Feeds:
Posts
Comments

Archive for the ‘Insect-plant interaction’ Category

IMustapha KSU248hessfly_adultHessian Fly

Mustapha El-Bouhssini (MS ’86, PhD ’92) Aleppo, Syria, is a global authority on plant resistance to insects in grains and has worked to develop crop varieties resistant to several important arthropod pests.

He recently received the Distinguished Scientist Award from the International Branch of the Entomological Society of America for significant contributions to entomological research.

El-Bouhssini serves as an adjunct faculty member in the Department of Entomology. This position has helped initiate collaborative projects between K-State and ICARDA on Hessian fly genetics and resistance in barley to the Russian wheat aphid.

From the KSU AgReport Spring 2015

Read Full Post »

http://www.vtnews.vt.edu/articles/2014/08/082214-outreach-oiredspeckledbeetle.html

BLACKSBURG, Va., Aug. 22, 2014 – An invasive weed poses a serious and frightening threat to farming families in Ethiopia, but scientists from a Virginia Tech-led program have unleashed a new weapon in the fight against hunger: a tiny, speckled beetle.

The weed, called parthenium, is so destructive that farmers in the east African nation have despairingly given it the nickname “faramsissa” in Amharic, which, translated, means “sign your land away.” Farmers have doused the weed in pesticides and ripped it out with their hands, but it has only spread further.

After a decade-long effort, scientists from the Integrated Pest Management Innovation Lab released a parthenium-eating beetle called Zygogramma bicolorata.

“Extensive research has shown us that the beetle eats and breeds only on parthenium leaves,” said Muni Muniappan, director of the Integrated Pest Management Innovation Lab, a program funded by the U.S. Agency for International Development. “It’s been tested in Australia, India, South Africa, and Mexico with similar results.”

Parthenium is native to the Americas, where a suite of natural enemies that includes the Zygogramma beetle keeps the weed in check. But in the early 1970s, parthenium entered Ethiopia in shipments of food aid from the United States. With no serious contenders, the plant flourished.

In the past three decades, parthenium has become the second most common weed in Ethiopia, suppressing the growth of all other plants and wreaking havoc in the fields and gardens of smallholder farmers.

“The plant is an aggressive invader. A single plant can produce 25,000 seeds and completes its life cycle in six to eight weeks,” said Wondi Mersie, a Virginia State University professor and principal investigator of the Virginia Tech-led project. “It displaces native species, affects human health, and negatively impacts quality of life.”

Parthenium is poisonous. People who come into contact with it can suffer from skin irritations, bronchial asthma, and fever. Animals that eat it can experience intestinal damage, and their milk and meat becomes bitter and useless.

The Innovation Lab built a quarantine facility in 2007 to ensure that the pea-sized beetle had eyes for parthenium alone. Testing under quarantine is one of the crucial steps involved in biological control, a rigorously tested method where an invasive species’ natural enemies are used to regulate it.

“Opportunities for biocontrol in Ethiopia are huge, and there would be enormous benefits,” said Arne Witt, a biologist not associated with the Virginia Tech program who works with UK-based nonprofit CABI.

After a laborious process involving many agencies and much red tape, Zygogramma bicolorata was approved for release. Researchers collaborated with farmers, local government officials, and extension agents to construct a breeding facility and increase the number of beetles.

Finally, on July 16, the Innovation Lab team joined a group of about 30 scientists and farmers in Wollenchitti, Ethiopia, to release the insects. The group moved from parthenium patch to parthenium patch, dumping beetles from containers.

Ethiopian researchers will monitor the sites and assess the impact. As a second step, scientists are poised to release a stem-boring weevil that will join Zygogramma. But even these measures will not eliminate parthenium from Ethiopian farmland.

“Biocontrol is control, not eradication,” said Witt. “But it means that a farmer sprays less pesticide. We need an integrated strategy, and biological control is the most cost-effective strategy – let’s embrace it.”

The Integrated Pest Management Innovation Lab is managed by the Office of International Research and Education at Virginia Tech.

Dedicated to its motto, Ut Prosim (That I May Serve), Virginia Tech takes a hands-on, engaging approach to education, preparing scholars to be leaders in their fields and communities. As the commonwealth’s most comprehensive university and its leading research institution, Virginia Tech offers 225 undergraduate and graduate degree programs to more than 31,000 students and manages a research portfolio of $496 million. The university fulfills its land-grant mission of transforming knowledge to practice through technological leadership and by fueling economic growth and job creation locally, regionally, and across Virginia.

