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{{short description|Fungal disease of flowering plants}}
{{Taxobox
{{Infobox plant disease
| name = Verticillium wilt
| name = Verticillium wilt
| regnum = [[Fungi]]
| image = Verticillium wilt.jpg
| divisio = [[Ascomycota]]
⚫
| caption = Healthy strawberry plant (left) and strawberry plant infected with verticillium wilt (right), photo by Howard F. Schwartz, Colorado State University, Bugwood.org
| subdivisio = [[Pezizomycotina]]
| common_names =
| classis = [[Sordariomycetes]]
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| causal_agents = *''[[Verticillium albo-atrum]]''
| ordo = [[Hypocreales]]
| familia = [[Incertae sedis]]
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| genus = [[Verticillium]]
| subdivision_ranks = Species
| subdivision =
Species include:
⚫
*''[[Verticillium albo-atrum]]''
*''[[Verticillium dahliae]]''
*''[[Verticillium dahliae]]''
*''[[Verticillium longisporum]]''
*''[[Verticillium longisporum]]''
*''[[Verticillium nubilum]]''
*''[[Verticillium nubilum]]''
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*''[[Verticillium theobromae]]''
*''[[Verticillium tricorpus]]''
*''[[Verticillium tricorpus]]''
| hosts =
| vectors =
| distribution =
| symptoms =
| treatment =
}}
}}


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'''Verticillium wilt''' is a [[wilting|wilt]] [[disease]] affecting over 350 [[species]] of [[eudicot]] [[plant]]s. It is caused by six species of ''[[Verticillium]]'' [[fungi]]: ''V.&nbsp;dahliae'', ''V.&nbsp;albo-atrum'', ''V.&nbsp;longisporum'', ''V.&nbsp;nubilum'', ''V.&nbsp;theobromae'' and ''V.&nbsp;tricorpus''.<ref>{{cite journal|author1=Barbara, D.J.|author2=Clewes, E.|date=2003|title="Plant pathogenic Verticillium species: how many of them are there?" |journal=Molecular Plant Pathology |volume=4|issue=4|pages=297–305|publisher=Blackwell Publishing|doi=10.1046/j.1364-3703.2003.00172.x |pmid=20569390 |doi-access=free}}</ref> Many economically important plants are susceptible including [[cotton]], [[tomato]]es, [[potato]]es, [[oilseed rape]], [[eggplant]]s, [[capsicum|pepper]]s and ornamentals, as well as others in natural vegetation communities. Many eudicot species and cultivars are resistant to the disease and all [[monocot]]s, [[gymnosperm]]s and [[fern]]s are immune.
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[[File:Verticillium wilt.jpg|thumb|right|250px|Healthy strawberry plant (left) and strawberry plant infected with verticillium wilt (right), photo by Howard F. Schwartz, Colorado State University, Bugwood.org]]
⚫
'''Verticillium wilt''' is a [[wilting|wilt]] [[disease]] affecting over 350 [[species]] of [[eudicot]] [[plant]]s. It is caused by six species of ''[[Verticillium]]'' [[fungi]]: ''V. dahliae'', ''V. albo-atrum'', ''V. longisporum'', ''V. nubilum'', ''V. theobromae'' and ''V. tricorpus''. (See, for example, Barbara, D.J. & Clewes, E. (2003). "Plant pathogenic Verticillium species: how many of them are there?" Molecular Plant Pathology 4(4).297-305. Blackwell Publishing.) Many economically important plants are susceptible including [[cotton]], [[tomato]]es, [[potato]]es, [[oilseed rape]], [[eggplant]]s, [[capsicum|pepper]]s and ornamentals, as well as others in natural vegetation communities. Many eudicot species and cultivars are resistant to the disease and all [[monocot]]s, [[gymnosperm]]s and [[fern]]s are immune.


Signs are superficially similar to ''[[Fusarium]]'' wilts. There are no fungicides characterized for the control of this disease but soil fumigation with chloropicrin has been proven successful in dramatically reducing Verticillium wilt in diverse crops such as vegetables using plasticulture production methods, and in potato production in North America (non-tarped). Additional strategies to manage the disease include crop rotation, the use of resistant varieties and deep plowing (to accelerate the decomposition of infected plant residue). In recent years, pre-plant soil fumigation with chloropicrin in non-tarped, raised beds has proven to be economically viable and beneficial for reducing wilt disease and increasing yield and quality of potato in North America. Soil fumigation is a specialized practice requiring special permits, equipment, and expertise, so qualified personnel must be employed.
Signs are superficially similar to ''[[Fusarium]]'' wilts. There are no fungicides characterized for the control of this disease but soil fumigation with chloropicrin has been proven successful in dramatically reducing ''Verticillium'' wilt in diverse crops such as vegetables using [[plasticulture]] production methods, and in non-tarped potato production in North America . Additional strategies to manage the disease include crop rotation, the use of resistant varieties and deep plowing (to accelerate the decomposition of infected plant residue). In recent years, pre-plant soil fumigation with chloropicrin in non-tarped, [[raised-bed gardening|raised beds]] has proven to be economically viable and beneficial for reducing wilt disease and increasing yield and quality of potato in North America. Soil fumigation is a specialized practice requiring special permits, equipment, and expertise, so qualified personnel must be employed.


==Hosts and symptoms==
==Hosts and symptoms==
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''Verticillium'' spp. attack a very large host range including more than 350 species of vegetables, fruit trees, flowers, field crops, and shade or forest trees. Most vegetable species have some susceptibility, so it has a very wide host range.<ref name="Agriose"/> A list of known hosts is at the bottom of this page.
''Verticillium'' spp. attack a very large host range including more than 350 species of vegetables, fruit trees, flowers, field crops, and shade or forest trees. Most vegetable species have some susceptibility, so it has a very wide host range.<ref name="Agriose"/> A list of known hosts is at the bottom of this page.


