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Garlic bulbs with white rot Sclerotium cepivorum, the causal agent of garlic white rot, showing reduced roots and tightly adhering soil. (S. Johnson photo)

Garlic and onion white rot are caused by the fungus, Sclerotium cepivorum Berk. White rot is the most important and destructive of the fungal diseases of onion and garlic. While all Allium-family plants can be infected with white rot, onion and garlic are the most susceptible.

White rot is not yet common in Maine. But the long-term consequences of this disease make it a concern for all garlic growers. Garlic and onion white rot, a previously unreported disease in Maine, appeared in several locations during the 2008 growing season. The source of the disease was traced back to garlic seed stock imported into Maine. Since 2008, additional diseased areas have appeared. Some farms have drastically reduced the amount of garlic and onion planted or abandoned garlic planting on a particular piece of land. Pathogen buildup and spread to uninfested areas is a serious concern because white rot can render a field unusable for garlic or onion production for as long as 40 years, even without an Allium host. The pathogen that causes this disease survives in the soil as sclerotia, which are dormant fungal structures. One sclerotium per 20 pounds of soil will cause disease and result in measurable crop loss; one to two sclerotia per pound of soil will result in all plants being infected.

The pathogen moves below ground at a rapid rate. Visual symptoms generally do not appear until the base of the plant is infected. Plant death soon follows. There are currently no chemical or cultural controls available to garlic growers, other than moving to fields free of the pathogen. By 2003, over 10,000 acres in California had become infested with Sclerotium cepivorum. In California, failure to completely clean boxes transporting bulbs to be planted for seed production has been blamed for white rot infestation in dozens of newly planted garlic fields. Parts of Washington State, California, and Nevada now have regulations on the white rot pathogen.

Biology

Garlic and onion white rot development is favored by cool and moist soil conditions. The soil temperature optimum for infection 60° to 65°F and infection can occur from 50° to 75°F. At soil temperatures above 78°F, the disease is inhibited. Soil moisture conditions that are favorable for garlic and onion growth are also favorable for white rot development.

The sclerotia that form on the decaying host will lay dormant until root exudates, unique to Allium spp., stimulate germination. Cool weather is needed for both sclerotia germination and mycelia growth. Optimum soil moisture for Allium root growth is also optimal for sclerotia germination. Mycelium will grow through the soil until it encounters an Allium root when it initiates the infection process. Mycelium can grow from one plant to a nearby plant. This allows the pathogen to move between plants. As the disease progresses, sclerotia are formed and eventually released into the soil.

Symptoms

Garlic plants in the field with yellowing and dying leaves from Sclerotium cepivorum, the causal agent of garlic white rot. (S. Johnson photo)

White rot initially appears as areas of yellowing lower leaves or stunted plants, which eventually die. The size of the infected area is related to the level of inoculum in the soil and will continue to enlarge as the season progresses. White rot may go unnoticed in a field for a period of time as sclerotia populations are building and spreading. During weather optimal for the disease, mycelial growth can occur on the base of the stem and on the bulb. Under ideal conditions, mycelia growth can cover the entire bulb, and eventually, tiny black sclerotia will form on the mycelium. Roots will also rot, making the plant easy to pull out of the soil.

Management

White rot management centers on disease avoidance and not introducing Sclerotium cepivorum into the field. Plant only clean, pathogen-free garlic cloves, onion transplants, or onion sets. The seller of the planting stock will most likely include information from a testing lab if the material has been tested free of white rot. Movement of infected planting stock is the primary introduction avenue into a previously uninfested field.

Garlic bulb with masses of Sclerotium cepivorum sclerotia, the causal agent of garlic white rot. (S. Johnson photo)

Once white rot is present in a field, little can be done other than to cease planting Allium crops in the field. The Allium crops from an infested field should not be used as seed. Infected plants should not be tilled under or composted, but rather disposed of off-farm. All equipment and tools that have been used in an infested field should be sanitized with an approved quaternary ammonia product. If you suspect the presence of white rot, contact your local Extension office for verification.

Sclerotia can be spread by plant material, water movement, soil movement, equipment movement, or human movement. Sanitation is important to prevent sclerotia from moving from an infested field to a clean field. Movement of plant material or soil from an infested field can spread the pathogen and thereby the disease. Crop rotation is of limited use in disease control owing to the long persistence of white rot sclerotia in the soil.

There are no available white rot-resistant varieties of garlic or onion. Biological approaches have been investigated, but results have been variable and they do not control the pathogen.

Reviewed by David Fuller, Extension Professional

Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

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White-Rot Fungi and their Enzymes as a Biotechnological Tool for Xenobiotic Bioremediation

2. Origin, threat, and biodegradation of xenobiotics; enzymatic system involved in xenobiotic biodegradation

While a huge amount of hazardous organopollutants is produced annually over the world, only 10% of these are disposed of safely. The most hazardous compounds are persistent in the environment and are known to have carcinogenic and/or mutanogenic effects. The prime source of xenobiotics is wastewater, landfill leachates , and solid residual releases from the industries . Solid wastes may contain volatile organic compounds as residues or incorporated into the structure of materials such as plastic foams, packaging, floor and wall coverings, solvents, paints, and adhesives .

Wastewaters, including domestic and industrial wastewaters, contain a variety of compounds. Some of the common compounds present in wastewaters and in other effluents are phenolic compounds, hydrocarbons, dyes, endocrine disrupting compounds, and pesticides .

Landfills generate large amounts of leachates containing high levels of organics and ammonia nitrogen . These substances with others like phenols and hydrocarbons can be a major source of contamination of the groundwater. Indeed, the variety of contaminants in landfill leachates, their synergistic and antagonistic effects as well as their physicochemical properties make them serious toxicants, which may survive different treatments . Landfill leachates exhibit consequently high toxicity levels . The efficiency of fungal remediation of landfill leachates has been proved on Trametes trogii, Lentinus tigrinus, and P. chrysosporium . The strains were able, via their extracellular enzymes, to reduce organics (chemical oxygen demand (COD), phenols, and hydrocarbons) as well as toxicity, for twofolds diluted LFL. However, raw LFL caused growth inhibition and enzyme secretion reduction, indicating the sensitivity of these strains to high levels of toxic compounds such as phthalates and phenol derivatives . Tigini et al. reported that autochthonous and allochthonous fungal strains were efficient in LFL treatment, showing a complete spectrum of action and being able to significantly reduce the wastewater toxicity for all the tested strains. Thus, Porostereum spadiceum showed the best activity with 40 % of decolorization within 1 week .

Solid waste residues can be domestic wastes, including food, paper, and garden wastes; waste from council activities associated with servicing residential areas: street sweepings, tree lopping, parks and gardens, and litter bins; and waste from institutional, commercial, industrial activities, generally containing higher proportions of metals and plastics than domestic wastes. They also can be derived from demolition and building activities, which contain high proportions of inert material (concrete, bricks) and low proportions of other materials. Many xenobiotic compounds are released from municipal solid waste and may be found in the leachates and the gaseous phase of landfills . They include 1,1-dichloroethylene, 2,4,6-trichlorophenol, dimethyl phthalate, phenol, benzoate, and phthalic acid .

