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A wheat crop from plants which yield year after year has huge attractions for both the farmer and the environment. There’s no yearly crop establishment. Plants develop strength and get deep rooting. Carbon capture is enhanced. Creating a commercially viable perennial wheat has been a fundamental challenge that has been taken up by The Land Institute in Salina Kansas, which is focussing entirely on creating perennial varieties of annual crops.

Written by Mike Donovan, editor

Founded in 1976 by geneticist Wes Jackson, the Land Institute’s work is led by a team of plant breeders and ecologists in multiple partnerships worldwide, and is focused on developing perennial grains, pulses and oilseed bearing plants to be grown in ecologically intensified, diverse crop mixtures known as perennial polycultures. The Institute’s goal is to create an agriculture system that mimics natural systems in order to produce ample food and reduce or eliminate the negative impacts of industrial agriculture.

As an undergraduate Wes Jackson noticed the inherent robustness of the native prairie compared with the fragility and the increasing chemical dependency of the annual monocultures that constitute the American breadbasket. Every acre planted is an uphill battle against the natural order, which favours diverse perennial polycultures — deep-rooted, enduring plants that form synergistic communities that define the essence of resiliency as demonstrated by the Dust Bowl experience — when an extended drought hit the lower Midwest in the 1930s, turning tens of thousands of acres of native prairie that had been ploughed up to plant wheat into massive, deadly clouds of dust. Meanwhile, the undisturbed prairie, with its deep roots and highly evolved survival traits, remained intact.

Jackson’s fundamental premise is that humankind took a wrong turn when it began ploughing up the land and planting homogeneous annual crops. As he told Modern Farmer, “… there was a dualism that developed — wild nature, with virtually no soil erosion, and then us with the plough… Now we have not only soil erosion but chemical contamination of the land and water with fertilisers and pesticides and so on.”

Perennial crop solutions

Perennial crops are robust; they protect soil from erosion and improve soil structure. They increase ecosystem nutrient retention, carbon sequestration, and water infiltration, and can contribute to climate change adaptation and mitigation. Overall, they help ensure food and water security over the long term. Perennial grains, legumes and oilseed varieties represent a paradigm shift in modern agriculture and hold great potential for truly sustainable production systems. The Land Institute is using two approaches to breed perennial grain, pulse, and oilseed crops:

1. Domestication of wild perennial plants

2. Perennialization of existing annual crops.

Domesticating wild perennials

Farmers have been domesticating wild perennial plants for the last 10,000 years. This is the approach that resulted in many of our current crops. Domestication starts with identification of perennial species that have one or more desirable attributes such as high and consistent seed yield, synchronous flowering and seed maturation, and seed retention, also called non-shattering (a feature of non-shattering plants that hold onto their seeds like an ear of corn rather than disperse them over the landscape like a dandelion). Large, diverse populations of the crop are grown out at The Land Institute, and plant breeders select the best individuals for the traits of interest. These individual plants are then cross-pollinated, and the resulting seeds are planted to produce the next improved breeding population.

The Land Institute established the perennial wheat program in 2001 with the goal of developing perennial wheat that is economically viable for farmers and replaces the global food calories of annual wheat. Annual wheat is grown on more acres than any other grain crop, at 548 million acres worldwide, followed by maize at 445 million and rice at 399. Wheat accounts for 20 per cent of human food calories and more protein calories than any other grain.

The programme at The Land Institute creates perennial wheat hybrids made from crossing annual wheat species with wheatgrass species (especially intermediate wheatgrass, which is the same species being domesticated as Kernza®). The annual types include bread wheat and durum wheat used for making pasta. Many successful hybrids have been achieved between wheat and wheatgrass. They are being used to understand the genetic contribution of the annual and perennial parents. Other research partners around the world have made similar crosses between annual and perennial wheat. Twenty of the most promising crosses are being grown in nine different countries to see how particular genetic types vary in performance when grown under a broad range of environmental conditions. The best performers have a grain yield grain about 50-70% that of annual wheat cultivars.

Perenniality (the ability of the plant to regrow after grain harvest and to survive harsh winters and/ or summers) is also highly variable depending on environmental conditions. Some of the perennial wheat plants in Kansas have lived for more than six years. In other locations, stands of perennial wheat have persisted for many more years. Their breeding program continues to seek improvements on a number of plant traits including perenniality and yield. Although we see steady improvement every year, we expect it could take another 10-20 years to develop an economically viable perennial wheat variety.

With a goal as bold as “changing the way the world grows its food,” all partners are critical to success. They provide insight, data, operations support, connectivity, and an expanded community of brainpower and technical capacity. The Institute currently has research partners in 41 different locations around the world, but none in the UK. Global partnerships spread researchers’ knowledge and botanical germplasm across six continents with diverse climates and soil types.

Partners are helping to fully develop Natural Systems Agriculture, and plant breeding is a numbers game. The more experimental lines evaluated, the better the odds of developing superior, high-yielding perennial crop varieties. The Institute is dedicated to ensuring worldwide food security without compromising ecosystems.

