crops

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Attract Pollinators, Grow More Food

It seems obvious to say that on farms that rely on insect pollinators for crops to set fruit, having more pollinators around can lead to higher yields. Beyond that, there are questions to consider. How many pollinators and which ones? To what extent can yields be increased? How does the size and location of the farm come into play? Etc. Thanks to a recent study, one that Science News appropriately referred to as “massive,” some of these questions are being addressed, offering compelling evidence that yields grow dramatically simply by increasing and diversifying pollinator populations.

It is also stating the obvious to say that some farms are more productive than others. The difference between a high yield farm and a low yield farm in a given crop system is referred to as a yield gap. Yield gaps are the result of a combination of factors, including soil health, climate, water availability, and management. For crops that depend on insects for pollination, reduced numbers of pollinators can contribute to yield gaps. This five year study by Lucas A. Garibaldi, et al., pubished in a January 2016 issue of Science, involving 344 fields and 33 different crops on farms located in Africa, Asia, and Latin America demonstrates the importance of managing for pollinator abundance and diversity.

The study locations, which ranged from 0.1 hectare to 327.2 hecatares, were separated into large and small farms. Small farms were considered 2 ha and under. In the developing world, more than 2 billion people rely on farms of this size, and many of these farms have low yields. In this study, low yielding farms on average had yields that were a mere 47% of high yielding farms. Researchers wanted to know to what degree enhancing pollinator density and diversity could help increase yields and close this yield gap.

By performing coordinated experiments for five years on farms all over the world and by using a standardized sampling protocol, the researchers were able to determine that higher pollinator densities could close the yield gap on small farms by 24%. For larger farms, such yield increases were seen only when there was both higher pollinator density and diversity. Honeybees were found to be the dominant pollinator in larger fields, and having additional pollinator species present helped to enhance yields.

These results suggest that, as the authors state, “there are large opportunities to increase flower-visitor densities and yields” on low yielding farms to better match the levels of “the best farms.” Poor performing farms can be improved simply by managing for increased pollinator populations. The authors advise that such farms employ “a combination of practices,” such as “sowing flower strips and planting hedgerows, providing nesting resources, [practicing] more targeted use of pesticides, and/or [restoring] semi-natural and natural areas adjacent to crops.” The authors conclude that this case study offers evidence that “ecological intensification [improving agriculture by enhancing ecological functions and biodiversity] can create mutually beneficial scenarios between biodiversity and crop yields worldwide.”

photo credit: wikimedia commons

photo credit: wikimedia commons

A study like this, while aimed at improving crop yields in developing nations, should be viewed as evidence for the importance of protecting and strengthening pollinator populations throughout the world. Modern, industrial farms that plant monocultures from one edge of the field to the other and that include little or no natural area – or weedy, overgrown area for that matter – are helping to place pollinator populations in peril. In this study, after considering numerous covariables, the authors concluded that, “among all the variables we tested, flower-visitor density was the most important predictor of crop yield.”

Back to stating the obvious, if pollinators aren’t present yields decline, and as far as I’m aware, we don’t have a suitable replacement for what nature does best.

This study is available to read free of charge at ResearchGate. If you are interested in improving pollinator habitat in your neighborhood, check out these past Awkward Botany posts: Planting for Pollinators, Ground Nesting Bees in the Garden, and Hellstrip Pollinator Garden.

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Speaking of Food: A Recap

The theme for the past 15 posts has been the October 2014 Special Issue of American Journal of Botany, Speaking of Food: Connecting Basic and Applied Plant Science. After a brief introduction to the issue, I spent the next 14 posts (spanning a period of 5 weeks) reading and writing summaries of each of the 17 articles. If you actually read every post, you are a champion in my eyes, and I probably owe you a prize of some sort. And even if you just read one or two, thank you, and I hope you found value in what you read.

I have to admit that it was kind of a grueling process. Many of the articles, along with being lengthy, included high level discussions that were beyond my current understanding, especially concerning topics like genetics, genomics, and phylogenetics. I learned a lot while reading them, but I am still far from truly grasping many of the concepts. For that reason, I did not feel completely comfortable writing summaries of some of these discussions. I made an effort not to misrepresent or oversimplify the research, but I can’t say for sure that my attempts were always successful. I welcome any criticisms, corrections, complaints, or comments in this regard, and I am open to making edits or updates to any of the posts as necessary. I consider this blog my learning platform, as well as a place to share my phyto-curiosity. Perhaps you find it a place for learning, too?

The main purpose of this post is to provide a Table of Contents for the last 14 posts, something that will make it easier to navigate through this series without having to scroll through each post. If you are interested in reading the entire series (again, you’re a champion), you can access them all in order here by clicking on the titles. Otherwise, you can pick and choose whatever topics interest you the most.