The signs are similar to most wilts with a few specifics to ''Verticillium''. Wilt itself is the most common sign, with wilting of the stem and leaves occurring due to the blockage of the xylem vascular tissues and therefore reduced water and nutrient flow. In small plants and seedlings, ''Verticillium'' can quickly kill the plant while in larger, more developed plants the severity can vary. Some times only one side of the plant will appear infected because once in the vascular tissues, the disease migrates mostly upward and not as much radially in the stem.<ref name="Pegg"/> Other symptoms include stunting, chlorosis or yellowing of the leaves, necrosis or tissue death, and defoliation. Internal vascular tissue discoloration might be visible when the stem is cut.<ref name="Agriose"/>
The symptoms are similar to most wilts with a few specifics to ''Verticillium''. Wilt itself is the most common symptom, with wilting of the stem and leaves occurring due to the blockage of the xylem vascular tissues and therefore reduced water and nutrient flow. In small plants and seedlings, ''Verticillium'' can quickly kill the plant while in larger, more developed plants the severity can vary. Some times only one side of the plant will appear infected because once in the vascular tissues, the disease migrates mostly upward and not as much radially in the stem.<ref name="Pegg"/> Other symptoms include stunting, chlorosis or yellowing of the leaves, necrosis or tissue death, and defoliation. Internal vascular tissue discoloration might be visible when the stem is cut.<ref name="Agriose"/>


In ''Verticillium'', the signs and effects will often only be on the lower or outer parts of plants or will be localized to only a few branches of a tree. In older plants, the infection can cause death, but often, especially with trees, the plant will be able to recover, or at least continue living with the infection. The severity of the infection plays a large role in how severe the signs are and how quickly they develop.<ref name="Agriose"/>
In ''Verticillium'', the symptoms and effects will often only be on the lower or outer parts of plants or will be localized to only a few branches of a tree. In older plants, the infection can cause death, but often, especially with trees, the plant will be able to recover, or at least continue living with the infection. The severity of the infection plays a large role in how severe the signs are and how quickly they develop.<ref name="Agriose"/>


==Disease cycle==
==Disease cycle==
While ''Verticillium'' spp. are very diverse, the basic life cycle of the pathogen is similar across species, except in their survival structures. The survival structures vary by species with ''V. albo-atrum'' forming mycelium, ''V. dahliae'' forming microsclerotia, ''V. nigrescens'' and ''V. nubilum'' forming chlamydospores, and ''V. tricorpus'' forming all three. While resting, many factors such as soil chemistry, temperature, hydration, micro fauna, and non-host crops all have an effect on the viability of the resting structure. Mycelium have been observed remaining viable for at least 4 years,<ref>Luck, J.V. (1954) Studies on the Verticillium wilt of ''Mentha piperita L.'' with special emphasis on the causal organism, ''Verticillium albo-atrum'' R. &B. Dissertation Abstracts 14, 916-917.</ref> while microsclerotia have been observed in fields planted with non-host crops for over 10 years <ref>Wilhelm, S. (1955) Longevity of the ''Verticillium'' wilt fungus in the laboratory and field. ''Phytopathology'' 455, 180-181.</ref> and even 15 years has been reported.<ref name="Agriose"/> Viability is reduced at these extremes, but the long survivability of these structures is an important aspect for ''Verticillium'' control.
While ''Verticillium'' spp. are very diverse, the basic life cycle of the pathogen is similar across species, except in their survival structures. The survival structures vary by species with ''V.&nbsp;albo-atrum'' forming mycelium, ''V.&nbsp;dahliae'' forming microsclerotia, ''V.&nbsp;nigrescens'' and ''V.&nbsp;nubilum'' forming chlamydospores, and ''V.&nbsp;tricorpus'' forming all three. While resting, many factors such as soil chemistry, temperature, hydration, micro fauna, and non-host crops all have an effect on the viability of the resting structure. Mycelium have been observed remaining viable for at least 4 years,<ref>Luck, J.V. (1954) Studies on the Verticillium wilt of ''Mentha piperita L.'' with special emphasis on the causal organism, ''Verticillium albo-atrum'' R. &B. Dissertation Abstracts 14, 916-917.</ref> while microsclerotia have been observed in fields planted with non-host crops for over 10 years <ref>{{cite journal |last=Wilhelm |first=S. |year=1955 |title=Longevity of the ''Verticillium'' wilt fungus in the laboratory and field |journal=Phytopathology |volume=45 |issue=3 |pages=180–181}}</ref> and even 15 years has been reported.<ref name="Agriose"/> Viability is reduced at these extremes, but the long survivability of these structures is an important aspect for ''Verticillium'' control.


When roots of a host crop come near the resting structure (about 2mm),<ref>Sewell, G.W.F. (1959) Direct observation of ''Verticillium albo-atrum'' in soil. ''Transactions of the British Mycological Society'' 42, 312-321.</ref> root exudate promotes germination and the fungi grows out of the structure and toward the plant. Being a vascular wilt, it will try to get to the vascular system on the inside of the plant, and therefore must enter the plant. Natural root wounds are the easiest way to enter, and these wounds occur naturally, even in healthy plants because of soil abrasion on roots. ''Verticillium'' has also been observed entering roots directly, but these infections rarely make it to the vascular system, especially those that enter through root hairs.<ref>Garber, R.H. (1973) ''United States Department of Agriculture Publication 1''. ARS-S-19. pp. 69-77.</ref>
When roots of a host crop come near the resting structure (about 2mm),<ref>{{Cite journal|doi = 10.1016/S0007-1536(56)80039-9|title = Direct observation of Verticillium albo-atrum in soil|year = 1959|last1 = Sewell|first1 = G.W.F.|journal = Transactions of the British Mycological Society|volume = 42|issue = 3|pages = 312–IN9}}</ref> root exudate promotes germination and the fungi grows out of the structure and toward the plant. Being a vascular wilt, it will try to get to the vascular system on the inside of the plant, and therefore must enter the plant. Natural root wounds are the easiest way to enter, and these wounds occur naturally, even in healthy plants because of soil abrasion on roots. ''Verticillium'' has also been observed entering roots directly, but these infections rarely make it to the vascular system, especially those that enter through root hairs.<ref>Garber, R.H. (1973) ''United States Department of Agriculture Publication 1''. ARS-S-19. pp. 69-77.</ref>

