Plant Pathology: Lab Quiz 4
Acervulus
A structure in which conidiophores may form. Appears as small black spots on the leaf surface. May have setae.
Activated defense
Resistant activators activate a plant’s natural resistance responses against abiotic stresses, insects, and disease. Stimulates disease resistance response. Can reduce plant growth rate and crop yield by drawing away resources. Can cause more negative effects if applied to plants that are stressed. Too much can cause plant death. The cuticle may become thicker, and the plant may produce anti-microbial compounds. Cell walls are made in order to quarantine the pathogen. Two main forms: systemic acquired resistance, and induced systemic resistance.
Aflasafe™
A new biopesticide. A non-toxic strain of Aspergillus is introduced to crops prior to harvest; it outcompetes toxic strains, virtually eliminating aflatoxin from the crop. Provides long-term benefits, and does not need to be applied every year.
Aflatoxin
A mycotoxin produced by some Aspergillus species. A colourless toxin; only laboratory tests can confirm its presence. Can cause liver cancer, suppress the immune system, retard growth and development in children, and cause liver failure and death. Caused the death of 200 people 2004 – 2006.
Aggressive strains
Later strains of Ophiostoma novo-ulmi. Arrived in the Great Lakes region in the 1940s. Moved to the UK in the 1960s, where it killed 80% of elm trees. Found in other European countries in the 1970s, and in New Zealand in 1989.
Agrostis stolonifera
A pathogen that causes dollar spot.
Albert Hofmann
In 1938, synthesized LSD, a strong hallucinogen, from alkaloids of Claviceps purpurea. It can be used to treat neurosis, sexual dysfunctions, and anxiety.
Alpha-Brazil
A race of Colletotrichum lindemuthianum that was introduced to Ontario in seeds from the USA.
Alternaria dauci
A deuteromycetes pathogen that causes carrot leaf blight.
Alternaria diseases
Common diseases occurring in many hosts. Symptoms are foliar spots, damping off, stem rots, and fruit rots.
Alternaria solani
A deuteromycetes that causes early blight. May be cultured on media such as V8 juice, producing a pigmented gray-black hairy colony. Haploid, septate mycelium become darkly pigmented with age. Sporulation is stimulated by light. Has simple conidiophores. Conidia are borne singly or in a chain of two on a conidiophore. Conidia are pigmented, sometimes beaked, and have 9 – 11 transverse septae. There may be races of Alternaria solani.
Alternaria sp.
A large and important genus of pathogenic ascomycetes fungi. Cause a significant number of important diseases, including decay and rot of fruits, a post-harvest disease. Some of the most common fungi in the air and soil: saprophytes and parasites. Associated with hay fever allergies. Often secondary invaders. Species with conidia with tails are usually pathogens.
American chestnut
Castanea dentata

Was one of the three most prevalent trees in North America. Highly susceptible to chestnut blight. Due to chestnut blight, it is now an endangered species in Canada. It is being bred with Asian chestnut to produce resistance.

Antheridium
Spermatium

The male gametangia. Its nucleus passes into the ascogonium to form the dikaryon, in the producion of an ascus.

Anthracnose
“Carbuncle disease”

A term coined in 1886 to refer to diseases characterized by a dark, sunken lesion. Common on the foliage of many plants, from deciduous trees to grasses. Each fungus is host specific. Includes several species of Colletotrichum. Penetrates hosts with an appressorium. There are often acervuli on the leaf surface.

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Apothecium
plural: Apothecia

An ascocarp. An open, cup or saucer-shaped structure where asci are exposed. Looks like an “upside down” mushroom. Found in white mould.

Apple
Has been a crop since 6500 BC. Play an important role in northern latitudes. It can prevent scurvy with vitamin C. It is an important symbol.
Appressorium
plural: Appressoria

A structure which forms from the germ tube during penetration. Forms at the junction between two host cells. After it forms, the spore dies. Uses enzymes to dissolve the cuticle and push it aside, forming a crater-shaped hole into which it presses itself. The cuticle glues it to the surface of the host. Produces a penetration peg.

Ascocarp
A structure in which asci may form. Includes chasmothecia, perithecia, pseudothecia, apothecia, and naked asci.
Ascogonium
The female gamete. The nucleus of the antheridium passes into it to form the dikaryon in production of an ascus.
Ascomycetes
Sac fungi

True fungi

A group of fungi classified by sexual structures. Produce ascospores in sacs; in ascocarps. May produce conidia with simple conidiophores or pycnidia. Septate mycelia.

Ascomycetes apple scab
The most important disease of apples, caused by Venturia inaequalis. Originated in Kazakhstan, where Malus species originate. It occurs worldwide, wherever apples are grown. It has been researched for over 100 years.
Ascomycetes apple scab conditions
Most ascospores mature when fruit buds open, and spores are discharged from pseudothecia for 3 – 5 weeks after petal fall; rainfall is needed for release. Ascospores require different amounts of time of continual wetness in order to germinate, depending on the temperature: 28 hours at 6°C, 14 hours at 10°C, 9 hours at 18 – 24°C, and 12 hours at 26°C. The optimal temperature is 20°C, requiring only 6 – 7 hours of wetness.
Ascomycetes apple scab dissemination
Ascospores of Venturia inaequalis are carried on the wind.
Ascomycetes apple scab hosts
Ascomycetes apple scab affects apple and crabapple.
Ascomycetes apple scab management
Reduce or eliminate inoculum on overwintering leaves. Prune trees to improve spray coverage, promote air and light, and reduce time for leaves and fruit to dry. Fungicides are the most common and successful method for commercial cultivars.
Ascomycetes apple scab symptoms
Light, olive-coloured irregular spots on the lower surface of sepals and young leaves; mycelia grow beneath the epidermis. Lesions become darker and develop a velvety surface, then they become black and raised. Lesions can develop on the upper surface of older leaves. Infected fruit develop circular, velvety, olive-green lesions, which become darker and scabby. The fruit is misshapen, cracked, and drops prematurely.

