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APRIL 18, 2022

Scientists record first case of harmful bacteria in ubiquitous weed found throughout US

by University of Florida

Scientists record first case of harmful bacteria in ubiquitous weed found throughout U.S.
Credit: University of Florida

Scientists at the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) have recorded the first North American case of a harmful phytoplasma disease known for its threat to fruit, vegetable and ornamental crops in South America and the Middle East.

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To make matters worse, scientists confirmed the host for the disease to be one of the most noxious and rapidly spreading weeds commonly found in a wide range of environments throughout the United States and into Canada.

Findings of the “First report of ‘Cadidatus Phytoplasma brasiliense‘ in North America and in a new host, yellow nutsedge (Cyperus esculentus)” were just published in the journal Plant Health Progress.

“The host of the disease is known as one of the most widespread and problematic weeds found everywhere—called yellow nutsedge,” said Brian Bahder, assistant professor of entomology at UF/IFAS Fort Lauderdale Research and Education Center. “It is one of the most aggressive weeds that commonly grows in lawns, home landscapes, vegetable and flower gardens and agricultural systems.”

The phytoplasma species called Candidatus Phytoplasma brasiliense is documented in regions of Brazil and Peru to harm hibiscus, papaya and cauliflower. Subsequently, research showed the same species infects peaches in the Middle East country of Azerbaijan.

Bahder and his team confirmed the phytoplasma and host in Fort Pierce. They found it while conducting research for a different disease—lethal bronzing—that attacks palm trees. Scientists were surveying and testing samples of grasses in hopes of finding a reservoir for lethal bronzing.

Research has shown that the adult planthopper insect that carries lethal bronzing feeds on the palm’s canopy, and the nymphs have been recorded among more than 40 species of grasses and sedges.

Because of the close association of nymphs with grasses and sedges, speculation has risen about the ability of these plants to serve as a reservoir for the lethal bronzing phytoplasma, Bahder said.

For the survey, scientists sampled three of the most abundant weeds known to serve as a host to the nymphs, yellow nutsedge being one of them.

While testing the samples, three of the outcomes resulted in a positive result.

“We thought we had found lethal bronzing in one of the grasses, so we proceeded to genetically sequence the sample,” said Bahder. “The results confirmed it was not lethal bronzing but that it was another phytoplasma.”

The DNA sequencing of that specimen confirmed their findings of a new phytoplasma in this weed, recorded for the first time in North America.

Implications of the disease and its spread through this weed cause scientists to consider it a threat to agriculture and ornamental industries. UF/IFAS scientists are seeking funding for the next steps of research.

“The next logical step is to find out which insect is spreading the disease. The good news is that we caught this early,” said Bahder. “We don’t know if this is an isolated incident or if the insect is spreading in the grass, and if it will feed on the papaya, hibiscus or cauliflower—which are economically important in Florida. The point is that we don’t know the extent of this disease in Florida or what threat it poses.”


Explore further

Palm tree disease in Florida transmitted by traveling bug from Jamaica


More information: Brandon Di Lella et al, First report of ‘Candidatus Phytoplasma brasiliense’ in North America and in a new host, yellow nutsedge (Cyperus esculentus), Plant Health Progress (2022). DOI: 10.1094/PHP-03-22-0027-BR

Provided by University of Florida 

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Getting to the Bottom of Common Scab in Canada

By

 Ashley Robinson

 ProMED

February 28, 2022

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The first national common scab research project has the Canadian potato industry seeing common scab in a whole new light.

Tubers across Canada have fallen victim to a bacterium lurking in the soil for years. When soils are dry, brown lesions appear on potatoes. And while these spuds can still be eaten safely, the lesions in some cases cut deep holes in them and cause problems for the industry.

While some research has been done in Canada on the potato disease common scab, there hasn’t been much done on a national level. It hasn’t just been one region of the Great White North affected by this disease, growers across the country have found themselves stuck with these ugly spuds.

For Tracy Shinners-Carnelley, vice president of research, quality and sustainability at Peak of the Market in Manitoba, and Newton Yorinori, director of plant breeding, seed development and research at Cavendish Farms in Prince Edward Island, they knew something needed to be done on a national level to address common scab.

At the time, the Canadian Potato Council (CPC) was looking for research projects to focus on. The group was applying for cluster projects funded by the Canadian Agricultural Partnership (CAP) with the Canadian Horticultural Council. Shinners-Carnelley and Yorinori thought a closer look at common scab was a good fit for the cluster projects.

