''Synchytrium endobioticum'' is a
chytrid fungus
Chytridiomycota are a division of zoosporic organisms in the kingdom Fungi, informally known as chytrids. The name is derived from the Ancient Greek ('), meaning "little pot", describing the structure containing unreleased zoöspores. Chytrid ...
that causes the potato wart disease, or black scab. It also infects some other plants of the genus ''
Solanum
''Solanum'' is a large and diverse genus of flowering plants, which include three food crops of high economic importance: the potato, the tomato and the eggplant (aubergine, brinjal). It is the largest genus in the nightshade family Solanaceae ...
'', though
potato
The potato is a starchy food, a tuber of the plant ''Solanum tuberosum'' and is a root vegetable native to the Americas. The plant is a perennial in the nightshade family Solanaceae.
Wild potato species can be found from the southern Unit ...
is the only cultivated
host
A host is a person responsible for guests at an event or for providing hospitality during it.
Host may also refer to:
Places
* Host, Pennsylvania, a village in Berks County
People
*Jim Host (born 1937), American businessman
* Michel Host ...
.
Systematics
Traditionally, ''Synchytrium endobioticum'' has been placed to the subgenus ''Mesochytrium'', but it has been suggested that on the basis of the mode of germination it should be transferred to the subgenus ''Microsynchytrium''. It was first identified and studied by
Vera Charles
Vera Katherine Charles (1877–1954) was an American mycologist. She was one of the first women to be appointed to professional positions within the U.S. Department of Agriculture. Charles coauthored several articles on mushrooms while working fo ...
.
The New Zealand scientist
Kathleen Maisey Curtis
Kathleen Maisey Curtis, Lady Rigg (15 August 1892 – 5 September 1994) was a New Zealand mycology, mycologist and was a founder of plant pathology in New Zealand.
Biography
Early life and education
Curtis was born in Foxton, New Zealand, Fox ...
also studied ''Synchytrium endobioticum'' for her doctoral thesis that, in 1919, resulted in her being recognised as producing groundbreaking research on the organism's pathology.
At least 18
pathotype
A pathovar is a bacterial strain or set of strains with the same or similar characteristics, that is differentiated at infrasubspecific level from other strains of the same species or subspecies on the basis of distinctive pathogenicity to one o ...
s of the fungus exist, most of them with quite limited ranges in Central Europe. The most widely distributed is the pathotype 1.
Morphology
Like some other Chytridiales, ''Synchytrium endobioticum'' develops no
mycelium
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 substrate (biology), substrates. A typical single ...
. The fungus produces a thick walled structure known as a winter
sporangium
A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their life cy ...
. It is 25-75 µm in diameter and contains 200-300 spores. Sporangia are clustered into thin-walled
sori. The motile life stage,
zoospore
A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves.
Diversity Flagella types
Zoospores may possess one or mo ...
is about 0,5 µm in diameter and has one posterior
flagellum
A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates.
A microorganism may have f ...
.
Life cycle
In spring, at higher temperature and moisture, overwintering sporangia germinate to release motile
zoospore
A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves.
Diversity Flagella types
Zoospores may possess one or mo ...
s which infect suitable host
epidermal
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water relea ...
cells. In infected cells, the summer sporangia develop, which quickly release new populations of zoospores. The infection cycle may be repeated as long as infection conditions are suitable. The infected plant cells swell, divide and surround the dividing zoospores resulting in the wart.
Under certain stress conditions some zoospore pairs fuse, resulting in a
zygote
A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism.
In multicellula ...
. The zygote bearing host cells divide, forming eventually the walls of a new winter sporangium. In autumn, the warts rot and disintegrate, releasing new thick-walled resting spores of the fungus into the soil. The
diploid
Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...
resting spores (pro-sori) undergo a dormancy period and before germination (probably) a
meiotic
Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately res ...
division and several
mitotic
In cell biology, mitosis () is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei. Cell division by mitosis gives rise to genetically identical cells in which the total number of chromosomes is maintai ...
divisions, becoming a sorus.
Ecology
''Synchytrium endobioticum'' is an
obligate parasite
An obligate parasite or holoparasite is a parasitic organism that cannot complete its life-cycle without exploiting a suitable host. If an obligate parasite cannot obtain a host it will fail to reproduce. This is opposed to a facultative parasite, ...
that infects several plants of the genus ''
Solanum
''Solanum'' is a large and diverse genus of flowering plants, which include three food crops of high economic importance: the potato, the tomato and the eggplant (aubergine, brinjal). It is the largest genus in the nightshade family Solanaceae ...