Once the pathogen enters the host, it makes its way to the vascular system, and specifically the xylem. The fungi can spread as hyphae through the plant, but can also spread as spores. ''Verticillium'' produce [[conidium|conidia]] on conidiophores and once conidia are released in the xylem, they can quickly colonize the plant. Conidia have been observed traveling to the top of cotton plants, 115&nbsp;cm, 24 hours after initial conidia inoculation, so the spread throughout the plant can occur very quickly.<ref>Presley, J. T., Carns, H.R., Taylor, E.E. and Schnathorst, W.C. (1966) Movement of conidia of ''Verticillium albo-atrum'' in cotton plants. ''Phytopathology'' 56, 375.</ref> Sometimes the flow of conidia will be stopped by cross sections of the xylem, and here the conidia will spawn, and the fungal hyphae can overcome the barrier, and then produce more conidia on the other side.<ref>Knoll, F.A. (1972) Untersuchungen zur Ausbrreitung gefassbesiedelnder ''Verticillium'' Arten in Luzernepflanzen. ''[[Zentralblatt für Bakteriologie, Parasitenkunde, Infektionskrankheiten und Hygiene]]'' 127, 332-345.</ref>
Once the pathogen enters the host, it makes its way to the vascular system, and specifically the xylem. The fungi can spread as hyphae through the plant, but can also spread as spores. ''Verticillium'' produce [[conidium|conidia]] on conidiophores and once conidia are released in the xylem, they can quickly colonize the plant. Conidia have been observed traveling to the top of cotton plants, {{Convert|115|cm|abbr=on}}, 24 hours after initial conidia inoculation, so the spread throughout the plant can occur very quickly.<ref>{{cite journal |last1=Presley |first1=J. T. |last2=Carns |first2=H.R. |last3=Taylor |first3=E.E. |last4=Schnathorst |first4=W.C. |year=1966 |title=Movement of conidia of ''Verticillium albo-atrum'' in cotton plants |journal=Phytopathology |volume=56 |pages=375}}</ref> Sometimes the flow of conidia will be stopped by cross sections of the xylem, and here the conidia will spawn, and the fungal hyphae can overcome the barrier, and then produce more conidia on the other side.<ref>{{cite journal |last=Knoll |first=F.A. |year=1972 |title=Untersuchungen zur Ausbreitung gefässbesiedelnder ''Verticillium''-Arten in Luzernepflanzen |journal=[[Zentralblatt für Bakteriologie, Parasitenkunde, Infektionskrankheiten und Hygiene]] |volume=127 |pages=332–345}}</ref>


A heavily infected plant can succumb to the disease and die. As this occurs, the ''Verticillium'' will form its survival structures and when the plant dies, its survival structures will be where the plant falls, releasing inoculates into the environment. The survival structures will then wait for a host plant to grow nearby and will start the cycle all over again.
A heavily infected plant can succumb to the disease and die. As this occurs, the ''Verticillium'' will form its survival structures and when the plant dies, its survival structures will be where the plant falls, releasing inoculates into the environment. The survival structures will then wait for a host plant to grow nearby and will start the cycle all over again.


Besides being long lasting in the soil, ''Verticillium'' can spread in many ways. The most common way of spreading short distances is through root to root contact within the soil. Roots in natural conditions often have small damages or openings in them that are easily colonized by ''Verticillium'' from an infected root nearby. Air borne conidia have been detected and some colonies observed, but mostly the conidia have difficulty developing above ground on healthy plants.<ref>Easton, G.D., Nagle, M.E. and Bailey, D.L. (1969) A method of estimating ''Verticillium albo-atrum'' propagules in field soil and irrigation waste water. ''Phytopathology'' 59, 1171-1172.</ref> In open channel irrigation, ''V. dahliae'' have been found in the irrigation ditches up to a mile from the infected crop.
Besides being long lasting in the soil, ''Verticillium'' can spread in many ways. The most common way of spreading short distances is through root to root contact within the soil. Roots in natural conditions often have small damages or openings in them that are easily colonized by ''Verticillium'' from an infected root nearby. Air borne conidia have been detected and some colonies observed, but mostly the conidia have difficulty developing above ground on healthy plants.<ref>{{cite journal |last1=Easton |first1=G.D. |last2=Nagle |first2=M.E. |last3=Bailey |first3=D.L. |year=1969 |title=A method of estimating ''Verticillium albo-atrum'' propagules in field soil and irrigation waste water |journal=Phytopathology |volume=59 |pages=1171–1172}}</ref> In open channel irrigation, ''V.&nbsp;dahliae'' have been found in the irrigation ditches up to a mile from the infected crop.


Without fungicidal seed treatments, infected seeds are easily transported and the disease spread, and ''Verticillium'' has been observed remaining viable for at least 13 months on some seeds. Planting infected seed potatoes can also be a source of inoculum to a new field. Finally, insects have also been shown to transmit the disease. Many insects including potato leaf hopper, leaf cutter bees, and aphids have been observed transmitting conidia of ''Verticillium'' and because these insects can cause damage to the plant creating an entry for the ''Verticillium'', they can help transmit the disease.<ref name ="Pegg">Pegg, G.F., Brady, B.L. (2002) Verticillium Wilts, CABI Publishing, New York, NY.</ref>
Without fungicidal seed treatments, infected seeds are easily transported and the disease spread, and ''Verticillium'' has been observed remaining viable for at least 13 months on some seeds. Planting infected seed potatoes can also be a source of inoculum to a new field. Finally, insects have also been shown to transmit the disease. Many insects including potato leaf hopper, leaf cutter bees, and aphids have been observed transmitting conidia of ''Verticillium'' and because these insects can cause damage to the plant creating an entry for the ''Verticillium'', they can help transmit the disease.<ref name ="Pegg">Pegg, G.F., Brady, B.L. (2002) Verticillium Wilts, CABI Publishing, New York, NY.</ref>
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While Verticillium wilts often have the same symptoms of Fusarium wilts, ''Verticillium'' can survive cold weather and winters much better than ''Fusarium'', which prefers warmer climates. The resting structures of ''Verticillium'' are able to survive freezing, thawing, heat shock, dehydration, and many other factors and are quite robust and difficult to get rid of. The one factor they do not tolerate well is extended periods of anaerobic conditions (such as during flooding).<ref name="Pegg"/>
While Verticillium wilts often have the same symptoms of Fusarium wilts, ''Verticillium'' can survive cold weather and winters much better than ''Fusarium'', which prefers warmer climates. The resting structures of ''Verticillium'' are able to survive freezing, thawing, heat shock, dehydration, and many other factors and are quite robust and difficult to get rid of. The one factor they do not tolerate well is extended periods of anaerobic conditions (such as during flooding).<ref name="Pegg"/>


