Plant Pathology: Lab Quiz 3
Acervulus

plural: Acervuli

A structure in which conidiophores may grow. Conidiophores, conidia, and setae are formed just below the epidermal or cuticle layer, and then they erupt through these plant layers. Exposed acervuli are usually saucer shaped.

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Albugo candida
An oomycete. Causes white rust. Not a true rust. Produces sporangia, zoospores, and oospores.
Alternaria solani
A deuteromycetes fungus that causes early blight. Overwinters in infected plant debris in the soil, but cannot last longer than three years in the soil. There is no fruiting body; conidia are formed directly on conidiophores. Conidia have transverse and longitudinal septa, and are dark-coloured.
Alternaria sp.
A genus of deuteromycetes. Common as saprophytes and parasites. Often secondary invaders. Many species produce toxins. Have simple conidiophores. Conidia are pigmented, multicellular, and air-dispersed. Conidia with long tails are often plant pathogens.
Anamorph
The asexual state of fungi.
Antheridium
Male component of sexual reproduction in oomycota. Fuse with oogonia to produce oospores.
Anthracnose
Any disease that causes a lesion that is lighter in the centre. Many different diseases have this name.
Ascomycetes

Ascomycota

A group of fungi that reproduce with asexual and sexual spores. Over 45,000 species. Includes lichenized fungi, yeast, morels, cup fungi, and pyrenomycetes.

Asexual fungi
Fungi which lack sexual stages in their life cycle. Includes deuteromycetes, and some ascomycetes (based on DNA techniques). Produce conidia.
Asexual reproduction
Produces less genetic variation, but takes less time and energy.
Bag test
A method to detect downy mildew of grape. Seal suspected leaves and/or fruit bunches in a moistened plastic bag, and incubate at 13 – 28 C in a dark place overnight. Fresh, white downy sporulation on infected tissue indicates downy mildew infection.
Bait crop
A control method for clubroot. Plants sensitive to clubroot are grown for 4 – 5 weeks to stimulate germination of resting spores. The crop is ploughed down before pathogen completes its lifecycle.
Basidiomycetes

Basidiomycota

Reproduce with asexual and sexual spores. Over 25,000 species. Includes rusts, smuts, mushrooms, gasteromycetes, jelly fungi, polyspores, yeasts, and puffballs.

Bean anthracnose

A disease caused by Colletotrichum lindemuthianum. Symptoms include dark brown to purple sunken lesions along veins of cotyledons and the lower leaf surface, petiole, and stem. Circular lesions with pale brown centre and raised dark brown margin occur on pods. Seeds from infected pods have circular brown spots. When infected seeds germinate, there is early senescence of cotyledons, and girdling of the stem. Symptoms generally start on the underside of the leaf and progress to the top surface. Rainy weather at frequent intervals is essential for disease development. Controllled by using disease-free seed, crop rotation, resistant bean varieties (not the most effective), and fungicide seed and/or foliar treatments.

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Biotroph
An organism which must feed on another living organism. Unlike dead organisms, living organisms continue to provide nutrients.
Black shank of tobacco

A root rot disease caused by Phytophthora megakarya.

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Blue whisker mould

A disease caused by Penicilium ulaiense. Affects oranges.

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Boreaux mixture
Copper sulfate and lime. Used to control downy mildew in France. The first chemical control for a plant disease to be developed. An important fungicide still used today.
Brassicaceae
A family of plants susceptible to clubroot of crucifer. Includes cabbage, canola, broccoli, and stinkweed.
Calendar-timed
Fungicide control scheduled by set time intervals.
Cercospora carotae
A deuteromycetes pathogen which causes cercospora leaf blight.
Cercospora leaf blight

A disease caused by Cercospora carotae. Affects carrot and celery.

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Certified seed
High-quality, well-cleaned, disease-free seed.
Chlamydospore
A type of reproduction in deuteromycota. Thick-walled spores that form within hyphal cells. An asexual resting spore which can be produced very quickly. Nutrients are moved from adjacent cells into one cell which swells, converts nutrients into oil droplets, then rounds off. Look like oospores. Can be spread by wind and water. Resistant to desiccation.
Chromista

Chromalveolata

Heterokont algae

Straminipila

Stramenopila

A eukaryotic supergroup, which may be treated as a kingdom, or included with Protista. Share a common ancestor with Oomycota. Until the 1990s, they were considered a fungus, and may have similarities with fungus in causing plant diseases. Most are photosynthetic, with chlorophyll c. Reproduce asexually and sexually. Most have cell walls of glucans and cellulose, a few with chitin. Have non-septate hyphae. Zoospores have whiplash or tinsel flagella. Includes brown algae, yellow-brown algae, egg fungi, chytrid fungi, diatoms, giant kelp, and golden algae. Plant diseases caused by Chromista pathogens include late blight of potato, pythium root and seed rot, downy mildwe, and sudden oak death.

