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NEWS RELEASE 19-OCT-2021

Bacteria, fungi interact far more often than previously thought

EurekAlert

DOE/LOS ALAMOS NATIONAL LABORATORYPrintEmail App

Unique bioinformatics approaches help understand extent of fungal bacteriome
IMAGE: A DIVERSE CULTURE COLLECTION OF FUNGAL ISOLATES OBTAINED FROM AROUND THE WORLD HAS BEEN SCREENED BY RESEARCHERS AT LOS ALAMOS NATIONAL LABORATORY FOR POTENTIAL BACTERIAL ASSOCIATES. view more CREDIT: LOS ALAMOS NATIONAL LABORATORY

Los Alamos, N.M., Oct. 19, 2021 – In a novel, broad assessment of bacterial-fungal interactions, researchers using unique bioinformatics found that fungi host a remarkable diversity of bacteria, making bacterial-fungal interactions far more common and diverse than previously known.

“Until now, examples of bacterial-fungal interactions were pretty limited in number and diversity,” said Aaron Robinson, a biologist at Los Alamos National Laboratory and lead author of a new paper describing the research in Nature’s Communications Biology journal. “It had been assumed that bacterial-fungal associations might not be that common. But we found a lot of diverse bacteria that appear to associate with fungi, and we detected those associations at a frequent rate.”

The research contributes to an emerging understanding of the fungal bacteriome, the existence of bacteria both within and in close association with a fungal host, opening up possibilities for studying the interactions more intimately and connecting that research to issues such as ecosystem functioning and climate change impacts.

“This is a starting point to investigate mechanisms of bacterial-fungal interactions at a more intimate level,” said Robinson. “That research will be valuable for understanding what allows bacteria to associate with fungi, and how to best leverage that insight to accomplish goals for the Laboratory, for the Department of Energy, and for society in general. Understanding how these organisms interact with each other and contribute to larger systems is highly valuable in everything from modeling things like climate change to societally beneficial activities such as agricultural or industrial utilization of microbes.”

Researchers screened a total of 294 diverse fungal isolates from four culture collections from Europe, North America, and South America for potential bacterial associates. Collaborations with the Center for Integrated Nanotechnologies at Los Alamos allowed researchers to visually examine several of these associations using fluorescence in situ hybridization techniques.

These fluorescence microscopy examinations complemented the screening and confirmed the widespread and variable presence of bacterial associates among diverse fungal isolates and even within the hyphae (fungal tissue) of a single fungal host.

In addition to screening the culture collections, the research team also screened 408 fungal genome sequencing projects from the MycoCosm portal, a repository of fungal genome projects developed and maintained by the Department of Energy Joint Genome Institute.

Bacterial signatures were detected in 79 percent of the examined fungal genome projects. In multiple cases, the authors recovered complete or nearly complete genomes of these bacterial associates. Recovery of these fungal-associating bacterial genomes allowed for comparisons between fungal-associating and free-living bacteria.

Of the 702 total fungal isolates examined by the research team, bacterial associates were found in 88 percent—an unexpected detection rate relative to previous, more limited studies. The results shed light on the complexity and diversity of the fungal bacteriome across the fungal tree of life.

The study’s overview and description of diverse fungal-bacterial associations provides a path forward for understanding the associations in more depth. Continued analysis of the interactions will aid in a more complete understanding of environmental microbiome processes, particularly fungal and bacterial contributions to nutrient cycling, plant health and climate modeling.

Within the context of changing climate conditions, understanding how bacterial-fungal interactions impact plants, animals, and general ecosystem functioning in diverse environments and under diverse conditions, such as drought and warming, will also help predict and potentially manipulate the impacts of these interactions.

About Los Alamos National Laboratory
Los Alamos National Laboratory, a multidisciplinary research institution engaged in strategic science on behalf of national security, is managed by Triad, a public service oriented, national security science organization equally owned by its three founding members: Battelle Memorial Institute (Battelle), the Texas A&M University System (TAMUS), and the Regents of the University of California (UC) for the Department of Energy’s National Nuclear Security Administration.

Los Alamos enhances national security by ensuring the safety and reliability of the U.S. nuclear stockpile, developing technologies to reduce threats from weapons of mass destruction, and solving problems related to energy, environment, infrastructure, health, and global security concerns.
LA-UR-21-30373


JOURNAL

Communications Biology

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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OCTOBER 6, 2021

Bacteria enters through natural openings at edges of corn leaves to cause Goss’s wilt

by American Phytopathological Society

Bacteria enters through natural openings at edges of corn leaves to cause Goss’s wilt
Bacterial colonization and movement. Credit: Alexander Mullens and Tiffany M. Jamann

Goss’s bacterial wilt and leaf blight is one of the most damaging diseases affecting corn. The most effective way to control this disease is to plant corn varieties that are resistant to the disease. In other words, growers avoid the disease by growing certain varieties of corn. In part, this is the easiest method because scientists don’t yet know much about Goss’s wilt.

Alexander Mullens and Tiffany Jamann, two plant pathologists at the University of Illinois, set out to better understand the mechanics of this disease by following the causal pathogen. They genetically modified the pathogen so it would display green fluorescence, which made it easier to track the bacteria inside the plant. They were able to see how the bacteria entered the plant and where the bacteria congregated inside the leaf.