“In Ontario, Prince Edward Island and New Brunswick, they had worked on scab a lot. But we hadn’t and my first thought was well, who do I know that’s been active in this research space? And that’s Claudia,” Shinners-Carnelley explains in a phone interview. “I was trying to find out what was already happening. And start to ask some questions about where we start potentially with some strategies around attempting to manage scab, which is always such a difficult one because there are no easy answers.”

Shinners-Carnelley and Yorinori approached Claudia Goyer, a research scientist at Agriculture and Agri-Food Canada (AAFC)’s Fredericton Research and Development Centre. They wanted to work with her to try and find a way to control the bacteria affecting potatoes.

What is Common Scab?

Common scab has been around for more than 100 years. It’s caused by a filamentous bacterium found in soil. When soil conditions are dry, it enters tubers through the lenticels making brownish lesions on spuds. As the potatoes grow the lesions become larger. As it’s a soil borne disease and a bacterium, Goyer says it’s harder to control as there are no chemicals available to control it.

“Once you have common scab in your fields, it’s really difficult to get rid of it. There’s different species that are causing common scab but the one that is found like pretty much everywhere in the world is Streptomyces scabies,” Goyer explains in a phone interview.

Claudia Goyer
Claudia Goyer holding potatoes with common scab symptoms. Photo: Julie Root

There are other species of common scab though that are found regionally, including Streptomyces acidiscabies and Streptomyces turgidiscabies. According to Goyer they all produce a group of plant toxins called thaxtomins — which is how common scab causes the brown lesions on potatoes.

Goyer notes the lesions aren’t dangerous to humans. Potatoes with common scab can still be consumed, however common scab makes them “ugly.” In the worse cases of common scab, the lesions can go deep making holes in the potatoes.

The industry rule is if more than five per cent of the surface of tubers are covered with common scab, they’re unable to be sold to the table market. Goyer says spuds with common scab are harder to peel, making them less desirable for the fry market also.

“It’s really an issue both for table and processing, then of course it’s even worse for seed production. They really don’t want common scab because nobody wants to spread that disease everywhere,” she adds.

Irrigation does help reduce common scab incidence though as it keeps soils from drying out, Goyer explains.

Searching for a Canadian Solution to Common Scab

In 2018, Goyer started on her common scab project. Working with collaborators in Manitoba, Ontario, P.E.I. and New Brunswick, they collected samples of potatoes with common scab symptoms for testing. Pathogens of common scab present in Canada were then isolated from infected tubers and characterized using molecular testing. So far Goyer says they have a collection of 300 isolates with at least 20 genetic groups.

“This shows that there’s a lot of diversity in the pathogens, which then might explain why we’re having so much trouble finding solutions to control the disease, right? Like it’s so widely different in how they behave, it becomes more difficult to find a control method that works everywhere,” she explains.

Goyer says the most common species found in Canada is Streptomyces scabies. Another species, Streptomyces acidiscabies, was also found to be present, but it’s more common in acidic soils and was first discovered in Maine.

“THIS SHOWS THAT THERE’S A LOT OF DIVERSITY IN THE PATHOGENS, WHICH THEN MIGHT EXPLAIN WHY WE’RE HAVING SO MUCH TROUBLE FINDING SOLUTIONS TO CONTROL THE DISEASE, RIGHT? LIKE IT’S SO WIDELY DIFFERENT IN HOW THEY BEHAVE, IT BECOMES MORE DIFFICULT TO FIND A CONTROL METHOD THAT WORKS EVERYWHERE.” CLAUDIA GOYER

After determining the genetic groups, Goyer and her team started to develop tools to look closer at how they are distributed across Canada. The group is also looking at ways to control common scab in fields.

Goyer says they’ve looked at how growing certain crops before potatoes can help hold soil moisture in to reduce common scab incidence. However, they’ve had trouble establishing the nurse crops. They have also tried beef manure compost, liquid mustard and peroxide based products.

“We also tried different fertilizer products like ammonium sulfate, which is supposed to make the soil more acidic. The common scab pathogen doesn’t grow well when it’s more acidic, so we thought perhaps this would help. And none of these really work,” she adds.

There have been two options which have shown promise though. They tried the biopesticide Serenade Soil in Fredericton and saw good results for several years. In Manitoba, it reduced common scab severity by 40 per cent compared to an untreated control. The best results were seen with an auxin product, 2,4-D, which is basically an herbicide Goyer says. Used in miniscule amounts applied as a fine mist in Manitoba, it reduced common scab severity and produced 69 per cent marketable tubers compared to less than five per cent in the untreated control.

“We’re now evaluating if we need to tweak how much 2,4-D to put in or maybe we need to apply it at a different time depending on the cultivars,” Goyer explains.

The project will complete its final year of trials in 2022 with full results released in 2023.

