Rust (fungus)
Rusts are plant diseases caused by pathogenic fungi of the order Pucciniales. About 7800 species are known. Rusts can affect a variety of plants; leaves, stems, fruits and seeds. Rust is most commonly seen as coloured powder, composed off tiny aeciospores which land on vegetation producing pustules, or uredia, that form on the lower surfaces. During late spring or early summer, yellow orange or brown, hairlike or ligulate structures called telia
Telia may refer to:*Telia - part of the reproductive cycle of Rusts*Telia Digital-tv - a Swedish TV platform*Telia, Nepal - a village in Nepal*TeliaSonera - a Swedish/Finnish telecom operator*Telia Challenge Waxholm - Golf tournament...

 grow on the leaves or emerge from bark of woody hosts such as Juniperus species. These telia produce teliospores which will germinate into aerial basidiospores, spreading and causing further infection.


The taxonomy of Pucciniales is complex and the darker coloured smuts
Smut (fungus)
The smuts are multicellular fungi, that are characterized by their large numbers of teliospores. The smuts get their name from a Germanic word for dirt because of their dark, thick-walled and dust-like teliospores. They are mostly Ustilaginomycetes and can cause plant disease...

 can be mistaken for rust. Rusts are so named after the reddish rusty looking sori
A sorus is a cluster of sporangia .In fungi and lichens, the sorus is surrounded by an external layer. In some red algae it may take the form of a depression into the thallus....

 and the disease is usually noticed after rain.

The group is considered as one of the most harmful pathogens to agriculture and horticulture.


Rusts can produce up to five spores types during their life cycle
  • 0-Pycniospores (Spermatia)-Haploid gametes in heterothallic rusts.
  • I-Aeciospores-non-repeating dikaryotic vegetative spores
  • II-Urediniospores-repeating dikaryotic vegetative spores. These spores are referred to as the repeating stage because they can cause auto-infection (re-infect the same host from which the spores were borne). These spores are red/orange and are a characteristic sign of rust fungus infection.
  • III-Teliospores-Diploid spores that produce basidia and are the survival stage of life cycle
  • IV-Basidiospores-stem from basidia. Haploid spores which infect the alternate host. although these are rarely observed outside of the laboratory
    A laboratory is a facility that provides controlled conditions in which scientific research, experiments, and measurement may be performed. The title of laboratory is also used for certain other facilities where the processes or equipment used are similar to those in scientific laboratories...


Rust fungi can be categorized by how many types of spores are produced during the life cycle. Fungi that produce all five spores (sometimes excluding pycniospores) are termed macrocyclic. Fungi that lack pycniospores, aeciospores, and urediniospores in their life cycle are termed microcyclic and always have an autoecious life cycle. Demicyclic fungi delete the uredial (repeating) stage from the life cycle. Understanding the life cycles of rust fungi allows for proper disease management.

Life cycle

All rusts are obligate parasites, meaning that they require a living host to complete their life cycle. They generally do not kill the host plant but can severely reduce growth and yield. Cereal crops can be devastated in one season and trees that get infected in the main stem within the first five years, invariably die.

Rust fungi can also be categorized by their life cycle. Heteroecious rust fungi require two unrelated hosts to complete their life cycle, with the primary host being infected by aeciospores and the alternate host being infected with basidiospores. This can be contrasted with an autoecious fungus which can complete its life cycle on a single host species.

Infection process

The fungi produce asexual
Asexual reproduction
Asexual reproduction is a mode of reproduction by which offspring arise from a single parent, and inherit the genes of that parent only, it is reproduction which does not involve meiosis, ploidy reduction, or fertilization. A more stringent definition is agamogenesis which is reproduction without...

In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...

s which disperse by wind, water or by insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...

 vectors spreading the infection.

Rust fungi are biotrophs taking nutrients from living cells. When airborne spore
Conidia, sometimes termed conidiospores, are asexual, non-motile spores of a fungus and are named after the greek word for dust, konia. They are also called mitospores due to the way they are generated through the cellular process of mitosis...

s settle on a plant, weak hydrophobic interactions are formed with the cutin
Cutin is one of two waxy polymers that are the main components of the plant cuticle, which covers all aerial surfaces of plants. The other major cuticle polymer is cutan, which is much more readily preserved in the fossil record,...

 on the plant cell surface, securing it. By a process not fully understood, the production of mucous like substances called 'adhesins', initially stick the spore to the plant surface.

