Archive for the ‘Host plant resistance’ Category

JULY 2, 2021


How the potato blight pathogen penetrates the plant

by Wageningen University

Scientists discover how the potato blight pathogen penetrates the plant
Credit: Wageningen University

In the 19th century, the notorious pathogen Phytophthora infestans caused a large famine in Ireland and other parts of Western Europe. To this day, it continues to pose a major threat to global food production. It has long been a mystery how this microscopically small organism and other members of the Phytophthora genus mechanically gain entry through the protective layer on the leaves of crops. In a unique collaboration, Wageningen University & Research experts in plant pathology, cell biology and physics have now found an answer to this question. Their discovery also provides new leads to making the control of Phytophthora more effective, more efficient and more sustainable on the long term. Their findings are published in Nature Microbiology.

Plants are under constant threat from all kinds of pathogens. A number of these intruders bearing the difficult name Phytophthora (literally: plant destroyer), cause enormous damage yearly to all kinds of crops, such as potatoes, tomatoes, eggplant, cocoa, peppers, soy and date palm, as well as to woodlands and nature reserves. Phytophthora not only poses a major threat to our food security, but also results in vast economic damages, causing annual damage to the potato sector of approximately 6-7 billion euros.

Combatting Phytophthora is and remains problematic, in part because the pathogen and its target are engaged in an ongoing arms race. Tremendous resources are invested in the development of resistant crops through plant breeding, with the aim of becoming less dependent on chemical crop protection. There is also increasing interest in new forms of mixed cropping.

Utilising Insights from Mechanics

Another option has now arisen; preventing Phytophthora from gaining access to a plant altogether. Plants come equipped with a protective layer that serves to keep intruders like Phytophthora out. Yet, this microscopically small pathogen (smaller than one tenth of the thickness of a human hair) is able to penetrate this layer and initiate its disease process in plants. Despite decades of research, it remained unknown how they mechanically penetrate this layer. To solve this problem, WUR plant pathologists and cellular biologists joined forces with WUR physicists. The latter are specialists in mechanics, a branch of physics that studies how objects and materials move and respond under the action of forces acting upon them. Their combined knowledge, and new research tools developed in collaboration, could finally bring resolution to this puzzle.

“We discovered that Phytophthora uses clever tricks to sharpen its tubular infection structure to then cut through the surface of the plant with a sharp knife. Using this strategy, Phytophthora is able to infect its host, without brute force and with minimal consumption of energy. This is the first time that this mechanism has been uncovered, and really a fundamental discovery,” Joris Sprakel, professor in Physical Chemistry and Soft Matter, says.

More effective and sustainable protection

Phytopathology Professor Francine Govers sees plenty of leads to make the control of Phytophthora more effective, more efficient and more sustainable in the long run, without the usual suspects—chemicals and plant breeding—to circumvent the arms race. “The laws of mechanics tell us that Phytophthora is unable to penetrate the plant without first attaching itself tightly to the leaf surface.” To test this idea, as initial proof of feasibility, the research team sprayed the leaves of potato plants with a non-toxic and inexpensive substance that removes the leaf’s stickiness. This resulted in a reduction of around 65% in the level of infection. The effect even rose towards 100% in an optimized trial on artificial surfaces.

Apart from the fundamental breakthrough and investigating tools for combatting this kind of plant disease from a new perspective, the research also resulted in a new methodology; a kind of rapid testing method, that can reveal the effect and efficiency of pesticides in a rapid, accurate and inexpensive way. These novel tools could also make a significant contribution to the ongoing battle against plant diseases.

“Thanks to the engagement of Joris Sprakel and his team, including Ph.D. candidate Jochem Bronkhorst, we now know that there are a number of fundamental physical principles that could give a new twist to the arms race between pathogens and plants,” says Govers. “All in all, this research is a truly wonderful example of how collaboration across disciplinary borders can lead to breakthroughs.”

Explore further New resistance gene to devastating potato disease that caused Irish Famine

More information: Jochem Bronkhorst et al, A slicing mechanism facilitates host entry by plant-pathogenic Phytophthora, Nature Microbiology (2021). DOI: 10.1038/s41564-021-00919-7Journal information:Nature Microbiology

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Why demand is expected to be strong for virus-resistant wheat

Wheat with the Bdv2 gene (left) and a non-Bdv2 crop © RAGTWheat with the Bdv2 gene (left) and a non-Bdv2 crop © RAGTf

Farmer’s Weekly

Insecticide-free wheat has moved a step closer with the arrival of the hard Group 4 winter wheat variety Wolverine, which is the first to offer barley yellow dwarf virus (BYDV) resistance.