Common Scab Project Breakdown

  • Research team
    • Claudia Goyer with AAFC in Fredericton, N.B.
    • Martin Filion with Université de Moncton in New Brunswick
    • Tracy Shinners-Carnelley with Peak of the Market in Manitoba
    • Newton Yorinori with Cavendish Farms in P.E.I.
    • Rick Peters with AAFC in Charlottetown, P.E.I.
  • Provinces where trials are being done:
    • Manitoba
    • New Brunswick
    • Prince Edward Island

Header Photo — Potatoes with common scab symptoms on them. Photo: Claudia Goyer

Related Articles

Common Scab, a Problem without a Solution?

Combatting Common Scab

Cultivar and Common Scab

Read Full Post »

Copied from PestNet

Thursday, 17 February 2022 06:49:28

Grahame Jackson posted a new submission ‘ PANTOEA LEAF BLIGHT, RICE – CHINA: FIRST REPORT’

Submission

PANTOEA LEAF BLIGHT, RICE – CHINA: FIRST REPORT

ProMED
http://www.promedmail.org

Source: Plant Disease [summ. Mod.DHA, edited]
https://doi.org/10.1094/PDIS-05-21-0988-PDN

Citation: Yu L, Yang C, Ji Z, et al. First Report of New Bacterial Leaf Blight of Rice Caused by _Pantoea ananatis_ in Southeast China. Plant Disease. 2022; 106 (1); doi: 10.1094/PDIS-05-21-0988-PDN.
—————————————————————————————————————————-
In autumn 2020, leaf blight was observed on a number of varieties of rice (_Oryza sativa_) in Zhejiang and Jiangxi provinces. The disease incidence was 45-60%. The symptoms were assumed to be caused by _Xanthomonas oryzae_ pv. _oryzae_ (Xoo), the pathogen of rice bacterial blight.

Sixty-three isolates were obtained from collected diseased leaves. 16S rRNA sequence analysis from 6 isolates revealed that the amplified fragments shared 98% similarity with the _Pantoea ananatis_ type strain in GenBank. Analysis of further sequences and phylogenetic analyses was carried out. Based on the obtained morphological, physiological, biochemical, and molecular data, the isolates were confirmed as _P. ananatis_. Pathogenicity tests resulted in symptoms similar to those in the field.

_P. ananatis_ has previously been reported to cause grain discolouration of rice in the country, but this is the 1st report of _P. ananatis_ as the causative agent of rice leaf blight. This raises the alarm that the emerging rice bacterial leaf blight might be caused by _P. ananatis_, instead of Xoo as traditionally assumed. Further, the differences of occurrence, spread, and control between these 2 diseases will need to be determined.


Communicated by:
ProMED

[_Pantoea ananatis_ symptoms in rice may include lesions on stems, stem necrosis, and leaf blight. The pathogen has also been reported to cause sheath and grain rot, as well as kernel discolouration. _P. stewartii_, previously known to occur on rice seeds, has also recently been associated with a leaf blight of the crop in Africa (ProMED post 20170504.5012251). Both species are considered emerging rice pathogens. The effects of different bacterial strains on hosts can vary dramatically. The bacteria are generally transmitted by insect vectors, plant material, and infected seed, making them a quarantine risk.

Species in the genus can cause diseases on a number of crops, such as Stewart’s bacterial wilt on maize and fruit bronzing of jack fruit (_P. stewartii_); leaf blights of cereals, including rice (_P. agglomerans_); pink disease of pineapple (_P. citrea_); brown stalk rot of maize (_P. ananatis_ and a novel _Pantoea_ species); and centre rot of onion (_P. ananatis_). A bacterial blight of _Eucalyptus_ and a leaf blotch disease of sudangrass have also been associated with _Pantoea_ species.

_Xanthomonas oryzae_ pv. _oryzae_ (Xoo) causes bacterial leaf blight (BLB) of rice. In Asia, millions of hectares of rice paddies are severely affected every year, with reported yield losses of up to 60% (e.g., see ProMED post 20211216.8700304). Xo pv. _oryzicola_ (Xoc) is the causal agent of bacterial leaf streak (BLS; e.g., see ProMED post 20210713.8514345), which is currently considered one of the most important emerging diseases of rice in the region. Xoc is thought to have originated in Asia but is now also spreading in Africa (e.g., recent 1st report from Senegal, see link below).

