Effects of different phytopathogenic bacteria on the scoto- and photomorphogenesis of vegetable bean seedlings

Relevance. The development of bacterial diseases and their severity are determined by the complex interaction between the pathogen, the host plant genotype, and environmental conditions. Light is a key abiotic factor that modulates both physiological processes during etiolation (in darkness) and photomorphogenesis (in light), as well as the pathogenesis process. Furthermore, the use of etiolated seedlings allows for the identification of the specific virulence expression of pathogens, which may be masked or compensated for under light conditions. The aim of this study was to comprehensively assess the influence of different types of pathogenic bacteria on the morphophysiological parameters of bean seedlings, depending on the cultivar genotype and lighting conditions. Methodology. Bean varieties with varying field resistance to bacterial diseases were used in the study: Lika, Si Bemol (SBM), and Rant. At the radicle emergence stage, seedlings were inoculated with suspensions of four species of phytopathogenic bacteria: Dickeya chrysanthemi (Dc), Curtobacterium flaccumfaciens (Cf), Pseudomonas syringae (Ps), and Xanthomonas phaseoli (Xp). The control was sterile water. After inoculation, seedlings were grown in plastic containers with sterile perlite under two conditions: a 16-hour photoperiod and complete darkness. Stem and root system length, primordial leaf area, and plant fresh weight were measured after 7 and 14 days, and the types of disease symptoms and their severity were recorded. Results and Conclusions. The analysis of the influence of phytopathogenic bacteria on the morphogenesis of bean seedlings confirmed that the observed effects are non-linear and determined by the specific combination of factors in the "plant-pathogen-light" triad. The cultivar-specific action on seedling growth processes indicates the leading role of genotype in resistance to bacterial invasion. In this context, growth parameters can serve as early indicators of the development of the infectious process. The most prognostically valuable indicators are plant mass and the area of primordial leaves. Each bacterial species formed a characteristic symptom complex: Ps exhibited a necrotic-toxic type of pathogenesis with the formation of localized necrosis and the ability to induce chlorosis; Xp showed pronounced variability in symptomatology depending on the host genotype, manifesting as depression of root system development and vascular disorders with the formation of vein necrosis; Cf displayed moderate aggressiveness and the ability to induce compensatory reactions in tolerant genotypes with elements of growth stimulation; and Dc exhibited properties of an aggressive vascular polyphage with pronounced tropism towards apical meristems and young leaves, causing wilting and rot of the apex of etiolated bean seedlings. The modulating role of the light regime involved the differentiation of "pathogen x plant" interaction strategies: induction of compensatory reactions under light in the tolerant cultivar 'Lika', growth inhibition and potentiation of symptoms in the dark in the susceptible cultivar 'Rant'; and light-dependent, divergent effects in the moderately susceptible cultivar 'Ci Bemol'. The identified group resistance to bacterial diseases makes the 'Lika' cultivar promising for use in breeding programs for immunity.