Peculiarities of the development of reproductive organs of ornamental crabapples (Malus spp.) depending on drought resistance

The current task for both pomiculture and ornamental horticulture is the formation of plant cultivars resistant to different environmental stress and maintaining their high productivity. Drought is one of the most significant environmental factors that inhibit plant growth and development and cause a set of morphological, physiological, and biochemical changes in plant organisms. The aim of our research was to discover the relationship between the development of the reproductive organs of ornamental crabapples and the physiological indicators determined by drought stress factors. The four species and three cultivars of the ornamental crabapples (Malus spp.) from the collection of the National Dendrological Park “Sofiyivka” of NAS of Ukraine were involved in the study: M. × floribunda Siebold ex Van Houtte, M. halliana Koehne, M. niedzwetzkyana Dieck, M. × purpurea (A. Barbier) Rehder, M. × purpurea ‘Ola’, M. × purpurea ‘Royalty’, and M. × purpurea ‘Selkirk’. Drought resistance was determined by the following quantitative indicators: leaf water content, relative turgidity, leaf water deficit, and excised leaf water retention capacity. The leaf water content ranged from 60.0% (M. × floribunda) to 67.2% (M. × purpurea), the relative turgidity ranged from 81.7% (M. × purpurea ‘Ola’) to 98.9% (M. halliana), and the leaf water deficit ranged from 6.8% (M. halliana) to 24.4% (of M. niedzwetzkyana). As a result, the leaves of M. halliana lost the smallest amount of water in 24 hours (50.2%), whereas M. × purpurea 'Ola' leaves lost the largest amount (77.4%). The development of the reproductive organs was estimated based on the fertility and viability of pollen grains, percentage of fruit and seed set. Pollen fertility ranged from 79.8% (of M. niedzwetzkyana) to 95.0% (M. × purpurea 'Ola'); its viability varied from 5.1% (M. niedzwetzkyana) to 51.5% (M. × floribunda). The highest fruit set percentages were recorded in M. floribunda (80.5%), while the lowest was in M. × purpurea 'Royalty' (16.4%). The average percentage of seed sets was 48.5%. The development of the reproductive organs of Malus specimens depended on their drought resistance. The fruit and seed set percentages had a strong negative correlation with the water deficit in leaves determined during the period of drought stress. The percentage of fruit set was also strongly correlated with relative turgidity. The leaf water deficit and relative turgidity were the most important physiological indicators in the drought resistance study, taking into account the need to maintain crop yield and the decorative effect of Malus plants.