Seed osmopriming improves plant growth, nodulation, chlorophyll fluorescence and nutrient uptake in alfalfa (Medicago sativa L.) - rhizobia symbiosis under drought stress

This study assesses the effect of seed osmopriming with PEG (−0.6 MPa) on growth and physiological parameters in six symbiotic combinations involving two Moroccan alfalfa populations Adis-Tata (Ad) and Demnate2 (Dm2) and an American Moapa (Mo) variety inoculated with RcRh09 and Sinorhizobium meliloti (Rm1021) strains. Inoculated plants were submitted to water deficit consisting in 40% field capacity (FC) of substrate versus 80% FC for the controls during five weeks. The results showed that seed priming increased growth, leaf area, plant height and nodulation in the tested combinations under water deficit. Physiologically, the priming increased the photosystem II (PSII) efficiency, stomata closure, and relative water content as well as nitrogen fixation and P and K+ uptake under this constraint. The combinations Ad-RcRh09, Ad-Rm1021 and Dm2-RcRh09 from primed seeds showed higher growth and K+ accumulation than all of the other combinations. They maintained also important levels of Fv/Fm ratio, ETR and TFm as well as nitrogen and phosphorus in their leaves under drought stress, resulting in increase of their drought tolerance. Overall osmopriming was effective in the enhancement of nodulation and drought tolerance in almost all of the studied combinations.