Maps
China:
http://www.beijing-travels.com/image/chinamap.jpg
China provinces:
http://www.chinadiscovery.com/assets/images/customer-support/maps/china-provinces-map-600.jpg

Pictures
_P. ananatis_ symptoms on rice:
http://www.publish.csiro.au/temp/AP04053_F1.gif

Links
_P. ananatis_ on rice:
http://dx.doi.org/10.1094/PDIS-06-11-0533
https://doi.org/10.1094/PDIS-94-4-0482B and
http://dx.doi.org/10.5197/j.2044-0588.2015.032.021
Information & review on _P. ananatis_:
https://doi.org/10.1111/j.1364-3703.2009.00542.x and
https://www.researchgate.net/figure/Host-range-of-Pantoea-ananatis_tbl1_24375785
_P. ananatis_ taxonomy and strains:
https://www.uniprot.org/taxonomy/553 and
https://doi.org/10.1128/JB.06450-11
Description of genus _Pantoea_:
http://www.tgw1916.net/Enterobacteria/Pantoea.html
Information on _Pantoea_ species and subspecies:
http://www.bacterio.net/pantoea.html and
https://doi.org/10.1128/JCM.01916-08
First report of Xoc in Senegal 2022:
https://doi.org/10.1094/PDIS-11-21-2481-PDN
Genus _Xanthomonas_ taxonomy, species & strains via:
https://www.uniprot.org/taxonomy/338
– Mod.DHA]


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Transforming tomatoes with molecular biotechnology

James Duduit, a Horticultural Science doctoral student, utilizes molecular biotechnology to transform tomatoes and improve the crop’s resistance to bacterial wilt and other common pathogens. Molecular biotechnology has many crop applications and is seen as a critical area of research because it increases the speed at which new varieties are developed.

Originally from Anderson, South Carolina, James Duduit studied Biology at Anderson University, where he graduated Magna Cum Laude, before attending NC State for his master of horticultural science degree. It was Wusheng Liu’s expertise in molecular biotechnology and translational genomics that convinced Duduit to stay and advance his doctoral degree.

James Duduit’s research efforts were recently awarded by U.S. Department of Education Graduate Assistance in Areas of National Need (GAANN) Program with a fellowship at NC State.

What brought you to NC State?
NC State seemed to have the broadest opportunities available for what I was interested in. The personnel with their diversity of expertise and experiences here has proven invaluable to my growth as an academic and scientist.

What are you doing now in research? What’s next?
My main focus right now is in trying to find a broadly applicable solution for the broad damage caused by bacterial wilt, especially in tomatoes. Using molecular biotechnology approaches, we hope that this economically devastating pathogen can be better mitigated. Another project that we are working on is related to a unique transformational technology for tomato and sweetpotato in order to increase the breeding speed with which new varieties can be developed. Our lab prioritizes biotechnological approaches to a broad diversity of horticulturally-relevant plants to overcome current challenges in pathogen/disease resistance, crop yield, transformation efficiency, and many other imposing but rewarding tasks.

How are you transforming challenges into opportunities?
Research is always a problem-solving process with unlimited challenges, but opportunities always naturally arise from these situations. I hope to critically think about each option and roadblock when performing experiments so that I can learn and make innovative and informative decisions throughout all of my actions. In addition, open communication with members of my lab and in the department allows a diversity of perspectives to be heard for more robust strategies to be employed.

What impact do you hope to have with your research?
My goal is to continue pushing the edge of our understanding in plant molecular biotechnology so that more enabling tools and choices can be developed for the betterment of growers and consumers. I hope that my work with tomato and sweetpotatoes can speed up cultivar development times to ultimately lead to cheaper and better products for consumers. And with my work in tomatoes, that the dangerous bacterial wilt disease can be better mitigated so that growers around the world can be benefited.

For more information:
North Carolina State University
www.ncsu.edu 

Publication date: Wed 26 Jan 2022

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Scientists identify genes key to microbial colonization of plant roots

EurekAlert

Identification of an enzyme that microbes deploy in the presence of plants leads to discovery of candidate genes involved in root colonization.

DOE/US DEPARTMENT OF ENERGY

Scientists Identify Genes Key to Microbial Colonization of Plant Roots
IMAGE: BIBLE, A.N., ET AL. (2021) IDENTIFICATION OF A DIGUANYLATE CYCLASE EXPRESSED IN THE PRESENCE OF PLANTS AND ITS APPLICATION FOR DISCOVERING CANDIDATE GENE PRODUCTS INVOLVED IN PLANT COLONIZATION BY PANTOEA SP. YR343. PLOS ONE 16 (7). view more CREDIT: BIBLE, A.N., ET AL. (2021) IDENTIFICATION OF A DIGUANYLATE CYCLASE EXPRESSED IN THE PRESENCE OF PLANTS AND ITS APPLICATION FOR DISCOVERING CANDIDATE GENE PRODUCTS INVOLVED IN PLANT COLONIZATION BY PANTOEA SP. YR343. PLOS ONE 16 (7).


