Archive for the ‘Plant Pathogens’ Category

Madagascan bananas may soon be extinct

Photo: ‘Green Bananas’ by Holger Link on Unsplash

Bananas we buy across the world could be threatened with extinction in the future. This claim is due to the decline of wild banana species which could be the last resort for saving the world’s most popular banana, the Cavendish.

According to a BBC article, a wild banana (Ensete perrieri) has been classified as Critically Endangered by the IUCN. These are only found in Madagascar, where there are just five mature trees left in the wild.

In light of this, scientists are advocating its conservation as it may hold the secret to saving the Cavendish banana. This cultivar could go into extinction in years to come due to its vulnerability to Fusarium (a disease also known as Panama disease that attacks the root of banana trees).

It is thought that the Madagascan banana, E. perrieri, could have certain properties making it resilient to attack from certain pests and diseases, and from drought. The species grows large seeds, making it difficult for humans to eat, but it could be crossbred with another more edible variety or cultivar (such as Cavendish) to create a more resilient cultivated banana.

To find out whether this could be done, Richard Allen, senior conservation assessor at the Royal Botanic Gardens, Kew, stated in the BBC article that more research had to be carried out on the species, but first of all it has to be saved.

Therefore, the race is on to develop new banana varieties that are both tasty and resilient enough to survive attack from pests and diseases such as Panama disease.

Sunmbo Olorunfemi is a graduate of Sustainable Agriculture and Food Security and currently working as an intern with the Plantwise Knowledge Bank.

Coming soon from CABI Books: Handbook of Diseases of Banana, Abacá and Enset

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John Innes Centre

Devastating plant virus is revealed in atomic detail

One of the world’s most lethal families of plant viruses has been revealed in unprecedented detail in a new study that may provide clues to preventing the global spread of the pathogen.

The complex 3D structure of the geminivirus  is revealed in the joint study carried out by researchers at the University of Leeds and the John Innes Centre.

Geminiviruses are responsible for diseases affecting crops such as cassava and maize in Africa, cotton in the Indian subcontinent and tomatoes across Europe.

Revealed in unprecedented detail – geminiviruses are a global plant pathogen

Being able to see its structrure in great detail is vital as it could help virologists and molecular biologists better understand the virus lifecyle, and develop new ways to stop the spread of these viruses and the diseases they cause.

These viruses are named for their curious shape. Viruses usually have a protective shell of protein, or capsid, that acts to protect their genetic material in the environment. In most viruses, this capsid is roughly spherical, but the geminivirus has a ‘twinned’ capsid formed by two roughly spherical shapes fused together.

The molecular details of how this twinned capsid is achieved – and how it assembles in cells or expands to release the genome and start a new infection – has remained a mystery, despite the risk posed by the virus to agricultural economies worldwide.

Researchers at the Leeds University’s Astbury Centre for Structural Molecular Biology used cryo electron microscopy techniques to study geminivirus structure at undprecedented resolution, and in the process have begun to untangle its assembly mechanisms.

Published in Nature Communications, the study reveals how the capsid of the geminivirus is built and how its single-stranded DNA genome is packaged.

“In many other types of virus, the spherical capsids are built from a single protein that adopts three different shapes, which then fit together to form a closed container,” explains Professor Neil Ranson, who led the research team at the Astbury Centre.

“But geminivirses are not spherical, so must be using a different set of rules. Using cryo-EM, we’ve been able to show that they do use three different shapes of the same protein, but with a completely different rulebook for assembly”

One of the difficulties in studying geminviruses is growing them in sufficient quantities for structural studies.

The team studied a type of geminvirus transmitted by whitefly called ageratum yellow vein virus, which was produced in tobacco plants under carefully controlled conditions by researchers at the John Innes Centre.

The team at the John Innes Centre led by Dr Keith Saunders and Professor George Lomonossoff also developed a method for assembling geminivirus particles within plants in the absence of infection.

This highlighted the role played by the single-stranded DNA in particle formation.

“Having worked for many years to understand the diseases geminiviruses cause, it was very satisfying to apply modern genetic methods to generate these geminate structures,” said Dr Saunders.

