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Increase in clubroot on oilseed rape in the United Kingdom

A ProMED-mail post
http://www.promedmail.org
ProMED-mail is a program of the
International Society for Infectious Diseases
http://www.isid.org

Date: Mon 12 Dec 2022
Source: Farmers Weekly [summ. Mod.DHA, edited]
https://www.fwi.co.uk/arable/crop-management/ahdb-variety-trials-reveal-wheat-pest-and-true-cost-of-clubroot

Clubroot is becoming more prevalent across the UK. Agriculture and Horticulture Development Board (AHDB) trials have revealed the huge cost it can have on oilseed rape [OSR] yields. The disease has been unexpectedly cropping up in variety trials despite choosing sites that had not previously seen it. Two trials were assessed for their final yields to investigate the impact of the disease.

On a trial in northern England on medium-textured soil, OSR had been grown for 4 years previously. The field was limed before the crop was sown in late August, and symptoms were discovered in October throughout the trial; by the following May, there was severe stunting. There were differences between varieties, with clubroot-resistant Crome showing a yield of approximately twice the average yield of the total trial.

On the other trial, in Scotland on lighter soil, no OSR had been grown in the previous 5 years. The crop was sown at the same time; patchy clubroot symptoms were observed in early November. No clubroot-resistant varieties were included. Results showed that 100% of the plot was infected, and yield was reduced by an average of 77%, demonstrating that losses can be severe.

The fact that clubroot is being found in places where it had not been seen before suggests that the risk is increasing. Warmer, wetter autumns combined with a move to earlier drilling to reduce the cabbage stem flea beetle [_Psylliodes chrysocephalus_] threat means crops are more vulnerable to clubroot. It may also need to be considered whether cover crops are playing a role since they may hide brassica weeds.

[Byline: Richard Allison]

--
Communicated by:
ProMED

[Clubroot of Brassicaceae is caused by the fungus-like organism _Plasmodiophora brassicae_. It is a destructive, soil-borne disease affecting nearly all cultivated members of the family, including oilseed rape (_Brassica napus_), cabbages, turnips, as well as many wild species which may serve as pathogen reservoirs. It is found worldwide and is most damaging in temperate regions and tropical highlands.

The pathogen enters through root hairs and wounded roots. It multiplies rapidly, causing abnormal enlargement of the underground stem, taproot, or secondary roots ("clubs"). Affected roots often decay before the crop has matured. Depending on the timing of infection in the crop cycle, symptoms may include wilting, stunting, and yellowing of plants, or premature ripening resulting in shriveled seeds. Due to the distortion of the roots, plants may wilt in dry weather and then recover at night.

Decaying roots release many resting spores, which can survive in the soil for a decade or more in the absence of a susceptible host plant. Thus, crop rotation of just a few years will not control clubroot. The disease can be spread with soil (for example on agricultural machinery), farming activities, and infected plant debris. Use of clean planting material and phytosanitary measures to prevent spread between fields is essential. Disease management is difficult due to the longevity of the spores and the inaccessibility of underground plant parts to fungicides. Raising soil pH by addition of lime and fumigation treatments have been used with varying degrees of success (e.g., ProMED post 20120521.1139354).

The species is composed of numerous pathotypes, which makes breeding crop cultivars with durable resistance difficult. It is therefore important to use multiple approaches to disease management simultaneously to counteract pathogen adaptation and extend the useful duration of both host resistances and effectiveness of fungicides.

Maps
UK:
https://www.worldometers.info/img/maps/unitedkingdom_physical_map.gif
UK regions and counties:
https://tinyurl.com/ml5ggkx
Europe, overview:
https://mapofeurope.com/wp-content/uploads/2018/03/europe-political-map.jpg

Pictures
Clubroot symptoms on roots of oilseed rape:
https://www.realagriculture.com/wp-content/uploads/2012/08/club-root.jpg and
https://www.agric.wa.gov.au/sites/gateway/files/styles/original/public/Club%20root.JPG
Clubroot-affected oilseed rape plants:
http://www.canolawatch.org/wp-content/uploads/2013/04/Clubroot-rotation-effect-cont.-canola.jpg (resistant vs. sensitive cultivars)
Clubroot symptoms on other brassica crops:
https://pnwhandbooks.org/sites/pnwhandbooks/files/plant/images/broccoli-brassica-oleracea-clubroot/broccolitransplantclubroot.jpg,
https://c8.alamy.com/comp/BG75EM/clubroot-plasmodiophora-brassica-distorted-root-on-a-cabbage-plant-BG75EM.jpg and
http://www.omafra.gov.on.ca/IPM/images/brassica/diseases/clubroot_brussels_zoom.jpg (affected field)

Links
Information on clubroot of oilseed rape:
https://www.canolacouncil.org/canola-encyclopedia/diseases/clubroot/,
http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/agdex8593?opendocument,
http://www.canolawatch.org/2013/04/04/rotations-role-in-clubroot-management/,
https://bit.ly/38SXxBC and
https://doi.org/10.1111/ppa.12949
Information on clubroot on crucifer crops:
https://www.agric.wa.gov.au/broccoli/managing-clubroot-vegetable-brassica-crops,
https://cropscience.bayer.co.uk/threats/diseases/field-brassica-diseases/clubroot-brassicas/,
http://vegetablemdonline.ppath.cornell.edu/factsheets/Crucifers_Clubroot.htm and
https://catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/em9148.pdf
Clubroot disease cycle:
https://www.gov.mb.ca/agriculture/crops/plant-diseases/images/fac63s00a_sm.jpg
_P. brassicae_ taxonomy:
http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=214750
Information on _P. chrysocephalus_ beetle:
https://cropscience.bayer.co.uk/threats/pest-and-slugs/cabbage-stem-flea-beetle/
AHDB:
https://ahdb.org.uk/
- Mod.DHA]