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The effects of water deficit on growth, nodulation, and several physiological and biochemical processes in six symbiotic combinations involving three Moroccan alfalfa (Medicago sativaL.) populations (Tafilalet1, Adis-Tata and Demnate2), an American Moapa variety and two rhizobial strains (RhL9 and RhL10) were studied. The experiment was conducted under greenhouse conditions. Seedlings were separately inoculated with the suspension of two rhizobial strains and grown under two irrigation regimes: 80% of field capacity (optimal irrigation) and 40% of field capacity (water deficit). The water stress was applied for five weeks and the agro-physiological and biochemical parameters related to water deficit tolerance were assessed. The results showed that the water deficit had significantly reduced the height of the plants, the dry biomass and nodulation. This constraint also negatively affected the relative water content of leaves, the membrane permeability, the stomatal conductance, the maximum quantum yield of photosystem II, the time to reach maximum fluorescence, the total chlorophyll content and the total nitrogen content. Comparison among the tested symbiotic combinations showed that their behaviors were significantly different. Under drought, oasis populations Ad and Ta maintained high PS II efficiency, membrane stability, relative water content, chlorophyll and nitrogen content in comparison to the mountain one Dm2 and the American Moapa variety. These parameters were maintained at adequate levels in the plants inoculated with the rhizobial strain RhL9 that showed a tolerance to water deficit conditions. [ABSTRACT FROM AUTHOR] more...

Osmopriming has a positive effect on the enhancement of seeds germination and seedlings growth, especially under stress conditions. This study investigated the effects of osmopriming with polyethylene glycol on alfalfa (Medicago sativa L.) seeds germination and seedlings antioxidant responses under drought stress. Seeds of five Moroccan alfalfa populations and an American Moapa variety were used to investigate the effect of osmopriming on seeds germination, seedlings growth, activities of antioxidant enzymes and membrane stability under two water deficit levels (-0.45 and -0.75 MPa). Seeds were primed with polyethylene glycol (PEG6000) (-0.6 MPa) for 24 h at 25 °C. The results showed that treated seeds presented higher germination rate and growth of 8 d-old seedlings than untreated ones. Particularly, osmoprimed seeds of 'Adis-Tata' (Ad) and 'Riche' (Rc) populations presented the highest final germination percentages of 90.8% and 64%, respectively, and seedlings shoot and root lengths under both levels of water deficit. The priming treatment enhanced the activity of peroxidase (PO) and catalase (CAT) and reduced the malonyldialdehyde (MDA) content and the electrolyte leakage under water deficit. Generally, the success of germination was positively correlated to PO and CAT activities and the degree of membrane stability in drought tolerant populations. However, the positive effect of the osmopriming technique on alfalfa drought tolerance remains limited in some tested populations, and severe water stress could inhibit germination and cause damages of alfalfa seedlings. [ABSTRACT FROM AUTHOR] more...