Once attached, the spore germinates by growing a germ tube
Germ tube
A germ tube is an outgrowth produced by spores of spore-releasing fungi during germination.The germ tube differentiates, grows, and develops by mitosis to create somatic hyphae....

 and eventually locates a stoma
In botany, a stoma is a pore, found in the leaf and stem epidermis that is used forgas exchange. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that are responsible for regulating the size of the opening...

 by a touch responsive process known as thigmotropism
Thigmotropism is a movement in which an organism moves or grows in response to touch or contact stimuli. The prefix thigmo- θιγμος comes from the Greek for "touch". Usually thigmotropism occurs when plants grow around a surface, such as a wall, pot, or trellis. Climbing plants, such as vines,...

. This involves growing towards a ridge between the epidermal cells
Epidermis (botany)
The epidermis is a single-layered group of cells that covers plants' leaves, flowers, roots and stems. It forms a boundary between the plant and the external environment. The epidermis serves several functions, it protects against water loss, regulates gas exchange, secretes metabolic compounds,...

, followed by a perpendicular growth which end at the stoma. Inside the stoma, the hyphae tips flatten out to form structures known as appresorium
Appresoria, the plural of appresorium, are the tips of infectious hyphae, often from a germinating spore, that make contact with their host cell wall and that flatten out into disc, fan or lobed shapes tightly affixed or appressed on the host cell wall...

 that lock to the cell walls. It is thought that the whole process is mediated by a mechano-sensitive calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...

 channel, located within the germ tube tip, which produces electric currents that stretch the cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

s, changing gene expression and forming the appresorium.

Then a peg grows into the plant's mesophyll
Mesophyll can refer to:* Mesophyll tissue, in plant anatomy, photosynthetic parenchyma cells that lie between the upper and lower epidermis layers of a leaf...

 cells. The peg produces specialised hyphal tips, known as haustorium
In botany, a haustorium is the appendage or portion of a parasitic fungus or of the root of a parasitic plant that penetrates the host's tissue and draws nutrients from it. Haustoria do not penetrate the host's cell membranes.Fungi in all major divisions form haustoria...

. These spread around the plant cells without invading the membranes. The plant cell membranes invaginate around the main haustorial body forming a space known as the extra-haustorial matrix. An iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 and phosphorus
Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...

 rich neck band bridges the plant and fungal membranes in the space between the cells for water flow, known as the apoplast
Within a plant, the apoplast is the free diffusional space outside the plasma membrane. It is interrupted by the Casparian strip in roots, air spaces between plant cells and the cuticula of the plant....

, thus preventing the nutrient
A nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. They are used to build and repair tissues, regulate body processes and are converted to and used as energy...

s reaching the plant's cells. The haustorium contains amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

 and hexose
In organic chemistry, a hexose is a monosaccharide with six carbon atoms, having the chemical formula C6H12O6. Hexoses are classified by functional group, with aldohexoses having an aldehyde at position 1, and ketohexoses having a ketone at position 2....

Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...

 transporters and H+-ATPases which are used for active transport
Active transport
Active transport is the movement of a substance against its concentration gradient . In all cells, this is usually concerned with accumulating high concentrations of molecules that the cell needs, such as ions, glucose, and amino acids. If the process uses chemical energy, such as from adenosine...

 of nutrients from the plant nourishing the fungus. It continues growing until spore growth occurs. The process repeats every 10 – 14 days, producing numerous spores, carried by wind to new hosts.

Common Rust Fungi in Agriculture

  • Puccinia sorghi causes common rust in corn
  • Gymnosporangium juniperi-virginianae
    Gymnosporangium juniperi-virginianae
    Gymnosporangium juniperi-virginianae is a plant pathogen that causes cedar-apple rust. In virtually any location where apples or crabapples and Eastern red cedar coexist, cedar apple rust can be a destructive or disfiguring disease on both the apples and cedars...

