Plant Pathology: Lab Quiz 6

Across species”

A haploid, dikaryotic spore produced by basidiomycetes in an aecium. Present in macrocyclic rusts. Travel from the host bearing aecia to the host bearing telia.

A structure in basidiomycetes which produces aeciospores. Resembles a pseudothecium.
Fusion of touching hyphae.
Anastomosis groups
Groups of strains of Rhizoctonia solani that cannot have anastomosis. The most common strain is AG-2-2 and AG-4.
Armillaria gallica
A basidiomycetse pathogen that causes armillaria root rot. Can form very large clones or genets. The “humongous fungus” that was featured in a front-page article of the New York Times. The largest genet is found in Oregon, 900 hectares in size, and 2,400 years old.
Amrillaria mellea
Honey mushroom

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A basidiomycetes pathogen that causes armillaria root rot in angiosperms.

Armillaria ostoyae
A basidiomycetes pathogen that causes armillaria root rot in conifers.
Armillara root rot
A disease caused by Armillaria species. Causes lethal, primary disease. Death is more likely when there is a secondary infection or stress. One of the most important diseases of trees in temperate regions, affecting native forests, planted forests, orchards, vineyards, and amenity plantings in urban areas. Less serious in tropical areas, occurring in higher elevations.
Armillaria root rot dissemination
Basidiospore are airborne, and can establish a new infection centre, although this is rare and dependent on moisture. Mycelia can disperse locally in root contacts or grafts, or through the soil as rhizomorphs.
Armillaria root rot hosts
Affects many trees and herbacious species including oak, conifers, and raspberries. Hosts weakened by stress factors such as drought, defoliation, other diseases, insects, or soil compaction are more susceptible. Locally adapted species and varieties are often more resistant.
Armillaria root rot management
There is no effective, practical means of reducing disease. Alleviation of other stresses. Removal of infected stumps can be effective in forests and orchards. Avoidance of sites affected by the disease. Biological control with antagonistic fungi. Trenching: a 1 m deep trench is dug around the tree, lined with plastic, and backfilled to protect the tree from infection. Fumigants such as chloropicrin, carbon disulphide, and methyl bromide may be used in orchard crops to eradicate inoculum from soil, usually after stump removal and before planting.
Armillaria root rot signs
Signs include mycelial fans, rhizomorphs, and mushrooms.
Armillaria root rot survival
Overwinters as mycelia in stumps or woody inocula for up to 50 years, depending on climate and the size of the stump.
Armillaria root rot symptoms
Symptoms include branch dieback, crown thinning, basal cankers above the roots, decayed roots, and resinosis. In conifers there may be chlorosis or reddening of foliage, and stress crop of cones. Wood has white rot, where lignin and polysaccharides are degraded, and remaining cellulose gives wood a fibrous texture. Black zone lines of fungal cells may be seen in the wood. Actively decaying wood may have bioluminescence in the dark.


Armillaria sp.
A basidiomycetes pathogen. There are about 40 species, some of which cause armillaria root rot. Soil-borne, and spreads by rhizomorphs and mycelia. Produce mushrooms near the base of hosts, which produce basidiospores in gills. Have an unusual nuclear cycle, and are predominantly diploid rather than heterokaryotic. Do not produce asexual spores. The mycelium is bioluminescent, especially in actively decaying wood.
Sac fungi

A group classified on sexual structures. Ascospores are produced on asci produced in naked asci, chasmothecia, perithecia, or apothecia. Conidia are produced on simple conidiophores or pycnidia.

Asparagus rust
An autoecious rust disease. Affects asparagus.
Autoecious rust
“Self house”

Monoecious rust

Rusts with one host. Includes asparagus rust.

The fruiting body of basidiomycetes. Produced from secondary mycelia. Forms the mushroom of some species.
Club fungi

Most are fleshy fungi, either saprophytes or causing wood decay. Non-pathogenic groups include mushrooms, puffballs, and shelf fungi. Pathogenic groups include smuts, rusts, and species of Rhizoctonia, Armillaria, and Typhula. Produce basidiospores, spermatia, aeciospores, urediospores, and teliospores. Some spore stages can infect alternate hosts.

Mnemonic for spores: BPAUT


Bring it on!”

A haploid, monokaryotic sexual spore produced by basidiomycetes in a basidium. Found in macrocyclic and microcyclic rusts. Usually forcibly ejected by the sterigmata, traveling a few micrometers. Often produced in the spring. Small in size, and can travel on wind and water. Germinates on hosts, generating primary mycelium.


