Posts Tagged: bacterial
Tomato Diseases in the Home Garden
As tomato growers, we might consider any ailing tomato to have a disease. That would end up making this blog post really, really long. However, we need to consider diseases separately from damage done by pests (both vertebrate and invertebrate—see blog post from July 18: Tomato Diseases in the Home Garden) or environmental disorders such as blossom end rot (see blog post from July 4: https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=57297). We will cover fungal, viral, and bacterial diseases here.
Fungal
The most common tomato diseases are fungal. Many of these fungal spores are nearly everywhere all the time, and given the right conditions, will find a home on your tomato plants. Some fungi prefer cool conditions while some prefer warm. Most prefer wetness and high humidity. Crowding can prevent proper air circulation and encourage fungal diseases. Nutritional deficiencies and injuries also encourage fungal diseases.
Damping Off Disease typically affects seedlings. It's caused by various soil fungi that grow under damp conditions. The affected tap roots of seedlings in contaminated, overly damp soil are dark and mushy and the seedlings usually die. Prevent this by using fresh clean soil and sanitized containers with good drainage. Use alcohol or a 10% bleach solution to sanitize. https://ipm.ucanr.edu/PMG/PESTNOTES/pn74132.html
Septoria Leaf Spot is favored when plants are exposed to cool, rainy weather or splashing from soil. It's relatively uncommon in Contra Costa County. Prune off infected leaves and twigs and keep plants dry. https://ipm.ucanr.edu/PMG/GARDEN/PLANTS/DISEASES/septorialfspot.html
Phytophthora Root and Crown Rot is a soil-borne fungus-like organism transmitted under wet conditions by splashing water or contaminated garden debris, pots, or tools. Plants appear drought-stressed since the vascular system is compromised, and often die. It can also cause damping-off. Look for darkening of the crown, roots, and stems. Good drainage, avoiding overwatering, and sanitizing any tools used on the diseased plants are preventive measures. In previously affected soil, avoid planting members of the Solanaceae family (tomatoes, eggplant, peppers, potatoes) in the infected soil and plant a resistant crop instead such as corn. https://ipm.ucanr.edu/PMG/PESTNOTES/pn74133.html
White Mold, also called Cottony Soft Rot, appears as bleached areas on stems from white mycelia. Fruit can be affected and appears gray. The mold favors hot, moist conditions and often spreads from dying flowers. Bury or dispose of infected tissue; avoid overhead watering, overwatering, and crowding. https://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/tomwhmold.html
Powdery Mildew looks different on artichoke, pepper, and tomato leaves from its appearance on other plants (see reference). It requires warm weather and living tissue to grow but does not require moist conditions. Prevention includes planting resistant varieties in sunny areas and avoiding crowding. Occasionally a fungicide or a biologic is needed. https://ipm.ucanr.edu/PMG/PESTNOTES/pn7406.html
Early Blight's name is somewhat misleading as it occurs on mature tomato plants and can affect fruit. It is uncommon in our Mediterranean climate. See reference for photos, prevention, and treatment: https://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/tomearlyblight.html
Late Blight (Phytopthora infestans) occurs in our coastal areas and is favored by average temperatures and high humidity. It can spread rapidly from other Solanaceae family members or their cullings. Avoid overhead sprinkling and crowding of plants and buy certified blight-free seeds and tubers. Dispose of affected plants and debris in green waste. https://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/lateblight.html
Black Mold typically affects ripe tomato fruit during conditions of warmth and high humidity. It can appear as small dark brown spots or grow into large, sunken areas. Pick fruit as soon as it ripens. https://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/tomblkmold.html
Verticillium and fusarium wilt are fungal diseases that will be discussed in an upcoming blog.
