Pectobacterium spp.

During periods of high humidity, bacteria of the genus Pectobacterium (formerly Erwinia) can be observed on tobacco leaves causing a black rot starting from the veins (figure 1). Then, through peduncles, they move in and cover the stem, which demonstrate  limited splits. Later, if the humidity persists, the rot extends to the cortex (figure 2) and pith (figure 3), which turn soft, brown to black.
 
For further information on these parasitic bacteria of tobacco, see the fact sheet of Pectobacterium spp ..