Potato has a wide range of pathogens that cause diseases of various etiologies in it. In the areas of commercial potato growing, such widespread diseases as rhizoctoniosis, dry fusarium rot, phomosis, late blight and alternariosis cause significant harm.
Potato rhizoctoniosis in a number of the above diseases is the most harmful. So, for example, phomosis and dry fusarium rot annually take an average of 15-20% of the crop, while from black scab the crop yield decreases by 45-50%. Rhizoctonia solani Kühn (Thanatephorus cucumeria (Franc) Donk) is a soil pathogen widely distributed in various ecosystems. The fungus is capable of causing damage in 230 species of cultivated and weed plants.
When potato plants are affected by rhizoctoniosis or black scab, dry brown ulcers form on the underground part of the stems, often ringing the stem and leading to damage to the sprouts, constriction and death of the shoots. Yellowing, wilting and curling of the leaves (starting from the top) may also be observed. From the beginning of tuberization, stolons and roots are damaged and fall off: they become brown, sclerotia of the fungus can form on them. As a result of this, thinning of plantings and attacks of seedlings are observed, and the crop yield is significantly reduced. In addition, the formation of sessile and air tubers is noted; and at high humidity in the soil layer of air at the base of the stems and around them, a dirty white coating of sporulation of the “white leg” fungus appears on the soil, which indicates an intensive pathological process on the underground organs during the growing season of plants. On tubers, the disease can manifest as sclerotia (dark brown crusts), net necrosis, deep spotting, ugliness, and cracks.
The fungus can exist in a wide range of temperatures (3-27°C) and soil moisture, the disease is especially harmful at low temperatures and high soil moisture and at high temperatures and low soil moisture. The increased humidity of the environment increases the intensity of rhizoctoniosis damage. The humidity factor only works in conjunction with temperature. Low temperature slows down the growth of the crop, and etiolated potato sprouts stay in the soil longer, accumulating a large amount of water-soluble simple sugars easily accessible to the fungus, and are more affected by the disease. Thus, tubers infected with rhizoctoniosis under natural lighting conditions at +20 C show the first signs of damage to the sprouts after 7-8 days, with additional lighting - after 4 weeks. An increased susceptibility of potato plants to R. solani was also established with a lack of potassium in the soil (potassium reduces the number of diseased plants from 66 to 10-15%).
List of sources used:
- Sneh B. Identification of Rhizoctonia species / B. Sneh, L. Burpee, A. Ogoshi // St. Paul, MN, USA: APS Press, 1991. - 133 p. 27.
- Sneh B. Rhizoctonia species: Taxonomy, Molecular Biology, Ecology, Pathology, and Control / B. Sneh, S. Jabaji-Hare, S. Neate, G. Dijst // Dordrecht, The Netherlands: Kluwer Academic Publishers, 1996. - 578 p.