  • On the Origins of Agriculture – A deep dive into plant domestication and the beginnings of agriculture, including the revision of theoretical approaches to thinking about the history of plant domestication and a discussion of emerging methods and tools for exploring early domestication and emerging agriculture.
  • The Legacy of a Leaky Dioecy – Does pre-Colombian management of North American persimmon trees explain why non-dioecious individuals are found in an otherwise dioecious species?
  • Dethroning Industrial Agriculture: The Rise of Agroecology – The environmentally devastating effects of industrial agriculture can and must be replaced by a more sustainable, ecologically-focused from of agriculture. This will require reforming our economic system and rethinking our “one size fits all” approach to scientific research.
  • An Underutilized Crop and the Cousins of a Popular One – Safflower, an underutilized oilseed crop, could be improved by introducing genes from wild relatives. Soybean, a very popular and valuable crop, could also be improved by introducing genes from its perennial cousins.
  • Carrots and Strawberries, Genetics and Phylogenetics – An exploration of the genetics and phylogenetics of carrots and strawberries. Better understanding of their genetics will aid in crop improvements; better understanding of their phylogenetics gives us further insight into the evolution of plants.
  • Exploring Pollination Biology in Southwestern China – A fascinating look at the pollination biology of edible and medicinal plants in southwestern China, revealing significant gaps in scientific understanding and the need for conservation and continued research.
  • Your Food Is a Polyploid – Polyploidy is more prevalent in plants than we once thought. This article examines the role of polyploidy in crop domestication and future crop improvements.
  • Tales of Weedy Waterhemp and Weedy Rice – How agriculture influenced the transition to invasiveness in two important weed species.
  • Cultivated Sunflowers and Their Wild Relatives – An investigation into the flowering times of wild sunflowers reveals potential for improvements in cultivated sunflowers.
  • The Nonshattering Trait in Cereal Crops – Is there a common genetic pathway that controls the shattering/nonshattering trait in cereal crops?
  • Apples and Genetic Bottlenecks – Domestication generally leads to a loss of genetic variation compared to wild relatives, but apples have experienced only a mild loss. That loss may increase as commercial apple production relies on fewer and fewer cultivars.
  • Improving Perennial Crops with Genomics – The nature of perennial crops can be an impediment to breeding efforts, which makes the introduction of new perennial crop varieties both time consuming and costly. Advances in genomics may help change that.
  • Using Wild Relatives to Improve Crop Plants – Crop plants can be improved through the introduction of genes from wild relatives. They could potentially experience even greater improvement through systematic hybridization with wild relatives.
  • Developing Perennial Grain Crops from the Ground Up – Some of the environmental issues resulting from agriculture could be addressed by switching from annual to perennial grain crops, but first they must be developed from wild species.
A small harvest of sweet potatoes (Ipomoea batatas ' Hong Hong') from this year's backyard mini-farm. Ipomoea batatas ' Hong Hong.'

A small harvest of sweet potatoes (Ipomoea batatas ‘ Hong Hong’) from this year’s backyard mini-farm.

If I had to pick a favorite article in this issue it would be Think Globally, Research Locally: Paradigms and Place in Agroecological Research (Reynolds et al.). I know I said it in the post, but this article really sums up the reasons why this special issue of AJB is so important. Humans are incredibly resourceful, creative, and resilient, and as we have spread ourselves across the globe and grown our population into the billions, we have found ways to produce enormous amounts of food relatively cheaply. Frankly, the fact that anyone is going hungry or dying of starvation is shameful and appalling as there is plenty of food to go around…for now. But we are doing a lot of things wrong, and the earth is suffering because of it. If the biosphere is in trouble, we are all in trouble. Thus, we are overdue for some major shifts in the way we do things, particularly agriculture as that’s what this series of posts is all about. I advocate for science-based sustainable agriculture, and I am hopeful, thanks to this issue of AJB and other signs I’ve seen recently, that we are moving more in that direction. I’ll step off my soapbox now and leave you with an excerpt from the article by Reynolds, et al.

“There is increasing recognition that the current industrial model of agricultural intensification is unsustainable on numerous grounds. Powered by finite and nonrenewable stores of fossil fuels over the last 200 years, humans have come to see themselves, their technology, and their built environments as controllers of nature rather than interdependent with it, even as our activities threaten to exceed planetary boundaries of resilience in multiple environmental dimensions, such as climate, biodiversity, ozone, and chemical pollution. … In the ‘full world’ we now live in, continuing to use high input, highly polluting methods of food production to support continued economic growth is counterproductive to achieving food security. Continued growth of population and per capita consumption on a finite planet fails to meet the basic requirement of sustainability, that of meeting needs within the regenerative and assimilative capacity of the biosphere. And prolonging the shift to a sustainable economic paradigm risks a harder landing.”