“The big surprise arising from this study was that fact that the virus coat protein can adopt different conformations that are dependent upon its location in the structure – it is different at the equator than at its apexes. That helps to explain how the particles form during virus infection. With this new knowledge, it now means that future studies can be directed to seek ways to disrupt geminate structure maturation by making antivirals that target those areas.”

Dr Suanders said the John Innes Centre team had been studying ageratum yellow vein virus for 20 years and their knowledge of the diease made it a good candidate for closer inspection.

It is part of white-fly transmitted group responsible for  tomato yellow leaf curl disease, a disease affecting tomato production in many countries around the Mediterranean Sea and cotton leaf curl disease affecting cotton plants in India and Pakistan.

Both diseases give rise to tremendous crop losses and so are economically very damaging.”

The work was funded by the Biotechnology and Biological Sciences Research Council.

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fresh plaza logo

WSU researchers combat parasitic worm

Plants that fight back

So small it can’t be seen with the naked eye, a parasitic worm called the root-knot nematode causes mammoth problems for Northwest farmers. But potatoes, grapes and other crops could gain a new, nature-based way to fight back, thanks to Cynthia Gleason and Jennifer Watts, scientists at WSU.

Notorious thieves
Nematodes cause billions of dollars in crop losses nationwide every year. In Washington, they cause significant losses to crops such grapes, onions, garlic and the state’s $734 million potato industry.

“Root-knot nematodes are a huge problem for farmers,” said Gleason, plant pathologist with WSU’s College of Agricultural, Human and Natural Resource Sciences (CAHNRS). The soilborne parasites move into the roots of crops, “then just sit there and feed on the plant. They’re stealing nutrients and water.”

Nematodes don’t kill the plants, but they leave them stunted, wilted from lack of water, and more susceptible to other pathogens, ultimately reducing farmers’ yields.

Chemical-free weapon pursued
“Plants don’t have many natural resistances to root-knot nematodes, so we need a way to combat them,” Gleason said. Traditionally, farmers have used anti-nematode pesticides -nematicides- to eliminate the tiny worms.

“But there aren’t many chemical options left, and they’re very expensive,” she said. “I’m looking for new, chemical-free controls that help growers move on.”

Acid stops nematodes
To help, Gleason is using a new $47,400 Emerging Research Issues grant from the CAHNRS Office of Research to seek genetic defenses that help crops like potatoes and tomatoes fight back against the persistent pest. “I’m developing plants that are basically toxic to nematodes,” she said.

Jennifer Watts, researcher in the School of Molecular Biosciences, discovered that a dietary fatty acid stops parasites from multiplying. Partnering with Jennifer Watts, researcher in the College of Veterinary Medicine’s School of Molecular Biosciences, Gleason is adding genes that tell plants to secrete a specific fatty acid that stops the nematode reproductive cycle.

Watts and her team of student researchers discovered that a certain fatty acid, referred to as DGLA (20:3n-6), stops egg production in a cousin species of the root-knot nematode.

“These fatty acids aren’t normally produced in plant tissue,” says Watts. “My team and I are working with Cynthia to introduce genes into plants so they can make them. If it works, it could be a new, chemical-free method to control nematodes.”

While the fatty acid is not known to be toxic to people or animals at low levels, the researchers plan to only express it in cover crops and plant tissues that aren’t normally eaten.

Future pest fighters
Farmers could one day plant a seed, Gleason said, that grows into a cover or cash crop with its own natural pest control. As nematodes feed on the plants, their populations will fall — leading to healthier plants, bigger crops and an improved food supply.

“Usually, the study of nematodes and the challenges they bring is about new chemicals and pesticide controls,” said Gleason. “This is a new and different approach, one that’s chemical free.

“By working across colleges, mine and Jennifer’s teams are discovering and accomplishing much more than we could individually,” she added. “We can use that information to fight parasites, help Washington farmers, and grow more food. It’s a collaboration that benefits everyone.”

