A New Chapter

Hi everyone!

It’s unfortunately been a while since my last post, but for exciting reasons! Since I last wrote, I have graduated from Michigan State University with my Master’s Degree in Plant Breeding, Genetics, and Biotechnology, where I researched disease resistance in tart cherries. My thesis, titled ‘Comparison of Resistant, Tolerant, and Susceptible Host Responses to Cherry Leaf Spot and Assesment of Trait Inheritance’ has since been published by the University, and a corresponding journal article is currently under review.

After graduation, I took a position with Harris Seeds/Garden Trends, a company in Rochester, NY which sells vegetable and flower seeds, as well as other products, to farmers and home gardeners around the country. At Harris Seeds, I am the Trials Manager which places me in charge of the in-house trialing of new varieties and products, as well as trials conducted by growers around the country. In addition to my responsibilities in this role, I am a contributor to the Harris Seeds blog ‘From the Ground Up‘ dedicated to professional growers, and the Garden Trends blog ‘The Garden Digs‘ for home gardeners. While I plan to continue writing for Cultivate Curiosity, I and my colleagues at Harris Seeds/Garden Trends will be making more regular contributions to these blogs, which I hope you’ll visit! They are a great source of growing tips and inspiration. My first post for ‘From The Ground Up’ outlines some of the crop species we are trialing on-site at Harris Seeds this year. As the season progresses, I will be following-up with our trial results and which new varieties we found the most impressive. For ‘The Garden Digs’, I will be featuring some gardening trends and projects that we are trying, including the construction of a spiral raised herb garden. I hope you’ll take a minute to check out these blogs and stay tuned for more from Harris Seeds’ trials and from Cultivate Curiosity!

Best wishes,

Kristen

 

Genetic engineering and the supermarket: Which crops are actually GE and why?

Product labeling at the supermarket has become very misleading. So many products are labeled with the words ‘Non-GMO’ or ‘GMO-free’ when this label is absolutely unnecessary. While this labeling is correct (the product truly doesn’t contain GE crops), lately we see these phrases on a majority of the packages on the supermarket shelves, regardless of what the product is made of and if GE varieties of these crops even exist. By labeling foods as ‘GMO-free’ when it is not possible for them to contain products from genetically engineered crops is misleading to consumers and proliferates a fear-based marketplace where ‘GMO-free’ has gained an unsubstantiated reputation of being healthier and safer.

For example, you pick out a bottle of grape juice from the store shelf and see that one brand is labeled ‘GMO free’ and the other isn’t, because of this you may assume that the second brand uses genetically engineered grapes, because if they didn’t why wouldn’t they label their bottle as ‘GMO-free’ too? Well, they wouldn’t because there are no genetically engineered grapes, they haven’t even been developed. So labeling grape juice as ‘GMO-free’ is almost the same as labeling it as ‘dairy-free’. We know that grape juice is dairy-free, so a label stating as much is unnecessary. The same goes for labeling things as ‘GMO-free’, but because of the atmosphere of fear and misinformation being proliferated in the media, companies can make use of marketing approaches that capitalize on people’s fears. By saying that their product doesn’t contain genetically engineered crops, they can take advantage of consumers who have been swayed by mass media’s negative portrayal of genetic engineering. This applies to both processed products and fresh fruits and vegetables. You can easily find fresh produce labeled as ‘Non-GMO’, even though genetically engineered varieties of nearly all of those crops don’t exist, again illustrating how misleading and unnecessary the current labeling practices are.

Globally, the four main crops in which genetic engineering technologies have been implemented are cotton, corn, soybean, and canola. In these crops, the traits that have been introduced are Bt insect resistance and herbicide tolerance, which have been introduced as single genes or combined as a pair, providing increased options to meet growers needs. GE varieties of other crops have been developed but most are not commercially available or they are grown in very small numbers. Some of these crops have been specifically developed to address challenges being faced in rural communities of developing nations and are not grown in countries like the U.S..

Bt Insect Resistance

This trait is derived from the soil bacterium Bacillus thuringiensis, which is present in soils all around the world. It was discovered that this bacterium produces crystalline proteins that are toxic to certain insects. When eaten by an insect, the proteins bind to receptors in the insect’s gut wall and cause it to breakdown, leading to the death of the insect. Because these proteins bind to receptors in the gut, this toxic effect only occurs in specific types of insects with the appropriate receptors. These proteins, frequently called Bt proteins, can be applied to crops as a biologic pesticide, have been used as a pesticide since 1920, and are approved for use in organic production systems. Crops that have been genetically engineered to produce the Bt proteins work in the exact same way, except that the pesticide does not have to be applied to the plants because they now have the genetic code needed to produce the protein themselves. When a pest insect eats from a Bt plant, it consumes the protein and is affected by the toxins. Bt targets primarily Lepidopteran insects, or caterpillars. This includes bollworms in cotton, European corn borer in corn, armyworms in soybean, diamondback moth in canola, and many other pest species. Crops engineered to contain the Bt gene have substantially reduced the need for insecticides and all Bt products are safe for the environment and have no effect on non-target insects and other animals, including humans.

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Soybean plants in a screen house, infected with velvetbean caterpillars. Left: Insect resistant Bt soybeans. Right: Soybeans susceptible to insect feeding damage. Source: AgBio Forum, Volume 7

Herbicide Tolerance

Herbicide tolerance is the ability of a plant to withstand exposure to herbicide chemistries that would be otherwise harmful. Herbicides can function to damage a plant in several different ways, and although some herbicides are effective on certain plants and not others (for example grasses vs. broadleaf plants), they do not discriminate between weeds and crop plants. This presents a big challenge for growers because it limits their options in choosing a herbicide chemistry as well as restricting them to applying herbicides at specific times in the season to avoid harming their crop plants. One of the most effective herbicides is glyphosate, or Roundup, which acts on nearly all types of plants. Due to its common use in production systems, crop tolerance to glyphosate was the first herbicide tolerance trait to be introduced. Glyphosate works by binding to an enzyme (called EPSPS) in plants and blocking its ability to synthesize certain amino acids, halting the plant’s growth and development and causing it to die. Plants that have been engineered to be glyphosate tolerant have an altered gene that produces the EPSPS enzyme with a slightly different shape. This different shape prevents glyphosate from binding and allows the enzyme to continue working to build the amino acids needed by the plant. By having crop plants that can tolerate exposure to glyphosate, growers can use the herbicide more effectively and efficiently to control weed pests.

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GE crops with herbicide tolerance allow growers to control weeds using herbicide without harming their crop. Left: Traditional soybeans cannot be safely treated with herbicide and are overcome with weeds. Right: Improved weed control in GE soybeans with herbicide tolerance. Source: Farm Week Now

 

 

Disease Resistance

Many scientists are working to develop genetically engineered crops that are resistant to diseases, which cause large yield losses and frequent pesticide applications in many crops. Disease resistant GE crops have not yet become widespread, however, one success story we’ve seen so far is the papaya with resistance to papaya ringspot virus. Papaya is a perennial herbaceous tree grown in tropical countries and most traditional cultivars are susceptible to papaya ringspot virus. This virus causes stunted trees and other symptoms, which lead to unmarketable fruit. In Hawaii, this disease was so serious that the papaya industry was nearly eliminated. The introduction of papaya cultivars with resistance to papaya ringspot virus saved the Hawaiian papaya industry and these cultivars are becoming more widespread in other papaya-growing regions of the world.

