Club Root
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Clubroot is a common disease of
cabbage Cabbage, comprising several cultivars of ''Brassica oleracea'', is a leafy green, red (purple), or white (pale green) biennial plant grown as an annual vegetable crop for its dense-leaved heads. It is descended from the wild cabbage ( ''B.&nb ...
s,
broccoli Broccoli (''Brassica oleracea'' var. ''italica'') is an edible green plant in the cabbage family (family Brassicaceae, genus ''Brassica'') whose large flowering head, stalk and small associated leaves are eaten as a vegetable. Broccoli is cl ...
,
cauliflower Cauliflower is one of several vegetables in the species ''Brassica oleracea'' in the genus ''Brassica'', which is in the Brassicaceae (or mustard) family. It is an annual plant that reproduces by seed. Typically, only the head is eaten – the ...
,
Brussels sprouts The Brussels sprout is a member of the Gemmifera cultivar group of cabbages (''Brassica oleracea''), grown for its edible buds. The leaf vegetables are typically 1.5–4.0 cm (0.6–1.6 in) in diameter and resemble miniature cabbages ...
,
radish The radish (''Raphanus raphanistrum'' subsp. ''sativus'') is an Eating, edible root vegetable of the family Brassicaceae that was domesticated in Asia prior to Roman Empire, Roman times. Radishes are grown and consumed throughout the world, be ...
es,
turnip The turnip or white turnip (''Brassica rapa'' subsp. ''rapa'') is a root vegetable commonly grown in temperate climates worldwide for its white, fleshy taproot. The word ''turnip'' is a compound of ''turn'' as in turned/rounded on a lathe and ' ...
s,
stocks Stocks are feet restraining devices that were used as a form of corporal punishment and public humiliation. The use of stocks is seen as early as Ancient Greece, where they are described as being in use in Solon's law code. The law describing ...
,
wallflower ''Erysimum'', or wallflower, is a genus of flowering plants in the cabbage family, Brassicaceae. It includes more than 150 species, both popular garden plants and many wild forms. The genus ''Cheiranthus'' is sometimes included here in whole o ...
s and other plants of the family
Brassicaceae Brassicaceae () or (the older) Cruciferae () is a medium-sized and economically important family of flowering plants commonly known as the mustards, the crucifers, or the cabbage family. Most are herbaceous plants, while some are shrubs. The le ...
(Cruciferae). It is caused by ''
Plasmodiophora brassicae ''Plasmodiophora'' is a genus in the phylum of cercozoa in the class Phytomyxea. It includes the species ''Plasmodiophora brassicae'', which causes the disease cabbage clubroot Clubroot is a common disease of cabbages, broccoli, caulifl ...
'', which was once considered a
slime mold Slime mold or slime mould is an informal name given to several kinds of unrelated eukaryotic organisms with a life cycle that includes a free-living single-celled stage and the formation of spores. Spores are often produced in macroscopic mu ...
but is now put in the group
Phytomyxea The Phytomyxea are a class of parasites that are cosmopolitan, obligate biotrophic protist parasites of plants, diatoms, oomycetes and brown algae. They are divided into the orders Plasmodiophorida (ICZN, or Plasmodiophoromycota, ICBN) and Pha ...
. It is the first phytomyxean for which the genome has been sequenced. It has as many as thirteen races.
Gall Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants, fungi, or animals. Plant galls are abnormal outgrowths of plant tissues, similar to be ...
formation or distortion takes place on latent roots and gives the shape of a club or
spindle Spindle may refer to: Textiles and manufacturing * Spindle (textiles), a straight spike to spin fibers into yarn * Spindle (tool), a rotating axis of a machine tool Biology * Common spindle and other species of shrubs and trees in genus ''Euony ...
. In the cabbage such attacks on the roots cause undeveloped heads or a failure to head at all, followed often by decline in vigor or by death. It is an important disease, affecting an estimated 10% of the total cultured area worldwide. Historical reports of clubroot date back to the 13th century in Europe. In the late 19th century, a severe epidemic of clubroot destroyed large proportions of the cabbage crop in
St. Petersburg Saint Petersburg ( rus, links=no, Санкт-Петербург, a=Ru-Sankt Peterburg Leningrad Petrograd Piter.ogg, r=Sankt-Peterburg, p=ˈsankt pʲɪtʲɪrˈburk), formerly known as Petrograd (1914–1924) and later Leningrad (1924–1991), i ...
. The Russian scientist
Mikhail Woronin Mikhail Stepanovich Voronin (also spelled Woronin; russian: Михаи́л Степа́нович Воро́нин, 1838-1903) was a prominent Russian biologist, a botanist with particular expertise in fungi. Voronin was born in St Petersbur ...
eventually identified the cause of clubroot as a "plasmodiophorous organism" in 1875, and gave it the name ''Plasmodiophora brassicae''. In 18th, 19th and early 20th century Britain clubroot was sometimes called ''finger and toe'', ''fingers and toes'', ''anbury'', or ''ambury'', these last two also meaning a soft
tumor A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
on a horse. The potential of cultural practices to reduce crop losses due to clubroot is limited, and chemical treatments to control the disease are either banned due to environmental regulations or are not cost effective. Breeding of resistant cultivars therefore is a promising alternative.


