FUNGAL PATHOGENIC COMPLEX OF THE ROOT ZONE OF CULTIVATED SOYBEAN PLANTS

Abstract

Objective. To characterize the fungal pathogenic complex of the root zone of cultivated soybean plants grown on sod-medium podzolic soil, to identify the most harmful pathogens of root diseases. Methods. Phytopathogenic micromycetes were isolated from affected soybean plants. For this, segments of plant material (roots, seeds, leaf blade) (3–5 mm) were thoroughly washed for 15 min under running water, their surface was sterilized with 96 % ethyl alcohol for 1 min, washed twice with sterile water and placed in Petri dishes on 4 % wort agar with 250 ppm streptomycin and placed in a thermostat (26 °C). At Day 4, isolates were obtained on wort agar and grown for 14 days at 26 °C. Confirmation of the pathogenicity of the selected isolates was carried out in a sterile vegetative experiment on Strive variety soybean plants. To do this, 1 dm3 glasses were filled with a substrate containing 50 g of consolidated vermiculite and 200 g of water and sterilized for 1 hour at 1.5 atm. Healthy soybean seeds were pre-selected, thoroughly washed under running water and sprouted in a humid chamber for 2 days so that the seedlings had a root length of 1–2 cm and carefully washed in sterile tap water. Ten soybean sprouts were placed in each glass and 3 mL of an aqueous spore-mycelial mixture of selected isolates (experiment) or 3 mL of sterile water (control) were added. At Day 14, the plants were removed, thoroughly and carefully washed, the number of affected plants was counted (% prevalence) and the dry matter of roots and shoots was measured. Results. A total of 16 strains of fungi, the causative agents of root diseases, were isolated in pure culture from roots, seeds and leaf plates of affected soybean plants. The isolated pathogens belonged to the genera Fusarium Link:Fr, Alternaria (Fr.) Keissler, Verticillium Nees. The phytopathogenic effect of fungi of the genus Verticillium isolated from the washed roots of soybean plants was insignificant. Fusarium was represented by F. oxysporum, F. solani, F. moniliforme var. lactis, F. gibbosum, among which F. gibbosum exerted the greatest phytopathogenic effect. The isolated F. gibbosum C4 affects seedlings first. The roots of the affected plants develop poorly, the plants are easily pulled out and lag behind in growth and development. Among the selected Alternaria strains, A. consortiale C8 which was characterized by rapid growth, turned out to be the most harmful. A. consortiale C8 first affects seedlings, then appears on other parts of plants: roots, stems, leaves. On soybean leaves, the first sign of alternaria leaf spots is dark brown spots of various sizes and shapes, the leaves wither and die. Affected plants lag behind in growth. Infection of soybean plants by phytopathogenic fungi leads to a decrease in the content of dry matter both in the roots and in the aboveground mass of the plants. In the case of F. gibbosum C4 infection, the content of dry matter in the roots decreased by 27 %, in the aboveground mass of plants — by 19 %. Infection with A. consortiale C8 led to a decrease in dry matter by 29 % and 27 %, respectively. Conclusion. The fungal pathogenic complex in soybean crops consisted of representatives of the Objective. To characterize the fungal pathogenic complex of the root zone of cultivated soybean plants grown on sod-medium podzolic soil, to identify the most harmful pathogens of root diseases. Methods. Phytopathogenic micromycetes were isolated from affected soybean plants. For this, segments of plant material (roots, seeds, leaf blade) (3–5 mm) were thoroughly washed for 15 min under running water, their surface was sterilized with 96 % ethyl alcohol for 1 min, washed twice with sterile water and placed in Petri dishes on 4 % wort agar with 250 ppm streptomycin and placed in a thermostat (26 °C). At Day 4, isolates were obtained on wort agar and grown for 14 days at 26 °C. Confirmation of the pathogenicity of the selected isolates was carried out in a sterile vegetative experiment on Strive variety soybean plants. To do this, 1 dm3 glasses were filled with a substrate containing 50 g of consolidated vermiculite and 200 g of water and sterilized for 1 hour at 1.5 atm. Healthy soybean seeds were pre-selected, thoroughly washed under running water and sprouted in a humid chamber for 2 days so that the seedlings had a root length of 1–2 cm and carefully washed in sterile tap water. Ten soybean sprouts were placed in each glass and 3 mL of an aqueous spore-mycelial mixture of selected isolates (experiment) or 3 mL of sterile water (control) were added. At Day 14, the plants were removed, thoroughly and carefully washed, the number of affected plants was counted (% prevalence) and the dry matter of roots and shoots was measured. Results. A total of 16 strains of fungi, the causative agents of root diseases, were isolated in pure culture from roots, seeds and leaf plates of affected soybean plants. The isolated pathogens belonged to the genera Fusarium Link:Fr, Alternaria (Fr.) Keissler, Verticillium Nees. The phytopathogenic effect of fungi of the genus Verticillium isolated from the washed roots of soybean plants was insignificant. Fusarium was represented by F. oxysporum, F. solani, F. moniliforme var. lactis, F. gibbosum, among which F. gibbosum exerted the greatest phytopathogenic effect. The isolated F. gibbosum C4 affects seedlings first. The roots of the affected plants develop poorly, the plants are easily pulled out and lag behind in growth and development. Among the selected Alternaria strains, A. consortiale C8 which was characterized by rapid growth, turned out to be the most harmful. A. consortiale C8 first affects seedlings, then appears on other parts of plants: roots, stems, leaves. On soybean leaves, the first sign of alternaria leaf spots is dark brown spots of various sizes and shapes, the leaves wither and die. Affected plants lag behind in growth. Infection of soybean plants by phytopathogenic fungi leads to a decrease in the content of dry matter both in the roots and in the aboveground mass of the plants. In the case of F. gibbosum C4 infection, the content of dry matter in the roots decreased by 27 %, in the aboveground mass of plants — by 19 %. Infection with A. consortiale C8 led to a decrease in dry matter by 29 % and 27 %, respectively. Conclusion. The fungal pathogenic complex in soybean crops consisted of representatives of the