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Left: Non-GE papaya trees susceptible to papaya ringspot virus. Right: GE papaya with resistance to the virus. Source: American Phytopathological Society

Refuge Areas

When growers use crops engineered with Bt insect resistance or herbicide tolerance, they plant several rows of non-engineered crops nearby. Growers do not anticipate any yield or profit from the plants in these rows because their purpose is to serve as a refuge area for the pest species. By introducing genetically engineered crops to their fields, growers are introducing a new selection pressure for the pest populations being targeted: for example, if there is only Bt corn available for corn borer larvae to feed on, eventually the individuals that are not killed by the Bt protein, due to a natural mutation or some other factor, will evolve and reproduce to the point that the protein is no longer toxic to them. Planting non-engineered crops in nearby refuge areas allows enough of the pest population to survive in order to avoid evolution in response to the engineered crops, thus ensuring that the GE traits will continue to be effective.

Takeaway Points:

  • Food labels claiming a product to be ‘Non-GMO’ or ‘GMO-free’ are often unnecessary and added just for marketing purposes. Learning more about how your food is produced is essential to make sense of all the marketing claims and make the healthiest and most cost-effective choices for you and your family.
  • The major crops with commercially available genetically engineered varieties are cotton, corn, soybean, and canola. There are no commercially available GE varieties of most vegetable and fruit crops.
  • The main GE crops being grown have been engineered to be insect and herbicide resistant, traits which work by affecting physiological pathways specific to certain insects and plants, respectively. Therefore, the environment, non-target insects, animals, and humans cannot be harmed by this technology.
  • Growers who use GE crops take care to ensure that there are refuge areas available for pest species, thereby maintaining genetic diversity within pest populations and ensuring the future efficacy of these GE crops.

Why we need genetically engineered crops, for the present and the future

This week’s post is a discussion about the need for and safety of genetically engineered crops. If you’ve not been following this debate in the news, questions in bold are common sentiments agricultural scientists face from the public. The arguments and opinions stated here are my own but are based on reproducible science and facts. Due to the breadth of supporting research, I will not link to many sources; however, if you have more questions, would like to have a conversation, or would like more information, please don’t hesitate to let me know and I will happily discuss it further or direct you to peer reviewed, non-biased, scientific studies. 

‘Why do we need genetically engineered crops?’

This is a question that agricultural scientists hear pretty regularly from people with concerns about genetic engineering. ‘Why do we need transgenic corn or soybeans?’ ‘We’ve successfully grown traditional varieties for all this time, why should we change anything and risk unforeseen challenges?’ ‘Why aren’t scientists working to improve the systems we already have?’ That’s where most scientists will stop you, because that’s exactly what genetic engineering aims to do.

Since the beginning of agriculture, farmers have aimed to get more food from fewer inputs. These goals helped to form the agricultural science fields as they are today, where researchers try to identify the optimum levels of inputs to get the highest yield and quality from their production systems, like fertilizers, water, organic matter, tillage, pesticides, and in controlled environments, temperature, light, and CO2. The advancements being made in crop biotechnology don’t seek to eliminate these advancements, but to further optimize, refine, and reduce the inputs needed for production.

‘Why can’t we continue to optimize traditional production inputs and continue making improvements as was done in the past?’ We can and we will continue to optimize these inputs, however, as we improve our practices the gains to be made from better use of fertilizers, for example, is less and less every year. In developed countries like the US, this level of improvement will do, for now. But farmers in developing countries without sufficient access to water for their crops, let alone the most advanced fertilizer mixtures and pesticide formulations, need more immediate and accessible solutions.

 

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source: United Nations World Food Program

 

There are 7 billion people on this Earth. Among these people 1 in 9 is undernourished, meaning they don’t have enough food, let alone enough food with high nutrient quality. ‘But developing countries have a surplus of food. We throw perfectly good food away. What we need is a way to redistribute the food supply’ Sure, that could help, but do you think that will happen soon enough to save the life of a child in rural Africa? The logistics required to ‘redistribute’ food wealth isn’t the only factor. What about the governments and economies of the countries with a food surplus? How do you propose American farmers would be compensated if the food they produced was sent to these starving nations? Would it even make it to the people who need it most? What about the people in our own country who go hungry every day? Look at our current political atmosphere. This issue certainly isn’t on the mind of our politicians now, and it won’t be anytime soon. The solution lies in giving farmers in developing countries access to agricultural technology, including GE crops, which will allow them to produce higher quality food with fewer inputs and reduced losses to pests and environmental stresses. This is believed by many to be an important step toward reducing poverty and improving the health of people in developing communities, which can, in turn, lead to improved education and equality, especially for girls, and ultimately a higher standard of living and slower population growth, which are all huge topics on their own, but are each linked to the power of positive change that improved agricultural practices, including GE crops, can have.

‘So what makes you think genetically engineered crops will solve anything?’ We don’t just think GE crops will improve agricultural practices, we know they will. As mentioned in previous posts, transgenic crop plants have been studied for nearly 50 years. The benefits of this technology have been proven across several crop species and against a significant span of limiting growth factors. No supporter of GE crops believes that this technology will solve all of our production problems or that it can be used without regard to optimizing other production practices. What we are saying, is that this technology allows us to overcome the plateau in food production that we have presently reached. This technology will help to produce more food on our existing arable land with reduced environmental impacts, allowing us to feed the starving people of today, and those of the future who will be a part of our rapidly growing population, which is predicted to reach 9.7 billion by 2050. That’s only 34 years from now.

‘Why don’t we just use new cultivars from traditional breeding?’ Plant breeders are working hard to address the major problems we have in crop production. They have and are still making great strides toward higher yielding and quality crops with reduced environmental impact; however, some of these challenges are difficult to address quickly and effectively through traditional breeding. For example, suppose you are a wheat breeder trying to combine 4 desirable traits into one cultivar. You have 4 plants that each have one of these traits, so you design a series of crosses to try to obtain offspring that have all four. Not only will this take a long time and a lot of plants, there is no guarantee that once you have a plant with 2 of the traits, you will be successful in adding the others. This is due to gene linkages and interactions within the plant genome and the environment that are out of a breeder’s control. Alternatively, you found the trait you want in another plant species but you cannot successfully cross it with your crop plant without complications. Genetic engineering is technology that breeders can add to their toolbox to quickly and reliably introduce a single gene or a set of genes into their breeding program, bringing better and more reliable cultivars to growers. By saving time in this manner, we will be better able to respond to changing environments and new pest threats to our food supply through targeted breeding efforts.

