Xanthomonas campestris pv. Vesicatoria

Xanthomonas campestris pv. vesicatora is a bacterium that causes bacterial leaf spot (BLS) on peppers and tomatoes. It is a gram-negative and rod-shaped. It causes symptoms throughout the above-ground portion of the plant including leaf spots, fruit spots and stem cankers. Since this bacterium cannot live in soil for more than a few weeks and survives as inoculum on plant debris, removal of dead plant material and chemical applications to living plants are considered effective control mechanisms.

Classification of the Xanthomonas species that cause bacterial leaf spot is currently in flux. Up until a few years ago, bacterial leaf spot causing Xanthomonads were divided into four groups, A, B, C, and D, based on pathogenicity and physiological characteristics. As of 2004 though, a new classification system was proposed that would change the name of X. campestris pv vesicatoria to X. euvesicatoria (previously group A), and recognized the species X. vesicatoria (group B), X. perforans (group C), and X. gardneri (group D). These changes have yet to be fully recognized, so this article will include information on all groups (A, B, C, and D) of bacterial leaf spot causing Xanthomonads.

The principal hosts of BLS causing Xanthomonads are tomatoes and peppers, though other incidental hosts have been recorded, mainly weeds. Group A contains most of the pepper infecting strains, though some strains from groups B and D have also been reported to cause symptoms on pepper plants. Strains from all four groups have been isolated from infected tomato plants. Some strains are able to infect both pepper and tomato plants, while some can only infect one of these plants.

Bacterial leaf spot affects all above ground parts of the plant:

Pepper fruit do not frequently show symptoms, largely due to the fact that developing fruit is often dropped if the pepper plant is infected. Fruit that isn’t dropped can also be damaged and misshapen due to increased sun exposure after plants drop infected leaves. When symptoms on the fruit do occur, they start as pale-green, water-soaked areas and eventually become raised, brown, and rough.

Bacterial colonization of intracellular spaces induces the macroscopically visible symptoms including water-soaked lesions on the leaves that later become necrotic . Though these spots start out at about .24 inches in diameter, they increase in size and number, eventually causing the leaves to drop off. Plants can drop 50-100% of their foliage. BLS can also affect the stems of plants, leading to elongated, raised, light-brown cankers, less than .25 inch long. (5) Defoliation occurs more commonly in pepper plants than tomatoes, so tomato plants with bacterial leaf spot often have a scorched appearance due to their diseased leaves.

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