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Phys Org

Researchers identify protein target to halt citrus tree disease

June 7, 2017

University of Florida researchers may have come a step closer to finding a treatment for a disease called Huanglongbing, or citrus greening, that has been decimating citrus trees in the state. In work published this week in mSphere, an open access journal from the American Society for Microbiology, the investigators describe identifying a small protein from one bacterium living in Asian citrus psyllids—the flying insects that spread the disease as they feed on the trees—that can “cross-talk,” moving to another bacterium within the insects to silence so-called “prophage genes” containing viral material in the second bacterium, helping prevent an insect immune reaction that would likely be detrimental to both bacteria.

The , from the Wolbachia bacterium, could serve as a potential target to develop spray treatments to protect trees against the psyllids, and could potentially help the trees themselves fight off bacterial invasion, said senior study author Dean W. Gabriel, Ph.D., a professor of Plant Pathology at the University of Florida in Gainesville. Wolbachia is a natural bacterium present in up to 60 percent of all insect species. (image: citrus greening disease on mandarin oranges, wikimedia commons)

“In this case, one bacterium is doing a favor to the whole bacterial community living within the psyllid by shutting down a potential threat to survival of insect host,” Gabriel said.

Gabriel and colleagues had been looking for ways to interrupt , a disease process caused when psyllids carrying but not affected by a bacteria called Candidatus Liberibacter feed on healthy trees and inject this bacteria into the trees’ phloem, a tubular system normally used to transport sugars produced during photosynthesis from the leaves of a plant to the rest. The bacterium suppresses the plants’ defenses as it moves, Gabriel said: “It’s like a little cunning burglar sneaking in under the radar.” It impacts the tree from its roots to its shoots, he said, and has a long incubation period: “By the time disease is detected in one tree, the entire grove is thoroughly infested and much more difficult to treat.”

Citrus greening causes a severe decline in the —leaves turn a blotchy, mottled yellow color, the fruits produced are smaller and have an off-taste, and fruit yield is much reduced. The disease has devastated Florida over the last 10 or so years, Gabriel said. As a result, the state’s overall citrus production has declined by about 60 percent over the last six years. Scientists have been desperately seeking a cure.

In a series of laboratory experiments, Gabriel’s team discovered that expression of proteins that help drive the spread of the Candidatus bacteria were suppressed when they were treated with extracts from the psyllids. Further studying the process, they identified a fragment of the protein doing part of suppression as encoded by the Wolbachia strain and secreted into the insect. This protein could move within the insect into the Candidatus bacteria causing greening, bind itself to a genetic region that would normally promote prophage activity, and repress these genes.

Gabriel’s group has a grant from the U.S. Department of Agriculture to grow the Candidatus Liberibacter bacterium in culture, a process that has been difficult because, once removed from its host, the bacterium historically has destroyed itself. Now that a protein target has been identified, it can be commercially synthesized and added to culture media, where the may be more likely to grow, Gabriel said.

Explore further: Blue-bellied insects may play a role in the fight against citrus greening

Read more at: https://phys.org/news/2017-06-protein-halt-citrus-tree-disease.html#jCp

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Entomology Today

pierces-disease-foliar-symptoms1.png

Pierce’s disease is one of many plant afflictions caused by the bacterium Xylella fastidiosa and spread by a variety of insects known as sharpshooters and spittlebugs. (Photo credit: Lisa Overall, Ph.D.)

In many areas across the southern United States and California, one bacteria species complex is responsible for a long list of plant diseases: Pierce’s disease of grape, citrus variegated chlorosis, phony peach disease, plum leaf scald, alfalfa dwarf, almond leaf scorch, oleander leaf scorch, and leaf scorch of blueberry, pecan, and many shade trees. The bacterium, Xylella fastidiosa, attacks plant xylem, and its primary means of spreading is a variety of insects that specialize in drinking from that plant tissue.

In a new profile published last week in the open-access Journal of Integrated Pest Management, researchers in Oklahoma offer an in-depth guide to the biology and vectors of X. fastidiosa and the diseases it causes—with an eye toward the southern United States, where research on vectors and management practices has been less extensive than in California.