“While the bacteria had previously been known to enter the plants through wounds caused by wind or hail damage, we discovered that in the absence of damage it enters the leaf through natural openings at the edge of the leaf,” said Mullens. “Once in the plant, the bacteria are able to grow through the veins and exit the plant through natural pores in the leaf’s surface.” They also show that high concentrations of bacteria cause the freckles associated with Goss’s wilt.

They found that in resistant corn varieties, the bacteria aren’t able to grow as far from the entry site. “We can now use these tools to understand more about how different plant varieties restrict bacterial entry and growth,” said Jamann. “These tools will be useful in understanding how corn defends itself against this and other pathogens.”

Some of the most important pathogens in agriculture are vascular bacterial pathogens, like the causal pathogen of Goss’s wilt, so this is a good model to understand resistance to vascular plant diseases of all kinds.


Explore further Corn one step closer to bacterial leaf streak resistance


More information: Alexander Mullens et al, Colonization and Movement of Green Fluorescent Protein-Labeled Clavibacter nebraskensis in Maize, Plant Disease (2020). DOI: 10.1094/PDIS-08-20-1823-RE Provided by American Phytopathological Society

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Ava-Asaja demands drastic measures to prevent the advance of the insect

Trioza erytreae, the vector that transmits HLB, arrives in the Portuguese Algarve

The Valencian Association of Farmers (Ava-Asaja) demands that the Spanish Government and the European Union (EU) assess and implement drastic measures to prevent the advance of the Trioza erytreae insect, the vector of the Huanglongbing (HLB) disease -the most devastating disease for citrus in the world that is known as citrus greening or yellow dragon disease- after learning that this insect had already reached Algarve, in southern Portugal. This insect’s advance from the north and center of the Portuguese country to the citrus fruits of the Algarve increases the possibility that this transmitting vector and the HLB bacteria will reach the citrus farms of Huelva and the rest of Spain and Europe.


Female Trioza erytreae.

Ava-Asaja urged authorities to take all the scientific actions possible to stop the spread of this plague or, at least, to slow down the speed of its geographical progression. The agrarian organization highlighted an ambitious plan endowed with community funds aimed at promoting lines of research, breeding, and carrying out a massive release of highly effective parasitoids against HLB transmitting vectors.

In this regard, the Tamarixia drii predator has managed to reduce the presence of Trioza erytreae by more than 90% in the citrus farms investigated in the Canary Islands. Meanwhile, there are international studies on parasitoids that could also combat the other HLB vector, Diaphorina citri, which is even better adapted to the Mediterranean climate.

In the event that the bacteria arrive, the association urges the exploration of stronger complementary measures such as cutting down infested trees because, just as with Xylella fastidiosa, there still is no cure for this disease that has caused unaffordable losses for citrus growers and the uprooting of trees in the countries it has affected. Finally, Ava-Asaja asked the Spanish Government to work hand in hand with the Portuguese executive so that they are informed of the evolution of the situation and can act in the most coordinated and forceful way possible.

“The terrible news we’ve received about the HLB vector is further proof of the little seriousness and rigor with which the European Commission toys with agricultural pests and diseases. In recent years, they have been unable to prevent the entry and expansion of many pests and diseases coming via imports from third countries, such as Xylella fastidiosa, South African cotonet, or the almond wasp. Now we are facing the worst threat to the world’s citrus industry. In the absence of curative solutions, the best medicine for HLB is prevention. However, that may not be enough so we might have to take stronger measures,” stated the president of Ava-Asaja, Cristobal Aguado.

For more information:

Ava-Asaja
Tel.: +34 963 804 606
info@avaasaja.org
www.avaasaja.org

Publication date: Mon 4 Oct 2021

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This tiny insect spreads a disease for which there’s no cure — and it’s coming for our citrus

Landline / 

by Kerry StaightPosted Fri 10 Sep 2021 at 9:21pmFriday 10 Sep 2021 at 9:21pm

Photo of citrus psyllid
The Asian citrus psyllid, at just 3-4mm long, poses a massive problem for healthy citrus orchards across the globe.((creative commons))

Help keep family & friends informed by sharing this articleabc.net.au/news/hlb-citrus-greening-biosecurity-australia-psyllid-finger-limes/100452594COPY LINKSHARE

Australia is ramping up biosecurity for an incurable disease that has crippled citrus-producing regions around the world and is posing a growing threat to the local industry.

Key points:

  • Huanglongbing (HLB) outbreaks are appearing in Timor-Leste, Indonesia, and Papua New Guinea.
  • HLB is a bacterial disease that originated in China and is largely spread by insects called citrus psyllids.
  • The citrus industry is ramping up its trapping program for the bacteria spreading bugs.

Huanglongbing (HLB), commonly called citrus greening, locks the arteries that transport nutrients in trees.

“I’ve been working on citrus diseases for 21 years now, and this is the worst,” said citrus pathologist Dr Nerida Donovan, who is part of a team trying to keep the disease out of Australia while also preparing for its arrival.

“It is marching across the globe, and it’s getting closer to our shores in the countries to our north.”

“So it’s in Timor-Leste. It’s in Indonesia. It’s in the corner of PNG.”

Photo of Dr Nerida Donavan inspecting a citrus tree
Citrus pathologist Dr Nerida Donovan is part of a team trying to keep the disease out of Australia.(Landline: Kerry Staight)

Florida in the United States has been one of the worst-hit regions.

Citrus producer Kyle Story said almost all the orchards were infected.

“We had roughly 12,000 growers when greening first came into the state of Florida in 2005,” said Mr Story.

“The most recent counts that we can go by is about 2,500 growers.”

