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Peronospora hyoscyami f. sp. tabacina

(blue mould, downy mildew)

Farmers and technicians fear the attacks of mildew. They recognise rather well the symptoms caused by Peronospora hyoscyami f.sp. tabacina. This stramenopile is an obligate parasite, which causes yellow spots on leaves which rather quickly become necrotic (figures 1-3). By a careful observation on the underside of the leaf one can distinguish a bluish mildew gradually covering the spots (figure 4). This is very characteristic of the disease and gives the origin of its English name "blue mould".
 
Note that Peronospora hyoscyami f.sp. tabacina is also responsible for systemic infections, which means that it colonises the vascular system of plants. This systemic infection results in growth reduction, young leaves are deformed and their veins become yellow and necrotic (figure 5). The presence of this stramenopile in the vessels causes longitudinal brown discoloration  or even small cankers on the stem (figure 6). This disease is fairly easily identified. Considering how dangerous it is to the crop, its early identification is important so that the necessary protection methods are implemented as quickly as possible.
 

For more details, please see the fact sheet of Peronospora hyoscyami f.sp. tabacina.

Last change : 04/11/13
  • Author :
  • D Blancard (INRAe)
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Figure 1
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Figure 2
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Figure 3
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Figure 4
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Figure 5
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Figure 6