Phenols and phenolic compounds are widely distributed compounds in the nature, especially in the plants, but also in marine systems, produced by marine plants and animals where they can be degraded by indigenous microbial population . Several types of industries, such as coal refineries, phenol manufacturing, pharmaceuticals, dying, petrochemical, pulp mill as well as agricultural wastes, contain phenols which are considered among the most prevalent pollutants due to their high toxicity even at low concentrations . Phenol is also employed in the production of resins and also used in the manufacture of plastic, biocides, disinfectants, textiles, medicines, explosives, pinks, perfumes, and photographic materials . Consequently, phenols have negative effects on the ozone layer and on the earth heat . Phenol, being a carcinogenic compound, must be removed from industrial wastewaters prior to their discharge, via biodegradation processes resulting in minimum secondary metabolites and harmless end products . Several studies have shown that phenol can be degraded by a wide variety of fungi including P. chrysosporium, Trametes versicolor, Trametes villosa, and Lentinus eodes .

Furthermore, chlorinated phenols are one of the most serious environmental pollutants. Lignin-degrading fungi and their enzymes have been used to detoxify these compounds through their transformation into non-toxic or less toxic substances . Ehlers and Rose found immobilized WRF cultures to be effective in removing phenolic and chlorinated phenolic pollutants . Leontievsky et al. reported that Panus tigrinus and Coriolus versicolor and their ligninolytic enzyme systems efficiently transform 2,4,6-trichlorophenol (TCP) to 2,6-dichloro-1,4-hydroquinol and 2,6-dichloro-1,4-benzoquinone . However, MnP and laccase differed in their specificity: in P. tigrinus culture, primarily the MnP attacked 2,4,6-TCP, whereas in C. versicolor culture, predominantly laccase catalyzed the transformation. Besides, P. chrysosporium has been the most extensively studied among the ligninolytic fungi, as a model system, and the pathways for degradation of 2,4-di, 2,4,5-, and 2,4,6-trichlorophenols were investigated .

Plastics are known to be hazardous materials due to the nature of components that are made of and including polystyrene, polyvinyl chloride, polyethylene, and its derivatives. They are very slowly degraded due to the molecular bonds and interactions. Biodegradation of plastics gained importance in the last few years, but the fragmented compounds released by this biodegradation also lead to other with environmental issues . Cameron et al. reported that P. chrysosporium was able to degrade plastics like nylon .

Polycyclic aromatic hydrocarbons and saturated hydrocarbons are usually found in petroleum effluents at high concentrations and cause an environmental pollution. Because physical-chemical degradation of such compounds is cost-effective and may lead to further disturbances in the environment, biological treatments offer the alternative to reduce the impact of these pollutants . Hence, bioremediation had a great potential as an alternative method for the rehabilitation of contaminated sites. The use of natural microorganisms, isolated for their ability to degrade a large variety of hydrocarbons , allows the elimination of such compounds from contaminated sites . Microorganisms that can degrade hydrocarbons are particularly isolated from petroleum-contaminated sites . Indeed, the microbial action depends on aromatics structure since the aromatic fraction is more difficult to degrade . Olusola and Anslem reported that Pleurotus pulmonarius was able to degrade crude oil . Other studies reported the effective fungal bioremediation of hydrocarbons . Bioremediation of anthracene and pyrene in soil, using mycelia of P. chrysosporium, T. versicolor, and Pleurotus ostreatus was reported as effective, since MnP and LAC were secreted at high levels in the soil. However, these high enzyme levels allowed a more efficient degradation of recalcitrant compounds in liquid media .

Volatile organic compounds and additives, such as emulsifiers and texturizers in paint, can be degraded by different tools such as chemicals (water as solvent), hygroscopic stresses, and microbial sources . Some fungi were reported as effective decomposers of paints. The development of microfungi on the surface of painting induces aesthetical, mechanical, and biochemical decay .

Textile effluents are one of the principal sources of pollution over the world. In particular, the release of colored effluents into the environment is undesirable, not only due to their color but also because many synthetic dyes with their complex aromatic molecular structure and their breakdown products are toxic and/or mutagenic . Due to the unspecific nature of their lignin-degrading enzymatic system, fungi can also degrade textile dyes . However, the well understanding of the fungal degradation mechanism involved is essential to identify the degradation products and to verify the toxicity removal, consequently. Until now, much research has been done on dye degradation by fungi and or laccases but few studies have focused on the intermediate products toxicity . Many fungal isolates and their enzymes were reported as efficient for the degradation or the decolorization of many polymeric dyes, including blue dextran and Poly R478 as well as the triphenylmethane dyes: cresol red, crystal violet, and bromophenol blue . Ben Younes et al. reported that laccase from the thermophilic fungal strain Scytalidium thermophilum catalyzed the decolorization and the detoxification of the azo dye Congo red and the triarylmethane dyes, commonly found in textile industry effluents . The team also reported, in previous studies, that the crude enzyme as well as the purified laccase from Perenniporia tephropora was able to decolorize dyes of the textile industries, including neolane pink, neolane blue, and remazol brilliant blue R (RBBR) . The latter was also efficiently decolorized by laccase from T. trogii . The ability of T. trogii laccase to decolorize azo and triarylmethane dyes was approved in the absence of redox mediators, since MG and BCG were completely degraded with crude laccase within 6 h of treatment. Toxicity evaluation showed a final product detoxification . On the other hand, the fungal decolorization of RBBR has been reported for other strains such as Dichomitus squalens, Ischnoderma resinosum, Pleurotus calyptratus , and P. ostreatus . Tekere et al. reported the ability of Trametes cingulata, T. versicolor, Datronia concentrica, and Pycnoporus sanguineus to decolorize the Poly R478 . Mohorcic et al. found that Bjerkandera adusta was able to decolorize the black-blue dye through violet and red to pale yellow via its extracellular enzyme; the MnP which was also reported for its ability to decolorize amaranth and remazol black B . Previously, Swamy and Ramsay reported since 1999 the ability of Bjerkandera sp., P. chrysosporium, and T. versicolor to decolorize remazol orange, remazol brilliant blue, reactive blue, and tropaeolin O in agar plates . Consequently, some strains including T. trogii and S. thermophilum were reported to be able to decolorize and detoxify textile effluents . Robinson et al. reported that B. adusta and Phlebia tremellosa provided a good efficiency to decolorize textile effluent in N-limited conditions .

Paper and pulp mills are effluents released from paper mill industries and cause serious environmental pollution because they contain chlorinated organic compounds, which are absorbable organic halides, including pentachlorophenols, tetrachlorocatechols, and tetrachloroguaiacols . They are often released to anaerobic conditions, exhibiting high acute and chronic toxicity levels and mutagenicity and/or carcinogenicity. Fungal enzymes were used for bleaching these effluents to obtain high-quality paper pulps . Indeed, it was reported that the laccase from Coriolopsis gallica has been implicated in the decolorization of effluents from the pulp and paper industry . Laccases have also been shown to be applicable for the bioremediation of pulp and paper industry wastes by effecting direct dechlorination for the removal of chorophenols and chlorolignins from bleach effluents . Other uses of laccases for the pulp and paper industry include reduction of the kappa number of pulp and an improvement in the paper-making properties of pulp .

A large variety of pesticides and insecticides, including organophosphorous compounds, and benzimidazoles, are intensively used and may contaminate the land due to their slow degradation . Despite the slow process, microbial degradation is considered as a tool to minimize the negative effects of these compounds on the ecosystem. Many studies reported the effective degradation of pesticides by fungal strains, including P. chrysosporium and T. versicolor, and involving two different enzyme systems: laccase and peroxidases .