The Science

Some microbes can form thin films called biofilms. These biofilms give them an advantage over other microbes by protecting them from stresses such as a lack of nutrients or the presence of harmful substances in the environment. Researchers often focus on the biofilms that pathogens use to resist antibiotics. However, some biofilms can be helpful to plants and other host organisms. In previous work, researchers found that Pantoea sp. YR343, a bacterium that promotes plant growth, forms robust biofilms along the root surface of Populus, the genus which includes willow and cottonwood trees. Scientists know relatively little about the mechanisms behind the formation of biofilms on plant roots, particularly at the genetic level. However, research has found that enzymes called diguanylate cyclases are key to biofilm formation. This new research has identified a diguanylate cyclase, DGC2884, that is expressed specifically in the presence of plants when bacteria colonize roots and form biofilms.

The Impact

Diguanylate cyclases are found in many species of bacteria. These enzymes control multiple behaviors, including how bacteria form biofilms, cause disease, and move. This research shows that a particular diguanylate cyclase, DGC2884, operates specifically during biofilm formation and when bacteria are near a plant. This research also identified genes that could be involved in root colonization, suggesting that root colonization may be controlled at the genetic level. This will help microbiologists and other researchers better understand how bacteria colonize root surfaces and how gene expression may play a part. The results may also help scientists study similar behaviors in microbes important to medicine and agriculture.

Summary

This study used promoter-reporter constructs to identify a diguanylate cyclase, DGC2884, that is expressed in the presence of a plant. The researchers characterized this enzyme further and determined that when overexpressed, it affected exopolysaccharide production, biofilm formation, motility, and pellicle formation. They also demonstrated that the N-terminal transmembrane domain, as well as a functional GGDEF active site, are required for the activity of DGC2884. Based on phenotypes associated with overexpression of DGC2884 in Pantoea sp. YR343, the scientists performed transposon mutagenesis to identify genes that no longer exhibited the unique phenotypes observed when DGC2884 was overexpressed. They identified 58 different genes with this screen and selected a subset of transposon mutants for further characterization. Interestingly, mutations affecting Type VI secretion, as well as a nucleoside-diphosphate kinase and ABC transporter, exhibited increases in colonization, while mutations affecting exopolysaccharide production resulted in decreases in colonization when compared to the wild type control. Further, they found that some mutants exhibited differences primarily in the patterns of root colonization, more than the amount of colonization, suggesting that certain patterns of root colonization may be modulated on a genetic level.

Funding

This research was supported by the Department of Energy Office of Science, Biological and Environmental Research Genomic Science Program as part of the Plant Microbe Interfaces Scientific Focus Area.


JOURNAL

PLoS ONE

DOI

10.1371/journal.pone.0248607 

METHOD OF RESEARCH

Experimental study

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

Identification of a diguanylate cyclase expressed in the presence of plants and its application for discovering candidate gene products involved in plant colonization by Pantoea sp. YR343

ARTICLE PUBLICATION DATE

21-Jul-2021

Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases

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DECEMBER 20, 2021

Microbe sneaks past tomato defense system, advances evolutionary battle

by Lauren Quinn, University of Illinois at Urbana-Champaign

tomato
Credit: CC0 Public Domain

When we think of evolution, many of us conjure the lineage from ape to man, a series of incremental changes spanning millions of years. But in some species, evolution happens so quickly we can watch it in real time.

That’s the case for Xanthomonas, the organism that causes bacterial leaf spot disease in tomato and pepper plants. Like many microbes with short generation times, it can evolve at lightning speed to acquire beneficial traits, such as the ability to elude its host’s defense system.

New research from the University of Illinois shows one Xanthomonas species, X. euvesicatoria (Xe), has evolved to avoid detection by the immune system of tomato plants.

“It’s part of the evolutionary warfare between plants and pathogens, where the plant has some defense trait and then some portion of the pathogen population evolves to escape it. The plant has to develop or acquire a new defense trait, but the process is much slower in plants compared to microbes. This study is a great example of that ongoing battle in progress. It tells us we can’t completely rely on this trait to combat bacterial spot disease caused by Xe,” says Sarah Hind, assistant professor in the Department of Crop Sciences at Illinois and co-author on a pair of recent studies published in Molecular Plant-Microbe Interactions and Physiological and Molecular Plant Pathology.