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Ascospore
A sexual spore produced by an ascus in an ascomycetes. Eight are present on each ascus, due to meiosis and mitosis which occurs. They are ejected one by one, following buildup of pressure. The first ascospore ejected goes the furthest. Have a wide variety of shapes and structures. Take more energy to produce than conidia.
Ascus
plural: Asci

A structure which produces ascospores. Found in ascocarps. An ascogonium fuses with an antheridium, producing a dikaryotic ascogenous hyphae. Nuclei fuse, producing a zygote. The crozier hook helps maintain dikaryotic state. Meiosis produces four haploid nuclei, which each undergo mitosis and walls form to produce eight haploid ascospores. There may be pressure in teh ascus which can shoot ascospores up to a metre away. After ascospores are ejected, the ascus can undergo another round of division to produce eight more ascospores.

Asexual stage
Anamorph

Imperfect stage

The mitosporic, asexual stage of a fungi.

Aspergillus flavus
An ascomycetes pathogen which infects corn kernels.
Aspergillus sp.
Caused decreased germination of barley seeds. Flour that is made from seeds that are over 20% infected has an “off” flavour; it is unknown if this is a helath hazard. Many species produce aflatoxins.
Barley scald
A disease caused by Rhynchosporium secalis.

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Basidiospore
Sexual spores produced by a basidium in basidiomycetes.
Basidium
A structure which produces basidiospores in basidiomycetes.
Bean anthracnose
Anthracnose of bean

A disease caused by Colletotrichum lindemuthianum. Almost worldwide distribution. There was an oubreak in Canada in 1976 due to introduction of new races.

Bean anthracnose conditions
Bean anthracnose favours cool to moderate temperatures with prolonged periods of high humidity and leaf wetness. Moisture is required for spore development, spread, germination, and infection.
Bean anthracnose dissemination
Spores of Colletotrichum lindemuthianum form from pink masses on lesions, and may spread by wind-blown rain, people, or machinery when plants are wet.
Bean anthracnose hosts
Bean anthracnose most commonly affects dry and snap beans, Phaseolus vulgaris. May also affect lima bean (P. lunatus), scarlet runner bean (P. multifolorus), mung bean (P. aureus), cowpea (Vigna sinensis), and broad bean (Vicia faba).
Bean anthracnose management
Use anthracnose-free seed and resistant varieties. Grow in semiarid areas with little rainfall and high temperatures during the growing season. Clean debris from shipments, and isolate shipments. Do not enter fields when plants are wet, and avoid unnecessary movement in fields. Till soil after harvest, and use a two-year crop rotation. Foliar application of fungicides. Seed treatments. Bioherbicides, and plant pathogens as biocontrol of weeds. Destroy infested material.
Bean anthracnose survival
Colletotrichum lindemuthianum overwinters in bean seed; survival in soil or plant residue depends on environmental conditions. It can survive for 5 years in bean pods that are dried and stored at 4?C, but survival is less when in contact with water.
Bean anthracnose symptoms
Poor seed germination, poor seedling vigour, and low yields. Seeds have low quality rating due to brown-black blemishes and sunken lesions. Seedlings of infected seeds have dark brown-black lesions on cotyledons and stems. Cotyledons senesce prematurely, and plant growth is stunted. Lesions may girdle the stem, killing the seedling. Time from infection of a healthy plant to symptoms is 4 – 9 days, depending on coniditions and host variety and age. Linear, dark, brick-red to black lesions form on veins on the undersides of leaves, and discolouration spreads to the upper side. Small, red-brown to black blemishes and circular, reddish brown lesions form on pods, which turn grey and become surrounded by a circular red-brown to black border. Severely infected pods may shrivel; these pods have infected seeds. Pink masses of spores may form on lesions in humid conditions.

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Bean rust
A disease. The pathogen forms a structure over the stomata of the host.

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Beetle gallery
A symptom of Dutch elm disease. Beetles plant eggs in the bark, and larvae hatch and eat away at the plant as they crawl away from the spot where they hatched. Graphium-type conidia of Ophiostoma novo-ulmi may be found in beetle galleries, and stick to beetle larvae.
Benzothiadiazole/Acibenzolar
A resistance activator. Includes Actigard and Dac Action.
Biological control
A control method for white mould. Uses mycoparasites, mostly applied to the soil where sclerotia survive.
Biotroph
Organisms which require living plant cells for nutrition. Cannot be cultured.
Bitunicate asci
“Two coats”

An ascus with two walls. Consists of a thin brittle outer wall, and a thick elastic inner wall. When spores are ready, the outer shell splits open and the inner wall takes up water, building up pressure that eventually shoots spores up to a metre away. Found only in pseudothecia.

Blumeria graminis f.sp. hordei
An ascomycetes pathogen which causes powdery mildew of barley. Produces chasmothecia and conidia.
Blumeria graminis f.sp. tritici
An ascomycetes pathogen which causes powdery mildew of wheat. Produces chasmothecia and conidia.
Botrytis cinerea
An ascomycetes pathogen that causes botrytis rot.
Botrytis rot
A common disease, caused by Botrytis cinerea. Affects cherries. Symptoms are similar to brown rot. Causes fruit rot problems in the field and post-harvest in stone and pome fruits.

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Botrytis sp.
An ascomycetes pathogen which causes grey mould of most fruits in storage, a post-harvest disease.
Brown rot
A common disease, caused by Monilinia fructicola.
Brown rot hosts
Brown rot affects stone fruits including peaches, cherries, plums, prunes, nectarines, and apricots.
Brown rot infection
Blossoms are infected with ascospores, which leads to quiescent infections that develop into brown rot in the fruit stage. Conidia can infect fruit later in the season.
Brown rot survival
Monilinia fructicola overwinters in mummies and in twig cankers.
Brown rot symptoms
Blossom blight, twig blight, twig canker, and brown fruit rot.

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Brown spot of soybean
Septoria brown spot

A disease caused by Septoria glycines. Not to be confused with bacterial leaf blight. Found in all soybean fields in Kentucky. Causes yield losses up to 15% in favourable conditions. Often plants can recover from early season infections with no permanent damage.