Chrysanthemum white rust (CWR)

A disease caused by Puccinia horiana. Very contagious in nursery and greenhouse environments; spreads by wind during rainy weather. Can render entire crops unmarketable. Native to Asia, but has been found in the US. Currently being eradicated. Federally regulated; detection must lead to quarantine and eradication. Localized outbreaks have occurred in the USA and Canada since the early 1990s.

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CWR conditions
Chrysanthemum white rust favours cool, wet weather, especially in the spring. Water is needed for spores to germinate and enter leaves. Spores spread by wind during rainy weather. Infected plants may show no symptoms in hot, dry, weather.
CWR dissemination
Chrysanthemum white rust spores are spread by wind, water splash, contaminated soil, litter, hands, and equipment.
CWR hosts
Chrysanthemum white rust affects twelve species of chrysanthemum and daisy in the genera Chrysanthemum and Ajania, including pot mums, spray mums, garden mums, Nippon daisy, and high daisy.
CWR infection
Chrysanthemum white rust spores land on a host surface in wet conditions, germinate, and penetrate the plant. Grows as a latent infection, then appears on the plant surface as pustules that produce infectious spores.
CWR management
Chrysanthemum white rust control can only be preventative. Buy cuttings from reliable sources, inspecting all chrysanthemums coming in. Avoid splashing when irrigating. Do not keep chrysanthemums on your property from year to year. Destroy infected plants by incineration or deep burial. Fungicide control can be used, but resistance has been reported in England.
CWR symptoms
Chrysanthemum white rust symptoms include small white, yellow, or light-green dimpled spots on the upper leaf surface, up to 5 mm in diameter, which become larger and brown. There are pink, white, or beige, swollen pustules on the lower leaf surface under the spots, which become white. Severely infected leaves dry up and hang down the stem.
Chytrid
A group similar to Saprolegniales. Water moulds which feed on small-celled organisms and debris in aquatic environments.
Cirrhus
A thick slimy ribbon-like sticky matrix in which pycnidio spores may be exuded during high humidity.
Claviceps purpurea
A fungus which causes ergot.
Clubroot

A polycyclic disease caused by Plasmodiophora brassicae. Can cause drastic yield reduction and total losses.

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Clubroot conditions
Clubroot favours wet weather. The zoospores cannot swim in dry soil. Symptoms are more severe in cold, wet, acidic soils.
Clubroot hosts
Clubroot affects over 300 species in 64 genera of Brassicaceae, including cabbage, broccoli, stinkweed, Brussel sprouts, cauliflower, turnip, rutabaga, and radish. Can infect cruciferous weeds as well as some grasses.
Clubroot inoculum
The primary inoculum of clubroot are resting spores, which are transmitted in the soil. Secondary inoculum is motile zoospores from infected roots, which swim in soil moisture and can survive for 6 – 8 years.
Clubroot management
Lime soil to above pH 7.2. Long rotations between brassica crops, at least 4 years. Improve soil drainage. Control brassica weeds. Avoid movement of infested soil into clean areas. Produce transplants in clean soil. Avoid contaminated irrigation water. Sanitize equipment. Restrict access to fields. Avoid use of materials from infected or suspicious areas. Use resistant varieties, and certified seed. Reduce erosion. Plant bait crops. Fungicides.
Clubroot of broccoli

Club-like, spindle-shaped swellings form on individual roots.

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Clubroot of cabbage

Club-like, spindle-shaped swellings form on individual roots.

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Clubroot of canola

A serious disease in Western Canada. Symptoms are wilting, stunting, chlorosis, premature ripening, and shriveling of seeds.

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Clubroot of radish

Galls form on taproot or secondary roots.

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Clubroot of turnip

Galls form on taproot or secondary roots.