In 1983, using Wes Jackson’s vision to develop perennial grain crops as inspiration and guidance, plant breeders at the Rodale Institute selected a Eurasian forage grass called intermediate wheatgrass (scientific name Thinopyrum intermedium), a grass species related to wheat, as a promising perennial grain candidate. Beginning in 1988, researchers with the USDA and Rodale Institute undertook two cycles of selection for improved fertility, seed size, and other traits in New York state.

The Land Institute’s breeding programme for intermediate wheatgrass began in 2003, guided by Dr. Lee DeHaan. Multiple rounds of selecting and inter-mating the best plants based on their yield, seed size, disease resistance, and other traits have been performed, resulting in improved populations of intermediate wheatgrass that are currently being evaluated and further selected by collaborators in diverse environments. Experiments are also underway to pair Kernza® with legumes in intercropped arrangements that achieve greater ecological intensification, and to utilise Kernza® as a dual purpose forage and grain crop in diverse farming operations.  

The breeding programme is currently focused on selecting for a number of traits including yield, shatter resistance, free threshing ability, seed size, and grain quality. In the next 10 years, the Institute’s aim is to have a crop with seed size that is 50% of annual bread wheat seed size. Our long-term goals include developing a semi-dwarf variety and improving bread baking quality. Ultimately, we hope to develop a variety with yield similar to annual wheat and to see Kernza widely grown throughout the northern United States and in several other countries around the world. If that vision becomes a reality, you might see perennial grain in common staples found on grocery store shelves.

Plant breeders report increasing success

At the 2018 Prairie Festival scientists from the Land Institute explained the advances they were making in the development of perennial wheat and other crops. Lead scientist Dr Shuwen Wang explained that the process in the past year had created 297 new cross-bred, 570 embryos created and 9,176 single flower heads compared. He told the audience that research was being carried out in eight separate countries ranging from equatorial to temperate. The 2017/18 results were better than previous years, with some tests being done on wheatgrass which has an additional 14 chromosomesto regular wheatgrass.

The crossing work started in 2011 when the first set of crosses was made and this has now created more than 500 plants which are available for testing and breeding. This year they were very pleased to have produced five rows of uniform plants which shows it is possible to get close to stability, and the seeds generated are being sent to the overseas research stations for further evaluation and experimentation. Some will be crossed with annual cultivars and will also be involved in gene stacking. Dr Wang said there were agronomic difficulties in these experiments. The toughest of these is weed control. Plant numbers remain small and the susceptibility of each of them to chemicals is different. When the numbers of individual plants of each cross are so few the opportunity to try out different herbicides is small. He said that weeds in these test circumstances “grow like crazy”. 

A similar problem occurs with fertilising. There’s no handbook to suggest the stages when the plant needs fertiliser, or indeed the compounds that are most effective. Research has shown that the perennial plants do better in mild seasons and have a tougher time in both high and low temperatures.

Kernza® Grain Goes to Market

The Land Institute developed the registered trademark for Kernza® grain to help identify intermediate wheatgrass grain that is certified as a perennial using the most advanced types of T. intermedium seed. The goal is to develop varieties that are economical for farmers to produce at large scale.

The aim is to create a recognisable and protected brand – they say “When you buy Kernza® perennial grain, you can be certain that you’re eating product grown on a perennial field that is building soil health, helping retain clean water, sequestering carbon, and enhancing wildlife habitat.” Patagonia Provisions was the first company to develop a commercial retail product for the mainstream marketplace. The company took the risk of product development and market entry for their product called, appropriately, Long Root Ale. A number of restaurants have taken up Kernza® as an ingredient, using the perennial growth as a marketing tool. Hopworks Urban Brewery in Portland, and Vancouver, brews Long Root Ale for Patagonia Provisions and has it on tap, in addition to the ale in four-pack cans being sold in Whole Foods in California. Bang! Brewing in St. Paul has a Kernza® beer available, as does Blue Skye Brewery in their home town of Salina. 

Innovative Dumpling & Strand produces Kernza® pasta which they retail through Twin Cities-area farmers’ markets. There are a few other small-scale retail food outlets scattered around the country, but to our knowledge, those are the most reliable sources right now. Additionally, Cascadian Farm is excited to incorporate Kernza® into some of its foods, with expectations for products made with Kernza® available in retail markets by late 2019. Cascadian Farm has agreed to purchase an initial amount of the perennial grain which allows us to arrange with farmers to plant on commercial-scale fields versus the test sized plots currently being grown.

General Mills (parent company of Cascadian Farm) approved a $500,000 charitable contribution to the Forever Green Initiative at the University of Minnesota in partnership with The Land Institute, to support advanced research to measure the potential of Kernza to significantly reduce greenhouse gas emissions associated with food production, determine best management practices for sustainable production, and increase Kernza yields through breeding. The hope is that increased demand for Kernza® products translates into more growers and acreage dedicated to Kernza® perennial grain, resulting in more Kernza® in production and on shelves, which in turn encourages more research and development into Kernza® and other perennial grains.

Patagonia’s and General Mills’ early commitments to create a market for Kernza® are significant milestones. Yet the transformation to an agriculture and a food system based upon perennial grain crops is a complex and long-term endeavour. Other perennial grains, oil-seeds, and legumes require agro-ecological research beyond that which market forces alone can provide at this critical juncture. The Institute says “We have been leading this research effort for forty years and we welcome your support of our work to help sustain the next vital stage of this agricultural revolution.”

