Mangrove-Derived Halotolerant Endophytic Bacteria Confer Strain-Specific and Consortium-Mediated Salt Tolerance in Peanut (Arachis hypogaea L.)

Soil salinity is a major abiotic stress that severely limits crop productivity worldwide. This study evaluated the potential of halotolerant endophytes isolated from mangrove plants to enhance salinity tolerance in the peanut (Arachis hypogaea L. cv. JL24). A two-step approach, including screening and validation methods, was applied. Initially, six mangrove endophytes, ACR52, EAR173, EAR191, EAR195, EAL318, and ACL463, were tested for their capacity to colonize the non-host peanut. Histochemical detection of gusA-tagged derivatives confirmed early tissue-associated colonization of peanut seedlings by all six isolates. Seed inoculation of six endophytes improved germination under severe salinity, with ACR52 maintaining 83% final germination at 200 mM NaCl, compared with 67% in the uninoculated controls. The six-strain consortium accelerated germination, giving the highest germination at every NaCl level on Days 1 and 4. Among the isolates, EAL318 (Bacillus subtilis), EAR195 (Proteus mirabilis), and ACR52 (Klebsiella quasipneumoniae subsp. similipneumoniae) exhibited strong PGP traits and were selected for further evaluation. In greenhouse experiments with 300 and 500 mM NaCl, inoculated plants showed significantly higher plant height (32–40% increase), shoot dry weight (28–35% increase), and chlorophyll content (20–30% increase) compared with uninoculated controls. Under severe greenhouse salinity, ACR52 showed the most consistent preservation of reproductive performance, whereas C3 produced the broadest antioxidant response, with elevated CAT and POD activities and reduced H2O2 and MDA accumulation. These findings identify mangrove-derived endophytes as potential candidates for future field evaluation under saline-soil conditions.