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Clubroot primary infection
The zoospore of Plasmodiophora brassicae swims to a root hair, and penetrates it. It develops into a plasmodium inside of the root hair, and produces more zoospores. Roots of both susceptible and resistant hosts are infected, but in resistant plants, secondary zoospores are not able to infect plants.
Clubroot secondary infection
Secondary zoospores produced by plasmodium in infected root hairs initiate yield loss symptoms: they infect the entire root surface, not just root hairs. They differentiate into plasmodia that spread deep into root tissue, causing swelling of roots and inhibition of water and nutrient uptake.
Clubroot symptoms
Symptoms of clubroot include pale yellow leaves, wilting of plants on hot days with overnight recovery, death in younger plants, and stunting in older plants. Seed production is reduced. Roots enlarge into galls of varying size and shape, depending on host. Pathogen inhibits the host’s ability to take up water and nutrients. Affected tissue is unprotected, and is susceptible to bacterial soft rot.
Collar rot
When the stem is completely girdled with an early blight lesion.
Colletotrichum acutatum
A deuteromycetes fungus which produces lesions on apples. Conidia can be seen sporulating in orange masses.
Colletotrichum lindemuthianum
A deuteromycetes fungus which causes bean anthracnose. Conidia are produced in an acervulus with dark setae. Sexual stage rarely occurs. Overwinters in seed and crop residue. Conidia are produced from infected seedlings and crop residues and are spread by rain, wind, and machinery. Has a series of races.
Conidia
A type of reproduction in deuteromycetes. Asexual, non-motile spores. Have a wide variety of shapes and sizes. Produced by conidiophores. Includes pycnidio spores.
Conidiophore
Structures which produce conidia. Have a variety of different shapes, including tree-shaped and stalks. Can be aseptate or septate. Grow singly, or are grouped into organized structures including acervuli, pycnidiums, sporodochiums, and synnemata.
Coremia
Conidiophores in a synnema which are loosely aggregated.
Cottony blight of turfgrass

A disease caused by Pythium aphanidermatum.

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Cyst
The overwintering structures of protozoa.
Damping off
A symptom of pythium root rot. Pre-emergence, seedlings die before they emerge. Post-emergence, rot occurs near the base, and plants fall over from root and crown attack after emergence.
Deuteromycota

Imperfect fungi

Produce asexual spores only. Over 25,000 species. Reproduce with conidia or chlamydospores.

Differential series
Used to determine race of Colletotrichum lindemuthianum. The pathogen is inoculated onto twelve different bean varieties, which each are assigned a number according to a binary scheme. The sum of the numbers of the vareities which are susceptible to the pathogen is the identification number of the pathogen race. Each combination of the twelve varieties produces a different number.
Disease Severity Values (DSV)
Used by TOMcast to predict early blight occurrence. If 25 DSVs have not been accumulated before July 11, apply first fungicide at that time. Subsequent applications should occur when 15 – 22 DSVs have accumulated since the previous application.
Dog vomit slime mould

Fuligo septica

A plasmodial slime mould. Lives on grass blades and stems. Often appears overnight. Can move several feet in a day in an ameboid manner. A saprophyte. Can move up blades of grass. Spores can germinate to produce amoeba-like cells or free-living motile flagellated spores if free water is present.

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Downy mildew

A disease caused by a chromista pathogen. All downy mildews are biotrophs. A foliar pathogen. Has sporangiophores for aerial dispersal.

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Downy mildew of grape

A polycyclic foliar disease caused by Plasmopara viticola. Occurs almost everywhere grapes are grown. The most devastating disease of grapes. Originated in North America and was brought to Europe on aphid-resistant rootstocks in 1878. Crop losses in individual years can be 100% in favourable conditions with no control; leads to lack of fruit ripening. Can be detected with a tape pull or bag test.