Brown spot of soybean conditions
Symptoms are worse in fields planted in late April, river bottom fields, and when there is fog or morning shade. Infection is greatest at 25?C, with leaf wetness lasting up to 36 hours. Disease development is hindered in hot, dry weather, but will resume when favourable conditions return.
Brown spot of soybean dissemination
Spores of Septoria glycines are splashed up from the ground onto the leaves.
Brown spot of soybean management
Do not grow soybeans after soybeans without tillage. Use late-maturing varieties and resistant varieties. Avoid early planting dates. Fungicides are only needed for late season infections, applied in R3 – R5. Manage host weeds. Till after soybeans.
Brown spot of soybean survival
Septoria glycines overwinters in crop residues and debris of weeds including velvetleaf, as well as in seed to a limited extent.
Brown spot of soybean symptoms
Small, 1/4 inch, irregular red-brown spots on both sides of unifoliate leaves 2 – 3 weeks after planting. Spots occur on trifoliate leaves later in the season, starting on the lower leaves and spreading upwards. Spots may coalesce to form black-brown irregular bltoches. Leaves yellow and drop.

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Butanediol
An ISR resistance activator.
Candida albicans
A yeast that is a human opportunistic pathogen.
Carrot leaf blight
A disease caused by Cercospora carotae and Alternaria dauci.

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Celery leaf curl
A disease caused by Colletotrichum acutatum.

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Cephalosporum-type conidia
Conidia produced by Ophiostoma novo-ulmi in the xylem of the host. Not sticky like graphium-type conidia. They spread through the xylem.
Cercospora apii
A deuteromycetes pathogen that causes cercospora early blight. Overwinters in plant debris and seed. Has dark, long, needle-like conidia which may disseminate on rain splash, machinery, people, and animals. Produces simple conidiophores arranged in fascicles.
Cercospora carotae
A deuteromycetes pathogen that causes carrot leaf blight.
Cercospora early blight
A leaf blight disease of celery caused by Cercospora apii. An important disease of celery, causing yield reduction.

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Chasmothecium
plural = Chasmothecia

Cleistothecium

An ascocarp. A closed structure with hyphal appendages, and one or more asci. Dark coloured with melanin for UV protection. Can survive teh winter. Found in powdery mildew.

Chelated metals
A resistance activator. Includes chelated iron (Fiesta).
Chestnut blight
A disease caused by Cryphonectria parasitica. Affects American chestnut. Introduced to the USA in 1904. Symptoms include cankers, with no foliar symptoms. Infected branches and stems die quickly. May be managed with hypovirulent strains of the parasite applied to cankers, to contain spread of the disease.

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Cirrhi
Long, gelatinous tendrils that release conidia from pycnidia of Septoria apiicola in wet weather.
Civitas + Harmonizer
An SAR and ISR resistance activator. A mineral oil and chelated copper, respectively. Effective against dollar spot. Civitas was developed by PetroCan.
Cladosporium paeonia
A deuteromycetes that causes peony leaf blotch.
Claviceps purpurea
A fungal pathogen that causes ergot of rye. Contains alkaloids that can prevent bleeding after childbirth, treat Parkinson’s disease, and be converted into pharmaceutical and illegal drugs.
Cochliobolus sativus
A leaf spotting pathogen which causes spot blotch.
Collar rot
When early blight lesions girdle the stem of a tomato seedling. Leads to reduced plant vigour or death of the seedling.
Colletotrichum acutatum
A deuteromycetes pathogen that causes celery leaf curl.
Colletotrichum gloeosporioides
A fungus used as a bioherbicide to kill northern jointvetch in the USA.
Colletotrichum lindemuthianum
Also known by its sexual stage, Glomerella cingulate.

A fungal pathogen that causes bean anthracnose. There are several races. Conidia are produced in acervuli with dark setae.

Colletotrichum sp.
A genus of deuteromycetes. Causes several anthracnose diseases. Penetrates hosts with an appressorium. Produces conidia in saucer-shaped acervuli with dark setae.
Conidia
Asexual spores of deuteromycetes, ascomycetes, and basidiomycetes. Have many shapes, sizes, and colours. Produced on conidiophores. Take less energy to produce than ascospores.
Conidiophores
Asexual structures of deuteromycetes. Have many shapes and sizes. Produce conidia. May occur singly, or in organized groups or clusters with specialized structures: acervuli, pycnidia, sporodochia, and synnema.
Crozier hook
A structure which helps maintain the dikaryotic state during production of an ascus.
Cryphonectria parasitica
An ascomycetes pathogen which causes chestnut blight. Produces perithecia in small stromata; perithecia necks are long and come togehter and protrude through the bark. Ascospores are forcibly ejected and dispersed by wind.
Cuticle
A physical barrier to infection. It can thicken with activated defense.
Deoxynivalenol (DON)
A mycotoxin produced by Fusarium graminearum which can contaminate grain. The limit for human consumption is 2 ppm in uncleaned soft wheat. Cattle and poultry can tolerate 5 ppm. Swine, young calves, and lactating dairy cows can tolerate 1 ppm. Causes decreased feed intake in animals and poor weight gain when over 2 mg/kg of feed; the animal refuses to eat, and can starve to death. Costs $40 – $50 million each year in swine losses in Ontario.
Deuteromycetes
Deuteromycota

Asexual fungi

Imperfect fungi

An artificial grouping of organisms, because they are difficult to classify. The asexual stages of ascomycetes or basidiomycetes, but the sexual stages are absent or rare. Description is based on conidia or mycelial characteristics. Produces conidia and chlamydospores. Conidia are formed in pycnidia, acervuli, sporodochia, and synnema. Not all produce conidia. May produce sclerotia. Cause diseases including leaf spots, blights, fruit rots, anthracnoses, stem rots, root rots, and vascular wilts.

Differential host series
Twelve standard varieties of bean that are used to identify race of Colletotrichum lindemuthianum. The fungus is inoculated onto each cultivar, and binary numbers assigned to each cultivar that is susceptible are added to get the identification number of the race.
Dikaryotic
(n+n)

Containing paired, unfused, haploid nuclei. Dikaryotic hyphae are produced on the same mycelium that produces conidia. The nucleus of the antheridium passes into the ascogonium, but there is no fusion of the nuclei.