For more information:

Washington State University
Cynthia Gleason
Department of Plant Pathology
Tel.: +1 509-335-3742
Jennifer Watts
School of Molecular Biosciences
Tel.: +1 509-335-8554


Publication date: 6/21/2018


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Biosecurity reduces invasions of plant pathogens over a national border

May 31, 2018, University of Kansas
Ben Sikes of the University of Kansas discovered biosecurity measures cut spread of fungal pathogens over a national border. Here, Sikes examines Picipes badius, the black-footed polypore that causes white rot on trees. Credit: University of Kansas

A major new study appearing in PLOS Biology on May 31 examines more than a century of fungal pathogens, finding well-aimed biosecurity measures cut the spread of unwanted fungi into a nation, even in the face of increased globalized trade.

“Although trade is closely tied to the number of new invasions we have from , if we have targeted we can start to break down this link,” said lead author Benjamin Sikes, assistant professor of ecology & evolutionary biology at the University of Kansas and assistant scientist at the Kansas Biological Survey. “Because globalization and imports to and from other countries are just going to keep increasing, most data have shown with that come lots of new invasive species around the world. The question is, can you slow that? This work shows that link can be slowed with implementation of targeted biosecurity measures.”

Sikes, a microbial ecologist whose research focuses on soil fungi, analyzed a New Zealand database of plant pathogens and diseases going back to the 19th century as part of a collaborative project among KU, New Zealand’s Bio-Protection Research Centre and Manaaki Whenua-Landcare Research.

“There’s a huge number of ways people can bring plant pathogens into New Zealand or a country like the United States,” he said. “Many are brought in with agricultural imports. People bring in seeds or plant materials—even soils or lumber can have pathogens that were on those plants to begin with or are in those materials once they bring them through. If they’re not screened properly, these pathogens can establish and start to spread to local crops and plant species.”

The term “biosecurity” is a “really big umbrella” that has evolved over the years reviewed in the new study, according to Sikes. The research focused primarily on the consequences of border surveillance, phytosanitary inspections and quarantine for incoming plant diseases.

“At ports of entry there are border-inspection people, like our USDA,” he said. “If they’re getting in a shipment of bananas to the U.S. from Costa Rica, there would be a person inspecting it, looking for visible symptoms and spot testing for the most prolific diseases from source countries. They might also have quarantine periods, where imports need to be held for a set amount of time to ensure they are pest-free.”

The consequences of invading pathogens are “massive” around the world and can include economic as well as ecological effects, according to the KU researcher.

“For fungal pathogens that we were looking at, they cause heavy losses economically for crops every year, into the billions of dollars and perhaps as much as 20 percent of yields,” said Sikes. “Even for an agricultural state like Kansas, my guess is that it would be hundreds of millions of dollars in most years. The pathogens are not all imported; some are localized. Imported pathogens, though, can also be a problem for native ecology. Chestnut blight is a great example that decimated chestnut trees in the eastern U.S.—it was a fungal blight from Asia. It changed how people see the forest. People in the eastern U.S. who lived the early 1900s wouldn’t recognize the forest today, because one in every three trees was a chestnut tree.”

Sikes and colleagues used data from New Zealand, which spends 0.3 percent of its gross domestic product on biosecurity measures, to assess whether the country’s program has been effective in slowing the introduction and spread of fungal . Sikes said New Zealand was a unique case because many of their crop plants are not native to the country.

Research shows biosecurity reduces invasions of plant pathogens over a national border
University of Kansas scientist Ben Sikes found biosecurity measures were effective in keeping unwanted plant pathogens out of New Zealand. Credit: University of Kansas

“Because all of these crops in New Zealand aren’t originally from there, almost all the bad diseases are not from there as well, so can be imported as well,” he said. “The danger from imported pathogens is about the highest it could be in New Zealand. Whereas in a large continent like here in the U.S. or in Asia, dangers from existing pathogens may be a lot higher.”

Drawing from a database of all known plant-pathogen associations in New Zealand going back to 1880, the researchers determined the rate at which new fungal pathogens arrived and became established on 131 economically important plant species over the last 133 years.

“We had this ability in New Zealand because of the records that were there and because it’s a relatively young country,” said Sikes. “They’re a world leader in biosecurity, and it’s important for them to know if those measures are working and worth spending money on.”