''. The most favourable conditions for its development are warm temperatures (but not over 20 °C) with enough humidity. Winter sporangia can remain viable for up to 20–30 years. It can survive at depths of 50 cm in the soil. Three different fungi have been observed to parasitize the resting sporangia.
''S. endobioticum'' originates from the Andean region of
South-America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the south ...
, with now almost worldwide distribution in areas where potatoes are cultivated (absent in most of tropical
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
,
Middle East
The Middle East ( ar, الشرق الأوسط, ISO 233: ) is a geopolitical region commonly encompassing Arabian Peninsula, Arabia (including the Arabian Peninsula and Bahrain), Anatolia, Asia Minor (Asian part of Turkey except Hatay Pro ...
, most of
Canada
Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
,
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
and
Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
).
Environment
Cool and wet soils are conducive to potato wart disease development. While there are discrepancies in the reported temperatures for maximal potato wart infection, summers with an average temperature of 18 °C or less, winters below 5 °C, and annual precipitation of 700 mm or more are considered to be favorable for the disease.
Soil pH does not appear to be associated with disease occurrence; ''S. endobioticum'' infections have been reported in soils with pH ranging from 3.9-8.5.
Overwintering sporangia of ''S. endobioticum'' are extremely resilient. Dry sporangia can survive at 100 °C for 11–12 h, composting for 12 days at 60– 65 °C, pasteurization for 90 min at 70 °C, the digestive system of animals feeding on infected tubers, as well as treatment in 1% formaldehyde and 0.1% mercuric chloride for one hour and three hours, respectively. A soil temperature of at least 8 °C and water is required for sporangia germination and the dispersal of zoospores. The microelements B, Cu, Zn, and Mo, have been reported to induce the germination of sporangia following overwintering.
Management
The resilient nature of the resting spores, the overwintering sporangia, is the principal challenge in managing the disease. Several means of control have been explored, including chemical and biological, but have been largely ineffective, impractical, or neglected. Cultivation of resistant varieties is the best management approach. However, the development of resistant varieties is challenged by the discovery of novel pathotypes and the polygenic nature of resistance to potato wart. Despite these challenges, legislative action has been taken that leverages the use of resistant varieties and has effectively curtailed the spread of potato wart. This action enforces the demarcation of contaminated plots and safety zones and the disposal of infected potato material. Safety zones are areas where only resistant varieties can be grown, and potatoes cannot be grown in sites until the absence of sporangia can be demonstrated. These legislative efforts also include measures that forbid the trade of infected potatoes and the presence of the disease in potato seed production.
Pathogenesis
Very little is known about the pathogenesis of ''S. endobioticum'' at a molecular level. Indeed, this is true of chytrids more generally, excepting a few well-studied species. However, recent genome sequencing and annotation of ''S. endobioticum'' has shed light on the potential molecular mechanisms of pathogenesis. For example, this analysis demonstrated the coding capacity of ''S. endobioticum'' to process complex sugars, which may include cellulose and starch. However, genes for cell wall degrading hemicellulases are reduced in ''S. endobioticum'' relative to the closely related, saprophytic chytrid, ''S. microbalum.'' The lack of hemicellulases may allow the pathogen to evade defense responses triggered by damage-associated molecular patterns from cell wall degradation. Several regions within the genome have been identified as possible effector coding regions, but further work will need to be done to verify this. ''S. endobioticum'' did not contain genes coding for enzymes that are crucial to the biosynthesis of purine and pyrimidine. It is probable ''S. endobioticum'' exacts purine and pyrimidine from its host.
Legal
Added to the United States' federal
bioterrorism
Bioterrorism is terrorism involving the intentional release or dissemination of biological agents. These agents are bacteria, viruses, insects, fungi, and/or toxins, and may be in a naturally occurring or a human-modified form, in much the same ...
list for agricultural plant
pathogens
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
in 2002, in accordance with the
.
Outbreaks
In late 2021, the discovery of the fungus in two potato fields on
Prince Edward Island
Prince Edward Island (PEI; ) is one of the thirteen Provinces and territories of Canada, provinces and territories of Canada. It is the smallest province in terms of land area and population, but the most densely populated. The island has seve ...
in Canada, led the country to ban potato exports from PEI to the United States.
References
Sources
* EPPO data sheet on ''S. endobioticum'
* Resting-spore germination in Synchytrium endobioticu
* Germination and parasitation of the resting sporangia of Synchytrium endobioticu
* About potato wart diseas
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{{Taxonbar, from=Q135449
Chytridiomycota
Fungal plant pathogens and diseases
Potato diseases
Fungi described in 1896