Written by Kelly Izlar

Read Full Post »

The Ecologist

2nd August 2014

http://www.theecologist.org/News/news_round_up/2501027/brazil_gmo_bt_corn_no_longer_resists_pest_attack.html

 

fall aw 382052

Fall armywom larva in a sweetcorn ear.

Photo: Judy Baxter via Flickr

 

 

 

 

 

GMO corn varieties that express insecticidal Bt toxins are failing in the field, with reports of infestations of the fall armyworm on Bt corn in Brazil and the USA. Now the EU is poised to approve one of the failing varieties for use on European farms.

There are barely any non-GMO seeds available … it is very uncomfortable that the companies are blaming the farmers.

The Association of Soybean and Corn Producers of the Mato Grosso region (Aprosoja-MT) has complained that its members’ genetically modified ‘Bt corn’ crops are no longer resistant to insect pests.

That’s corn which has been genetically modified to produce an insecticidal toxin that repels or kills pests – principally Spodoptera frugiperda, also known as fall armyworm, corn leafworm or southern grassworm.

The Bt toxin is meant to provide protection to the crop without needing to be sprayed with insecticide. But reports from farmers allege that the Bt corn is actually less resistant to attack by Spodoptera caterpillars than non-GMO varieties.

Now farmers have been forced to apply insecticides to their crops, racking up additional environmental and financial costs – after having already paid a premium price for the GM corn seeds.

Deceptive advertising?

The loss of resistance to Bt corn caterpillars was identified by Aprosoja-MT in March, when the first reports of emerged from Mato Grosso producers frightened by what they saw on the field.

Aprosoja-MT began to gather technical reports with data, photos and economic analysis of producers’ financial losses, estimated at $54 per hectare in terms of extra insecticide and application costs.

The association is now calling on Monsanto, DuPont, Syngenta, and Dow companies to offer solutions as well as compensate the farmers for their losses.

“We want companies point to a rapid solution to the losses and also a way to compensate those who were harmed”, says the president of Aprosoja-MT, Ricardo Tomczyk. “It is a typical case of product that promised an outcome that was never delivered – i.e., deceptive advertising”

Blame the farmers

The association has given the seed companies ten days in which to offer solutions to the problems presented by the GM varieties, as well as a way to compensate the losses faced by farmers in Mato Grosso.

But Monsanto and other seed companies are unlikely to accommodate the farmers. According to Reuters, “seed companies say they warned Brazilian farmers to plant part of their corn fields with conventional seeds to prevent bugs from mutating and developing resistance to GMO seeds.”

However Tomczyk responded that the seed companies instructions on creating insect refugia of non-GMO corn were vague and hard to follow. And in any case, he added, “There are barely any non-GMO seeds available … it is very uncomfortable that the companies are blaming the farmers.”

Aprosoja-MT is attempting to negotiate an agreement with the seed companies, but insists that farmers are ready to sue for their pesticide costs.

Not for the first time

Earlier this year, a similar problem arose in the US, when scientists confirmed that corn-destroying rootworms had evolved to be resistant to the GMO corn engineered to kill them.

And according to the non-profit TestBioTech, the GMO maize 1507 -which may soon be approved for cultivation in the European Union – is one of those now failing in Brazil.

This maize variety, developed by US companies Pioneer/DuPont and Dow, combines a Bt insecticidal protein with tolerance to glufosinate herbicides.

According to a study published in the journal Crop Protection, certain pests in Brazil are becoming resistant to this maize line only few years after market approval.

Farias et al. (2014) found resistant populations of Spodoptera in the federal states Bahia and Rio Grande del Sul. According to the authors, development of resistance in fall armyworm was first noticed in 2012, the third year after the start of cultivation of maize 1507 in Brazil.

Industry response – add more GM traits

The industry response to such loss of efficacy is not to encourage biodiversity, but to further modify the organisms, according to TestBioTech:

“The case of Brazil is an example for an overall trend showing that nearly twenty years after the start of commercialization of Bt crops, there are problems in several countries growing this kind of genetically engineered crop.

“Industry tries to tackle this issue by commercialization of so called ‘stacked traits’ that produce several different Bt toxins. The best known example is Monsanto’s SmartStax maize that produces six different Bt toxins.”

