Enhancing drought tolerance in Pisum Sativum and Vicia faba through interspecific interactions with a mixed inoculum of Rhizobium laguerreae and non-host beneficial rhizobacteria

Asma Hami ^1* Imane El Attar ^1,2* Najoua MGHAZLI ¹ Salah Ennajah ^1* EL HOUCINE Ait-Ouakrim ¹ Meryeme Bennis ^1,2* Said Oulghazi ³ Badaoui Bouabid ^3* Jamal AURAG ¹ Laila Sbabou ¹ Kaoutar TAHA ^1*

• ¹ Laboratory of Microbiology and Molecular Biology, Faculty of Sciences, Mohammed V University of Rabat, Rabat, Morocco
• ² Agro Bio Sciences Research Division, Mohammed VI Polytechnic University, Ben-Guerir, Morocco
• ³ Faculty of Science, Mohammed V University, Rabat, Morocco

Harnessing plant growth-promoting rhizobia presents a sustainable and cost-effective method to enhance crop performance, particularly under drought stress. This study evaluates the variability of plant growth-promoting (PGP) traits among three strains of Rhizobium laguerreae LMR575, LMR571, and LMR655, previously isolated from lentil root nodules, alongside two native PGP strains, Bacillus sp. LMR698 and Enterobacter aerogenes LMR696, under drought conditions. Our primary objective was to assess the host range specificity of these strains with three legume species: Pisum sativum, Vicia faba, and Phaseolus vulgaris. We conducted controlled experiments to evaluate their effectiveness in enhancing drought tolerance. Results indicated significant variability in PGP potential among the strains. R. laguerreae LMR655 exhibited high phosphate solubilization, achieving 113.85 mg mL -1 of PO4² -, while R. laguerreae LMR571 produced the highest indole-3-acetic acid concentration of 25.37 mg mL-1. Notably, E. aerogenes LMR696 demonstrated 82% siderophore production. Among the R. laguerreae strains, only LMR571 and LMR655 successfully formed symbiosis with P. sativum and V. faba, with none establishing compatibility with Phaseolus vulgaris. Greenhouse experiments using a mixed inoculum of R. laguerreae LMR571 and LMR655 and E. aerogenes LMR696 revealed significant improvements in growth-related traits, including increases in proline, total soluble sugars, proteins, and chlorophyll content under drought stress. V. faba showed the most pronounced response, highlighting the importance of selecting inocula based on their specific interactions with plant root systems. These findings provide valuable insights for optimizing microbial inoculants to enhance legume resilience in challenging environments.