The tomato defense system keeps tabs on Xanthomonas and other bacteria with immune receptors that chemically detect flagella, the long whip-like tail structures that allow bacteria to move or “swim” through soil and plant tissues. Hind and her colleagues used laboratory and genomic modeling techniques to show one of tomato’s receptors, FLS3, no longer works to detect flagellin proteins in Xe.

Their work shows Xe’s flagellin proteins have changed by just one amino acid, but it’s enough to escape detection by tomato’s FLS3 receptors.

Graduate student and study co-author Maria Malvino says, “It was surprising to see that only one amino acid change was making all the difference. It made us wonder how binding between flagellin and FLS3 could be so dramatically altered.”

The fact that Xe can sneak past tomato’s defenses means farmers can rely even less on inherent disease resistance. Instead, they’ll have to combat the disease in other ways, such as spraying copper-based pesticides.

In some locations, including the Midwest region and in Illinois specifically, Xe isn’t as much of a problem as two other Xanthomonas species, X. perforans and X. gardneri (Xp and Xg). Tomato can still hold its own against these species for the time being, but Hind is concerned Xe will share its evasion strategy.

“X. euvesicatoria [Xe] had been the predominant strain for a long time, but within the last decade or two, it’s become less prominent and has been overtaken by another species, Xp,” she says. “Xp and Xe are really genetically close, and it’s been shown that they can share their genetic material with each other. So it wouldn’t be out of the realm of possibility that that Xe’s evasion strategy could make its way into Xp and provide the same advantage against tomato.”

Hind says the tendency of these bacteria to defeat host defenses through rapid evolution makes breeding for disease resistance difficult in tomato.

“It’s like whack-a-mole for breeders. It takes a long time to release a resistant variety. Often, by the time they go to release a new one, the pathogen population shifts,” Hind says. “And when you add to that the difficulty of maintaining all the desirable traits of a tomato, it’s a tough situation. Again, that leaves us relying on fungicides and copper treatments to keep tomato production profitable here in Illinois.”


Explore furtherScientists find new system in tomato’s defense against bacterial speck disease


More information: Maria Laura Malvino et al, Influence of flagellin polymorphisms, gene regulation, and responsive memory on the motility of Xanthomonas species that cause bacterial spot disease of solanaceous plants, Molecular Plant-Microbe Interactions (2021). DOI: 10.1094/MPMI-08-21-0211-R

Julius Pasion et al, Utilizing Tajima’s D to identify potential microbe-associated molecular patterns in Xanthomonas euvesicatoria and X. perforans, Physiological and Molecular Plant Pathology (2021). DOI: 10.1016/j.pmpp.2021.101744Journal information:Molecular Plant-Microbe InteractionsProvided by University of Illinois at Urbana-Champaign

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EUROPE, UK, IRELANDNEWS JANUARY 2022PESTS AND DISEASESRESEARCHSTUDIES/REPORTS

Smart soil bugs offer farmers an ecofriendly route to controlling diseases such as potato scab

on January 20, 2022

More in Europe, UK, Ireland:

An innovative method of controlling a range of damaging crop diseases using native, beneficial soil bacteria has emerged from a research-industry collaboration. The agri-tech innovation hopes to give farmers a way to reduce the cost and environmental damage caused by the chemical treatments currently in use to control crop diseases, such as common scab in potatoes.

The John Innes Centre team in the UK isolated and tested hundreds of strains of Pseudomonas bacteria from the soil of a commercial potato field, and then sequenced the genomes of 69 of these strains. By comparing the genomes of those strains shown to suppress pathogen activity with those that did not, the team were able to identify a key mechanism in some of the strains that protected the potato crop from harmful disease-causing bacteria.

Then using a combination of chemistry, genetics and plant infection experiments they showed that the production of small molecules called cyclic lipopeptides is important to the control of common potato scab.

These small molecules have an antibacterial effect on the pathogenic bacteria that cause common potato scab, and they help the protective Pseudomonas move around and colonise the plant roots. The experiments also showed that irrigation causes substantial changes to the genetically diverse Pseudomonas population in the soil.

First author of the study Dr Alba Pacheco-Moreno said, “By identifying and validating mechanisms of potato pathogen suppression we hope that our study will accelerate the development of biological control agents to reduce the application of chemical treatments which are ecologically damaging.

“The approach we describe should be applicable to a wide range of plant diseases because it is based on understanding the mechanisms of action that are important for biological control agents,” she added.

The study, which appears in eLife, proposes a method by which researchers can screen the microbiome of virtually any crop site, and take into account varying soil, agronomic and environmental conditions.

By exploiting advances in high-speed genetic sequencing, the method can screen the soil microbiome for therapeutic bacteria and work out which molecules are being producedto suppress pathogenic bacteria.