Pharmaceuticals are discharged directly by pharmaceutical manufacturers or in wastewaters from hospitals. These compounds have performed their biologically intended effect, but their degradation into toxic substances in the body is often a cause for concern since they unfortunately get passed into the environment in either their complete or fragmented forms. These pharmaceuticals, used in personal care products (PCPs) or being endocrine-disrupting chemicals (EDCs), mainly include hormones, anesthetics, and antibiotics, and can be accumulated in an organism and passed on to the other through the common food chain . Even though they are the indirect sources, they cause adverse effect on the ecological cycle . Nonsteroidal anti-inflammatory drugs are also a large and diverse chemical group of drugs used on humans and animals for the treatment of inflammation, pain, and fever . The use of diclofenac in animals has been reported to have led to a sharp decline in the vulture population reaching 99% . These compounds, including nonylphenol (4-nonylphenol), bisphenol A (2,2-bis(4-hydroxyphenol) propane), triclosan (5-chloro-2(2,4-dichlorophenoxy) phenol) and others, are frequently detected in receiving waters downstream of intense urbanization . The latter can mimic or interfere with the action of animal endogenous hormones by acting as estrogen agonists, binding to the estrogen receptor or eliminating a normal biological response . The promise of laccase for the transformation or the elimination of PCPs and EDCs from both aqueous solutions and polluted soils has been recently established . Cabana et al. demonstrated that the resulting chemicals do not have any estrogenic activity .

It is known that white-rot fungi can degrade lignin in the way that the mycelia of the organisms penetrate the cell cavity and release ligninolytic enzymes to decompose materials to a white sponge-like mass . The ability of fungi to transform a wide variety of hazardous chemicals has aroused interest in using them in bioremediation . Enzymatic treatment, involving mainly peroxidases and/or laccases, is currently considered as an alternative method for the removal of toxic xenobiotics from the environment .

2.1. Peroxidase system

The lignin degradation system consists on peroxidases, H2O2-producing enzymes, veratryl alcohol, oxalate, and manganese. All of these enzymes are glycosylated heme proteins that couple the reduction of hydrogen peroxide to water with the oxidation of a variety of substrates. The redox potentials of LiP and MnP are higher than for others peroxidases; that is why they have been shown to oxidize chemicals that are not easy to be oxidized by other microorganisms. These chemicals include Polycyclic aromatic hydrocarbons (PAH), phenol and its derivatives, cyanide, TNT, and others . This finding was reported for the fungus P. chrysosporium, which has been shown to degrade many xenobiotics and recalcitrant compounds, both in soil and in liquid cultures, suggesting the attractive use of such fungus in bioremediation.

Lignin peroxidases (LiPs) belong to the family of oxidoreductases and were firstly described in the basidiomycete P. chrysosporium in 1983 . This enzyme has been recorded for several species of white-rot basidiomycetes . LiP is dependent of H2O2, with an unusually high redox potential and low optimum pH . This enzyme is able to oxidize a variety of substrates including polymeric ones and has consequently a great potential for application in various industrial treatment processes .

Manganese peroxidases (MnPs) belong to the family of oxidoreductases . Following the discovery of LiP in P. chrysosporium, MnP secreted from the same fungus was found as another lignin-degrading enzyme and was secreted by almost all white-rot fungi. MnP catalyzes the oxidation of phenolic structures to phenoxyl radicals . The product Mn3+, being highly reactive, complex with chelating organic acids, such as oxalate, lactate, or malonate. On the other hand, it was reported that MnP may oxidize Mn(II) without H2O2 and with decomposition of acids, and concomitant production of peroxyl radicals .

2.2. Laccase system

Laccases which are blue multicopper oxidases, catalyze the monoelectronic oxidation of a large spectrum of substrates, for example, ortho- and para-diphenols, polyphenols, aminophenols, and aromatic or aliphatic amines, coupled with a full, four electron reduction of O2 to H2O. Laccases act on both phenolic and nonphenolic lignin-related compounds as well as highly recalcitrant environmental pollutants, and they can be effectively used in paper and pulp industries, textile industries, xenobiotic degradation, and bioremediation and can act as biosensors. Some studies reported the identification of genes that are differentially regulated during fungal growth in the presence of different environmental pollutants. However, abiotic stress caused by many factors including water potential, temperature, and pH can influence the metabolism of the degradation process. Hence, considering bioremediation in soil, the conditions that favor fungal activity in soil, such as temperature, moisture, nutrient status, pH, and aeration, need to be optimized to promote metabolic degradation of xenobiotics. Magan et al. studied the effect of abiotic factors on the fungal degradation of pesticides by T. versicolor and P. chrysosporium for soil bioremediation purposes . In fact, the potential property of laccase is its highly non-specific nature of substrates . Furthermore, the common presence of one or more substructures in the lignin molecule and in xenobiotics explains the ability of white-rot fungi to degrade such a wide range of environmental organic pollutants, even at high levels . Otherwise, it has been shown that laccase metabolizes these compounds without any net energy gain . Indeed, the oxidation of lignin is performed to access to wood polysaccharides, being their main energy source . This implies that the presence of lignin-cellulosic substrates is required to ensure the degradation of xenobiotic compounds .

General features of white rot and brown rot fungi

General features of white rot and brown rot fungi

  1. 1. General Features of White Rot and Brown Rot Fungi
  2. 2. Introduction  Plant matter is constantly under attack by fungi, insects, bacteria, marine borers and the weather.  It is estimated that roughly 1/10 of the forest products generated each year are destroyed.  Wood decay or wood rot is caused by fungi – organisms that live on other organic matter such as wood.  While this can be bad, without these processes we would be buried in a sea of old dead plant matter. 2
  3. 3. Occurrence  Decay of timber occurs only when wood is allowed to remain permanently or regularly damp.  Decay is described as either wet rot or dry rot; although both can occur together in damp wood.  Can develop on susceptible wood if the moisture content of the wood remains above about 22% regularly for prolonged periods.  Develop from minute airborne spores which germinate if they land on a suitable substrate such as damp wood.  Produce thread-like hyphae, which collectively form a mycelium.  The hyphae making up the mycelium penetrate the wood, breaking down the wood cell walls and feeding on them.  Mycelium produces a fruit-body; this releases spores to the atmosphere, completing the life cycle. 3
  4. 4. Types and Forms  White rot – all components removed  Brown rot – primarily carbohydrates lost, lignin mostly remains  Soft rot – carbohydrates preferred, but some lignin lost too  Slash rot – decay of dead material left behind after logging Positions  Heart rot – decay in the stem that develops primarily in the heartwood or inner wood of living trees  Sap rot – saprobic decays that develop in the sapwood  Butt and root rot – decay primarily in the roots or at the base of a tree heart rot – decay in the stem that develops primarily in the heartwood or inner wood of living trees 4
  5. 5. Types and Forms (Cont’d) 5
  6. 6. White Rot Fungi  This group of organisms is known as white rot because of their ability to degrade lignin. Can delete up to 100% of Timber weight.  The decaying wood looks white.  Cellulose and hemicelluloses are also degraded.  Generally decay occur from lumen outwards.  White rot fungi typically decay hardwoods  They will decay softwoods but hardwoods are their food of choice. 6
  7. 7. White Rot Fungi (Cont’d)  Largest number of species belong to Basidiomycotina  Xyariaceous and Diatrypacsous also numerous. 7
  8. 8. Brown Rot Fungi  With brown rot fungi, cellulose and hemicelluloses are degraded with only limited lignin degradation. Can delete up to 65% of timber weight.  Decayed wood is brown and crumbly.  Brown rot fungi typically decay softwoods.  Attack starts at the cell lumen and works outwards.  Cellulose is rapidly degraded. 8
  9. 9. Brown Rot Fungi (Cont’d)  Most species belong to Basidiomycotina. 9
  10. 10. Features of white and brown rot 10
  11. 11. Defense Against Decay  Wall thickening  Phenolic chemistry  Wound periderm  Programmed cell death  Outer physical/chemical barrier  Bark/cuticle  H2O, O2, N limits  Heartwood chemistry  Extractives 11
  12. 12. Benefits 12 Woody says, Fungi are great! I wouldn’t have a home without them!
  13. 13. THANK YOU For Your Attention!