    (Cedar-apple rust); the Juniperus virginiana
    Juniperus virginiana
    Juniperus virginiana is a species of juniper native to eastern North America, from southeastern Canada to the Gulf of Mexico, east of the Great Plains...

    is the primary (telial
    Teliospore is the thick-walled resting spore of some fungi , from which the basidium arises.-Development:They develop in telia ....

    ) host and the apple
    The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...

    , pear
    The pear is any of several tree species of genus Pyrus and also the name of the pomaceous fruit of these trees. Several species of pear are valued by humans for their edible fruit, but the fruit of other species is small, hard, and astringent....

     or hawthorn
    Crataegus , commonly called hawthorn or thornapple, is a large genus of shrubs and trees in the rose family, Rosaceae, native to temperate regions of the Northern Hemisphere in Europe, Asia and North America. The name hawthorn was originally applied to the species native to northern Europe,...

     is the secondary (aecial) host.Heteroecious and demicyclic
  • Cronartium ribicola (White pine blister rust); the primary host are white pines
    Pinus classification
    There are three main subgenera of Pinus, the subgenus Strobus , the subgenus Ducampopinus , and the subgenus Pinus...

    , and currants
    Ribes is a genus of about 150 species of flowering plants native throughout the temperate regions of the Northern Hemisphere. It is usually treated as the only genus in the family Grossulariaceae. Seven subgenera are recognized....

     the secondary. Heterocyclic and macrocyclic
  • Hemileia vastatrix (Coffee rust); Primary host is coffee plant; Unknown alternate host. Heteroecious
  • Puccinia graminis (Stem rust of wheat and Kentucky bluegrass); Primary hosts include: Kentucky bluegrass, barley, and wheat; Common barberry is the alternate host. Heteroecious and macrocyclic
  • Puccinia coronata (Crown Rust of Oats and Ryegrass); Oats are the primary host; Rhamnus spp. (Buckthorn) is alternate host. Heteroecious and macrocyclic
  • Phakopsora meibomiae and P. pachyrhizi (Soybean Rust); Primary host is soybean and various legumes. Unknown alternate host. Heteroecious
  • Uromyces phaseoli (Bean rust); Primary host:bean. Autoecious and macrocyclic
  • Puccinia hemerocallidis (Daylily rust); Daylily is primary host; Patrina sp is alternate host. Heteroecious and macrocyclic
  • Puccinia persistens subsp. triticina causes wheat rust in grains. It is also known as 'brown or red rust'.
  • P.sriiformis causes 'Yellow rust' and P. graminis causes 'black rust' in cereals.
  • Phakopsora pachyrhizi or P. meibomiae cause serious rust damage to soyabean.
  • Uromyces appendeculatus is a problem on beans

Management of Rust Fungi Diseases

The control methods of rust fungus diseases depend largely on the life cycle of the particular pathogen. The following are examples of disease management plans used to control macrocyclic and demicyclic diseases:-

Macrocyclic Disease: Developing a management plan for this type of disease depends largely on whether the repeating stage (urediniospores) occur on the economically important host plant or the alternate host. For example, the repeating stage in white pine blister rust disease does not occur on white pines but on the alternate host, Ribes spp. During August and September Ribes spp. give rise to teliospores which infect white pines. Removal of the alternate host disrupts the life cycle of the rust fungi Cronartium ribicola, preventing the formation of basidiospores which infect the primary host. Although spores from white pines cannot infect other white pines, survival spores may overwinter on infected pines and reinfect Ribes spp. the following season. Infected tissue is removed from white pines and strict quarantines of Ribes spp. are maintained in high risk areas.

Puccinia graminis is a macrocyclic heteroecious fungus that causes wheat stem rust disease. The repeating stage in this fungus occurs on wheat and not the alternate host, barberry. The repeating stage allows the disease to persist in wheat even though the alternate host may be removed. Planting resistant crops is the ideal form of disease prevention, however, mutations can give rise to new strains of fungi that can overcome plant resistance. Although the disease cannot be stopped by removal of the alternate host, the life cycle is disrupted and the rate of mutation is decreased because of reduced genetic recombination. This allows resistance bred crops to remain effective for a longer period of time.

