Pseudomonas spp.

These two bacteria Pseudomonas syringae pv. tabaci (Wild fire) and Pseudomonas syringae pv. angulata (Angular leaf spot) (identical for some plant pathologists) cause same types of small brown spots (figures 1-2). They have a moisty appearance and different shapes early in evolution (1-5 mm) then they turn brown to black due to necrosis (figure 3). The spots easily coalesce. These bacteria are difficult to see and require isolation on culture medium. 

Note that these two bacteria also have similar biological characteristics and similar control methods. Their symptoms often appear on many leaves randomly located on the plant, both in the nursery and the field. Plants affected by these two bacterial diseases usually show foci distribution in the field. In France, Pseudomonas syringae pv. tabaci has been reported. At a time, this bacterium was endemic in some production areas in France and caused considerable damage, both in nurseries and fields. This bacterial disease is rare, it has been observed only once in recent years, in Isère (France).

Another Pseudomonas seems to cause similar spots on tobacco in China. In fact Pseudomonas melleum (Johnson) Stapp. has been repeatedly reported in several regions of this country and particularly in Yunnan. The bacterium causes small brown spots surrounded by a yellow halo, both on the lower and intermediate tobacco leaves. It occurs especially after heavy rains and storms, or when plants are subjected to excess or lack of potassium. Control methods to fight it are identical to those recommended to control the two pathovars of Pseudomonas syringae.

Pseudomonas aeruginosa (Schroeter) Migula, a worldwide bacterium, has been  observed on tobacco only in the Philippines. It causes white, opaque leaf spots of a few millimeters in diameter, especially on lower leaves. These spots may coalesce, turn brown, be rather zoned and surrounded by a discrete yellow halo.

For further information, see the fact sheet of  Pseudomonas syringae pv tabaci.