Collar rot is a symptomatically described disease that is usually caused by any one of various

fungal A fungus ( : fungi or funguses) is any member of the 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, separately from ...

and

oomycete Oomycota forms a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the resul ...

plant pathogens. It is present where the pathogen causes a lesion localized at or about the

collet A collet is a segmented sleeve, band or ''collar''. One of the two radial surfaces of a collet is usually tapered (i.e a truncated cone) and the other is cylindrical. The term ''collet'' commonly refers to a type of chuck that uses collets ...

between the stem and the root. The lesions develop around the stem eventually forming a "collar". Observationally, collar rot grades into "basal stem rot", and with some pathogens is the first phase of "basal stem rot" often followed by "root rot". Collar rot is most often observed in seedings grown in infected soil. The pathogens that cause collar rot may be species or genera specific. But generalist pathogens such as ''

Athelia rolfsii ''Athelia rolfsii'' is a corticioid fungus in the family Atheliaceae. It is a facultative plant pathogen and is the causal agent of "southern blight" disease in crops. Taxonomy The species was first described in 1911 by Italian mycologist Pier ...

'' (aka ''Sclerotium rolfsii'') are known to attack over 200 different species. While bacteria caused collar rot is not common, trees infected with

Fire blight Fire blight, also written fireblight, is a contagious disease affecting apples, pears, and some other members of the family Rosaceae. It is a serious concern to apple and pear producers. Under optimal conditions, it can destroy an entire orch ...

(''Erwinia amylovora'') may develop collar rot. Non-parasitic collar rot may be caused by winter damage. The symptomatically described disease Southern blight is often the first observed precursor of the collar rot caused by the fungus ''Athelia rolfsii''. Causally known as Sclerotial blight, ''Athelia rolfsii'' survives in the soil as

sclerotia A sclerotium (; (), is a compact mass of hardened fungal mycelium containing food reserves. One role of sclerotia is to survive environmental extremes. In some higher fungi such as ergot, sclerotia become detached and remain dormant until favor ...

, and in infected decomposing plant material as

mycelia Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrates. A typical single spore germinates in ...

. Collar rot that is caused by the oomycete ''

Phytophthora ''Phytophthora'' (from Greek (''phytón''), "plant" and (), "destruction"; "the plant-destroyer") is a genus of plant-damaging oomycetes (water molds), whose member species are capable of causing enormous economic losses on crops worldwide, a ...

'' is causally called Phytophthora collar rot, and is a common disease of fruit and nut trees, as well as other flowers and crops. ''Phytophthora'' species remain in the soil, as spores, and in infected plant tissue, as mycelia, so absent control measures (sterilization, toxic applications) the disease continues so long as susceptible plants are grown in that soil.

Hosts and agents

*In

carnation ''Dianthus caryophyllus'' (), commonly known as the carnation or clove pink, is a species of ''Dianthus''. It is likely native to the Mediterranean region but its exact range is unknown due to extensive cultivation for the last 2,000 years.Med ...

s (''

Dianthus caryophyllus ''Dianthus caryophyllus'' (), commonly known as the carnation or clove pink, is a species of ''Dianthus''. It is likely native to the Mediterranean region but its exact range is unknown due to extensive cultivation for the last 2,000 years.Med ...

'') by '' Alternaria dianthi'', *In

chili Chili or chilli may refer to: Food * Chili pepper, the spicy fruit of plants in the genus ''Capsicum''; sometimes spelled "chilli" in the UK and "chile" in the southwestern US * Chili powder, the dried, pulverized fruit of one or more varieties ...

(''Capsicum'') by ''

'', *In

cinchona ''Cinchona'' (pronounced or ) is a genus of flowering plants in the family Rubiaceae containing at least 23 species of trees and shrubs. All are native to the tropical Andean forests of western South America. A few species are reportedly natu ...

(''Cinchona officinalis'') by ''

Phytophthora quininea ''Phytophthora'' (from Greek (''phytón''), "plant" and (), "destruction"; "the plant-destroyer") is a genus of plant-damaging oomycetes (water molds), whose member species are capable of causing enormous economic losses on crops worldwide, as ...

'', *In Chinese evergreens (''

Aglaonema ''Aglaonema'' is a genus of flowering plants in the arum family, Araceae. They are native to tropical and subtropical regions of Asia and New Guinea.

'') by '' Fusarium subgutinans'', *In

coffee plants ''Coffea'' is a genus of flowering plants in the family Rubiaceae. ''Coffea'' species are shrubs or small trees native to tropical and southern Africa and tropical Asia. The seeds of some species, called coffee beans, are used to flav ...

(''Coffea'') by '' Gibberella stilboides'', *In

dogwood ''Cornus'' is a genus of about 30–60 species of woody plants in the family Cornaceae, commonly known as dogwoods, which can generally be distinguished by their blossoms, berries, and distinctive bark. Most are deciduous trees or shru ...

s (genus ''Cornus'') by ''

Phytophthora cactorum ''Phytophthora cactorum'' is a fungal-like plant pathogen belonging to the Oomycota phylum. It is the causal agent of root rot on rhododendron and many other species, as well as leather rot of strawberries. . Hosts, symptoms, and diagnosis ''Phy ...

'' where the disease is also called "crown canker", *In eggplant/brinjal (''Solanum melongena'') by ''

Sclerotinia sclerotiorum ''Sclerotinia sclerotiorum'' is a plant pathogenic fungus and can cause a disease called white mold if conditions are conducive. ''S. sclerotiorum'' can also be known as cottony rot, watery soft rot, stem rot, drop, crown rot and blossom blight. ...

