore the adaptive signifi cance of seedling emergence timing, it should be studied under realistic conditions and in the context of other traits that infl uence fi tness.  Methods: In a common garden, we monitored maternal families from seed to fl(including over winter) with intra- and interspecifi c competition. We assessed the effects of emergence timing and plant size on survival to anthesis in different genetic backgrounds and under varying competition.  Key Results: We found genetic variation for emergence (probability and timing), size, and survival to anthesis. We also found negative selection, both phenotypic and genetic, on emergence time, such that early emergers (day 8) had almost twice as great a predicted probability of surviving as later emergers (day 28). Size had strong positive effects on survival and, furthermore, the benefi cial effects of early emergence may be mediated through size. Maternal family and competitive environment can also affect selection on emergence timing.  Conclusions: Our results indicate that early emergence is related to greater survival in wild sunfl ower, although there may be little direct selection on this trait; rather, its importance may be mediated by its effects on highly adaptive traits associated with size. Also, the effects of early emergence may vary across genetic backgrounds and competitive conditions, facilitating the maintenance of variation for this trait across a diverse landscape.

Landraces cultivated in centers of crop diversity result from past and contemporary patterns of natural and farmer-mediated evolutionary forces. Successful in situ conservation of crop genetic resources depends on continuity of these evolutionary processes. Climate change is projected to affect agricultural production, yet analyses of impacts on in situ conservation of crop genetic diversity and farmers who conserve it have been absent. How will crop landraces respond to alterations in climate? We review the roles that phenotypic plasticity, evolution, and gene flow might play in sustaining production, although we might expect erosion of genetic diversity if landrace populations or entire races lose productivity. For example, highland maize landraces in southern Mexico do not express the plasticity necessary to sustain productivity under climate change, but may evolve in response to altered conditions. The outcome for any given crop in a given region will depend on the distribution of genetic variation that affects fitness and patterns of climate change. Understanding patterns of neutral and adaptive diversity from the population to the landscape scale is essential to clarify how landraces conserved in situ will continue to evolve and how to minimize genetic erosion of this essential natural resource.

An intense environmental dispute surrounds the maize-fields of Mexico. Mexican maize traditional varieties (or ‘landraces’) constitute a global genetic resource that may well be critical to future agricultural development and corn breeding. Many environmentalists, farmers, and consumers in Mexico are therefore concerned that their maize landraces may have been ‘contaminated’ by imported transgenic maize, grown in the USA. The criticisms of this transgenic technology are complex and call into question the nature of the boundary between political and ecological (i.e. scientific) disputes. Our paper surveys these criticisms, and this political–scientific boundary, in a three-part analysis. First, we turn to Gramsci’s notes on science from his eleventh prison notebook to rethink the political ecology of transgenic maize, i.e., the way the ecological analysis of transgenic introgression is treated as politics. Second, we present the multiple criticisms of transgenic maize as scalar phenomena. Third, we review the recent scientific literature on transgene introgression to evaluate recent calls for the ‘decontamination’ of Mexican maize. Our reading illustrates two dilemmas facing the group that occupies the hegemonic subject-position in this dispute, ecological scientists. First, the popular desire to ‘decontaminate’ Mexican maize exceeds their capacities (due to complications involved with sampling). Second, although the political debate surrounding ‘contaminated’ Mexican maize exceeds science, the boundary between the dispute’s scientific and parascientific elements cannot be adjudicated scientifically. In other words, the boundary between science and politics is porous. Thus in two respects the dispute is ecological, yet beyond the capacity of this science to resolve. Yet, following Gramsci, these findings should not lead us to see science as mere ideology, or apolitical, or encourage a retreat into metaphysics. Rather it points to the need for a social transformation that sees science as “humanity forging its methods of research … in other words, culture, the conception of the world.” By exploring the dilemmas of decontamination, the dispute over transgene introgression in Mexican maize-fields provides an opportunity to elaborate upon Gramsci’s neglected insights into the politics of science.

Crop landraces are managed populations that evolve in response to gene flow and selection. Cross-pollination among fields, seed sharing by farmers, and selection by management and environmental conditions play roles in shaping crop characteristics. We used common gardens to explore the local adaptation of maize (Zea mays ssp. mays) landrace populations from Chiapas, Mexico to altitude. We sowed seeds of 21 populations from three altitudinal ranges in two common gardens and measured two characteristics that estimate fitness: likelihood of producing good quality seed and the total mass of good quality seed per plant. The probability of lowland plants producing good quality seed was invariably high regardless of garden, while highland landraces were especially sensitive to altitude. Their likelihood of producing good seed quadrupled in the highland site. The mass of good quality seed showed a different pattern, with lowland landraces producing 25% less seed mass than the other types at high elevations. Combining these two measures of fitness revealed that the highland landraces were clearly adapted to highland sites, while lowland and midland landraces appear more adapted to the midland site. We discuss this asymmetry in local adaptation in light of climate change and in situ conservation of crop genetic resources.

