A natural adaptive syndrome as a model for the origins of cereal agriculture

The Promotion of Alternative Crop Production Paradigms Should Be Founded on Proven Science-Based Approaches

Recent discourse on the need to adopt alternative approaches to sustainable crop production has strongly criticized modern, usually referred to as "industrial", agriculture as the main cause of environmental problems and a loss of biodiversity, which is concerning given that modern agriculture currently feeds over 90% of the global population. Ongoing criticisms of modern agriculture have escalated into calls to replace it, largely based on the belief that alternative approaches will lead to sustainable crop production, although food production potential is rarely mentioned. This paper critically analyzes two such alternatives, agroecology and the Vision for Adapted Crops and Soils (VACS), a sub-set of agroecological approaches with a focus on the Global South. In the case of agroecology, this paper considers the role of diversity in cropping systems and the input reduction paradigm, as well as labor productivity. Modern agriculture already provides a wide range of science-based, proven crop and field diversification options without the need to rely on in-field crop species diversity. Furthermore, a reduction in or the elimination of chemical fertilizers with a preference for compost and manure is not a viable strategy where soils are severely degraded. In the case of the VACS, the planned emphasis on "opportunistic", locally adapted, traditional/indigenous crops is challenged by the importance of introduced crops to food production, especially in Africa. We conclude by recommending a pragmatic approach to using all of the available agricultural practices wisely to produce enough food in an environmentally responsible manner. Global leadership is needed to bring the divergent views of scientists and environmentalists together to improve food production and nutrition, livelihoods, and the agricultural environment.

Crop Diversity in Agroecosystems for Pest Management and Food Production

During the past 30 years, there has been a growing belief in and promotion of agroecosystem diversity for pest management and future food production as an agroecological or nature-based approach. Monoculture agriculture, which produces most of our food, is considered to be highly vulnerable to pests in contrast to plant species-diverse agroecosystems which may possess a greater abundance of natural enemies, keeping pest populations under control. In this paper, we question the role of crop diversity for pest management and explore the relationship between crop and associated diversity and pests through the following processes: environmental stresses that favor monodominance; evolutionary adaptations that resist insect herbivores (genetic resistance response); mechanisms of spatial escape from insect herbivores (escape response); and the role of crop-associated biodiversity. We present strong evidence that not only questions the high vulnerability of monocultures to pest damage but also supports why monocultures continue to produce most of the world's food. Reference is made to the importance of targeted plant breeding and the role of trans-continental crop introduction supported by efficient quarantine for pest management. We conclude that-with the exception of irrigated rice-much more research is needed to better understand the role of crop diversity in agroecosystems for pest management and food production.

Early human selection of crops' wild progenitors explains the acquisitive physiology of modern cultivars

Crops have resource-acquisitive leaf traits, which are usually attributed to the process of domestication. However, early choices of wild plants amenable for domestication may also have played a key role in the evolution of crops' physiological traits. Here we compiled data on 1,034 annual herbs to place the ecophysiological traits of 69 crops' wild progenitors in the context of global botanical variation, and we conducted a common-garden experiment to measure the effects of domestication on crop ecophysiology. Our study found that crops' wild progenitors already had high leaf nitrogen, photosynthesis, conductance and transpiration and soft leaves. After domestication, ecophysiological traits varied little and in idiosyncratic ways. Crops did not surpass the trait boundaries of wild species. Overall, the resource-acquisitive strategy of crops is largely due to the inheritance from their wild progenitors rather than to further breeding improvements. Our study concurs with recent literature highlighting constraints of crop breeding for faster ecophysiological traits.

Fertile Crescent crop progenitors gained a competitive advantage from large seedlings

Cereal domestication during the transition to agriculture resulted in widespread food production, but why only certain species were domesticated remains unknown. We tested whether seedlings of crop progenitors share functional traits that could give them a competitive advantage within anthropogenic environments, including higher germination, greater seedling survival, faster growth rates, and greater competitive ability.Fifteen wild grass species from the Fertile Crescent were grown individually under controlled conditions to evaluate differences in growth between cereal crop progenitors and other wild species that were never domesticated. Differences in germination, seedling survival, and competitive ability were measured by growing a subset of these species as monocultures and mixtures.Crop progenitors had greater germination success, germinated more quickly and had greater aboveground biomass when grown in competition with other species. There was no evidence of a difference in seedling survival, but seed size was positively correlated with a number of traits, including net assimilation rates, greater germination success, and faster germination under competition. In mixtures, the positive effect of seed mass on germination success and speed of germination was even more beneficial for crop progenitors than for other wild species, suggesting greater fitness. Thus, selection for larger seeded individuals under competition may have been stronger in the crop progenitors.The strong competitive ability of Fertile Crescent cereal crop progenitors, linked to their larger seedling size, represents an important ecological difference between these species and other wild grasses in the region. It is consistent with the hypothesis that competition within plant communities surrounding human settlements, or under early cultivation, benefited progenitor species, favoring their success as crops.