''Verticillium'' will grow best between 20 and 28 degrees Celsius,<ref name="Agriose"/> but germination and growth can occur well below (or above) those temperatures. Water is necessary for resting structure germination, but is not as important for the spread of the fungus as in many other fungi. While not an environmental requirement for the fungus, stressed plants, often brought on by environmental changes, are easier to attack than healthy plants, so any conditions that will stress the plant but not directly harm the ''Verticillium'' will be beneficial for Verticillium wilt development.<ref name="Pegg"/>
''Verticillium'' will grow best between 20 and 28 degrees Celsius,<ref name="Agriose"/> but germination and growth can occur well below (or above) those temperatures. Still, ''Verticillium'' will generally not survive in the branches and trunks of infected trees during hot, dry seasons in regions such as summer in southern California. This does not generally "cure" the entire tree, however, and recurrence can happen via a reinfection from the roots during winter and spring.<ref name="sinclair" /> Water is necessary for resting structure germination, but is not as important for the spread of the fungus as in many other fungi. While not an environmental requirement for the fungus, stressed plants, often brought on by environmental changes, are easier to attack than healthy plants, so any conditions that will stress the plant but not directly harm the ''Verticillium'' will be beneficial for Verticillium wilt development.<ref name="Pegg"/>


==Management==
==Management==
''Verticillium'' wilt begins as a mild, local infection, which over a few years will grow in strength as more virile strains of the fungus develop. If left unchecked the disease will become so widespread that the crop will need to be replaced with resistant varieties, or a new crop will need to be planted altogether.<ref name="Agriose">Agrios, George N. Plant Pathology, 5th Edition.</ref>
''Verticillium'' wilt begins as a mild, local infection, which over a few years will grow in strength as more virile strains of the fungus develop. If left unchecked the disease will become so widespread that the crop will need to be replaced with resistant varieties, or a new crop will need to be planted altogether.<ref name="Agriose">Agrios, George N. Plant Pathology, 5th Edition.</ref>


Control of ''Verticillium'' can be achieved by planting disease&ndash;free plants in uncontaminated soil, planting resistant varieties, and refraining from planting susceptible crops in areas that have been used repeatedly for [[solanaceous]] crops. Soil fumigation can also be used, with chloropicrin being particularly effective in reducing disease incidence in contaminated fields.
Control of ''Verticillium'' can be achieved by planting disease&ndash;free plants in uncontaminated soil, planting resistant varieties, and refraining from planting susceptible crops in areas that have been used repeatedly for [[solanaceous]] crops. Soil fumigation can also be used, with chloropicrin being particularly effective in reducing disease incidence in contaminated fields.


In tomato plants, the presence of ethylene during the initial stages of infection inhibits disease development, while in later stages of disease development the same hormone will cause greater wilt. Tomato plants are available that have been engineered with resistant genes that will tolerate the fungus while showing significantly lower signs of wilting.<ref name="Agriose"/>
In tomato plants, the presence of ethylene during the initial stages of infection inhibits disease development, while in later stages of disease development the same hormone will cause greater wilt. Tomato plants are available that have been engineered with resistant genes that will tolerate the fungus while showing significantly lower signs of wilting.<ref name="Agriose"/>


''Verticillium albo-altrum'', ''Verticilium dahliae'' and ''V. longisporum'' can overwinter as melanized mycelium or microsclerotia within live vegetation or plant debris. As a result, it can be important to clear plant debris to lower the spread of disease. ''Verticilium dahliae'' and ''V. longisporum'' are able to survive as microsclerotia in soil for up to 15 years.<ref name="Agriose"/>
''Verticillium albo-altrum'', ''V.&nbsp;dahliae'' and ''V.&nbsp;longisporum'' can overwinter as melanized mycelium or microsclerotia within live vegetation or plant debris. As a result, it can be important to clear plant debris to lower the spread of disease. ''V.&nbsp;dahliae'' and ''V.&nbsp;longisporum'' are able to survive as microsclerotia in soil for up to 15 years.<ref name="Agriose"/>

Susceptible tomato seedlings inoculated with arbuscular mycorrhizal fungi and ''Trichoderma Harzianum'' show increased resistance towards ''Verticillium'' wilt.<ref>{{cite journal|last1=Chliyeh|first1=Mohamed|last2=Chahdi|first2=Abdellatif Ouazzani|last3=Selmaoui|first3=Karima|last4=Touhami|first4=Amina Ouazzani|last5=Abdelkarim|first5=Filali-Maltouf|last6=Modafar|first6=C. El|last7=Abdelmajid|first7=Moukhli|last8=Oukabli|first8=Ahmed|last9=Benkirane|first9=Rachid|last10=Douira|first10=Allal|title=EFFECT OF TRICHODERMA HARZIANUM AND ARBUSCULAR MYCORRHIZALFUNGI AGAINST VERTICILLIUM WILT OF TOMATO|journal=International Journal of Recent Scientific Research|date=February 2014|url=https://www.researchgate.net/publication/260657691_Effect_of_Trichoderma_harzianum_and_arbuscular_mycorrhizal_fungi_against_Verticillium_wilt_of_Tomato|accessdate=16 April 2017}}</ref>


==Importance==
==Importance==
Verticillium wilt occurs in a broad range of hosts but has similar devastating effects on many of these plants. In general, it reduces the quality and quantity of a crop by causing discoloration in tissues, stunting, and premature defoliation and death.<ref name="apsnet">http://www.apsnet.org/edcenter/intropp/lessons/fungi/ascomycetes/Pages/VerticilliumWilt.aspx</ref> Stock from infested nurseries may be restricted. Once a plant is infected, there is no way to cure it. Verticillium wilt is especially a concern in temperate areas and areas that are irrigated. ''Verticllium spp.'' can naturally occur in forest soils and when these soils are cultivated, the pathogen will infect the crop.<ref name="Agriose"/>
Verticillium wilt occurs in a broad range of hosts but has similar devastating effects on many of these plants. In general, it reduces the quality and quantity of a crop by causing discoloration in tissues, stunting, and premature defoliation and death.<ref name="apsnet">{{Cite journal|doi = 10.1094/PHI-I-2000-0801-01|title = Verticillium wilt|year = 2000|last1 = Berlanger|first1 = I.|last2 = Powelson|first2 = M. L.|journal = The Plant Health Instructor|doi-access=}}</ref> Stock from infested nurseries may be restricted. Once a plant is infected, there is no way to cure it. Verticillium wilt is especially a concern in temperate areas and areas that are irrigated. ''Verticllium spp.'' can naturally occur in forest soils and when these soils are cultivated, the pathogen will infect the crop.<ref name="Agriose"/>