In cabbages

''Cabbage clubroot'' is a
disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not immediately due to any external injury. Diseases are often known to be medical conditions that a ...
of
Brassicaceae Brassicaceae () or (the older) Cruciferae () is a medium-sized and economically important family of flowering plants commonly known as the mustards, the crucifers, or the cabbage family. Most are herbaceous plants, while some are shrubs. The le ...
(mustard family or cabbage family) caused by the soil-borne ''Plasmodiophora brassicae''. The disease first appears scattered in fields, but in successive seasons it will infect the entire field, reducing the yield significantly and sometimes resulting in no yield at all. Symptoms appear as yellowing, wilting, stunting, and
galls Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants, fungi, or animals. Plant galls are abnormal outgrowths of plant tissues, similar to be ...
on the roots. It is transmitted by contaminated transplants, animals, surface water runoff, contaminated equipment, and irrigation water. The pathogen can survive in a field for years as
resting spores A resting spore is a resistant cell, used to survive adverse environmental conditions. Resting spore is a term commonly applied to both diatoms and fungi. In fungi A resting spore can be a spore created by fungi which is thickly encysted (has a ...
without a host present and will infect the next crop planted if it is a susceptible host. This pathogen prefers a wet climate and a pH around 5.7, so proper irrigation and the addition of compounds that raise the pH can be used to control this disease. Other control methods include sanitation to prevent transmission, chemical control, and resistant varieties.


Hosts and symptoms

Cabbage Clubroot affects cabbage, Chinese cabbage, and Brussels sprouts most severely, but it has a range of hosts that it affects less severely like kohlrabi, kale, cauliflower, collards, broccoli, rutabaga, sea kale, turnips, and radishes. Developing plants may not show any
symptoms Signs and symptoms are the observed or detectable signs, and experienced symptoms of an disease, illness, injury, or condition. A sign for example may be a higher or lower temperature than normal, raised or lowered blood pressure or an abnormali ...
but as the plants get older they will start to show symptoms of chlorosis or yellowing, wilting during hot days, and exhibit stunted growth. Below ground, the roots experience
cell proliferation Cell proliferation is the process by which ''a cell grows and divides to produce two daughter cells''. Cell proliferation leads to an exponential increase in cell number and is therefore a rapid mechanism of tissue growth. Cell proliferation re ...
due to increased
auxin Auxins (plural of auxin ) are a class of plant hormones (or plant-growth regulators) with some morphogen-like characteristics. Auxins play a cardinal role in coordination of many growth and behavioral processes in plant life cycles and are essenti ...
or growth
hormone A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required ...
production from the plant as well as the pathogen. This causes the formation of galls that can grow big enough to restrict the
xylem Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...
tissue inhibiting efficient water uptake by the plant. Galls appear like clubs or spindles on the roots. Eventually the roots will rot and the plant will die.


