White rot of sunflower

Abstract

Goal. To study the spread and development of white rot on sunflower in the Right bank of Forest-Steppe of Ukraine.
 Methods. The research was conducted during 2014—2018 in the forest-steppe zone of Ukraine (Kyiv and Khmelnytsky region). The selection of plant samples was carried out with further analysis in laboratory conditions The observations were conducted according to generally accepted methods; spread and severity of diseases were determined.
 Results. During the years of investigation, the root, stem and head types of the disease have been identified. There were significant differences in both the symptoms and the degree of disease development in different years. During the vegetative periods of 2014, 2015, and 2017 disease development was compiled — 2—5%. Symptoms of the disease were detected on the stems of plants and heads, starting with the phase of seed development — milk ripeness. The weather conditions of 2016 and 2018 (GTK in June-July 1.2—1.9) were favorable for white rot infection. The disease appeared from the phase of “star” in 2016 and at the beginning of flowering in 2018. The development of the disease was significantly higher compared to other years and reached 12.0—15.1% in 2016 with the spread of 61.2—75.0%. In 2018 its severity in Khmelnitsky region was 11.2% while spread reached 78.6%. Firstly, the root and stem, and later the head form of the disease were marked. In addition to the typical symptoms, spots with brown concentric circles were found on the basal part of the stem. At the same time, the tissue almost did not collapse, and small sclerotic could be detected only in its lower part.
 Conclusions. Under favorable weather conditions, white rot of sunflower is becoming widespread and may be epiphytotic. In the conditions of the Right bank of Forest-Steppe Ukraine, the disease occurs at different stages of organogenesis. Symptoms of three forms of infection were observed. To improve the phytosanitary condition of crops, it is necessary to optimize the saturation of crop rotation with sunflower and other technical crops, which are also one of the host plants of the pathogen, and to follow of all elements of the protection system.