The Salinas Valley in California has had severe problems with ''Verticillium'' wilt since 1995, most likely due to flooding in the winter of 1995. Many areas in the Salinas and Pajaro Valleys are unable to grow lettuce due to the high levels of ''Verticillium dahliae'' in the soil.<ref>http://www.calseed.org/documents/Verticillium%20Dahliae%20Information%20Sheet%20ver%206%201%2009.doc</ref> Potatoes grown in ''Verticillium'' infested soils may have a reduced yield between 30–50% compared to potatoes grown in "clean" soil. Verticillium wilt has also caused a shift in peppermint cultivation from the Midwest in the mid- to late-1800s to western states such as Oregon, Washington and Idaho, to new, non-infested areas within these states now.<ref name="apsnet"/>
The Salinas Valley in California has had severe problems with ''Verticillium'' wilt since 1995, most likely due to flooding in the winter of 1995. Many areas in the Salinas and Pajaro Valleys are unable to grow lettuce due to the high levels of ''Verticillium dahliae'' in the soil.<ref>{{Cite web |url=http://www.calseed.org/documents/Verticillium%20Dahliae%20Information%20Sheet%20ver%206%201%2009.doc |title=Archived copy |access-date=2010-12-07 |archive-date=2011-07-25 |archive-url=https://web.archive.org/web/20110725125256/http://www.calseed.org/documents/Verticillium%20Dahliae%20Information%20Sheet%20ver%206%201%2009.doc |url-status=dead }}</ref> Potatoes grown in ''Verticillium'' infested soils may have a reduced yield between 30–50% compared to potatoes grown in "clean" soil. Verticillium wilt has also caused a shift in peppermint cultivation from the Midwest in the mid- to late-1800s to western states such as Oregon, Washington and Idaho, to new, non-infested areas within these states now.<ref name="apsnet"/>


==Lists of plants susceptible or resistant==
==Lists of plants susceptible or resistant==


Replanting susceptible species on the site of a removed plant that has succumbed to ''V. albo-atrum'' or ''V. dahliae'' is inadvisable because of the heightened risk of infection. Instead, resistant or immune varieties should be used. The following two lists show both susceptible and resistant/immune plants by Latin name.<ref>W. A. Sinclair and G. W. Hudler, "Cornell Tree Pest Leaflet A-3 (Revised), 12/84. Diseases of Trees and Shrubs, 2nd Edition, Sinclair and Lyon, 2005".</ref><ref>R. J. Stipes, Professor of Plant Pathology, Virginia Tech and Mary Ann Hansen, Extension Plant Pathologist, Virginia Tech, "[http://www.ext.vt.edu/pubs/plantdiseasefs/450-619/450-619.html Verticillium Wilt of Shade Trees] {{Webarchive|url=https://web.archive.org/web/20090117161736/http://www.ext.vt.edu/pubs/plantdiseasefs/450-619/450-619.html |date=2009-01-17 }}", Publication Number: 450-619, Posted May 2000"</ref><ref>Cynthia L. Ash, "[http://www.extension.umn.edu/distribution/horticulture/DG1164.html Verticillium Wilt of Trees and Shrubs]", 1994)</ref><ref>Department of Crop Sciences, University of Illinois at Urbana-Champaign: "[http://web.aces.uiuc.edu/vista/pdf_pubs/VERTWILT.PDF Report on Plant Diseases]", 1997)</ref><ref>University of California Agriculture and Natural Resources, "[http://depts.washington.edu/hortlib/resources/ucdavis_verticillium.pdf Resistant or susceptible to Verticillium Wilt]", Publication 2703
Replanting susceptible species on the site of a removed plant that has succumbed to ''V.&nbsp;albo-atrum'' or ''V.&nbsp;dahliae'' is inadvisable because of the heightened risk of infection. Instead, resistant or immune varieties should be used. The following two lists show both susceptible and resistant/immune plants by Latin name.<ref name="sinclair">{{cite book |last1=Sinclair |first1=Wayne A. |last2=Lyon |first2=Howard H. |date=2005 |title=Diseases of Trees and Shrubs |edition=Second |location= |publisher=Cornell University Press |pages=242–245 |isbn=978-0-8014-4371-8}} See also W. A. Sinclair and G. W. Hudler, "Cornell Tree Pest Leaflet A-3 (Revised), 12/84."</ref><ref>R. J. Stipes, Professor of Plant Pathology, Virginia Tech and Mary Ann Hansen, Extension Plant Pathologist, Virginia Tech, "[http://www.ext.vt.edu/pubs/plantdiseasefs/450-619/450-619.html Verticillium Wilt of Shade Trees] {{Webarchive|url=https://web.archive.org/web/20090117161736/http://www.ext.vt.edu/pubs/plantdiseasefs/450-619/450-619.html |date=2009-01-17 }}", Publication Number: 450-619, Posted May 2000"</ref><ref>Cynthia L. Ash, "[http://www.extension.umn.edu/distribution/horticulture/DG1164.html Verticillium Wilt of Trees and Shrubs]", 1994)</ref><ref>Department of Crop Sciences, University of Illinois at Urbana-Champaign: "[http://web.aces.uiuc.edu/vista/pdf_pubs/VERTWILT.PDF Report on Plant Diseases]", 1997)</ref><ref>University of California Agriculture and Natural Resources, "[http://depts.washington.edu/hortlib/resources/ucdavis_verticillium.pdf Resistant or susceptible to Verticillium Wilt]", Publication 2703
First published 1981</ref><ref>Verticillium wilt of vegetables and herbaceous ornamentals,2011-3-20</ref>
First published 1981</ref><ref>Verticillium wilt of vegetables and herbaceous ornamentals,2011-3-20</ref>


(*) indicates that the plant occurs on both lists because different varieties or cultivars vary in their resistance.<br/>
(*) indicates that the plant occurs on both lists because different varieties or cultivars vary in their resistance.<br />
(#) indicates that some strains are resistant.<br/>
(#) indicates that some strains are resistant.<br />
(+) indicates susceptibility to some European strains of ''Verticillium albo-atrum''.
(+) indicates susceptibility to some European strains of ''Verticillium albo-atrum''.