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Downy mildew of grape conditions
Downy mildew favours wet conditions, low areas, and shady areas. Interwintering spores germinate in the spring when temperatures reach 10?C. Favours spring and summer rainfall that occurs at over 10?C. Scout during wet weather in the sprin. Zoospores die after 3 hours of low humidity and sunlight, but can survive in cool humid conditions for 24 hours. Sporangiophores require 95 – 100% relative humidity, and at least 4 hours of darkness with temperatures exceeding 11?C to produce spores.
Downy mildew of grape dissemination
Sporangia from sporangiophores, or zoospores from germinated oospores are transported by wind or rain splash. Spores form on the underside of infected leaves.
Downy mildew of grape infection
Zoospores from germinated oospores swim in free water on the plant surface, and penetrate the plant through stomata with a germ tube. There must be an incubation period of 5 – 21 days, depending on temperature, before symptoms appear.
Downy mildew of grape inoculum
Interwintering spores are primary inoculum. Swimming spores are secondary inoculum, which require water to move, and are produced on branched stalks that protrude from stomata of infected leaves.
Downy mildew of grape management
Improve drainage and air circulation. Minimize leaf wetness. Reduce leaf litter. Use resistant varieties. Pre-infection and post-infection fungicides. Destroy infected plants (burry, burn, or place in closed container). Bordeaux mixture. DM Cast publishes forecast models for disease control.
Downy mildew of grape survival
Plasmopara viticola overwinters as a thick-walled oospore in tissue such as leaf debris, which are produced near the end of the growing season.
Downy mildew of grape symptoms
Small, pale yellow, irregular spots with oily appearance on the upper surface of leaves. Young spots are surrounded by a brown halo, wchich fades as the spot matures. Spots are yellow in white grapes, and red in some red grapes. Spots tend to be angular and limited by leaf veins. Spots often coalesce to form large dead areas. Lesions turn grey or brown and necrotic, causing early leaf drop. In wet conditions, white downy growth forms on the underside of these spots which produces spores. Can kill inflorescences and developing berries. Infected fruits quickly turn brown to purple and become covered with downy growth, causing yield loss.
Downy mildew of impatiens

A very serious disease in Ontario caused by Plasmopara obducens. Its only host is Impatiens walleriana. Symptoms are yellowing on leaf tissue, and drop of leaves and flowers, with white growth on the underside of leaves.

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Early blight

A polycyclic disease caused by Alternaria solani. Affects tomato and potato. Symptoms are target spot lesions, sunken lesions, concentric rings, and collar spot. Controlled by using disease-free seed, removing and destroying or plowing crop residue, crop rotation with non-susceptible crops for three years, controlling volunteers and susceptible weeds, using resistant or tolerant varieties, and application of preventative fungicide on a calendar-timed or weather-timed schedule.

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Early blight of potato

Symptoms include dark, sunken lesions with raised margins, concentric rings, and corky texture of tubers.

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Early blight of tomato

Symptoms include dark-coloured, sunken lesions, fruit rot, leathery texture, and premature drop of fruit.

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Egypt
Rejected 8,000 tons of Canadian wheat due to a zero-tolerance policy on ergot. The media promoted baseless claims that ergot causes cancer and other diseases. The policy was cancelled, but cost Egypt over $860 million.
Endoparasitic slime mould
An obligate endoparasite. Feeding stage forms inside host cells. Causes hypertrophy and hyperplasia of host cells, and stunting of the host. Causes clubroot of crucifers.
Ergot

A disease caused by Claviceps purpurea. In most countries, a level of 0.05% is accepted in wheat.

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Fungi

Eumucota

Small, generally microscopic eukaryotic organisms. More closely related to animals than to plants. Usually filamentous, branched, and spore-bearing. Sexual reproduction results in zygospores, ascospores, or basidiosopres. Vegetative mycelium are haploid or dikaryotic. Cell walls are composed of chitin and rarely cellulose. Lacks chlorophyll. May have mycotoxins. If zoospores have flagella, it is posteior whiplash flagella. Mitochondria have flattened cristae. Have five groups, including chytrids and zygomycetes. More than 100,000 known species, as many as 1.5 million. There are 100 animal pathogens, and over 10,000 fungi pathogens. The largest kingdom of plant pathogens. May be used in food production.

Fungus identification
Fungi are identified based on morphology of sexual structures, which are not always present. Many fungi do not have sexual structures at all.
Glomeromycota
Root-associated fungi. One of the first organisms to colonize land.
Histoplasmosis

Histoplasma capsulatum

A fungal pathogen that affects animals and humans.

Holomorph
The entire fungus, anamorph as well as teleo morph states. Many fungi have this state.
Hydroponic crops
Crops grown in water. Susceptible to attacks from Pythium sp.
Hyphae
Strands or filaments of the vegetative body of fungal-like organisms or fungus. Clusters of cells in a fungus that grow in a branch-like design. Grow at a rate of 7.2e-6 km/hr. May be septate or aseptate.
Impatiens walleriana
The only host affected by Plasmopara obducens, downy mildew of impatiens.
Interwintering spores
The primary inoculum of downy mildew of grape. An oospore. Overwinter in leaf debris. Germinate in the spring when temperatures reach 13?C.
Irish potato famine

Great Irish famine

Occurred in the mid-1840s. Caused by late blight of potato. 1 million people died, and 1.5 million people emigrated. Changed Europe and North America.