A club-shaped structure in basidiomycetes that germinates from a teliospore. Diploid and monokaryotic. Undergoes meiosis to produce four basidiospores on sterigmata which forcibly eject them. Similar production process to ascospores, but there is no mitosis event after meiosis.

Cedar apple rust
A gymnosporangium rust caused by Gymnosporangium juniperi-virginianae.
Cedar apple rust infection in apple
Basidiospores infect apple hosts. Spermatia form on the upper surface of the leaf.
Cedar apple rust infection in cedar
Aeciospores infect cedar in the fall or late summer.
Cedar apple rust management
Control is usually focused on apple hosts. Remove cedars within a one mile radius of apples; this is often impractical. Fungicide sprays applied in a timely manner in the mid-spring. These fungicides can also be used on cedar in July and August; the pathogen is most vulnerable when telial horns appear.
Cedar apple rust survival
Overwinters as mycelia in the cedar host.
Cedar apple rust symptoms in apple
Aecia form on the lower surface of the leaf, with a “flower” appearance due to shredding of the peridium membrane.


Cedar apple symptoms in cedar
Gelatinous telial horns appear in the summer after infection.


Cedar quince rust
A gymnosporangium rust caused by Gymnosporangium clavipes. Infects the stems and fruits of hawthorn. Aecia form on fruits, and the peridium does not shred; it remains intact, shaped like a straw through which aeciospores are shot.


Ceratobasidium sp.
The rare sexual, binucleate stage of Rhizoctonia species including R. solani.
Clamp connection
Forms in basidiomycetes, and not in ascomycetes. Forms in dikaryotic hyphae. After nuclei undergo synchronous division, a clamp cell grows backwards, taking one of the nuclei with it. A septum forms at the base of the clamp cell, forming a septum between cells so that each cell has one nuclei of each type. Sometimes they are not visible.
Common rust of corn
A disease caused by Puccinia sorghi.


Corn smut
Blister smut

Boil smut

Common smut

Corn mushroom

Corn truffle

Mexican caviar

A potentially polycyclic, mostly monocyclic disease caused by Ustilago maydis. Occurs wherever corn is grown. Reduces yield by an average of 2%, but can approach 100% in individual fields. It first spread to Australia in 1911, where it remained localized in Bathurst for many years due to quarantine efforts, however it spread to other regions in 1996. Economic losses in the USA have been minor since development of resistant hybrids in 1940. Loss is greatest when infection occurs in young plants, where it can lead to plant death. It is of greater consequence in sweet corn, since even a small amount of disease makes an ear unmarketable. It is edible as cuitlacoche.

Corn smut conditions
Favours humid weather. Wounds from weather can increase occurrence. Hot, dry conditions cause reduced pollination, which can increase occurrence.
Corn smut dissemination
Basidiospores and teliospores are carried by wind or rain.
Corn smut hosts
Affects corn (Zea mays) and teosinte (Zea mexicana). No line of corn is immune, however some lines are more resistant than others. Flint corn is more susceptible than dent corn. Sweet corn is more susceptible than field corn.
Corn smut infection
Basidiospores germinate on the host surface, producing fine hyphae that enter epidermal cells. If the hyphae do not encounter haploid hyphae of a compatible mating type from another basidiospore, it withers. All meristematic tissues are susceptible to infection, including ears, tassels, stems, and leaf nodes. Infection of individual ovaries usually occurs at the tip or base of the ear. Ovaries are not susceptible to infection once they have been fertilized because the silk dies. Galls may form in meristematic tissues nearby wounds. The dikaryon grows into tissues intercellularly, causing a local infection.
Corn smut management
Use resistant varieties and hybrids: this is the only practical method of management. Crop rotations. Sanitize small plantings. Avoid over-fertilization. Avoid mechanical injury. Manage insects. Plow residues to bury infected tissue. Seed treatment. Foliar fungicides. Modification of fertility. Biologcial control.
Corn smut survival
Overwinters as teliospores in crop debris and soil.
Corn smut symptoms
Tissues may appear chlorotic before galls form. Mycelia stimulate cell division and enlargement, and loss of vasculature, producing a gall, 1 – 30 cm in diameter. Galls are noticeable 10 – 14 days after infection, found on ears, tassels, stalks, nodal shoots, and mid-ribs of leaves. Young plants may have galls in the root as well as the shoot, and the plant remains stunted or dies. At first galls are firm, and have a greenish-white, semi-glossy perdierm. The interior then becomes semi-fleshy, and streaks of black tissues occur, then galls become a mass of powdery teliospores, 16 – 18 days after infection. At 21 – 23 days the peridum ruptures and galls become sloppy, wet, masses of teliospores that are sooty and powdery when dehydrated. A single gall may produce 200 billion spores.


