Effects of genetically modified alfalfa plants on their interaction with Sinorhizobium meliloti

The aim of our study was to evaluate the effect of three types of genetically modified alfalfa (Medicago sativa L.) plants grown in soils of different pH on their growth characteristics and interactions with Sinorhizobium meliloti. Transgenic alfalfa plants contained the genes Ov from Japanese quail (Coturnix coturnix) coding for ovalbumine, AMVcp-s from Alfalfa Mosaic Virus (AMV), coding for the viral coat protein, and combination of genes uidA encoding ß-glucuronidase, and nptII, encoding neomycinphosphotransferase II, respectively. Seven strains of Sinorhizobium meliloti were used to inoculate alfalfa, of which some showed high tolerance to low pH in an in vitro assay system. The experiment also included a non-transgenic isogenic alfalfa line SE/22-GT2 as a control. The highest total dry weight (DW) of green matter in neutral pH soil was determined in transgenic line GTAMV1 (containing the AMVcp-s gene). Plants grown in neutral soil produced 28% moregreen matter DW in comparison with those grown in the acidic soil. Inoculation with N2-fixing bacteria increased the DW of green matter from 40% (neutral soil) to 87% (acidic soil). The highest agronomic efficiency, defined as the ratio of difference between the total aboveground biomass DW in inoculated and non-inoculated variant to non-inoculated control, was observed in S. meliloti strains 7T4 and 4T8. The number of nodules on the roots of plants was significantly affected by the genotype and inoculation with rhizobial strain (P less than 0.05). The highest number of nodules was observed in transgenic clones containing the AMVcp-s gene, i.e. 85% more than in clones with Ov gene, and 77% more than in marker genes only containing clones of alfalfa. Alike, transgenic alfalfa lines containing the AMVcp-s gene had higher numbers of nodules by 140% in neutral soil and 4-times more in acidic soil in comparison with isogenic non-transgenic lines. The highest N2-fixation efficiency (11.5%), defined as the ratio of increase in the total N content in aboveground biomass of inoculated variant to total N content in non-inoculated variant, was found in strain 4T5. Our results showed a transgene-dependent (positive) interaction of rhizospheric nitrogenic microorganisms with roots of transgenic alfalfa plants.