Anthropogenic Seed Dispersal: Rethinking the Origins of Plant Domestication

It is well documented that ancient sickle harvesting led to tough rachises, but the other seed dispersal properties in crop progenitors are rarely discussed. The first steps toward domestication are evolutionary responses for the recruitment of humans as dispersers. Seed dispersal-based mutualism evolved from heavy human herbivory or seed predation. Plants that evolved traits to support human-mediated seed dispersal express greater fitness in increasingly anthropogenic ecosystems. The loss of dormancy, reduction in seed coat thickness, increased seed size, pericarp density, and sugar concentration all led to more-focused seed dispersal through seed saving and sowing. Some of the earliest plants to evolve domestication traits had weak seed dispersal processes in the wild, often due to the extinction of animal dispersers or short-distance mechanical dispersal.

Grazing animals drove domestication of grain crops

In addition to large-seeded cereals, humans around the world during the mid-Holocene started to cultivate small-seeded species of herbaceous annuals for grain, including quinoa, amaranth, buckwheat, the millets and several lost crops domesticated in North America. The wild ancestors of these crops have small seeds with indigestible defences and do not germinate readily. Today, these wild plants exist in small fragmentary stands that are not appealing targets for foragers. This combination of traits has led many to argue that they must have been a food of last resort. We propose a new explanation: the domestication of small-seeded annuals involved a switch from endozoochoric dispersal (through animal ingestion) to human dispersal. Humans encountered these plants in dense stands created by grazing megafauna, making them easy to harvest. As humans began to cultivate these plants they took on the functional role of seed dispersers, and traits associated with endozoochory were lost or reduced. The earliest traits of domestication-thinning or loss of indigestible seed protections, loss of dormancy and increased seed size-can all be explained by the loss of the ruminant dispersal process and concomitant human management of wild stands. We demonstrate, by looking at rangeland ecology and herd animal herbivory patterns, that the progenitors of all of these species evolved to be dispersed by megafaunal ruminants and that heavy herbivory leads to dense homogenous clusters of endozoochoric plants. Hence, easily harvested stands on nitrogen hot spots near water sources would have existed in regions where these plants were domesticated. Future experimental and ecological studies could enhance our understanding of the relationships between specific crops and their possible ruminant dispersers.

Origins of the Apple: The Role of Megafaunal Mutualism in the Domestication of Malus and Rosaceous Trees

The apple (Malus domestica [Suckow] Borkh.) is one of the most economically and culturally significant fruits in the world today, and it is grown in all temperate zones. With over a thousand landraces recognized, the modern apple provides a unique case study for understanding plant evolution under human cultivation. Recent genomic and archaeobotanical studies have illuminated parts of the process of domestication in the Rosaceae family. Interestingly, these data seem to suggest that rosaceous arboreal crops did not follow the same pathway toward domestication as other domesticated, especially annual, plants. Unlike in cereal crops, tree domestication appears to have been rapid and driven by hybridization. Apple domestication also calls into question the concept of centers of domestication and human intentionality. Studies of arboreal domestication also illustrate the importance of fully understanding the seed dispersal processes in the wild progenitors when studying crop origins. Large fruits in Rosaceae evolved as a seed-dispersal adaptation recruiting megafaunal mammals of the late Miocene. Genetic studies illustrate that the increase in fruit size and changes in morphology during evolution in the wild resulted from hybridization events and were selected for by large seed dispersers. Humans over the past three millennia have fixed larger-fruiting hybrids through grafting and cloning. Ultimately, the process of evolution under human cultivation parallels the natural evolution of larger fruits in the clade as an adaptive strategy, which resulted in mutualism with large mammalian seed dispersers (disperser recruitment).