Pratylenchus spp.

(brown root rot of tobacco)

Migratory endoparasitic nematodes "root lesion nematodes" (figure 1) penetrate into root cortex and gradually destroy many cells, inducing abundant reddish-brown to black lesions on roots (figures 2-4). These are similar to those induced by T. basicola, except for the presence of corky sleeves on roots. Adults, larvae and eggs are often visible in cortex cells (figure 5), they can confirm the diagnosis.
 
Identification of these nematodes on tobacco is rather recent. Observations of black rot on roots of tobacco varieties resistant to T. basicola has led to the detection of these nematodes  and eliminate the possibility of the existence of a pathotype of this fungus able to circumvent resistance. It seems obvious that these nematodes have existed on tobacco for several years, but their symptoms have certainly been confused with those of black root rot. Two species of Pratylenchus on tobacco have been observed in France mainly in the Southeast and the Southwest: Pratylenchus crenatus and Pratylenchus penetrans.
 
For further information on Pratylenchus, please see the fact sheet of Migratory endoparasitic nematode