Disease cycle

In the spring, resting spores in the soil germinate and produce
zoospores 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 mor ...
. These zoospores swim through the moist soil and enter host plants through wounds or
root hairs Root hair, or absorbent hairs, are outgrowths of epidermal cells, specialized cells at the tip of a plant root. They are lateral extensions of a single cell and are only rarely branched. They are found in the region of maturation, of the root. Root ...
. A
plasmodium ''Plasmodium'' is a genus of unicellular eukaryotes that are obligate parasites of vertebrates and insects. The life cycles of ''Plasmodium'' species involve development in a blood-feeding insect host which then injects parasites into a vert ...
is formed from the division of many amoeba-like cells. This plasmodium eventually divides and forms secondary zoospores that are once again released into the soil. The secondary infection by the zoospores can infect the first host or surrounding hosts. These secondary zoospores can be transmitted to other fields through farm machinery or water erosion. They form a secondary plasmodium that affects plant hormones to cause swelling in root cells. These cells eventually turn into galls or “clubs”. The secondary plasmodium forms the overwintering resting spores which get released into the soil as the “clubs” rot and disintegrate. These resting spores can live in the soil for up to 20 years while they wait for a root tip to come in close proximity for them to infect.


Environment

Clubroot is a disease that prefers warmer temperatures and moist conditions. Ideal conditions for the proliferation of this disease would be a soil temperature between 20–24 °C and a pH less than 6.5; therefore, this disease tends to be prominent in lower fields where water tends to collect.


Management

Clubroot is very hard to control. The primary step for management and long-term control is exclusion of the disease. Good sanitation practice is important with regard to the use of tools and machinery in order to prevent the introduction of the pathogen to a disease-free field. It is not uncommon for an inattentive farmer or gardener to unknowingly carry in the pathogen after being previously exposed to it at a different time. One should avoid purchasing infected transplants of cabbage so as to prohibit the infestation of ''P. brassicae''. Soil type is also an important factor in the development and spread of cabbage clubroot; the use of sand will allow for the plants to grow in well-drained soil, thereby eliminating the possibility of the pathogen to proliferate in a hospitable environment. Although it is difficult to eradicate the pathogen once it is introduced to a field, there are several methods for its control. Keeping the soil at a slightly basic pH of 7.1–7.2 by the addition of
agricultural lime Agricultural lime, also called aglime, agricultural limestone, garden lime or liming, is a soil additive made from pulverized limestone or chalk. The primary active component is calcium carbonate. Additional chemicals vary depending on the mineral ...
as well as the integration of
crop rotation Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing seasons. It reduces reliance on one set of nutrients, pest and weed pressure, and the probability of developing resistant ...
will reduce the occurrence of cabbage clubroot in already infected fields.
Fumigation Fumigation is a method of pest control or the removal of harmful micro-organisms by completely filling an area with gaseous pesticides—or fumigants—to suffocate or poison the pests within. It is used to control pests in buildings (s ...
using
metam sodium Metam sodium is an organosulfur compound with the formula . The compound is a sodium salt of a dithiocarbamate. The compound exists as a colorless dihydrate, but most commonly it is encountered as an aqueous solution. It is used as a soil fumig ...
in a field containing diseased cabbages is yet another way to decrease the buildup of the pathogen. Control and management practices on already infected fields help to reduce the overall impact that ''P. brassicae'' has on a field of cabbage and other cruciferous plants, but it is extremely difficult to rid an individual plant of the disease once it is already infected.


Importance

Clubroot can be a reoccurring problem for years because it is easily spread from plant to plant. ''P. brassicae'' is able to infect 300 species of cruciferous plants, making this disease a recurring problem even with crop rotation. This wide
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 ...
range allows the pathogen to continue its infection cycle in the absence of cabbages. Additionally, cabbage clubroot may be a stubborn disease due to its ability to form a
microbial cyst A microbial cyst is a resting or dormant stage of a microorganism, usually a bacterium or a protist or rarely an invertebrate animal, that helps the organism to survive in unfavorable environmental conditions. It can be thought of as a state of ...
as an overwintering structure. These cysts may last many years in the soil until it comes into contact with a suitable host, making it difficult to entirely avoid the introduction of the disease. Those growing cabbage need to be aware of the possibility of ''Plasmodiophora'' infestation by simply growing in particular fields that may have had cabbage clubroot previously.