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Developing Perennial Grain Crops from the Ground Up

This is the fourteenth in a series of posts reviewing the 17 articles found in the October 2014 Special Issue of American Journal of Botany, Speaking of Food: Connecting Basic and Applied Science.

Useful Insights from Evolutionary Biology for Developing Perennial Grain Crops by Lee R. DeHaan and David L. Van Tassel

The environmental impacts of modern agriculture are diverse and extensive. Our growing population needs to be fed; however, practices that have long-term negative effects on soil, water, and air quality are unsustainable. It is imperative that we find better alternatives. Developing perennial grain crops is one way that plant breeders are working to address this issue.

Moving from annual to perennial grain crops could potentially “increase water quality, reduce soil erosion, increase soil carbon, and improve habitat for wildlife.” It may also help “address the looming challenges of land degradation, food security, energy supply, and climate change.” Sounds like a major win if we can do it, right? And maybe we will, but first we must domesticate perennial grain varieties that perform on a similar level with annual ones. Most plant breeding today involves “improvement of previously domesticated species;” however, new perennial grain crops must be developed “de novo” (i.e. from wild species) in a matter of “decades rather than centuries to millennia.”

The roots of perennial grasses are considerably more extensive than annual grasses. (photo taken from an article about perennial grain crops at nationalgeographic.com)

The roots of perennial grasses are considerably more extensive than annual grasses, which helps reduce erosion and limits the need for fertilizer applications. (photo taken from an article about perennial grain crops at nationalgeographic.com)

Little has been published concerning “strategies for the wholesale remodeling of plants,” and so the authors reviewed findings in other fields, such as evolutionary biology and population genetics, in order to devise strategies for developing perennial grain crops. In this article, the authors summarize the published research they reviewed and describe how it relates to breeding perennial grains. It is a dense and lengthy article, so rather than offering a thorough review, I will briefly describe some of the main areas explored by the authors and then summarize their conclusions.

  • Trade-offs – This occurs when “resources allocated to one trait are unavailable for other traits.” Can perennial grain crops achieve yields comparable to annual varieties when faced with “trade-offs between seed and perennial organs?” Are such yields only attainable by “sacrificing longevity?” Strategies must be devised to “create herbaceous perennial crops with abundant seed production.”
  • Genetic Loads – This is simply defined as “the presence of deleterious alleles in a population.” In perennials, compared to annuals, “highly recessive deleterious alleles can arise at a rate faster than they can be efficiently eliminated.” Low seed set, among other things, may be a result of genetic load, so breeders of perennial grains must “account for and actively reduce genetic load.”
  • Bottlenecks – This refers to the loss of genetic diversity that occurs when population size is reduced. During a bottleneck, “previously rare deleterious recessive genes” can accumulate; however, some models indicate that “inbreeding and the associated bottlenecks may be useful in accelerating domestication.” If the population is isolated and introduced to a new environment simultaneously, “the newly exposed variation could now be adaptive.” Also, “if additional genetic diversity is required,” crosses can be made with wild populations.
  • Pleiotropy – This means that “a single gene [is] affecting multiple traits.” When domesticating wild species, “it would be useful to predict the prevalence of pleiotropy and whether to expect positive or negative pleiotropy to dominate.”
  • Epistatsis – This occurs when the effect of one gene is dependent on the presence of another gene or genes. This is particularly important if “large-effect genes” (pleiotropy) are dependent on a “particular genetic background to function optimally,” because “removing one critical element will severely impact the whole structure.” Perennial grain crops will have to undergo “many generations of plant breeding” in order to ensure that desired genes are found “within a genetic background where their benefits can be used without negative side effects.”
  • Cryptic Variation – Genetic variation is cryptic when “the inheritance of a particular mutated allele has no effect on phenotype and thus is hidden from natural and artificial selection.” New environments or mutations can release cryptic variation. “Ranking candidate species for their likely domesticability” may be an effective approach to cryptic variation. “The best candidates for domestication” originate from areas where conditions are highly favorable for growth and reproduction as opposed to areas that are “resource-limited,” because they have experienced periods of “selective enrichment” that make them suitable for agriculture settings.
  • Past Domestication – Domestication involves a series of “evolutionary changes that may decrease the fitness of a species in the wild but increase it under human management.” Historically this was “likely driven by unconscious selection pressures,” but currently it is “driven by conscious selection.” Studies of past domestication events reveal “somewhat predictable stages” in the process. Even though “current domestication efforts might not follow historical precedent,…the order in which traits are subjected to strong selection may be important.” Investigation into domestication also suggests that “dramatic changes” in plant morphology can be accomplished by selection for a “small number of major-effect genes,” so breeding programs are advised to “first search for useful major genes and evaluate their effects before moving on to strategies designed to accumulate genes of small effect.”
  • Selection – The authors describe “four major limits to selection.” 1.) Desired traits “may only exist in our imagination.” 2.) “The necessary genetic variation may not exist in the population,” and so waiting for or inducing mutations may be required. 3.) There may be “negative genetic correlations between characters being selected,” which will slow response to selection. This can be addressed by subdividing the population, evaluating the population in a new environment, or crossing with other populations. 4.) Conversely, “insufficient genetic correlation between traits may reduce the response to selection.” This makes “finding superior genotypes challenging,” so the authors suggest breeding plants in a “uniform environment,” and then later the plants can “accumulate genes for tolerance to specific stresses in separate populations.”
Intermediate wheatgrass (Thinopyrum intermedium) "produces much larger seeds in the greenhouse during the winter than ever seen in the field during the summer," an example of phenotypic plasticity. (photo credit: www.eol.org)

