- Author: Emily C. Dooley, UC Davis
Pathogen native to U.S. but had not infected pines until recently
Fungal pathogens that cause die-back in grape, avocado, citrus, nut and other crops has found a new host and is infecting conifer trees causing pine ghost canker in urban forest areas of Southern California.
The canker can be deadly to trees.
Scientists from University of California, Davis, first spotted evidence that the pathogens had moved to pines during a routine examination of trees in Orange County. Over four years, they found that more than 30 mature pines had been infected in an area of nearly 100 acres, according to a report in the journal Plant Disease.
Akif Eskalen, a professor of Cooperative Extension in the Department of Plant Pathology at UC Davis, suspects drought and other stress conditions brought on by climate change weakened the tree species, making it more susceptible to new threats.
“We have been seeing this on pine trees for the last several years,” he said. “Our common crop pathogens are finding new hosts.”
Pine ghost canker – caused by the fungal pathogens Neofusicoccum mediterraneum and Neofusicoccum parvum – usually infects the lower part of a tree's canopy, killing branches before moving on to the trunks. This dieback in some cases can be deadly.
Points of entry
The pathogens infect a tree by entering through wounds caused by either insects such as red-haired pine bark beetles or pruning – meaning trees in managed or landscaped areas could be at risk. Another route is via tiny natural openings known as lenticels that fungi can make their way through, said Marcelo Bustamante, a Ph.D. candidate in Eskalen's lab who is first author on the paper.
Spores from the fungi can disperse and the higher the prevalence means an increased chance of transmission. Rain, irrigation water and humidity by fog can trigger the right circumstances for the spores to spread, he said.
“The detection of these pathogens in urban forests raises concerns of potential spillover events to other forest and agricultural hosts in Southern California,” Bustamante and others wrote in the report.
Dead branches can indicate a canker. Detecting the fungi is not an emergency but “people should keep an eye on their plants when they see abnormalities,” Eskalen said.
Cankers are localized areas on stems, branches and tree trunks that are usually dead, discolored and sunken. On bark, the spores can look like strings of discolored dots.
The lab has posted a brochure bout how to best manage wood canker diseases.
Tips include:
* Keep your trees healthy: Proper irrigation and maintenance will keep trees strong.
* Prune dead branches to reduce sources of infestation.
* Avoid unnecessary pruning; perform structural pruning only.
Karina Elfar, Molly Arreguin, Carissa Chiang, Samuel Wells and Karen Alarcon from the Department of Plant Pathology contributed to the paper, as did experts from Disneyland Resort Horticulture Department, State University of New York's College of Environmental Science and Forestry, UC Irvine and UC Los Angeles.
/h3>/h3>- Author: Karey Windbiel-Rojas
Ever heard of Bot canker? "Bot" stands for Botryosphaeria which is a plant disease that results in cankers of trees and other woody plants.
This fungal disease can be worse under drought conditions when trees are stressed. Early symptoms like yellowing leaves and a sparse canopy could be mistaken for other issues like Verticillium wilt and Phytophthora root rot. After cankers form on branches and the trunk, the dark wedge-shaped stains inside the wood can help you confirm the cause as Botryosphaeria canker.
Managing Bot canker relies on keeping plants healthy so that they can resist the infection. When planting, choose plants that are well-suited for the location, including soil type and sunlight. Under drought conditions, trees may need supplemental irrigation to stay healthy.
You can read more in the new UC ANR publication Pest Notes: Botryosphaeria Canker by Jim Downer, UC Cooperative Extension Environmental Horticulture Advisor for Ventura County, and plant pathologists Dee Vega, Cal Poly Pomona and Themis Michailides, Kearney Agricultural Research and Extension Center. This free publication has more diagnostic tips and information on management of this disease.
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- Author: Ben Faber
There are a number of causes for the white exudate from cankers on the trunk and limbs of avocado. Any wound will cause the tree sap to run and crystalize on the surface. It is a seven-carbon sugar of mannoheptulose, or its alcohol form perseitol. It's sweet. The leaking sap is the tree's attempt to staunch the wound (More about the sugar can be found at: https://www.sciencedirect.com/science/article/pii/S0254629911001372 ). Any wound that might be caused by woodpeckers, pickers or little kids climbing the trees will damage the bark, and where the damage has occurred, the sugar will form. So fire damage can cause wounding and so can insect infestation like shot hole borer. Any wound will cause the sugar to leak out in a response to heal the damage. This sugar exudate is a sing of health in the tree, showing that it can respond to attack/infestation/disease. No response is a bad sign.
Physical damage from kids clambering around in a tree
Fire/heat damage exudate
Shot Hole Borer Damage
There are also diseases that can cause a wound that will exude the sugar sap. Three of these are due to water stress of some form that allows infection to occur. These cankers can be quite a problem in avocado, as well as some other tree species, during drought years. With rainfall, the sugar stain is washed away and if there is adequate rainfall, the cankers might even heal. But they can easily reappear once the right stress conditions reappear. The other tree species don't exude the white sap, which is unique to the laurel family. The cankers have also appeared regularly in orchards that have irrigation and salinity management problems. All of these diseases can lead to unthrifty looking trees, which can lead one to conclude that they have Avocado Root Rot. Often, though the trees can have the cankers and the whole canopy can look quite healthy.