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‘Even if they do improve production, how do we know that genetically engineered crops are safe to the environment and our health?’ The last few Cultivate Curiosity posts have focused on DNA, natural variation, and transgenic technology. You’ll remember that genetically engineered crops are generated by altering a single gene within the entire organism’s DNA and that due to the specificity of transcription of these genes from DNA into proteins, certain genes are only expressed in certain tissues. Why is this relevant to safety? Well first of all, in some GE crops, the altered gene is only expressed in certain tissues of the plant, often tissues that are not consumed by humans. Therefore, you never eat the proteins that result from the altered gene. Secondly, if the genes are expressed in the plant tissues that we use as food, the resulting proteins are not toxic to humans. They are often compounds that are found in nature elsewhere, and they are designed to act within the plant with such specificity that they only target pest species, for example. Therefore, unless you are a caterpillar, virus, nematode, beetle, etc., absolutely nothing is going to happen to you. Also, you consume such small quantities of these compounds that they couldn’t truly have an effect on you anyway.

‘So what about the environment and non-target organisms? Don’t GE crops hurt bees?’ No, GE crops don’t hurt bees because bees are not crop pests. What does hurt bees are pesticides. The large amounts of pesticides used on our crops, especially insecticides, are not nearly as species specific as GE crops. An insecticide will kill any insect, not just pest species. Therefore, they kill bees and other beneficial insects that are present within and near crop fields. GE crops have the ability to reduce and sometimes eliminate the need for pesticides because they make their own. This goes back to the concept of reducing inputs and improving practices. Some propose that this reduction in pesticide use can be solved by organic practices. On some farms, it does; however, pesticide use is permitted in organic production, the limitation is only on what these pesticides are made of.  Organic rarely means pesticide-free. This topic will get its own post soon, but it is so often presented as an alternative to GE crops that it warranted mentioning here.

‘What about herbicide resistant weeds? Isn’t that caused by using Roundup Ready crops?’ The natural variation post from a couple of weeks ago talked about the natural evolution of species in response to a selection pressure, where individuals strong enough to withstand a selection force survive to reproduce and pass on their specific traits. This is what is happening when any pest develops resistance to a pesticide. In this case, weed plants that survive herbicide applications live and reproduce. Over time the herbicide is no longer effective. This happens not only with Round-up Ready crops that can protect themselves from specific herbicides but in all cases where herbicides are applied. This issue has been known by scientists long before the introduction of Roundup Ready crops and is being addressed through herbicide rotation programs, where herbicides with different modes-of-action (or how they work to kill a weed) are used to prevent resistant weeds from evolving.  When used properly, this technique is very effective. The second thing to note is that the use of herbicide-resistant crop plants (like Roundup Ready crops) does not necessarily mean increased use of herbicides on these fields. Farmers don’t want to use pesticides if they don’t have to. They are expensive and require time and labor to apply, therefore farmers will use as little herbicide as they can without having losses to their crops. Herbicide-resistant crop plants allow farmers to get better herbicide coverage and less crop damage from the applications that they do make, so when the herbicides work better, they don’t need to use as much of them. More successful weed control permits reduced tillage practices, which are more sustainable because they lessen soil erosion, improve soil health, protect micro-ecosystems, and reduce fuel needs for equipment.

 

There’s a lot more to the story of GE crops than most media discussion leads you to believe. When formulating your own opinions on GE crops, be sure to consider all aspects: how and why they have been developed, how they work, who they can help, and when used correctly how they can contribute to solving some of the biggest food security challenges of today and the future.

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‘Don’t judge a book by its cover’: the science behind genetic engineering

In the last two posts, I addressed the topics of DNA and natural genetic variability. Here I’d like to use those topics as a starting point for a discussion about the technology behind genetic engineering. You probably recognize the saying “don’t judge a book by its cover”. While this saying is applied to people and, well, books, I think it is also a good sentiment to consider when looking at genetic engineering. For nearly 50 years, scientists have been transforming organisms through genetic engineering techniques and studying the effects of such changes. To date, scientists have thoroughly examined possible concerns regarding genetic engineering, finding nothing that isn’t seen elsewhere in natural systems. So today, why are we still surrounded by such negativity and fear about genetic engineering? I’d say it’s because people are judging the book by its cover – believing statements for which there is no supporting evidence. With people, we cannot make an accurate judgment of their character before we know them, and the same goes for the products of genetic engineering—in order to make educated choices for ourselves and for future generations, we must understand how and why genetically engineered plants are made, starting with how the technology works.

So, how does genetic engineering work?

As with all modern technology, genetic engineering has changed greatly since its initiation. It has become increasingly accurate, efficient, and refined, and improvements in other areas of science and technology have permitted comprehensive analysis of all possible effects on the resulting plants and products. Here I’d like to give a brief summary of some milestones in the history of genetic engineering and how these technologies work. To keep this post from being too long, these descriptions will be slightly summarized, so if you find you have additional questions or would like more information, please don’t hesitate to let me know!

Tissue Culture

Almost all methods of genetic engineering rely heavily on tissue culture, a technique that was established in the early 1900s. Tissue culture is the growth of living cells in an artificial medium, usually composed of water, agar, nutrients, and compounds, such as natural hormones. In plants, tissue culture cells are often obtained by cutting pieces of leaves or stems and placing them on an artificial medium containing specific hormones. These hormones, and other compounds, encourage new, undifferentiated cells to grow. These cells have the potential to grow into a new plant, a characteristic called totipotency. To encourage the cells to grow into plants, the tissue culture recipe can be adjusted to contain different levels of the necessary growth hormones and nutrients. Eventually, whole plants can grow from single cells. Tissue culture techniques vary for different species of plants and the methods have been refined for nearly one hundred years, with new advancements still being made today. Tissue culture is used for plant propagation (generating more plants of a specific cultivar), as well as for genetic engineering. In genetic engineering, the DNA of a single cell is altered through various techniques and then grown into a new plant, where all of the cells will have the altered DNA. The following addresses some transformation techniques:

tissue-culture-series
Tissue culture steps. Far left: leaf tissue cut from a mature leaf, placed on tissue culture medium. Center left: new cells develop from the leaf tissue and form a callus (a mass of undifferentiated cells). These cells will be used for genetic transformation. Center right: the cells divide and begin to form new shoots. Far right: small plantlets have developed. *at each step, the tissue is transferred to new tissue culture medium, often with different concentrations of hormones and nutrients.

Induced Mutation

Initial methods of genetic engineering were through induced mutations. Scientists would expose a cell to certain sources of radiation, causing DNA mutations to occur. In this method, scientists have no control over what genes are being mutated and what effects this will have on the cell and eventually the whole plant. For this reason, induced mutations are not commonly used for crop improvement purposes but rather for the discovery of new genes. This works because scientists can look for individuals with unique characteristics and then compare the mutated DNA with that of a non-mutated individual, thereby discovering the gene that controls the trait.

Transformation Technology

The next advancement was transformation technology, or the ability to add a specific gene to a cell. This was achieved in 1972 when the first recombinant organism was created. A segment of DNA known to produce antibiotic-resistant proteins was inserted into a bacterial cell. The cell combined the foreign DNA sequence with its own DNA and therefore became capable of producing the protein. This discovery eventually led to the production of human insulin from bacterial cells in 1982, when the human insulin gene was incorporated into bacterial DNA, technology that is still used today to produce insulin.