Canola infestation in Alberta

In 2003 clubroot was identified in
Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...
,
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 ...
, as an outbreak in
canola Close-up of canola blooms Canola flower Rapeseed oil is one of the oldest known vegetable oils. There are both edible and industrial forms produced from rapeseed, the seed of several cultivars of the plant family Brassicaceae. Historically, i ...
crops in the central area of the province mainly isolated to the
Edmonton Edmonton ( ) is the capital city of the Canadian province of Alberta. Edmonton is situated on the North Saskatchewan River and is the centre of the Edmonton Metropolitan Region, which is surrounded by Alberta's central region. The city ancho ...
area. Clubroot is a soilborne disease caused by the biotrophic protist ''Plasmodiophora brassica''. The infection causes the formation of large
galls Galls (from the Latin , 'oak-apple') or ''cecidia'' (from the Greek , anything gushing out) are a kind of swelling growth on the external tissues of plants, fungi, or animals. Plant galls are abnormal outgrowths of plant tissues, similar to be ...
on the roots which look like clubs. These formations impede nutrient and water uptake and can cause plant death, wiping out important money generating canola crops. Initially 12 commercial fields of canola were identified, but that number grew to over 400 by 2008. In 2007, Alberta declared ''P.brassicae'' a pest via the foundation legislation in hopes to help contain spread of the disease. The Pathotype 3, is the predominant source for Alberta outbreaks. Studies showed that out of the 13 strains of ''P. brassicae'', the most virulent form is dominant in Alberta. Studies have shown that infestation numbers are highest at common field entrances and decline as you move further into the field, away from the entrance. From these results, it was concluded that infested soil on
farm machinery Agricultural machinery relates to the mechanical structures and devices used in farming or other agriculture. There are many types of such equipment, from hand tools and power tools to tractors and the countless kinds of farm implements that the ...
was increasing spread of the pathogen. Some natural field to field spread is starting to be seen Liming has been an effective control measure to curb clubroot since the 19th century. This method does not eradicate clubroot but it will slow its development by creating unfavorable conditions. In addition, calcium and magnesium can be added to the nutrition profile of the soil to help control clubroot. To get efficient results the field soil, Hmust be kept above 7.5. This takes massive applications to field soil in order to treat all of the soil where spores of clubroot are found. Combining lime with one other treatment has shown most effective. Several strains of canola have been tried, including European winter canola cv. Mendel (Brassica napus L.), as a clubroot-resistant crop. It has been found that few cultivators exist. Specific genotypes do exist, of the Mendel strain, which could be a solution for canola crops in the Canadian prairies.
Crop rotation Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing seasons. It reduces reliance on one set of nutrients, pest and weed pressure, and the probability of developing resistant ...
with non-host crops is another method to help prevent clubroot. The half life of P. Brassicae is 3.6 years. Unfortunately, long rotations of approximately 20 years are required in order to be effective. This is very difficult with typical canola rotations not being more than three years. Canola crop brings in high revenue to farmers. This would also require complete removal of Cruciferae crops, such as
wild radish ''Raphanus raphanistrum'', also known as wild radish, white charlock or jointed charlock, is a flowering plant in the family Brassicaceae. One of its subspecies, ''Raphanus raphanistrum'' subsp. ''sativus'', includes a diverse variety of cultiv ...
and
mustard Mustard may refer to: Food and plants * Mustard (condiment), a paste or sauce made from mustard seeds used as a condiment * Mustard plant, one of several plants, having seeds that are used for the condiment ** Mustard seed, seeds of the mustard p ...
. Some fungicide has been found to help with clubroot but it is very pricey and would take huge amounts to saturate the soil. The best way to prevent contamination between fields is to clean agricultural equipment and
vehicles A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses, mobility scooters for disabled people), railed vehicles (trains, trams), wate ...
which have come in contact with club root before moving to a new field. All contaminated soil, equipment and tools must not be moved to clean, disease-free fields. The best preventative method is field monitoring. Throughout the season, plants should be monitored for early symptoms of club root. More research is being conducted for early detection of club root in fall soils.Trembly, N., et al. (1999). Clubroot of Crucifiers: Control Strategies. "Agriculture and Agrifood Canada." Retrieved from http://publications.gc.ca/collections/Collection/A42-85-1999E.pdf March 2012.


References


External links


Cabbage monstrosities
(clubroot of cabbage with rotating QuickTime image). Cornell Mushroom Blog. {{Taxonbar, from=Q1378682 Parasitic rhizaria Parasites of plants Crucifer diseases