Diploid
Having two complete sets of chromosomes.
Disease Severity Value (DSV)
In TOMcast, accumulation of daily DSVs results in recommendations for fungicide applications.
Dissemination
The seventh step of infection. Spores fly away, or are vectored away, to infect other tissues.
Dollar spot
A disease caused by Agrostis stolonifera. Can be managed with Civitas + Harmonizer activated defense treatment.

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Dreschlera sp.
A genus of deuteromycetes.
Dutch elm disease (DED)
A disease caused by Ophistoma novo-ulmi. Discovered in 1919 by a Dutch botanist. First had nonaggressive strains, then aggressive strains. One billion wild and 0.5 billion domestic elm trees were killed, costing $50 billion. In 1950, $12 billion was spent on removal of dead elm trees. Spread in Canada was disrupted by the successful use of quarantine processes.
Dutch elm disease dissemination
Ophiostoma novo-ulmi is vectored by native elm bark beetle and European elm bark beetle. Graphium-type conidia stick to the beetles. Humans can be vectors by movign wood or beetles; this is how the disease was able to spread across oceans to North America and New Zealand.
Dutch elm disease management
Biological controls include inoculation of trees with microorganisms that can reduce the disease; this is still experimental. Weakly virulent strains of Ophiostoma ulmi or Verticillium sp. can induce resistance to O. novo-ulmi. This was developed in the Netherlands, and is now being tested in the USA and Canada.
Dutch elm disease symptoms
Vascular bundles turn brown. There are beetle galleries in the bark. Death of the elm tree; the tree dies standing and must be removed.

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Early blight
A polycyclic disease caused by Alternaria solani. Worldwide distribution; occurs where tomatoes and potatoes are grown. Problematic east of the Rocky Mountains.
Early blight conditions
Early blight favours warm (24 – 29°C), humid conditions. Conidia germinate in free moisture at 28 – 30?C. Desiccated germ tubes can grow when re-wetted, allowing infection and sporulation to occur in alternating dry and wet periods. Wet conditions at harvest are favourable for spore germination. Conidiophore formation and spore production occur during wet nights.
Early blight dissemination
Conidia of Alternaria solani are disseminated by wind and rain splash.
Early blight hosts
Early blight affects tomato, potato, and eggplant. Weed hosts include horse nettle and nightshade.
Early blight infection
The germ tube of Alternaria solani penetrates the leaf epidermis directly, through stomata, or through wounds. Older tissues are more susceptible to infection.
Early blight management
Remove potentially infected materials. Control volunteers and weeds prior to planting. Use pathogen-free seed and transplants. Rotate fields with non-susceptible crops. Minimize wounding of tubers during harvest, and avoid harvest in wet conditions. Store tubers at 10 – 13?C at high relative humidity with plenty of aeration, promoting wound healing. Minimize leaf wetness. Improve soil drainage and air circulation. Maintain adequate soil fertility. Manage other diseases to reduce plant stress. Use resistant cultivars. Protective and curative fungicides, every 7 – 10 days; timing of sprays may be based on FAST or TOMcast for tomatoes, or P-DAY for potatoes.
Early blight of potato
Symptoms occur on the stem, foliage, and tubers. Lesions on tubers are sunken and irregular, often surrounded by a raised purple border. Tuber tissue beneath the lesion is leathery or corky with brown discolouration. Tuber lesions are dry.

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Early blight of potato infection
Potato tubers are usually infected through wounds in the tuber skin inflicted during harvest, or swollen lenticels.
Early blight of tomato
Symptoms occur on fruit, stem, and foliage. In young seedlings lesions may girdle the stem, leading to collar rot. Lesions on fruit can reach considerable size, and appear leathery and sunken, and may have concentric rings. Infected fruit often drop prematurely. Can result in reduced fruit size and number. Can reduce yields 9 – 52%.

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Early blight survival
Mycelia and conidia of Alternaria solani overwinter in infected plants, debris, volunteers, weed hosts, seeds, and tubers. Can survive in the soil for several years. Rarely overwinter in thick-walled chlamydospores.
Early blight symptoms
Time from infection to symptoms depends on conditions and host age and cultivar; usually within 5 – 7 days. Black-brown lesions, 1 – 2 mm in diameter enlarge and are often surrounded by a yellow halo. Lesions greater than 100 nm in diameter often become target spot lesions. Lesions on stems are often sunken and lens-shaped with a light centre with concentric rings.

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Elm Recovery Project
A project of the University of Guelph designed as a “dating service” for elm trees. Elms that survived Dutch elm disease are often resistant, but isolated from other elm trees, thus prevented from reproducing. This project brings trees into a nursery for testing, and collects seeds and pollen for reproduction.
Enzymes
May be released by the germ tube cells during penetration. Common in oomycetes. Degrade nutrient sources, allowing nutrients to be absorbed by the fungus; external digestion. There is risk that other fungi may feed on the digeste food.
Erysiphe sp.
A genus of ascomycetes that causes powdery mildew. The chasmothecium has many asci, and strait hyphal appendages.
European elm bark beetle (EEBB)
A shiny, dark red-brown beetle with a black thorax. A vector of Dutch elm disease. Tunnels parallel to the grain of the wood. More attracted to elms with Dutch elm disease infections.
Falih and Wainwright
In 1995, suggested use of soil yeasts to stimulate beneficial processes such as sulfur oxidation and phosphorus solubilisation in the soil.
Fascicle
A bundle of conidiophores.
FAST
Forecasting Alternaria solani on Tomatoes

A method for timing fungicide control of early blight of tomato. Developed by Madden, Pennypacker, and MacNab, and was further modified by Pitbaldo to make TOMcast.

Feng Li
A Chinese diplomat from 5000 BC. Gave up his position to become a farmer of peaches, almonds, persimmons, pears, and apples.
Filamentous stage
The pathogenic, sexual stage of Taphrina deformans. Cannot be grown in culture medium.
Forma specialis (f.sp.)
plural: Forma speciales

A fungal parasite or pathogen that is adapted to a specific plant host species. Have few or no morphological differences from each other. Analogous to pathovars of bacteria.