National Science Foundation – Where Discoveries Begin

News Release 12-117

Study on Fungi Evolution Answers Questions About Ancient Coal Formation and May Help Advance Future Biofuels Production

Study reveals the potentially large influences of fungi, one of the most biologically diverse classes of organisms, on our energy supplies

A scanning electron micrograph of wood decayed by white rot.

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June 28, 2012

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A new study–which includes the first large-scale comparison of fungi that cause rot decay–suggests that the evolution of a type of fungi known as white rot may have brought an end to a 60-million-year-long period of coal deposition known as the Carboniferous period. Coal deposits that accumulated during the Carboniferous, which ended about 300 million years ago, have historically fueled about 50 percent of U.S. electric power generation.

In addition, the study provides insights about diverse fungal enzymes that might be used in the future to help generate biofuels, which are currently among the most promising and attractive alternatives to fossil fuels for powering vehicles.

The study, which was conducted by a team of 71 researchers from 12 countries, appears in the June 29, 2012 issue of Science and was partially funded by the National Science Foundation (NSF).

There are almost 1.5 million fungi species on Earth. They perform essential ecological roles that include decomposing organisms and serving as food for many insect species and larger organisms.

However, only about five percent of fungi species have, thus far, been classified. The new study is part of an effort–supported by NSF’s Assembling the Tree of Life and Partnerships for Enhancing Expertise in Taxonomy programs–to resolve evolutionary relationships between fungi species, define the diversity of fungi, and explain the early evolutionary history of fungi. Information produced by this effort is integral to the story of life on Earth and the evolution of its varied ecosystems.

The end of a geologic era

Coal is composed of the fossilized remains of plants–mostly lignin, which is a complex polymer that is an important component of the cell walls of plants and helps give wood its strength and rigidity. The study indicates that white rot fungi, which are the only types of microorganisms that can break down lignin, evolved at the end of the Carboniferous green period, and that the synchrony between the rise of white rot fungi and the close of the Carboniferous was no coincidence.

According to the study, once white rot, which breaks down lignin via enzymatic activity, became an ecological force, it destroyed huge accumulations of woody debris that would have otherwise escaped decay to ultimately be fossilized as coal.

So if not for the advent of white rot, large coal deposits may have continued to form long after the end of the Carboniferous period. This study supports a paper published in 1990 by Jennifer M. Robinson that pegged the evolution of white rot as a potential contributing factor to the end of the Carboniferous period.

The matrix

Lignin exists in cell walls as part of a tough matrix with cellulose, which is a carbohydrate composed of sugar subunits. But once white rot attacks and destroys lignin, the matrix collapses, and the cellulose is freed–to be devoured by the white rot as food.

The ability of white rot fungi to decay lignin may ultimately be used to help conquer what is among the world’s most longstanding and vexing problems associated with the large-scale production of biofuels: that is, obtaining plant carbohydrates that could be converted into biofuels via fermentation processes.

It may ultimately be feasible to use white rot to break down lignin to release cellulose from cell walls, which could then be broken down into sugars. Next, the sugars would be fed to yeast that would be fermented into alcohols that would provide the bases for new biofuels.

In addition, because enzymes from white rot fungi are able to break down complex organic molecules, they have been investigated for use in bioremediation operations that involve breaking down contaminants to remove them from the environment.

Genomic comparisons

“Our study was designed to reconstruct the evolution of lignin decay mechanisms in fungi, analyze the distribution of enzymes that enable fungi to break down lignin, and better define the evolution of the gene families that encode those enzymes,” said David Hibbett of Clark University, who led the study.

Hibbett and his team focused on a large group of fungi known as Agaricomycetes, which include white rot fungi as well as mushroom species that have the familiar cap-and-stem shape. The Agaricomycetes group also includes brown rot fungi that can destroy wood by breaking down cellulose and hemicellulose, which is another component of cell walls–all the while without breaking down lignin.

The researchers compared 31 fungal genomes–26 of which were sequenced at the Department of Energy’s Joint Genome Institute, including 12 that were sequenced at the DOE JGI specifically for the study, and were then annotated and analyzed by NSF-funded researchers in collaboration with JGI and other partners.

“The 12 new genome sequences could serve as potential resources for industrial microbiologists aiming to develop new tools for producing biofuels, bioremediation or other products, perhaps by using recombinant DNA methods or by selecting new organisms for fermentation,” said Hibbett.

“This study exemplifies the tremendous gains we can make in understanding complicated biologic processes such as lignin decomposition when we learn about the genealogical relationships of organisms,” said Charles Lydeard, an NSF program director.

The evolution of white rot

The study also involved tracking the evolution of lignin-decomposing enzymes back through time. This was done via so-called “molecular clock analyses.” Such analyses are based on the assumption that genes accumulate mutations through evolution at fairly predictable rates–similar to the way that the hands of a clock advance around a clock at predictable rates. The ability to estimate these mutation rates enables researchers to trace mutations back in time and estimate how recently fungal lineages shared a common ancestor but then diverged from one another.

Results of molecular clock analyses suggest that the oldest ancestor of the Agaricomcyetes was a white rot species that possessed multiple lignin-degrading enzymes and lived roughly 300 million years ago. Many surviving lineages of Agaricomycetes-including fungi species known as wood-decaying polypores and bracket fungi-produce lignin-degrading enzymes. “Our results suggest that the ability of fungi to break down lignin evolved only once,” said Hibbett.

In addition, Hibbett said, “This study underscores the adaptability of fungi.” This adapatability is underscored by the fact that some Agaricomycete lineages have maintained their lignin-degrading enzymes. By contrast, other Agaricomycete lineages, including brown rot and mycorrhizal species, which survive via symbiotic relationships with the roots of certain trees without decaying them, ultimately lost their lignin-degrading enzymes as they developed alternative methods of obtaining nutrition, said Hibbett.

Potential payback

The economic value of fungi is already almost incalculable: fungi currently impact diverse applied disciplines, including agriculture, medicine and drug discovery. The more scientists learn about these important organisms, the more likely they will be to identify additional uses for them that will benefit the economy, the environment, and human welfare, as well as to develop new ways to fight wood rot that, at great costs, kills trees and destroys wood structures, including homes and ships.

Joseph Spatafora of Oregon State University who is a co-author on the study said, “It’s a really exciting time in fungal biology, and part of that is due to the technology today that allows us to address the really longstanding questions.”

-NSF-

  • The researchers’ work is described in the June 29, 2012 issue of the journal Science.
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Program Contacts
Charles Lydeard, National Science Foundation, (703) 292-7207, email: [email protected]

Principal Investigators
David Hibbett, Clark University, (508) 793-7332, email: [email protected]

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Plant Problems – Onion White Rot

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Onion white rot – Stromatinia cepivora (syn. Sclerotium cepivorum) — the unforgiving fungal pestilence of the allium family. There is nothing so annoying as expectantly walking up to the lovely crops you’ve grown, picking your first onion, and looking at it in dismay, wondering what happened to it. This happened to me this week as I picked my very first onion of the season, only to look at the base of it and see that it is covered in onion white rot. As soon as I spotted it, I knew that it is likely that the entire crops of onions, shallots, leeks, and garlic will show signs of infection and be useless. It’s very disheartening after working so hard to keep your crops from bindweed and pests to suddenly find you’ve got white rot in the soil, and there’s not that much you can do. So, this inspired me to write this post to discuss what white onion rot is and what you can do to treat it — naturally, of course.