What is Huanglongbing (HLB)?

HLB is a bacterial disease that originated in China and is largely spread by insects called citrus psyllids.

It shows itself in several ways, from uneven, yellow, blotchy marks and raised veins on leaves to misshapen and sour fruit.

Photo of discoloured leaf
Citrus greening locks the arteries of trees, blocking nutrients.(Landline: Kerry Staight)

“Pre-greening, you could easily see a grove that was between 50 and 100 years old,” said Kyle Story.

 “Today, most people plant an orange grove with a lifespan of 20 to 30 years.”

While Kyle Story and his team have learned to adapt management of their infected trees to get the best out of them and stay in business, local growers say Australia must do everything to keep the disease out.

“It was scary what I saw in Florida,” said Riverland grower Ryan Arnold.

“It just looked like an orchard in Australia that we’d be pushing it out and starting again, and they were trying to live with that and get some production out of it.”

“I didn’t want my beautiful green trees looking like that.”

Photo of citrus trees being removed
The lifespan of Florida’s citrus trees has fallen from 50-100 years to as low as 20 years. (Landline)

Operation ‘citrus watch’

To protect Australian growers’ trees, the citrus industry is ramping up surveillance for the bacteria-spreading bugs, in particular the Asian citrus psyllid.

As part of a new biosecurity program dubbed “citrus watch” about 1,000 sticky traps are distributed each year.

The traps are sent to vulnerable urban areas as well as commercial citrus properties because it’s not just fruit trees the psyllids are attracted to.

Photo of Ryan Arnold checking psyllid trap
Citrus psyllid traps are being sent to vulnerable urban areas as well as commercial citrus properties in Australia. Pictured: Riverland grower, Ryan Arnold.(Landline: Kerry Staight)

They’re fans of murraya, a common hedge plant also known as orange jasmine.

“In most countries where they’ve found the disease and the psyllid, it’s been found in the urban areas first,” said Nerida Donovan

“So that’s why our biosecurity system is so important and educating people not to bring in plant material from other countries.”

If the disease does spread to Australia, there’s another safeguard.

At Dareton, in the far west of NSW, there’s a bank of every commercial citrus variety grown in the country.

Photo of workers in a greenhouse
Mother trees are tested for disease annually and are used to produce budwood for commercial nurseries.(Landline)

These mother trees are tested for disease annually and are used to produce budwood for commercial nurseries.

They’re also protected from citrus psyllids by a giant screen.

“The facility has been built to grow around a million buds per year,” said manager Tim Herrmann.

“We’ve got plans in place to double that to about two million buds per year, which we predict will be enough to get the industry through an incursion.”

One of the biggest challenges with HLB is there’s no cure.

Growers in the US have been using antibiotics and heat treatments to try and slow the reproductive cycle of the psyllid.

“We do actively, and have for the last 15 plus years, tried to control the Asian citrus psyllid, but we have not had a tremendous amount of success,” said Mr Story.

Could finger limes be the answer?

In a surprise twist, with a decidedly Australian flavour, a promising new treatment is being developed.

Researchers at the University of California in Riverside have discovered a peptide in native finger limes that attacks the bacteria and protects healthy plants.

Red coloured finger limes inside the bush, some have scratches on their skin.
Researchers have discovered a peptide in native finger limes that attacks the bacteria and protects healthy plants.(ABC Rural: Jennifer Nichols)

“Our data show that our antimicrobial peptide is much more effective than those antibiotics,” said lead researcher Hailing Jin.

“We can use a much less concentration and that can kill bacteria much faster.”

Hailing Jin says the peptide also isn’t heat sensitive, like antibiotics.

Photo of Florida University conducting field trials
Florida University has been conducting field trials of finger lime peptides to combat the disease.(Landline)

After successful greenhouse trials, the new treatment is now being tested in the field by the University of Florida.

“There is a very long history of things looking pretty good in a greenhouse and failing in the field,” said Dr Megan Dewdney, who is running the trials over a couple of years.

“I have high hopes that this one will not, but one never knows.”

See more about this story on ABC TV’s Landline at 12:30pm on Sunday, or on iview.Posted 10 Sep 2021

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From PestNet

Palm tree disease in Florida transmitted by traveling bug from Jamaica

Phys.Org

by American Phytopathological Society

What began as a curious survey of an insect in Florida revealed a much larger network of movement across the Caribbean basin. Haplaxius crudus, commonly known as the American palm cixiid, transmits phytoplasmas (bacteria that cause plant diseases) in palm. The American palm cixiid is known to transmit lethal yellowing disease and lethal bronzing disease, both of which are lethal to a variety of palm species, especially coconut and date palms.

While many scientists have assumed these pathogens migrated to Florida in infected plants, Brian Bahder at the University of Florida wondered if the real culprits were the insects themselves. To test this suspicion, Bahder and his colleagues began by categorizing the insect’s DNA in Florida, where they found four distinct groups.

Next they looked beyond the United States and tested populations in Costa Rica, Colombia, and Jamaica, three places that were distinct and relatively isolated. They found different insect DNA in Costa Rica and Colombia. In Jamaica, however, they found an exact match to one of the groups in Florida.

Read on: https://phys.org/news/2021-09-palm-tree-disease-florida-transmitted.html Haplaxius_crudus

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Phys.Org

Infection method behind ‘crop killer’ bacteria revealed

by Nanyang Technological University

Infection method behind ‘crop killer’ bacteria revealed
Credit: Nanyang Technological University

An interdisciplinary team of scientists from NTU Singapore has identified, for the first time, a key mechanism by which a dangerous plant disease can infect crops.

