Rhizoctonia solani and Pectobacterium sp.

(Sore shin and Black leg)

Damage by Rhizoctonia solani (sore shin) can always be observed in tobacco nurseries, especially in the traditional ones. It is a common soilborne fungus, particularly in soils that have had several times tobacco or other crops, namely vegetables. It can give rise to:

- damping-off following the stem  rot at the soil line which rapidly expands on the petioles and leaves (figure 1);
- corky and canker lesions in these same areas in older seedlings (figure 2.)

Note that the presence of brown mycelium on the altered tissues or adjacent ones allows us to identify the fungus with certainty. 
 
In tobacco nurseries where plant density is important and where the seedlings have particularly succulent tissues, it is quite common to see the development of black rot in stems. In general, it is due to the  bacterium, Pectobacterium sp. which, at first colonises  the leaves that are in contact with the soil or senescent leaves and then moves to the stem and causes a rather characteristic wet and black rot, known as black leg of tobacco seedling (figures 4 and 5).
 
Wounds of all types, including those made during clipping, are also very prone to contaminations.
 
For a better understanding of the biology of these pests, please see the related fact sheets of Rhizoctonia solani and Pectobacterium spp.