The aim of the study was to determine the effect of the phytoplasma Acholeplasma laidlawii var. granulum 118 on alfalfa plants under conditions of artificial salinization of their growing medium. In a micro-vegetation experiment, the response of leguminous plants — Medicago sativa and M. truncatula — (morphometric parameters, and organic acids and saccharides content) was studied. Additionally, to enhance the plants’ tolerance to a complex of stressors (salinity and phytoplasma infection), the formation of a symbiosis between alfalfa plants and an effective strain of the bacterium Rhizobium meliloti 425a was investigated. It was established that salinization of the nutrient medium intensifies the detrimental effect of A. laidlawii var. granulum 118 on alfalfa plants, which should be taken into account when growing them under conditions of changing soil parameters. Inoculation of plants with R. meliloti 425a results in a slight reduction in phytoplasmosis symptoms at 50 mM NaCl under micro-vegetation experiment conditions. In the M. sativa plants, the content of organic acids and saccharides changed under infection by A. laidlawi var. granulum 118: it decreased in the early stages of the interaction and increased in the later stages. There was an intense accumulation of organic acids and saccharides in plants infected with phytoplasma under effect of salinity, it accompanied by an acceleration in their degradation. It indicates an increase in the negative effects of cumulative stress due to the suppression of the plants’ physiological status under adverse conditions and confirms a decrease in plant tolerance to phytoplasmas as a result of soil salinization.
Keywords: Medicago, Rhizobium, phytoplasma, organic acids, saccharides
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