Fungal cell
Releases pectinases to dissolve plant cell walls. Releases anti-chitinase to counteract chitinase produced by the plant cell.
Fungi
A kingdom of generally microscopic, eukaryotic organisms, usually filamentous with branched, septate hyphae. Spore-bearing, and lack chlorophyll. Cell walls contain chitin and glucans, with no cellulose. Many have asexual and sexual stages. Live as saprophytes or as parasites and pathogens. Some are biotrophs.
Fusarium graminearum
The asexual stage of Gibberella zeae. Penetrates hosts through stomata. Can penetrate a closed stomata. Produces conidia. Produces mycotoxins that contaminate grain including zearalenone and DON.
Fusarium head blight of wheat
A disease caused by Gibberella zeae. Causes yield losses due to floret sterility and poor seed filling. Alters milling and baking qualities of seed.
Fusarium head blight of wheat conditions
Favoured in high temperatures and high relative humidity during flowering. In warm, humid weather conidia are produced and spread to adjacent spikelets.
Fusarium head blight of wheat dissemination
Conidia of Gibberella zeae are splashed onto the heads of wheat.
Fusarium head blight of wheat symptoms
Impaired seed germination.

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Fusarium sp.
An ascomycetes pathogen which causes pink or yellow mould, especially in root crops, a post-harvest disease.
Gametangia
Gametes

Sexual cells produced for dikaryon formation. Includes antheridia and ascogonia.

Geotrichum sp.
An ascomycetes pathogen which causes sour rot of citrus, tomato, and carrot, a post-harvest disease.
Germination tube
Germ tube

A structure that emerges from the spore during pre-penetration. Multiple germ tubes may form to increase the pathogen’s chances. May produce an appressorium, or release enzymes to aid in penetration. It can find stomata by sensing gas gradeints, and can find wounds by sensing exudates such as polysaccharides.

Gibberella ear rot of corn
A disease caused by Gibberella zeae. Causes yield losses due to floret sterility and poor seed filling. Alters milling and baking qualities of seed.
Gibberella ear rot of corn symptoms
Light pink to red mould grows down the ear. Cobs become spongy. Husks are bleached and cling to kernels. Perithecia may be visible as black spots. Impaired seed germination.

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Gibberella zeae
Also known by its asexual stage, Fusarium graminearum. An ascomycetes pathogen which causes fusarium head blight of wheat, gibberella ear rot of corn, as well as diseases of certain grasses. Produces ascospores in perithecia. Launches ascospores at 34.5 m/s, using pressure of 1.54 MPa. The ascospores accelerate at 87,000 g, the highest acceleration in any biological system. Without wind, spores can travel 0 – 8.5 mm.
Glomerella cingulate
The rare sexual stage of Colletotrichum lindemuthianum.
Glume blotch
A leaf spotting disease caused by Stagonospora nodorum.

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Graphium-type conidia
Conidia produced by Ophiostoma novo-ulmi in beetle galleries. They are sticky, and stick to beetle vectors.
Grey leaf spot
A disease caused by Magnaporthe grisea.

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Haploid
Having a single complete set of chromosomes.
Haustorium
plural: Haustoria

A feeding structure produced by fungi which punches into the epidermal cells of the host. Produced by powdery mildwe and late blight of potato. Haustoria have a wide variety of shapes.

Heterokaryon
(n+n)

Containing unfused nuclei from two or more genetically different cells.

Humic acid
A resistance activator.
Hypersensitive response
When a plant cell is infected, the pathogen is detected and the nucleus fights and resists it, and emits chemical signals to other cells. If it cannot defeat the pathogen, there is autolysis, which kills the plant cell, and alerts neighboring cells to arm themselves. Autolysis can kill the pathogen, if response is quick enough, and occurs before the pathogen has a chance to feed.
Incubation
The fifth step of infection. The fungus incubates in the plant tissues during the latent period.
Induced systemic resistance (ISR)
Priming

A type of activated defense. When the cell recieves the signal, it arms its defenses against pathogens. Specific attack; defenses act specifically against the pathogen. Resistance activators include Civitas, Harmonizer, and butanediol.

Infection
Steps are: inoculation, pre-penetration, penetration, intracellular infection, incubation, sporulation, and dissemination.
Infection cushion
A type of appressorium which appears to pinch the surrounding host tissue into a convex mound.
Inoculation
The first step of infection. The spore comes into contact with the plant.
Intracellular infection
The fourth step of infection. Primary hyphae form in the infected cell.
Karyogamy
Fusion of two haploid nuclei, forming a diploid zygote.
Latent period
The time from infection to symptom expression.
Leaf blight of celery
Includes septoria late blight and cercospora early blight of celery. Symptoms are small yellow spots on both sides of leaves, which enlarge and may develop into circular, grey lesions up to 2 cm in diameter, with reddish-purlpe margins. Elongated lesions may appear on petioles. Mycelia are visible in lesiosn in wet conditions at 15 – 30?C.
Leaf blotch
A leaf spotting disease caused by Septoria sp. and Stagonospora sp.

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Leaf spotting complex of wheat
A disease. Plants that emerge from disease seeds are infected directly. Spores produced on infected plants can spread, causing additional infections. Favoured by high relative humidity, and temperatures around 20?C. The disease moves up the plant and the head and kernels can become infected.

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Leaf spotting diseases
Diseases that affect wheat grown on the Canadian Prairies and the Great Plains of the USA. Cause significant yield losses. Caused by one or a combination of the following leaf spotting pathogens: Pyrenophora tritici-repentis, Septoria sp., Stagonospora sp., Staonospora nodorum, Cochliobolus sativus, and Pyrenophora teres f.sp. maculata. Includes tan spot, leaf blotch, glume blotch, spot blotch, and net blotch.
Lettuce drop
A disease caused by Sclerotinia sclerotiorum.