TestBioTech also argues that the European Food Standards Agency should re-consider its likely approval for maize 1507 given the fast developing resistance to it among pests, also citing “fundamental data gaps in risk assessment.”

Further information:

Farias et al. (2014), Field-evolved resistance to Cry1F maize by Spodoptera frugiperda (Lepidoptera: Noctuidae) in Brazil
Industry influence in the risk assessment of genetically engineered Maize 1507 (2014)
Genetically engineered maize 1507 – Industry and EFSA are disguising true content of Bt toxin in the plants (2014)
High-Level-Risk-Maize 1507 (2013)Testbiotech figure: Bt crops: Resistance development in pest insectsA fall armyworm (Spodoptera frugiperda) caterpillar in a sweetcorn cob. Photo: Judy Baxter via Flickr.

Read Full Post »

PUBLIC RELEASE DATE: 3-Jul-2014

Contact: Caroline Wood
cwood4@sheffield.ac.uk
44-7771-765335
Society for Experimental Biology

http://www.eurekalert.org/pub_releases/2014-07/sfeb-owh062714.php

 

Many modern crops have high productivity, but have lost their ability to produce certain defence chemicals, making them vulnerable to attack by insects and pathogens. Swiss scientists are exploring ways to help protect 21st century maize by re-arming it with its ancestral chemical weapons.

The researchers, led by Dr Ted Turlings (University of Neuchâtel, Switzerland), found that many varieties of modern maize have lost their ability to produce a chemical called E-β-caryophyllene. This chemical is normally produced by traditional ancestors of modern maize roots when the plant is under attack from invading corn rootworms. The chemical attracts ‘friendly’ nematode worms from the surrounding soil which, in turn, kill the corn rootworm larvae within a few days.

The scientists used genetic transformation to investigate if restoring E-β-caryophyllene emission would protect maize plants against corn rootworms. After introducing a gene from oregano, the transformed maize plants released E- β-caryophyllene constantly. As a result, these plants attracted more nematodes and suffered less damage from an infestation of Western Corn Rootworms.

“Plant defences can be direct, such as the production of toxins, or indirect, using volatile substances that attract the natural enemies of the herbivores” says lead scientist, Dr Ted Turlings (University of Neuchâtel, Switzerland). One of the types of toxins that maize plants produce against their enemies is a class of chemicals called benzoxazinoids. These protect maize against a range of insects, bacteria and fungi pests, yet some species have developed resistance against these toxins and may even exploit them to identify the most nutritious plant tissues.

These results show how knowledge of natural plant defences can be practically applied in agricultural systems. “We are studying the wild ancestor of maize (teosinte) to find out which other chemical defences may have been lost during domestication of maize” Dr Turlings added. “These lost defences might then be reintroduced into modern cultivars”.

Read Full Post »

http://www.newswise.com/articles/uf-ifas-researchers-find-chemicals-that-treat-citrus-greening-in-the-lab

Released: 6/4/2014 9:35 AM EDT
Source Newsroom: University of Florida
more news from this source

