The influence of nutrient media and temperature on the growth of Sclerotinia sclerotiorum, the causative agent of white mold of sunflower

Purpose. To determine the influence of nutrient media and different temperature regimes on the growth and development of the fungus Sclerotinia sclerotiorum, which is the causative agent of white mold of sunflower. Methods. The study was conducted in the laboratory of “Mycology and Phytopathology” of the Department of Phytopathology of the National University of Life and Environmental Sciences of Ukraine. The object of the study was the fungus S. sclerotiorum, isolated from affected sunflower plants selected in the Kyiv region. The extraction of the micromycete was carried out using a biological method. The radial growth rate of the mycelium of S. sclerotiorum was studied on agarized nutrient media that included lupine, bean, carrot, oat, soybean, corn, Chapek, pea and potato-glucose agar. The effect of temperature on the growth of the fungus was studied at 5, 10, 15, 20, 25 and 30 °C. Every 24 hours, the radius of the colonies was measured, and the time of the onset of sclerotia formation was also recorded. Results. All nutrient media promoted the mycelial growth of the fungus S. sclerotiorum. On the fourth day of incubation, the radius of the micromycete colonies on the studied media ranged between 20.4 and 45.0 mm. The most intensive mycelial growth was observed on potato-glucose agar (45.0 mm) and Čapek's medium (41.5 mm). On other substrates, this indicator was as follows: soybean – 20.4 mm, corn – 21.5 mm, oat – 23.3 mm, lupine – 25.7 mm, pea – 28.2 mm, carrot – 29.5 mm and bean – 32.2 mm. The pathogen was characterized by mycelial growth in the temperature range from 5 to 25 °C. The optimum temperature was 20–25 °C. Sclerotia production occurred at temperature conditions of 5–25 °C. At the same time, an increase in temperature from 15 to 25 °C accelerated the onset of sclerotia formation, while a decrease to 5–10 °C slowed down this process. Conclusions. It was found that the optimal nutrient medium for in vitro cultivation of the causative agent of white mold of sunflower (S. sclerotiorum) is potato-glucose agar, which provides the highest growth rate of the pathogen's mycelium. The temperature from 20 to 25 °C was optimal for the vegetative growth of the fungus and the production of sclerotia. The obtained research results should be used to obtain the pathogen inoculum in laboratory conditions.