What is Onion White Rot?

Onion white rot is one of the most serious and common problems with growing allium crops. The fungus appears during the summer and is prevalent until early autumn. It stays in the soil for up to 15 years so if you have a break out of onion white rot, the chances are you won’t be able to grow any more alliums for a long time. If your alliums have been infested by the allium leaf miner, they are even mores susceptible to white rot.

Symptoms of Onion White Rot

The problem with onion white rot is that the chances are you won’t know you’ve got it until you harvest the first crop from the allium family. The first sign of onion white rot is the wilting of the foliage on your veg. Unfortunately, this happens at the same time as you would expect the foliage to begin to change color and wilt for healthy plants, so by then it is far too late and a waste of the entire onion growing season. In wet conditions, the onions’ foliage won’t wilt, but the onion gets loose in the soil. Once you remove the onion, you’ll see a white fluffy mold on the bottom of the bulb. It is soft to the touch and appears rotten. Severely infected onions have small black small growths on them that look like poppy seeds.

Life Cycle of Onion White Rot

Onion white rot starts as sclerotia, which are tiny organisms. They lay dormant in the soil until they sense a member of the allium family. It’s believed by the scientific community that the sclerotia detect the odors that the onion roots give off. Once they know the onions are there, they germinate and produce smaller fungi that attach themselves to the roots of the onions. As these fungi mature, they produce more sclerotia and the cycle repeats itself. In late autumn the fungus lays dormant until the following season. The only flaw in this life cycle is that if they do not sense a member of the allium family, then the organism dies.

How Does Onion White Rot Spread?

The most common way that onion white rot is spread is on gardening equipment and items of footwear. Simply treading on an affected area and wandering to another is enough for onion white rot to infect a new area.

Treating Onion White Rot

The simple answer to “how to treat onion white rot” is that you can’t. There’s no known cure for this fungus. There may, however, be a glimmer of hope. Research is currently being carried out on garlic extract and whether adding this to your soil may reduce onion white rot. The theory behind this is that the sclerotia sense the garlic and begin to germinate. However with no host to feed on, the sclerotia will starve and die. Water an area where allium crops are not being grown with one crushed garlic bulb mixed in 2 gallons of water if you want to try this trick to clear up your soil.

Preventing Onion White Rot

The best way to prevent onion white rot in your garden is by keeping everything clean. From your gardening boots to spades, forks, and trowels, they need to be clean at all times, especially when moving around different areas. You can learn how to clean and care for your boots here. Beware of any gardening equipment bought at yard sales and always clean them before using them. Plants with onion white rot should be burnt and not placed in the composting bin.

Can You Eat Plants Infected With Onion White Rot?

There seems to be some debate on whether or not vegetables that have onion white rot should be eaten. If the infection is not too severe, then some of the crops can be eaten. They need to be eaten straight away though as they will not store or dry. Wash the vegetables well, and either use fresh or freeze.

As soon as you notice the beginning of onion white rot in your soil, then dig up the affected vegetables as soon as possible. This limits the chance of every member of the allium family being destroyed and all your hard work going up in smoke.

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Organic Farm Calls: White Rot on Garlic, Leek, & Onion

The APS Compendium of Onion and Garlic Diseases and Pests offers white rot guidance: avoid introduction, plant removal, long rotations, avoid over-watering during ideal infection periods 60-65 degrees F, and try and identify varieties reported to offer some field tolerance. UC Davis offers similar advice: http://www.ipm.ucdavis.edu/PMG/r584100511.html>

Even conventional agriculture has limited effective options for onion white rot. These include fungicides like Folicur 3.6F (tebuconazole) or pre-plant fumigation with Vapam HL (Metam Sodium) or Telone C-35 (Dichloropropene and chloropicrin). Metam Sodium is among the most widely used crop protection chemicals in the US because of its water-soluble ease of use as a fumigant, solving many problems on a wide variety of horticultural crops. These are all unavailable in organic production.

Buyers beware of gimmicky products. While investigators worldwide test onion white rot control alternatives, they show mixed reliability. High cost, inconsistency, and insufficient control prevent wide adoption of alternatives.

What’s in literature for organic production? Spent mushroom compost had no effect on onion white rot. Onion waste compost materials have reduced sclerotia viability and disease incidence as effective as Folicur fungicide in field trials. These likely work by acting as sclerotia germination stimulants.

Commercial products containing vesicular-arbuscular mycorrhiza, Glomus intradices, were shown to provide season long onion white rot disease suppression nearly as effective as Folicur 3.6F fungicide on organic muck soils of Ontario, Canada. I am not sure if the tested product, MIKRO-VAM, is available as an OMRI Listed product.

Other natural or synthetic fungal germination stimulants have been tested as pre-plant treatments. This is because fungal sclerotia are stimulated to germinate by volatile thiols and sulfides released by soil microorganisms from secretions from the roots of Allium spp. Diallyl disulfide (DADS), or mixing macerated onion products and spraying on fields two weeks prior to planting has been tested; similar in concept to stale seedbed technique for weeds. Biological control with Trichoderma spp. has been tested.

White Rot

White Rot – Sclerotium Cepivorum

This summary is based on a talk by Professor Fred Crowe from Oregon State University. The transcript can be viewed here. The original sound recording is here.

White Rot: Description

White Rot is a fungus that prefers cold weather (it won’t grow above 20-22 degrees C). It doesn’t have functional spores, and it only can spread by being physically moved around, surviving in the soil as small, round, seed-like structures known as sclerotia. These sclerotia can survive in the soil for decades. White rot can also be carried around as active mold inside a plant.

White rot can only grow a centimeter away from the sclerotium or root. It then has to find a root or a bulb to grow on in order to continue growing. White Rot appears on Alliums as a fluffy white growth, which develops at the base of the bulb. It generally it’s found in the first two feet of soil.

Prevention, Treatment and Control

Below are some methods that might work to prevent, treat and control white rot.

