Fungal Diseases of Plants

diseases of plants caused by phytopathogenic fungi (parasites and semiparasites).

Fungal diseases are both more widespread and more destructive than the other diseases of plants; they diminish harvests and decrease crop quality significantly, and they shorten the productive life span of fruit trees and berry fields.

Under the influence of pathogenic fungi, pathological processes arise in plants that are accompanied by destruction of the structure and physiological functions of the plant or its parts. For example, excrescenses and calluses form, and there are changes in respiration, assimilation, and enzyme activity; growth and development are impaired, the affected tissues die. Outwardly, these diseases are characterized by some sort of damage (localized or general). Local affections, covering small parts of the plant or its individual organs, include blights (leaf spot of beets, apple scab, and pear scab), fungal blooms (powdery mildews), and ulcers; and blisters (plant rusts). General affections include plant wilt.

The fungal diseases of plants are passed on by seeds, tubers, heads, roots, seedlings, and cuttings. The infection can survive in postharvesting debris and in the soil; it can be spread by the wind, by drops of rain, by animals and man, and by packaging, machines, and equipment. Pathogenic fungi can penetrate plant tissue through stomata (as in grape mildew), through water pores, lenticles, epidermal cells, and the cuticle (as in cabbage clubroot and potato cancer), through wounds caused by hail (as in blister smut of corn), through sun scorch and frost cracks (as in apple-tree cancer), and through cracks. Many insects that damage plants open the gates to infection, at the same time often introducing the pathogens.

The intensity of development of the disease depends on environmental conditions, which affect plant and parasite alike, as well as the interaction between them and the course of the infection. For example, adding lime to the soil increases alkalinity and reduces incidence of cabbage clubroot. When the soil is too low in boron, beets often become infected with core rot. Addition only of nitrogen to the soil when phosphorus and potassium are low increases infection of grasses with rust and of potato with late blight. Relatively low temperature and high soil moisture after planting beets promotes undesirable sprouts and their infection with black root.

To protect plants from fungal diseases, a complex of ag-rotechnical and chemical measures are used. The former are aimed at the restriction and elimination of the source of infection on seeds and in the soil, the alteration of the conditions of plant cultivation in directions that are favorable to them and unfavorable to parasites; and the maintenance and increase of plant resistance. These measures include the isolation and cultivation of resistant varieties, rational crop rotation, the proper treatment and care of the soil during the growing season, proper application of the various kinds of fertilizers, and observance of the optimal dates of sowing and harvesting.

The chemical countermeasures consist of processing seeds as well as growing plants with fungicides, as well as disinfecting agricultural buildings, storehouses, soil, and other possible sites for infection.