With transformation technology, scientists can introduce a gene of interest into a tissue culture cell through several techniques, two common ones being agrobacterium and biolistics.

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Natural Agrobacterium gall on a horse chestnut tree

 

Agrobacterium is a soil bacterium that infects plants in nature. When it infects a plant, it inserts its DNA into the plant’s DNA and causes the plant to form a gall (or tumor) for the bacteria to grow within. By inserting a gene of interest into the agrobacterium cell and infecting tissue culture cells with the transformed bacteria, the gene of interest can be inserted into the plant DNA and subsequently expressed in the plant cells that grow.

When using biolistics for transformation, microscopic gold particles are coated with the gene of interest and are shot into young plant cells using a ‘gene gun’, typically a hydrogen gas-powered particle delivery system. The DNA on the gold particle enters the cell and is incorporated into the plant cell DNA, just as in the agrobacterium transformation.

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Schematic of a biolistic particle delivery system

In both methods, the cells will be screened to select those that were successfully transformed (containing the new gene), this is done using selectable markers. A selectable marker is a gene, that is included in the DNA segment containing the gene of interest, which codes for a specific trait that scientists can test for. In plants, it is often a fluorescent protein, a protein that turns blue when stained or an herbicide resistance gene, which allows cells with the gene to be easily identified. Scientists will keep the transformed cells and grow them into whole plants so they may study them and see the effects of the added gene.

Unfortunately, there is no way to control where within the plant DNA the new gene has been inserted, so scientists examine all aspects of the transformed plants to determine how many copies of the foreign DNA were inserted, where they were inserted, and how they affect plant growth and function. Sometimes concern is raised that the added selectable marker genes, for fluorescence or herbicide resistance, for example, are being expressed in genetically engineered plants; however, through traditional breeding, these genes are selected against and after one generation the resulting transformed plants will contain only the gene of interest.

Intragenics and Cisgenics

Oftentimes, the gene of interest being used in a plant transformation is derived from bacterium DNA or that of another plant or non-plant species; however, in some cases, a gene can be used from the same plant species or a compatible relative, known as intragenics and cisgenics, respectively. Essentially, this means that it is biologically possible for the gene of interest to be transferred to the host plant through traditional breeding practices, however, traditional methods have proven unsuccessful or inefficient, so the gene is inserted through transformation instead. Even though the processes are the same and the molecular composition of the DNA is the same regardless of what species of organism it originated from, plants genetically engineered using intragenics and cisgenics tend to have fewer regulations than those engineered with a non-related species’ gene.

Targeted Gene Editing

The most recent advancement in genetic engineering technology is the use of endonucleases to facilitate targeted gene editing. Endonucleases are enzymes that exist naturally in the cell and make breaks in DNA molecules. Scientists can design endonucleases that will bind to specific DNA sequences and make a targeted break at that location, which means they can make a cut in a specific gene or at another exact DNA location. When the break is made, it may be repaired by reattachment of the cut ends. When this occurs, it is common for some nucleotides at the break in the DNA sequence to be lost, resulting in a nucleotide deletion and loss of function for that gene—known as ‘gene knockout’. Alternatively, because scientists know where the endonuclease will generate a break, they can construct a DNA sequence of the gene of interest with nucleotide ends that match those at the break. Then, after the cut is made, the original DNA will repair itself by inserting the new gene sequence in the break—known as ‘gene replacement’. There are a few slightly different technologies that have been developed to conduct targeted gene editing: ZFN (zinc finger nucleases), TALENS (transcription activator-like effector nucleases), and CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats, with the Cas9 protein).  The most important feature of these techniques is that, much like editing a word document, they allow scientists to precisely edit the DNA sequence, changing only one or a few nucleotide bases as a very specific location in the genome, and because the nucleases exist naturally in cells, they are degraded by the cell once the genome edit has been made, leaving behind only the edited gene DNA sequence.

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Steps of targeted gene editing, CRISPR/Cas9 shown. Image: igtrcn.org

Takeaway points:

  • Scientists have conducted genetic engineering for almost 50 years, giving them time to improve upon the techniques used and thoroughly evaluate the resulting genetic changes that occur in the bacteria, plants, or animals, that they’re studying.
  • Genetic engineering techniques make use of naturally occurring processes to introduce new DNA into a cell, be it soil agrobacterium or endonucleases.
  • Cells are transformed while in tissue culture and then grown into mature plants. Scientists can then study the altered plant genetics for several generations through traditional breeding methods. Primary research is always conducted in controlled environments, never in field settings until the effects of the genetic change are well understood.
  • Scientists study any possible change that may have occurred in their host organism as a result of genetic engineering, and consider all conceived risks associated with their specific genetic change. If a less desirable trait has unintentionally arisen from their efforts, the transformed plants are discarded and a new approach is taken to ensure the stability and safety of the resulting plants.

Hopefully, this summary of genetic engineering techniques provided new insights toward plant biotechnology and why it’s important to understand the science of genetic engineering rather than ‘judging the book by its cover’. The following posts will address the reasons why plants are genetically engineered as well as which crops are genetically engineered and for what traits.

 

Genetic Modification as a Natural Process: How nature generates genetic variability

Last week’s post discussed the science behind DNA and how DNA works to generate the proteins needed for an organism to grow, develop, and function, but how do different species, and even different individuals belonging to the same species, do these things while still having distinctly unique characteristics? This is explained by natural recombination and mutations, which influence species populations over the short term, but also play a role in species evolution and ecosystem interactions.

First, let’s talk about reproduction. When two individuals of a species reproduce, they each contribute a gamete, which is the equivalent of one-half of their genome. What does this mean on the scale of DNA? Reproductive cells (i.e. sperm and egg or ovule and pollen, etc.) form from the division of a cell which contains a complete set of the organism’s DNA. Through this process, called meiosis, two gamete cells are formed from this original cell, meaning that the DNA of the original cell is split in half between these two gametes. Each time gamete cells are formed, the DNA is divided in different ways, generating gametes with distinctly unique sets of DNA sequences, and therefore unique combinations of genes. Reproduction occurs when a male gamete cell fuses with a female gamete cell and the two half-sets of DNA are combined into a complete set, creating a new individual with a unique DNA sequence. When thought of in human context, this explains why siblings from the same two parents have similar characteristics but are still unique in their combination of these traits.

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Natural recombination results in offspring that segregate for different traits. In this image showing trait heredity in primrose, the two flowers in row 1 represent the parent plants of the flower in row 2. Notice that the flower in row 2 looks different than that of either parent but has certain similarities to both, this is because one-half of its DNA came from each parent. The flowers in rows 3, 4, and 5 are all siblings which resulted from a self-pollination of the flower in row 2. In plants, self-pollination means that the male and female gametes came from the same individual plant, a cross which often reveals genetic combinations that may have been masked by dominant genes in the parent. 