Viral
Tobacco Mosaic Virus is a disease primarily of Solanaceae, of which tobacco is a member. It is transmitted by infected seeds or by tobacco residue on the hands of smokers. The leaves appear mottled and stringy, but the fruit is edible. Herbicide damage can appear similar. Many tomato cultivars have resistance. https://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/tobaccomosvir.html
Curly Top Virus and Spotted Wilt Virus are fairly unusual afflictions. Curly Top Virus is carried by the beet leafhopper and causes curling, puckering, and stunting of leaves. Fruit is usually discolored and small. Spotted Wilt Virus is transmitted by the western flower thrip. It can be difficult to diagnose as it presents differently depending on the stage of plant growth. Fortunately, it's rare in Contra Costa County. Both have wide host ranges. For severe infections in the garden, testing may be warranted since the viruses can mimic other diseases. Affected plants will need to be removed and disposed of. Unfortunately, insecticides do not kill thrips or leafhoppers in time once the damage has been noticed. https://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/curlytop.html
https://ipm.ucanr.edu/PMG/GARDEN/VEGES/DISEASES/tomspotwltvir.html
Bacterial
Bacterial Speck, Bacterial Spot, and Bacterial Canker are all easily confused. They tend to be introduced on infected seeds, and can overwinter on garden debris, flats, and stakes. They all prefer wet conditions. All three cause lesions on fruit. Speck and Spot cause similar leaf lesions and are chiefly distinguished by their appearance on fruit.
Bacterial Speck prefers cooler conditions such as in coastal regions. A Pseudomonas bacterium causes small sunken spots with white halos that can become scabby. The leaf spots are similar and appear greasy, and leaf margins can turn brown in an angular pattern. Stems can also be affected.
Bacterial Spot is caused by Xanthomonas bacteria, resulting in large, black, sunken spots on fruit and irregular black spots on leaves. Warm, humid conditions favor its appearance. The fruit may be eaten once the black spots and any underlying maceration are removed. https://u.osu.edu/vegetablediseasefacts/tomato-diseases/bacterial-leaf-spot/basics/
Bacterial Canker also prefers warm, humid conditions. Stunting, wilting, scorching of leaf margins, cankers on stems, and vascular discoloration are distinguishing features.
https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=27926&postnum=27926
Bacterial diseases can be managed somewhat with copper sprays and these sprays are acceptable for organic farming.
Prevention
Prevention is the ideal way to manage all these diseases:
• Rotate crops
• Don't overwater or spray the plant
• Don't crowd plants
• Remove lower leaves that can touch the soil
• Use mulch to prevent spread from soil
• Buy resistant varieties
• Control weeds to prevent thrip and leafhopper invasions
• Dispose of infected plant parts and debris, sanitize tools, planting flats, and hands
• Baby heirloom tomatoes because they typically have little resistance
For more information about pests and diseases of tomatoes, see this website: https://ipm.ucanr.edu/home-and-landscape/tomato/index.html
Help Desk of the UC Master Gardeners of Contra Costa County (EAS)
What’s Up with my Avocado Tree?
So a question comes in about a problem with a backyard avocado tree. And it would seem the first question would be about the overgrowth happening at the base of the trunk. This a ‘Fuerte' avocado that is grafted on a seedling avocado rootstock. It's not unusual to see an overgrowth, but this is the most extreme example I have ever seen. So it's basically an incompatibility between the graft and the rootstock. In many cases this is no big problem and trees can live a long time, as this tree has.
But the homeowner wasn't asking about the unusual growth at the base, but the canker that had appeared in the center of the trunk near the base.
This has the classic white sugar exudate that occurs with a wound of any kind in avocado. The sugary sap that contains the unusual mannoheptulose 7-carbon sugar characteristic of the laurel family to which avocado belongs will ooze out of the wound and result in a white crust (Read more about this sugar at: https://www.sciencedirect.com/science/article/pii/S0254629911001372 ).
Anyway, so this backyard tree is in an area that is getting 10 minutes of lawn watering a day. Lawns and avocados don't get along. And avocados don't get along with short, shallow irrigation that result in salt accumulating in the root zone. Which is what has happened here. Salt stress and the result is an infection of bacterial canker (https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=7920 ).
It's not fatal in an old tree like this, but it can predispose the tree to root rot. And that's not something that is easy to treat in backyard settings.
Wait, Don't Prune Apricot or Cherry Trees Just Yet!
Winter is the time of year when many people prune their deciduous fruit trees. However, did you...
Fungal Control of Citrus Canker Bacteria
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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fungal mats
Weather Forecast is Favorable for Many Plant Diseases
A chance of thunderstorms most of the week and moderating air temperatures will promote prolonged...