Évaluation des effets d'un traitement bactérien sur la germination et le développement précoce des plantules soumises au stress salin

Abstract

This study aimed to evaluate the potential of endophytic bacteria as plant growth-promoting agents. First, bacterial isolates were obtained from vegetable samples. Phenotypic identification was based on physiological and biochemical criteria, including Gram staining, catalase activity, sugar fermentation, growth temperature and thermos-resistance, as well as growth at different NaCl concentrations and pH values. The selection of isolates was carried out through biocompatibility and phosphate-solubilization tests. The second part of the study focused on in vivo and in vitro assays to evaluate the effects of bacterial treatments on seed germination and early root system development in durum wheat seedlings (Triticum durum). A total of five bacterial isolates were obtained from tomato and white cabbage samples. They exhibited a typical profile related to the genus Enterococcus sp. Characterized by remarkable tolerance to pH fluctuations, they also demonstrated strong adaptation to extreme saline stress conditions, highlighting their resistance to various NaCl concentrations. Their metabolic profile revealed fermentation of the tested sugars, supported by fermentative activity in TSI medium without H₂S production. The phosphate-solubilization test performed on PVK medium revealed the formation of clear halos around bacterial colonies. The measured solubilization zones ranged from 10 to 21 mm, corresponding to solubilization indices between 1.67 and 3.5. The in vivo and in vitro experiments showed a positive impact of the selected isolate (C1) on germination, seedling growth, and root system expansion. At the highest concentration of 200 mM NaCl, the germination rate of seeds inoculated with C1 reached 24%, compared with only 12% in the stressed non-inoculated control (Tn3). A notable improvement in morphological parameters under saline stress was recorded at 150 mM NaCl, with root lengths reaching 5.5 cm and seedling lengths 8 cm, while maintaining a number of leaves comparable to the controls. Fresh root and shoot weights reached 0.37 g and 0.16 g, respectively. The effect of strain C1 produced a statistically significant protective effect by reducing chlorophyll pigment degradation (5.60 mg L⁻¹ at 150 mM NaCl). Soil bacterial counts indicated that bacterial density in inoculated treatments was higher than in stressed controls. This increase reflects the isolate’s ability to colonize and persist in the rhizosphere after inoculation. The protective and stimulatory effects observed in inoculated plants are directly linked to the PGPR characteristics of the bacterium. These results suggest that this strain has considerable potential for biotechnological applications aimed at improving plant growth and tolerance to saline stress.