They can also show how these beneficial bugs are affected by agronomic factors such as soil type and irrigation.

The next step for the new approach is to put the beneficial bugs back into the same field in greater numbers or in cocktails of mixed strains as a soil microbiome boosting treatment.

Dr Jacob Malone, Group Leader at the John Innes centre and co-corresponding author of the study explains the benefits, “The massive advantage of this approach is that we are using bacterial strains that are taken from the environment and put back in the same specific biological context in larger numbers so there is no ecological damage.”

Potential methods to apply the microbiome boosters include applying the bacterial cocktails as seed coatings, as a spray or via drip irrigation.

Dr Andrew Truman, Group Leader at the John Innes Centre, and corresponding author of the study tells us about the long-term vision for this method, “In the future  it’s not the molecule produced by the bacteria that we would use, it would be the Pseudomonas strain itself. It offers a more sustainable route – we know these bacteria colonize the soil where potatoes grow, and they provide protection to the crop. Using a bacterium, you can easily grow and formulate it in an appropriate way and apply it to the field, and it is much greener than using a synthetic chemical.”

Plant diseases are an agricultural problem that leads to major losses of crops, such as potatoes. Important potato pathogens include Streptomyces scabies, a bacterial pathogen that causes potato scab, and Phytophthora infestans, an oomycete pathogen that causes potato late blight.

Pseudomonas bacteria are commonly associated with plants and have been widely studied as biological control agents, as they secrete natural products which promote plant growth and suppress pathogens. However, their use in the past has been hampered by inconsistency.

Previous studies on the suppression of potato scab have indicated a potential biocontrol role for Pseudomonas. However, progress was hampered by a lack of mechanistic knowledge. It was also widely known that irrigation can suppress Streptomyces scabies infection and now this study suggests that this is because of the effect that water has on microbial populations.

Pan-genome analysis identifies intersecting roles for Pseudomonas specialized metabolites in potato pathogen inhibition, appears in eLife.

Source: John Innes Centre. Original news story here
Photo: John Innes Centre
Journal Reference:
Francesca L Stefanato, Alba Pacheco-Moreno, Jonathan J Ford, Christine Trippel, Simon Uszkoreit, Laura Ferrafiat, Lucia Grenga, Ruth Dickens, Nathan Kelly, Alexander DH Kingdon, Liana Ambrosetti, Sergey A Nepogodiev, Kim C Findlay, Jitender Cheema, Martin Trick, Govind Chandra, Graham Tomalin, Jacob G Malone, Andrew W Truman. Pan-genome analysis identifies intersecting roles for Pseudomonas specialized metabolites in potato pathogen inhibitioneLife, 2021; 10 DOI: 10.7554/eLife.71900

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TIRUCHIRAPALLI

Watch out for bacterial leaf blight disease, farmers told

The Hindu Bureau TIRUCHI, DECEMBER 11, 2021 18:34 ISTUPDATED: DECEMBER 13, 2021 09:47 IST

Paddy crop with symptoms of bacterial leaf blight disease in a field near Pullampadi in Tiruchi district.  

It has been found in standing paddy crop in some parts of Tiruchi district

With sporadic incidence of bacterial leaf blight disease in the standing samba and thaladi paddy crop in a few parts of the district, the Agriculture Department has advised farmers to take up appropriate measures to check its spread if symptoms appear in their fields.

Samba and thaladi paddy crop has been raised on about 49,000 hectares in the district. Due to the intermittent rains during the north-east monsoon and favourable climatic conditions, symptoms of bacterial leaf blight are appearing in the crop in some places. The bacterium enters through the cut wounds in the leaf tips and edges, becomes systemic and causes orange and yellow coloured wavy margins in the leaf tips and edges.

The disease symptoms first appear as small water-soaked translucent lesions on the edges of the leaf blade which later turn yellowish orange or brown, mostly confined to the edges of the leaf with wavy margins. As the disease progresses, the yellowish orange or brown lesions cover the entire leaf blade which may turn straw coloured .This will affect the photosynthesis of the plant, thereby reducing the yield.

For easy diagnosis, the leaf blade of the plant can be cut and dipped in water. If affected, white bacterial ooze could be noticed making the water turbid. Further, the bacterial infestation could lead to secondary infestation of the fungal pathogens which causes fungal diseases in the later stage of the crop.

Clipping of the tip of the seedling at the time of transplanting, heavy rain or dew, flooding, deep irrigation water, severe wind and application of excessive nitrogen, especially late top dressing are some of the favourable conditions for the spread of the disease.

