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Plant Pathology Guidelines for Master Gardeners

Contact: Dr. Richard Raid

Specific Symptoms & Signs Of Bacterial Diseases

So far, we have talked primarily about signs of fungi that cause plant disease. But we now come to specific symptoms and signs associated with bacterial diseases. While fungi cause about 85% of plant diseases, bacteria cause some that are the most difficult to control. This is especially true in Florida, because bacterial diseases are most intense in warm, humid, rainy environments.

Figure 48

This is the underside of a tomato leaf. The symptom you see is called watersoaking. The spots look like drops of water and are caused by water accumulation in tissues as a direct result of bacterial attack. Watersoaking is a very common symptom of many bacterial diseases. It occurs early in the development of bacterial diseases.

Figure 40: watersoaking due to bacterial attack

Figure 49

This is an image of a much later stage in the development of a bacterial disease (bacterial spot of malanga). Now we are at the stage where bacterial lesions are often described as "greasy looking". There just is not a better way to describe the late stage of many bacterial diseases.

Figure 40: bacterial spot

Figure 50

A sign of the bacterial spot of malanga pathogen is evident here. It is the bacterial "ooze" or exudate seen coming out of water soaked lesions (see arrows). The "ooze" forms in the readily seen droplets. These droplets are a sign of the pathogen, being composed mostly of bacterial cells.

Figure 40: bacterial ooze

Figure 51

Here is another sign of a bacterial disease. It is bacterial streaming. This tomato plant was wilted. To properly diagnose bacterial wilt, a horizontal cut was made in the lower stem and the cut stem immersed partway in water. Within a few minutes, copious amounts of bacterial exudate emerged from the cut end, forming the white streamers you see in the water. This only occurs with bacterial wilt and not with any other type of pathogen or abiotic cause. It is virtually foolproof and should be in the diagnostic arsenal of every master gardener.

Figure 40: bacterial streaming

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