Kernza® grain is the first perennial crop from The Land Institute’s work to be introduced into the agriculture and food markets, but our researchers are currently working on others, including perennial wheat, perennial rice, perennial sorghum, and wild sunflower, with more to come.

Followup: The Land Institute, 2440 E Water Well Rd, Salina,Kansas 67401 https://landinstitute.org/

info@landinstitute.org

Dr Tom Dykstra is an American agriculturalist who specialises in entomology. Many farmers see pollination as the main
benefit of the insect population, but as he describes, there are many more. Insect damage is often an indication of an
unhealthy crop, and this is caused by crop stress which results from heavy applications of N, pesticide damage to soil
microbes, and mechanical soil damage. Through his laboratory and talks to farmers he helps them move away from chemical farming. In 2018, with John Kempf he published a seminal podcast with Regenerative Agriculture. The hour long broadcast explores the direction of his research, and this article brings out the points of greatest relevance to practical farmers.

Photosynthesis thoughts

Dr. Dykstra says “Photosynthesis can be increased substantially, and is most easily measured through spectrometer analysis using the Brix scale.” The system determines levels of sugar in plant sap and the reading is compared with standard figures for each plant species to produce a Brix measurement. Most plants score between Brix 4-8. At this level plants are productive and produce crops which most will consider satisfactory. Yet they are susceptible to disease and damage. Plants with higher Brix levels are less prone to damage and when the Brix level reaches around 12 serious insect damage stops. Higher scores in the range of 14 show a genuinely healthy plant. The Brix scores suggest that plants are not working up to anywhere near their potential and achieving this is a matter of getting the photosynthetic rate up. The problem is that farming methods particularly pesticides create blockages in the plant which cause weakness to disease.

Doing an experimental fallow

“How much land can you afford to leave fallow for a year or more?” asks Dykstra. He suggests that 5 acres from 1000 would be possible, and he wants farmers to choose some high ground which won’t get pesticide residue run-off. “let weeds grow and spray a sugar solution of 5lbs per acre as often as feasible. Planting cover crops is another useful method of getting rid of pesticide residues.” The purpose of sugar or molasses is to feed the important microbes in the soil. Microbes including fungi, insects and bacteria feed nutrients to plants and the population of microbes is heavily reduced by fungicides, insecticides and other spray products. Soil without microbial action becomes fluffy and is easily eroded.

How insects smell

In the podcast John Kemph asked Tom “what topic have you been puzzling over for a long time?” and the answer was “How insects smell”. He explained that insects have highly tuned receptors that can detect suitable food over distances of a mile or more. But insects have poor digestive systems and so look for food which is deteriorating. “The bad apple, the over-ripe plum in the basket is the one which the flies go for, and in the field insects go for plants which are weaker with poorer cell walls.” For more than 10 years Tom’s research yielded little, but by Nov 2016 his lab had worked out the mystery of an insect’s sense of smell. The signal comes from both antenna and palps.

Certain insects are tuned into certain smells – the ones which are easily digested, that are rotting and unhealthy. In the same way some plants advertise themselves as unhealthy. This might explain why insects attack the crop in one field while ignoring that in the next, even though both look much the same. Locusts are a classic and devastating example, swarming and stripping plants in a specific field. For Tom Dykstra the question is “why?” And the follow up is “how can we use this to help protect vulnerable crops?” What are some of the compounds that serve as insect attractants we could manage and monitor? Ethanol is a universal odorant which advertises plants as unhealthy – a lot of plants will release some sort of alcohol which is attractive to many insects.

These in turn have a Brix cutoff beyond which they won’t attack the plant but instead go looking for something easier and tastier. Dykstra’s dogged in-field research has shown that the Brix number is not static, but will vary with weather conditions. In particular, plants will lower their defences shortly before a storm hits, causing insects to become increasingly active and feed. Insect olfaction is the science of how insect’s smell. Although the predominant theory has revolved around a “lock and key” mechanism for multiple decades, direct evidence for it was and is lacking. Dykstra’s own research, along with that from many other laboratories, has made it more certain that the insects actually smell “wavelengths”. In 2016 the mechanisms involved became clearer and many of the details have been worked out to give a firm grasp on not only how insects smell, but how we can prevent them from doing so, and how we can simulate insect olfaction with uncanny precision.

Two discoveries are of considerable interest. The first is that nitrates and ammonium are indirectly attractive to certain insects and this increases as the level of N is raised. The plant advertises this stress making it more susceptible to insect attack. The second is that the detection distances for these insect signaling compounds are extraordinarily great.

His work concludes with the statement:

“Insects are only attracted to unhealthy plants”

The consequence is that if healthy plants don’t attract insects they don’t need pesticides for their protection. Plant protection then comes not from a can but from the conditions under which it is grown. And what is a healthy plant? One with a Brics of 12 or more. Bric scores are raised by soil microbes, and they are damaged by pesticides and soil damage.