Line 102: Line 99:
* ''[[Brassica oleracea|Brassica oleracea var. botrytis]]'' (Cauliflower)
* ''[[Brassica oleracea|Brassica oleracea var. botrytis]]'' (Cauliflower)
* ''[[Brassica oleracea|Brassica oleracea var. capitata]]'' (Cabbage)
* ''[[Brassica oleracea|Brassica oleracea var. capitata]]'' (Cabbage)
* ''[[Brassica oleracea|Brassica oleracea var. gemmifera]]'' (Brussel Sprouts)
* ''[[Brassica oleracea|Brassica oleracea var. gemmifera]]'' (Brussels Sprouts)
* ''[[Buxus]]'' (Box, boxwood)
* ''[[Buxus]]'' (Box, boxwood)
* ''[[Calceolaria]] spp.'' (Slipperwort)
* ''[[Calceolaria]] spp.'' (Slipperwort)
Line 150: Line 147:
* ''[[Echinacea purpurea]]'' (Eastern purple coneflower)
* ''[[Echinacea purpurea]]'' (Eastern purple coneflower)
* ''[[Elaeagnus]]'' (Oleaster, Russian Olive)
* ''[[Elaeagnus]]'' (Oleaster, Russian Olive)
* ''[[Erica]] spp.'' (Heather)
* ''[[Erica (plant)|Erica]] spp.'' (Heather)
* ''[[Erigeron]]'' (Fleabane)
* ''[[Erigeron]]'' (Fleabane)
* ''[[Eschscholzia californica]]'' (California poppy)
* ''[[Eschscholzia californica]]'' (California poppy)
Line 231: Line 228:
* ''[[Salpiglossis sinuata]]'' (Painted tongue)
* ''[[Salpiglossis sinuata]]'' (Painted tongue)
* ''[[Salvia farinacea]]'' (Mealycup sage)
* ''[[Salvia farinacea]]'' (Mealycup sage)
* ''[[Salvia haematodes]]'' (Sage)
* ''[[Salvia pratensis|Salvia haematodes]]'' (Sage)
* ''[[Salvia azurea]]'' (Blue sage)
* ''[[Salvia azurea]]'' (Blue sage)
* ''[[Sambucus]] spp.'' (Elderberry)
* ''[[Sambucus]] spp.'' (Elderberry)
Line 269: Line 266:
===Plants resistant or immune===
===Plants resistant or immune===


====Families====
==== Clades ====


* ''[[Cactaceae]]'' (Cactii)
* ''[[Polypodiopsida]]'' ([[ferns]] and allies)
* ''[[Graminae]]'' (Grasses, Grains, etc.)
* ''[[Gymnospermae]]'' (pines, firs, cycads, ginkgos, etc.)
* ''[[Gymnospermae]]'' (Firs, Pines, etc.)
* ''[[Monocotyledoneae]]'' ([[grasses]], [[bananas]], [[Arecaceae|palms]], [[Liliaceae|lilies]], etc.)
⚫
* ''[[Cactaceae]]'' (cacti)
* ''[[Monocotyledoneae]]'' (Bamboos, Bananas, Gladiolae, Grasses, Lilies, etc.)
* ''[[Polypodiaceae]]'' (Ferns)


====Species====
====Species====


''[[Acer pseudoplatanus]]'' (Sycamore)
* ''[[Acer pseudoplatanus]]'' (Sycamore)
* ''[[Ageratum]] spp.'' (Ageratum)
* ''[[Ageratum]] spp.'' (Ageratum)
* ''[[Alnus]] spp.'' (Alder)
* ''[[Alnus]] spp.'' (Alder)
Line 322: Line 318:
* ''[[Gleditsia]] spp.'' (Honey locust)
* ''[[Gleditsia]] spp.'' (Honey locust)
* ''[[Gypsophila paniculata]]'' (Baby's breath)
* ''[[Gypsophila paniculata]]'' (Baby's breath)
⚫
* ''[[Hebe anonda]]'' (Hebe)
⚫
* ''[[Hebe x franciscana]]'' (Hebe)
⚫
* ''[[Hebe x menziesii]]'' (Hebe)
* ''[[Hebe salicifolia]]'' (Hebe)
* ''[[Helianthemum nummularium]]'' (Sun rose)
* ''[[Helianthemum nummularium]]'' (Sun rose)
* ''[[Helleborus niger]]'' (Hellebore, Christmas Rose)
* ''[[Helleborus niger]]'' (Hellebore, Christmas Rose)
Line 374: Line 366:
* ''[[Umbellularia californica]]'' (Californian laurel)
* ''[[Umbellularia californica]]'' (Californian laurel)
* ''[[Verbena hybrida]]'' (Verbena)
* ''[[Verbena hybrida]]'' (Verbena)
* [[Veronica x franciscana|''Veronica'' x ''franciscana'']] (Hebe)
⚫
* ''[[Veronica elliptica]]'' (syn. ''Hebe'' x ''menziesii'') (Hebe)
⚫
* ''[[Veronica salicifolia]]'' (Hebe)
* ''[[Vinca minor]]'' (Periwinkle)
* ''[[Vinca minor]]'' (Periwinkle)
* ''[[Viola (plant)|Viola]] spp.'' (Pansy, Viola, Violet)
* ''[[Viola (plant)|Viola]] spp.'' (Pansy, Viola, Violet)
Line 381: Line 376:
==References==
==References==
{{Reflist|30em}}
{{Reflist|30em}}

{{Taxonbar|from=Q500536}}


{{DEFAULTSORT:Verticillium Wilt}}
{{DEFAULTSORT:Verticillium Wilt}}
[[Category:Fungal plant pathogens and diseases]]
[[Category:Fungal plant pathogens and diseases]]
[[Category:Tomato pathogens and pests]]
[[Category:Tomato diseases]]
[[Category:Fungal tree pathogens and diseases]]
[[Category:Fungal tree pathogens and diseases]]
[[Category:Fungus common names]]
[[Category:Fungus common names]]

Latest revision as of 01:49, 10 August 2024

Verticillium wilt
Healthy strawberry plant (left) and strawberry plant infected with verticillium wilt (right), photo by Howard F. Schwartz, Colorado State University, Bugwood.org
Causal agents

Verticillium wilt is a wilt disease affecting over 350 species of eudicot plants. It is caused by six species of Verticillium fungi: V. dahliae, V. albo-atrum, V. longisporum, V. nubilum, V. theobromae and V. tricorpus.[1] Many economically important plants are susceptible including cotton, tomatoes, potatoes, oilseed rape, eggplants, peppers and ornamentals, as well as others in natural vegetation communities. Many eudicot species and cultivars are resistant to the disease and all monocots, gymnosperms and ferns are immune.