Covered smut
Common bunt

Stinking smut

A disease caused by Tilletia sp. Managed by using certified smut-free seed, or hot water seed treatment.


Covered smut of barley
A disease caused by Ustilago hordei.


Cronartium ribicola
A heteroecious, macrocyclic basidiomycetes rust pathogen that causes white pine blister rust. Teliospore are two-celled, and after they are produced they rapidly geminate to form a metabasidium that produces four basidiospores. Basidiospores have two mating types: + and -.
Crown rust of oat
A disease caused by Puccinia coronate f.sp. avenae. Affects oats and barley.



The young, edible galls of corn smut on ears of corn. A highly prized delicacy in Mexico, eaten since pre-Columbian times. Each year, 400 – 500 tons are sold fresh, and over 100 tons are processed and/or canned. It is served in soups, appetizers, and entrees.

Damping off
A symptom of rhizoctonia diseases. Destruction of seedlings near the soil line, resulting in the seedlings falling over onto the ground.
Cells or compartments containing a pair of closely associated compatible nuclei.
Containing two complete sets of chromosomes.
Floral infection
A type of infection of smut. Teliospores germinate on healthy heads, attacking young ovaries, forming mycelia within the embryo of the grain. Infected seeds have seedling infections.
Grey snow mould (GSM)
Snow scald

Speckled snow mould

Typhula blight of turfgrass

Winter scald

A disease caused by Typhula ishikariensis and T. incarnata. Affects golf fields.

Grey snow mould conditions
Favours cold, 0 – 2?C, wet conditions. Extended periods of snow cover for at least 3 months is required for heavy damage. Some pathogenic activity occurs in the fall in cool, wet weather.
Grey snow mould dissemination
Basidiospores are produced by sporocarps from sclerotia, and may be spread on wind or rain.
Grey snow mould hosts
Affects cool season turfgrasses, including creeping bentgrass, annual bluegrass, and perennial ryegrass. Kentucky bluegrass, red fescue, and tall fescue have moderate susceptibility.
Grey snow mould management
Minimize thatch by mowing in the fall until leaf growth stops. Do not apply nitrogen after mid-fall. Rake matted areas to encourage drying of damaged areas, and overseed as soon as possible to repair patches. Promote new growth by lightly fertilizing damaged turf. Strategic removal of snow, and use of snow fences. Preventative fungicides in the fall. Creeping bentgrass must be dormant at the time of PCNB fungicide application; it can be toxic to actively growing bentgrass.
Grey snow mould survival
This pathogen survives the summer rather than the winter. It over-summers as sclerotia in thatch. Sclerotia germinate to produce hyphae or sporocarps.
Grey snow mould symptoms
Patches appear in the spring after snowmelt, with scalded or bleached appearance, 10 – 25 cm in diameter, often overlapping to form larger irregular patches. Patches may be larger on taller-mown turf. Patches have white fluffy mycelia at the edges, and are matted and bleached in the centre. Once patches are visible, the fungus is not longer active. Sclerotia may be found on dead leaf blades after snow melt.


Gymnosporangium clavipes
A basidiomycetes rust pathogen that causes cedar quince rust.
Gymnosporangium juniperi-virginianae
A basidiomycetes rust pathogen that causes cedar apple rust.
Gymnosporangium rust
A category of heteroecious rust diseases. Rarely cause serious damage to hosts, and often requires no management in a home landscape. Highly susceptible hosts may suffer shoot death or defoliation. Produce no urediospores. Incldues cedar apple rust, hawthorn rust, cedar quince rust, juniper broom rust, and Japanese apple rust.
Having a single set of unpaired chromosomes.
Hawthorn rust
A gymnosporangium rust.


