Final diagnosis


Black shank (Phytophthora nicotianae)

Several lower leaves of this plant have turned yellow and wilted due to infection by <b><i>Phytophthora nicotianae</i></b> (black shank)
A collar canker <b><i>Phytophthora nicotianae</i></b> has destroyed these tobacco plants, they have wilted, yellowed and dried up.
A canker developing at the base of this tobacco plant. <b><i>Phytophthora nicotianae</i></b>
In addition to root browning, also the stem is browning near the soil line <b><i>Phytophthora nicotianae</i></b> (black shank)
A brownish canker girdles the stem base of this tobacco plant. <b><i>Phytophthora nicotianae</i></b>
Stem lesion (shank), brown at the beginning, eventually will turn black (origin of the name black shank). This lesion grows sometimes 30 cm above ground (black shank). <i><b>Phytophthora nicotianae</i></b>
The pith not only dries up but also turns brown to black. <i><b>Phytophthora nicotianae</i></b> (black shank)
In some cases it may be interesting to check the conditions of the pith as well. It is sometimes altered and/or retracted, looking like a stack of discs. <i><b>Phytophthora nicotianae</i></b>
A longitudinal cut of the stem reveals that the pith is brown to black in colour, shrinking in some places, appearing to form stacked disks (pile of plates). <i><b>Phytophthora nicotianae</i></b> (anc. <i>P. parasitica </i>var. <i>nicotianae</i></b>)
Two papillate sporangia filled with mobile zoospores. <i><b>Phytophthora nicotianae </b></i>(black shank), a heterothallic chromist, produces also spherical chlamydospores and thick-walled oospores.