The research and logic of its meaning is considerable for farming who have largely considered the benefits of organic farming to be with the consumer, and with the higher price they pay for the product. Tom Dykstra is telling the farmer that he benefits as much as anyone through the use of natural controls and the abandonment of pesticides. That chemicals weaken plants and cause them to be unhealthy and therefore open to disease and attack. He goes on to say that raising the Bric score produces crops and product which have greater flavour and longer shelf life, because they are inherently healthy, and this is translated to further benefit for the grower. If his fruit tastes better, it sells better.

Though technical as well as conversational, the podcast is well worth taking the time to listen to. Scan the QR Code below to listen to the whole podcast now.

Above top to bottom: Damaging soil microbes weakens plant health and invites insect damage ; Microbes in this soil increase the health of crop which makes it less vulnerable to insect and other damage ; Sward diversity lifts health of plants and livestock Image credit: Practical Farm Ideas

Author: Mike Donovan
editor@farmideas.co.uk

How innovative root research creates practical solutions

Written by Dr. Ulf Feuerstein • Asendorf, DSV Research Innovation Centre

The root system forms the starting point for a plant‘s performance. In the past it has been very difficult for breeders to select plants by root growth, but current research is now shedding new light in this field and creating new opportunities.

It’s the same spectacle year on year: swirling clouds of dust follow the giant combines as they harvest fields of cereal and oilseed rape. At harvest time little thought is given to the very organ of the plant on which this yield is built – the roots. Farmers, breeders and researchers however have ignored this invisible system in the past. It’s not that crop scientists are unaware of the root system’s role in crop yields, but up till now there has been a lack of systematic analysis. Growing underground, roots simply evade any obvious means of observing them and so efforts to measure and observe root development involve elaborate, time consuming procedures. A number of institutes have developed new methods which enable us to discover more about roots. Inspired by science and issues raised by farmers, breeders including Deutsche Saatveredelung AG are now starting to put roots at the centre of their breeding research programmes. The methods developed through scientific research, however, must be adapted to the high throughputs needed in plant breeding.

The radicle

Roots react more sensitively to different conditions than the plant’s organs above ground. Even minor differences in temperature, moisture, nutrient supply or soil compaction cause major variations in root growth. This root sensitivity makes it extremely difficult to conduct large-scale comparative studies. During the first few weeks, root growth can take place in special glasswalled containers known as rhizotrons. However, to investigate the root growth of older plants, the roots have to be extracted from the soil in the field. Seeds need water and the right temperature in order to germinate. Breeders know that roots respond to gravity and grow downwards towards the earth‘s centre – a phenomenon known as geotropism.

By placing seeds on filter paper arranged in an upright position, it is easy to observe how they germinate and how the radicle (the embryonic root) develops. Quick, uniform seed germination and strong radicle growth is important for a crop to become established. Every batch of seed will contain some seeds which germinate more quickly than others and produce a particularly strong radicle. Figure 2 illustrates the different rates of radicle growth of flax seedlings 48 hours after the start of germination. By observing different growth rates, breeders can select the plants which best match their breeding objectives and use them for further breeding trials. 

Germination temperature

Temperature in particular has a major impact on the germination behaviour of seeds. Germination will not take place if the temperature is too low or too high. Each species has an optimum temperature range for germination and there are great differences even between individual varieties. A Kofler-style hot bench can be used to illustrate how seedlings develop at different rates according to their thermal requirements. A steel strip is selectively heated and cooled to produce a temperature gradient on its surface. At one end, for example, the temperature can be set to 6 °C and at the other, 25 °C. The surface is calibrated to indicate all the temperatures in between in equal increments. By placing the seed on these gradients, it is possible to observe the temperature at which a given variety first germinates and under what conditions it fails to germinate. A grid is placed over the hot bench to make it easier to identify the individual zones.

Making root growth visible in the rhizotron

Whilst the growth of the radicle is initially influenced by only a few factors, the positive – and negative – factors increase day by day. Therefore, it makes sense to continue observing root growth underground. The rhizotron was developed to bring a certain degree of consistency to the conditions and the observation process. Rhizotrons are flat, rectangular chambers with a sheet of glass on one side. They are filled with a special substrate which serves as a growing medium for the plants. Rhizotrons are inclined at an angle of 60° to exclude light and encourage the roots to grow along the panes of glass so that they can easily be observed. Figure 3 shows a pit containing rhizotrons planted with a variety of different legumes. Every three to seven days all the rhizotrons are photographed and the images are analysed using special software. The information about root growth rates and lateral root formation is vital for selection. Since minor differences in terms of soil content, watering and temperature cannot be ruled out entirely, it is necessary to repeat the trials several times before it is possible to assess the root growth of a particular variety correctly.

Figure 1 illustrates the dynamic root growth of a maize plant. It is wonderful to watch the lateral roots developing day by day and to see how the root system gradually expands to fill the available space. The rhizotron can be used to equally good effect to compare the roots of diploid and tetraploid varieties of perennial ryegrass. Perennial ryegrass is known to be relatively sensitive to periods of drought, with diploid varieties being particularly susceptible. By observing the root system of diploid and tetraploid ryegrass plants, it quickly becomes apparent that variations in drought tolerance can be explained by the characteristic shape of their root systems (Figure 4).