  1. Hot Water Bath (before planting)The fungus is vulnerable at temperatures above 45 degrees C, thus dipping seed garlic in hot water will greatly reduce the amount of pathogen and is a good preventative measure, although it may not completely eradicate the fungus. Also, temperatures above 49 degrees C may kill the garlic, so careful temperature control is essential.
  • Diluted Bleach or Alcohol Bath (before planting)Similarly, a 10:1 water and bleach solution was mentioned. Dilute alcohol and hydrogen peroxide might also work. Soaking too long may kill the garlic and these methods should be checked with certifying bodies.
  • Root Exudate Solution (before planting)A solution to stimulate the sclerotia to germinate in the soil can be made using onion or garlic juice using culls from your crop. Once the sclerotia are stimulated and germinate they then die due to lack of nutrient reserves because the garlic is not actually present. The optimum conditions for germination of sclerotia occur when soil temperatures are between 15 degrees to 18 degrees C. Garlic works better because it’s stronger than onions. An effective dilution for garlic is one to a thousand parts garlic and water. The idea is to somehow distribute it over the area that you’re going to crop in the future getting this juice stimulant concoction across the area and down into the soil. It needs to get it as deep as you’ve tilled it. It usually takes 6 months before the sclerotia are receptive. Garlic powder that’s tilled in at 250lbs/acre has also been used.
  • Cessation of irrigation (when disease is observed in the soil)When the disease has been observed, drying out he soil as much as possible has been shown to be beneficial.
  • Compost teaCompost tea has been shown to be effective in disease prevention causing the plants to be more resilient to disease.
  • RoguingIf you see the leaf flagging you’re going to remove it no matter what’s causing it. By the time you see the leaf flagging you usually see a fair amount white fluffy growth present on the bulb or roots, Dig these out with a shovel and remove all that soil around there also. Roguing isn’t perfect because although 99.9% of the sclerotia form on bulbs there’s a few that form on roots, and that’s one reason why it is encouraged to actually dig soil up also, and even then you’re probably not going to get every single sclerotium.
  • FloodingDyking fields up around affected areas and flooding them from May to November can be effective. White rot doesn’t like it wet for long periods of time. It’s a heroic measure but you could actually do it in your home garden. If you dyked up the area that had white rot and flooded it for an entire season and even into the winter if you could, you would probably do as well as if you had applied methyl bromide. Flooding will probably kill over 99% of the sclerotia. It might not kill them in the dyke itself, but could take them back to the point where they could be eliminated in the future
  • SolarizationSolarization is achieved by covering (mulching, tarping) the soil with transparent polyethylene during the hot season, thereby heating it and killing the sclerotia. Solarization can kill white rot, but it can also live deeper than the temperature will penetrate and it might survive below the solarization level.
  • Crop rotationFinally, a 4 year rotation can be used to mitigate white rot damage. 3 years is probably ok and 5 is probably more than you need. The 4 year timeline is the basis that big industry uses as it’s standard for rotation.

Other Resources

  1. “Diseases and Pests of Vegetable Crops in Canada”– The Canadian Phytopathological Society
  2. “Compendium of Onion and Garlic Diseases” – American Phytopath Society

Turns out that onions are nothing to cry over — these flavorful bulbs are packed with nutrients.

“Onions are super-healthy,” said Victoria Jarzabkowski, a nutritionist with the Fitness Institute of Texas at the University of Texas at Austin. “They are excellent sources of vitamin C, sulphuric compounds, flavonoids and phytochemicals.”

Phytochemicals, or phytonutrients, are naturally occurring compounds in fruits and vegetables that are able to react with the human body to trigger healthy reactions. Flavonoids are responsible for pigments in many fruits and vegetables. Studies have shown that they may help reduce the risk of Parkinson’s disease, cardiovascular disease and stroke.

A particularly valuable flavonoid in onions is quercetin, which acts as an antioxidant that may be linked to preventing cancer. “It also might have heart health benefits, though more studies need to be done,” said Angela Lemond, a Plano, Texas-based registered dietitian nutritionist and spokesperson for the Academy of Nutrition and Dietetics.

Quercetin has a host of other benefits, as well, according to the University of Maryland Medical Center, reducing the symptoms of bladder infections, promoting prostate health and lowering blood pressure.

Other important phytochemicals in onions are disulfides, trisulfides, cepaene and vinyldithiins. They all are helpful in maintaining good health and have anticancer and antimicrobial properties, according to the National Onion Association.

Partly because of their use in cooking around the world, onions are among the most significant sources of antioxidants in the human diet, according to a 2002 report in the journal Phytotherapy Research. Their high levels of antioxidants give onions their distinctive sweetness and aroma.

“Foods that are high in antioxidants and amino acids allow your body to function optimally,” said Lemond. “Antioxidants help prevent damage, and cancer. Amino acids are the basic building block for protein, and protein is used in virtually every vital function in the body.”

Sulfides in onions contain necessary amino acids. “Sulfur is one of the most common minerals in our body that assists with protein synthesis and building of cell structures,” said Lemond.

“I like to recommend eating onions because they add flavor without salt and sugar,” Jarzabkowski said. Onions are low in calories (45 per serving), very low in sodium, and contain no fat or cholesterol. Furthermore, onions contain fiber and folic acid, a B vitamin that helps the body make healthy new cells.

Onions are healthy whether they’re raw or cooked, though raw onions have higher levels of organic sulfur compounds that provide many benefits, according to the BBC. A 2005 study in the Journal of Agricultural and Food Chemistry found that there is a high concentration of flavonoids in the outer layers of onion flesh, so you’ll want to be careful to remove as little of the edible part of the onion as possible when peeling it.

Here are the nutrition facts for onions, according to the U.S. Food and Drug Administration, which regulates food labeling through the National Labeling and Education Act.

Nutrition facts

Serving size: 1 medium onion (5.3 oz / 148 g) Calories: 45 (Calories from Fat: 0)

Amount per serving (%DV*) *Percent Daily Values (%DV) are based on a 2,000-calorie diet.

Total fat: 0g (0%)

Total Carbohydrate: 11g (4%) Dietary Fiber 3g (12%) Sugars 9g

Cholesterol: 0mg (0%) Sodium: 5mg (0%) Potassium: 190mg (5%) Protein: 1g

Vitamin A: (0%) Vitamin C: (20%) Calcium: (4%) Iron: (4%)

Health benefits

Heart health

According to Jarzabkowski, onions encourage a healthy heart in many ways, including “lowering blood pressure and lowering heart attack risk.” A 2002 study in the journal Thrombosis Research suggested that sulfur acts as a natural blood thinner and prevents blood platelets from aggregating. When platelets cluster, the risk for heart attack or stroke increases. This research further supports a similar 1992 study in Thrombosis Research that focused on sulfurs in garlic. Furthermore, a 1987 animal study in the Journal of Hypertension demonstrated delayed or reduced onset of hypertension with sulfur intake. However, the authors said more research was needed to determine if this benefit might be found in humans.

Recently, health researchers have noticed a relationship between messaging molecules called oxylipins and high cholesterol management. A 2016 study in the journal Redox Biology found that consuming onions increases oxylipins that help regulate blood fat levels and levels of cholesterol.

The quercetin in onions may also help prevent plaque buildup in the arteries, which reduces the risk of heart attack and stroke, according to the University of Maryland Medical Center. But since most of the studies in this regard have focused on animals, more research is needed to understand the effects in humans.

Anti-inflammatory

Onions’ sulfurs may be effective anti-inflammatory agents, according to a 1990 study in the journal International Archives of Allergy and Applied Immunology.

Quercetin has been found to relax the airway muscles and may provide relief of asthma symptoms, according to a 2013 study in the American Journal of Physiology.

Immune system

“The polyphenols in onions act as antioxidants, protecting the body against free radicals,” said Anne Mauney, a dietitian based in Washington, D.C. Eliminating free radicals can help encourage a strong immune system. According to the University of Maryland Medical Center, the quercetin in onions also reduces allergic reactions by stopping your body from producing histamines, which are what make you sneeze, cry and itch if you’re having an allergic reaction.

Cancer

A 2015 meta-analysis found that intake of allium vegetables, including onions, were associated with reduced gastric cancer risk. According to World’s Healthiest Foods from the George Mateljan Foundation, eating between one and seven servings of onions per week may help reduce the risk of colorectal, laryngeal and ovarian cancer. Eating several servings of onions a day may help decrease the risk of oral and esophageal cancer.

