The vegetative body of actinomycetes has a very thin branching mycelium, resembling the mycelium of some fungi. They are similar to fungi by the appearance of radiant colonies on dense nutrient media. But unlike fungi, the mycelium of actinomycetes does not have partitions; cells do not have a pronounced nucleus, which is how they resemble the nuclear apparatus of bacteria. Also, some actinomycetes are able to produce antibiotics.
Actinomycetes are now taxonomically classified as bacteria, but indeed they continue to occupy an intermediate position between bacteria and fungi.
Actinomycetes reproduce by pieces of aerial mycelium, spore-bearing branches, and spores. Spores are formed by the breakup of the spore-bearing branch into separate sections by transverse partitions (segmentation) or by the disintegration of the internal contents of the spore-bearing branches without the formation of transverse partitions (fragmentation). The spores germinate into a sprout or several thin sprouts.
According to their biological characteristics, the majority of actinomycetes are typical saprophytes, widely distributed in nature: in the soil, on straw, and in manure. Many of them are bacterial and fungal antagonists and are used to make antibiotics. Some species of actinomycetes have adapted to a parasitic existence on plants and animals, causing diseases – actinomycosis.
According to the structure and development of vegetative organs and the method of their fruiting, all actinomycetes are divided into orders, families and genera with a different number of species. Among phytopathogenic actinomycetes, species of the genus Streptomyces, which cause scab in plants, are of the greatest interest. The most famous are the common scab of potato tubers and the scab of beet roots.
Potato scab S. scabies develops on tubers during the growing season of potatoes. Cracks, small warts appear at the sites of infection, corking of the affected tissue occurs, and ulcers form. With severe scab damage, the ulcers merge, and the entire tuber is covered with a scab. Actinomycetes, which cause common tuber scab, accumulate in the soil and remain on the affected tubers, in ulcers, cracks.
In the protection of crops from actinomycosis, techniques that prevent the accumulation of phytopathogenic species in the soil are of great importance. Among the measures that regulate the quantitative composition of actinomycetes, the following are primarily used: crop rotation with the removal of the affected crop from the field for several years and alternation of crops in crop rotation, which reduce the amount of infection in the soil due to the effect of root secretions on its microflora.
Tags: Actinomycetes, Crop rotation, Phytopathogenic, Streptomyces, Soil microflora, Agricultural techniques, Biological control agents.