Demicyclic Disease: Because there is no repeating stage in the life cycle of demicyclic fungi, removal of the primary or the alternate host will disrupt the disease cycle. This method, however, is not highly effective in managing all demicyclic diseases. Cedar-apple rust disease, for example, can persist despite removal of one of the hosts since spores can be disseminated from long distances. The severity of Cedar-apple rust disease can be managed by removal of basidiospore producing galls from junipers or the application of protective fungicides to junipers.

Home control

Rust is very hard to treat. Fugicides such as Mancozeb or Triforine may help but may never eradicate the disease. Some organic preventative solutions are available and Sulphur powder is known to stop germination. High standards of hygiene and good soil drainage and careful watering may minimise problems. Any appearance of rust must be immediately dealt with by removing and burning all affected leaves. Composting, or leaving infected vegetation on the ground spread the disease.

Commercial control

In large plantations in USA, fungicides are applied by air. The process is expensive and fungicide application is best reserved for seasons when foliar diseases are severe. Research indicates, the higher the foliar disease severity, the greater the return from the use of fungicides. There are a variety of preventative methods that can also be employed.
  • Symptoms of rust disease are correlated to relatively high moisture. The avoidance of overhead watering at night, using drip irrigation, reducing crop density, and using fans to circulate air flow will lower the relative moisture and decrease the severity of rust infection.
  • The use of rust resistant plants
  • Crop rotation can break the disease cycle because many rusts are host specific.
  • Inspect all imported plants and cuttings for symptoms. It is important to continuously observe these plants because rust diseases have a latent period (plant has the disease but shows no symptoms).
  • Many crops, such as wheat, are replanted with disease-free seed.

Host plants affected

Rusts are often named after the host species that they infect. For example; Puccinia xanthii infects the flowering plant Cocklebur
Cockleburs are a genus of flowering plants in the family Asteraceae, native to the Americas and eastern Asia.-Growth:They are coarse, herbaceous annual plants growing to 19.69-47.24 in tall. The leaves are spirally arranged, with a deeply toothed margin. Some species, notably X...

. It is probable that most plant species are affected by some species of rust. Some of the better known hosts include
  • Arisaema triphyllum, Jack-in-the-pulpit
  • Avena sativa, Oats
    OATS - Open Source Assistive Technology Software - is a source code repository or "forge" for assistive technology software. It was launched in 2006 with the goal to provide a one-stop “shop” for end users, clinicians and open-source developers to promote and develop open source assistive...

  • Barberis vulgaris, Barberry
  • Broad beans
  • Crataegus monogyna - Hawthorn
  • Chrysanthemum
    Chrysanthemums, often called mums or chrysanths, are of the genus constituting approximately 30 species of perennial flowering plants in the family Asteraceae which is native to Asia and northeastern Europe.-Etymology:...

  • Cydonia
    Cydonia may refer to:* Cydonia , the goddess of heroic endeavour in Greek mythology* 1106 Cydonia, a main belt asteroid* Cydonia, Crete* Cydonia , a 2001 album by The Orb...

    - Quince
  • Euphorbia maculata, Spotted Spurge
  • Fuchsia spp, Fuchsia
    Fuchsia is a genus of flowering plants that consists mostly of shrubs or small trees. The first, Fuchsia triphylla, was discovered on the Caribbean island of Hispaniola in 1703 by the French Minim monk and botanist, Charles Plumier...

  • Garlic
    Allium sativum, commonly known as garlic, is a species in the onion genus, Allium. Its close relatives include the onion, shallot, leek, chive, and rakkyo. Dating back over 6,000 years, garlic is native to central Asia, and has long been a staple in the Mediterranean region, as well as a frequent...

  • Hordeum vulgare, Barley
    Barley is a major cereal grain, a member of the grass family. It serves as a major animal fodder, as a base malt for beer and certain distilled beverages, and as a component of various health foods...