Quercetin may be a powerful anti-cancer agent, according to Jarzabkowski. The University of Maryland Medical Center said that quercetin may especially inhibit cancer cells in “breast, colon, prostate, ovarian, endometrial, and lung tumors.”

The National Onion Association discussed a recent study from the Netherlands that showed that people who ate onions absorbed twice as much quercetin as those who drank tea, and more than three times as much quercetin as those who ate apples, which are other high-quercetin sources. Red onions are especially high in quercetin, according to the association. Shallots and yellow onions are also good options. White onions contain the least amount of quercetin and other antioxidants.

Onions may help with some side effects from cancer treatments, as well. A 2016 study published in Integrative Cancer Therapies found that consuming fresh yellow onion helped lessen insulin resistance and hyperglycemia in breast cancer patients undergoing a form of chemotherapy known to cause insulin resistance.

Digestion

The fiber in onions promotes good digestion and helps keep you regular. Additionally, onions contain a special type of soluble fiber called oligofructose, which promotes good bacteria growth in your intestines. One 2005 study in Clinical Gastroenterology and Hepatology found that oligofructose may help prevent and treat types of diarrhea. The phytochemicals in onions that scavenge free radicals may also reduce your risk of developing gastric ulcers, according to the National Onion Association.

Regulating blood sugar

The chromium in onions assists in regulating blood sugar. The sulfur in onions helps lower blood sugar by triggering increased insulin production. One 2010 study in the journal Environmental Health Insights revealed that this might be especially helpful to people with people with diabetes. People with Type 1 and Type 2 diabetes who ate red onions showed lower glucose levels for up to four hours.

A 2014 meta-analysis in the journal Nutrition found that patients with Type 2 diabetes saw more normalized liver enzymes and lower glycemic levels when consuming sliced onions.

Bone density in older women

A 2009 study in the journal Menopause found that daily consumption of onions improves bone density in women who are going through or have finished menopause. Women who ate onions frequently had a 20 percent lower risk of hip fracture than those who never ate onions.

Health risks

While not especially serious, eating onions can cause problems for some people. The carbohydrates in onions may cause gas and bloating, according to National Digestive Diseases Information Clearinghouse. Onions, especially if consumed raw, can worsen heartburn in people who suffer from chronic heartburn or gastric reflux disease, according to one 1990 study in the American Journal of Gastroenterology.

Eating a large amount of green onions or rapidly increasing your consumption of green onions may interfere with blood thinning drugs, according to the University of Georgia. Green onions contain a high amount of vitamin K, which can decrease blood thinner functioning.

It is also possible to have a food intolerance or an allergy to onions, but cases are rare, according to an article in the Journal of Allergy and Clinical Immunology. People with onion allergies may experience red, itchy eyes and rashes if an onion comes into contact with the skin. People with an intolerance to onions may experience nausea, vomiting and other gastric discomfort.

Lastly, Jarzabkowski encouraged people to make sure their onions are fresh. “Onions keep for a long time,” she said, “but they still spoil.” Onions spoil much faster if they are chopped or sliced. If you cut up your onions for later use, be sure to refrigerate them in a closed container. A 2015 study found that unrefrigerated yellow onions showed potential growth of E.coli and salmonella, though refrigerated ones did not.

Onion history

According to the National Onion Association:

Onions probably originated in central Asia, in modern-day Iran and Pakistan. Prehistoric people probably ate wild onions long before farming was invented. Onions may have been among the earliest cultivated crops.

Onions also grew in Chinese gardens as early as 5,000 years ago, and they are referred to in the oldest Vedic writings from India. As early as the sixth century B.C., a medical treatise, the Charaka Sanhita, celebrates the onion as medicine, a diuretic, good for digestion, the heart, the eyes and the joints.

A Sumerian text dated to about 2500 B.C. tells of someone plowing over the governor’s onion patch.

In Egypt, onions were planted as far back as 3500 B.C. They were considered to be objects of worship, and symbolized eternity because of the circle-within-a-circle structure. Paintings of onions appear on the inner walls of pyramids and other tombs.

Onions were buried with mummies. Some Egyptologists theorize that onions may have been used because it was believed that their strong scent and/or magical powers would prompt the dead to breathe again.

Onions are mentioned in the Bible. In Numbers 11:5, the children of Israel lament the meager desert diet enforced by the Exodus: “We remember the fish, which we did eat in Egypt freely, the cucumbers and the melons and the leeks and the onions and the garlic.”

The Greeks used onions to fortify athletes for the Olympic games. Before competition, athletes would consume pounds of onions, drink onion juice and rub onions on their bodies.

The Romans ate onions regularly. Pedanius Dioscorides, a Roman physician of Greek origin in first century A.D., noted several medicinal uses of onions.

Pliny the Elder catalogued Roman beliefs that onions could cure poor vision, induce sleep, and heal mouth sores, dog bites, toothaches, dysentery and lumbago. Pliny wrote of Pompeii’s onions and cabbages, and excavators of the doomed city found gardens where, just as Pliny had said, onions had grown. The bulbs had left behind cavities in the ground.

By the Middle Ages, the three main vegetables of European cuisine were beans, cabbage and onions. Onions were prescribed to alleviate headaches, snakebites and hair loss. They were also used as rent payments and wedding gifts.

The Pilgrims brought onions with them on the Mayflower. However, they found that Native Americans were already using wild onions in a variety of ways: eating them raw or cooked, as a seasoning or as a vegetable. Onions were also used in syrups, as poultices, as an ingredient in dyes, and even as toys.

Onion facts

Slicing onions makes you cry because when you cut into it, the onion produces a sulfur-based gas. The gas reacts with the water in your eyes and forms sulfuric acid. To rid your eyes of this fiery irritant, your tear ducts work overtime. For no more (or fewer) tears, try moving your face farther away from the onion so the gas disperses before reaching your eyes.

Another suggestion for reducing tears is to first chill the onions for 30 minutes. Then, cut off the top and peel the outer layers leaving the root end intact.

Bulb onions are yellow, red or white. In the United States, yellow onions make up about 87 percent of the commercial onion crop; red onions are 8 percent; white onions, 5 percent.

Onions range in size from less than 1 inch to more than 4.5 inches in diameter. The most common sizes sold in U.S. markets are 2 to 3.75 inches.

Scallions, or green onions, are actually immature yellow, red or white onions, harvested before the bulb begins to form. “Spring onions” and “salad onions” are other aliases for immature onions.

A scallion is not a shallot. This misnomer probably occurs because “échalion” is another name for the shallot, derived from the French échalote. Shallots have a distinctive taste, but the flavor is closer to that of mature onions than to that of scallions.

The largest onion ever grown weighed 10 lbs. 14 ounces (about 5 kilograms), according to the Guinness Book of World Records.

U.S. farmers plant about 125,000 acres of onions each year and produce about 6.2 billion pounds a year. The top onion-producing areas are Washington, Idaho, eastern Oregon and California.

The leading onion production countries are China, India, United States, Turkey and Pakistan.

The average American eats 20 lbs. (9 kg) of onions per year.

To avoid “onion breath,” eat a sprig of parsley, or rinse your mouth with equal parts lemon juice and water, or chew a citrus peel.

  • Why Does Slicing Onions Make Me Cry?
  • 7 Strange Signs You’re Having an Allergic Reaction
  • What Are Flavanoids?

Originally published on Live Science.

Onions not only provide flavor, they also provide important nutrients and health-promoting phytochemicals.

  • High in vitamin C, onions are a good source of dietary fiber, and folic acid.
  • They also contain calcium, iron, and have a high protein quality (ratio of mg amino acid/gram protein).
  • Onions are low in sodium and contain no fat.
  • Onions contain quercetin, a flavonoid (one category of antioxidant compounds).

