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: February 15, 2008
Source: Australian Food News [edited]
<http://www.ausfoodnews.com.au/db/node/56881>

White blister, a damaging disease of brassica vegetables, was 1st detected in Queensland in 2005 on a broccoli farm at Gatton in the Lockyer Valley. Caused by the fungus _Albugo candida_, white blister appears as yellow-brown spots on the upper surface of leaves with small raised white blisters about 1-2 mm in diameter or pustules underneath. Swellings may also be found on roots, stems and flowers.
The swellings and pustules contain masses of white dusty spores.

The disease mainly occurs in cauliflower and broccoli and has been found in Tasmania, Victoria and New South Wales in the past few years. The disease causes the plants to distort and reduces the marketability of flower heads and the production of seeds.

Dr Elizabeth Minchinton from Victorian Department of Primary Industries (VICDPI) has researched white blister for several years under a national vegetable levy funded project. Horticulture organization Growcom invites brassica growers to attend a workshop to hear Dr Minchinton outline the results of her research and her recommendations for white blister management.

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[White blister (also called white rust) caused by the fungus _Albugo candida_ affects most plants of the brassica or crucifer family, including a range of cabbage crops, radishes and oilseed rape. There are several known races worldwide, each of which infects a limited range of brassica species. A common strain of the fungus is widely distributed throughout Australia and was known to occur in Queensland on Chinese cabbage and some cruciferous weeds like Shepherd's purse.
However, a new strain has been recently identified in the Lockyer Valley (a farming region between Brisbane and Toowoomba) which infects broccoli and cauliflower crops.

The fungus may cause both local and systemic symptoms. Early local symptoms of white blisters can only be seen on the underside of leaves. Later, circular leaf discolourations appear on the upper leaf surface corresponding to the blisters on the underside. These symptoms may continue to develop after harvest, reducing potential storage time. Systemic infections can cause abnormal growth and distortion of affected plants leading to a significant reduction in marketability of the vegetables and also affecting seed production.
Affected seedlings may be defoliated, which slows down their growth.
Swellings may be found on roots, stems, and flowers. The swellings and pustules contain masses of white spores.

Fungal development is favoured by high humidity and temperatures of 10-25 C. The pathogen can be spread by wind, water, seed, on plant material (for example seedlings for transplanting) and by mechanical means, including common insect pests. For example, diamond back moths (_Plutella xylostella_) carrying spores on their wings are thought to have been responsible for the spread of the disease to Tasmania when they were blown across by wind. Disease management includes clean planting material (hot water treatment may be effective for seed disinfestation), cultural practices (such as reduction of free moisture, removal of weed reservoirs) and fungicides. Germplasm with varying levels of resistance or tolerance to different white blister strains is available, and new crop varieties are being developed.

The Queensland brassica vegetable industry is estimated at AUD 30 million [USD 27.5 million], which is about 20 percent of the Australian industry. Crops are located primarily in the cooler southern regions of Queensland, including the Lockyer Valley.
Cabbage, cauliflower and broccoli are the major crops, with smaller quantities of Chinese cabbage and other Asian vegetables grown.

Maps
Australia:
<http://www.ga.gov.au/image_cache/GA4073.jpg> and <http://healthmap.org/promed?v=-25.7,134.5,4>
Queensland:
<http://www.ozhorizons.com.au/qld/map.gif>

Pictures
White blister on brassicas:
<http://www.shootgardening.co.uk/uploaded/images/plant_disease_20051204160354.jpg>
and
<http://www.hri.ac.uk/site2/research/path/blister.jpg>

Links
Information on white blister of brassicas:
<http://www.growcom.com.au/_uploads/22331white_blister_handout.pdf>
White blister and other foliar fungal pathogens of brassicas:
<http://www.hri.ac.uk/site2/research/path/pathogen.htm>
_A. candida_ taxonomy:
<http://www.indexfungorum.org/Names/SynSpecies.asp?RecordID=122113>
VICDPI white blister research:
<http://www.dpi.vic.gov.au/dpi/nrensr.nsf/LinkView/
26575B47D2AF60CDCA256F820000432C827C907D43162D6BCA256F8C007F5E21#crucifer>
Growcom:
<http://www.growcom.com.au/home/default.asp>
- Mod.DHA]