“There are unique features associated with each insect species that is capable of serving as a potential vector of X. fastidiosa. However, the first step to improving control practices for these species is to identify those insects feeding on a susceptible crop that can acquire the pathogen and transmit it to healthy plants,” says Eric J. Rebek, Ph.D., associate professor of entomology and plant pathology at Oklahoma State University and co-author of the research. The JIPM article is an adapted version of the literature review from the doctoral thesis of lead author Lisa Overall, who completed her Ph.D. at OSU in 2013 and is now an instructor of biology at Rogers State University.

“Dr. Overall conducted a survey of potential insect vectors occurring across the state, identified species harboring X. fastidiosa, and verified their ability to transmit the pathogen to susceptible plants through feeding assays. Armed with this information, we can now tell our growers what vector species to monitor, how to identify them, and how best to control them,” says Rebek.

glassy-winged-sharpshooter1

The glassy-winged sharpshooter (Homalodisca vitripennis) and other insect vectors of Xylella fastidiosa spread the bacteria when they use their piercing-sucking mouthparts to feed on plant xylem, where X. fastidiosa colonizes and multiplies. (Photo credit: Lisa Overall, Ph.D.)

As in California, the glassy-winged sharpshooter (Homalodisca vitripennis) is the most important vector of diseases caused by X. fastidiosa in the southern United States, but Overall’s research identifies a dozen other species that have been shown to vector the pathogen across the South, as well as some that reach the East Coast or even north into Canada. They include several species of sharpshooters in the family Cicadellidae, as well as three species of spittlebugs in the family Cercopidae.

Growers can employ a range of integrated pest management methods for glassy-winged sharpshooter, such as applications of imidacloprid and dinotefuran, screen barriers, and parasitoid wasps of the genus Gonatocerus. Researchers have also found that introducing a modified version of the glassy-winged sharpshooter’s gut bacteria through feeding can reduce its ability to transmit X. fastidiosa.

The JIPM profile also compiles various agricultural methods for reducing the spread of X. fastidiosa—a tricky pathogen that Overall and Rebek note is the only known insect-transmitted pathogen that can both reproduce in the insect’s foregut and spread to other plant hosts without first passing through the insect’s digestive tract. Rebek says the research will prove useful to growers in the southern United States.

“The Journal of Integrated Pest Management offers an ideal venue for publishing this type of work that typically ends up sitting on a shelf, unseen by most extension practitioners and stakeholders who can use the valuable information contained within a thesis,” he says.

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Insect Vectors and Current Management Strategies for Diseases Caused by Xylella fastidiosa in the Southern United States

Journal of Integrated Pest Management

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From Pestnet

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2017/065 First reports of a new bacterial leaf blight of rice caused by Pantoea anana and Pantoea stewartii in Benin and Togo

In Benin, surveys were carried out from 2011 to 2015 in rice fields to assess the importance of bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae (EPPO A1 List). Symptomatic leaf samples were collected and tested. As all isolates gave negative results in a multiplex PCR test for X. oryzae, further studies were conducted and revealed the presence of bacteria belonging to the genus Pantoea. Molecular and pathogenicity tests (to fulfill Koch’s postulates) confirmed that the bacteria which had been isolated from rice leaves were P. ananatis and P. stewartii (EPPO A2 List). It is noted that symptoms were  observed in all surveyed localities (14 sites) with a disease incidence varying from 30 to 100%. In Togo, surveys were also carried out in 2013 and 2014 in the main rice-growing regions (Kovié and Kpalimé) to evaluate the prevalence of plant-pathogenic bacteria. Rice leaves showing characteristic symptoms of bacterial leaf blight were collected and tested. Similarly, the bacteria which were isolated from rice leaves and grains were shown to be P. ananatis and P. stewartii. According to the authors, this is the first time that P. ananatis and P. stewartii species are found causing a leaf blight disease on rice crops in Benin and Togo. According to the EPPO Secretariat this is also the first time that P. stewartii is reported from Africa.

Source: Kini K, Agnimonhan R, Afolabi O, Milan B, Soglonou B, Gbogbo V, Koebnik R, Silué D (2017) First report of a new bacterial leaf blight of rice caused by Pantoea ananatis and Pantoea stewartii in Benin. Plant Disease 101(1), p 242. Kini K, Agnimonhan R, Afolabi O, Soglonou B, Silué D, Koebnik R (2017) First report of a new bacterial leaf blight of rice caused by Pantoea ananatis and Pantoea stewartii in Togo. Plant Disease 101(1), 241-242.