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M.F. Barrus
From Cornell University. Demonstrated that bean anthracnose is seed-borne.
Madden, Pennypacker, and MacNab
From Pennsylvania State University. Developed FAST.
Magnaporthe grisea
A pathogen that causes grey leaf spot. Penetrates the host with an appressorium.
Meiosis
The number of chromosomes per nucleus is halved. The cell is converted from diploid state to haploid state. Occurs in sexual reproduction.
Microsphaera sp.
A genus of ascomycetes that causes powdery mildew. The chasmothecium has many asci, and branched hyphal appendages.
Mitosis
A nuclear division in which the chromosome number remains the same. Occurs in asexual reproduction.
Monilinia fructicola
An ascomycetes pathogen which causes brown rot of tender fruits. Releases sexual and asexual spores in the spring.
Mummy
A mummified fruit from a previous season. May be found on the ground or on the tree. Monilinia fructicola overwinters in mummies of its host.
Mycoparasite
A fungal parasite of another fungi. May be used in biological control of white mould; they attack sclerotia of Sclerotinia sclerotiorum.
Naked ascus
An ascocarp. A single ascus which grows without a surrounding structure. Found in peach leaf curl.
Native elm bark beetle (NEBB)
A greyish-brown beetle with rough texture. A vector of Dutch elm disease. Tunnels perpendicular to the grain of the wood. More attracted to elms with Dutch elm disease.
Net blotch
A leaf spotting disease. Severely infected leaves may die. The disease moves up the plant, and the head can become infected. Has two forms: net form and spot form.

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Net form net blotch
The more common form of net blotch. Caused by Pyrenophora teres f.sp. teres. Starts as tiny green or brown spots, which enlarge into narrow brown blotches with a cross-hatched apperance. Often tissue surrounding the lesion becomes yellow.

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Nonaggressive strain
Early strains of Ophiostoma novo-ulmi. Killed less than 50% of elm trees between 1919 and 1979. Found in the Netherlands in 1919, then in Britain in 1927 where it killed 10 – 20% of elm trees. It spread to the USA in 1930, then to Canada in the 1940s, where it affected trees in Manitoba and Saskatchewan, but still has not spread to Alberta or BC.
Oidium sp.
The asexual stage of Podosphaera pannosa.
Oidium tuckeri
The asexual stage of Unicula necator.
Ophiostoma novo-ulmi
An ascomycetes pathogen that causes Dutch elm disease. Produces graphium-type conidia on beetles in beetle galleries. Produces cephalosporium-type conidia in xylem. Produces conidia in synnema, and produces ascospores in perithecia. Perithecia have a long structure, helping the spores emerge from beneath the bark.
Ophiostoma ulmi
A weakly virulent strain which can be used to induce resistance to Ophiostoma novo-ulmi.
Ostiole
The opening at the tip of a perithecium.
Pathogen-free seed
A management strategy for bean anthracnose. Bean seed that is bean anthracnose-free is produced by growing seed in dry areas with little rain, where the pathogen cannot be dispersed, such as semiarid areas of western USA. Not entirely foolproof.
Peach leaf curl
A disease caused by Taphrina deformans. Affects hosts in the Prunus genus: peaches and almonds. Symptoms include discolouration and curling of leaves, later developing whitish bloom which is naked asci. Germination of conidia requires a minimum of 3 mm of rainfall followed by at least 12 days where conidia remain damp and temperatures are below 19?C. Conidia germinate to produce hyphae which have intercellular growth during the 9 – 33 day incubation period. When symptoms develop, asci are produced at nighttime.

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Penetration
The third step of infection. The germ tube enters through natural openings such as stomata, or wounds. Specialized fungal structures such as appressoria and penetration pegs may penetrate the plant.
Penetration peg
A structure that emerges from the appressorium during penetration. Has very high osmotic pressure, created by concentrations of sugars or salts. The pressure pushes the peg into the host cell. Produces primary and secondary infections of hyphae.
Penicillium sp.
An ascomycetes pathogen which causes blue and green moulds, a post-harvest disease. Produces mycotoxins.
Peony leaf blotch
A disease caused by Cladosporium paeonia.

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Perithecium
plural: Perithecia

An ascocarp. A flask-shaped structure with an ostiole at the tip. Forms beneath the surface of bark. Has perithecial walls, and unitunicate asci. Found in Dutch elm disease.

Phosphites
A resistance activator. Includes Aliette, Appear, SwardPhite, Magallan, and Alude.
Phyllactinia sp.
A genus of ascomycetes that causes powdery mildwe. The chasmothecium has many asci, and spiny hyphal appendages.
Pitbaldo
From Ridgetown College. Developed FAST to create TOMcast.
Plant cell
Releases glucanases and chitinases to dissolve fungal cell walls.
Plasmogamy
Fusion of the cytoplasm of two cells, but not the nuclei. Formation of a heterokaryotic state.
Podosphaera pannosa
Also known by its asexual stage, Oidium sp.

Formly known as Sphaerotheca pannosa. An ascomycetes pathogen which causes powdery mildew of rose. Produces chasmothecia and conidia.

Podosphaera sp.
A genus of ascomycetes that causes powdery mildwe. The chasmothecium has one ascus, and branched hyphal appendages.
Post-harvest diseases
Diseases that develop on plant products during harvest, grading, packing, or transportation. Primarily caused by ascomycetes and deuteromycetes, with some oomycetes, basidiomycetes, and bacteria. Tender and succulent products such as flowers, bulbs, and fleshy fruits are the most susceptible. Post-harvest losses of cereals can be large. Can destroy 10 – 30% of total yield. Mycotoxins may contaminate products. Competition with field fungi prevents invasion of the host until after harvest, and/or, the pathogen’s optimal conditions occur in storage.
Powdery mildew
A disease caused by several genera of ascomycetes pathogens. Pathogens are host-specific biotrophs. Hosts include wheat, barley, cucurbits, grape, strawberry, rose, lilac, apple, and oak. Produce conidia, as well as ascospores formed in chasmothecia. Genera of pathogens are distinguished by the number of asci in the chasmothecium and morphology of its hyphal appendages. Mycelia grow on the surface of the plant, never invading host tissue. Nutrients are absorbed by haustoria.

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Powdery mildew of barley
A disease caused by Blumeria graminis f.sp. hordei.