PLOS Pathogens
Newswise — GAINESVILLE, Fla. — A University of Florida research team is cautiously optimistic after finding a possible treatment in the lab for citrus greening, a disease devastating Florida’s $9 billion citrus industry. It is the first step in a years-long process to bring a treatment to market.
Claudio Gonzalez and Graciela Lorca led the research team that examined three biochemical treatments: phloretin, hexestrol and benzbromarone.
The team sprayed greenhouse tree shoots separately with one of the three biochemicals and were successful in stopping the bacteria’s spread, particularly with benzbromarone, which halted the bacteria in 80 percent of the infected trees’ shoots. They expect to begin field experiments with this treatment later this year. Their research was published in late April by the online open access journal PLOS Pathogens.
Gonzalez and Lorca are UF associate professors in the microbiology and cell science department, part of UF’s Institute of Food and Agricultural Sciences. The team also works under the auspices of the UF Genetics Institute.
The researchers found that benzbromarone targets a specific protein, known as LdtR, in the citrus greening bacterium. When benzbromarone binds to LdtR, it inactivates the protein, which disrupts a cell wall remodeling process critical for the greening bacterium’s survival inside a citrus tree.
“As a consequence of the chemical treatment, several genes were not expressed and the bacteria were not able to survive inside the phloem of the plant where osmotic pressure from sugar is high,” said Fernando Pagliai, a co-author of the study and a UF graduate assistant. Phloem is the living tissue that carries organic nutrients to all parts of the plant.
Benzbromarone is typically used to treat gout in humans.
Citrus greening first enters the tree via a tiny bug, the Asian citrus psyllid, which sucks on leaf sap and leaves behind bacteria. The bacteria then move through the tree via the phloem. The disease starves the tree of nutrients, damages its roots and the tree produces fruits that are green and misshapen, unsuitable for sale as fresh fruit or for juice. Most infected trees die within a few years.
The disease has already affected millions of citrus trees in North America and could wipe out the industry in the next decade if a viable treatment is not found.
UF/IFAS researchers have attempted everything from trying to eradicate the psyllid to breeding citrus rootstock that shows better greening resistance. Current methods to control the spread of citrus greening include removing and destroying infected trees.
Florida growers say they desperate for a treatment that will work.
“Every grower I know is just hanging by their fingernails, hoping and praying for a new discovery for treatment,” said Ellis Hunt Jr. of Lake Wales, whose family has been in the citrus business since 1922.
Industry experts, though, say it could be five to seven years before a new active-ingredient product could be commercially available because of the amount of time field testing takes and government regulations.
Jackie Burns, director of the UF/IFAS Citrus Research and Education Center in Lake Alfred, said because of those regulations, which are meant to ensure a safe food supply, researchers can’t accelerate testing and approval. And she noted that although the initial results of the research are promising, there is no guarantee the compounds will work under field conditions.
Other co-authors on the paper: Christopher Gardner, a research technician in microbiology and cell science; Max Teplitski, an associate professor in soil and water science; Svetlana Folimonova, an assistant professor in plant pathology; Lora Bojilova, a research technician; Anastasia Potts, a graduate assistant; and Amanda Sarnegrim and Cheila Tamayo, undergraduate students.

Read Full Post »

Image

28 April 2014 Newcastle University

Bombarding pests with smells from many different plants temporarily confuses them and hinders their ability to feed, new research has shown.

Biologists at Newcastle University, UK, have been exploring the potential of harmless plant volatiles as an alternative to pesticides in greenhouses.

Testing a phenomenon known as the ‘confusion effect’ – whereby animals and humans become inefficient at a task when they are bombarded with lots of distracting information – the team pumped a mixture of plant smells into a greenhouse growing tomato plants.

Exposing the whitefly to a heady aroma of cucumber, courgette, watercress, watermelon, cabbage and bean, the team found the insects became temporarily disorientated.

Like other insect pests, whitefly feed by pushing their long mouthpiece – or stylets – into the leaf until it reaches the plant’s main source of nutrients travelling through the phloem. Weaving their way between the plant cells to reach the sap is technically challenging and the team found the whiteflies failed to feed while they were being bombarded with the different plant chemicals.

Publishing their findings this week in the academic journal Agronomy of Sustainable Development, research leads Dr Colin Tosh and Dr Barry Brogan said this method of control could be an important step towards a more sustainable method of pest control.

“It’s like trying to concentrate on work while the TV’s on and the radio’s blaring out and someone’s talking to you,” explains Dr Tosh, based in Newcastle University’s School of Biology. “You can’t do it – or at least not properly or efficiently – and it’s the same for the whitefly.

“Whiteflies use their sense of smell to locate tomato plants. By bombarding its senses with a range of different smells we create ‘sensory confusion’ and the result is that the insect becomes disorientated and is unable to feed.

“Because the effect is temporary – we saw it last no more than 15 hours – it’s unlikely this method alone could be used to control crop pests. But this is an easy and safe way of buying the plants time until their own chemical defence mechanisms kick in. Used in conjunction with other methods, sensory confusion opens up a whole new area in sustainable pest control.”

Trialeurodes vaporariorum – or whitefly – is a major worldwide pest of greenhouse crops and is traditionally controlled using chemical pesticides or biological methods such as parasites.

Previous studies have shown that whitefly become ‘restless’ when a number of plant species are mixed together rather than being exposed to a single crop. The aim of this latest research, funded by the Natural Environment Research Council (NERC), was to artificially create this mixed environment for a single crop greenhouse.