Added to the latest AHDB Recommended List on a yield of 102%, Wolverine has a specific recommendation for resistance to BYDV and sets an exciting tone for future wheat variety introductions from breeder RAGT, many of which will have resistance to both BYDV and orange wheat blossom midge.

While Wolverine is a high-yielding feed variety, the company also has bread-making wheats with both types of resistance in development – many of which should eliminate the need to apply insecticides throughout the entire growing season.

Against a background of the loss of insecticidal seed treatments, rising resistance levels in pests to the remaining foliar sprays and greater scrutiny of pesticide use, the development of these varieties is a breakthrough.

Their arrival is expected to be as well-received by the supply chain as it is by farmers, in the industry’s quest to sharpen its environmental credentials.

Seed demand

After a limited seed release last year ahead of the recommendation decision, there is enough seed of Wolverine available to meet demand for this autumn’s wheat plantings, RAGT managing director Lee Bennett confirms.

He believes the variety could take a significant market share.Lee Bennett in a trial plot

Lee Bennett © RAGT

“The ideal situation is to have this BYDV resistance in a variety that suits early drilling,” he says. “That’s exactly what we have in Wolverine.”

After two consecutive wet autumns and difficulties with wheat drilling schedules, the opportunity for farmers to get under way while conditions are good, without putting the crop at unnecessary risk from virus-carrying aphids, is a bonus, he notes.

“This will be the second year without the Deter (clothianidin) seed treatments that gave such cost-effective control. The approval of Wolverine gives them a different, more environmentally friendly solution.”

Genetic solution

The genetic alternative to chemical control is performing well in the field, says his colleague Tom Dummett, who confirms that the Bdv2 gene used in Wolverine brings season-long protection from the aphids that transmit the virus.

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“The aphids still arrive, but Wolverine doesn’t express any virus symptoms and the virus doesn’t multiplicate in the plant,” he explains.

“We’re very happy with the way that the gene is working. It’s proved effective in Australia for almost 20 years and is now in the right genetic background to work well in the UK.”

Having previously conducted trials to look at the value of the resistance at different sowing dates and whether the use of one insecticide spray could protect the gene or give a yield uplift, this year’s work by RAGT has a different focus.

The plots were all drilled in early September and then inoculated with aphids infected with the PAV strain of BYDV, both in the autumn and the spring.

BYDV pressure

The idea was to create severe BYDV pressure, explains Mr Dummett, with one-third being left untreated, one-third receiving an autumn insecticide, and the remaining plots getting both an autumn and spring insecticide.

At the time of Farmers Weekly‘s visit in June, varieties without the BYDV resistance gene were showing clear symptoms of the virus in the untreated plots.

Wolverine and the other RAGT lines with the Bdv2 gene were symptom-free.

The PAV strain of BYDV is the most common, Mr Dummett says, but the company is confident that the resistance is broad-spectrum as tests have confirmed that it also controls the MAV and RPV strains.

Wolverine’s agronomic features

Agronomically, Wolverine is a later-maturing type, with a +2 for ripening.

It has stiff straw and good resistance to brown rust, but is middle-of-the-road for septoria (5.3) and did take on some yellow rust last year, so has a score of 5. As such, it needs to be grown with care and frequent monitoring.

Seed cost

The previous cost of using Deter (clothianidin) seed treatments and an insecticide for BYDV control has been factored into the cost of growing Wolverine.

As it was last year, the variety will be sold via the Breeders’ Intellectual Property Office system, which means that the value of the trait will be charged direct to farmers on an area basis rather than by tonnage.

That charge will be £33/ha, and RAGT points out that it covers season-long protection and eliminates the need to monitor aphid populations or repeatedly spray at a busy time of year.

Competitive advantage

RAGT has a head start over other breeding companies when it comes to BYDV resistance, as it is the only UK plant breeder with Bdv2.

The company has two feed wheat varieties coming along closely behind Wolverine, followed by four bread-making types with both BYDV and orange wheat blossom midge resistance.