The Xanthomonas bacteria, known as the “crop killer,” is a globally prevalent bacterium capable of infecting 400 different plant species. It causes bacterial spots and blights in the leaves and fruits of the plants it infects. In some cases, once the disease takes root, a farmer’s only recourse is to cut down and burn the entire crop of plants to stem the spread of disease.

The NTU researchers identified the exact cellular-level mechanism by which the bacteria can penetrate and hijack a plant’s immune system, therefore leaving them vulnerable to infection.

The Xanthomonas bacteria infects and damages plants by injecting toxic proteins into the plant host. These proteins hijack and take over the plant’s normal biological processes, preventing them from mounting an immune response.

The research team discovered that the toxic proteins interacts with plant cells like liquid droplets, allowing the bacteria protein to “glue” onto the plant cell and merge into it. This lets the Xanthomonas bacteria infiltrate and invade the plant cell, leaving it vulnerable to infection.

Understanding exactly how plants and crops are infected by bacteria is a crucial step in developing methods to prevent their infection and produce crops that can resist the disease.

The team has obtained a provisional patent for a toolkit they have developed that allows scientists to replicate the infection process. This will allow researchers to test potential solutions for strengthening crop immunity in laboratory settings. It also has potential applications for future synthetic biology and agri-food technology.


Explore furtherSymbiotic bacteria in root cells may be key to producing better crops, study finds


Provided by Nanyang Technological University

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Three main components causing the digital agriculture revolution

“The farming industry is undergoing a digital revolution. Thanks to the large-scale availability of sensors, cameras and other mobile and computing technologies that we could only dream of in the past, growers have great amounts of data at their disposal,” says Dr. Gajendra Pratap Singh.

Cause of the revolution
In his view, there are three main components that are causing the digital revolution in agriculture. Firstly, there is the availability of affordable and portable sensors, that enable growers to monitor their crops more closely. Secondly, communication technology has allowed growers to be in closer contact with each other and with suppliers. But most of all, the massive availability of data analytics that the use of Artificial Intelligence (AI) technology allows for is helping to make smart decisions on time and increase productivity.  


Gajendra Pratap Singh

Gajendra is Principal Investigator and Scientific Director at Disruptive & Sustainable Technologies for Agricultural Precision (DiSTAP) at Singapore-MIT Alliance for Research and Technology (SMART), MIT’s research enterprise.

“AI technologies allow real-time interpretation of crop health data obtained from field sensors. Sensors in irrigation systems have been designed to provide water only when no rain is forecast, just to give one example. This both saves water and improves crop yield,” Dr. Singh explains.

The wealth of useful information that new technologies provide can also be used to breed resilient crops to withstand plant diseases. “In my view, AI technologies combined with sensor and mobile communication technologies have the potential to empower farmers like never before in history. This way, the huge amounts of data obtained from plants using novel sensors can help to increase farm productivity, develop new heat-tolerant varieties of crops, and to curtail the predicted food shortage due to climate change and population increase.”

Still room for improvements
However, the industry is not there yet, Dr. Singh claims. “AI technology on its own is not powerful enough to boost agriculture. Collaboration is needed with sensor and communication technologies to render them useful. Right now, sensors only measure the morphology or appearance of the plants or environmental factors such as temperature. They don’t monitor the biochemical changes occurring inside the plants in real-time yet. But when a plant is stressed due to the lack of nutrients or proper light, it generates a wealth of biochemical information. Being able to use this information will help growers even further.”

And this is exactly what DiSTAP wants to achieve with their new, portable Raman sensors that measure data concerning nitrate stress, shade avoidance syndrome, and bacterial infections in plants within a few hours. “For that reason, we’ve developed nano-sensors that can measure plant hormones, giving vital feedback to the farmer on a daily basis. Thus, it is possible to monitor the health of each plant every day by measuring the plant itself and not the symptoms or the environment only. Also for vertical farms, it is technologies these nano-sensors combined with AI that have the potential to improve crop productivity several times.”

This is important, according to Dr. Gajendra Pratap Singh, as agriculture has a profound impact on every human being. “In Bangladesh, for example, just two days of heat in April this year destroyed more than 60,000 hectares of rice, affecting more than quarter-million farmers with losses of about US$40 million. The availability of mobile technology in the remotest parts of the world will allow universal participation of farmers in the digital revolution in agriculture.”

For more information:
Dr. Gajendra Pratap Singh, Principal Investigator and Scientific Director
Disruptive & Sustainable Technologies for Agricultural Precision (DiSTAP)
Singapore-MIT Alliance for Research and Technology (SMART), MIT’s research enterprise in Singapore
gajendra@smart.mit.edu
distap@mit.edu 
www.smart.mit.edu

Publication date: Thu 12 Aug 2021

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Wineries in California have been under siege for decades. There’s finally hope that grapevines can be saved from bacterial disease

Agostino Petroni | August 12, 2021

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Pierce's disease. Credit: California Department of Food and Agriculture
Pierce’s disease. Credit: California Department of Food and Agriculture

This article or excerpt is included in the GLP’s daily curated selection of ideologically diverse news, opinion and analysis of biotechnology innovation.In 1961, Adam Tolmach planted a five-acre vineyard on land he had inherited from his grandfather in the wine-growing region of Ventura County, California, a few miles east of Santa Barbara. As an undergraduate, Tolmach had studied grape growing and winemaking (areas of study known as viticulture and enology, respectively) and then worked for a couple of years at a winery not far from his grandfather’s land. In 1983, he started producing his own wines, which he sells under the Ojai Vineyard label.

