Final diagnosis


Black root rot (Thielaviopsis basicola, Chalara elegans)

These young seedlings show a characteristic black rot in their root system. <i><b>Thielaviopsis basicola</b></i>
Some completely rotten root systems have totally disappeared, the fungus also attacks the part of the stem in the soil causing longitudinal black cankers. <i><b>Thielaviopsis basicola</b></i>
The root system of the tobacco is reduced and a black rot can been seen on a few remaining roots, some chlorotic and necrotic lesions are also observed on lamina. <i>Thielaviopsis basicola </i>(black root rot).
The lower leaves of this young tobacco plant are slightly wilted, chlorotic and more or less necrotic; they are infected by <i><b>Thielaviopsis basicola</b></i> (black rot)
<i>Thielaviopsis basicola </i>(<i>Chalara elegans </i>, black root rot): a) during severe attacks, the entire root system can be affected; b) the entirely rotten cortex (Co) has disappeared when the roots are pulled out, only the central cylinder (Cc) remains entangled in some areas.
Lesions are more localised on large roots; one can observe sleeves of various sizes, sometimes brown and wet, frequently corky and cracked, <i><b>Thielaviopsis basicola </b></i>(<i>Chalara elegans</i>, black root rot)
<i><b>Thielaviopsis basicola</b></i>
The entire rotten cortex (Co) disappeared when the roots were pulled out, only the central cylinder (Cc) remains in some areas. <i>Thielaviopsis basicola </i>(<i>Chalara elegans</i>, black root rot)
One can observe several corky 'sleeves' on this root system. <i><b>Thielaviopsis basicola</b></i> (black rot)
A black, suberised 'sleeve' on tobacco roots. <i><b>Thielaviopsis basicola</b></i> (black rot)
A detail of a 'sleeve' caused by <i><b>Thielaviopsis basicola</b></i> (black rot) on tobacco roots.
<i>Thielaviopsis basicola</i> produces multicellular and brown chlamydospores inside and on the surface of root tissues colonised by the fungus.