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Powdery mildew of grape
A disease caused by Unicula necator. Symptoms include patches of white-gray powdery mycelial growth. Chasmothecia may appear as tiny dark specks in the mycelia. Symptoms are most common on the upper surface of leaves, young shoots and stems, buds, flowers, and young fruit.

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Powdery mildew of rose
A disease caused by Podosphaera pannosa. Symptoms include patches of white-grey powdery mycelial growth. Chasmothecia may be visible as dark specks in the mycelia.

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Powdery mildew of wheat
A disease caused by Blumeria graminis f.sp. tritici.

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Pre-penetration
The second step of infection. The pathogen gets ready for penetration. The spore germinate; a germination tube emerges. Can take 6 – 12 hours, depending on pathogen. A film of water must be present on the plant surface for the entire time.
Primary infection hyphae
Thick hyphae that arise from the penetration peg during intracellular infection. Limited to the cell which is initially infected. Doesn’t cause symptoms. The plant cannot tell that it is being attacked.
Pseudothecium
plural: Pseudothecia

An ascocarp. A cavity within a mass of hyphal tissue, usually a black stroma, in which asci are located. Similar to a perithecium, but asci are bitunicate. Found in apple scab.

Pycnidium
A structure in which conidiophores may grow.
Pyrenophora teres f.sp. maculata
A fungal leaf spotting pathogen which causes spot form of net blotch. Overwinters on crop residue and seed. Produces spores in the spring, which are spread to young plants by wind and rain.
Pyrenophora teres f.sp. teres
A fungal leaf spotting pathogen which causes the net form of net blotch. Overwinters on crop residue and seed. Produces spores in the spring, which are spread to young plants by wind and rain.
Pyrenophora tritici-repentis
An ascomycetes leaf spotting pathogen which causes tan spot. Overwinters in crop debris. Conidia are produced on older lesions, and spread to cause secondary infections. Ascospores are produced in pseudothecia. Spores are carried by wind to infect young plants.
Quiescent infection
“Quiet” infection

Latent infection

The host is infected with a pathogen, but there are no symptoms.

Race
Morphologically identical, but genetically distinct strains of Colletotrichum lindemuthianum, affecting different bean varieties. There are more than 100 races reported worldwide. Used to be identified by Greek letters. Now a binomial numbering method is used, using a differential host series.
Race 73
A race of Colletotrichum lindemuthianum. An outbreak occurred in eastern North America. Efforts are underway to develop varieties of bean with resistance. Hosts susceptible to race 73 are MMihelite, Cornell, and Red Mexican (1 + 8 + 64 = 73).
Resistance activators
Chemicals that induce activated defense. Includes phosphites, benzothiadiazole/acibenzolar, chelated metals, Civitas, Harmonizer, silicon, butanediol, and humic acid.
Rhynchosporium secalis
A dueteromycetes pathogen that causes barley scald.
Saccharomyces cerevisiae
A saprophytic yeast. Used in wine making.
Sclerotinia minor
An ascomycetes that is related to Sclerotinia sclerotiorum. Can be used as a biological control for dandelion and other broadleaf weeds on turfgrass. Can be used as a biological control for white mould; it outcompetes it for space.
Sclerotinia rot
A disease caused by Sclerotinia sclerotiorum.

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Sclerotinia sclerotiorum
An ascomcyetes pathogen which causes white mould, lettuce drop, sclerotinia wilt, and sclerotinia rot. Does not produce conidia.
Sclerotinia sp.
An ascomycetes pathogen which causes white and cottony rot, a post-harvest disease.
Sclerotinia wilt
A disease caused by Sclerotinia sclerotiorum. Affects sunflowers.

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Sclerotium
plural: Sclerotia

A small, compact mass of pigmented mycelia that facilitates long-term survival of deuteromycetes fungi in the soil. May become detached and remain dormant until favourable growth conditions return. Composed of a thick, dense shell with thick and dark cells, and a core of thin colourless cells. Rich in oils, and has very little water. Can survive in dry conditions for several years. Germinates in favourable conditions to form fruiting bodies or mycelium with conidia.

Secondary infection hyphae
Hyphae thinner than primary infection hyphae. Found in neighhboring cells of the cell which is initially infected. Form quickly, when the plant is weak.
Secondary metabolites
Chemical compounds that protect an organism from pathogens.
Seed treatments
A management strategy for bean anthracnose. Chemical or biological substances, or a physical process applied to seeds or seedlings, protecting tissue and assuring optimum emergence of the crop. Typically contains a mixture of three fungicides and insecticides, with very small volumes used. Efficacy is variable; infections can survive the treatment.
Septoria apiicola
A deuteromycetes pathogen which causes septoria late blight of celery. Produces pycnidia. Conidia are light-coloured, long, and needle-shaped, and may disseminate on rain splash, machinery, people, or animals. Released from pycnidia during wet weather as cirrhi. Overwinters in plant debris and seed.
Septoria glycines
A fungus which causes brown spot of soybean. Produces a host-specific toxin which causes yellowing and defoliation.
Septoria late blight of celery
A leaf blight of celery caused by Septoria apiicola. An important disease of celery, causing yield reduction. Affects mature celery plants, causing damage to leaves and reducing marketability of stalks. Infection is dependent on duration of leaf wetness, and favourable air temperatures (10 – 30?C). Chlorotic spots on outer leaves become brown-red, and may coalesce to form large necrotic areas. Stalks may have brown lesions. Pycnidia form within lesions, giving them a speckled appearance, and may release conidia in cirrhi.

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Septoria sp.
A genus of deuteromycetes. A leaf spotting pathogen; causes leaf blotch.
Setae
A hair-like structure that forms in acervuli.
Sexual stage
Teleomorph

Perfect stage

The meiosporic, sexual stage of a fungi.