One of these trunk cankers is bacterial – Bacterial Canker –caused by Xanthomonas campestris. The name” campestris” means “field” in Latin, and it is a bacterium commonly found in nature. So the bacterium is widespread, and it is not unusual to see a large part of an orchard infected, but it is not commonly found in most orchards. The infection causes a pocket of infection that will ooze sap. The oozing pockets will often appear in a series along a branch or the trunk. It is associated with poor water distribution, and irrigation timing and water/salinity stress. It can be quite a sight, but it rarely kills trees and when the water problems are identified and corrected the cankers will dry up on their own. More on Avocado Bacterial Canker: http://ipm.ucanr.edu/PMG/r8101111.html.
Bacterial Canker
A group of fungi, which we once labelled as Dothiorella, causes another canker but we now know a much larger group of fungi that includes Botryosphaeria and Phomopsis causes the canker. On leaves, the symptoms are called blight; on stems, called dieback and on larger branches and trunks, called simply cankers. UCR plant pathologists have actually identified at least seven different species of fungi that invade the wood and can eventually weaken the tree so limbs can break and the tree becomes unthrifty. In the case of very young trees, they can be killed by these fungal infections, so they are pathogenic. They also are saprophytic on dead tissue and can survive in mulch. The cankers will appear in blotches or patches on the trunk and branches.
Again, these cankers most commonly occur in orchards with irrigation management problems, although there are exceptions where it is unclear what the underlying cause might be. When drought issues are addressed, these cankers will often heal on their own. Read on about Dieback and Canker : http://ipm.ucanr.edu/PMG/r8100611.html.
Trunk Canker
The third cause of sugary cankers is Black Streak, the cause of which has been unclear. It has been tested as a virus, viroid, fungus and bacteria, but it does not seem to fall into any of those groupings. It acts like Trunk Canker, but so far, it has defied a fungal classification. Unlike Trunk Canker, it will usually show up as a widely scattered area of small cankers, often on the undersides of branches and along the trunk.
The correction is similar to Trunk Canker and they mostly appear after a low rainfall year, where irrigation pressures are insufficient, where emitters have clogged and where general water or salinity stress has occurred. More on Black Streak: http://ipm.ucanr.edu/PMG/r8100311.html.
Black Streak
The bacteria and fungi that cause these cankers are everywhere in most orchards and are just waiting for the stressed tree to appear. The grower just needs to identify where this stress is occurring, correct the problem (clogging, low pressure, poor irrigation design, infrequent scheduling, inadequate leaching, etc.) and if the damage is not too extensive, often these symptoms will disappear with time.
The fourth cause of canker is caused by Phytophthora mengei (previously P. citricola); a relative of Avocado Root Rot called Crown Rot, but this fungus attacks the crown roots and lower trunk. The environment that encourages this canker is a moist trunk, either from irrigation water hitting the trunk, or on the north side of the tree that doesn't dry out from morning dew/fog/rain. This is a much slower acting disease than root rot, although it can rapidly kill young trees. The cankers occur at about 18 inches from the ground and gradually girdle the tree. The first thing to do before ever seeing this disease is to make sure irrigation water isn't hitting the trunks. If you do have cankers appear, though, it responds to the same materials used for root rot control, but the materials should actually be sprayed right on the canker.
Crown Rot
So here we have four different trunk diseases all caused by water management. The first three usually from amount and timing and how salts are managed. Crown Rot really is simply irrigation splash on trunks. All four of these can easily be managed with improved irrigation management. You can read more about drought-induced problems in orchards at:
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=20381,
Winter is the time of year when many people prune their deciduous fruit trees. However, did you know that now is not the right time to prune apricot and cherry trees?
In the past, home gardeners were advised to prune stone fruit trees (cherries, apricots, plums, peaches, and nectarines) after trees lose their leaves and go dormant. However, cherry and apricot trees are more likely to be attacked by certain diseases that can be spread by rain.
Gardeners who prune cherry and apricot trees during winter create wounds that may be invaded by fungal and bacterial canker diseases. Symptoms show up in spring and summer, when infected tree limbs wilt and suddenly die with their leaves still attached, or when bark becomes discolored and limbs produce an amber-colored ooze.
This year, wait to prune apricot and cherry trees until late spring or early summer. For more information about fruit trees, visit The California Backyard Orchard.
- Author: Ben Faber
Antarctic fungi found to be effective against citrus canker
Brazilian researchers have identified activity against Xanthomonas citri in 29 fungi isolated from samples collected in Antarctica; one of the compounds inhibited reproduction of the bacterium by up to 98 percent
A research team at the São Paulo State University's Bioscience Institute (IB-UNESP) in Rio Claro, Brazil, has identified 29 fungi with proven action against Xanthomonas citri, a bacterium responsible for citrus canker, an endemic disease in all citrus-producing countries. The origin of the fungi is surprising. They were isolated from samples of soil and marine sediment collected in Antarctica.
