Sirococcus clavigignenti-juglandacearum
Encyclopedia
Sirococcus clavigignenti-juglandacearum is a mitosporic fungus
that causes a lethal canker
disease of Butternut trees
(Juglans cinerea). Known in the vernacular
as butternut canker, it is also known to parasitize other members of the Juglans
genus on occasion, and very rarely other related trees including hickories
. The fungus is found throughout North America
, occurring on up to 91% of butternut trees, and may be threatening the viability of butternut as a species.
to North Carolina
.
Butternut canker was identified as an invasive species
in 1967. It was first discovered in Wisconsin
, but has since spread to other states and into Canada
. Its native origin is unknown, but possibly in Asia
given the resistance of Asian walnuts to the disease. The United States Forest Service
found that 84% of all butternuts in Michigan
as well as 58% of all trees from Wisconsin have been affected; later surveys by the Wisconsin Department of Natural Resources
revealed that 91% of all living trees in Wisconsin were diseased or cankered. In Virginia
and North Carolina
, the butternut population has been reduced from 7.5 million to 2.5 million.
cracks. The fungus forms a dark mat of branching mycelium
below the bark, from which arise peg-like hypha
that lift and rupture the bark. In the later stages of infection, the bark above the canker is shredded.
S. clavigignenti-juglandacearum produces its spores asexually; its sexual form of reproduction has never been observed.
Pycnidiospores are released during rainy periods. When the spore
s make contact with wounds or broken branch
es, they germinate
and penetrate deep into the tree to produce cankers. Infection hyphae typically penetrates through the parenchyma
phloem
intracellularly but they can also penetrate intercellularly through uni and multiceliate xylem
ray cells and paranchyma cells. Later, the fungus will produce mycelial mats of stroma and mycelial pegs.
Stroma mats will produce uni or multilocular pycnidia. Inside the pycnidia are branched and unbranched conidiophores with two-celled pycniospores, which later are ejected from the pycnidial ostiole.
Additionally, the stroma will produce a peg of interwoven mycelium. These pegs put pressure on the outer peridium of the host bark, which exposes the pycnidia below. These pegs also produce pycnidia that are smaller than the pycnidia in the stroma. While different in size, the spores produced are identical.
, such as the heartnut, Butternut
, and the Japanese, Black, and Persian Walnut
s. It is sometimes claimed that higher levels of resistance result from thicker bark; however, since the disease enters through breaks in the bark, it is unlikely that bark thickness influences resistance. Additionally, both trees produce phenolics immediately upon attack, later producing gums and tyloses to surround the pathogen.
Recent reports have shown that the fungus can be internally seed-borne, so seed
s should be subjected to intense quarantine
protocols; most especially if destined for plantings where the disease is not already established.
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...
that causes a lethal canker
Canker
Canker and anthracnose are general terms for a large number of different plant diseases, characterised by broadly similar symptoms including the appearance of small areas of dead tissue, which grow slowly, often over a period of years. Some are of only minor consequence, but others are ultimately...
disease of Butternut trees
Butternut (tree)
Juglans cinerea, commonly known as Butternut or White Walnut, is a species of walnut native to the eastern United States and southeast Canada. Its range extends east to New Brunswick, and from southern Quebec west to Minnesota, south to northern Alabama and southwest to northern Arkansas...
(Juglans cinerea). Known in the vernacular
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
as butternut canker, it is also known to parasitize other members of the Juglans
Walnut
Juglans is a plant genus of the family Juglandaceae, the seeds of which are known as walnuts. They are deciduous trees, 10–40 meters tall , with pinnate leaves 200–900 millimetres long , with 5–25 leaflets; the shoots have chambered pith, a character shared with the wingnuts , but not the hickories...
genus on occasion, and very rarely other related trees including hickories
Hickory
Trees in the genus Carya are commonly known as hickory, derived from the Powhatan language of Virginia. The genus includes 17–19 species of deciduous trees with pinnately compound leaves and big nuts...
. The fungus is found throughout North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, occurring on up to 91% of butternut trees, and may be threatening the viability of butternut as a species.
Distribution
Butternut, the primary host of S. clavigignenti-juglandacearumis, is found in mixed hardwood forests throughout central North America, from New BrunswickNew Brunswick
New Brunswick is one of Canada's three Maritime provinces and is the only province in the federation that is constitutionally bilingual . The provincial capital is Fredericton and Saint John is the most populous city. Greater Moncton is the largest Census Metropolitan Area...
to North Carolina
North Carolina
North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...
.
Butternut canker was identified as an invasive species
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
in 1967. It was first discovered in Wisconsin
Wisconsin
Wisconsin is a U.S. state located in the north-central United States and is part of the Midwest. It is bordered by Minnesota to the west, Iowa to the southwest, Illinois to the south, Lake Michigan to the east, Michigan to the northeast, and Lake Superior to the north. Wisconsin's capital is...