The researchers found as trade between nations all over the world, including New Zealand, became more globalized, the number of pathogens introduced into the country rose in direct proportion. However, pathogens started to level off in particular industries like crops after New Zealand implemented specific biosecurity measures to target pathways for those pathogens.

“We see an exponential increase over time in the number of bad things that get introduced,” Sikes said. “But around the 1980s, if we look at all the at once, that rate starts to slow. Fewer new things are coming in. When you drill into why that is, it’s caused by two counteracting trends between industries. For crops and pasture species familiar to us here in Kansas—like corn and wheat—they started slowing down in the number of pathogens they were getting back in the ’60s and ’70s. This timing is about a decade after they instituted important biosecurity measures like looking at seeds to make sure they were pathogen- and pest-free and creating a USDA equivalent to go out and survey crops. This timing coincides with the slowdown in new pathogens coming in.”

By contrast, Sikes said other primary industries in New Zealand that lacked targeted biosecurity saw increasing rates of new pathogens.

“Forestry and fruit trees continue to have many new pathogens each year, and that’s still accelerating—their patterns go right along with the acceleration in trade,” said the KU researcher.

As part of the work, Sikes and his colleagues modeled both the arrival of new pathogens and the nation’s rate of detection. From these, the team was able to predict how many are present but remain undetected in a country like New Zealand.

“For the first time, we can quantify how fast these things are coming into a country, and that’s actually super hard to do,” Sikes said. “Given the amount of investment the U.S. or, say, Germany is making in biosecurity, we now can say, ‘You’ve found this number of things, and you looked this many times—and based on what we know, this is about how many things you would find if you were able to find them all.”

Explore further: Battling bubbles: How plants protect themselves from killer fungus

More information: PLOS Biology (2018). DOI: 10.1371/journal.pbio.2006025

Read more at: https://phys.org/news/2018-05-biosecurity-invasions-pathogens-national-border.html#jCp

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An Increasing Threat to Global Citrus Production

Citrus production accounts for over 110 million tonnes of fruit per year globally (© CC0)

Yellow dragon disease, also known as citrus greening disease is one of the greatest bacterial threats to citrus trees on a global scale, affecting crop production across Africa, Asia and North America.

The disease is caused by the bacteria Candidatus Liberibacter asiaticus, causing severe signs of stress in infected trees. General symptoms include yellowing of leaves, defoliation and eventually the loss of entire canopies following the spread of infection. The main damage to the citrus industry is the effect of the disease on fruit, with infection causing small, poorly coloured and irregularly shaped fruit which often have a sour/bitter taste and thus rendering them not commercially viable.

Currently, there is no treatment to combat this bacterial disease apart from removing and destroying entire trees if infected. With the severity of its symptoms coupled with a lack of effective treatment, yellow dragon disease is spreading across multiple continents causing havoc to the citrus industry and threatening the livelihoods of citrus farmers. In the USA alone, the disease has caused losses of over one billion dollars to the agriculture sector.

The spread of the bacteria is worsened by the psylla fly (African and Asian), which carry the bacteria on their abdomens. Targeting the vector as a method of reducing the further spread of this disease has been the primary aim within multiple countries. The most common tool for removing the insect vector from specific sites is an insecticide called thiamethoxam. The use of this chemical was authorised in Europe in 2014 soon after the species was first identified in Europe.

Thiamethoxam had been a successful treatment for the disease vector, but due to the implications of the over-use of the chemical on the environment and human health, it has now been banned across the EU. This has opened up the market for thiamethoxam production outside of the EU, with China buying the manufacturer of the insecticide last month for $40 billion.

The increasing threat from this disease on global citrus production, the lack of disease treatments, the recent alterations to pesticide regulations and awareness for the use of such chemicals has identified gaps in research needed for creating suitable strategies for combating this bacterial disease.


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From PestNet

Previously Unknown Rice Blast Resistance Isolated

By Sharon Durham
May 23, 2018

A never-before-described gene that gives rice resistance to a disease that has been costing about $66 billion a year in global damage has been isolated by a team of scientists led by Agricultural Research Service (ARS) plant pathologist Yulin Jia.