"These fungi live in isolated conditions and proliferate under inhospitable conditions including low temperatures and high levels of ultraviolet radiation," says Daiane Cristina Sass, a Professor at UNESP who heads a project engaged in a search for microorganisms that produce compounds with antibacterial action for use in agriculture, with support from the São Paulo Research Foundation - FAPESP.
"How have they adapted to survive in an environment so hostile to life? We wanted to see if they produced molecules with unique structures that protected them from infections and might therefore be capable of antibacterial action." Sass wrote an article published in Letters in Applied Microbiology - jointly with IB-UNESP colleagues Lara Durães Sette and Henrique Ferreira, among others - which shows some of the research's results.
More efficiency on fighting citrus canker
Although the bacterium can be combated in several ways, none is sufficient to eradicate the disease. Therefore, new chemical or biological methods of protecting citrus groves have to be pursued.
The disease is controlled directly by growers. The recommended measures include spraying trees with copper-based products and replacing infected trees with healthy new plantings derived from more resistant varieties. Control of the citrus leaf miner (Phyllocnistis citrella) is also advisable. The wounds made by larvae of this moth in feeding on the plant exacerbate citrus canker by serving as an entry point for X. citri.
"The main method for combating citrus canker consists of spraying trees with copper compounds. The downside is that when even small amounts are used for a long period, copper accumulates in the fruit, soil and water, eventually contaminating the entire environment. For this reason, we're looking for new compounds that are less aggressive to the environment and also less harmful to humans," Sass explained.
Collection and isolation of the Antarctic fungi
On the extent of the Sass-headed project and its research on biotechnology, the team came up with the idea of investigating the collection of fungi curated by Professor Sette, which resulted from Antarctic summer expeditions to the South Shetland Islands in 2013 and 2015 as part of Project Microsfera, conducted under the aegis of the Brazilian Antarctic Program (PROANTAR) and sponsored by the National Council for Scientific & Technological Development (CNPq).
Sette leads the project "Marine and Antarctic mycology: diversity and environmental application", also supported by FAPESP.
Sette isolated 33 filamentous fungi from samples collected in soil under rotten wood on Deception Island and 53 filamentous fungi from marine sediments at a depth of 20 meters in Admiralty Bay, King George Island. All fungal strains are kept at UNESP's Microbial Resource Center (CRM).
The FAPESP-funded research found that 29 of the 86 Antarctic fungi they isolated (19 of marine origin and ten terrestrial) contained compounds with proven action against X. citri.
Isolating the compounds produced by the fungi and verifying their antibacterial activity involved several stages. The process began with isolation of the fungi, which were then grown for several days in culture dishes with nutrients.
The fungi were cultured in liquid medium and shaken for 20 days at 15 °C. The solid biomass was separated from the liquid portion, and both parts were submitted to processing with solvents to obtain intracellular and extracellular extracts.
Tests
The researchers obtained 158 extracts. Each extract was diluted at several concentrations (2.10 mg/ml-0.02 mg/ml) and tested against X. citri. In the case of the soil fungi, most of the extracts with antibacterial action were intracellular in origin, while for the marine fungi, only the extracellular extracts hindered the bacterium's growth.
"We wanted to determine the lowest concentration of each extract that inhibited growth in 90% of cases," Sass said.
Some (12) of the extracts affected bacterial growth at lower concentrations than the highest tested, and ten of these inhibited growth in more than 90% of cases at concentrations of 1.5 mg/ml-1.0 mg/ml.
"At maximum concentration, one extract inhibited growth by up to 98%, and another inhibited it by about 80% at 0.52 mg/ml," Sass said. "It's important to note that we're talking about extracts [which contain varying amounts of molecules]. If an extract contains only one compound that's responsible for this bioactivity, the compound may display good antibacterial activity at much lower concentrations."
Twenty of the isolated fungi with action against X. citri belonged to the genus Pseudogymnoascus and were extracted from terrestrial and marine samples. Next came Penicillium (five), followed by Cadophora (two), Paraconiothyrium (one) and Toxicocladosporium (one), all extracted from marine sediments.
Having identified the extracts with action against X. citri, the researchers are now working to find out which chemical compounds give them this antibacterial capability.
"We expect to identify and purify some of these bioactive compounds, as well as to complete toxicology testing on them, within 18 months or less," Sass said.
The researchers plan to patent the compounds they identify. They also hope to persuade pesticide manufacturers to develop commercial products for combating citrus canker based on these compounds.
https://www.eurekalert.org/pub_releases/2018-06/fda-aff061318.php
Twenty of the isolated fungi with action against X. citri belonged to the genus Pseudogymnoascus and were extracted from terrestrial and marine samples. Next came Penicillium (five), followed by Cadophora (two), Paraconiothyrium (one) and Toxicocladosporium (one), all extracted from marine sediments.
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