Roots in the field

The described methods enable breeders to gain insights into the early development of a plant’s root system. They are suitable for large-scale root studies and facilitate selection for specific traits even at this early stage in the breeding process. Ultimately, however, the strains selected by these methods have to be tested in the field and this step is extremely time-consuming. Non-destructive methods such as the use of x-rays or the measurement of electrical conductivity between the plant and the soil are still in their infancy and are being developed primarily for individual observations.

As yet, these methods are unsuitable for the types of large-scale studies that are required for breeding. All other methods currently available are destructive, i.e. the crop is no longer usable once the tests have been completed. The most widely used field-based method of root analysis still involves taking a soil core and carefully exposing the roots. But this approach is not suitable for breeding purposes since the level of intervention in the field needed for a large-scale study would be far too great, as would the effort required. The equally time-consuming sieving method, on the other hand, has proved effective. This involves removing the soil beneath the crop on a designated area in successive 10 cm increments. The soil is sieved out to expose the roots (Figure 5).

If the soil is very sticky, the roots will have to be washed. Since conditions in the field are never entirely uniform, several samples must be taken from each crop to obtain a valid root analysis. By calculating the root mass in conjunction with the mass of above-ground vegetation, it is possible to obtain a good indication of the growth of individual specimens. In a test series on two plots conducted at the DSV’s Hof Steimke breeding station in October, the root mass of a range of cover crops that had been sown in July was determined using the sieving method described above.

Table 1 shows variations in the distribution of the roots of individual species in different soil layers in sandy soil and loam. In the sandy soil, which tends to dry out quickly, on average 60 % of the roots were found in the 0–10 cm layer, whilst for the loamy soil this figure was 81 %. The lowest root penetration occurred in the 10– 20 cm layer for both soil types (16 % and 8 %). In contrast, root penetration increased again to 24 % and 11 % in the lowest layer of topsoil (20–30 cm).

Conclusion

Crop growers and breeders are increasingly turning their attention to the root. In the last few years, Deutsche Saatveredelung AG has developed a range of lab and greenhouse methods which are suitable for large-scale breeding studies. However, any form of root analysis conducted in the field is still very time-consuming, so plant breeders are keen to focus more strongly on this much neglected area. Why go to all this effort? Initially it was found that the root system has a major influence on yields, but this is only half the story. After all, the events that take place in the soil are extremely complex and the root is involved in multiple interactions with soil, nutrients and microorganisms. Legumes, for example, have a symbiotic relationship with bacteria called rhizobia which enables them to fix nitrogen. If legumes are mixed with grasses, the grasses also benefit from the interaction between the legumes and the rhizobia. More numerous interactions occur in mixes containing several different species, which is increasingly the case with cover cropping.

Deutsche Saatveredelung AG intends to gain a better understanding of the processes taking place in the soil around the roots (the rhizosphere) in order to select suitable strains for different growing conditions and soil types and make them available to growers.

Written By Laura Barrera First Published on AGfuse.com

If someone asked you, “How do plants take up the water and nutrients they need?” you’d probably tell
them through the roots. But did you know that for many crops, those roots aren’t working alone?
That’s because most plant species associate with mycorrhizal fungi.

What are mycorrhizal fungi? University of Alberta biological scientist JC Cahill says that mycorrhizas are actually the interaction between a fungus and a plant. Although there are many different types of mycorrhizae, the only one crop farmers need to be concerned about is arbuscular mycorrhizal fungi (AMF), as 65% of plant species associate with it.  

And barring anything extreme that’s happened to your fields — such as mining or a toxic spill — your soils should already have AMF in it, says Miranda Hart, a soil microbial ecologist at the University of British Columbia. The way AMF works, Cahill explains, is that they grow inside the plant’s roots, and in exchange for sugar from the plant, the hyphae — the threadlike filaments of the fungi — capture water and nutrients in the soil for the plant. While this symbiotic relationship is often seen and discussed as a benefit to crop production, Cahill and Hart warn that’s not always the case. But there are steps farmers can take to help AMF be more of an advantage than a disadvantage for their crops.

Benefits of Mycorrhizae

One of AMF’s benefits to crops, and perhaps the most significant, is phosphorus uptake.

A study at the University of Adelaide in Australia was conducted to quantify the contribution of AMF to phosphorus uptake in wheat. The researchers used phosphorus 32, a radioactive isotope of phosphorus, and grew the wheat in compartmented pots with highly calcareous and phosphorus-fixing soil from a major cereal-growing area in South Australia. Researchers found that over 50% of phosphorus uptake in plants was absorbed via AMF, and phosphorus 32 was only detected in the AMF plants. In fact, an influx of phosphorus in roots colonized by mycorrhizal fungi can be three to five times higher than in non-mycorrhizal roots, according to the article “Phosphorus Uptake by Plants: From Soil to Cell.” The reason for this is because mycorrhizae allows the plant to explore a greater volume of soil.