Measuring the time it took from the insect settling on a plant to accessing the plant sap, the team showed that hardly any of the whiteflies exposed to a range of smells started feeding from the phloem within 15 hours from the time of exposure. By comparison, the majority of whiteflies exposed to just the single smell released by the tomato plants started feeding within this time.

Dr Brogan, also based in the School of Biology, adds: “Plants talk to each other when they are under attack – producing chemicals which warn other plants close by of the threat. At the same time, they produce a chemical which is unpleasant to the predator.

“But this response doesn’t happen immediately, so if we can confuse the insects long enough to give the plants time to defend themselves this may go someway to reducing crop losses.”

The team have now started the next phase of the study to investigate ways of helping plants to talk to each other and better switch on their defences.

Full bibliographic information
“Control of tomato whiteflies using the confusion effect of plant odours”. Colin Tosh and Barry Brogan. Agronomy for Sustainable Development. DOI 10.1007/s13593-014-0219-4

http://www.alphagalileo.org/ViewItem.aspx?ItemId=141300&CultureCode=en&dm_i=1ANQ,2F2AB,6LPWNX,8SEQE,1

Read Full Post »

Image

Released: 4/1/2014 8:00 AM EDT
Source Newsroom: Michigan Technological University

http://www.newswise.com/articles/view/615881/?sc=swtn

Newswise — As the Earth’s human population marches toward 9 billion, the need for hardy new varieties of grain crops has never been greater.

It won’t be enough to yield record harvests under perfect conditions. In an era of climate change, pollution and the global spread of pathogens, these new grains must also be able to handle stress. Now, researchers at Michigan Technological University have identified a set of genes that could be key to the development of the next generation of super rice.

A meta-data analysis by biologist Ramakrishna Wusirika and PhD student Rafi Shaik has uncovered more than 1,000 genes in rice that appear to play key roles in managing its response to two different kinds of stress: biotic, generally caused by infectious organisms like bacteria; and abiotic, caused by environmental agents, like nutrient deficiency, flood and salinity.

Traditionally, scientists have believed that different sets of genes regulated plants’ responses to biotic and abiotic stress. However, Wusirika and Shaik discovered that 1,377 of the approximately 3,800 genes involved in rice’s stress response played a role in both types stress. “These are the genes we think are involved in the cross talk between biotic and abiotic stesses,” said Wusirika.

About 70 percent of those “master” genes are co-expressive—they turn on under both kinds of stress. Typically, the others turn on for biotic stress and turn off for abiotic stress.

The scientists looked at the genes’ response to five abiotic stresses—drought, heavy metal contamination, salt, cold and nutrient deprivation—and five biotic stresses—bacteria, fungus, insect predation, weed competition and nematodes. A total of 196 genes showed a wide range of expressions to these stresses.

“The top genes are likely candidates for developing a rice variety with broad stress-range tolerance,” Wusirika said.

Next, they would like to test their findings. “We want to do experimental analysis to see if five or 10 of the genes work as predicted,” he said.

Their study is described in the paper, “Machine Learning Approaches Distinguish Multiple Stress Conditions using Stress-Resposive Genes and Identify Candidate Genes for Broad Resistance in Rice,” published in the January edition of Plant Physiology.

Read Full Post »

Midwest Producer

No crisis yet: With confirmed resistance, western corn rootworm is worthy of being watched

No crisis yet With confirmed resistance, western corn rootworm is worthy of being watched

 

It isn’t an epidemic and it won’t shut down corn production anytime soon. However, researchers have confirmed that western corn rootworms have developed resistance to Bt corn hybrids that express the Cry3Bba trait in some areas of Nebraska.

University of Nebraska-Lincoln entomologist Lance Meinke said testing in areas of northeast and southwest Nebraska has been conducted over the last few years to determine the cause of “greater than expected rootworm injury,” (GPE) observed in some cornfields.

We started seeing some fields with GPE as early as 2011,” Meinke said. “Our testing has included evaluation of factors other than western corn rootworm that could have caused corn plant damage. We’ve used a bioassay technique to assess the susceptibility of rootworms to various rootworm-active Bt traits. In that process, we collect the western corn rootworm beetles from GPE fields, bring them back to the laboratory and provide an environment for them to lay eggs.”

In their lab, Meinke’s team placed newly hatched

larvae on corn plants at the five-leaf stage under identical conditions.

