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Bacterial Leafspot

Bacterial Leafspot is a bacterial disease on plants caused by the Xanthomonas vesicatoria bacteria. Xanthomonas campestris pv. vesicatora is a bacterium that causes bacterial leafspot (BLS) on peppers and tomatoes.  It causes symptoms throughout the above-ground portion of the plant including leaf spots, fruit spots and stem cankers. It is a gram-negative and rod-shaped. (Gram negative bacteria are so described because they have an extra layer of cell wall around them which prevents the cell wall from being dyed during laboratory tests). 
Xanthamonas campestris pv. Vesicatoria survives on tomato and pepper plants, seeds, and debris from infected plants as it cannot live in the soil for more than a few weeks. If the bacterium survives on debris, it may infect healthy plants through stomata (spores on the leaves) as well as wounds on leaves and fruit. It is spread by direct contact of plants with debris, human movement of the bacteria from debris to plants, and can easily travel from debris to healthy plants through saturated soils via water movement. Once infected, plants begin to develop lesions on the leaves as well as fruit, becoming inoculum (pathogen spores that causes infection) sources. 

Curbing this disease therefore requires that all infected plant material should be destroyed through burning or removed as far as possible from the infected area. Composting infected material is not advised, neither is burying it. Soil should be turned and worked over as thoroughly as possible in infected areas.

File:Bacterial leaf spot symptoms.jpg
Image Credit: wikipedia.org 

bacterial spot (Xanthomonas vesicatoria ) on pepper (Capsicum spp. ) - 5362922
Leaf of a pepper plant showing signs and symptoms of bacterial leaf spot (Xanthomonas vesicatoria).
Howard F. Schwartz, Colorado State University, Bugwood.org
Image Credits: Howard F. Schwartz, Colorado State University, Bugwood.org

bacterial spot (Xanthomonas vesicatoria ) on sweet pepper (Capsicum annuum ) - 5362699
Bell pepper showing signs of infection with Xanthomonas vesicatoria 
Image Credits: Howard F. Schwartz, Colorado State University, Bugwood.org

Basic Facts of Plant Diseases
Many fungi, bacteria, viruses, and nematodes are plant pathogens. A plant pathogen is an organism or agent that incites infectious disease. A distinct sequence of events occurs in the development of a plant disease; these events are known as the disease cycle. The main stages of events comprising the disease cycle include the following:
- production and dissemination of the primary inoculum,
- primary infection,
- growth and developement of the pathogen,
- secondary infection, 
- overwintering.
Pepper Disease and Pest Mangement Programme - Agriculture and Natural Resources, University of California