Late blight

A polycyclic disease caused by Phytophthora infestans. A fungus-like pathogen, an obligate parasite that cannot survive in the soil. Worldwide distribution in potato growing areas; it can be imported in potato tubers. Outbreaks have occurred in Oregon, Washington, and Idaho.

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Late blight conditions
Favours temperatures 16 – 27?C, with humid weather. Sporangia produce swimming spores in cool, wet conditions. Sporangia may be harboured in plants during dry weather, and continue sporulation when wet weather returns.
Late blight desiccation
Sporangia emerge from the edge of lesions on the bottom of infected leaves, and from stomata, and produce swimming spores, which can move for miles on the wind. Spread on water on the plant surface or rainwater and irrigation.
Late blight hosts
Late blight affects Solanum sp., including potato, tomato, pepper, and eggplants. It can be harboured on related weed species, including climbing nightshade.
Late blight infection
Sporangia germinate on wet leaves or stems, and penetrate the cuticle or stomata.
Late blight inoculum
Primary inoculum is mostly sporangia, zoospores, or oospores that overwinter in infected tubers. Secondary inoculum is sporangia from zoospore-infected plants and tubers, which can cme from related weed species such as climbing nightshade.
Late blight management
Late blight is controlled by using certified seed, never saving seed. Curative or preventative fungicides. Infected tissues should be destroyed to avoid spread of the disease, by feeding to animals or burying two feet deep. Do not harvest potato tubers when wet. Cull diseased tubers from storage. Remove volunteer potatoes from fields.
Late blight of potato
Caused the Irish potato famine. If the infection came from the tuber, there is black growth on the stem. Tubers have discoloured brown to purple skin, and brownish dry or wet rot. Infections can appear in tubers in storage. Sporangia can form and spread in storage. Often accompanied by secondary infection of soft rot bacteria, which may spread rot in tubers in storage.
Late blight of tomato
Secondary inoculum can cause water-soaked lesions on the stems. Stem lesions can girdle infected stems, and develop white growth, and release spoers. Gray-green water soaked spots form on green fruit, enlarge, coalesce, and darken causing large, firm, brown, leathery lesions. In humid conditions white moulds develop on lesions, and secondary soft rot bacteria result in slimy wet rot of the fruit. Lesions have cream-coloured or brown concentric zones on ripe fruit, which coalesce and affect the whole fruit. The fruit becomes shrunken.
Late blight survival
Late blight overwinters as sporangia, zoospores, or oospores on tubers, in seed potato, and tomato transplants.
Late blight symptoms
Symptoms include green, brown, or black water-soaked lesions on the leaf upper surface or stem. In humid conditions white mould appears on the underside of the leaf below lesions. Symptoms spread rapidly.
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Macroscopic fungi
Includes mushrooms, puffballs, and rusts.
Many headed slime

Muciturbo crustaceae

A slime mould.

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Melanin
Protects sclerotia from UV rays. It is toxic.
Microscopic fungi
Includes moulds and yeasts.
Mycelium
A mass of hyphal filaments composing the vegetative body of a fungus. Many hyphae joined. Grows outwards from a central point.
Mycotoxin

“Fungus toxin”

Toxins produced by a fungus. Includes ergot.

Myxomycota
True slime moulds. May represent an independent evolutionary lineage to other kingdoms including Fungi, Animalia, Plantae, Chromista, and Alveolates.
Necrotroph
Saprotrophic and pathogenic organisms.
NEWA tomato disease forecast
A tool developed at Cornell University. Predicts waves of tomato diseases.
Nonseptate hyphae
Hyphae which lack septa. Nuclei can travel anywhere in the protoplast.
Obligate parasite
An organism which needs living tissue to survive.
Oogamous reproduction
Haploid oospheres are fertilized by haploid gametes to form diploid oospores.
Oogonium
The female component of sexual reproduction in oomycota. Fuse with antheridium to produce oospores.
Oomycota

“Egg-like”