'' and ''Sclerotium rolfsii'', *In elephant foot yams (''Amorphophallus paeoniifolius'') by ''Sclerotium rolfsii'', *In fruit and nut trees by a variety of pathogens including ''

Sclerotium rolfsii ''Athelia rolfsii'' is a corticioid fungus in the family Atheliaceae. It is a facultative plant pathogen and is the causal agent of "southern blight" disease in crops. Taxonomy The species was first described in 1911 by Italian mycologist Pier ...

'', ''

Alternaria ''Alternaria'' is a genus of Deuteromycetes fungi. All species are known as major plant pathogens. They are also common allergens in humans, growing indoors and causing hay fever or hypersensitivity reactions that sometimes lead to asthma. They ...

'' and ''

'', *In groundnut/peanut (''

Arachis hypogaea The peanut (''Arachis hypogaea''), also known as the groundnut, goober (US), pindar (US) or monkey nut (UK), is a legume crop grown mainly for its edible seeds. It is widely grown in the tropics and subtropics, important to both small and la ...

'') by ''

Aspergillus niger ''Aspergillus niger'' is a mold classified within the ''Nigri'' section of the ''Aspergillus'' genus. The ''Aspergillus'' genus consists of common molds found throughout the environment within soil and water, on vegetation, in fecal matter, on de ...

'' which also causes wilt and crown rot, and by ''

Lasiodiplodia theobromae ''Lasiodiplodia theobromae'' is a Plant pathology, plant pathogen with a very wide host (biology), host range. It causes rotting and Forest dieback, dieback in most species it infects. It is a common post harvest fungus disease of citrus known a ...

'', *In hardwoods and conifers by ''

Phytophthora cinnamomi ''Phytophthora cinnamomi'' is a soil-borne water mould that produces an infection which causes a condition in plants variously called " root rot", "dieback", or (in certain ''Castanea'' species), "ink disease". The plant pathogen is one of the w ...

'', *In

maize Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn ( North American and Australian English), is a cereal grain first domesticated by indigenous peoples in southern Mexico about 10,000 years ago. ...

(corn, ''Zea mays'') by ''

'', *In

papaya The papaya (, ), papaw, () or pawpaw () is the plant species ''Carica papaya'', one of the 21 accepted species in the genus '' Carica'' of the family Caricaceae. It was first domesticated in Mesoamerica, within modern-day southern Mexico and ...

by ''

Calonectria ''Calonectria'' (anamorph ''Cylindrocladium'') is a genus of ascomycete fungi. ''Calonectria'' species are plant pathogens. Species *'' Calonectria acicola'' *'' Calonectria adianti'' *'' Calonectria agnina'' *'' Calonectria ambigua'' *'' Calon ...

'', *In

pine A pine is any conifer tree or shrub in the genus ''Pinus'' () of the family (biology), family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoideae. The World Flora Online created by the Royal Botanic Gardens, Kew and Missouri Botanic ...

s by both ''Phytophthora'' and '' Diplodia pinastri'', *In

rhododendron ''Rhododendron'' (; from Ancient Greek ''rhódon'' "rose" and ''déndron'' "tree") is a very large genus of about 1,024 species of woody plants in the heath family (Ericaceae). They can be either evergreen or deciduous. Most species are nativ ...

, China aster,

marigold Marigold may refer to: * Marigold (color), a yellow-orange color It may also refer to: Plants * In the genus ''Calendula'': ** Common marigold, '' Calendula officinalis'' (also called pot marigold, ruddles, or Scotch marigold) * In the genus ' ...

, gloxinia and

zinnia ''Zinnia'' is a genus of plants of the tribe Heliantheae within the family Asteraceae. They are native to scrub and dry grassland in an area stretching from the Southwestern United States to South America, with a centre of diversity in Mexico. ...

by '' Phytophthora cryptogea'', *In sunflowers by ''

'', and by '' Phytophthora cryptogea''. *In

sweet potato The sweet potato or sweetpotato ('' Ipomoea batatas'') is a dicotyledonous plant that belongs to the bindweed or morning glory family, Convolvulaceae. Its large, starchy, sweet-tasting tuberous roots are used as a root vegetable. The young ...

es (''Ipomoea batatas'') by ''Sclerotium rolfsii'', *In

tobacco Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ch ...

by ''

''. *In

tomato The tomato is the edible berry of the plant ''Solanum lycopersicum'', commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word gave rise to the Spanish word , ...

es (''Solanum lycopersicum'') by ''

Alternaria solani ''Alternaria solani'' is a fungal pathogen that produces a disease in tomato and potato plants called early blight. The pathogen produces distinctive "bullseye" patterned leaf spots and can also cause stem lesions and fruit rot on tomato and tube ...

'',

Related diseases

* Rootstock blight''Symptoms of rootstock blight can be confused with Phytophthora collar rot.'' *

Stem rot Stem rot is a disease caused by a fungus infection in the stem. Fungus that causes stem rot are in the ''Rhizoctonia'', ''Fusarium'' or ''Pythium'' genera. Stem rot can readily infect crops that are in their vegetative or flowering stages. The dis ...

Notes and references

{{Reflist Crop diseases Tree diseases Eudicot diseases Fungal plant pathogens and diseases Water mould plant pathogens and diseases