Signs are superficially similar to Fusarium wilts. There are no fungicides characterized for the control of this disease but soil fumigation with chloropicrin has been proven successful in dramatically reducing Verticillium wilt in diverse crops such as vegetables using plasticulture production methods, and in non-tarped potato production in North America . Additional strategies to manage the disease include crop rotation, the use of resistant varieties and deep plowing (to accelerate the decomposition of infected plant residue). In recent years, pre-plant soil fumigation with chloropicrin in non-tarped, raised beds has proven to be economically viable and beneficial for reducing wilt disease and increasing yield and quality of potato in North America. Soil fumigation is a specialized practice requiring special permits, equipment, and expertise, so qualified personnel must be employed.

Hosts and symptoms

[edit]
Verticillium dahliae infected sunflowers, photo by Howard F. Schwartz, Colorado State University, Bugwood.org
Verticillium albo-atrum infected tree crown, USDA Forest Service Archive, USDA Forest Service, Bugwood.org

Verticillium spp. attack a very large host range including more than 350 species of vegetables, fruit trees, flowers, field crops, and shade or forest trees. Most vegetable species have some susceptibility, so it has a very wide host range.[2] A list of known hosts is at the bottom of this page.

The symptoms are similar to most wilts with a few specifics to Verticillium. Wilt itself is the most common symptom, with wilting of the stem and leaves occurring due to the blockage of the xylem vascular tissues and therefore reduced water and nutrient flow. In small plants and seedlings, Verticillium can quickly kill the plant while in larger, more developed plants the severity can vary. Some times only one side of the plant will appear infected because once in the vascular tissues, the disease migrates mostly upward and not as much radially in the stem.[3] Other symptoms include stunting, chlorosis or yellowing of the leaves, necrosis or tissue death, and defoliation. Internal vascular tissue discoloration might be visible when the stem is cut.[2]

In Verticillium, the symptoms and effects will often only be on the lower or outer parts of plants or will be localized to only a few branches of a tree. In older plants, the infection can cause death, but often, especially with trees, the plant will be able to recover, or at least continue living with the infection. The severity of the infection plays a large role in how severe the signs are and how quickly they develop.[2]

Disease cycle

[edit]

While Verticillium spp. are very diverse, the basic life cycle of the pathogen is similar across species, except in their survival structures. The survival structures vary by species with V. albo-atrum forming mycelium, V. dahliae forming microsclerotia, V. nigrescens and V. nubilum forming chlamydospores, and V. tricorpus forming all three. While resting, many factors such as soil chemistry, temperature, hydration, micro fauna, and non-host crops all have an effect on the viability of the resting structure. Mycelium have been observed remaining viable for at least 4 years,[4] while microsclerotia have been observed in fields planted with non-host crops for over 10 years [5] and even 15 years has been reported.[2] Viability is reduced at these extremes, but the long survivability of these structures is an important aspect for Verticillium control.

When roots of a host crop come near the resting structure (about 2mm),[6] root exudate promotes germination and the fungi grows out of the structure and toward the plant. Being a vascular wilt, it will try to get to the vascular system on the inside of the plant, and therefore must enter the plant. Natural root wounds are the easiest way to enter, and these wounds occur naturally, even in healthy plants because of soil abrasion on roots. Verticillium has also been observed entering roots directly, but these infections rarely make it to the vascular system, especially those that enter through root hairs.[7]

Once the pathogen enters the host, it makes its way to the vascular system, and specifically the xylem. The fungi can spread as hyphae through the plant, but can also spread as spores. Verticillium produce conidia on conidiophores and once conidia are released in the xylem, they can quickly colonize the plant. Conidia have been observed traveling to the top of cotton plants, 115 cm (45 in), 24 hours after initial conidia inoculation, so the spread throughout the plant can occur very quickly.[8] Sometimes the flow of conidia will be stopped by cross sections of the xylem, and here the conidia will spawn, and the fungal hyphae can overcome the barrier, and then produce more conidia on the other side.[9]

A heavily infected plant can succumb to the disease and die. As this occurs, the Verticillium will form its survival structures and when the plant dies, its survival structures will be where the plant falls, releasing inoculates into the environment. The survival structures will then wait for a host plant to grow nearby and will start the cycle all over again.

Besides being long lasting in the soil, Verticillium can spread in many ways. The most common way of spreading short distances is through root to root contact within the soil. Roots in natural conditions often have small damages or openings in them that are easily colonized by Verticillium from an infected root nearby. Air borne conidia have been detected and some colonies observed, but mostly the conidia have difficulty developing above ground on healthy plants.[10] In open channel irrigation, V. dahliae have been found in the irrigation ditches up to a mile from the infected crop.

Without fungicidal seed treatments, infected seeds are easily transported and the disease spread, and Verticillium has been observed remaining viable for at least 13 months on some seeds. Planting infected seed potatoes can also be a source of inoculum to a new field. Finally, insects have also been shown to transmit the disease. Many insects including potato leaf hopper, leaf cutter bees, and aphids have been observed transmitting conidia of Verticillium and because these insects can cause damage to the plant creating an entry for the Verticillium, they can help transmit the disease.[3]

Environment

[edit]

While Verticillium wilts often have the same symptoms of Fusarium wilts, Verticillium can survive cold weather and winters much better than Fusarium, which prefers warmer climates. The resting structures of Verticillium are able to survive freezing, thawing, heat shock, dehydration, and many other factors and are quite robust and difficult to get rid of. The one factor they do not tolerate well is extended periods of anaerobic conditions (such as during flooding).[3]

Verticillium will grow best between 20 and 28 degrees Celsius,[2] but germination and growth can occur well below (or above) those temperatures. Still, Verticillium will generally not survive in the branches and trunks of infected trees during hot, dry seasons in regions such as summer in southern California. This does not generally "cure" the entire tree, however, and recurrence can happen via a reinfection from the roots during winter and spring.[11] Water is necessary for resting structure germination, but is not as important for the spread of the fungus as in many other fungi. While not an environmental requirement for the fungus, stressed plants, often brought on by environmental changes, are easier to attack than healthy plants, so any conditions that will stress the plant but not directly harm the Verticillium will be beneficial for Verticillium wilt development.[3]

Management

[edit]

Verticillium wilt begins as a mild, local infection, which over a few years will grow in strength as more virile strains of the fungus develop. If left unchecked the disease will become so widespread that the crop will need to be replaced with resistant varieties, or a new crop will need to be planted altogether.[2]

Control of Verticillium can be achieved by planting disease–free plants in uncontaminated soil, planting resistant varieties, and refraining from planting susceptible crops in areas that have been used repeatedly for solanaceous crops. Soil fumigation can also be used, with chloropicrin being particularly effective in reducing disease incidence in contaminated fields.