Intermediate wheatgrass (Thinopyrum intermedium) “produces much larger seeds in the greenhouse during the winter than ever seen in the field during the summer,” an example of phenotypic plasticity. (photo credit: www.eol.org)

The authors determined that the best candidates for perennial grain breeding programs are plant populations that have high diversity between and within individual plants, plastic phenotypes (i.e. adaptable to changes in the environment), and “an evolutionary history that includes adaptation to high resource environments.” They also suggest that breeders “focus more on the required functions [like nonshattering fruits] than on morphological traits” because it will increase the feasibility of evaluating “very large experimental populations.” The ideal experimental set-up would consist of very large populations of widely spaced plants that are subdivided in order to perform evaluations from various angles. Lastly, the authors encourage breeders to embrace new plant forms and breeding strategies and be open to the possibility that perennial grain crops may not “look like modern annual grains.”

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On the Origins of Agriculture

This is the first in a series of posts reviewing the 17 articles found in the October 2014 Special Issue of American Journal of Botany, Speaking of Food: Connecting Basic and Applied Science.

Agricultural Origins from the Ground Up: Archaeological Approaches to Plant Domestication by BrieAnna S. Langlie, Natalie G. Mueller, Robert N. Spengler, and Gayle J. Fritz

Concern about food and the environment has been on the rise for a while now. Interest in healthy food grown and produced in a responsible manner has prompted people to investigate where their food is coming from. Archaeologists studying plant domestication and the rise of agriculture are also concerned with where our food came from; however, their research efforts are more focused on prehistoric events rather than on what is being stocked on today’s grocery store shelves.

The authors of this paper, all archaeologists specializing in paleoethnobotany or archaeobotany, offer a broad overview of the study of plant domestication and the emergence of agricultural economies. In their studies the authors “treat domestication as a process that originally preceded the formation of agricultural economies” and they define domestication as “genetic and morphological changes [in] a plant population in response to selective pressures imposed by cultivation.”

The first section of the paper explains why certain theoretical approaches to thinking about early plant domestication should be revised. These approaches include a centric view of plant domestication, single domestication trajectories, rapid pace plant domestication, and domestication being coupled with the development of agricultural economies.

The concept of centers of origin refers to specific regions in the world where the majority of crop domestication is thought to have occurred. Often these are regions where a high number of wild relatives of crops are found and where large civilizations emerged. But research has revealed numerous locations in various parts of the world where crop domestication occurred independently from traditional centers of origin leading archaeologists to further explore a noncentric view of domestication.

Related to the centers of origin debate is the single vs. multiple domestications debate. Single site domestication refers to a plant being domesticated in one location and then spread to other locations. Multiple site domestication refers to the same plant being domesticated in multiple sites independently. With the aid of genetic research, crops that were once thought to have been domesticated in a single region and then disseminated to other regions are now being shown to have multiple domestication sites. For example, it has been suggested that barley was domesticated independently in various locations, including the western Mediterranean region, Ethiopia, Morocco, and Tibet, as well as various parts of Southwest Asia.