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Kiwi bacteriosis control now a reality

The international Journal of Plant Disease and Protection finally published the research financed by MIPAAF and coordinated by Prof. Giorgio M. Balestra which saw the cooperation between the Department of Agricultural Sciences (DAFNE) of Università della Tuscia and the Department of Life Sciences and Biotechnology (SVeB) of the University of Ferrara

Title: “Microparticles containing gallic and ellagic acids for the biological control of bacterial diseases of kiwifruit plants

Authors: Antonio Rossetti, Angelo Mazzaglia, Massimo Muganu, Marco Paolocci, Maddalena Sguizzato, Elisabetta Esposito, Rita Cortesi, Giorgio Mariano Balestra.

It is a lengthy study that demonstrates how it is possible to use vegetable substances to monitor the different phytopathogenic bacteria that cause much worry in all the areas growing Actinidia spp..

The cultivation of actinidia to produce kiwis has become increasingly important in Italy as well as in various areas around the world. At the same time, however, bacterial diseases are affecting its cultivation. The most dangerous is without doubt the bacterial canker caused by Pseudomonas syringae pv. actinidiae (Pss) Takikawa et al., also known as Psa, which damages all vegetative organs.

Serious damage is caused also by the drop in temperatures in spring, as is the case this year, associated with other two bacteria – Pseudomonas syringae pv. syringae (Pv) van Hall, responsible for floral bud necrosis and Pseudomonas viridiflava (Burkholder) Dowson, the bacterial blight which affects leaves and floral organs.

In Italy, prevention is carried out by using copper salts as well as a biological control agent (B. a. subsp. plantarum ceppo D747) during blossoming. Other areas outside the EU employ antibiotics with serious repercussions on the environment and leading to the development of antibiotic-resistant bacteria strains.

This study assessed the effectiveness of gallic and ellagic acids, i.e. natural substances that are easily attainable from many vegetable tissues and with high anti-microbial properties.

These natural, active principles proved effective as pure substances both in the lab and in vivo (greenhouses, then open-field actinidia orchards naturally affected by Pss, Pv and Psa).The vegetable active principles significantly reduced the various bacterial populations as well as the damage caused both through artificial contamination and by using them on orchards naturally affected by Pss, Pv and Psa.

In association with the intrinsic activities, the active principles proved particularly effective when employed through micro-formulations in micro-capsules, thus preventing alterations (physical-chemical) and enabling a controlled release of the principles over two weeks protecting all vegetable organs.

In addition, the activity of these formulations on both plant development and final production was also assessed. All parameters showed how these micro-formulations do not affect plant development (the plants treated with micro-capsules had a higher chlorophyll content in the leaves and the fruits, though with the same size and Brix level, were more compact).

The results obtained with this study represent a significant contribution towards the attainment of formulations that can successfully counter dangerous micro-organisms like those affecting actinidia with a sustainable/organic approach.

Reducing the use of copper salts to protect crops is a process dictated by the EU. As of January 2018, further reductions of Cu++ will be introduced, thus valid alternatives must be found.

This study suggests how gallic and ellagic acids, when formulated together in microformulations, can be successfully employed in sustainable/organic defence strategies against pathologies like those currently affecting actinidia.

The active principles and technology used in this research constitute an important base, as what described can be applied to different pathogens/ crops, thus reducing the use of chemicals and therefore chemical residue.

Additional studies are currently being carried out concerning organic nano-formulations for the protection of different crops both in the fields and during the storage and commercialisation stages. They aim at a further reduction of the (natural) active principles used, at a prolonged controlled release and at making it so that formulations can penetrate fruit/plants and target the pathogen.

For further information:
Prof. Giorgio M. Balestra
DAFNE (Department for Agriculture, Forestry, Nature and Energy)
University of Tuscia
Via S. Camillo de Lellis
01100 Viterbo
Tel.: (+39) 0761 357474
Cell.: (+39) 333 4246404
Fax: (+39) 0761 357473
Email: balestra@unitus.it
Web: www.unitus.it
Skype: giorba5618
Personal page: www.dafne.unitus.it/web/interna.asp?idPag=1118

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Black Rot Disease Affecting Cabbage Growing Season

Posted: May 04, 2017 6:33 PM CDT Thursday, May 4, 2017 7:33 PM EDTUpdated: May 04, 2017 6:33 PM CDT Thursday, May 4, 2017 7:33 PM EDT

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NEAR EDINBURG – Many Rio Grande Valley farmers are trying to recoup their losses after the black rot disease invaded their cabbage crops.

