IMMUNOLOGICAL CHARACTERISTICS OF THE COLLECTION MATERIAL OF CUCUMBER FOR RESISTANCE TO DOWNY MILDEW IN GREENHOUSE CONDITIONS
The most harmful and economically significant disease affecting cucumber in greenhouses is downy mildew, the causative agent is Pseudoperonospora cubensis Rostw. An effective method of reducing the loss of the commodity component of the product from this disease is the creation of resistant varieties and hybrids of cucumbers. Therefore, an integrated assessment of breeding material in order to search for and select downy mildew-resistant output forms and the subsequent creation of a resistant cucumber starting material on their basis is an important task. The purpose of the research - to carry out an immunological evaluation of the collecting material of the parthenocarpic cucumber gherkin type for resistance to downy mildew. Materials and methods of research. The research was conducted during 2016-2018 in film greenhouses of the Laboratory of Selection of Cucurbits of the Institute of Vegetable and Melon Growing of HAAS. Collection specimens were evaluated on a rigid natural infectious background (permanent greenhouse soil plus monoculture). The level of oxidative-reducing enzymes was studied in laboratory conditions using the Boyarkin method in the leaves of cucumber of the upper layer in the phases of the beginning and mass fruiting. The results of the immunological evaluation among the collection specimens were not found highly resistant specimens (score 9). Collectible specimens of cucumber with high resistance (score 7) to downy powdery mildew are highlighted: Golubchik F<sub>1</sub>, Zircon F<sub>1</sub>, Chinese climbing F<sub>1</sub> and Dutch F<sub>1</sub>, recommended for involvement in the breeding process. The activity of redox enzymes of peroxidase and polyphenol oxidase in healthy and diseased plants was analyzed. It has been established that the level of activity of peroxidase in healthy cucumber leaves differs depending on the resistance group and ranges from 22.73 to 25.00 mg-eq. / g s in very low-resistance, 33.78 - 36.46 mg-eq. / g s, in highly resistant specimens. Peroxidase activity in cucumber leaves increased when they were infected with pathogene: in highly resistant specimens, the increase in enzyme activity in affected leaves compared to healthy ones was 240-290 %, in specimens with low and very low resistance, 130-67 %. There was no significant difference in polyphenol oxidase activity in cucumber healthy leaves by groups of resistance, however, in the affected leaves of highly resistant specimens, this parameter increased by 363-388 %, in medium resistant ones by 100-220 %, in specimens with low and very low resistance - by 30 -74 %. It has been proved that the activity of redox enzymes in cucumber leaves can be an additional diagnostic specific parameter in the selection of valuable sources for the selection of parthenocarpic type cucumbers on downy mildew resistance.