The book, “Phosphorus in action – Biological processes in soil phosphorus cycling. Soil Biology Vol. 26,” explains that while root hairs can only extend a few millimeters, the hyphae of some AMF can extend many centimeters away. Alice Roy-Bolduc and Mohamed Hijri, authors of the article “The Use of Mycorrhizae to Enhance Phosphorus Uptake: A Way Out The Phosphorus Crisis,” say that in addition to the larger surface area, phosphorus is also highly immobile and phosphate ions become rapidly bound with cations, making it unavailable to plants. However, they say it is known that the presence of mycorrhizal fungi improves phosphate solubility..

Phosphorus uptake is not the only benefit of AMF. Roy-Bolduc and Hijri say that because they extends the root system, they help absorb more water and can access water in smaller pores, thereby increasing plant water uptake. They also improves soil structure, contribute to soil aggregation and decrease erosion. AMF can also help plants resist and overcome pathogen infections, as the authors note that it’s well-documented that mycorrhizal associations protect tomato plants from Phytophthora parasitica and potato plants from Fusarium sambucinum.

Cahill notes that part of the reason mycorrhizae may help with crop protection is because the AMF are already living in the plant. “They’re actually taking up space that other parasitic fungi can’t then take up themselves,” he explains. “So they may actually help protect crop plants from some soil pathogens by filling up the roots.” The combination of all these benefits ultimately can contribute to higher yields and healthier crops.

When Mycorrhizae Becomes Parasitic

While AMF can provide many benefits for plants, Cahill says that in some situations the relationship can be parasitic. An example of this would be if a plant doesn’t need phosphorus or water. The AMF is still present and taking carbon and sugar from the plant, but not giving anything in return. “So what we see in nature is this relationship between the fungus and the plant goes from beneficial to the crop to detrimental, depending on exact conditions at any point in time,” Cahill explains. It’s important to understand this because farmers can help avoid creating situations that would cause the mycorrhizae to become parasitic.

The best way to prevent a parasitic situation is by ensuring the soil isn’t too fertile, Cahill says. Unfortunately, there’s no measurement established that determines the fine line between when a soil is fertile enough for crops, but not so fertile mycorrhizae becomes parasitic. “One of the reasons there isn’t is because it’s so dependent on what species of fungi you have,” he explains. “There are different levels of parasitism, and different crops are going to be differently able to prevent or not prevent parasitism.” Because phosphorus uptake is the No.1 benefit AMF provide plants, Cahill says that if there’s no evidence of phosphorus limitation in your fields, then you might not need to be concerned about mycorrhizae. He adds that mycorrhizae can also change over time — whether it’s from applying an inoculant or introducing a different crop — the effects of which could be positive or negative.

Testing for Mycorrhizae

Unfortunately, at this time it’s difficult for growers to determine whether their AMF is benefitting their crops or not, Cahill says, because it’s not enough to know whether the plants are infected by mycorrhizae. Instead, it’s a question of whether the plant would do better on its own.

Because phosphorus uptake is the No.1 benefit AMF provide plants, Cahill says that if there’s no evidence of phosphorus limitation in your fields, then you might not need to be concerned about mycorrhizae.

“We want to be very skeptical of anybody pulling up a root system and showing you all of this infection because that’s no big deal,” he explains. “We know, typically, the amount of infection in the roots, the quantity of it, isn’t related to the yield of the plant. It’s more complicated than that. It’s the physiological functioning.”

One way to think about it, Cahill explains, is if a plant is infected with mycorrhizae in a positive way, then we can expect the plant to produce fewer roots because the fungi is doing more foraging for it. If you took the fungi away, then the plant would probably produce more roots. But having more or less roots doesn’t guarantee that the plant would produce more or less yield. “You might not actually see a shift in yield because the plants are outsourcing their foraging to the fungus or doing it themselves, but they’re spending a lot of their energy either way,” Cahill explains. If a grower is seeing unhealthy crops or lower yields than expected, then he can determine if it might be an issue with his mycorrhizae by replicating a test Cahill does in his lab. Growers simply take a little soil from their fields, put into a pot of sterile soil and see how the plants in that pot grow compared to plants grown in just sterile soil. “There’s no measure of fungal biomass that we care about,” he adds. “It simply is, put it on your plants and see what happens.”

Best Practices for Healthy Mycorrhizae

Increase Crop Diversity

The best way farmers can help AMF be beneficial for their crops is by increasing their plant diversity.

“The No. 1 way to increase the diversity of fungi, which will also increase the functioning of the fungi, is to increase plant diversity in agroecosystems,” says Hart. Keith Berns, a farmer, agricultural educator and co-owner of Green Cover Seed in Bladen, Neb., recommends having eight to 10 different species in a cover crop mix, with at least six of them being highly mycorrhizal. Aside from brassicas, which do not associate with AMF, Bern says most cover crops are beneficial for AMF. “It doesn’t mean you couldn’t have brassicas in your mix,” he adds. “You just wouldn’t want to have only those in your mix. Buckwheat is also not really highly mycorrhizal.” Almost all legumes, including peas, lentils, vetch, cowpeas, chickpeas and mung beans, are good for mycorrhizal fungi growth, he says. Grasses like sorghums, millets, rye, triticale, barleys — and oats in particular — are also excellent colonizers. He also likes to see flax and sunflowers in the mix, noting they both have excellent mycorrhizal hosting capabilities.