Rice blast, caused by the fungus Magnaporthe oryzae, results in annual yield losses large enough to have fed 60 billion people each year, according to the team’s paper just published in the journal Nature Communications.

In the United States’ mid-south rice-growing region, the cost of mitigating rice blast infection with fungicide applications can reach almost $20 per acre; plus, the fungus may still cause significant yield loss depending on the susceptibility of each rice variety and the degree of infection at the time of fungicide application, according to the U.S. Department of Agriculture’s (USDA) Economic Research Service.

Amazingly, Ptr, the disease resistance gene Jia and his team found, has a structure that has not been seen in plants before. It has been previously deployed unknowingly in blast-resistant rice cultivars because it has been tightly linked to another disease resistance gene, Pi-ta, which has a genetic structure that is well-described in scientific literature.

Ptr has essentially been living in the shadow of Pi-ta.. “Our research was able to separate the two genes and demonstrate that Ptr is independently responsible for its own broad-spectrum blast resistance without Pi-ta,” says Jia. “This will provide a new strategy for developing blast-resistant rice cultivars.” The full genomic sequence of the Ptr gene was put into GenBank for use by public researchers worldwide.

Jia, along with his colleagues Haijun Zhao, Melissa H. Jia and Jeremy D. Edwards, is with the ARS Dale Bumpers National Rice Research Center in Stuttgart, Arkansas. Other contributors include Xueyan Wang and Yeshi Wamishe at the University of Arkansas Rice Research and Extension Center (Stuttgart, Arkansas); Bastian Minkenberg, Matthew Wheatly and Yinong Yang at the Pennsylvania State University (University Park, Pennsylvania); Jiangbo Fan and Guo-Liang Wang at the Ohio State University (Columbus, Ohio); Adam Famoso at Louisiana State University (Rayne, Louisiana); and Barbara Valent at Kansas State University (Manhattan, Kansas).

The Agricultural Research Service is the U.S. Department of Agriculture’s chief scientific in-house research agency. Daily, ARS focuses on solutions to agricultural problems affecting America. Each dollar invested in agricultural research results in $20 of economic impact.

This is one of the news reports that ARS Office of Communications distributes to subscribers on weekdays.
Send feedback and questions to the ARS News Service at NewsService@ars.usda.gov.



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From PestNet

penn state

UNIVERSITY PARK, Pa. — Use of the powerful gene-editing tool CRISPR-Cas9 could help to breed cacao trees that exhibit desirable traits such as enhanced resistance to diseases, according to Penn State plant scientists.

The cacao tree, which grows in tropical regions, produces the cocoa beans that are the raw material of chocolate. Reliable productivity from cacao plants is essential to the multibillion-dollar chocolate industry, the economies of producing countries and the livelihoods of millions of smallholder cacao farmers.

But each year, several plant diseases severely limit global production, with 20-30 percent of cocoa pods destroyed preharvest, noted lead author Andrew Fister, postdoctoral scholar in plant science, College of Agricultural Sciences, Penn State.

“In West Africa, severe outbreaks of fungal diseases can destroy all cacao fruit on a single farm,” said Fister. “Because diseases are a persistent problem for cacao, improving disease resistance has been a priority for researchers. But development of disease-resistant varieties has been slowed by the need for sources of genetic resistance and the long generation time of cacao trees.”

The researchers reported recently, in Frontiers in Plant Science, the study results, which were thought to be the first to demonstrate the feasibility of using cutting-edge CRISPR technology to improve Theobroma cacao.

CRISPR stands for clustered regularly interspaced short palindromic repeats. It is a way to modify an organism’s genome by precisely delivering a DNA-cutting enzyme, Cas9, to a targeted region of DNA. The resulting change can delete or replace specific DNA pieces, thereby promoting or disabling certain traits.

Previous work in cacao identified a gene, known as TcNPR3, that suppresses the plant’s disease response. The researchers hypothesized that using CRISPR-Cas9 to knock out this gene would result in enhanced disease resistance.

Andrew Fister with cacao trees

Andrew Fister, postdoctoral scholar in plant science, stands among cacao trees in the African country of Ivory Coast. Pods turning yellow and black are infected with black pod disease.