The formation of gametes through meiosis occurs every time an organism reproduces sexually, therefore with the creation of each new individual, a shuffling of DNA has occurred. This shuffling of parental genes generates a population of unique individuals who then reproduce to shuffle the genes even further. On a population scale, you might think that over time, the genes of each individual have been equally mixed throughout the population, but this is where the ideas of gene flow, natural selection, and mutations come into play. Gene flow is the movement of genes between populations, for example, if two mice colonies overlap and begin to reproduce with one another, the genes from these two colonies can then begin to mix and new combinations of traits created. Over time, individuals with certain combinations of traits will be more successful in surviving and reproducing than others. This is called survival of the fittest, meaning that individuals who have traits that make them more suited to their environment will be more likely to survive and reproduce, therefore passing their genes onto the next generation. Over several generations with this environmental selection pressure, populations will shift toward having more of the genes that make an individual more suited to survival. (If you remember from the ancient agriculture post, this process also occurs during domestication, where the selection of individual plants or animals by humans, acts as an artificial selection pressure for the maintenance of certain genes within a population. This is also how antibiotic and pesticide resistances form in bacteria or pest populations, respectively, but with the antibiotics/pesticides/etc. acting as the selection pressure.)

 

Natural-selection
Image: Teacherweb.com

 

Another important aspect of this process is that of natural mutations. In nature, spontaneous changes can occur in an individual’s DNA nucleotide sequence, caused by external factors or just by chance. These spontaneous changes can be manifest as deletions or additions of nucleotides, or the inversion of nucleotide sequences (so that they are in reverse order), among other changes. If these mutations occur in genes essential for an organism to grow, develop, and function, they may prevent the gametes from fusing or be fatal to the developing organism. If a mutation occurs in a gene where it does not alter function, it may be less advantageous (and lost from the population gene pool with the death of that organism) or it may prove advantageous and make that organism better suited to its environment, in which case it will be more likely to reproduce and pass the mutation on to its offspring. Over the billions of years that life has existed on earth, this process of natural recombination, gene flow, mutations, and natural selection has contributed to the evolution of all living species that have ever lived, and these forces continue to work today, both through natural and artificial (human-promoted) selection.

So why is this relevant to today’s technologies like transgenics? Oftentimes we hear transgenic or genetically engineered organisms referred to as ‘genetically modified’, however, this is a misnomer as the DNA and genes of organisms have been ‘modified’ since the beginning of life on earth through natural recombination, mutations, and the other forces discussed above. Without this ‘modification’, humans as well as all other species, would not exist as they do today because evolution cannot occur without the presence of gene variability. The next post will discuss some of the science behind the development of transgenic organisms and compare the effects of those techniques with natural genetic recombination as discussed here.

Takeaway Points:

  • Reproduction occurs through the combination of a male and female gamete which each represent one-half of the parent individual’s DNA sequence. Each gamete contains a unique combination of the parent’s genes, and will therefore result in offspring who have similar traits, but in different combinations.
  • Within a population, individuals have different combinations of genes which determine their level of ‘fitness’ for survival in their particular environment. The individuals with more suitable traits will survive and reproduce, passing the genes for these traits on to their offspring.
  • New traits can arise through new gene combinations or through natural mutations. Over time, these new traits will encourage the evolution of existing species, or the divergence of some individuals to form a new, but related, species.
  • DNA sequences and genes have been naturally ‘modified’ since the beginning of life on earth to generate the genetic variability essential for evolution to occur. Without changes in DNA, there would be no species diversity or adaptation to new and changing environments.

 

DNA: Life’s Instruction Manual

Through the next several posts I’d like to talk about crop improvement through genetic advancements. This does include transgenics, also known as genetic modification, but that is definitely not the only topic to discuss when addressing the genetics behind crop improvement. The first topic I’ll cover in this series of posts is DNA. Some of you may remember learning about DNA in biology courses in high school and you might be wondering why I’ve chosen devote a whole post to this topic. Before I talk more about the science behind technology like transgenics, I want to be sure to discuss DNA in a context that is relevant to these topics and that may serve, at the very least, as a science refresher.

Unfortunately, many people who do not work directly in biological sciences may not be exposed to much more basic biology than what they learn in a high school science class. This was illustrated by some recent surveys where 80% of people surveyed stated that they want food containing DNA to be labeled as such, forgetting that almost ALL food contains DNA (Survey conducted by McFadden and Lusk). This is a prime example of how most of the discussion surrounding topics like genetic modification, pesticide/antibiotic resistance, and vaccines has come to consist of only opinions, rather than actual information and scientific perspectives. Hopefully, this short post about DNA, and those to follow in this series on crop genetic improvement, can help to clarify some of the science behind current technologies and offer additional perspectives to the overwhelming dialogue of weakly supported opinions.

DNA: Life’s Instruction Manual

Although scientists have studied biology and living organisms for hundreds of years, it wasn’t until the 1950s that DNA, or deoxyribonucleic acid, was identified as the molecule that carries biological information. It was discovered that DNA consists of a linear series of four molecular building blocks, called nucleotides or nitrogenous bases, held together by a sugar-phosphate backbone. The chemical bonds within DNA are arranged in such a way that cause it to be a double helix-shaped molecule. The specific sequence of nucleotides constitutes the genetic code which is the information, or the ‘instruction manual’, needed for living things to develop, grow, and function.

dna structure
(a) The sequence of four nucleotides, or nitrogenous bases, encodes the genetic information necessary for cell development and function.  (b) Of the four nucleotides, Thymine always pairs with Adenine and Guanine pairs with Cytosine, with each nucleotide pair connected to the sugar-phosphate backbone. (c) Double helix structure of DNA  Image:Boundless.com

All living things, from bacteria to mice to sunflowers to humans, have DNA with the same molecular structure, the result of all life on earth having a common evolutionary ancestor. Every single cell in a living organism’s body contains DNA with an identical sequence of nucleotides, the result of mitosis (cell division for growth) and meiosis (cell division for reproduction). All organisms have a unique sequence of nucleotides which is a combination of the DNA sequences of its parents, however, between organisms of the same species, and even between more distantly related species, the percent of the variation in nucleotide sequences can be quite small.  Although sequences may be similar between organisms, this variability is enough to result in obvious and important physical differences.

dna compaction
DNA wraps around histones and is further wound and compacted into chromosomes

In order to fit into cells, DNA molecules are packaged tightly into chromosomes, compacting them down to microns (millionths of a meter) in size. If you were to stretch out all of a human’s DNA from just one cell it would be over 2 meters long, with each chromosome being about 5 cm long (humans have 23 pairs of chromosomes). Within a cell, DNA exists within the nucleus, however, there is also DNA in mitochondria (the cell organelle for respiration and energy production) and chloroplasts (the plant cell organelle where photosynthesis occurs), known as the extranuclear genome. This additional DNA can play important roles in certain cell functions, and is inherited separately from the nuclear DNA.