Head smut
A disease caused by Sphacelotheca reilana. Affects corn. Apeared in Ontario in 1979, and spread to Quebec. Not as common as corn smut. Symptoms are similar to corn smut, but teliospores can be distinguished under a microscope. Floral structures are converted into sori containint masses of powdery teliospores in which vascular bundles of the host are usually present as thread-like structures.


Heteroecious rust
“Different house”

Rusts with two alternating hosts. Includes wheat stem rust and white pine blister rust.

Hollyhock rust
A monoecious, microcyclic, polycyclic disease caused by Puccinia malvacearum.
Hollyhock rust conditions
Teliospores require humid conditions to germinate, and epidemics are worse.
Hollyhock rust dissemination
Basidiospores are carried on air currents. Seeds could carry infection in the form of spores on accompanying bracts or flower parts, however the pathogen is not carried in the embryo.
Hollyhock rust hosts
Affects hollyhock (Althaea rosea), as well as species from Malva, Abutilon, Hibiscus, Lavatera, Malvastrum, and Sidalcea.
Hollyhock rust management
Management strategies used depends on how much you love your hollyhocks. Check plants regularly and remove infected plants and material. Monitor plants being brought in. Grow hollyhocks as a biennial, discarding plants after flowering. Avoid dense plantings of hollyhock. Encourage good root development; avoid too wet or too dry soil. Control weed hosts including common mallow. Avoid growing another host nearby. Fungicides, with many applications.
Hollyhock rust symptoms
Early in the spring, orange pustules form on the underside of leaves. Pustules contain teliospores, and turn ash-grey when they germinate into basidiospores a few days or weeks later.


Japanese apple rust
A gymnosporangium rust.


Juniper broom rust
A gymnosporangium rust.


“Kernel marriage”

Fusing together of two haploid eukaryotic cells. Occurs in teliospores, followed by meiosis.

Leaf rust of wheat
Brown rust

A disease caused by Puccinia triticina. Affects wheat, barley, and rye.


Local infection
A type of infection of smut. Leaves, stalks, and flower parts are infected by basidiospores, dispersed from teliospores in crop residues and soil. There is no general spread of the pathogen within the tissue.
Hollyhock rust survival
Overwinters in plant materials.
Loose smut of barley
A disease caused by Ustilago nuda. Symptoms are seen as dense heads emerging from the boot. Kernels and glumes form as black masses of teliospores which blow away, leaving the rachis bare.


Loose smut of wheat
A disease caused by Ustilago tritici. Symptoms are seen as diseased heads emerging from the boot. Kernels and glumes form as black masses of teliospores which blow away, leaving rachis bare. Plants are infected during flowering.


Basidiomycetes which have two hosts. Rusts which have all five spore types present. The common ancestor of macrocyclic and microcyclic rusts was macrocyclic.
Reduces the number of chromosomes in the parent cell by half, and produces four gamete cells.
A four-celled structure which germinates from the teliospore of Cronartium ribicola. Produces four basidiospores.
Basidiomycetes which have one host. Rusts which produce only basidiospore and teliospores.
A sign of armillaria root rot. Produced in the late summer or autumn. Erratic fruiting; may be absent in some years. Morphology varies with species of pathogen. Caps are honey-brown, usually with small tufts of dark hairs, and whitish gills with notched attachment. Spore prints are white, and stems are white-brown, usually with an irregular, mottled appearnce. Most species have a partial veil resulting in a more or less delicate annulus on the stem. They are edible.
Mycelial fans
A sign of armillaria root rot. Nearly always present in infected and recently killed trees. White mats of fungal mycelia between inner bark and wood. Has a mushroom odour, and a fan-like pattern, and may be peeled off in small pieces.
Obligate parasite
Needs to take food from a host.
Onion smut
A disease caused by Urocystis cepulae. Affects onions and related crops. The flag leaf is infected, and black-brown streaks and blisters appear in the leaves and small bulbs later in the growing season. As lesions mature, they turn brown and contain a mass of dark powdery spores, giving tops a sooty appearance. Darkened bulbs contain teliospores.


