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October 11, 2007
Source: BBC News [edited]
<http://news.bbc.co.uk/1/hi/england/7039948.stm>

Root vegetables could soon be more expensive and in short supply as wet weather spread disease through crops. Cavity spot disease has hit carrots and parsnips while onions suffered slow growth. The crops go to food processors in Cambridgeshire, Norfolk, and Suffolk.

Wholesalers are preparing for shortages in the late autumn at harvest time. Producer Simon Pearce from Setchey in Norfolk, said yields were down as costs had risen, so everyone in the industry would lose money. "About 15 percent of the crop is affected by disease as far as we can see and this will mean shortages," he said.

"Also, everybody has to make a living and this includes producers and retailers who have all experienced rises in wage and energy costs as well. Anyone involved in producing, transporting, or distributing these crops will have higher costs and someone will have to pay the extra if the sector is to survive. It has to be said that this is a tough industry at present and it is made worse when climatic conditions go against us. There has to be some kind of inflation of prices and many people are talking about a 20 percent price increase this year [2007]," he said.

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[Cavity spot is a disfiguring disease of carrots and related root crops such as parsnips. Tonnage of the crop is not reduced but the cavities make the roots unmarketable. Roots are rejected at grading with one or 2 visible lesions, and when disease incidence passes a relatively low threshold it becomes uneconomic to harvest crops. The disease is caused by species of soil fungi belonging to the genus _Pythium_. _P. violae_ is reported to be the primary cause of cavity spot in European temperate areas. It is slow-growing and is favoured by cool soil temperatures. It grows well in soil during the winter months devastating early-sown crops. Disease outbreaks may also occur later in the season after prolonged rain. Symptoms are elliptical to irregularly shaped, depressed lesions, which tend to be more abundant on the upper third of the root. They generally enlarge as roots mature. _P. violae_ can also affect lucerne (alfalfa). Infections of other hosts such as celery, black eye beans, wheat, cucumber, and beets may not result in symptoms. The fungi can be dispersed by water and mechanical means.

Hosts are generally more susceptible when the conditions are unfavourable for plant growth. A diagnostic test for prediction of likely risk of cavity spot in commercial fields has been developed in the UK. Control measures include growing tolerant host varieties, cultural practices, and crop rotation. Chemicals are used to control the disease in some parts of the world, however this is not always reliable.

_Pythium_ species cause damping off and root rots in a range of host plants, including onion. It is not clear, if this report suggests that the problem on onions is due to another _Pythium_ species, or whether the onion crops are held back due to other problems.

Map of the UK:
<http://www.lib.utexas.edu/maps/europe/united_kingdom.gif> and <http://healthmap.org/promed?v=54.5,-2,5>

Pictures of symptoms on carrot:
<http://www.hri.ac.uk/site2/research/path/pythium/cavspot2.jpg> and <http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/prm7736/$FILE/car_csp48_l.jpg>

Links
Disease information:
<http://www1.agric.gov.ab.ca/$department/deptdocs.nsf/all/prm7736> and <http://www.agric.wa.gov.au/content/PW/PH/DIS/VEG/F02999.PDF>
Cavity spot and other _Pythium_ diseases in the UK:
<http://www.hri.ac.uk/site2/research/path/pythium/pythium.htm>
Factors influencing cavity spot development:
<http://www.apsnet.org/pd/SEARCH/1991/PD_75_519.asp>
_P. violae_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=290365>
_Pythium_ species affecting onion:
<http://www.apsnet.org/online/common/comment/onion.asp>
Diseases caused by _Pythium_ species:
<http://www.rbgsyd.nsw.gov.au/science/hot_science_topics/Soilborne_plant_diseases/Vietnam_template3/Pythium>
List of _Pythium_ species via:
<http://www.indexfungorum.org/Names/Names.asp>. - Mod.DHA

[see also in the archive:
Fungal disease, cardamom - India (Kerala) 20071011.3339
2004
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Pythium leaf blight, lettuce - Spain (Asturias) 20041221.3363 Pythium irregulare, lentil - USA (WA): first report 20040219.0533
2003
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Phytophthora capsici, tomato - South Africa 20031130.2971
2002
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Pythium sp., lettuce - South Africa 20021005.5473 2000
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Vine decline, watermelon - USA (Indiana) 20000901.1475]

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