The Bdv2 gene originated in goat grass and was translocated onto a wheat chromosome by Australian researchers, who went on to breed BYDV-resistant wheats.

There are four other known BYDV resistance genes, most of which are being investigated by RAGT. Bdv3 and Bdv4 work differently to Bdv2, for example, but may bring other benefits when put into the right genetic background.

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Joe Louis Studies the Molecular Battles Between Plants and Insects
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Joe Louis Studies the Molecular Battles Between Plants and Insects

The University of Nebraska–Lincoln entomologist wants to help pave the way for creating environmentally friendly tools to replace insecticides to control agricultural pests.

Shawna Williams
Mar 1, 2020



It’s not easy to monitor electrical activity in an aphid. But it can be done with wire and glue. This electrical penetration graph technique involves gluing a wire onto an aphid’s back so that the insect is still able to walk around. When the animal is allowed to eat a plant conducting an electrical current, the resulting readout from the plant can provide valuable information about its feeding behavior. As an entomology master’s student at Kansas State University in the mid-2000s, Joe Louis set out to learn how to use the technique.

“He had to learn to apply the electronics and the technical side of that, which not many people have ever mastered,” says John Ruberson, who worked at Kansas State at the time and is now head of the entomology department at the University of Nebraska–Lincoln (UNL), where Louis is an associate professor. It might not have been obvious to others why Louis needed to go to the trouble, Ruberson explains, but mastering the technique would pay off.

When a wired aphid pricks its needle-like stylet into a plant conducting electricity, it completes an electrical circuit and generates a voltage spike in the readout from the wire. By using RNAi to block a gene’s product in insects and then employing their technique to monitor the feeding behavior, Louis was part of a team that figured out that a saliva protein in pea aphids (Acyrthosiphon pisum) called C002 is essential for the insects to feed on fava bean plants. It was the first aphid saliva protein identified.

After completing his master’s in 2006, Louis stayed at Kansas State to begin working toward a PhD with plant biologist Jyoti Shah, using the same electrical monitoring system in combination with molecular and biochemical approaches to study defenses the plant Arabidopsis thaliana deploys against hungry insects. Working with colleagues, they discovered an Arabidopsis gene, MPL1, that’s expressed in response to aphid infestation and is critical to the plant’s protection against the pests. While the exact mechanism wasn’t clear, the enzyme the gene codes for breaks down lipids, and appeared to limit the insects’ ability to reproduce, the researchers reported in 2010. Shah and Louis both moved to the University of North Texas in 2007.

Louis was “a go-getter,” Shah says. Rather than needing to be pushed to publish his work, for example, he would take the initiative to draft papers. “He was ambitious. . . . Even at that early stage of his career, he was quite independent with how he did things,” Shah recounts. “At the same time, he was open to advice.”

After earning his PhD from the University of North Texas, Louis went on to a postdoc with Gary Felton and Dawn Luthe at Pennsylvania State University before starting his own lab at UNL. There, he’s continued to delve into what he calls the “tug-of-war” between pest and plant. “We are trying to understand how plants can recognize those insects . . . so that they can rapidly and accurately activate . . . defenses,” he says. In a study published last year, he worked with graduate student Suresh Varsani and other colleagues to identify a chemical called 12-oxo-phytodienoic acid that is produced by aphid-resistant maize. The acid enhances the deposition of a protective polysaccharide called callose along the inside of cell walls, boosting the plant’s defenses. 

Ultimately, Louis hopes that findings like these will lead to innovative ways to protect crops from pests without harming the environment as today’s insecticides do. “This kind of research helps to [attain] a cleaner environment, and we can reduce the usage of these pesticides or chemical insecticides.” 

Shawna Williams is a senior editor at The Scientist. Email her at swilliams@the-scientist.com or follow her on Twitter @coloradan.


aphidsArabidopsiscropsecology & environmentelectricitygenetics & genomicsplant biologyplant defensesproteinScientist to watch

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“Our lettuce varieties have resistance against new downy mildew race BI:37EU”

Downy mildew is a major threat in lettuce. The fungus can damage the lettuce leaves in both protected and open-field crops, resulting in a loss of yield. Last year the European Commission of the International Bremia Evaluation Board (IBEB-EU) identified a widely occurring new variant of downy mildew in lettuce. As of 1 June 2021, it has officially been named Bl:37EU. The large majority of Rijk Zwaan’s current lettuce varieties are resistant to the new race of downy mildew.