 

So, all organisms have DNA in each of their cells, which provides the instructions for their growth, development, and function, but how does this actually work within organisms? All organisms consist entirely of proteins or materials made by proteins. This is made possible by the DNA code, which provides the instructions for protein synthesis through a series of steps. Within the DNA nucleotide sequence, there are functional regions called genes. These functional regions are the parts of the ‘instruction manual’ that code for proteins and provide the information important to the organism’s development and function. Within the nucleus, these functional regions of DNA are transcribed into another molecule, RNA (ribonucleic acid). Through this process of transcription, several copies of RNA are made from the single copy of DNA. This RNA is then processed to remove nonessential regions, and transported out of the nucleus into the cytoplasm where ribosomes attach to it to translate the code from the nucleotide sequence into amino acids. Each sequence of three nucleotides (called a codon) codes for one of 20 specific amino acids. These amino acids then form proteins which can function within the cell or within the entire body of the organism.

dna-replication-transcription-and-translation-1-638
The nucleotide sequence of DNA is transcribed into an RNA molecule, which is then translated into a sequence of amino acids, or polypeptide.

An important thing to remember about the first step, transcription, is that the gene and other regulatory elements are both transcribed by RNA. These regulatory elements flank the gene and determine when and in what cells it will be transcribed and translated into proteins. Therefore, different sets of genes are active in different cell types and under different environmental conditions. Amazingly, DNA molecules contain all of the information needed for a living organism to grow through its entire life cycle, from a single-celled embryo to a reproductive adult, as well as maintaining all of an organism’s daily functions and physiological responses, it is just a matter of different genes being active at different times.

DNA and the expression of genes underly all of an individual organism’s traits, be it the color of your eyes, the shape of a leaf, or how quickly a puppy grows into an adult dog. In crop plants, these traits are most significant when they impact the ease of producing food and the quality of the end product available to consumers. As discussed in the past post regarding ancient agriculture, crop plants have changed significantly since the time when our ancestors first began cultivating them. All of these changes trace back to alterations in DNA, gene expression, and the resulting proteins produced. Watch for the next post in this series which will address natural recombination, until then, hold on to these takeaway points regarding DNA.

Takeaway Points:

  • DNA exists in ALL living things: humans, animals, insects, plants, fungi, bacteria, microorganisms, etc.  Therefore it also exists in all food derived from living organisms.
  • Functional DNA, or genes, provide the instructions for the production of proteins, which then act within the cell to serve a function or to trigger another series of cell activities.
  • Genes determine an organism’s development, growth, and function, which results in unique physical characteristics, however, gene expression and the resulting characteristics can also be influenced by external forces like environment and nutrition.
  • Every cell of an organism contains DNA with the same nucleotide sequence, but not all genes are expressed in each cell. Regulatory DNA elements control when certain genes are expressed, and in what cells. These elements are triggered by changes in the environment or signals from other cells.
  • The DNA of crop plants has been changing since they were first cultivated thousands of years ago, long before plant breeding and improvement became scientific fields.

July Means Cherries

 

Linda4
‘Linda’ sweet cherries

Summertime means delicious fresh fruits and vegetables, and July means cherries. Since starting my graduate thesis in tart cherry breeding, I have developed an adoration for cherry production, and if you love cherries, Michigan is the right place to be. Within the United States, Michigan produces around 75% of the nation’s tart cherries and Washington, Oregon, and California collectively produce 90% of the sweet cherries.

 

The Cherry Family Tree

Cherries belong to the Rosaceae family which originated in Eastern Europe. Other members of this family are peaches, strawberries, plums, apricots, apples, pears, raspberries, almonds, roses, and others. Within the Rosaceae family, cherries belong to the Prunus genus. The two cherry species that we grow for fruit are sweet cherries (Prunus avium) and tart/sour cherries (Prunus cerasus). Sweet cherries are a progenitor species of tart cherries: in the ancient past, sweet cherries hybridized with another species, ground cherry, to produce what we know today as tart cherry. Cherries were brought to North America by Europeans and are now grown across the continent, particularly in areas like the Great Lakes and the Northwest United States where the effects of climate extremes are reduced by the surrounding topography.

rosaceae
Painting by Marcella Art & Illustration

So what’s the difference between sweet and tart cherries?

The major difference, of course, is that one is sweet and the other sour, but there are several other differences in both physical characteristics and production practices. Let’s start with the different characteristics. Commercially available sweet cherries are typically large, dark purple colored, and firm. You may recognize names like ‘Bing’, ‘Regina’, and ‘Sweetheart’. Sweet cherries can also be lighter yellow with a red blush, like the popular cultivar ‘Rainier’. There are fewer commercially grown tart cherry cultivars, with the most common being ‘Montmorency’, which is smaller and soft with red skin and light flesh. Another tart cherry cultivar you may recognize is ‘Balaton’ which is dark purple in color. ‘Balaton’ is grown on a small percentage of the total tart cherry acreage and is more commonly found  in farmer’s markets and you-pick locations than in grocery stores. ‘Balaton’ has a charming origin story and was brought to the U.S. by my advising professor Dr. Amy Iezzoni, read more about its history here.

Sweet and tart cherries are both grown in monoculture over many acres of orchards and require similar growing conditions. Even though the two species are closely related they do differ in some cultural practices. One example of this is the use of fungicides to control the fungal disease Cherry Leaf Spot, which defoliates trees and is devastating to growers. Tart cherries are more susceptible to Cherry Leaf Spot than sweet cherries, and therefore
require more frequent fungicide sprays.

2015-07-20 18.03.18
Cherry Leaf Spot causes severe leaf chlorosis and defoliation on ‘Montmorency’ trees

Because my thesis is regarding different host-tree responses to Cherry Leaf Spot and breeding tart cherries for resistance to it, I will save these details for another post. Nonetheless, there are slightly different cultural inputs for sweet and tart cherries. The biggest difference, however, is the end use of these two cherry species and how this changes the way they are harvested and the ideal traits for each.

 

 

Sweet cherries are sold to consumers in the fresh market, while tart cherries are usually sold frozen and dried or as a component of baked goods, juices, and jams. Because sweet cherries are eaten fresh, they are picked and transported around the country shortly after harvest. This is why it is difficult to find sweet cherries out of season. Consumers prefer sweet cherries with the stem still attached, therefore all sweet cherries are hand-picked in order to keep the stems, which cannot be accomplished with a mechanical harvester. For fresh eating, it is preferred that the cherries be large in size and firm. Size appeals to consumers and increases grower profits while firmness allows the fruit to be transported long distances with less damage.

Oppositely, tart cherries tend to be processed just after harvest and are eaten as an ingredient in other food products. They are typically soft and therefore difficult to transport as a fresh product. About two weeks prior to harvest, tart cherries are sprayed with a plant growth regulator, Ethephon, which loosens the stems from the fruit. This allows the cherries to be more easily harvested with mechanical shakers that grasp the trunk of the tree and shake the fruits from the branches, catching them on a tarp (*see links to videos below). Once collected on the tarp, a conveyor belt moves the fruit into a large square bin of cold water. This cold water helps to preserve the quality of the soft fruit. These bins are then taken to a platform, or cooling pad, where cold water is continuously pumped throughout the bins until they can be transported to a nearby processing plant that same day. At the processing plant, the pits will be removed and the cherries will eventually be made into products like canned pie filling, dried cherries, frozen cherries, jam, and juice. Because tart cherries are harvested using mechanical shakers, fruit can only be harvested from trees that are at least 6 years old: any younger and the trunk may break. This is a big restriction to tart cherry growers, as cherries can flower and produce fruit when they are 3 years old. To address this issue, alternative methods, such as the use of precocious dwarfing rootstocks and over-the-row harvesting systems, are being explored for both young orchards and high-density plantings.