Over the years, Tolmach’s grapevines began to suffer. The plants lost vigor and the leaves dried. It turned out the vineyard was affected by Pierce’s disease, a sickness that had long plagued southern California, but had become more severe in the 1990s after the invasion of the glassy-winged sharpshooter, a large leafhopper insect that feeds on plant fluids and can spread a bacterium known as Xylella fastidiosa, usually just called Xylella (pronounced zy-LEL’-uh). This bacterium has existed in the United States since as far back as the 1880s, and over the years, it has destroyed at least 35,000 acres of the nation’s vineyards.

Adam Tolmach. Credit: Ojai Vinyard

Tolmach witnessed the slow but certain death of his grapevines. By 1995, there were just too many missing plants, he said. So he decided to pull out the infected vineyard. To continue making wine, he bought grapes from other producers. Tolmach became a winemaker with no vineyard of his own.

Every year, American winemakers lose about $56 million worth of vines, while government agencies, nurseries, and the University of California system invest another $48 million in prevention efforts, according to research published in the journal California Agriculture. At least 340 plant species serve as hosts to Xylella, though the bacteria only harm some of them. Across the globe, Xylella has devastated orange trees in Brazil and olive fields in southern Italy, and recently a newly identified species, Xylella taiwanensis, has been infecting pear trees in Taiwan. As of now, there is no permanent solution. Each time a Xylella species has invaded a new region, it has proved impossible to eradicate.

Countries have long fretted about the potential for infected plant imports to spread the bacteria, and more recently, climate change has been identified as an additional threat, pushing the disease vectors’ habitat north, both in Europe and in the U.S. As winters become warmer, experts say, Xylella could enter new territories, upending their regional economies and landscapes.

Yet there might be some hope. After 40 years of crossbreeding European grape varieties with wild grapes, a plant geneticist recently patented five hybrid grapes that appear to be resistant to Pierce’s disease. While scientists caution that it’s not yet clear how long the resistance will endure, wine producers like Tolmach hope that these new grapes will allow their vineyards to flourish once again.

A variety of grape species are indigenous to America, and a recent study suggests that Native Americans might have used them to make alcoholic beverages more than 500 years ago. In North America, native varieties tend to have thick skin and an astringent, peppery, acidic taste that is quite different from the grapes used in most wines.

In the 1500s, Spanish settlers brought Vitis vinifera, the common European grapevine for winemaking, to Florida. Farmers never succeeded in cultivating European grapes in the new territory — after a few years, the plants would just die. Then, in the 1860s, the Los Angeles Vineyard Society led grape-planting efforts in the Santa Ana Valley. By 1883, there were a total of 50 wineries and 10,000 acres of grapevines. Then, just a couple of years later, the grapevines had all died inexplicably.

In 1889, the U.S. Department of Agriculture instructed one of the first formally trained American plant pathologists, Newton Pierce, to figure out what was killing the European grapevines. Pierce studied the disease, eventually speculating that it was caused by a microorganism, but he never identified one. Still, in recognition of his effort, the disease was eventually named after him.

In the 1970s, a University of California, Berkeley entomologist named Alexander Purcell helped solve the mystery. At the time, researchers were beginning to think Pierce’s disease was caused by bacteria but had yet to pin down a culprit. Purcell and his colleagues proved the then-unnamed Xylella was responsible by growing the bacterium from samples taken from plants infected by blue-green sharpshooters, and then directly infecting healthy plants with the lab-grown pathogen. Over time, a more complete picture of disease transmission emerged.

The glassy-winged sharpshooter feeds on the green stems and leaves of grapevine plants, which contain water and dissolved nutrients, Purcell told Undark. If the plant is infected with Xylella, some of the bacteria linger in the insect’s needle-like mouthparts. The next time the glassy-winged sharpshooter feeds upon a grapevine, the insect can transfer the Xylella to the new plant. Inside the plant’s vascular tissues, the bacteria multiply, obstructing the normal flow of water and nutrients and interfering with the plant’s metabolism and physiology — a process that ultimately kills the plant.

In the late 1980s, Purcell mapped swaths of the U.S. and Europe by how conducive they are to disease spread. Knowing that Xylella do not thrive in regions with cold winters, that are far from large bodies of water, and that lack a disease-carrying vector such as the glassy-winged sharpshooter, Purcell drew out maps by hand. He then marked the regions with the right combination of geographic and climatic conditions to allow for Pierce’s disease to spread, noticing a pattern emerge.

At the time, the European Union was not very concerned about Xylella, though Purcell contends that the bacteria had almost certainly arrived in the region. In talks and at conferences, he warned that European countries were facing a great danger. He urged the E.U. to increase its regulations of plant imports. Those warnings went unheeded, Purcell said, and in 2017, Pierce’s disease was first detected on the grapevines of the Spanish island of Mallorca, jeopardizing the future of winemaking there. Today, Xylella is spreading through the Mediterranean region and other parts of Europe — just as Purcell predicted.