A highly publicized study in 2001 reported that maize landraces in Oaxaca, Mexicowere found to contain transgenes, yet not all follow-up research has detected transgenes in the same region. Continued testing for transgenes in Mexican maize, and calls for the removal of transgenes from landraces, have only fueled the debate about the dynamics of gene flow from transgenic maize to landraces in Mexico. This paper reviews these recent findings and discusses how evolution may be expected to alter the frequency of transgenes in crop populations over time. Further, it shows that calls for removing transgenes must be interpreted in light of two ecological complexities: (a) it may be impossible to purge a particular gene from a population and (b) scientists’ ability to accurately determine the presence or absence of transgenes is limited by challenges related to sampling. The paper concludes by outlining two ways forward for removing transgenes from landraces. # 2007 Elsevier B.V. All rights reserved.

After a decade of transgenic crop production, the dynamics of gene introgression into wild relatives remain unclear. Taking an ecological genetics approach to investigating fitness in crop-wild hybrid zones, we uncovered both conditions and characteristics that may promote introgression. We compared diverse crop-wild hybrid genotypes relative to wild Helianthus annuus under one benign and three stressful agricultural environments. Whereas relative fitness of crop-wild hybrids averaged 0.25 under benign conditions, with herbicide application or competition it reached 0.45 and was more variable. In some instances, hybrid fitness matched wild fitness (approximately 1). Thus, wild populations under agronomic stress may be more susceptible to introgression. Although 'domestication' traits are typically considered unlikely to persist in wild populations, we found some (e.g. rapid growth and early flowering) that may enhance hybrid fitness, especially in stressful environments. Rigorous assessment of how particular genotypes, phenotypes, and environments affect introgression will improve risk assessment for transgenic crops.

Gene flow between crop fields and wild populations often results in hybrids with reduced fitness compared to their wild counterparts due to characteristics imparted by the crop genome. But the specifics of the evolutionary outcome of crop-wild gene flow may depend on context, varying due to local environmental conditions and genetic variation within and among wild populations and among crop lines. To evaluate context-dependence of fitness of F1 hybrids, sunflower crop lines were crossed with nine wild populations from across the northern United States. These crop-wild hybrids and their wild counterparts were grown under agricultural conditions in the field with and without wheat competition. Hybrids were far less fecund than wild plants, yet more likely to survive to reproduce. There was considerable variability among wild populations for fecundity and the specific crop line used to generate the crop-wild hybrid significantly affected fecundity. The fitness deficit suffered by crop-wild hybrids varied by population, as did the rankings of the crop-wild hybrids from three different crop lines. Wheat competition decreased fecundity and survival considerably and hampered seed production of wild plants more than that of hybrids. Genotype × environment interactions indicated that the response of fitness to competition differed by population. Consequently, the fitness of hybrids relative to wild plants varied considerably among wild populations and was not consistent across environments. Notably, relative fitness of hybrids was greater under competitive conditions. This research is the first study of its kind to demonstrate that the consequences of crop-wild gene flow are context dependent and contingent on the genetics of the specific wild populations and the local biotic and abiotic conditions.

orative efforts to implement such transformations. t oward this end, we have integrated methods from systems thinking, soft- systems methodology, and agroecosystems analysis, and used a service-learning component to provide students with an op - portunity to apply and evaluate these methods in practice. Most students favorably evaluated the course. Ultimately, we expect that the course will help our students to develop a civic profes - sionalism through which they apply their professional skills to complex public problems in agriculture.

Agroecology derives much of its strength from interactions between disciplines that produce a holistic perspective on agricultural systems and issues. Although ongoing integration of social dynamics into agroecology has strengthened the field, evolution and genetics have not been embraced to the same degree, despite the fact that they have been are discussed in some common agroecology texts. I argue that the field of agroecology could extend its reach and depth by embracing the evolutionary study of agroecosystems. Areas of evolutionary inquiry with relevance to agriculture focus on long or short term processes, encompass a range of scales, incorporate molecular or quantitative genetic analyses, and explore ecological processes to differing degrees.

The genetic variation of quackgrass as a species and the array of environments in which it is found indicate that selection in these different environments could lead to differentiation among quackgrass populations. Yet, a highly diverse environment might not promote the genetic divergence of quackgrass if it poses contradictory selection pressures. To assess the extent of divergence among quackgrass populations, this study compared the morphology of populations of quackgrass for 1 yr in Rosemount, MN, in a “common garden” study. The quackgrass was initially collected from three different farming systems in southeast Minnesota: corn–soybean (CS), oats–hay–corn (OHC), and permanent pasture (PP). The systems represent pasture or arable land and differ in cropping rotations and levels of disturbance. Although no differences among farming systems were detected in multivariate or univariate comparisons, a significant farming system effect was detected between CS and PP systems when the most diversifie...