, but has since spread to other states and into Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. Its native origin is unknown, but possibly in Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...
given the resistance of Asian walnuts to the disease. The United States Forest Service
United States Forest Service
The United States Forest Service is an agency of the United States Department of Agriculture that administers the nation's 155 national forests and 20 national grasslands, which encompass...
found that 84% of all butternuts in Michigan
Michigan
Michigan is a U.S. state located in the Great Lakes Region of the United States of America. The name Michigan is the French form of the Ojibwa word mishigamaa, meaning "large water" or "large lake"....
as well as 58% of all trees from Wisconsin have been affected; later surveys by the Wisconsin Department of Natural Resources
Wisconsin Department of Natural Resources
The Wisconsin Department of Natural Resources is an agency of the state of Wisconsin. Its purpose is to preserve, protect, manage and maintain the natural resources of the state. The WDNR has the authority to set policy for itself and to recommend regulations for approval by the State Legislature...
revealed that 91% of all living trees in Wisconsin were diseased or cankered. In Virginia
Virginia
The Commonwealth of Virginia , is a U.S. state on the Atlantic Coast of the Southern United States. Virginia is nicknamed the "Old Dominion" and sometimes the "Mother of Presidents" after the eight U.S. presidents born there...
and North Carolina
North Carolina
North Carolina is a state located in the southeastern United States. The state borders South Carolina and Georgia to the south, Tennessee to the west and Virginia to the north. North Carolina contains 100 counties. Its capital is Raleigh, and its largest city is Charlotte...
, the butternut population has been reduced from 7.5 million to 2.5 million.
Symptoms
Broad dead areas known as cankers form on the main stem, branches, young twigs, and exposed roots. Most cankers are covered with barkBark
Bark is the outermost layers of stems and roots of woody plants. Plants with bark include trees, woody vines and shrubs. Bark refers to all the tissues outside of the vascular cambium and is a nontechnical term. It overlays the wood and consists of the inner bark and the outer bark. The inner...
cracks. The fungus forms a dark mat of branching mycelium
Mycelium
thumb|right|Fungal myceliaMycelium is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae. The mass of hyphae is sometimes called shiro, especially within the fairy ring fungi. Fungal colonies composed of mycelia are found in soil and on or within many other...
below the bark, from which arise peg-like hypha
Hypha
A hypha is a long, branching filamentous structure of a fungus, and also of unrelated Actinobacteria. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium; yeasts are unicellular fungi that do not grow as hyphae.-Structure:A hypha consists of one or...
that lift and rupture the bark. In the later stages of infection, the bark above the canker is shredded.
Life cycle
Pycnidiospores are released during rainy periods. When the spore
Spore
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 make contact with wounds or broken branch
Branch
A branch or tree branch is a woody structural member connected to but not part of the central trunk of a tree...
es, they germinate
Germination
Germination is the process in which a plant or fungus emerges from a seed or spore, respectively, and begins growth. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. However the growth of a sporeling from a spore, for example the...
and penetrate deep into the tree to produce cankers. Infection hyphae typically penetrates through the parenchyma
Parenchyma
Parenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, f. Greek παρέγχυμα - parenkhuma, "visceral flesh", f. παρεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour"...
phloem
Phloem
In vascular plants, phloem is the living tissue that carries organic nutrients , in particular, glucose, a sugar, to all parts of the plant where needed. In trees, the phloem is the innermost layer of the bark, hence the name, derived from the Greek word "bark"...
intracellularly but they can also penetrate intercellularly through uni and multiceliate xylem
Xylem
Xylem is one of the two types of transport tissue in vascular plants. . The word xylem is derived from the Classical Greek word ξυλον , meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant...
ray cells and paranchyma cells. Later, the fungus will produce mycelial mats of stroma and mycelial pegs.
Stroma mats will produce uni or multilocular pycnidia. Inside the pycnidia are branched and unbranched conidiophores with two-celled pycniospores, which later are ejected from the pycnidial ostiole.
Additionally, the stroma will produce a peg of interwoven mycelium. These pegs put pressure on the outer peridium of the host bark, which exposes the pycnidia below. These pegs also produce pycnidia that are smaller than the pycnidia in the stroma. While different in size, the spores produced are identical.
Resistance
Many species of tree show varying degrees of resistanceDisease resistance in fruit and vegetables
There are a number of lines of defence against pests and diseases in the organic garden, principal among these being the practice of good husbandry, creating healthy soil and ensuring high standards of garden hygiene...
, such as the heartnut, Butternut
Butternut (tree)
Juglans cinerea, commonly known as Butternut or White Walnut, is a species of walnut native to the eastern United States and southeast Canada. Its range extends east to New Brunswick, and from southern Quebec west to Minnesota, south to northern Alabama and southwest to northern Arkansas...
, and the Japanese, Black, and Persian Walnut
Walnut
Juglans is a plant genus of the family Juglandaceae, the seeds of which are known as walnuts. They are deciduous trees, 10–40 meters tall , with pinnate leaves 200–900 millimetres long , with 5–25 leaflets; the shoots have chambered pith, a character shared with the wingnuts , but not the hickories...
s. It is sometimes claimed that higher levels of resistance result from thicker bark; however, since the disease enters through breaks in the bark, it is unlikely that bark thickness influences resistance. Additionally, both trees produce phenolics immediately upon attack, later producing gums and tyloses to surround the pathogen.
Control
Breeding for resistance is important for fighting butternut canker. While standard practice has been that infected trees should be removed to prevent further spread, there is a growing opinion that the time for this is past. The disease has now been found in virtually all parts of the butternut range. Additionally, it is suggested that "removing diseased trees" is a guarantee that infected, but not dying trees, i.e. those that are specifically "partially resistant" to the fungus, will be killed; eliminating any chance of increased resistance in progeny. Instances are known of long-term survival of pure butternuts infected by the canker.Recent reports have shown that the fungus can be internally seed-borne, so seed
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
s should be subjected to intense quarantine
Quarantine
Quarantine is compulsory isolation, typically to contain the spread of something considered dangerous, often but not always disease. The word comes from the Italian quarantena, meaning forty-day period....
protocols; most especially if destined for plantings where the disease is not already established.