The glassy-winged sharpshooter spreads Xylella bacteria when it feeds on the vascular tissues of plants. Credit: Courtesy of University of California, Riverside

Alberto Fereres, a Spanish entomologist and researcher at the Spanish National Research Council, is concerned about the devastating effects of the European outbreaks, including one in southern Italy that has infected and killed 20 million olive trees, more than a third of the region’s population. “[Xylella] is present in many more countries than we indeed thought,” Fereres said, adding that his research group recently discovered that the bacteria have been present in Spain for more than 20 years, but for much of that time it only lived in plants that don’t show symptoms of the disease.

Fereres hopes at least some plants will adapt to the presence of the bacteria and that farmers will be able to control the indigenous European vector, the meadow spittlebug, by tilling the land to kill the bug’s juveniles and placing barriers or nets to separate the insects from susceptible plants.

So far, the U.S. has largely used insecticides to get rid of infected insects. The Temecula Valley in California, for example, experienced a severe outbreak of Pierce’s disease in the late 1990s. Back then, stakeholders managed to defeat the disease in less than two years by introducing specific pesticides into the farming of grapevines.

Matt Daugherty, an entomologist at the University of California, Riverside, studied the resulting decline in Temecula’s glassy-winged sharpshooter population. He said the insect’s numbers remained low until around 2017, when the population exploded for a second time.

“Now the bad news is this,” Purcell said: “After about 18 years, the insect is now resistant to the insecticide.” In entomology, Purcell added, such resistance is common if the same insecticide is used year after year. He and Fereres maintain that pesticides are not a viable long-term solution to the problem. In some countries, this approach has also run up against public opinion. In Italy, for example, consumers have strongly opposed the use of pesticides on olive trees threatened by Xylella.

Rodrigo Almeida, a plant pathologist at the University of California, Berkeley, warns that climate change might worsen the situation: While low winter temperatures in many grape-growing regions have traditionally limited the spread of Pierce’s disease, the past few years have brought warmer winters, allowing Xylella to spread.Follow the latest news and policy debates on agricultural biotech and biomedicine? Subscribe to our newsletter.SIGN UP

“With warming temperatures and warmer winters, you’re going to have sort of more disease where you already have it, and you’re probably going to see the range expand north as well,” Almeida said. Warmer temperatures favor greater survival of the insects and increase the likelihood that an infection will persist through the winter. Almeida added that it’s difficult to predict precisely how much the disease will increase and how it will impact the new territories, but that there is the possibility that the disease will find a home in areas where a dry climate combines with warmer winters.

“We’re expecting things to get worse and worse,” Daugherty said.

Yet, in territories where European grapes die because of Xylella, wild indigenous grape varieties that are not a good fit for winemaking thrive. Those plants bear a unique gene that prevents them from succumbing to the disease, and that specific gene could be a counteroffensive to the bacteria and might well change the future of winemaking.

In 1989, University of California, Davis plant geneticist and viticulturist Andrew Walker inherited grapevine seeds that he was told were produced from crossbreeding two known Vitis species. But as the plants grew, he soon noticed they were behaving weirdly. For one thing, their vines had sprouted fine hairs along the stems. More importantly, the plants proved resistant to Pierce’s disease. Walker decided to investigate. Perhaps, he speculated, the parent plants, which were still flourishing in an abandoned vineyard owned by his university, had accidentally crossbred with the native grapevines that were growing wild nearby.

Indeed, this turned out to be the case. Vitis arizonica grows wild in the southwest U.S. and Mexico, and Walker matched the genetic fingerprint of the male V. arizonica in his own plants. The wild plant carries a dominant gene that passes along Pierce’s disease resistant traits to its offspring.

Sensing that this could lead to breakthrough for new varieties of grapevine, Walker began the slow process of crossbreeding. This technique goes back about 10,000 years and involves selectively breeding plants and animals with desired traits. In this case, Walker wanted to cross disease-resistant V. arizonica with winemaking varieties like cabernet sauvignon.

A grapevine leaf affected by Pierce’s disease. As the plant’s vascular structure is obstructed by bacteria, the flow of water and nutrients is impeded, and the leaves become brown and dry. Credit: Agricultural Research Service/USDA

The first generation’s seedlings all carried the gene for disease resistance. Walker selected the highest quality among them, and when the plants flowered, he crossed them again with various V. vinifera varieties. He did this for four to five generations, reaching a point where 97 percent of the plant’s genome came from V. vinifera and 3 percent came from V. arizonica. It took Walker about 20 years to develop these new plants, five varieties of which have been patented and given out to a few producers, and sold through a handful of nurseries. Tolmach, the winemaker from Ojai, was one of the few lucky ones to receive them.

“I guess what’s shocking to me is that the quality is there — these can be standalone wines by themselves,” said Tolmach. In 2017, he planted about 1,800 plants on 1.2 acres with four of Walker’s varieties, and he recently bottled the 2019 vintages. (These vintages won’t be available until this fall, when they will be priced between $30 and $40 per bottle, which is comparable to his vintages that use traditional grapes.) Tolmach said that his new plants are healthy and thriving with no sign of the disease, and he’s now thinking of planting more on a 10-acre vineyard that he purchased in northern Santa Barbara County.

Matt Kettmann, a California writer and wine critic who has been following Tolmach’s work for years, tasted Tolmach’s wines produced with resistant grape varieties. He said they are unique and interesting wines with characteristics reminiscent of wines of European heritage. He described Tolmach’s 2019 wine using Walker’s paseante noir grape as tasting of “black cherry, mocha, clove, baking spice,” while praising its “smooth texture and rich mouthfeel.” “That one,” said Kettmann, “was really kind of impressive to me.”

