Goal. Assess potato varieties and hybrids for resistance against rhizoctonia disease and identify highly resistant varieties. Methods. The fundamental principle of the existing methodology for evaluating varieties is to test varieties, hybrids and species of potatoes on natural or artificial infectious backgrounds using a pure culture of the fungus Rhizoctonia solani Kuhn. The culture grown in Petri dishes was introduced when the tubers were planted in the soil. The assessment of the degree of damage to tubers and stems was carried out according to the damage to the underground organs of plants, the yield of potatoes, and then the level of variety samples was determined by resistance to the disease. Evaluation of potato varieties and hybrids for resistance against the causative agent of the disease Rhizoctonia solani Kuhn was carried out on a nine-point scale, where score 9 — no damage to stems and tubers, 7 — disease development up to 10% (high resistance); 5 — disease progression 11—25% (medium resistance); score 3 — disease progression 26—50% (low resistance). Results. Based on the test of potato varieties and hybrids for resistance against rhizoctonia, Dubravka, Vesta, Lugovska, Obriy, Serpanok, Yavir, Scarbnytsia, Tyras and hybrids P.207.407 (Zov × Polisska Rozheva), 205.17-24 (Adretta × 23-16s/73) and others; to medium-resistant (5 points) — Chervona Ruta, Povin, Vodogray, Horlytsia, Zov, Cupava, Nadiyna, Belarossa, Olvia, Svitanok Kyivskyi, Ukrainska Rozheva, Beregynia, Charunka, Okolytsia, Slutch, hybrids P.210.14-23 (Adretta × Posvit), 211.20-31 (Prolisok × Lugovska); to susceptible — 51, or 32.9% of the tested varieties. Conclusions. We have proved that mid-early ripening and early ripening cultivars as well as selection hybrids are more infected with black scab than mid-ripening, mid-late ripening and late ripening cultivars. These relatively resistant potato cultivars and hybrids are expedient to use in the selection on the resistance against black scab.
Goal. To establish the symptoms of pathogens of fomose rot on potato varieties of different resistance, to isolate pathogens from the genus Phoma, parasitizing on tubers and stems of plants. Methods. Symptoms of phomotic rot were determined visually by the determinant of diseases and the method of microbiological diagnosis was used. Pathogens were isolated from stems and tubers affected by fomose rot. Results. On the basis of psychopathological examination, it was experimentally proved for the first time in Ukraine that fomozna potato rot is widespread in commodity and seed potato plantings. The degree of harmfulness reaches 35%. Pathogens of the genus Phoma (Ph. Solanicola Prill. Et Del Ph tuberosa Malkomcon) affect potato stems and tubers. On the stems, the first symptoms appear as spots during the flowering phase of the plants, and on tubers the gangrene appears as round, depressed and hard spots, light or dark brown in color, on the top of which pycnids form. According to the harmfulness of the pathogen, the Polesye of Ukraine is divided into three zones: 1. The zone of strong development includes the Volyn and Zhytomyr regions, where the number of affected plants with phomosis exceeds 5%, affected tubers — 8—10%; 2. The zone of moderate development, it includes the Rivne and Khmelnitsky regions, where the number of plants affected by phomosis is 2—3%, and tubers during storage of the crop — 5—7%; 3. The zone of insignificant development of the disease includes Kiev and Chernihiv regions, where the number of plants affected by gangrene is up to 2%, and tubers after storage of the crop — up to 4%. Conclusions. According to the results of psychopathological surveys, three zones of development of fomose rot of potatoes (severe, moderate and minor damage to phomosis) were identified and a scheme for the development cycle of the infection of the genus Phoma (Solanicola Prill. et. Del. And Ph. Tuberosa Melh.) was established. Symptoms of fomose rot appear on the stems in the form of elongated blurry spots, on which pycnids form from light brown (Eurostar) to dark brown (Riviera) color. On potato tubers, fomosis appears in the form of round, hard, sunken spots of a dark color. It is proved that during the interaction of potato plants with pathogens of the genus Phoma complex physiological, biochemical and pathological processes occur that significantly reduce productivity, quality, taste and other economically valuable traits.
The pathogens involved in rotting potato tubers at harvest or in store have been identified in the forest and forest-steppe zones of Ukraine. Fusarium spp., Phytophthora infestans, Erwinia carotovora and Ditylenchus destructor are the most important. Identification of rot pathogens in stored tubersThere is little scientific information on the development and spread of rot of potato tubers in Ukraine, and we now report on our research on this subject in the forest and forest-steppe zones of Ukraine. Our first aim was to identify the pathogens that are involved in tuber rot. Samples of tubers with mixed rot symptoms were selected on farms of the Zhitomir, Kyiv, Cherkasy, Sumy and Rivne regions in autumn (a month after harvest) and in spring (before grading). Pathogens were detected visually (by symptoms) and then diagnosed by inoculation of healthy tubers with the organisms involved, followed by microbiological analysis (Table 1).Thirteen microbial species or subspecies were detected. No tubers were found with symptoms of only one disease. Fungi, bacteria and nematodes were found: Fusarium and Phytophthora spp., Envinia spp. and Ditylenchus destructor. identification of rot pathogens at harvestIn a second series of investigations, we determined the types of mixed rot observed after harvest. Ten Table 1. Main pathogens identified in potato tubers showing mixed rot symptoms Frequency (%)
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