New official denominated race
On 1 June 2021, the European Commission of the International Bremia Evaluation Board (IBEB-EU) officially denominated the new race BI:37EU. This variant of downy mildew (Bremia lactucae, Bl) has been found in multiple regions in France in the past years and more recently also in Spain, Portugal, and Italy. IBEB-EU expects this race to spread further in the summer and autumn of this year, although it is currently difficult to predict which areas will actually be affected.

Resistances in lettuce
The development of resistances against downy mildew is one of the pillars of vegetable breeding company Rijk Zwaan’s lettuce breeding program. “Downy mildew is evolving genetically all the time and a large number of isolates of the plant fungus are already known worldwide. In our breeding program, we are continuously working on improving the traits of our lettuce varieties, including resistances to new downy mildew variants. The large majority of Rijk Zwaan’s current lettuce varieties are resistant to the new BI:37EU race of downy mildew,” comments Johan Schut, Breeding Manager Lettuce.

Sustainable solution
Rijk Zwaan is a strong advocate of an integral approach to combating plant diseases in order to reduce the use of chemicals. Although resistant varieties play an important role in this, the company also advises crop protection agents and hygiene measures to prevent new downy mildew variants from developing. Good hygiene practices such as burying crop residues and promptly removing diseased plants help to limit the spread of downy mildew in lettuce.

International Bremia Evaluation Board
The International Bremia Evaluation Board (IBEB) is a joint initiative of lettuce breeding companies in the USA, France and the Netherlands, the University of California-Davis, the Netherlands Inspection Service for Horticulture (Naktuinbouw) and the French National Seed Station (GEVES). IBEB’s mission is to identify new races of Bremia lactucae that pose a significant threat to the North American or European lettuce market and to promote the use of standardized race names in communication with growers.

Races are identified and nominated by regional IBEB committees specifically for each continent. For more information, visit the International Seed Federation’s website. For more information:
Rijk Zwaan

Publication date: Tue 1 Jun 2021

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Japanese Beetle Resistant Roses

May 15, 2021Blaine HowertonGardens & Landscapes0

Photo by Chris F from Pexels

Rita Jokerst, Horticulturist, Gardens on Spring Creek

Japanese beetles are the scorn of any rose gardener, and we at the Gardens on Spring Creek are disappointed to report these pests are officially here in the Northern Colorado area. These concerning beetles do not just target rose gardens – they attack a wide variety of landscape, edible, and ornamental plants as they damage plants in two different ways. 

The larvae (or grubs) feed on the roots of turfgrass, thereby producing drought-stress symptoms in large swathes of off-color, unhealthy-looking lawn. The grubs’ presence in turn attracts further damage by other critters. Skunks, raccoons, and many birds will dig into lawns infested with Japanese beetle larvae to feed upon them. Secondly, the highly mobile adults damage plants above ground, chewing on the leaves and flowers of many, many plants. So, what preemptive actions can a gardener take against these pests? Follow the data and plant wisely!

In 2016 and 2017, Colorado State University Professor Whitney Cranshaw evaluated Japanese beetle damage on roses at the War Memorial Garden in Littleton, Colorado. Over the course of a growing season, seven observations were made and included beetle damage, ranked on a scale of 0-3 (no damage to heavy damage) and flower visitation by bees, ranked 0-3 (no visitation to high visitation). Studying both the beetle damage and how preferred a plant is by bees is important because many of the go-to insecticides that will successfully control the beetles can also harm globally declining bee populations. 

Below are some takeaways from Dr. Cranshaw’s research. “Not recommended” roses had both high levels of beetle damage and high bee visitation, making Japanese beetle control difficult and insecticide application unwise. “Maybe” roses had no bee visitation and varying levels of beetle damage, meaning they could be effectively treated with insecticidal controls without risking negative impacts to our local bees. “Recommended roses” had no beetle damage, therefore not in need of any interventive action as Japanese beetles move into our region. Asterisked roses can be found on the grounds at the Gardens on Spring Creek.

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Is genetically modified corn the answer to fall armyworm? 