Image: Désiré Pokou


To test their hypothesis, they used Agrobacterium — a plant pathogen modified to remove its ability to cause disease — to introduce CRISPR-Cas9 components into detached cacao leaves. Subsequent analysis of treated tissue found deletions in 27 percent of TcNPR3 copies.

When infected with Phytopthera tropicalis, a naturally occurring pathogen of cacao and other plants, the treated leaves showed greater resistance to the disease. The results suggested that the mutation of only a fraction of the copies of the targeted gene may be sufficient to trigger downstream processes, resulting in systemic disease resistance in the plant.

The researchers also created CRISPR gene-edited cacao embryos, which they will grow into mature trees to test the effectiveness of this approach at a whole-plant level.

This research builds on more than 30 years of biotechnology research aimed at building a better cacao tree, according to senior author Mark Guiltinan, professor of plant molecular biology and leader of Penn State’s endowed cocoa research program.

“Our lab has developed several tools for the improvement of cacao, and CRISPR is just one more tool,” he said. “But compared to conventional breeding and other techniques, CRISPR speeds up the process and is much more precise. It’s amazingly efficient in targeting the DNA you want, and so far, we haven’t detected any off-target effects.”

In addition to providing a new tool to accelerate breeding, CRISPR-Cas9 technology can help deliver insights into basic biology by offering a method to efficiently assess gene function, the researchers said.

“With CRISPR, we can quickly ‘break’ a gene and see what happens to the plant,” Guiltinan explained. “We have a list of genes in the pipeline that we want to test.”

There may be thousands of genes involved in disease resistance, Fister added.

“We want to evaluate as many as we can,” he said.

The ultimate goals of Penn State cacao research are to help raise the standard of living for smallholder growers and stabilize a threatened cocoa supply by developing plants that can withstand diseases, climate change and other challenges, according to co-author Siela Maximova, senior scientist and professor of horticulture.

“Any production increases in the last 20 years have been mostly due to putting more land into production,” said Maximova, who co-directs the cacao research program. “But land, water, fertilizer and other inputs are limited. To enhance sustainability, we need plants that are more vigorous and disease resistant and that produce more and better-quality beans.

“This study provides a ‘proof of concept’ that CRISPR-Cas9 technology can be a valuable tool in the effort to achieve these goals,” she said.

Lena Landherr Sheaffer, research assistant in plant science, Penn State, also was a co-author on the paper.

This work was supported by the Penn State College of Agricultural Sciences, the Huck Institutes of the Life Sciences, the Penn State Endowed Program in the Molecular Biology of Cacao, the National Science Foundation and the U.S. Department of Agriculture’s National Institute of Food and Agriculture.

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From PestNet

Mars aims to triple cocoa yield through development of disease-resistant cocoa

Company, cocoa farmers to tap genetic knowledge to improve crops, reduce pesticide use.



Mars, Inc., plans to triple its global cocoa yield by developing more disease-resistant clones and continuing to improve farmer practices based on genetic knowledge of cocoa.

The global confectionery/pet food conglomerate has published research in the journal Frontiers of Plant Science that builds on work done by Mars, IBM and the USDA to help sequence the cocoa genome and make it publicly available.

The research also adds to work on higher-yielding pest- and disease-resistant clonal varieties Mars has helped develop with cocoa-growing countries. Applying this knowledge is expected to help farmers produce more cocoa on less land and with fewer pesticides, which can improve farmers’ livelihoods.

Specifically, Mars, Inc., in partnership with governmental and academic research organizations, used genetic markers to connect genetically-related cocoa trees and identify genes related to resistance of frosty pod, black pod and Ceratocystis wilt diseases.

In a keynote speech he delivered at the Fourth World Cocoa Conference in Berlin last month, Frank Mars, fourth-generation family member and member of the company’s board of directors, outlined Mars’ objectives in relation to this research.

“Over the next 10 years, Mars aims to develop even better disease-resistant clones,” Mars told conference attendees. “We’ll focus on both simple and advanced production methodologies and improved farmer practices with a goal to triple cocoa yields globally. This would free up land occupied with unproductive cocoa trees for farmers to grow other crops, including those for their own consumption. But to achieve this will require all of us in this room to think differently and work harder together; not only on better plant varieties and farming practices and models, but also on pest and disease control.”