If the disease is in the initial stage, 20% cow dung extract can be sprayed twice at 15 days interval. To control developed symptoms, 120 grams of streptomycin sulphate and tetracycline hydrochloride combination along with 500 grams of copper oxychloride mixed in 200 litres of water should be sprayed per acre. The spraying should be repeated 15 days later.

Farmers could contact the officials at the nearest Agricultural Extension Centres for more details and appropriate advice, Agriculture officials said.


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HLB can infect an entire tree weeks before symptoms become apparent

Brazilian scientists have been able to measure the speed of a bacterium that causes the incurable citrus greening disease (Huanglongbing). HLB is the most devastating citrus disease in the world. Afflicted trees grow yellow leaves and low-quality fruit and eventually stop producing altogether.

Silvio A. Lopes, a plant pathologist based at Fundecitrus, research institution maintained by citrus growers of the State of Sao Paulo in Brazil: “We found that CLas can move at average speed of 2.9 to 3.8 cm per day. At these speeds a tree that is 3 meters in height will be fully colonized by CLas in around 80 to 100 days, and this is faster than the symptoms appear, which generally takes at least 4 months.”

Lopes and colleagues also studied the impact of temperature on the speed of colonization. They already knew that CLas does not multiply well in hot or cold environments, but now they have more specific data.

“We estimated that 25.7°C (78°F) was the best condition for CLas to move from one side to the other side of the tree,” said Lopes. This is the first time impact of temperature on plant colonization of CLas has been experimentally demonstrated. “The grower can use this information to select areas less risky for planting citrus trees.”

Source: eurekalert.org

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Novel Plantibodies show promise to protect citrus from Greening Disease

Citrus greening [huanglongbing (HLB)] has emerged as the most significant disease in citrus (Citrus sp.) agriculture. The disease is associated with the Candidatus Liberibacter species of bacteria. The most prevalent and virulent species in this group is Candidatus Liberibacter asiaticus. It is primarily vectored by the Asian citrus psyllid [ACP (Diaphorina citri)]. 

The bacteria and insect vector are present in many citrus orchards worldwide, including the United States, China, and Brazil. HLB often has a devastating impact on infected citrus; causing a rapid decline, with loss of fruit yield and quality and potentially leading to tree death. The bacteria has had a significant negative impact on the citrus industry, causing loss of fruit quality and yield, as well as loss of root mass, leading to tree decline. Finding a cure has been challenging due to the complexity of the CLas bacteria interactions with the citrus host and the Asian citrus psyllid. Another factor that has made it hard to recover from the disease is the tendency of the citrus industry to focus on a small number of cultivars with commercially desirable traits, but little genetic diversity.

Researchers who are working to find a citrus cultivar that is HLB resistant have a choice of either adding genetic variation through breeding with distant relatives or modifying the trees transgenically. In an article published this month in the Journal of the American Society for Horticultural Science, scientists present promising results from transgenic populations that produce antibodies that can bind with CLas proteins and reduce the bacteria’s ability to replicate. 

This study advances the research needed to test the durability and strength of any resistance conferred by expression in rootstocks to a grafted tree and will hopefully lead to the development of a novel protection strategy for HLB.

According to Ed Stover, a Research Horticulturalist with the USDA Agricultural Research Service, “The Florida citrus industry desperately needs more HLB tolerant trees. If sufficient tolerance can be conferred by a single transgenic rootstock then it will greatly expedite implementation. Any transgenic solution will require extensive validation and analyses for non-target effects and food safety.” 

For more information: doi.org

Publication date: Wed 15 Dec 2021

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PestNet: Grahame Jackson posted a new submission ‘Bacteria and plants fight alike ‘

Submission

Bacteria and plants fight alike

Phys.Org
Bacteria and plants fight alike

by Weizmann Institute of Science

by Weizmann Institute of Science
A brown blotch on a plant leaf may be a sign that the plant’s defenses are hard at work: When a plant is infected by a virus, fungus or bacterium, its immune response keeps the disease from spreading by killing the infected cell, as well as a few surrounding ones. A new study at the Weizmann Institute of Science points to the evolutionary origins of this plant immune mechanism. The study may help explain how major plant defenses work and how they may one day be strengthened to increase resilience against plant diseases that each year cause billions of dollars of crop losses worldwide.

About two years ago, scientists in the United States and Australia discovered that when a plant’s immune system kills infected cells to contain disease, this action involves a protein with a segment called TIR that produces a certain signal molecule. In a new study led by Prof. Rotem Sorek of Weizmann’s Molecular Genetics Department and Dr. Gal Ofir, then a graduate student, Sorek’s team has revealed that bacteria also use TIR as an immune mechanism, and that TIR achieves immunity in plants and bacteria in similar ways.

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