Paton’s Silver Splendor
A variety of eastern white pine that is resistant to white pine blister rust.
The protective layer encasing a mass of spores in an aecium. In white pine blister rust it is underneath the bark layer of the pine host. In cedar apple rust it is shredded, producing the “flower” appearance. In cedar quince rust it remains intact like a straw.
Primary mycelium
Monokaryotic, haploid, weak hyphae produced from a germinating microcyclic basidiomycetes. Combines with mycelia of a different mating strain, producing secondary mycelium.
A race of Puccinia graminis f.sp. tritici race Ug99 which was detected in Ethiopia in 2007.
A race of Puccinia graminis f.sp. tritici race Ug99 which was detected in Ethiopia in 2007. It was present in Eritrea, Mozambique, and Zimbabwe in 2010.
Puccinia coronate f.sp. avenae
A basidiomycetes rust pathogen that causes crown rust of oat.
Puccinia graminis f.sp. avenae
A basidiomycetes rust pathogen that causes stem rust of oat.
Puccinia graminis f.sp. secalis
A basidiomycetes rust pathogen which causes stem rust of barley. Not as significant as P. graminis f.sp. tritici.
Puccinia graminis f.sp. tritici
A heteroecious, macrocyclic basidiomycetes rust pathogen which causes wheat stem rust and stem rust of barley. Teliospores germinate in the spring to produce basidiospores which infect barberry. The aecium on barberry is an upside-down, sac-shaped structure.
Puccinia graminis f.sp. tritici Ug99
A new race of wheat stem rust, first reported in Uganda in 1999. It is a spreading epidemic. It was reported in Iran, Tanzania, and Zimbabwe in 2008. Can cause up to 100% crop loss. There are eleven races, each believed to have evolved from a common ancestor: TTKSK, TTKSF, TTKST, TTTSK, TTKSP, PTKSK, PTKST, TTKSF+, TTKTT, TTKTK, and TTKSK.
Puccinia malvacearum
A basidiomycetes rust pathogen that causes hollyhock rust. Teliospores are produced in pustules, and have a latent period of a few days to several weeks, after which they germinate to produce basidiospores on the leaf.
Puccinia Pathway
The path that urediospores of Puccinia graminis f.sp. tritici are blown on as they come up from the USA into Canada on the wind.
Puccinia sorghi
A basidiomycetes rust pathogen that causes common rust of corn.
Puccinia triticina
A basidiomycetes rust pathogen that causes leaf rust of wheat.
Ball-shaped basidiomycetes fungi with basidia packed tightly in their interior. Basidia disintegrate and basidiospores dry up. Raindrops or wind cause the delicate skin of the fruiting body to break, and spores puff out like smoke, and are carried away by wind.
Forms of rust fungi within a special form which attack only certain varieties of the species. Identified using a differential host series.
Receptive hyphae
Produced by a spermatogonium. The spermatia of one mating type fuse with the receptive hyphae of a compatible mating type, and transfer the nucleus through a pore wall.
Exudation of resin from conifers. A symptom of armillaria root rot: the most diagnostic symptom of the disease.
Rhizoctonia diseases
Diseases caused by Rhizoctonia sp. Occur throughout the world. Includes rhizoctonia stem canker and rhizoctonia root rot.
Rhizoctonia diseases conditions
Favours cool, wet soils during seed germination and emergence.
Rhizoctonia diseases hosts
Affects almost all vegetable and flower crops, several field crops, turfgrasses, and some perennial ornamentals.
Rhizoctonia diseases management
Provide good conditions for seed germination: aerated seed bed, good drainage, and warm soil.
Rhizoctonia diseases symptoms
Symptoms vary considerably. Common symptoms include pre- and post-emergence damping off, root and stem rots, and cankers of growing and mature plants. Symptoms are more severe when plant growth is slow due adverse conditions.


Rhizoctonia root rot
Rhizoctonia stem rot

A common rhizoctonia disease caused by Rhizoctonia solani. Affects many crops, including soybeans, corn, and alfalfa. Typically damages seedlings. Can result in significant yield loss. Symptoms are rust-brown, dry, sunken lesions on stems and roots near the soil line. Lateral roots may decay. Plants may become stunted, yellow, and wilted. Lesions can girdle the stem and kill or stunt plants. Favoured by high soil moisture and warm temperatures, and delayed emergence. Plant stresses such as herbicides make plants more susceptible. Managed with good agronomic practices, high quality seed, crop rotation, and seed treatments. Some cultivars have greater tolerance.