“We compared survival of GPE collected populations and susceptible control population across the different Bt events on the market,” Meinke said. “We also did some on-farm trials, testing across different rootworm Bt traits to evaluate the level of rootworm control each provided in areas where western corn rootworm populations resistant to the Cry3Bb1 trait have shown up.”

What Meinke and hit team have found is that farmers who have planted corn hybrids that express the Cry3Bb1 trait numerous years in a row have provided a natural selection environment for western corn rootworms.

“When a few of the rootworms survive the Bt corn trait, they reproduce larger numbers of survivors and then the number of individuals in that population that can survive exposure to the Bt trait continues to expand,” Meinke said. “Resistance doesn’t mean the entire field will be a failure. Typically, this scenario begins with just a few survivors and it takes several years for the resistant proportion of a population to increase. That means the level of control the Bt corn hybrid provides in that field may decline over time as more rootworms survive exposure to the Bt trait.”

What researchers like Meinke hope to convey to corn growers is that western corn rootworm resistance isn’t yet a crisis, but it could become much more difficult to manage rootworms if available Bt technologies are overused and resistance to many or all rootworm Bt traits evolves.

“We need to understand that it takes millions of dollars and as long as 10 years to develop a new corn transgenic trait,” Meinke said. “That means, if we lose the technology in our current Bt hybrids, we won’t necessarily have a new one to replace it.”

Alternating tactics on a farm over years is a good way to proactively reduce the chance of resistance occurring or addressing resistance that has evolved.

“Crop rotation is the best tool,” Meinke said. “Generally, one year of soybeans in a field with resistant western corn rootworms wipes out that population. The beetles will lay eggs that hatch, but when larvae try to feed on soybean plants, they don’t find the nutrients they need and they die.”

If some level of crop rotation can be worked into the overall farm plan, over time rootworm populations densities will be suppressed and all tactics will work better.

Corn prices have enticed growers to plant corn-on-corn in recent years, and Meinke said industry specialists know that some operations may face significant risk and/or profit loss if they change their cropping strategy.

“In continuous corn, moving away from single trait Bt hybrids to pyramided trait hybrids (i.e. two or more Bt traits expressed in a hybrid that target the same pest) provides a high level of rootworm control and better resistance management,” Meinke said. “Resistance will likely evolve more slowly to a pyramid hybrid than a single trait hybrid because the insect population has to overcome two Bt traits and not just one.”

Through research, Meinke and his collaborators have found that strategic use of insecticides can be useful to complement other rootworm management tactics, but should be used on an as-needed basis.

“Use of a soil insecticide with a single trait hybrid that is failing the field can improve rootworm protection, but selection for resistance to the trait will continue,” Meinke said. “In most cases, adding soil insecticide over the top of pyramid trait hybrids at planting will not significantly improve rootworm protection but will only add to rootworm management costs.”

Integrated pest management (IPM) plans that utilize a variety of Bt or conventional corn hybrids, crop rotation, careful use of insecticide and other pest management practices give growers the best opportunity to maximize profits and manage western corn rootworm.

“IPM isn’t a use of every tool in every field during one season,” Meinke said. “Working with crop consultants to identify the best integrated plan for each field and farm will bring the best possible results.

“I want to encourage farmers to move away from the ‘silver bullet’ approach with Bt hybrids,” Meinke added. “The Bt traits should be viewed as one of many pest management tools we can incorporate into an effective IPM framework.””

http://www.midwestproducer.com/news/crop/no-crisis-yet-with-confirmed-resistance-western-corn-rootworm-is/article_7adb90b0-99a3-11e3-9d66-001a4bcf887a.html

Copyright 2014 Midwest Producer. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

Read Full Post »

15-Jan-2014

http://www.eurekalert.org/pub_releases/2014-01/mpif-apa011514.php

Contact: Dr. Wilhelm Boland
boland@ice.mpg.de
49-364-157-1201
Max Planck Institute for Chemical Ecology 

Researchers discover an additional level of this insect-plant symbiosis

This news release is available in German.

 IMAGE: Leaves of Acacia hindsiiplants colonized by mutualistic (left) or parasitic ants (right). Plants associated with the mutualistic ant speciesPseudomyrmex ferrugineus are visibly healthier than their neighbors….

Click here for more information.