ABC Rural / By Megan HughesPosted 3ddays ago

A close up of a caterpillar on a stalk of corn. It's clear the grub has done a lot of damage
Fall armyworm has been detected across the country from North Queensland to Western Australia and even Tasmania.(Supplied: DPIRD)


  • It’s a tiny caterpillar that’s difficult to detect, but for more than a year it’s been having a massive impact on crops in Australia, especially corn. 

Key points:

  • Fall armyworm is causing damage to corn crops around Australia 
  • Farmers are asking whether genetically modified corn could help
  • The Maize Association says it will need whole-of-industry support before GM corn can be introduced  

Fall armyworm (FAW) has infiltrated six states and territories and is so hard to control farmers are whispering about a method that’s been off the table for almost two decades — genetically modified (GM) corn.

Maize Association of Australia chairman Stephen Wilson said questions were being raised about whether GM corn could manage the armyworm incursion.

“Anecdotally, I am hearing from the field farmers saying we need GM to help us control the insect,” he said. 

“It’s a major discussion point for the industry as a whole because for the last three decades we, as an industry, as the Maize Association, have been working uniformly to say we do not need GM in Australia.” 

Lessons from the US 

Since arriving in Australia in February 2020, fall armyworm has been detected in Queensland, the Northern Territory, Western Australia, New South Wales, Victoria and, most recently, in Tasmania. 

Fall armyworm is native to the United States, where it has devastated multiple agricultural crops, but growers there have different tools to fight it. 

Fall armyworm on corn plants
Fall armyworm outbreaks are contained by insecticide use and GM crops in the United States.(Supplied: Queensland Department of Agriculture and Fisheries)

North Carolina State University professor and extension specialist Dr Dominic Reisig said in their industry, corn was genetically modified to produce insecticidal proteins that naturally occurred in a bacteria found in soil. It is known as BT corn.

Dr Reisig said while it was not specifically designed to treat FAW it had had an impact. 

“It was first commercially planted in 1996 but that particular crop that was planted did not control fall armyworm,” he said.

“So it wasn’t until different BT toxins were introduced that we really started to see fall armyworm control. 

“But because it’s a sporadic outbreak pest throughout the US it wasn’t like a huge, earth-shattering moment when we were able to control fall armyworm.” 

Are GMO crops the silver bullet? 

According to Dr Reisig, treating FAW across ag industries was a multi-pronged approach with insecticides and a GM crop. 

He said in corn the pest could infest a crop in different stages of its development. 

“Once it gets into the whirl it’s very difficult to control,” he said. 

“But the good thing is when it attacks in those (earlier) stages it’s not that damaging to yield — so the corn looks really bad but it usually pops out of it and it’s not a problem. 

“If fall armyworm attacks later in the season when maize has an ear, then it’s a problem. 

“Once it’s inside that ear you can’t control it and then it’s a really damaging pest in terms of yield and it’s really difficult to control with insecticides so BT (corn) is the way to go.”

He said insecticides were able to control the pest in other crops like soya beans or vegetables because the plants were structured differently.

Weighing up the losses 

Australia only grows three GM crops — cotton, safflower and canola. 

A sea of yellow flowers under a blue sky as the canola crop is in full bloom.
Canola is one of thee genetically modified crops in Australia.(Supplied: Riverine Plains Inc)

Corn has remained GM-free and, as a consequence, the industry has been able to access different markets including Japan and Korea. 

“End users such as snack food and cornflake breakfast cereal manufacturers have told us the whole time they do not want GM in their raw materials,” Mr Wilson said. 

“It would impact on both the export market and also on all the domestic markets — everything from dairy cows utilising the maize as grain or silage right through to beef cattle and right through to human consumption. 

“It’s a major, major, major impact that would need to be agreed to by all sectors of the industry.” 

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A person opens a corn's covering to check if it's ripe.
Australia has been able to access multiple international markets as the corn grown here is GM free.(Pexels: Frank Meriño)

He said any trial would be complicated.

“You have all the regulatory issues of actually bringing germplasm into the country, you have the quarantine issues of having the facilities that could handle the GM product, then you’ve got the issues of field testing,” he said. 

“It would be a long, drawn-out process and we’d have to consider the impact on the industry as a whole because it’s very hard, if not impossible, to have part-GM, part-non-GM. 