Silicon
An SAR resistance activator.
Soil yeast
Yeast which live in the soil. Can stimulate beneficial processes in the soil, such as sulfur oxidation, and phosphorus solubilisation. Includes Candida, Cryptococcus, Debaryomyces, Hansenula, Lipomyces, Pichia, Aureobasidium, Rhodotorula, Saccharomyces, Schizoblastosporion, Sporobolomyces, Torulaspora, Torulopsis, Trichosporon, Kluyveromyces, and Zygosaccharomyces.
Sphaerotheca sp.
A genus of ascomycetes that causes powdery mildew. The chasmothecium has one ascus, and strait hyphal appendages.
Spilocaea pomi
The asexual stage of Venturia inaequalis. Producse conidia.
Sporodochia
A structure in which conidiophores may form.
Sporulation
The sixth step of infection. Spores are produced on the plant surface. Epidermal cells split, and spores erupt.
Spot blotch
A leaf spotting disease caused by Cochliobus sativus.

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Spot form net blotch
The less common form of net blotch. Caused by Pyrenophora teres f.sp. maculata.

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Stagonospora nodorum
A leaf spotting pathogen which causes glume blotch.
Stagonospora sp.
A leaf spotting pathogen which causes leaf blotch.
Synnema
A structure in which conidiophores may form.
Systemic acquired resistance (SAR)
Induction

A type of activated defense. When the cell receives the signal, it prepares for defense against the pathogen. General attack; defenses act randomly. Resistance activators include phosphites, Actigard, Harmonizer, and silicon.

Tan spot
A leaf spotting disease caused by Pyrenophora tritici-repentis. Infection requires six hours of continuous leaf wetness, and disease development is greatest at 20 – 28?C; it is a summer disease. Symptoms initially include small dark spots on lower leaves, then oval tan spots, 5 – 15 mm, form on veins, sometimes with a yellow halo. No pycnidia form on lesions.

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Target spot lesion
Bull’s eye lesion

Characteristic lesions of early blight, with concentric circular rings of alternating bands of light and dark. Rings develop due to successive periods of conidia production that occur every night. May form on leaves, fruit, or stems.

Taphrina deformans
An ascomycetes pathogen that causes peach leaf curl. Survives unfavourable conditions and overwinters on the bark or buds of the host as ascospores or conidia. In the spring as leaves emerge, conidia are released which infect new plants. Has two stages: unicellular yeast stage and filamentous stage.
TOMcast
A disease-warning model for early blight and other disease management in processing tomatoes. Derived from FAST. Based on weather data; leaf wetness, and temperature. Accumulation of DSVs results in recommendation for fungicide. Increases efficacy of disease management, can result in decreased numbers of fungicide applications, reduces risk of pathogen developing resistance to fungicides, and reduces exposure of non-target organisms to fungicide.
Uncinula necator
Also known by its asexual stage, Oidium tuckeri. An ascomycetes pathogen which causes powdery mildew of grape. Produces ascospores in a chasmothecium, as well as conidia. Overwinters as chasmothecia in bark, on canes, leftover fruit, and leaf litter. Ascospores are released in the spring after rainfall, and need a period of wetness to infect.
Uncinula sp.
A genus of ascomycetes that causes powdery mildew. The chasmothecium has many asci, and curly hyphal appendages.
Unicellular yeast stage
The saprophytic, asexual stage of Taphrina deformans. Can be grown in culture medium. Can survive on the host in this form for long periods of time.
Unitunicate ascus
“One coat”

An ascus with one wall. Found in perithecia.

Venturia inaequalis
Also known by its sexual stage, Spilocaea pomi.

An ascomycetes pathogen which causes ascomycetes apple scab. Overwinters in a pseudothecium in dead leaves; ascosporse mature as weather becomes favourable. Conidia have two cells, unequal in size.

Verticillium albo-atrum
A deuteromycetes pathogen which causes verticillium wilt of maple. Produce simple conidiophores.
Verticillium dahliae
A deuteromycetes pathogen which causes verticillium wilt of maple. Produces simple conidiophores and microsclerotia.
Verticillium sp.
A genus of deuteromycetes. A weakly virulant strain that can be used to induce resistance to Ophiostoma novo-ulmi.
Verticillium wilt of maple
A disease that occurs worldwide. Caused by Verticillium albo-atrum and V. dahliae. Affects over 200 species: vegetables, field crops, and trees. Most important in temperate regions. Favours warm, moist soils. Conidia enter young, actively growing plant roots directly, or through wounds. Pathogen enters the vascualr system xylem elements, resulting in plugging and vascualr wilt. Sapwood may appear brown.

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White mould
White rot

A monocyclic disease caused by Sclerotinia sclerotiorum.

White mould hosts
White mould affects over 400 species in 75 families, including bean, cabbage, canola, carrot, clover, lettuce, peanut, potato, pumpkin, soybean, sunflower, stinging nettle, tabasco, tomato, and tulip.
White mould infection
Ascospores of Sclerotinia sclerotiorum germinate and affect senescent tissues of the upper root, crown, and lower leaves directly.
White mould management
Fungicides. Three year crop rotations with non-susceptible crops. Avoid dense crop canopy. Biological control including mycoparasites and Sclerotinia minor.
White mould of carrot
Managed by trimming the canopy to limit moisture.

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White mould survival
Sclerotinia sclerotiorum overwinters in soil or crop residues as sclerotia. The sclerotia can survive in the soil for a year, sometimes up to 2 – 4 years. They germinate to produce an apothecium.
White mould symptoms
Tan-brown lesiosn with fluffy white mycelium. Black sclerotia form in the mycelia and in the stem. Stem rot; foliage above lesiosn wilts and dies.

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Yarrowia lipolytica
A yeast that increased the native arbuscular mycorrhizal fungi in the soil.
Yeast
Structurally simple, unicellular fingu. Reproduce asexually by budding or fission. Can be used as biocontrol of post-harvest and foliar diseases, with limited efficacy. They rapidly and effectively colonize and compete for nutrients, producing antibiotics. A small portion of yeasts promote plant growth.
Zearaleonone
A mycotoxin produced by Fusarium graminearum which can contaminate grain. Cattle and poultry can tolerate 5 ppm, and swine can tolerate 1 ppm. Acts like a female sex hormone. In female animals it can cause swollen red vulva, vaginal prolapse, and rectal prolapse. In male animals it causes feminizing effects. Costs $40 – 50 million each year in swine losses in Ontario.
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