The reason Berns recommends growing so many different species is because it’ll provide a diversity of root exudates. “There may be different strains of mycorrhizae that will like something better than another one,” Berns says. He adds that it also helps ensure there will be something available to feed the mycorrhizae. “If we have weather conditions that are too hot, too cold, too dry, too wet, that may affect some of the species in the mix, but it’s likely not going to affect everything the same amount,” he explains. “It’s not so much the species as much as having the resiliency built into the system to make sure there’s something growing there, because the one thing that we do know is that having fallow ground is literally death to the mycorrhizae, because they have to have a living host.”

Rotate Brassicas and Maintain Weed Control

Because brassicas don’t associate with AMF, Hart recommends farmers who are growing them space them out in their rotation. “In Canada, because prices are good for canola right now, a lot of farmers are going back to mono-cropping,” she says. “But if you mono-crop brassicaceous crops, you’re going to destroy the fungal communities in a couple years completely, because they need carbon. And if they can’t form it with the crop plant, they’ll eventually become extinct in that site.” Hart says that having a brassica in rotation with at least two other crops would be ideal. But for growers who are in a two-crop rotation where one is a brassica, they need to look at ways of getting other plant species in their soil, such as through intercropping or cover crops.

The reason Berns recommends growing so many different species is because it’ll provide a diversity of root exudates.

Brassicas aren’t the only species that don’t associate with AMF. Some weeds, such as lambsquarters and pigweed, are also non-mycorrhizal — another reason why preventing and controlling weed infestations like palmer amaranth is so important. “Whatever plants become dominant in a field, be they crop or weed, we know that changes the composition of the organisms that live in the soil,” Cahill says. “So if you have a plant that doesn’t form mycorrhizae becoming very dominant, those fungi in the soil are likely to become a little bit starved and those populations are likely to go down.”

Reduce Tillage

One practice growers will want to reduce or avoid when trying to promote healthy mycorrhizal fungi and soil biology is tillage. “Tilling is terrible for fungal communities. It destroys the mycelium,” Hart says. “Some fungi can handle it, but some fungi really can’t and they’ll disappear. So you’re going to decrease diversity by tilling.” Cahill agrees, noting that tillage often contributes to soil compaction, which is also detrimental to soil life. “When you have really compacted soil, we know that impacts water penetration and can impose drought, but it also doesn’t give the air spaces and pockets that all these fungi, bacteria and even nematodes and other things need to live,” he explains. “So you need to keep that soil light, which is typically done through no-till.” However, Hart warns that no-tilling often increases a farmer’s herbicide use, which could also negatively impact fungi. But there are some no-tillers like Russell Hedrick andGabe Brown who are successfully no-tilling with fewer herbicide applications by implementing a holistic, systems’ approach.

Be Mindful of Fungicides, Fertilizers

Farmers also need to be mindful of the products they apply if they want to promote AMF growth. “Fungicides will kill fungi, and many of them will kill mycorrhizal fungi,” Cahill says, adding that if you’re concerned that a fungicide may have a negative effect on the soil life, you should test it. This can be done by putting some soil from your field into a couple pots, applying fungicide to one, then growing plants in both and seeing what happens. Growers should also be mindful of fertilizers, Cahill adds, as they often impose some acidity. And as soil pH decreases, it will kill off a lot of fungi and other soil organisms. “Fungi seem to be really sensitive to change in the acidity of soil and salt contents,” he says.  

Should You Use Inoculants?

If you’re growing a perennial like alfalfa or a crop that’s going to be there for 10 years, then applying an inoculant may provide a jumpstart for AMF, says Berns. “With a perennial you have no fallow period breaks, so that’s where the mycorrhizae really shine because they never have to jump from one host to another,” he says, adding that it can be harder to justify the cost of an inoculant on an annual crop. But Berns has done some testing with these products on his farm, and has observed some differences between plots treated with inoculants vs. the control plots, particularly with aboveground growth and root mass. This year he put a lot on his corn and soybean acres and is waiting to see if they made any difference.

Cahill encourages all farmers to do as Berns has and become scientists on their own farms, “because they’ll be able to see with their own eyes whether it does or doesn’t have an effect.” He also recommends growers test these products before applying it to their whole fields by again testing them in pots. Farmers can do this by growing some plants in a pot of sterile soil with the inoculant and some in a pot without the inoculant, and seeing if there’s a yield difference.

Growers should also be mindful of fertilizers, Cahill adds, as they often impose some acidity. And as soil pH decreases, it will kill off a lot of fungi and other soil organisms.

The reason he wants growers to do some small trials first is because there’s no widespread evidence these products are beneficial all the time, and if a parasitic inoculant establishes in a field, there’s no easy way to remove it. In fact, he tells his students every year that the one thing he wants them to remember from his class is to not let their moms buy a bag of inoculum from the garden store and just apply it to their gardens. “She’s most likely paying to put parasites on her garden,” he says. “Until you can prove it works in that garden, it’s not worth the money.” He says to think of mycorrhizal inoculants like fertilizer. “We know that adding fertilizer doesn’t always increase crop yield because there are going to be some farms and conditions that have enough fertilizer, or you get toxicity,” he explains. “That’s going to happen with inoculum too.