Barley - Hordeum vulgare (photo credit: Wikimedia commons)

Barley – Hordeum vulgare (photo credit: wikimedia commons)

Concerning the pace of crop domestication, “many scholars have presented evidence that domestication was slower and more gradual than previously envisioned” probably because the first domesticated crop plants were not “developed by plant breeders with clear end products in mind.” On this point, the authors conclude that debates over timelines are “likely to continue for some time,” and that “close communication between geneticists and archaeologists, including those with archaeobotanical expertise” will be necessary to tell the full story.

Domestication is typically viewed as a precursor to agriculture. But the authors point out that domestication occurred first and that agriculture did not immediately follow. To illustrate this point, they tell the story of the bottle gourd (Lagenaria siceraria), possibly the oldest domesticated plant. Native to Africa, the gourds likely floated across the Atlantic Ocean to the Americas (they also made their way to East Asia and other places) where they were domesticated multiple times by various groups of people at least 10,000 years ago. The gourds had numerous potential uses including containers, rattles, net floats, and even food (the young, immature fruits are edible). Large gourds with thick rinds were preferred by early humans, and the seeds of these were planted. The plants needed little attention, so caring for them did not mean having to adopt a sedentary lifestyle. The authors conclude that “although this example might seem peripheral to the development of serious food-producing economies or social complexity, it highlights early, intimate plant-people relationships and the abilities of people to modify their environments to enhance availability of desirable resources.”

Bottle gourds (Lagenaria sicericia) were possibly the earliest domesticated plant species (photo credit: eol.org)

Bottle gourds (Lagenaria siceraria) were possibly the earliest domesticated plant species (photo credit: www.eol.org)

In the next section of the paper, the authors discuss new and improved methods being used today to “address questions about the timing, scale, and causes of domestication.” Narrowing down the dates that plants were first domesticated is a major interest of archaeologists, and advances in radiocarbon dating have assisted in this quest. When DNA is being extracted, it is important to know the age of the material being analyzed in order to better reveal its history. Combining several methods for analyzing the data – especially as these methods are improved and new methods are developed – is  crucial.

Advances in microscopy have helped to better analyze morphological changes in plants over time as well as to examine microfossils, like starch granules, pollen, and phytoliths (silica particles left behind after a plant decays). Observing phenotypic changes in fruits, seeds, and other plant parts and determining the presence of things like starch granules and pollen helps us to understand the pace and scope of domestication as well as to determine when certain domesticated plants were introduced to areas outside of their perceived center of origin. Advances in the science of taphonomy – “the study of decay processes following the death of an organism until it is fossilized or exhumed” – also aid researchers in better understanding the stories behind plant domestication.

Scanning electron microscope (SEM) image of pollen grains from common sunflower - Helianthus annuus (photo credit: Wikimedia commons)

Scanning electron microscope (SEM) image of pollen grains from common sunflower – Helianthus annuus (photo credit: wikimedia commons)

Working with experts in other areas of archaeology will also lead to greater understanding of plant domestication and the emergence of agricultural economies. The authors give examples of how studying human and animal bones can provide information about plant domestication and state that “other classes of archaeological data, such as household structure and storage features, agricultural and culinary tools, and soil morphology” will aid in better understanding “how and why domestication occurred as an historical and evolutionary process.”

Next the authors discuss anthropological views on the causes of plant domestication. One of the main debates among anthropologists when discussing agriculture is whether or not early humans were “pushed” or “pulled” into agricultural economies. Did increasing populations and/or decreasing availability of resources compel people to produce more of their own food or did human populations cultivate and domesticate plants in areas where resources were readily available, allowing them to live sedentary and stable existences? The authors conclude that “it is not necessary for one of these scenarios to explain all transitions to agriculture” as agriculture emerged independently in multiple locations around the globe, each time under its own specific set of circumstances.

The final section of the paper is a short discussion on the relatively under-researched topic of the diet and cuisine of ancient humans. Surely, a desire for particular foods and beverages lead to cultivation and domestication. The authors assert that “cuisines provide people with social identities, nationalism, spirituality, and a package of cognitive tools for coping with their environment. Without a doubt, culturally constructed food preferences played a role in the origins and spread of agriculture.”

This is a brief summary of a well-researched and detailed article concerning the fascinating topic of early plant domestication. Honestly, my synopsis hardly does it justice, so I urge you to read it for yourself if this topic interests you. I particularly appreciated the emphasis that the authors placed on using multiple methods and tools to collect and interpret data and how our perspectives should be revised as new and updated data emerge. The call for multiple disciplines to come together in collaboration to better understand the history of domestication and agriculture is also encouraging. In summation the authors state that “archaeological evidence indicates that every case of transition form hunter-gatherers to agricultural economies was unique … Identifying the specific nature of when, where, and how domestication occurred will undoubtedly elucidate how agriculture transformed the trajectory of human societies.”