New concept of the relationship between broomrape and sunflower. Report 1 - Hypothesis of natu-ral approach grafting of broomrape and sunflower and callus origin of tubercles

Throughout the history of the study of broomrape and sunflower, well-founded ideas about the biology of their relationship have been formed. At the same time, a number of questions have accumulated that cannot be explained by the established ideas about the mechanisms of the primary contact of the broomrape seedling with the sunflower root, the formation of haustoria, its germination in the sunflower vascular system, and the formation of tubercles and shoots of the broomrape. The reasons for the continuous formation of trait polymorphism in broomrape, including the overcoming of broomrape resistance in sunflower, have not been reliably determined. The aim of this research was to study the relationship between broomrape and sunflower based on the natural mechanism of spontaneous approach grafting. The researches were conducted in 2021–2023 at V.S. Pustovoit All-Russian Research Institute of Oil Crops, Krasnodar on sunflower varieties SPK plus and VNIIMK 8883 improved, and on broomrape seeds of races G and F in the ratio of 50:50, collected in 2021–2023 in Krasnodar, Voronezh and Volgograd regions. The possibility of merging of adult shoots of broomrape and sunflower as a result of reciprocal grafting between them was experimentally confirmed. The hypothesis of merging of the primary seedling of broomrape seed with the sunflower root as a natural interspecific approach grafting with the formation of a dense callus from the scion tissues in the form of undifferentiated broomrape tubercles was formulated. Then, the broomrape shoots formed from tubercles may represent callus regenerants with non-zero probability of genetic recombination formation for various traits, including overcoming broomrape resistance of sunflower. In our studies, broomrape shoots with different coloration were found on individual sunflower roots. When broomrape seeds were germinated on atypical media, individual germinated seeds were also found. These facts support the hypothesis of continuous formation of genetic polymorphism of broomrape caused by cellular recombinogenesis inherent in callus tissues, to which broomrape tubercles can be attributed.