Osmotically dependent formation of charcoal rot Macrophomina phaseolina (Tassi) Goid in the tissues of cultivated and wild species of soybean (report i)

The studies have shown that the fungus Macrophomina phaseolina penetrates soybean plants during germination, first in intercellular pectin layers, then in vascular system of host plants. Due to the smaller diameter of the hyphae in comparison with an internal diameter of vessels, the fungus does not cause any damage to the vascular cells and do not prevent intake of water and nutrients from the root system. The hypothesis of osmotically dependent formation of microsclerotia in ontogenesis of soybean was suggested based on the gradient of osmotic pressure inside and outside the mycelium of the fungus. The model experiment on different variety samples of 4 different soybean species has shown that harmfulness of charcoal rot is detected under the development of water stress in the soil and increase of the concentration of the cell juice in the tissues of a host plant. In addition, the mass formation of microsclerotia is observed in conducting vessels that is fully covering the inner opening of the soybean vascular system.