“It’s a very expensive process and it makes the non-GM corn being in the minority a very expensive product that people have to pay a premium for.” 

In a statement, a spokesperson from the Federal Department of Agriculture, Water and the Environment said genetically modified maize seeds may only be imported into Australia under an import permit issued by the department, but that no applications had been made. 

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Scientists uncover how resistance proteins protect plants from pathogens




In plants, disease resistance proteins serve as major immune receptors that sense pathogens and pests and trigger robust defense responses. Scientists previously found that one such disease resistance protein, ZAR1, is transformed into a highly ordered protein complex called a resistosome upon detection of invading pathogens, providing the first clue as to how plant disease resistance proteins work. Precisely how a resistosome activates plant defenses, however, has been unclear.

A joint team led by Profs. ZHOU Jianmin, CHEN Yuhang and HE Kangmin at the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences and Prof. CHAI Jijie at Tsinghua University recently employed state-of-the-art electrophysiology and single-molecule imaging to investigate the molecular mechanism by which the ZAR1 resistosome activates plant immunity.

By using Xenopus oocyte- and planar lipid bilayer-based electrophysiology studies, the researchers first showed that the ZAR1 resistosome is a cation-selective, calcium-permeable ion channel. They then applied single-molecule imaging to show that the activated ZAR1 resistosome forms pentameric oligomers in the plasma membrane of the plant cell, confirming previous structural data.

The formation of ZAR1 resistosome in the plant cell triggers sustained calcium ion influx and subsequent immune signaling events leading to cell death, and these processes are all dependent on the activity of the ion channel.

Together, these results support the conclusion that the calcium signal triggered by the ZAR1 channel initiates immune activation, thus providing crucial insights into the working of plant immune systems.

Disease resistance proteins are the largest family of plant immune receptors and are of major agricultural importance in protecting crop plants from assault by diverse pathogens and pests including viruses, bacteria, fungi, oomycetes, nematodes, insects, and parasitic weeds.

The findings of this study shed light on the precise biochemical function of many disease resistance proteins, and suggest new methods for controlling diseases and pest damage in crop plants.

This work “presents important findings that will change our view of ETI-triggered cell death,” said a reviewer from Cell. “The use of TIRF to visualize and monitor in real-time membrane-associated resistosomes is very exciting and many researchers will strive to emulate this method.”


This study, entitled “The ZAR1 resistosome is a calcium-permeable channel triggering plant immune signaling,” was published online in Cell on May 12.

The research was supported by the National Natural Science Foundation of China and the National Key Research and Development Program of China.

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.

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China develops GM corn variety to combat yield-cutting fall armyworm

Dong Xue | CGTN | April 12, 2021

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Credit: Miaoli County Agriculture Office
Credit: Miaoli County Agriculture Office

This article or excerpt is included in the GLP’s daily curated selection of ideologically diverse news, opinion and analysis of biotechnology innovation.

Food security is a major policy issue in China. To strengthen the nation’s seed industry, the country has approved a series of supporting policies, including in South China’s Hainan Province.

Like James Bond once said, “Nothing is impossible.” Lyu Yuping, a veteran plant breeder, had a similar belief and so [he] named his genetically modified corn seed “the 007”.

Lyu has devoted himself to agricultural technology and the seed breeding industry for more than two decades. He believes the corn seeds he’s developed are the real deal.

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LSU student identifies fungus causing soybean taproot decline

This image has an empty alt attribute; its file name is delta-f-perss.png

TAGS: CROP DISEASELSUGarciaArocajpg.jpgTeddy Garcia-Aroca, an LSU Ph.D. student, holds a sample of a fungus he found and named that causes the disease soybean taproot decline.Discovery just “tip of the iceberg” as scientists strive to learn more about this devastating soybean disease.

Bruce Shultz, Louisiana State University | Apr 13, 2021

An LSU graduate student has identified and named a new species of fungus that causes a devastating soybean disease. 

LSU doctoral student Teddy Garcia-Aroca identified and named the fungus Xylaria necrophora, the pathogen that causes soybean taproot decline. He chose the species name necrophora after the Latin form of the Greek word “nekros,” meaning “dead tissue,” and “-phorum,” a Greek suffix referring to a plant’s stalk. 