The biological term “symbiosis” refers to what economists and politicians usually call a win-win situation: a relationship between two partners which is beneficial to both. The mutualistic association between acacia plants and the ants that live on them is an excellent example: The plants provide food and accommodation in the form of food bodies and nectar as well as hollow thorns which can be used as nests. The ants return this favor by protecting the plants against herbivores. Researchers at the Max Planck Institute for Chemical Ecology in Jena, Germany, have now found that ants also keep harmful leaf pathogens in check. The presence of ants greatly reduces bacterial abundance on surfaces of leaves and has a visibly positive effect on plant health. Study results indicate that symbiotic bacteria colonizing the ants inhibit pathogen growth on the leaves. (New Phytologist, January 6, 2014, doi: 10.1111/nph.12664)

Myrmecophytes are plants which live in a symbiotic relationship with ants. The acacia species Acacia hindsii, which is native to tropical dry forests in Central America, is such a myrmecophyte. Its inhabitants are ants of the genus Pseudomyrmex. The ants depend completely on their host plants for nectar and the food bodies rich in proteins and lipids which they require. The acacia also provides shelter, the so-called domatia, in the hollows of its swollen thorns. In return for room and board, mutualistic Pseudomyrmex ferrugineus ants become bodyguards, protecting their host against herbivores and competing plants. However, some ants also benefit from the plant’s services without giving anything in return, such as the parasitic ant species Pseudomyrmex gracilis.

Scientists at the Max Planck Institute for Chemical Ecology have now looked more deeply into the insect-plant interaction, asking whether the tiny bodyguards also provide protection against microbial pathogens. They compared the leaves of acacia plants which were inhabited by either mutualistic or parasitic ants to leaves from which ants had been removed. Intriguingly, the leaves of acacia colonized by parasitic ants showed more leaf damage from herbivores and microbial pathogens than did the leaves that had mutualistic ants. The presence of the right symbiotic partner seemed to have a positive effect on the plant’s health.

 IMAGE: MutualisticPseudomyrmex ferrugineus ants on an acacia plant. The ants love nectar from the plant’s extrafloral nectaries.

Click here for more information.

Analysis of the surfaces of the leaves revealed that the number of plant pathogens as well as of necrotic plant tissues increased considerably when mutualisticPseudomyrmex ferrugineus ants were absent. These plants also showed strong immune responses in the form of an increased concentration of salicylic acid, a plant hormone which regulates defense against pathogens. Detailed analysis of the bacterial composition on the surfaces of the leaves suggested that the presence of mutualistic ants changed the bacterial populations and reduced harmful pathogens. Although far less pronounced, this effect could also be observed in parasitic ants.

How antimicrobial protection is transferred from ants to plant is still unclear. Chilean researcher Marcia González-Teuber, first author of the publication, suspected that microorganisms associated with the ants might play a role. Because acacia leaves are touched mainly by ants’ legs, she extracted the legs of mutualistic and parasitic ants and tested the effect of the extracts on the growth of bacterial pathogens in the lab. Plant pathogen Pseudomonas syringae was sensitive to the application of leg extracts of both ant species and its growth was inhibited. In the next step, the scientist isolated and identified bacteria from the legs of the ants. In lab tests, bacterial strains of the genera Bacillus, Lactococcus, Pantoeaand Burkholderia effectively inhibited the growth of Pseudomonas bacteria isolated from infected acacia leaves. Interestingly, some of the bacterial genera associated with the ants are known to produce antibiotic substances.

The Jena researchers have thus added another level of interaction to the symbiosis between ants and their host plants. “Such mutualistic relationships are much more complex than previously thought. In the future, we will have to include bacteria and other microorganisms in our considerations,” says Wilhelm Boland, head of the Department of Bioorganic Chemistry at the Max Planck Institute. Studies on symbiotic relationships between ants and myrmecophytic plants should not overlook the role of bacterial partners that help the ants protect “their” plants. [AO]

###

Original Publication:

González-Teuber, M., Kaltenpoth, M., Boland, W. (2014). Mutualistic ants as an indirect defence against leaf pathogens. New Phytologist, DOI 10.1111/nph.12664

http://dx.doi.org/10.1111/nph.12664

Further Information:

Prof. Dr. Wilhelm Boland, Max Planck Institute for Chemical Ecology, E-Mail boland@ice.mpg.de, Tel.: +49 3641 57 1201

Read Full Post »

« Newer Posts