There are going to be some situations where they’re not beneficial and they might be parasitic, but we don’t know if they are yet.” Hart agrees with Cahill that there’s no guarantee the effect of an inoculant will be beneficial. In fact, she says that the particular isolate being mass commercialized actually depresses phosphorus uptake. “A plant without that fungus is getting more phosphorus than the plant with the fungus,” she explains. “They’re not always mutualistic in every situation. Sometimes, depending on the soil nutrients, the plant and the growth stage, they will actually suppress plant growth and performance.”

But Hart says that in most cases, the inoculant is probably not even establishing. She recalls a 2-year field trial where the commercial inoculant only established in one out of 4 farms. “Where it established, it established quickly and it spread fast,” she says. “But in the other plots, it would’ve been a waste of money for the farmers to use it.” She’s also concerned about the effects these products may have on non-target species, pointing out that there have been studies where this particular fungus has occluded every other fungus in the community. The studies were short-term, Hart says, so it’s too early to make generalizations about it. But she says she can’t in good conscience tell farmers they should be using these products because we don’t know the dangers yet.

Grow Native Species

Instead, Hart recommends growers focus on promoting the mycorrhizal fungi populations already in their fields by trying to grow plants that are native to the land — whether it be through cash crops, intercropping or cover crops — so the mycorrhizal fungi and all of the soil microbes become more diverse, sustainable, and ultimately, more functional. “You want to make it as close as possible to what was original before the land was tilled,” she says. “Because native plants and fungi have evolved together, so they are more likely more beneficial for each other.”

Charlotte Rowley, AHDB Crop Protection Scientist runs the rule over CSFB in 2019

If you are a regular Twitter user, you might be wondering how there is any oilseed rape left in some parts of the country following the onslaught of cabbage stem flea beetle this year. Pictures have been posted from across the country of OSR filled with larvae, and not just flea beetle but rape winter stem weevil too. This year seems to have been the perfect storm for flea beetle misery: newly sown crops unable to grow away in dry ground, and then a prolonged period of mild weather allowing egg laying and larval development to continue late into the season. In some areas this has resulted in high numbers of larvae, with 19 found in a single stem at a site assessed by ADAS. With the threat of spreading insecticide resistance and a need to look after our beneficial insects, tackling cabbage stem flea beetle has to go further than just another pesticide spray. 

What’s in the pipeline?

This outbreak comes in the final year of a 3-year AHDB funded project into cabbage stem flea beetle IPM, led by researchers at ADAS in collaboration with Fera, Bayer, Syngenta and Cotton Farm Consultancy Ltd. This project is aiming for a truly integrated approach to pest management, investigating a range of factors including weather, seed rate, variety, alternative control options, and the effect these might have on flea beetle damage. One area of alternative control being explored is the use of volunteer OSR as a trap crop. Trap crops can be effective in drawing flea beetle and other pests away from the cash crop, but can also be expensive to sow and manage.

As part of their research, Steve Ellis and Sacha White at ADAS have instead been looking at the effectiveness of leaving volunteer oilseed rape in a field neighbouring this year’s crop to attract migrating cabbage stem flea beetle away from newly emerging seedlings. This work is based on a suspected biological quirk of cabbage stem flea beetle where their wing muscles deteriorate after the initial migration, making it difficult for them to move into another crop. 

Not destroying volunteers until midSeptember therefore, could help to protect the cash crop during the main migration period. So far, the results from trials using this technique suggest that it can be effective if a large enough area of volunteers is left. We know that like many insect pests, cabbage stem flea beetle locate their host crop at long range by detecting certain volatiles given off by the plants. It makes sense then that there needs to be enough plants to give off a sufficiently strong signal to attract large numbers of migrating adults. This might limit the fields in which this technique can be used, but some forward planning could help create a large enough volunteer environment to protect adjacent crops. 

Other points to consider

As with any integrated pest management strategy, suitability should be looked at on a field by field basis. Risk assessments of disease and erucic acid levels should come into play when thinking about management of OSR volunteers.

However, where this technique has proved effective, it has shown reduced adult numbers and increased plant populations in the adjacent new OSR crop.

Early results from autumn 2018 also suggest lower larval numbers in the new crop – so keep an eye out for more results later this year. As well as trap cropping, the ADAS researchers have also been investigating defoliation over winter as a way of reducing larval numbers. Teaming up with Innovative Farmers, they have set up field labs to get farmers trying this out in tramline trials.

So far the results have shown promising reductions in larval numbers but time will tell whether there is an impact on yield in a particularly difficult year. Other avenues of research being looked at elsewhere include companion cropping OSR and the impact of natural enemies on flea beetle populations. Cabbage stem flea beetle larvae and adults are susceptible from attack by parasitoid wasps, so any insecticide sprays in spring or summer can be particularly harmful to these beneficial insects. These areas of research could all form part of a bigger IPM strategy, in time helping farmers to both reduce insecticide usage and overcome the challenges of cabbage stem flea beetle. 

For further information, please visit: https://ahdb.org.uk/knowledge-library/ cabbage-stem-flea-beetle.