Rhizoctonia solani
Also known by its sexual stage with multinucleate cells, Tanatephorus cucumeris, or with binucleate cells, Ceratobasidium sp. The most prevalent Rhizoctonia species, causing rhizoctonia root rot. A collection of several unrelated strains, attacking different crops, differentiated into anastomosis groups, or groups based on nuclei per cell.
Rhizoctonia sp.
Hyphae sterilia

Mycelia sterilia

Also known by its sexual stage with multinucleate cells, Thanatephorus sp., or with binucleate cells, Ceratobasidium sp. A basidiomycetes pathogen that causes rhizoctonia diseases. Produces no aseuxal spores, and rarely produces basidiospores. Produces mycelia only in culture. Hyphae develop in branches at right angles to parent hyphae. There is a slight constriction and cross-wall at the junction of a branch and parent hyphae.

Rhizoctonia stem canker
A rhizoctonia disease. Causes significant damage in cool, wet soils. Symptoms include delayed or reduced emergence, stunting of plants, smaller and/or deformed tubers, underground stem or stolon cankers, and reduced yield. The pathogen survives in plant residues and soil as mycelia and sclerotia. Sclerotia can survive on the surface of potato tubers without causing symptoms.


A sign of armillaria root rot. Shoestring-like, cylindrical or flattened masses of hyphae 1 – 5 mm in diameter, reddish-brown to black, with cream-coloured tips when actively growing. Inner tissue is white, and may become tan. Often attached to infected roots, and may be mistaken for roots. Helps spread Armillaria mellea.
Root-disease centre
An expanding group of trees killed by armillaria root rot. Develops when the pathogen spreads through root grafts. Typically the oldest mortalities are in the centre.
A very common destructive pathogenic group of basidiomycetes. There are about 5,000 species. Best known for losses in grain crops, but also affects vegetables, field crops, ornamentals, and trees. Attack mostly leaves and stems. Infections can appear as orange, yellow, or white spots that rupture the epidermis, hence the name “rust”. Most are very specialized obligate parasites that attack only certain genera, or varieties of plants. Many have special forms. Most are macrocyclic, and some are microcyclic. May be heteroecious or autoecious. Can have very complex life cycles. In Ancient Greece dogs were sacrificed to the gods to prevent rust epidemics.
Rust pustule
The uredium of wheat stem rust, found on wheat hosts. Reddish in colour, producing several generations of urediospores. Near the end of the summer it turns into a black telium.
Eats dead material.
Secondary mycelium
Dikaryotic, haploid hyphae produced when two primary mycelia of different mating types of a microcyclic basidiomycetes combine. The dormant stage of the fungus. Generates a basidiocarp.
Seedling infection
A type of infection of smut. Seedlings are infected following germination of teliospores carried on the seed, or that overwintered in soil or crop residues. The smut infects the plant systemically, giving rise to smutted heads.
A very common destructive pathogenic group of microcyclic basidiomycetes. There are about 1,200 species. Attack ovaries of grasses, wheat, barley, oats, corn, sorghum, onion, and ornamentals. Seldom kill the host, but can stunt growth. Produces black, powdery spore masses of teliospores in diseased tissue resembling soot or smut. Fairly well controlled; losses are low, except in localized situations. Teliospores may be carried by wind and water, and can survive in the soil for many years; rotations may not reduce disease. Seed treatments may be effective. Types of infection include seedling, floral, and local infections.
Special form (f.sp.)
Formae specialis

Rust fungi that are morphologically identical, but attack different host genera. Within these forms, there may be races.


Partners meet”

A haploid, monokaryotic spore produced by basidiomycetes in a spermatogonium. Present in macrocyclic rusts. They apepar similar to sperm. Water is needed for them to meet and fertilize receptive hyphae, fusing to produce haploid, dikaryoitc hyphae.


A structure in basidiomycetes which produces spermatia, and has receptive hyphae for spermatia fertilization. Resembles a pyncidium.

Sphacelotheca reilana
A basidiomycetes smut pathogen that causes head smut.
Fruiting bodies produced by Typhula ishikariensis and T. incarnata. Produce basidiospores.
Stem rust of barley
A disease caused by Puccinia graminis f.sp. tritici and P. graminis f.sp. secalis.


Stem rust of oat
A disease caused by Puccinia graminis f.sp. avenae.


The stalk holding a basidiospore on a basidium. It can forcibly eject basidiospores using surface tension or electrostatic charges.
Stress crop
A symptom of armillaria root rot. A confier tree produces a greater than normal amount of cones.
Stripe rust
Yellow rust

A disease which affects wheat.