Kettmann anticipates that the new wines will be appreciated by connoisseurs, but he wonders how the larger American market will respond. Europeans emphasize the value of terroir — the taste imparted to a wine by a particular region’s soil, topography, and climate. Americans, on the other hand, tend to care more about the variety of the grape, like pinot gris, cabernet sauvignon, or zinfandel — and Walker’s varieties are entirely new.

“Tradition is a huge consideration in choosing wine varieties for winemaking. Can you name any new grape varieties introduced during the last 50 years that are now widely used for wine?” wrote Purcell in an email.

It’s also not clear whether new genotypes of Xylella might evolve to infect the hybrid grapes, Purcell and Fereres wrote to Undark. Currently, only a single gene confers the resistance. For this reason, it might be necessary to incorporate new resistance genes by crossbreeding additional varieties of grapevine, said Purcell.

Still, growers like Tolmach are excited by Walker’s resistant varieties, and some are planting them in areas that have been impacted by Xylella, Walker saidThough Tolmach has made wines with the new grapes exclusively, he suggests many wineries may opt to blend the grapes with other mainstream varieties.

For his part, Walker believes that any skepticism about his grapes’ novelty will fade in the face of climate change. “It is going to force people to reevaluate how we improve grapevines,” he said.

Agostino Petroni is a journalist, author, and a 2021 Pulitzer Reporting Fellow. His work appears in a number of outlets, including National Geographic, BBC, and Atlas Obscura. Find Agostino on Twitter @PetroniAgostino

A version of this article was originally posted at Undark and is reposted here with permission. Undark can be found on Twitter @undarkmag

The GLP featured this article to reflect the diversity of news, opinion and analysis. The viewpoint is the author’s own. The GLP’s goal is to stimulate constructive discourse on challenging science issues.

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Engineering broad-spectrum disease-resistant rice by editing multiple susceptibility genes

Journal of Integrative Plant Biology

Hui TaoXuetao ShiFeng HeDan WangNing XiaoHong FangRuyi WangFan ZhangMin WangAihong LiXionglun LiuGuo-Liang WangYuese NingFirst published: 25 June 2021 https://doi.org/10.1111/jipb.13145

Edited by:: Xuewei Chen, Sichuan Agricultural University, ChinaRead the full textPDFTOOLSSHARE

ABSTRACT

Rice blast and bacterial blight are important diseases of rice (Oryza sativa) caused by the fungus Magnaporthe oryzae and the bacterium Xanthomonas oryzae pv. oryzae (Xoo), respectively. Breeding rice varieties for broad-spectrum resistance is considered the most effective and sustainable approach to controlling both diseases. Although dominant resistance genes have been extensively used in rice breeding and production, generating disease-resistant varieties by altering susceptibility (S) genes that facilitate pathogen compatibility remains unexplored. Here, using CRISPR/Cas9 technology, we generated loss-of-function mutants of the S genes Pi21 and Bsr-d1 and showed that they had increased resistance to M. oryzae. We also generated a knockout mutant of the S gene Xa5 that showed increased resistance to Xoo. Remarkably, a triple mutant of all three S genes had significantly enhanced resistance to both M. oryzae and Xoo. Moreover, the triple mutant was comparable to the wild type in regard to key agronomic traits, including plant height, effective panicle number per plant, grain number per panicle, seed setting rate, and thousand-grain weight. These results demonstrate that the simultaneous editing of multiple S genes is a powerful strategy for generating new rice varieties with broad-spectrum resistance.

Supporting Information

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JUNE 25, 2021

Kiwi disease study finds closely related bacterial strains display different behaviors

by American Phytopathological Society

Kiwi disease study finds closely related bacterial strains display different behaviors
Elodie Vandelle, Annalisa Polverari, Davide Danzi, Vanessa Maurizio, Alice Regaiolo, Maria Rita Puttilli, Teresa Colombo, Tommaso Libardi. Credit: Elodie Vandelle

Over the last decade, severe outbreaks of bacterial canker have caused huge economic losses for kiwi growers, especially in Italy, New Zealand, and China, which are among the largest producers. Bacterial canker is caused by the bacterial pathogen Pseudomonas syringae pv. actinidiae (Psa) and more recent outbreaks have been particularly devastating due to the emergence of a new, extremely aggressive biovar called Psa3.

Due to its recent introduction, the molecular basis of Psa3’s virulence is unknown, making it difficult to develop mitigation strategies. In light of this dilemma, a group of scientists at the University of Verona and University of Rome collaborated on a study comparing the behavior of Psa3 with less-virulent biovars to determine the basis of pathogenicity.

They found that genes involved in bacterial signaling (the transmission of external stimuli within cells) were especially important, especially the genes required for the synthesis and degradation of a small chemical signal called c-di-GMP, that suppresses the expression of virulence factors. Compared to other biovars, Psa3 produces very low levels of c-di-GMP, contributing to an immediate and aggressive phenotype at the onset of infection before the plant can corral a defense response.

“It was exciting to discover this diversified arsenal of pathogenicity strategies among closely related bacterial strains that infect the same hosts but display different behaviors,” said Elodie Vandelle, one of the scientists involved with this study. “Although their ‘small’ genomes mainly contain the same information, our research shows that bacterial populations within a pathovar are more complex than expected and their pathogenicity may have evolved throughout different strategies to attack the same host.”

