Bacterial Diseases of Plants

bacterioses, plant diseases caused by bacteria. They do great harm to many agricultural crops, especially cotton, tobacco, tomatoes, potatoes, cabbage, and cucumbers. The diseases may be systemic (causing the death of the entire plant or individual parts thereof; they may appear on the roots [root rot] or in the vascular system [vascular disease]) or local (limited to infection of individual parts or organs of the plant and also appearing in parenchymatous tissues [parenchymatous diseases—rot, spots, blights]), or they may be of a mixed nature. Diseases involving neoplasms (tumors) occupy a special place.

The causative agents of bacterial plant diseases are mainly nonspore-forming bacteria from the families Mycobac-teriaceae, Pseudomonadaceae, and Bacteriaceae. They include polyphagous bacteria that attack many plant species, as well as specialized microorganisms that attack closely related plants of the same species or genus. Polyphagous bacteria cause the following widespread bacterioses: soft rot of potatoes, cabbage, onions, and, less commonly, of carrots, rustic tobacco, and tomatoes; and crown gall of fruit trees and grapes. Specialized bacteria cause bacterial spot of beans, bacteriosis of cucumbers, black spot and bacterial cancer of tomatoes, black rot of cabbage, wildfire of tobacco, black and basal bacterioses of wheat, bacterial blight of drupaceous fruit crops, fire blight of pears, bacterial blight of mulberry and citrus trees, ring rot and wire stem of potatoes, bacterial blight of cotton, striped bacteriosis of millet and barley, and other diseases.

The origin and development of bacterial plant diseases depend on the presence of an infectious principle and a susceptible plant, as well as on environmental factors which, if changed, may control the course of the infectious process. For example, bacteriosis of cucumbers occurs in greenhouses only if drops of moisture are present and the air temperature is between 19° and 24° C. Ventilating the greenhouse and raising the temperature can halt the development of the disease.

Bacteria penetrate into plants through various injuries and natural passages. For example, the causative agents of spot diseases enter through the leaf stomata; those of blight, through flower nectaries; and those of vessel bacterioses of the Cruciferae family, through water pores in the leaves. The pathogens can be transmitted with seeds (bacterial blight of cotton), with incompletely rotted residues of diseased plants, when caring for plants, upon inoculation, with air currents, by the splashing of rain, and by insects, mollusks, and nematodes.

Control measures include the treatment of seeds, disinfection of seedlings, slips, and soil in seed beds and hothouses; spraying growing plants with bactericides or antibiotics; destruction of residues of diseased plants; pruning of diseased shoots and disinfection of injured branches; destruction of diseased plants; correct alternation of crops on crop rotation fields; correct nutrient and irrigation regimes; and breeding of resistant varieties.