*There are a few different designs of cherry shakers, two of the more commonly used models are the batwing shaker and the newer double incline shaker.

Tart Cherry Breeding Goals

As mentioned in previous posts, plant breeders tend to target specific traits depending on the crop, environment, and needs of growers. As far as tart cherry breeding goes, Michigan State University is home to the only tart breeding program in the United States, led by Dr. Amy Iezzoni. As a student in this program, I have been lucky enough to see firsthand the progress made in improving tart cherry traits and the impact this work has on growers. So what are the traits being targeted in tart cherry breeding? You may have been able to guess a few from the above descriptions of various fruit traits and production practices.

When it comes to fruit traits we are looking for larger and firmer fruits that have both red skin and red flesh, and detach easily from the stems for harvest purposes. Because consumers associate red color with cherries, it is the color preferred by processors. The current major cultivar ‘Montmorency’ has red skin but nearly clear flesh, so red food dyes are often added to cherry products; however, fruit with naturally red flesh would eliminate this use of added dyes. For processing, it is best if the fruits are round so that they sit appropriately in the pitting equipment, and firm enough that they do not break apart when the pit is poked out. It is also essential for the pit to be round so that it is not chipped by the machinery, freestone so that it easily detaches from the flesh of the fruit, and small enough so that it doesn’t take up too much of the fruit size but large enough that it is not missed by the pitting equipment. In addition to fruit traits we are breeding for increased fruit yields, resistance to Cherry Leaf Spot, and late bloom time. Later bloom time reduces the risk of yield losses caused by flower death in the occurrence of Spring frosts.

Progress in breeding for these traits has been hastened through the use of genetic markers which provide information to be used in designing breeding crosses and selecting individuals. To learn more about how this technology is being used in breeding Rosaceous crops like cherries, visit these links for the RosBREED Project and Dr. Iezzoni’s Program and look for a future Cultivate Curiosity post on genetic markers in breeding.

cherryThis summer, enjoy fresh sweet cherries while they are in season and keep an eye out for any local fresh markets with tart cherries! The rest of the year, enjoy tart cherries in pies, jams, juices, as well as dried and frozen. To learn more about tart cherry’s admirable qualities and to get some creative cherry recipes visit choosecherries.com.

 

 

The Invasion of Native Ecosystems

What is an invasive species?

An invasive species is an organism that is not native to an area that becomes problematic because it outcompetes native species for the resources needed to survive. In addition to competition for resources, invasive species may target native species as a host or food source. Some commonly discussed examples of invasive species in the United States are the emerald ash borer, purple loosestrife, zebra mussels, and pythons. As you can see, these examples are all from different families of organisms: insects, plants, and animals can all be considered invasive if they endanger the success of native organisms and environments. Because invasive species tend to thrive and grow quickly in an area, they easily change the structure of a natural ecosystem.

In the case of plants, invasive species can overtake an area and eliminate native species by outcompeting them for resources like sunlight, water, nutrients, and space. Aquatic invasive plants cause additional challenges by overtaking waterways, lakes, and ponds, inhibiting their use for commercial and recreational purposes, as well as changing the environmental structure by capturing the sunlight that would normally reach deeper waters.

aquatic invasive
Aquatic invasive plants can quickly overtake waterways

The introduction of non-native species can have far-reaching effects and can quickly become out-of-control. This has been seen with the emerald ash borer, which is an invasive beetle that uses ash trees as a host. Adults drill into the wood of ash trees to lay their eggs, which then hatch into larvae that feed on the inner bark, in the process killing the ash tree. Natural reproduction of ash trees is not rapid enough to help these

eab-adult
Adult Emerald Ash Borer

populations recover, and the progression of the forest ecosystem replaces these trees with smaller shrubs and brush that can survive in the understory. Rapid declines in ash populations foreshadow the possible extinction of this tree, all caused by an invasive beetle.

 

 

How did these invasive species get here?

In terms of aquatic invasive species like zebra mussels and some aquatic plants, these species were unintentionally and unknowingly brought to North America in the ballast of or attached to ships coming from other parts of the world. When these ships arrived in eastern North America, the species were introduced to new bodies of water and soon thrived when having the opportunity to inhabit new environments.

JustMussels
Zebra mussels grow densely on underwater surfaces and are about the size of a fingernail, but can reach 2 inches.

Similarly, unwanted insects and other animal species can be brought here in shipments of goods and raw materials from other parts of the world. For example, emerald ash borer was brought to North America in shipments of wood.

Invasive species are often introduced unknowingly, however in the case of many invasive plants, species are introduced to new places for use in ornamental landscape plantings. At the times of introduction, it was not anticipated that these species would become invasive, and they were sold to homeowners across the country. An excellent example of this is purple loosestrife, a plant with beautiful purple flowers that you may have seen while driving along highways or in other natural areas. This plant was used in landscaping for many years until it was discovered to be growing wild in natural areas. Once the negative effects of this and other ornamental plants were seen, their use in landscape plantings was discouraged. Unfortunately, in many cases of invasive plants we are still working to eradicate these species from natural areas, prevent their spread to unaffected regions, and encourage the regrowth of native plant species.

Purple_Loosestrife_page_image
Purple Loosestrife

A major source of invasive animal species is the accidental or intentional release of exotic pets.  A common case of this is the intentional release of pet pythons that have grown too large to easily keep as pets. These pythons and other such animals interfere with natural ecosystem dynamics and the balance of food chains. While invasive pythons thrive primarily in places like the everglades, other species of amphibians, reptiles, and fish have become invasive in many native ecosystems.

In some places, it seems like the battle against invasive species is a lost cause, but there are things that we can do to prevent further damage by invasive species.

The easiest thing that can be done by all is the prevention of the future spread of these species. For example, if you have a boat that you use on public waters, the best thing to do is to take advantage of the boat cleaning stations located at most docking points. Why is this important? While your boat is in Lake X, an invasive plant or animal may become attached to it, and then next time when you visit Lake Y or Lake Z, you could easily and unknowingly be responsible for the infection of that body of water with this invasive species that had not yet been introduced there. Even if the species already exists in all of the bodies of water that you visit, you can help to reduce the problem by cleaning your boat at the washing stations provided to remove any invasive hitchhikers.

In the case of invasive insects, like the emerald ash borer, you can adhere to restrictions on the transport of firewood when you are heading off on your camping trips. In most states, parks prefer that you do not bring your own firewood and that you do not transport firewood across state lines. Because invasive insects may be living within the firewood that you use, you could easily transport them to a new area where they’ve not yet been introduced.