Edinburg farmer Tommy Hanka’s company, Tommy Hanka Farms, grows cabbage as well as other cool season vegetables in a 1,000-acre farm land.

Hanka said the recent record heat was terrible news for farmers.

“Well, it affected me on my green cabbage and red cabbage. I had some black rot issues. I ended plowing under over 75 percent… It was just not marketable. It was a real disaster, a real train wreck this year,” he said.

Hanka said farmers and the local economy are affected when there is a bad growing season.

“The box companies don’t get paid, the trucking companies don’t get paid because there is no product to move. There’s no produce to sell. We just can’t employ these guys because there is no work,” he said.

Texas A&M AgriLife Extensions vegetable specialist Juan Anciso said other farmers also saw big losses this growing season.

He said about half of the 3,000 acres of cabbage planted this season was lost due to black rot.

“Warm weather – for example for bacteria – it increases their reproduction rate so you have more bacteria,” he said. “And we have had a serious problem with black rot, which is a bacterial pathogen in cabbage. It’s a disease that has been around since cabbage has been around. But we haven’t had these problems since the 1980s.”

Anciso explained black rot enters through the leaves and causes them to turn black and brown, making the cabbage unsellable.

But Hanka said although this year’s season was extremely tough he’s not giving up.

“Let’s move on. We are going to stick to the game plan. We are going to do the same thing we did this year. We are going to be here next year…. It’s only going to get better,” he said.

Anciso said Texas AgriLife will continue to look for black rot resistant strains of cabbage. He said farmers will then be better equipped to turn a profit during unusually warm season.

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Subject: Cucurbit wilt- Erwinia tracheiphila

Scientific American

https://www.scientificamerican.com/article/how-bacteria-laden-poop-is-killing-american-squash-and-melons/

  •  spotted cucu beet
  • Spotted cucumber beetle, one of two species confirmed to carry the Erwinia trachaephila  bacterium, on a zucchini leaf. Credit: Scott Chimelski

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Huanglongbing is causing concern in California – California Agriculture News | California Agriculture


https://californiaagtoday.com/wp-content/themes/calagtodaynew/js/html5.js?ver=3.7.3

April 27, 2017

Increase of Huanglongbing in California Causes Concern

 By Brian German, Associate Broadcaster

Southern California has seen a concerning increase in the amount of trees that are infected with Huanglongbing, or citrus greening disease. California Ag Today discussed the news with Beth Grafton-Cardwell, an IPM Specialist and Research Entomologist for the UC Riverside Entomology Department stationed in the San Joaquin Valley.  She agreed that there is an increased concern surrounding HLB.

“It kind of exploded this fall, and it’s kind of continuing. And, that’s not unexpected. The Department of Food and Ag removes only the trees that are polymerase chain reaction – positive. And sometimes, it takes one to two years for a tree for you to be able to detect the bacteria using that method,” Grafton-Cardwell said.

Beth Grafton-Cardwell

There is no cure currently available for HLB, so once a tree is infected, it will eventually die.  Researchers continue working to find a possible cure for HLB, or at the very least, a more effective means of diagnosing infected trees. “Most of the techniques that are going to help us cure or prevent the disease from being transmitted are five to ten years away. Yet, I think we’re going to see a rapid expansion of the disease in Southern California in this coming year,” Grafton-Cardwell said.

Early detection is one of the most important things.  Grafton-Cardwell noted that many farmers are “helping to get the research accomplished and, for example, helping to get early detection techniques tested, and things like that so that we can try and stay on top of the disease.”

In California, production trees are not required to be screened, but many nurseries are now shifting towards putting all of their trees under screening in an effort to be more proactive in guarding against the spread of HLB.

Biological controls like Tamarixia are used as a means to reduce the number Asian citrus psyllids, which cause HLB, but that type of control method is not designed to completely eradicate insects.

“They’re starting to release the Tamarixia Wasps in Bakersfield. So we’re getting them up into the San Joaquin Valley so they can help out in those urban areas,” Grafton-Cardwell said.

Dogs are also used as a means to detect infected trees, but there is still a need for more effective techniques.  “A large team of dogs can do maybe 1,000 acres a day, and we’ve got 300,000 acres of commercial citrus. So I think we need a multitude of techniques,” Grafton-Cardwell said.

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