“It’s certainly a great opportunity for a graduate student to work on describing a new species,” said Vinson Doyle, LSU AgCenter plant pathologist and co-advisor on the research project. “It opens up a ton of questions for us. This is just the tip of the iceberg.” 

Taproot decline

The fungus infects soybean roots, causing them to become blackened while causing leaves to turn yellow or orange with chlorosis. The disease has the potential to kill the plant. 

“It’s a big problem in the northeast part of the state,” said Trey Price, LSU AgCenter plant pathologist who is Garcia-Aroca’s major professor and co-advisor with Doyle. 

“I’ve seen fields that suffered a 25% yield loss, and that’s a conservative estimate,” Price said. Heather Kellytaproot decline in soybeans

Yellowing leaves are early symptoms of taproot decline in soybeans.

Louisiana soybean losses from the disease total more than one million bushels per year. 

Price said the disease has been a problem for many years as pathologists struggled to identify it. Some incorrectly attributed it to related soybean diseases such as black-root rot. 

“People called it the mystery disease because we didn’t know what caused it.” 

Price said while Garcia-Aroca was working on the cause of taproot decline, so were labs at the University of Arkansas and Mississippi State University. 

Price said the project is significant. “It’s exciting to work on something that is new. Not many have the opportunity to work on something unique.” 


Garcia-Aroca compared samples of the fungus that he collected from infected soybeans in Louisiana, Arkansas, Tennessee, Mississippi and Alabama with samples from the LSU Herbarium and 28 samples from the U.S. National Fungus Collections that were collected as far back as the 1920s. 

Some of these historical samples were collected in Louisiana sugarcane fields, but were not documented as pathogenic to sugarcane. In addition, non-pathogenic samples from Martinique and Hawaii were also used in the comparison, along with the genetic sequence of a sample from China. 

Garcia-Aroca said these historical specimens were selected because scientists who made the earlier collections had classified many of the samples as the fungus Xylaria arbuscula that causes diseases on macadamia and apple trees, along with sugarcane in Indonesia. But could genetic testing of samples almost 100 years old be conducted? “It turns out it was quite possible,” he said. 

DNA sequencing showed a match for Xylaria necrophora for five of these historical, non-pathogenic samples — two from Louisiana, two from Florida, and one from the island of Martinique in the Caribbean — as well as DNA sequences from the non-pathogenic specimen from China. All of these were consistently placed within the same group as the specimens causing taproot decline on soybeans. 

Why now? 

Garcia-Aroca said a hypothesis that could explain the appearance of the pathogen in the region is that the fungus could have been in the soil before soybeans were grown, feeding on decaying wild plant material, and it eventually made the jump to live soybeans. 

Arcoa’s study poses the question of why the fungus, after living off dead woody plant tissue, started infecting live soybeans in recent years. “Events underlying the emergence of X. necrophora as a soybean pathogen remain a mystery,” the study concludes. 

But he suggests that changes in the environment, new soybean genetics and changes in the fungal population may have resulted in the shift. 

The lifespan of the fungus is not known, Garcia-Aroca said, but it thrives in warmer weather of at least 80 degrees. Freezing weather may kill off some of the population, he said, but the fungus survives during the winter by living on buried soybean plant debris left over from harvest. It is likely that soybean seeds become infected with the fungus after coming in contact with infected soybean debris from previous crops. These hypotheses remain to be tested. 

Many of the fungal samples were collected long before soybeans were a major U.S. crop, Doyle said. “The people who collected them probably thought they weren’t of much importance.” 

Garcia-Aroca said this illustrates the importance of conducting scientific exploration and research as well as collecting samples from the wild. “You never know what effect these wild species have on the environment later on.” 

What’s next? Now that the pathogen has been identified, Price said, management strategies need to be refined. Crop rotation and tillage can be used to reduce incidence as well as tolerant varieties. 

“We’ve installed an annual field screening location at the Macon Ridge Research Station where we provide taproot decline rating information for soybean varieties,” Price said. “In-furrow and fungicide seed treatments may be a management option, and we have some promising data on some materials. However, some of the fungicides aren’t labeled, and we need more field data before we can recommend any.” 

He said LSU, Mississippi State and University of Arkansas researchers are collaborating on this front. 

Doyle said Garcia-Aroca proved his work ethic on this project. “It’s tedious work and just takes time. Teddy has turned out to be very meticulous and detailed.” 