In tomato plants, the presence of ethylene during the initial stages of infection inhibits disease development, while in later stages of disease development the same hormone will cause greater wilt. Tomato plants are available that have been engineered with resistant genes that will tolerate the fungus while showing significantly lower signs of wilting.[2]

Verticillium albo-altrum, V. dahliae and V. longisporum can overwinter as melanized mycelium or microsclerotia within live vegetation or plant debris. As a result, it can be important to clear plant debris to lower the spread of disease. V. dahliae and V. longisporum are able to survive as microsclerotia in soil for up to 15 years.[2]

Importance

[edit]

Verticillium wilt occurs in a broad range of hosts but has similar devastating effects on many of these plants. In general, it reduces the quality and quantity of a crop by causing discoloration in tissues, stunting, and premature defoliation and death.[12] Stock from infested nurseries may be restricted. Once a plant is infected, there is no way to cure it. Verticillium wilt is especially a concern in temperate areas and areas that are irrigated. Verticllium spp. can naturally occur in forest soils and when these soils are cultivated, the pathogen will infect the crop.[2]

The Salinas Valley in California has had severe problems with Verticillium wilt since 1995, most likely due to flooding in the winter of 1995. Many areas in the Salinas and Pajaro Valleys are unable to grow lettuce due to the high levels of Verticillium dahliae in the soil.[13] Potatoes grown in Verticillium infested soils may have a reduced yield between 30–50% compared to potatoes grown in "clean" soil. Verticillium wilt has also caused a shift in peppermint cultivation from the Midwest in the mid- to late-1800s to western states such as Oregon, Washington and Idaho, to new, non-infested areas within these states now.[12]

Lists of plants susceptible or resistant

[edit]

Replanting susceptible species on the site of a removed plant that has succumbed to V. albo-atrum or V. dahliae is inadvisable because of the heightened risk of infection. Instead, resistant or immune varieties should be used. The following two lists show both susceptible and resistant/immune plants by Latin name.[11][14][15][16][17][18]

(*) indicates that the plant occurs on both lists because different varieties or cultivars vary in their resistance.
(#) indicates that some strains are resistant.
(+) indicates susceptibility to some European strains of Verticillium albo-atrum.

Susceptible plants

[edit]

Plants resistant or immune

[edit]

Clades

[edit]

Species

[edit]

References

[edit]
  1. ^ Barbara, D.J.; Clewes, E. (2003). ""Plant pathogenic Verticillium species: how many of them are there?"". Molecular Plant Pathology. 4 (4). Blackwell Publishing: 297–305. doi:10.1046/j.1364-3703.2003.00172.x. PMID 20569390.
  2. ^ a b c d e f g h i Agrios, George N. Plant Pathology, 5th Edition.
  3. ^ a b c d Pegg, G.F., Brady, B.L. (2002) Verticillium Wilts, CABI Publishing, New York, NY.
  4. ^ Luck, J.V. (1954) Studies on the Verticillium wilt of Mentha piperita L. with special emphasis on the causal organism, Verticillium albo-atrum R. &B. Dissertation Abstracts 14, 916-917.
  5. ^ Wilhelm, S. (1955). "Longevity of the Verticillium wilt fungus in the laboratory and field". Phytopathology. 45 (3): 180–181.
  6. ^ Sewell, G.W.F. (1959). "Direct observation of Verticillium albo-atrum in soil". Transactions of the British Mycological Society. 42 (3): 312–IN9. doi:10.1016/S0007-1536(56)80039-9.
  7. ^ Garber, R.H. (1973) United States Department of Agriculture Publication 1. ARS-S-19. pp. 69-77.
  8. ^ Presley, J. T.; Carns, H.R.; Taylor, E.E.; Schnathorst, W.C. (1966). "Movement of conidia of Verticillium albo-atrum in cotton plants". Phytopathology. 56: 375.
  9. ^ Knoll, F.A. (1972). "Untersuchungen zur Ausbreitung gefässbesiedelnder Verticillium-Arten in Luzernepflanzen". Zentralblatt für Bakteriologie, Parasitenkunde, Infektionskrankheiten und Hygiene. 127: 332–345.
  10. ^ Easton, G.D.; Nagle, M.E.; Bailey, D.L. (1969). "A method of estimating Verticillium albo-atrum propagules in field soil and irrigation waste water". Phytopathology. 59: 1171–1172.
  11. ^ a b Sinclair, Wayne A.; Lyon, Howard H. (2005). Diseases of Trees and Shrubs (Second ed.). Cornell University Press. pp. 242–245. ISBN 978-0-8014-4371-8. See also W. A. Sinclair and G. W. Hudler, "Cornell Tree Pest Leaflet A-3 (Revised), 12/84."
  12. ^ a b Berlanger, I.; Powelson, M. L. (2000). "Verticillium wilt". The Plant Health Instructor. doi:10.1094/PHI-I-2000-0801-01.
  13. ^ "Archived copy". Archived from the original on 2011-07-25. Retrieved 2010-12-07.{{cite web}}: CS1 maint: archived copy as title (link)
  14. ^ R. J. Stipes, Professor of Plant Pathology, Virginia Tech and Mary Ann Hansen, Extension Plant Pathologist, Virginia Tech, "Verticillium Wilt of Shade Trees Archived 2009-01-17 at the Wayback Machine", Publication Number: 450-619, Posted May 2000"
  15. ^ Cynthia L. Ash, "Verticillium Wilt of Trees and Shrubs", 1994)
  16. ^ Department of Crop Sciences, University of Illinois at Urbana-Champaign: "Report on Plant Diseases", 1997)
  17. ^ University of California Agriculture and Natural Resources, "Resistant or susceptible to Verticillium Wilt", Publication 2703 First published 1981
  18. ^ Verticillium wilt of vegetables and herbaceous ornamentals,2011-3-20
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