Peronosporomycota

Oomycetes

A sub-group of chromista. Consists of more than 800 species, saprobic or parasitic on terrestrial or aquatic plants and animals. Used to be considered a fungi because they have filamentous hyphae, but they are now classified as separate from fungi; a “colourless algae”. Vegetative mycelium are diploid and aseptate. Cell walls are made of beta glucans and cellulose, lacking chitin. Mitochondria have tubular cristae. Undergo oogamous reproduction. Most produce zoospores, which have whiplash or tinsel flagella. Reproduce asexually with sporangiophores. Reproduce sexually with heterogametangia: oogonium is fertilized by an antheridium to form an oospore. Includes slime moulds, chytrids, zygomycetes, and arbuscular mycorrhizae.

Oospore
Produced when an antheridium fuses with an oogonium in sexual reproduction of oomycota. May be large and solitary, or smaller and numerous inside the oogonium.
Pathovar
Strains of a pathogen which infect different host species.
Penicilium ulaiense
A deuteromycetes pathogen which causes blue whisker mould.
Penicillin
Comes from a fungus. In the past, people would use mould bread to treat infections.
Peronospora tabacina
An oomycete. Causes tobacco blue mould.
Physarum pusillum
A slime mould.
Phytomyxea
A group which includes Plasmodiophora brassicae.
Phytophthora infestans
An oomycete. Causes late blight of potato. Oospores and antheridium fuse in sexual reproduction to form a sporangium which produces zoospores. Sporangiophores emerge from stomates for asexual reproduction. Asexual reproduction is more common, but sexual reproduction is important in some regions. Life cycle can be completed in four days.
Phytophthora megakarya
An oomycete. Causes black shank of tobacco.
Phytophthora ramorum
An oomycete. Causes sudden oak death. Spread by airborne spores and wind-blown rain.
Phytophthora sp.

“Plant destroyer”

A genera of chromista. A relatively host-specific parasite. Has soil and foliar pathogens. Has a more complex sporangiophore than Pythium sp. Reproduces asexually with resting spores, and sexually with oospores. A water-bound soil and foliar pathogen, a hemibiotroph.

Plasmodial slime mould
A type of slime mould. Feeding stage is a diploid plasmodium which has phagotrophism. Live in moist habitats, requireing moisture for movement. Under favourable conditions the plasmodium forms sporangia, which undergo meiosis to produce haploid spores which germinate and fuse to form a diploid zygote that develops into a new plasmodium. For sexual reproduction the plasmodium searches for a dry, lit area. Survives non-favourable conditions as spores which can last for several years. Do not damage the plants they live on, but can cause chlorosis by shading the plant from the sun. Turfgrass may have patchy areas, streaks, or rings that are dusty, grey, blue, or white, where reproductive structures are formed.
Plasmodiophora brassicae
Causes clubroot. Used to be considered a slime mould, but it is a Phytomyxea, Plasmodiophoromycota. Its peculiar classification makes it difficult to control. Resting spores germinate into zoospores that have two flagella they use to swim through soil moisture to reach a root hair. Lives as a plasmodia parasite within the cells of host plants, which alters hormone balances of the root, causing the root to grow more tissue, leading to swollen formation of the root, and more tissue for the pathogen to infect.
Plasmodiophoromycota
A group previously included as fungi. A protista. May have a common ancestor with Chromista. Includes Plasmodiophora brassicae.
Plasmodium
A multinucleate mass of protoplasm. Can be maintained under cool, moist, shady conditions in the late summer, on rotted logs, mulch, or grass.
Plasmopara obducens
An oomycete. Causes downy mildew of impatiens.
Plasmopara viticola
An oomycete water mould in the order Peronosporales. Causes downy mildwe of grape. An obligate parasite; absorbs nutrients from living host tissue with globose haustoria. Has aseptate mycelium. Produces asexual, biflagellate zoospores and sexual oospores. Oospores formed when oogonia in host tissue fuse with antheridia. Overwinters as an oospore in host tissues, and germinates forming a germ tube terminating with a sporangia that produces zoospores. Sporangia also form on tree-like sporangiophores that emerge from stomata of host, forming a mycelial mat within host tissue.
Powdery mildew

Spots are circular, not limited to veins. Yellowing occurs after the fungus has been present for some time. Fungus grows on leaf surface. Spores produce in a chain on a single stalk, and grows on either leaf surface.