The final chapter in Garcia-Aroca’s study, Doyle said, will be further research into the origins of this fungus and how it got to Louisiana. Source: Louisiana State University, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.  

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Fall armyworm ‘worsens hunger among smallholders’

maize farm

Maize farmer inspecting her crops. Copyright: Axel Fassio/CIFORCC BY-NC-ND 2.0

Speed read

  • Fall armyworm destroys maize worth almost US$5 billion annually in 12 African countries
  • In a Zimbabwe study, the pest increased likelihood of hunger by 12 per cent
  • Farmers need cost-effective, environmentally sustainable control measures, experts say
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By: Onyango Nyamol

[NAIROBI] The invasive crop pest fall armyworm is well known for its devastating effects on maize yields in Africa, but few studies have been done on its broader impact on poverty levels and food security.

Now a study in Zimbabwe has found that smallholder maize-growing households blighted by fall armyworm are more likely to experience hunger and could see their income almost halved in severe cases, highlighting the urgency of strategies to tackle the pest.

“Our study suggests that the outbreak is threatening food security and negatively affecting farmers’ livelihoods, hence urgent actions are needed.”

Justice Tambo, CABI

According to the study, estimates from 12 maize‐producing countries in Sub-Saharan Africa including Benin, Cameroon, Ethiopia, Ghana, Malawi, Mozambique, Nigeria, Tanzania, Uganda, Zambia and Zimbabwe indicate that without control measures, the pest could cause maize losses of up to 17.7 million tonnes, translating into revenue loss of up to almost US$5 billion a year.

But researchers say that the negative impacts of the pest are far more than yield losses, with the potential to significantly impact food security and livelihoods.

The study, published in Food and Energy Security last month (15 March), shows that households affected by fall armyworm were 11 per cent more likely to experience food shortages, while their members had a 13 per cent higher likelihood of going to bed hungry or a whole day without eating. It also found that found that severe levels of infestation reduced per capita household income by 44 per cent.

“Our study suggests that the outbreak is threatening food security and negatively affecting farmers’ livelihoods, hence urgent actions are needed to address the menace posed by fall armyworm,” says Justice Tambo, the study’s lead author and a socio-economist at the Centre for Agriculture and Bioscience International (CABI, the parent organisation of SciDev.Net).

According to the study, fall armyworm was first reported in Zimbabwe during the 2016 and 2017 cropping season, and has continued to spread in subsequent seasons.

Researchers used survey data from 350 smallholder maize-growing households in six of Zimbabwe’s main maize production provinces. Data was collected in September 2018 by CABI in collaboration with Zimbabwe Plant Quarantine and Plant Protection Research Services Institute.

“We decided to conduct this study to provide evidence [of] how the fall armyworm outbreak is affecting farmers’ livelihoods beyond reductions in maize yields,” Tambo says. “While fall armyworm cannot be eradicated, taking actions to at least prevent severe level of infestation can significantly reduce welfare losses in terms of income and food security.”

Boddupalli Prasanna, director of the global maize programme at the International Maize and Wheat Improvement Center, tells SciDev.Net that fall armyworm is a serious concern to resource-constrained smallholders who have multiple challenges to tackle.

“We certainly need to provide effective, scalable and affordable technologies to the farming communities to combat the pest in a sustainable manner. Farmers cannot afford to rely on expensive chemical pesticides to and control fall armyworm,” says Prasanna, who was not involved in the study.

Prasanna adds that there is no single specific technology that can provide sustainable control of a pest like fall armyworm.

“We need to adopt an integrated pest management (IPM) strategy, including effective integration of improved varieties with resistance to the pest, environmentally safer pesticides, biological control … and good agronomic practices,” he says. “We need to [increase] extensive awareness among extension agents and farming communities about IPM strategy for the control of fall armyworm.”

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According to Tambo, the findings have implications for policymakers, researchers and farmers. Farmers need to adopt low-risk pesticides products such as biopesticides, and combine them with safe non-chemical options including rotation and intercropping with other crops such as beans and cassava, he explains.

This piece was produced by SciDev.Net’s Sub-Saharan Africa English desk.


Justice A. Tambo and others Impact of fall armyworm invasion on household income and food security in Zimbabwe (Food and Energy Security, 15 March 2020)

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