Final diagnosis


Blue mould, Downy mildew (Peronospora hyoscyami f.sp. tabacina)

The very first spots of blue mould are visible on the upperside of this tobacco leaf. <i><b>Peronospora tabacina</b></i>.
Yellow spots diffused on the upper side of the lamina. <b><i>Peronospora hyoscyami </i></b>f.sp. tabacina (tobacco blue mould, downy mildew)
Yellow interveinal spots on a Virginia type tobacco leaf. <b><i>Peronospora hyoscyami</i> f. sp.<i> tabacina</i></b> (tobacco blue mould, downy mildew)
Several diffused yellow spots on a tobacco leaf. <b><i>Peronospora hyoscyami</i> f.sp. <i>tabacina</i></b> (tobacco blue mould, downy mildew)
Finally severely attacked leaves are covered by necrotic lesions. <i>Peronospora hyoscyami</i> f.sp. <i>tabacina</i>
The yellow spots become necrotic and turn to light brown. <i>Peronospora hyoscyami</i> f.sp. <i>tabacina</i>
On the lower surface of the leaf one can observe a discrete bluish felting corresponding to spots. <b><i>Peronospora hyoscyami</i> f. sp. <i>tabacina</i></b> (downy mildew)
First visible spots of tobacco blue mould on the lower surface of the leaf. <i><b>Peronospora tabacina</b></i>
Characteristic spots on the underside of leaves caused by mildew. <i><b>Peronospora hyoscyami</i> f.sp. <i>tabacina</b></i> (downy mildew)
When the conditions are highly favorable the bluish felting can be seen ; it sometimes covers almost the whole underneath side of the leaf. <b><i>Peronospora hyoscyami</i> f. sp. <i>tabacina</i></b> (tobacco blue mould, downy mildew)
The presence of mildew in the vessels results in reduced plant growth, young leaves are often distorted, many midribs turn yellow and become necrotic. <i>Peronospora hyoscyami f. sp. tabacina</i> (tobacco blue mould, downy mildew)
Necrotic lesions are also visible at the inflorescence level. <b><i>Peronospora hyoscyami</i> f. sp. <i>tabacina</i> </b>(tobacco blue mould, downy mildew)
The stem shows longitudinal browning on some sectors and sometimes even elongated canker alterations. <b><i>Peronospora hyoscyami</i> f. sp. <i>tabacina</i></b> (tobacco blue mould, downy mildew)
By a longitudinal cut of the stem one can observe that the vessels and sometimes even the adjacent tissues (pith) demonstrate browning. <b><i>Peronospora hyoscyami</i> f. sp. <i>tabacina</i></b> (tobacco blue mould, downy mildew)
<b><i>Peronospora hyoscyami</i> f. sp. <i>tabacina</i></b> (tobacco blue mould, downy mildew) produces mainly arbuscular conidiophores bearing lemon-shaped sporangia.
Brown oospores can be observed in altered tissues, they ensure the sexual reproduction of the fungus. <b><i>Peronospora hyoscyami</i> f. sp. <i>tabacina</i></b> (tobacco blue mould, downy mildew)