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Protozoa

“Fungal-like”

A kingdom of eukaryotic organisms with membrane-bound organelles, but lacking a cell wall. May have asexual (binary fission and budding) and sexual reproduction. May be motile or sessile. Some produce cysts. Generally unicellular, but may have colonial stages. Heterotrophic; absorb food by phagocytosis and absorption. Includes slime moulds and club root.

Puccinia horiana
A fungus that causes chrysanthemum white rust. Completes its life cycle in a single host.
Pycnidio spores
Conidia which are produced in a pycnidium. May be exuded in a cirrhus when humidity is high.
Pycnidium
A structure in which conidiophores may grow. A flask-shaped chamber that encloses conidiophores and conidia. Produces pycnidio spores. Embedded, or superficial to host tissue. May or may not have a nostiole at the apex. Opens when pycnidio spores are ready. Spores may be released in a cirrhus.
Pythium aphanidermatum
An oomycete. Causes cottony blight of turfgrass.
Pythium blight of turfgrass

A disease. Symptoms are thinning, stunting, and yellowing of turfgrass. Can kill large areas of turf in a day. Pathogen survives as a saprotroph or as an oospore in thatch or soil. Able to spread quickly in wet, warm conditions.

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Pythium root rot

A disease caused by a chromista pathogen. Develops  in saturated or poorly drained soil. Turfgrass dies back from leaf tip. Roots and other below-ground parts may appear greasy and disintegrated. There may be cottony white growth.

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Pythium seed rot

A disease caused by a chromsita pathogen. Seeds fail to germinate, turn soft and mushy, and disintegrate.

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Pythium sp.
A genera of chromista which have hyphae that can grow up to a centimeter a day. Have a wide host range. Survive in soil for a long time as a saprotroph, feeding on decaying plant matter. Loves water, and often attacks greenhouse or hydroponic crops. There is pre-emergence or post-emergence damping-off. Older plants have reduced growth due to root lesions. Fruit in contact with soil develop soft white cottony growth on the surface. Includes pythium seed and root rot, and pythium blight. A soil pathogen, necrotrophic, with simple non-aerial dispersal sporangiophores.
Races
Not to be confused with pathovar. Morphologically identical, but genetically distinct strains of Colletotrichum lindemuthianum. Characterized by the bean varieties they attack. Resistant genes can be bread into bean vareities to make them resistant to specific races of pathogen. A differential series is used to determine race.
Red raspberry slime

Tubulifera arachnadea

A slime mould.

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Resting spores
The primary inoculum of clubroot. 3 – 4 ?m in diameter. May be found in infected root cells, and are relased as the shoot disintegrates. Billions of resting spores can be produced by a single infected root. Can persist in the soil for up to 20 years. Normally found in the upper layers of the soil. Can be spread by ploughing equipment, drainage water, shoes, and transplants. Repeated growth of susceptible hosts can lead to build-up in the soil. Germinate when stimulated by plant root exudates, undergoing cellular division to form zoospores.
Ringworm

Tinea corporus

A fungal animal pathogen.

Saprolegnials
Water moulds. An oomycete. Causes diseases of fish and other aquatic vertebrates.
Saprotroph
Rot diseases. Many fungi are saprotrophs.
Sclerotium

plural: Sclerotia

A compact mass of hyphae, usually within a darkened rind. Capable of surviving unfavourable conditions. Contains melanin.

Septoria leaf blotch

A disease caused by Septoria tritici. Symptoms are yellow flecks between veins of lower leaves, which elongate into reddish-brown blotches restricted by veins. Small dark pycnidia devleop in blotches. Affects wheat.

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Sptoria leaf blotch complex

A disease caused by Stagonospora nodorum and Septoria tritici together. Controlled with crop rotation with cereals no more than once every three years, ploughing wheat residue after harvest, double-cropping soybeans, resistant varieties, certified seed, avoiding excessive seeding rates, avoiding nitrogen deficiency or excesses, and limiting canopy density to increase air circulation and light.

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Septoria leaf blotch of wheat

A disease. Symptoms are brown spots and yellowing areas between spots. Spots may coalesce into long, brown areas of infection.

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Septoria tritici
A deuteromycetes fungus which causes septoria leaf blotch, and contributes to septoria leaf blotch complex. Produces conidia in pycnidia. Overwinters in wheat stubble or infested seed. Spores are produced in wet weather in the fall and spring, with spring infections causing greatest yield damage. Infection is temperature-dependent, and is greatest during cool to moderate temperatures and abundant moisture.
Septum

plural: Septa

A cross-wall within a hyphae.