Take a break”

A diploid, monokaryotic spore produced by basidiomycetes in a telium. Produced by macrocyclic and microcyclic rusts. During production there is karyogamy of haploid nuclei in the telium, producing a diploid zygote. Many rusts overwinter in this form; they are the longest-lasting spore of basidiomycetes. Germinates to produce a basidium.

A structure in basidiomycetes which produces teliospores.
Thanatephorus cucumeris
The sexual stage of Rhizoctonia solani with multinucleate cells.
Thanatephorus sp.
The rare sexual, multinucelate form of Rhizoctonia sp.
Dead grass from last season. Sclerotia of Typhula ishikariensis and T. incarnata over-summer in thatch.
Tilletia caries
A basidiomycetes smut pathogen that can cause covered smut. The teliospore has rough walls. If spore masses are crushed to release spores, there is a distinctive odour, similar to decaying fish.
Tilletia foetida
A basidiomycetes smut pathogen that can cause covered smut. The teliospore has rough walls. If spore masses are crushed to release spores, there is a distinctive odour, similar to decaying fish.
Tilletia sp.
A basidiomycetse smut pathogen that causes covered smut. Basidiospores are formed in a cluster at the tip of the basidium, and unite with compatible mating types on the basidium, restoring dikaryotic state. Spore masses burst during harvest, spreading spores into host and into the soil. The fungus is found on the outside of seeds. The spores of some species have a distinctive odour similar to decaying fish.
A race of Puccinia graminis f.sp. tritici Ug99 which was detected in South Africa in 2000.
A race of Puccinia graminis f.sp. tritici race Ug99 which was detected in South Africa and Zimbabwe in 2010.
The first race of Puccinia graminis f.sp. tritici race Ug99 to be characterized. It may have been present in Kenya in 1993. It was detected in Kenya in 2001, in Ethiopia in 2003, in Sudan and Yemen in 2006, and in Kenya in 2007.
A race of Puccinia graminis f.sp. tritici race Ug99 which was detected in South Africa in 2007.
A race of Puccinia graminis f.sp. tritici race Ug99 which was the predominant stem rust race in Kenya. It was present in Eritrea in 2010.
A race of Puccinia graminis f.sp. tritici race Ug99 which was confirmed in Egypt in 2014.
Typhula incarnata
A basidiomycetes pathogen that causes grey snow mould. Remains dormant during warm summer months as red-brown to tan sclerotia, 5 mm, which germinate in cold conditions to produce sporocarps, or mycelia that cause damage under snow cover. Spores are larger than those of T. ishikariensis, outbreaks are less severe, and infected patches recover more quickly in the spring. Cultures are white when mature, often with sclerotia. Hyphae often have clamp connections.
Typhula ishikariensis
A basidiomycetes pathogen that causes grey snow mould. Remains dormant during warm summer months as small black-brown sclerotia, 2 mm, which germinate in cold conditions to produce sporocarps, or myclelia that cause damage under snow cover. Spores are smaller than those of T. incarnata. Infections can progress downward into the crown, resulting in plant death or severe and lasting damage. Cultures are white when mature, often with sclerotia. Hyphae often have clamp connections.
Until summer’s end”

A haploid, dikaryotic spore produced by basidiomycetes in a uredium. Present in macrocyclic rusts. Act as a secondary inoculum to the host bearing uredia. Often orange in colour, giving the name “rust”.

A structure in basidiomycetes which produces urediospores.
Urocystis cepulae
A basidiomycetes pathogen that causes onion smut. Teliospores overwinter in soil and residue, and infect the flag leaf as it grows through the soil.
Urocystis sp.
A basidiomycetse smut pathogen. Forms no basidiospores; forms hyphal branches instead.
Ustilago hordei
A basidiomycetes smut pathogen that causes covered smut of barley.
Ustilago maydis
A basidiomycetes smut pathogen that causes corn smut. Basidiospores have many mating types, and are lightweight and don’t last very long, however they are easily maintained in culture of many different media, where they display considerable variation in morphology, colour, size, and growth, budding in a yeast-like manner. The basidiospores are only infectious once they have fused with a compatible mating type. The dikaryon acts as a biotroph, with hyphae growing mainly intracullarly, causing local infection. There are no haustoria; nutrients are absorbed through an electron-dense matrix material between host and fungal wall. Teliospores are ellipsoid, olive-brown to black, and overed in tiny spines, and they can last for several years. Can be used as a model organism to study a variety of interesting biological phenomena, including fungal mating type, fungal dimorphism, plant-pathogen interactions, and genetic recombination and repair. Its genome has been sequenced.
Ustilago nuda
A basidiomycetes smut pathogen that causes loose smut of barley. Spores are disseminated by rain and insects. Mycelia grow into the ovary wall and into the embryo of the developing seed.
Ustilago sp.
A basidiomycetes smut pathogen. Basidiospores are formed laterally on sepatate basidia.
Ustilago tritici
A basidiomycetes smut pathogen that causes loose smut of barley. Spores are disseminated by rain and insects. Mycelia grow into the ovary wall and into the embryo of the developing seed.
Wheat stem rust
Black stem rust

