An important disease of cabbages in the tropical highlands
Source: Poland Posts English [summ. Mod.DHA, edited]
Clubroot (_Plasmodiophora brassicae_) is becoming more and more dangerous in Poland. The threat is increased by the fact that in large commercial farms oilseed rape is grown in the same field every 2-3 years, in rotation with cereals, which is too short.
The disease had already occurred before in the country but did not cause large economic losses due to lower intensity of cultivation. A problem appeared in the early 2000s when the area under oilseed rape increased and cultivation technology changed.
The 1st outbreaks of the disease were observed in eastern regions of Poland, but now it occurs in almost the entire country. Incidence is usually higher in areas with intensive cultivation. The acreage at risk of clubroot is estimated at over 200 000 hectares.
[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, as mentioned above, crop rotation of just a few years will not control the disease.) 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 experimental fumigation treatments have been shown to be effective (see 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.
http://www.lib.utexas.edu/maps/europe/poland_pol00.jpg (with provinces):
Clubroot symptoms on roots of oilseed rape:
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:
http://www.omafra.gov.on.ca/IPM/images/brassica/diseases/clubroot_brussels_zoom.jpg (affected field)
Information on clubroot of oilseed rape:
https://doi.org/10.1111/ppa.12949 (crop rotation)
Information on clubroot on crucifer crops:
Clubroot disease cycle:
_P. brassicae_ taxonomy: