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. The infective sclerotia remain viable in the soil for many years and are stimulated to germinate by the presence of a susceptible crop.
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. In the case of onions, the first symptoms of damage are wilting and yellowing of the foliage. The older leaves die first followed by all the aerial parts of the plant. The scales of the bulb become watery and disintegrate. White mycelia appear at the base of the bulb, spreading over its surface and causing it to rot. Black globular sclerotia, 200-500 µm in diameter, appear on the fluffy white mould and sometimes larger, black sclerotic crusts also form. The sclerotia become detached and remain dormant in the soil for many years ready to infect a future Allium crop.
Sclerotinia germinate when in contact with chemicals emitted by the roots of Allium plants. They remain infective in the soil for fifteen years or more. At low densities clusters of affected plants develop as the infection spreads from plant to plant. At higher densities, the entire crop may be affected. 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).
Where the disease has occurred, recropping with further Alliums 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.
Use in biocontrol
The three-cornered leek (Allium triquetrum) is a species of Allium that 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. Stromatinia cepivora is being investigated as a possible biological control agent for the plant. There are no naturally occurring members of the genus Allium 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 that "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."
- "White rot: Stromatinia cepivora (Berk.) Whetzel". Invasive.org. Retrieved 2013-03-29.
- "Sclerotium cepivorum Berk.". Species Fungorum. Retrieved 2013-03-29.
- Cherry, Kathryn. "Sclerotium cepivorum". Department of Plant Pathology, North Carolina State University. Retrieved 2013-03-29.
- Crowe, F.J.; Hall, D.H.; Greathead, A.S.; Baghott, K.G. (1997). "Inoculum Density of Sclerotium cepivorum and the Incidence of White Rot of Onion and Garlic". Phytopathology 70: 64–69. doi:10.1094/Phyto-70-64.
- "Onion and Garlic: White Rot". UC IPM Pest Management Guidelines: Onion and Garlic. Retrieved 2013-03-30.
- 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". Seventeenth Australasian Weeds Conference. pp. 219–222. Retrieved 2013-03-29.