Their research highlights the importance of working on a multitude of real-life pathogenic bacterial strains to shed light on the diversity of virulence strategies. This approach can contribute to the creation of wider pathogenicity working models. In terms of kiwi production, Vandelle hopes their findings can help scientists develop new mitigation methods. In the long-term, their research could lead to the identification of key molecular switches responsible for the transition between high and low bacterial virulence phenotypes.

“This identification would allow, at industrial level, to develop new targeted strategies to control phytopathogenic bacteria, weakening their aggressiveness through switch control, instead of killing them,” Vandelle explained. “This would avoid the occurrence of new resistances among bacterial communities, thus guaranteeing a sustainable plant protection.”


Explore furtherUnpacking the two layers of bacterial gene regulation during plant infection


More information: Elodie Vandelle et al, Transcriptional Profiling of ThreePseudomonas syringaepv.actinidiaeBiovars Reveals Different Responses to Apoplast-Like Conditions Related to Strain Virulence on the Host, Molecular Plant-Microbe Interactions (2020). DOI: 10.1094/MPMI-09-20-0248-RJournal information:Molecular Plant-Microbe InteractionsProvided by American Phytopathological Society

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The new species of bacteria killing palms in Australia

by Microbiology Society

The new species of bacteria killing palms in Australia
Symptoms found in ornamental palms in Cairns. (a) Dypsis poivreana (RID7866) showing early symptoms of leaf yellowing and marginal necrosis; (b) Archontophoenix alexandrae (RID8088) showing mid stage symptoms of canopy browning. (c) Euterpe precatoria (RID7936), (d) Cocos nucifera (RID7941), (e) Euterpe sp. (LMJ1271) and (f) Phoenix sp. (RID8094) all displaying advanced symptoms in which all or most leaves have died, with older leaves retained and hanging like a skirt. Credit: Richard Davis et al.

As reported in the International Journal of Systematic and Evolutionary Microbiology, a newly-discovered bacterium named Candidatus phytoplasma dypsidis has been found to cause a fatal wilt disease.

In 2016, several ornamental palms within a conservatory in the Cairns Botanic Gardens, Queensland, died mysteriously. A sample was taken from one of the diseased plants and investigated by Dr. Richard Davis and colleagues from the Australian Government Department of Agriculture, Water and the Environment, and state and local government. They compared the characteristics and genome of the bacterium identified as the cause of the disease and found the bacterium was similar to other species of Candidatus phytoplasma, many of which are responsible for disease epidemics in palms elsewhere, but was different enough to be an independent species. “When the laboratory testing indicated it was something close to, but not the same as, devastating palm pathogens overseas, we were very surprised,” said Dr. Davis.

“At first we thought it was most likely an unrelated fungal disease. Almost as an afterthought, I suggested we screen for phytoplasma because there are some very bad phytoplasma diseases of palms moving around the world, including in neighboring Papua New Guinea,” he explained.

So far, infection with Candidatus phytoplasma dypsidis has been found to cause disease in 12 different species of palms, including Cocos nucifera, which produces coconuts. “Although palms are not grown as a cash crop in Australia, they are important ornamental garden and amenity plants. Coconuts and other palms are an economically significant component of Australia’s tourism industry in the tropics,” said Dr. Davis.

“Palms take on a much greater significance in most of the countries near Australia, in southeast Asia and the Pacific, where coconuts are ‘the tree of life.’ It is important to raise awareness of a new disease threat, such as this, so that regional biosecurity measures can be prioritized.”

The bacterium is thought to be spread from plant-to-plant by insects that feed on phloem, the tissue which transports nutrients around the plant, said Dr. Davis: “It seems certain from our observations of how this thing has spread through the local area that there must be an insect vector. Finding out what vector species are involved is a vital next research priority.”

Outbreaks of exotic plant pathogens in Australia are rare due to the country’s stringent biosecurity measures. “Australia, New Zealand and the Pacific island countries and territories have an enviable plant and animal health status compared to much of the rest of the world. Because we are islands, we have escaped many significant plant disease threats that have traveled around the world, over history,” explained Dr. Davis. “As biosecurity plant pathologists for the Australian Government Department of Agriculture, Water and the Environment, our team’s main role is to look out for and detect incursions of exotic plant pathogens. We usually do this in remote parts of Australia’s north, so to come across something much closer to home in the suburbs of Cairns, in far North Queensland, Australia, was unusual. However, we have no evidence to suggest this is an incursion from overseas because it is a unique organism. It may well be indigenous to Australia and some as yet unknown factor has triggered a disease outbreak.”

Dr. Davis is concerned that this new disease could spread outside of Cairns and affect palm populations further north. “North of Cairns, we have threatened ecological communities of fan palms which are of great environmental significance,” he said. It is important for Dr. Davis and his team to continue to monitor the spread of Candidatus phytoplasma dypsidis. A number of questions remain, including which insect vectors are spreading the disease, and whether the bacterium is capable of infecting other types of plant, including important crops such as bananas.


Explore further Phytoplasma effector proteins devastate host plants through molecular mimicry


More information: Lynne M. Jones et al, ‘Candidatus Phytoplasma dypsidis’, a novel taxon associated with a lethal wilt disease of palms in Australia, International Journal of Systematic and Evolutionary Microbiology (2021). DOI: 10.1099/ijsem.0.004818Provided by Microbiology Society Citation: The new species of bacteria killing palms in Australia (2021, May 27) retrieved 2 June 2021 from https://phys.org/news/2021-05-species-bacteria-palms-australia.htmlThis document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.8 shares

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