Domestication has resulted in selection upon seed traits found in wild populations, yet crop-wild hybrids retain some aspects of both parental phenotypes. Seed fates of germination, dormancy, and mortality can influence the success of crop allele introgression in crop-wild hybrid zones, especially if crop alleles or crop-imparted seed coverings result in out-of-season germination. We performed a seed burial experiment using crop, wild, and diverse hybrid sunflower (Helianthus annuus) cross types to test how a cross type's maternal parent and nuclear genetic composition might affect its fate under field conditions. We observed higher maladaptive fall germination in the crop- and F1- produced seeds than wild-produced seeds and, due to an interaction with percent crop alleles, fall germination was higher for cross types with more crop-like nuclear genetics. By spring, crop-produced cross types had the highest overwintering mortality, primarily due to higher fall germination. Early spring germination was identical across maternal types, but germination continued for F1-produced seeds. In conclusion, the more wild-like the maternal parent or the less proportion of the cross type's genome contributed by the crop, the greater likelihood a seed will remain ungerminated than die. Wild-like dormancy may facilitate introgression through future recruitment from the soil seed bank.

Understanding the likelihood and extent of introgression of novel alleles in hybrid zones requires comparison of lifetime fitness of parents and hybrid progeny. However, fitness differences among cross types can vary depending on biotic conditions, thereby influencing introgression patterns. Based on past work, we predicted that increased competition would enhance introgression between cultivated and wild sunflower (Helianthus annuus) by reducing fitness advantages of wild plants. To test this prediction, we established a factorial field experiment in Kansas, USA where we monitored the fitness of four cross types (Wild, F1, F2, and BCw hybrids) under different levels of interspecific and intraspecific competition. Intraspecific manipulations consisted both of density of competitors and of frequency of crop-wild hybrids. We recorded emergence of overwintered seeds, survival to reproduction, and numbers of seeds produced per reproductive plant. We also calculated two compound fitness measures: seeds produced per emerged seedling and seeds produced per planted seed. Cross type and intraspecific competition affected emergence and survival to reproduction, respectively. Further, cross type interacted with competitive treatments to influence all other fitness traits. More intense competition treatments, especially related to density of intraspecific competitors, repeatedly reduced the fitness advantage of wild plants when considering seeds produced per reproductive plant and per emerged seedling, and F2 plants often became indistinguishable from the wilds. Wild fitness remained superior when seedling emergence was also considered as part of fitness, but the fitness of F2 hybrids relative to wild plants more than quadrupled with the addition of interspecific competitors and high densities of intraspecific competitors. Meanwhile, contrary to prediction, lower hybrid frequency reduced wild fitness advantage. These results emphasize the importance of taking a full life cycle perspective. Additionally, due to effects of exogenous selection, a given hybrid generation may be especially well-suited to hastening introgression under particular environmental conditions.

Gene flow between crop fields and wild populations often results in hybrids with reduced fitness compared to their wild counterparts due to characteristics imparted by the crop genome. But the specifics of the evolutionary outcome of crop-wild gene flow may depend on context, varying due to local environmental conditions and genetic variation within and among wild populations and among crop lines. To evaluate context-dependence of fitness of F1 hybrids, sunflower crop lines were crossed with nine wild populations from across the northern United States. These crop-wild hybrids and their wild counterparts were grown under agricultural conditions in the field with and without wheat competition. Hybrids were far less fecund than wild plants, yet more likely to survive to reproduce. There was considerable variability among wild populations for fecundity and the specific crop line used to generate the crop-wild hybrid significantly affected fecundity. The fitness deficit suffered by crop-wild hybrids varied by population, as did the rankings of the crop-wild hybrids from three different crop lines. Wheat competition decreased fecundity and survival considerably and hampered seed production of wild plants more than that of hybrids. Genotype x environment interactions indicated that the response of fitness to competition differed by population. Consequently, the fitness of hybrids relative to wild plants varied considerably among wild populations and was not consistent across environments. Notably, relative fitness of hybrids was greater under competitive conditions. This research is the first study of its kind to demonstrate that the consequences of crop-wild gene flow are context dependent and contingent on the genetics of the specific wild populations and the local biotic and abiotic conditions.

Gene flow from crop fields to wild populations produces hybrids that often differ from their wild counterparts in growth form, phenology, and life history characteristics. Germination and dormancy dynamics have a strong influence on population persistence, competitive dynamics, and ultimately, plant fitness. They may also play a role in modifying crop gene introgression, which has been of primary interest since the release of transgenic crops. We investigated how seed germination and dormancy were affected by sunflower crop–wild hybridization in both laboratory and field experiments. Hybridization increased seed germination and decreased dormancy. Of the nine wild populations we assayed, most of their hybrids had higher germination than the wilds of the same population. However, absolute germination levels varied by population and testing environment. Hybrids produced by three different crop lines differed in germination, and their germination rankings shifted across populations. Increased germination in hybrids could accelerate crop gene introgression, provided that hybrids germinate in an appropriate period. Differences in relative germination of wild and hybrid seed indicated that the effect of germination on introgression will likely vary by population due, in part, to initial levels of dormancy in the population. Therefore, the implications of gene flow from crops with novel characteristics or from transgenic crops will also vary by population.