Setae
Dark hair-like structures which form alongside conidiophores in acervuli. May be seen by the naked eye.
Slime moulds
Protozoa including plasmodial and endoparasitic slime moulds. Includes wolf’s milk, many headed slime, red raspberry slime, and Physarum pusillum.
Sporangia
Bud off sporangiophores for asexual reproduction of oomycota. Produce zoospores. May be spread by wind or water.
Sporangiophores
Chains of beads of sporangia, which are released when ruptured, for asexual reproduction of oomycota. May emerge through the stomates of the host plant.
Sporodochium
A structure in which conidiophores may grow. A cushion-shaped mass of short conidiophores, forming a stroma.
St. Anthony’s Fire
A human disease caused by eating ergot. Circulation is cut off from the hands.
Stagnospora nodorum
Contrubtes to septoria leaf blotch complex. Infection can occur over a wide range of temperatures, but is favoured in the middle to late stages of crop development when plants are most susceptible to infection.
Stroma
An aggregation of hyphae in a sporodochium.
Sudden oak death

A disease caused by Phytophthora ramorum. There are more than 200 host species, including oak and rhododendron. First detected in Canada in 2003 in BC, and was successfully eradicated. The disease must be quarantined. Symptoms include cankers, dieback, red coloured wood, and death.

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Swimming spores (downy mildew)
The secondary inoculum of downy mildew of grape. A zoospore. Produced from the sporangiophores forming the downy growth on the underside of infected leaves. Require free water to move.
Swimming spores (late blight)
Zoospores produced by sporangia on the edge of lesions on the underside of infected leaves. Quickly colonize a plant, forming brown lesions. Spread on rainwater and irrigation.
Synnema

plural: Synnemata

A structure in which conidiophores may grow. Conidiophores are fused at the base, and conidia form at the apex or side. Looks like a bundle of wheat. Includes coremia.

Target spot lesions
A symptom of early blight. Dark brown lesions with faint concentric rings, often bound by larger leaf veins. Sporulation of the pathogen occurs after a dark period.
Teleomorph
The sexual state of fungi.
Theilaviopsis
A disease caused by Pythium sp. The roots lack root hairs.
Tinsel flagella
A type of flagella found on Oomycota or Chromista zoospores. Fibrous, ciliated structures oriented anteriorly.
Tobacco bluemould

A disease caused by Peronospora tabacina.

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TOMcast
A disease-warning model which establishes a timed fungicide spraying program for controlling early blight, septoria leaf spot, and anthracnose on processing tomatoes. Based on weather data: leaf wetness, and temperature. Disease control is based on accumulation of daily Disease Severity Values.
Volunteer
A plant that grows on its own instead of being deliberately planted.
Weather-timed
Fungicide control scheduling using NEW tomato disease forecast or TOMcast. Uses weather data to predict disease occurrence. Based on a mathematical formula.
Whiplash flagella
A type of flagella found on Oomycota or Chromista zoospores. Oriented posteriorly.
White rust

A polycyclic disease caused by Albugo candida. Economically damaging. Includes chrysanthemum white rust. Symptoms include white rust-like pustules on the underside of leaves. Favours cool, wet conditions. Common in the autumn and spring, in weather between 13 and 15?C. Hosts include crucifers, pigweed, and Amaranthus species such as spinach. Primary inoculum is zoospores and oospores. Secondary inoculum is sporangia, zoospores, and oospores. Control by minimizing irrigation in cool weather, improving air flow, removing infected plant material, controling susceptible weeds. There are conventional and organic fungicides. Use resistant vareities. Rotate non-suseceptible crops for at least three years.

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Wolf’s milk

Lycogala epidendium

A slime mould.

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Zoospores

“Little animals”

Motile spores. Produced by sporangia for asexual reproduction of oomycota. Chromista and Oomygota zoospores have whiplash or tinsel flagella, where fungi have one flagella if present, and there are differences in structure and function. Often zoospores are poor swimmers. May be spread by wind or water.

Zygomycetes

Zygomycota

A group of fungi. Have non-septate mycelium, which is a superficial resemblance to Oomycota. Reproduce with asexual and sexual spores. Includes bread moulds, as well as freshwater and marine species. About 1,000 species.

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