Mars cited the need for continuing innovation, such as the company’s work through the Mars Center for Cocoa Science in Bahia, Brazil. Opened in 1982, the center has evolved to include private-public plant science partnerships with researchers and governments around the world. The center helps lead Mars’ efforts in areas such cocoa breeding, farming best practices, and pest and disease research and management.

Nonetheless, Mars said action the industry has taken so far hasn’t been sufficient to move the needle on sustainable cocoa.

“My hope is that 10 years from now, I can reflect on our efforts, both individually, and collaboratively,” Mars said. “I hope that I can look in the mirror and say I am proud of what we have achieved together. And know that cocoa does in fact have a sustainable future. And it’s one that uses science and technology to put farmers first.”

–Candy Industry


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Study could spawn better ways to combat crop-killing fungus

Rutgers-led genome research finds fungus that causes disease in rice became harmful 21 million years ago

Rutgers University

IMAGE: Ning Zhang, associate professor in the Department of Plant Biology and the Department of Biochemistry and Microbiology at Rutgers University-New Brunswick, holds a Petri dish with switchgrass seedlings inoculated with… view more 

Credit: Nick Romanenko/Rutgers University

About 21 million years ago, a fungus that causes a devastating disease in rice first became harmful to the food that nourishes roughly half the world’s population, according to an international study led by Rutgers University-New Brunswick scientists.

The findings may help lead to different ways to fight or prevent crop and plant diseases, such as new fungicides and more effective quarantines.

Rice blast, the staple’s most damaging fungal disease, destroys enough rice to feed 60 million people annually. Related fungal pathogens (disease-causing microorganisms) also infect turfgrasses, causing summer patch and gray leaf spot that damage lawns and golf courses in New Jersey and elsewhere every summer. And now a new fungal disease found in wheat in Brazil has spread to other South American countries.

Results from the study published online in Scientific Reports may lead to better plant protection and enhanced national quarantine policies, said Ning Zhang, study lead author and associate professor in the Department of Plant Biology and the Department of Biochemistry and Microbiology in the School of Environmental and Biological Sciences.

“The rice blast fungus has gotten a lot of attention in the past several decades but related species of fungi draw little attention, largely because they’re not as severe or not harmful,” Zhang said. “But they’re all genetically related and the relatives of severe pathogens have been little-studied. You have to know your relatives to have a holistic understanding of how the rice blast pathogen became strong and others did not.”

The study is the outcome of a 2016 international symposium at Rutgers-New Brunswick hosted by Zhang and Debashish Bhattacharya, study senior author and distinguished professor in the Department of Biochemistry and Microbiology. The National Science Foundation, Rutgers Center for Turfgrass Science, and School of Environmental and Biological Sciences funded the symposium by researchers from the U.S., France and South Korea.

The scientists studied Magnaporthales, an order of about 200 species of fungi, and some of the new members were discovered in the New Jersey Pine Barrens. About half of them are important plant pathogens like the rice blast fungus – ranked the top fungal pathogen out of hundreds of thousands. After the first sign of infection, a rice field may be destroyed within days, Zhang said.

To get a holistic understanding of how the rice blast fungus evolved, scientists genetically sequenced 21 related species that are less harmful or nonpathogenic. They found that proteins (called secretomes) that fungi secrete are especially abundant in important pathogens like the rice blast fungus.

Based on previous research, the proteins perhaps became more abundant over time, allowing the fungi to infect crops, Zhang said. The researchers identified a list of genes that are abundant in pathogens but less so in nonpathogens, so the abundant genes might promote pathogens that can infect crops. The results will allow scientists to look into the mechanism behind the infection process.

“With climate change, I think the rice blast problem can only get worse because this is a summer disease in warm climates where rice is grown,” Zhang said, adding that wheat, turfgrass and other important plants may also be affected.


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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Alberta farmer

Key source of clubroot resistance goes AWOL

‘Grandparent’ can defeat new mutated clubroot strains but somehow it doesn’t get passed down

The ‘grandparent’ of clubroot resistance in most Canadian canola varieties is resistant to new virulent strains of clubroot — but its offspring aren’t.