A polycyclic, heteroecious, macrocyclic rust disease caused by Puccinia graminis f.sp. tritici. Results in 1 million metric tons of lost yield per year, in severe years 100s of millions of tons. In 1943 – 1969, the USA and USSR produced strains of it to be used as biological weapons. The disease was classified, dried, and stored in Fort Detrick and the Rocky Mountain Arsenal; these agents were tested at least 31 times by the US military.

Wheat stem rust dissemination
Basidiospores are wind-blown onto barberry. Spermatia are vectored to receptive hyphae by insects or water. Aecospores are blown on the wind to infect wheat. Urediospores are blown up from the USA into Canada as the primary inoculum on the Puccinia Pathway. Urediospores produced can act as secondary inoculum in wheat.
Wheat stem rust hosts
Affects wheat (Triticum aestevium), barley, oats, and rye. Its alternate hosts is barberry (Berberis sp.)
Wheat stem rust infection in barberry
Basidiospores are formed in the spring, and are the primary inoculum in barberry. They are blown onto barberry leaves, where they infect and produce spermatogonia on the upper leaf surface which secrete spermatia in a sticky ooze. Dikaryotic mycelia grow through the leaf, and produce aecia on the lower leaf surface.
Wheat stem rust infection in wheat
Aeciospores or urediospores are blwon onto wheat leaves, where they germinate when a layer of free mositure is present, producing rust pustules on the site of infection. Several generations of urediospores can be produced by a pustule. As the plant matures, the pustule begins to produce teliospores.
Wheat stem rust management
Use resistant wheat varieties. Eradicate all barberry; salt can be used to kill plants. Fungicides.
Wheat stem rust survival
Overwinters in warmer climates as urediospores on fall-planted wheat. Overwinters in colder climates as teliospores in crop debris.
Wheat stem rust symptoms
All aboveground parts can be affected. Fewer tillers are produced. Fewer seeds set per head. Smaller kernel size, usually shriveled with poor quality. Severe infections can result in lodging or plant death. Reddish structures which are uredia form at points of infection, which turn into black pustules as the plant matures.


White pine blister rust
A heteroecious, macrocyclic, polycyclic rust disease caused by Cronartium ribicola. Introduced from Asia to Europe and North America in the 1900s. One of the most important forest diseases in North America. Kills white pine in all life stages; volume of pine can be depleted to the point where it is no longer a commercially viable species.
White pine blister rust hosts
Affects native five-needle pine, whitebark pine, sugar pine, western white pine, limber pine, eastern white pine, and Swiss stone pine. Paton’s Silver Splendor is a resistant variety. Alternate hosts are Ribes species including currants and gooseberries.
White pine blister rust infection in pine
Basidiospores infect in the fall through needles. The fungus spreads down the branch into the stem, where it grows into the phloem and produces no visible symptoms for threeyears.
White pine blister rust infection in Ribes sp.
Aeciospores infect Ribes sp. hosts. Urediospores are produced on the leaves throughout the summer and act as secondary inoculum in Ribes sp. hosts. Teliospores are produced in the fall which rapidly germinate into basidiospores.
White pine blister rust management
Used resistant cultivars. Prune off branches with cankers. Reduce moisture on white pine needles. Remove lower branches gradually as the pine tree matures. Space plants to promote good air movement around trees. Do not plant eastern white pine nearby currants or gooseberry.
White pine blister rust survival
Overwinters as a latent infection in the phloem of pine hosts. Teliospores are unable to survive in the winter.
White pine blister rust symptoms in pine
Galls form on branches which contain discrete black bodies beneath the bark which are spermatogonia. Ooze is secreted from the galls, containing spermatia. After fusion of receptive hyphae, white blisters break through the bark, containing aecia.