Stromatinia cepivora
| Stromatinia cepivora | |
|---|---|
| Scientific classification | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Ascomycetes |
| Order: | Helotiales |
| Family: | Sclerotiniaceae |
| Genus: | Stromatinia |
| Species: | S. cepivora |
| Binomial name | |
| Stromatinia cepivora Berk.[1] | |
| Synonyms[1] | |
| |
Stromatinia cepivora is a fungus in the division Ascomycota. It is the teleomorph of Sclerotium cepivorum, the cause of white rot in onions, garlic, and leeks.[2] The infective sclerotia remain viable in the soil for many years and are stimulated to germinate by the presence of a susceptible crop.
Biology
Sclerotium cepivorum is the asexual reproductive form of Stromatinia cepivora and is a plant pathogen, causing white rot in Allium species, particularly onions, leeks, and garlic. It is a soil-borne fungus and affects susceptible crops planted in infected soil. Sclerotia can be spread to other fields by farm machinery, vehicles, boots, wind-borne onion husks, or flood water. Infection can occur when the soil temperature is in the range 50 to 75 °F (10 to 24 °C).[3]
Symptoms
The first symptoms noted with S. cepivora are the foliar symptoms. Plants are stunted in growth with yellow and wilting foliage. The leaves eventually die and fall off [4] with the older leaves dying first and then the aerial leaves. Soil conditions and the environment are determinants for extent of damage to the plant. The pathogen grows in moist cold temperatures.[5] So, in the right conditions, pathogenic activity increases as the root systems develop. The disease attacks at all stages of growth, which leaves the plant to turn yellow and wilt when fully developed because the roots are rotting. Mycelial growth is another symptom that appears on the roots and spreads to the bulb causing it to rot. This mycelial growth can be seen at the base of the stem when foliage is yellowing and the foliar symptoms are first appearing. Black globular sclerotia, that resemble poppy seeds can also appear on the mycelium. These survival structures (sclerotia) can detach and persist for years in a dormant state, waiting for a susceptible host.[4]
Disease Cycle
Stromatinia cepivora is a soil borne fungus. This is a unique fungus as it does not produce any spores of importance to a normal life cycle.[6] It exists and overwinters as sclerotia (the survival stage). These small black globular structures are resistant to adverse temperatures and can remain dormant in the soil for years even without a host. Sclerotia germinate in response to root exudates.[7] Weather is also a factor is germination and hyhae growth. Mycelium grow through the soil and form an appresoria once a host root is available. Appresoria are able to attach and penetrate the host. Mycelium grow out from the roots and can spread to a neighboring plant which creates the row of disease. Even small amounts of sclerotia can cause disease and be difficult to control. Sclerotia infect the host and spread. They are formed on the decaying host tissue and then are left free in the soil.[8] To control the disease there needs to be a reduction in the number of sclerotia in the soil so fungus growth can be halted. Overall, multiple controls are necessary to produce an adequate yield in infected fields.
How disease spreads: Anything that moves the infested soil will move sclerotia and cause it to spread. I.e. wind, wateIr, equipment, boots etc.
Importance
This is serious disease for plants of the allium family. The soil borne fungus can persist in the soil for many years. This disease is present in all allium-producing regions making it a threat in the allium production industry and a worldwide disease. It has been found in the United States 10 times with the first in 1918 in Oregon and the latest in 2014 in an onion field.[5] Onions and garlic are economically important vegetables in the world. S. cepivora is one of the most destructive diseases carrying high loss in onion and garlic. Once land has been infested, it is considered not suitable for garlic or onion production for up to 40 or more years.[9] Even at significantly reduced levels, if grown in white rot infested fields, can yield losses up to 20 to 40%.[7] During favorable weather conditions and susceptible hosts, the disease can cause 100% yield loss.[7] Therefore, awareness of the environment, host plant and cultural practices are important in managing this deadly disease.
White Rot in the United States:[5]
1918: First found in La Grande, Oregon
1930’s: San Francisco area
1940’s: Gilroy, Tulelake, Walla Walla, Klamath Falls
1950’s: Salinas, Nevada, Willamette Valley, OR
1970’s: Central Oregon, San Joaquin Valley
1989: Treasure Valley
2004: Marion Co., OR
2008: Crook Co.
2010: Palouse Falls region- home grown garlic
2014: onion field
Management
Where the disease has occurred, recropping with further Allium species should be avoided for many years. The risk of infection can be reduced as far as possible in clean land by using disease-free planting material and avoiding contamination from infected fields. Dipping seed garlic in water at 115 °F (46 °C) is effective, but higher temperatures may kill the cloves. Onion seed is unlikely to be infected, but transplants or sets may be. Some fungicides are available to control white rot, but an alternative method of control is to stimulate the sclerotinia to germinate in the absence of an Allium crop. This can be done by applying a garlic extract or the use of certain petroleum-based products.[3]
Use in biocontrol
The three-cornered leek (Allium triquetrum) has been introduced into Australia where it has spread and become established in nutrient-deficient, damp habitats. The plant is now considered to be a noxious invasive species, as it is difficult to control or eradicate. S. cepivora is being investigated as a possible biological control agent for the plant. No naturally occurring members of the genus Allium occur in Australia, and in a trial, the fungus was found to be effective at killing all but one of the target samples on which it was tested. However, the researchers involved in the study acknowledged, "Releasing a virulent pathogen for cultivated Allium species into bushland or pasture is controversial and any field release would require safeguards against spread to areas suitable for the production of cultivated Allium species, such as onions, leeks and garlic, before S. cepivora could be introduced as a potential biological control agent."[10]
References
- 1 2 "White rot: Stromatinia cepivora (Berk.) Whetzel". Invasive.org. Retrieved 2013-03-29.
- ↑ "Sclerotium cepivorum Berk.". Species Fungorum. Retrieved 2013-03-29.
- 1 2 "Onion and Garlic: White Rot". UC IPM Pest Management Guidelines: Onion and Garlic. Retrieved 2013-03-30.
- 1 2 "Onion white rot/RHS Gardening". www.rhs.org.uk. Retrieved 2016-11-17.
- 1 2 3 University of Guelph, Guelph ,Ontario, Canada, MARY RUTH MCDONALD, MARIA JAIME, MARILYN HOVIUS, MICHAEL TESFAEDRIAS, LAURA BARBISON , GREG BOLAND. "White Rot Identification and Control" (PDF). Retrieved 11/12/16. Check date values in:
|access-date=(help) - ↑ "Onion Rot". 2016-07-18. Retrieved 2016-11-17.
- 1 2 3 "Academic Journals - Journals" (PDF). academicjournals.org. Retrieved 2016-11-17.
- ↑ "Sclerotium cepivorum". projects.ncsu.edu. Retrieved 2016-11-17.
- ↑ "Developing New Integrated Strategies for Controlling White Rot in Garlic" (PDF). Retrieved 2016-11-12.
|first1=missing|last1=in Authors list (help) - ↑ Tehranchian, Parsa; Lawrie, A.C.; Adair, Robin. "In vitro assessment of Stromatinia cepivora as a potential biological control agent for angled onion (Allium triquetrum) in Victoria, Australia" (PDF). Seventeenth Australasian Weeds Conference. pp. 219–222. Retrieved 2013-03-29.