Verticillium stem stripe was first confirmed on winter oilseed rape in the UK in 2007. This publication provides an overview of the disease and management options.
Verticillium longisporum (scientific name)
Note: Verticillium wilt has recently been renamed as verticillium stem stripe. This new common name better reflects the symptoms caused by the disease.
Verticillium is a soil-borne fungal disease of many fruit, vegetables and ornamental plants. The disease affects brassicacea, such as oilseed rape and vegetable brassicas.
Verticillium longisporum was first confirmed on winter oilseed rape in the UK in 2007. Initially termed ‘verticillium wilt’, the name verticillium stem stripe was proposed in 2016. The pathogen does not cause typical wilting symptoms in oilseed rape crops. However, other crops, affected by related species, do show wilt symptoms (e.g. potatoes).
In oilseed rape crops, occasional leaf yellowing may be seen. This tends to affect only one side of the leaf lamina. The most significant symptoms are not seen until the end of the season, usually towards the end of June and early July.
Initially, yellow or brown stripes occur on stems. These extend from soil level up to upper branches as ripening begins. Usually, symptoms occur on a few branches but whole plants can be affected. Severely affected plants ripen prematurely. Vertical grey stripes are visible as surface stem layers start to decay. At harvest, the stems, pith and roots are grey in colour with black microsclerotia.
Symptoms are easy to overlook and difficult to identify, especially if phoma cankers and stem lesions are present.
The life cycle starts either with microsclerotia incorporated with plant debris (that can persist for over 10 years) or with contaminated/infected seed. Germination is stimulated by root exudates of the next oilseed rape crop. Infection usually takes place during the seedling stage, with root and stem base tissue becoming infected. The fungus finally colonises the vascular tissue. At the end of the growing season, black microsclerotia form, which infect crop residues and seed.
V. longisporum was initially confirmed in England in 2007. An AHDB study of disease incidence on 292 randomly selected crops of winter oilseed rape in harvest years 2009, 2010 and 2011 found, on average, that 16% of crops and 3.3% of plants were affected. About 5% of crops had quite high levels (over 20% of plants affected). The affected crops were most prevalent in parts of eastern England, though some crops were affected as far north as Yorkshire. Studies on single plants with different severities of the disease indicate that yield loss can occur when more than half the stem circumference is affected and plants are ripening prematurely. Severely affected plants showed decreases in thousand seed weight of between 12% and 24%. Larger yield losses can occur if the crop canopy collapses and there is seed shedding. Yield impact is expected to vary from year to year, depending on weather and crop factors.
Rotations – as with other soil-borne diseases, short rotations increase pressure. Although, microsclerotia can survive for over a decade and crops in long rotations may also be affected.
Seed – seed harvested from heavily infected crops can lead to internal seed-borne infection. The outsides of seed can also be contaminated by infected sources of dust.
Crop development – poorly established crops are at a higher risk of infection. As verticillium stem stripe can develop over a wide range of soil temperatures, late sowing does not allow the crop to escape infection.
Other diseases – crops that are stressed or affected by other diseases are more prone to verticillium stem stripe.
There is no specific chemical treatment option for this soil-borne disease.
Crops should be monitored pre-harvest and verticillium stem stripe levels determined. If verticillium stem stripe is established, be prepared to extend rotations. Do not use seed from crops with verticillium stem stripe. Consider using varieties with good early vigour on problematic land.
There have been few replicated variety trials for verticillium stem stripe in the UK. An experiment in 2010 identified significant differences between varieties in the occurrence and severity of disease symptoms. Similar differences have been found in experiments supported by plant breeders. AHDB is working towards the development of a verticillium stem stripe resistance rating for the AHDB Recommended List.
Verticillium wilt disease ratings ‘one step closer’, says AHDB (news item, May 2019)