Antioxidants are compounds that help delay or slow the oxidative damage to cells and tissue of the body. Studies have indicated that quercetin helps to eliminate free radicals in the body, to inhibit low-density lipoprotein oxidation (an important reaction in the atherosclerosis and coronary heart disease), to protect and regenerate vitamin E (a powerful antioxidant), and to inactivate the harmful effects of chelate metal ions.

Want to try some great onion recipes? Go here.

How to get more quercetin in your diet:

  • Apples
  • Tea
  • Onions

Recent studies at Wageningen Agricultural University, the Netherlands, showed that the absorption of quercetin from onions is twice that from tea and more than three times that from apples.

Based on studies conducted at The Queen’s University at Belfast, Ireland and Wageningen Agricultural University, the content of quercetin in onions is estimated to be between 22.40 mg and 51.82 mg per medium-sized onion (100 grams). Further research at the Agricultural University of Wageningen showed that daily consumption of onions may result in increased accumulation of quercetin in the blood.

Studies are in progress to determine whether the increased quercetin accumulation from eating onions translates into significant antioxidant benefit.

Onions – Phytochemical and Health Research

Click here to view or download the guide (PDF)

Other studies have shown that consumption of onions may be beneficial for reduced risk of certain diseases.

A 2019 study in China found that regular consumption of allium vegetables (of which the onion is a member) could reduce the incidence of colorectal cancer by as much as 79 percent. The study recommended consumption of 35 pounds of alliums per year. (That’s slightly higher than the average American consumption of onions, which sat at 21.9 pounds per person in 2017.

A study published in August 2019 showed a clear link between the amount of onions and garlic consumption and the reduced risk of breast cancer.

Consumption of onions may prevent gastric ulcers by scavenging free radicals and by preventing growth of the ulcer-forming microorganism, Heliobacter pylori.

  • University of Wisconsin-Madison researchers found that the more pungent onions exhibit strong anti-platelet activity. Platelet aggregation is associated with atherosclerosis, cardiovascular disease, heart attack, and stroke.
  • A study in progress at the University of Wisconsin is determining the extent to which onion consumption and specific onion compounds affect the in vivo aggregation of blood platelets. “Using an in vivo model, we are beginning to investigate and, in some cases, confirm the potency of the onion as a blood thinner and platelet inhibitor.

“Onions may be among the vegetables that will be prized not only for their addition to our cuisine, but for their value-added health characteristics,” said Irwin Goldman, Associate Professor of Horticulture, University of Wisconsin-Madison.

A recent study at the University of Bern in Switzerland showed that consumption of one gram dry onion per day for four weeks increased bone mineral content in rats by more than 17% and mineral density by more than 13% compared to animals fed a control diet. This data suggests onion consumption has the potential to decrease the incidence of osteoporosis.

Several studies have shown quercetin to have beneficial effects against many diseases and disorders including cataracts, cardiovascular disease as well as cancer of the breast, colon, ovarian, gastric, lung, and bladder.

In addition to quercetin, onions contain the phytochemicals known as disulfides, trisulfides, cepaene, and vinyl dithiins. These compounds have a variety of health-functional properties, including anticancer and antimicrobial activities.

10 Magical Benefits of Onions That Keep the Doctor Away

I was born in Delhi and spent most of my childhood here. It was only in college that I left for Ahmedabad and later worked for a few years in Mumbai. As a food enthusiast, I realised early on in life that there is so much variety in India, that you can spend a lifetime sampling it and yet not end up trying everything. Every state, or rather each district, has its own unique cuisine, love for certain ingredients and traditions around food. The one thing that I noticed most when I moved from Delhi to West India, was the absence of onions on my thali, in Maharashtra, Gujarat or even further south like Karnataka and Kerala. There was the odd chopped ‘kaanda’ alongside pav bhaji, but that was a rarity with other dishes. Onions are a staple in parts of North India – Punjab, Haryana, UP, Rajasthan, etc. No meal is complete without some raw onion on the side. Can you imagine a plate of chole bhature without lachcha pyaz? Or a seekh kebab without onion dunked in green chutney? Onion may be a humble ingredient but it holds centrestage in our meals here. Like many traditions, this one too has it’s basis in scientific reasoning. My grandmother would squash a whole onion with the palm of her hand and add it to our plates in summers. Fondly called ‘mukka pyaz’, it was meant to keep us cool in this scorching heat. Biji (grandmom) wasn’t wrong. There are many benefits of onions, and one of them is that it has cooling properties.

Here’s a look at some of the incredible raw onion benefits:


Onion also has cooling properties

Nutritional Composition of Raw Onions

One cup of chopped onion contains approximately:

a) 64 calories

b) 15 grams of carbohydrate

c) 0 grams of fat

d) 3 grams of fibre

e) 2 grams of protein

f) 0 grams of cholesterol

g) 7 grams of sugar

h) 10% or more of the daily value for vitamin C, vitamin B-6 and manganese.

i) They also contain small amounts of calcium, iron, folate, magnesium, phosphorus and potassium and the antioxidants quercetin and sulfur.
(Also Read: Health Benefits Of Amchur: How To Use And Make Amchur Powder At Home​)
Raw onion is known to lower the production of LDL

10 Magical Raw Onions Benefits You Must Know :

1) Raw onion is known to lower the production of LDL (bad cholesterol) and keep your heart healthy.

2) The vitamin C (which remains intact while they are in the raw form) along with the phytochemicals present in onions helps build immunity.

3) Quercetin, a powerful compound found in onions, has been suggested to play a role in preventing cancer, especially stomach and colorectal cancers.

4) Chromium, also present in this root vegetable, may help regulate blood sugar.

5) A mixture of onion juice and honey (which helps make it less pungent) is said to be effective as a cure for fever, common cold, allergies, etc.

6) Keep a small piece of onion under the nostrils and inhale, to stop or slow down a nose bleed.

7) Folate in onions also helps with depression and aids sleep and appetite.

8) The vitamin C helps formation of collagen that is responsible for skin and hair health.

9) Antibacterial and anti-inflammatory properties of onions have been proven. One study also suggested that freshly chopped raw onions have these anti-bacterial properties, not chopped onion which has been allowed to sit for a day or two.

10) Chewing raw onions improve our oral health (though your breath may stink). They help eliminate bacteria that can lead to tooth decay and gum issues.
(Also Read: 8 Health Benefits Of Turmeric (Haldi): Getting Back To The Roots)
Chewing raw onions improve our oral health ​
Did You Know?

The flavonoids in onion, which are responsible for many of the health benefits above, are usually more concentrated in the outer layers of the bulb. To get the maximum benefit, try to peel as little of the outer skin as possible. Over-peel and you can end up with unwanted loss of flavonoids. It is estimated that a red onion may lose about 20% of its quercetin and almost 75% of its anthocyanins if it is over-peeled.
(Also Read: 6 Amazing Benefits of Aloe Vera for Hair, Skin and Weight-Loss)

The flavonoids in onion which are responsible for many of the health benefits

An estimated 105 billion pounds of onions are grown across the world every year and the vegetable is supposed to have been cultivated since 5000 years. They are very popular in some cuisines in India, Chinese, Mexican etc. You may hate chopping them because of the tears, but there are some quick tips to take care of that too. Love it or hate it, onions play a pivotal role in the food culture of our country. And given the health benefits above, it is no surprise.

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