Even though invasive species already exist in the US, their spread across the country can be much slower if we pay close attention to our role in introducing them to new areas. We can also aid in this effort by joining initiatives to combat the spread of invasive plants and restore native species. Many areas have local preservation groups who work to eliminate invasive plants in native environments. Even when hiking, you may see signs asking for your help to pull up specific invasive plants that you might come across. While these efforts can help to contain invasive species, it will not stop the problem from eventually spreading on its own. So what are scientists doing to help reduce the threat from invasive species?

While many scientists are also on the front lines of manually removing invasive species from native environments, they are also working to develop innovative solutions to these problems. A good example of this is the effort to prevent landscape plants from becoming new invasive species. This is done by breeding ornamental plants that are sterile, which means that they cannot produce the seeds that would form new plants, therefore preventing these plants from spreading to unintended areas near the landscape where they’ve been planted.

Scientists are also working to counter invasive insect species. Recently, several states have approved the release of parasitic wasps to control the spread of emerald ash borer. A wasp will lay her eggs inside a beetle larva and upon hatching, the wasp larvae eat the beetle larva. This interaction occurs in nature between wasps and many insect species and is an effective biological control of pests. Read this brief article for more details about this wasp release project.

The issue of invasive species is not only nationwide, but worldwide.

Species that are native to the Americas have become invasive in Europe, Africa, Asia, and Australia, just as species from these continents have proven troublesome here in the Americas. The challenges brought about by existing invasive species have illustrated the importance of monitoring human activities that contribute to this problem, however, there is always a chance that new species will be introduced. To counter our existing invasives, do your part by cleaning your boat, using local firewood, planting native plant species, and taking appropriate responsibility for exotic pets; and if you’re interested, join a local invasive plant removal task force!

For more information, check out these links or ask about invasive species and plant removal efforts at your local extension office.

More on Invasive SpeciesEmerald Ash BorerInvasive Ornamental Plants Release of Exotic Pets

 

 

Irrigation and Agricultural Water Use

70% of the freshwater used by people of the world is for irrigation.

40% of the world’s food supply comes from irrigated systems, the other 60% is rain-fed.

Whether farmers irrigate their crops depends on the climate and weather of their location, the types of crops they grow, and their financial ability and access to water. In many parts of the world, crops require little to no supplemental irrigation as they receive sufficient water from natural rain events, however in other parts of the world, it would be impossible to achieve a crop without the provision of water through irrigation systems. In addition, irrigation can multiply yields in some crops by 2 to 3 times, which can help to offset the various inputs associated with it. Irrigation not only requires a reliable source of water, but also structural equipment that entails assembly, maintenance, and sometimes transportation between fields. Of course, not all areas of the world have access to the abundance of water or the technologies and scale of irrigation equipment that we commonly see in the United States.  It is important to note that the use of water for irrigation does not solely equate to agricultural uses (i.e. food production), but also irrigation of golf courses and landscapes.

The daily drinking water requirement per person is 2-4 liters, however, it takes between 2000 to 5000 liters of water to produce one person’s daily food.

When crops require such high volumes of water it is easy to see how difficult crop irrigation can be in areas where clean drinking water is unavailable or requires traveling several miles daily, however, these numbers also impact those of us in areas with greater access to water. Because water can be treated and re-used in addition to its natural journey through the water cycle, it is easy to think of water as indefinitely renewable. However, while our supply of freshwater is replenished through the water cycle, this rate of renewal is much slower than the rate at which we draw from the supply, which includes groundwater, ponds, lakes, and streams.

Forms of irrigation have been used for centuries (think of the Roman aqueducts), but over time irrigation methods and materials have become much more efficient.  Any time water is exposed to air there is the potential for it to evaporate into the atmosphere. In the case of irrigation, this is considered water loss, as a portion of the water intended for the plant never reaches it. As opposed to the Romans, today’s growers can choose from a variety of irrigation systems that can be customized to suit particular crops and settings, each having advantages and shortcomings.


Common Irrigation Systems

Flood/Furrow Irrigation

Flood irrigation was likely the first method of irrigation used by ancient peoples, and it is still commonly used today. In flood irrigation systems water is delivered to the field through pipes or ditches and allowed to flow over the ground and through the crop.  This method uses a lot of water and has the highest losses, with only about one-half of the supplied water actually irrigating the crop. The other half is lost to evaporation, runoff, or infiltration (where water flows through the soil, past the depth of plant roots or saturates nearby soil not planted with crops). Because flood irrigation supplies water to all areas of the field, it also encourages the growth of weeds between crop rows and can facilitate the spread of plant diseases.

AGS-161544-D-5762 - © - David Gubernick
Furrow Irrigation of an Iceberg Lettuce Field

While flood irrigation will never be as efficient as some other techniques, there are steps growers can take to reduce water loss, such as leveling fields to ensure all areas receive water and to prevent excessive runoff due to sloping fields, capturing runoff and re-using it for the next water application, and using surge/interval flooding to allow the water time to infiltrate the soil.

Overhead/Spray Irrigation

Overhead irrigation uses sprinklers or other emitters to broadcast water over the crop. This method uses a lot of machinery and can be very large-scale to cover high acreages of land. Overhead irrigation uses less water than flood irrigation and does not produce as much runoff volume, however, it is still subject to high levels of evaporation, especially when used in dry, windy environments. Because many plant diseases are spread by water splash, overhead irrigation can also exacerbate disease outbreaks.

A common set-up for overhead irrigation in agriculture is the center-pivot system where a length of pipe with either spray guns or hanging emitters along its length, is extended above the crop and supported by wheeled frames. In the center of the field, the pipe is attached to the pump and water source and when in use the system moves in a circle around this center pump to irrigate all areas of the field. As a result, fields irrigated in this way are circular when viewed from above. Some growers also use their center-pivot systems to apply fertilizers and crop protection products, a method with its own pros and cons.

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A center-pivot system irrigating cotton (Left). Center-pivot irrigated fields in Kansas, viewed from above (Right). 

 

Drip Irrigation

drip
Drip irrigation is often used for vegetable crops, like Brassicas

 

Drip irrigation is commonly used when growing fruit and vegetable crops and is much more efficient than other methods of irrigation, although less economically viable for large acreages. In this method, plastic tubing (made to have small emitter holes at specific intervals) lies alongside the crop and can be buried, left on the surface, or covered with an organic or plastic mulch. This system of tubing is attached to a water source and when in use provides a steady drip of water directly to the base of the plants. As a result, evaporation is reduced, there is no runoff, the space between crop rows is not being watered (and therefore neither are the weeds), and the spread of disease is reduced due to the lack of splash.


Growers who irrigate their crops put a lot of consideration toward which method they use and how often they irrigate. Installing and operating these systems also requires a lot of maintenance and calculation, including economic costs, water pressures and application rates, and water laws and availability.

If you’re interested in learning more about irrigation and water use, visit these sites:

Fast FactsFurrow IrrigationWater use in agriculture, Water use statistics by state