New concept of the relationship between broom-rape and sunflower. Report 2 – Response of broomrape seedlings to phytohormonal secretions from sunflower roots

According to our new concept of the re-lationship between broomrape and sunflower, the pri-mary broomrape seedling is a natural explant with a high callusogenic capacity that initiates callusogenesis with the formation of a dense callus in the form of a broomrape tubercle upon contact with the sunflower root. Therefore, it is hypothesized that the primary broomrape seedling, which initiates grafting by ap-proaching sunflower, is highly responsive to the main exogenous phytohormones regulating callusogenesis, auxin and cytokinin, which are widely used in callus culture in vitro. The aim of the present research was to study the response of primary broomrape seedlings, as an explant initiating grafting by approaching sunflower with subsequent callus formation, to exogenous phyto-hormones regulating callusogenesis – auxin and cyto-kinin. The research was carried out in 2022–2024 at V.S. Pustovoit All-Russian Research Institute of Oil Crops on the sunflower variety VNIIMK 8883 im-proved and sunflower hybrid Natalie, and on seeds of broomrape of races G and F in the ratio 50 : 50, col-lected in 2021–2023 in the Krasnodar, Voronezh and Volgograd regions. It was experimentally proved that the addition of auxin and cytokinin to solutions of sun-flower root secretions during the germination of broomrape seeds showed their high modifying effect. The addition of auxin accelerated the formation of pri-mary broomrape seedlings and was accompanied by the thickening of their apical part. In the presence of cytokinin, germination of broomrape seeds was com-pletely blocked. The addition of cytokinin to the water solution of sunflower root secretions with germinated broomrape seeds caused the formation of loose callus in the apical part of broomrape seedlings. The treat-ment of sunflower plants in pots with auxin and cyto-kinin solutions in the concentration of 0.005% in the presence of broomrape seeds in the soil reduced the number and mass of broomrape sprouts formed on sun-flower roots. The highest effect, which inhibited the development of broomrape, was obtained when sun-flower was treated with cytokinin, which reduced the number and mass of broomrape sprouts more than twice in comparison to the control.