Ulvan, carrageenan, alginate and laminarin were tested in olive trees' twigs to elicit phenolic metabolism and control verticillium wilt of olive (VWO) caused by Verticillium dahliae. The elicitation effect was determined through phenylalanine ammonia-lyase activity, total polyphenol content and lignin content. VWO was assessed in twigs previously elicited (24 h) and maintained in a solution containing bio-elicitors (2 g/L) and conidial suspension (10 6 conidia/mL). Our results showed stimulation of the phenolic metabolism and the decline of wilt symptoms. Ulvan reduced significantly the area under the disease progress curve for severity to 39.9% and the final incidence to 28.9%. Ulvan and alginate produced significant inhibitory rates on mycelial growth of the fungus in vitro. Seaweed polysaccharides might help to overcome VWO by strengthening the host defense metabolism and restricting the pathogen's growth.

Our study was undertaken to ascertain whether the change of the water status and the activation of superoxide dismutase and their isoenzymes in Argan tree can support edaphic drought tolerance and its recovery under rehydration. An experiment was conducted on four contrasting ecotypes of Argania spinosa plants: two contrasting coastal ecotypes (Admine (Adm) and Rabia (Rab)) and two contrasting inland ecotypes (Aoulouz (Alz) and Lakhssas (Lks)). Drought stress significantly decreased the leaf water potential and stomatal conductance in the four contrasted ecotypes. In terms of biochemical responses, significant accumulation of carbonyl groups, hydrogen peroxide and superoxide radical has been recorded in the leaves of stressed plants reflecting oxidative stress. In parallel, the activities of total superoxide dismutase (SOD) and their isoenzymes Cu/Zn-SOD, Cu/Zn-SOD and Fe-SOD were also found to have increased to scavenging ROS and protecting the cell against induced oxidative stress. The recovery kinetics of A. spinosa, as a response to rehydration, were significant and rapid. According to the traits having the most discriminating power, both inland ecotypes (Lks and Alz) showed a better upregulation of its protective mechanisms compared to coastal ecotypes (Rab and Adm). All these adaptive traits make the inland ecotypes as an elite resource of drought tolerance and might become the new focus of domestication research of argan tree in arid and semi-arid environments.

No abstract

No abstract

Salinization of soil is a major problem affecting many plant physiological processes. The use of arbuscular mycorrhizal fungi (AMF) plays a key role in improving the growth and the crops yield. The aim of this study was to evaluate the combined effects of salt stress and AMF on agro-physiological and biochemical responses of Stevia rebaudiana Bertoni. The experiment was carried out in a completely randomized design with ten replicates under the green house conditions. Stevia plants were inoculated with AMF consortium (MC) or with Rhizophagus irregularis (Ri) on the presence (80 mM of NaCl) or the absence (0 mM of NaCl) of salt stress. The results showed that plant height, dry biomass of shoots and roots parts, mycorrhizal frequency and intensity, relative water content, chlorophyll fluorescence, stomatal conductance, chlorophyll a, and total chlorophyll were significantly reduced by 29%, 72%, 36%, 84%, 65%, 24%, 17%, 60%, 28.50%, and 40.9% respectively under salt stress. These changes were associated with a significant increase in antioxidant enzymes (activity of polyphenol oxidase, peroxidase, superoxide dismutase, and catalase), electrolyte leakage, lipid peroxidation, and hydrogen peroxide contents. The application of AMF (MC and Ri) improved growth and physiological parameters through rising the activities of antioxidant enzymes and reduction of the oxidative damage caused by the salt stress. The better results were recorded with MC-inoculated plants. These findings suggested that AMF could be an effective strategy to alleviate the adverse effects of salt stress on Stevia rebaudiana.