“It’s possible that, in the course of breeding, some of the resistant genes were lost,” said provincial research scientist Rudolph Fredua-Agyeman.

European clubroot differential (ECD) 04 is a key source of clubroot resistance for canola-breeding programs around the world, including in Canada, Fredua-Agyeman said at Alberta Canola’s Science-O-Rama last month.

Because of its resistance to all the clubroot strains found in Canada so far, ECD 04 has been bred into most clubroot-resistant canola varieties, including Mendel — a European winter canola cultivar that has also been used as a source of resistance for Canadian varieties.

“When clubroot was found in Alberta, the natural source of resistance was ECD 04 and Mendel, which were resistant to most of the strains of clubroot that we had at the time,” said Fredua-Agyeman.

But in 2013, clubroot strains started to shift to overcome the resistance, and new, more virulent strains of the disease began to appear in Alberta canola fields. As of 2017, these new strains have been confirmed in at least 104 fields in Alberta — a conservative estimate, as researchers only test fields that have been brought to their attention. Most notable of these strains is 5x, which can cause disease severity of up to 90 per cent.

“We’ve found that these strains are causing much more severe disease on canola than the other strains,” said Fredua-Agyeman, adding at least nine other strains have also been identified.

“The challenge posed to the canola industry by these new strains is real and very aggressive.”

The good news is that ECD 04 still shows complete resistance to these new strains, including 5x. Unfortunately, Mendel — and the commercial varieties that were spawned from it — are not.

“We went from ECD 04 — complete resistance — to Mendel, where we’re getting resistance to only 50 per cent of the new strains, and then to the commercial varieties, none of which are resistant to these new strains,” he said. “Not all the resistant genes were passed on from ECD 04 to Mendel, and from Mendel to the commercial varieties.

“The loss of this gene has contributed significantly to the breakdown of resistance.”

Integrated approach needed

Until new resistant varieties can be developed and new resistant sources found, canola growers will need to take a more “integrated” approach to clubroot management.

“Our resistance is very good, but it’s not a magic bullet,” said Stephen Strelkov, a plant pathologist and professor at the University of Alberta.

“Resistance is vulnerable, and we need proper resistance stewardship.”

When clubroot was first discovered in Alberta in 2003, producers were interested in finding a variety of tools to manage the disease. But when the first clubroot-resistant canola variety came online in 2009, farmers began to rely heavily on resistance instead of integrated disease management (which includes equipment sanitation and extended rotations).

“Clubroot resistance was such a strong tool that the extension messaging probably fell on deaf ears a little bit, and farmers grew resistant varieties in very short rotations,” said Strelkov, who also spoke at Science-O-Rama.

“People thought, ‘We have resistant varieties that do so well now — why should we worry about it?’”

But that reliance on resistant varieties has caused resistance to break down in record time. It only takes about two crops of a resistant variety for the pathogen to start to shift to overcome the resistance, and if those two crops are seeded back to back, it takes less than three years for the resistance to break down — not nearly enough time to find new sources of resistance or breed new resistant varieties.

“Resistance is the most widely used management strategy — nothing really compares to genetic resistance,” said Strelkov. “But these new strains highlight that our crop is still at risk from clubroot.”

Researchers are exploring other tools for clubroot management — including soil fumigants, liming, and bait crops — but until producers have more tools to add to their tool box, they need to take care of the ones they already have. That means using resistant varieties, rotating sources of resistance, sanitizing equipment, and (yes) extending rotations to four years.

If they don’t, they risk finding themselves in the same boat if and when new sources of resistance are found.

“It’s not a stable situation. The pathogen is changing and evolving,” said Strelkov.

“We’ll need a more integrated way of thinking to sustainably manage clubroot. Resistance will need to be used in conjunction with other tools.”

About the author


Jennifer Blair is a Red Deer-based reporter with a post-secondary education in professional writing and nearly 10 years of experience in corporate communications, policy development, and journalism. She’s spent half of her career telling stories about an industry she loves for an audience she admires–the farmers who work every day to build a better agriculture industry in Alberta.


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