  • Juniperus virginianae, Red Cedar
    Juniperus virginiana
    Juniperus virginiana is a species of juniper native to eastern North America, from southeastern Canada to the Gulf of Mexico, east of the Great Plains...

     (Juniper apple disease)

  • Juniperus communis
    Juniperus communis
    Juniperus communis, the Common Juniper, is a species in the genus Juniperus, in the family Cupressaceae. It has the largest range of any woody plant, throughout the cool temperate Northern Hemisphere from the Arctic south in mountains to around 30°N latitude in North America, Europe and Asia.-...

    - Juniper
  • Allium ampeloprasum
    The leek, Allium ampeloprasum var. porrum , also sometimes known as Allium porrum, is a vegetable which belongs, along with the onion and garlic, to family Amaryllidaceae, subfamily Allioideae...

    - Leek
  • Malus
    Malus , the apples, are a genus of about 30–35 species of small deciduous trees or shrubs in the family Rosaceae. Other studies go as far as 55 species including the domesticated Orchard Apple, or Table apple as it was formerly called...

    – Apple
  • Mespilus - Medlar
  • Onion
    The onion , also known as the bulb onion, common onion and garden onion, is the most widely cultivated species of the genus Allium. The genus Allium also contains a number of other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion The onion...

  • Pelargonium
    Pelargonium is a genus of flowering plants which includes about 200 species of perennials, succulents, and shrubs, commonly known as scented geraniums or storksbills. Confusingly, Geranium is the correct botanical name of a separate genus of related plants often called Cranesbills. Both Geranium...

  • Primula veris
    Primula veris
    Primula veris is a flowering plant in the genus Primula. The species is found throughout most of temperate Europe and Asia, and although absent from more northerly areas including much of northwest Scotland, it reappears in northernmost Sutherland and Orkney.-Names:The common name cowslip derives...

  • Primula vulgaris
    Primula vulgaris
    Primula vulgaris is a species of Primula native to western and southern Europe , northwest Africa , and southwest Asia...

  • Pyrus - Pear
  • Rosa spp, Roses
  • Triticum spp., Wheat
    Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...

  • Oxalis spp., Oxalis
    Oxalis is by far the largest genus in the wood-sorrel family Oxalidaceae: of the approximately 900 known species in the Oxalidaceae, 800 belong here...

  • Secale cereale, Rye
    Rye is a grass grown extensively as a grain and as a forage crop. It is a member of the wheat tribe and is closely related to barley and wheat. Rye grain is used for flour, rye bread, rye beer, some whiskeys, some vodkas, and animal fodder...

  • Senecio vulgaris -Common groundsel
  • Xanthium canadenseCocklebur
    Cockleburs are a genus of flowering plants in the family Asteraceae, native to the Americas and eastern Asia.-Growth:They are coarse, herbaceous annual plants growing to 19.69-47.24 in tall. The leaves are spirally arranged, with a deeply toothed margin. Some species, notably X...

See also

  • Wheat leaf rust
    Wheat leaf rust
    Wheat leaf rust, is fungal disease that effects wheat, barley and rye stems, leaves and grains. In temperate zones it is destructive on winter wheat because the pathogen overwinters. Infections can lead up to 20% yield loss - exacerbated by dying leaves which fertilize the fungus. The pathogen is...

  • Leaf rust (barley)
    Leaf rust (barley)
    Leaf rust is a fungal disease of barley caused by Puccinia hordei. It is also known as brown rust and it is the most important rust disease on barley.- Symptoms :...

  • Fungus
    A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

  • Smut (fungus)
    Smut (fungus)
    The smuts are multicellular fungi, that are characterized by their large numbers of teliospores. The smuts get their name from a Germanic word for dirt because of their dark, thick-walled and dust-like teliospores. They are mostly Ustilaginomycetes and can cause plant disease...

  • Soybean rust
    Soybean rust
    Soybean rust, also known as Asian soybean rust, is a disease that affects soybeans and other legumes. It is caused by two types of fungi, Phakopsora pachyrhizi and Phakopsora meibomiae. P. meibomiae is the weaker pathogen of the two and generally does not cause widespread problems...

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