Cacti thrive in arid and coastal environments partly through associations with beneficial endophytic and rhizosphere bacteria; however, current knowledge remains limited. This study aimed to assess the diversity of cultivable bacteria associated with Opuntia dillenii and evaluate their potential as Plant Growth-Promoting (PGP) agents. Endophytic bacteria were isolated from cladodes and roots, while rhizobacteria were recovered from rhizosphere soil. Bacterial isolates were identified using morphological characteristics and 16S rRNA/gyrB sequencing, followed by screening for PGP traits, pH and temperature tolerance. A total of 31 isolates were obtained, including 23 endophytes and 8 rhizobacteria, mainly affiliated with Firmicutes, Actinobacteria, and Proteobacteria. Bacillus (35.48%) and Priestia (32.25%) predominated, with Priestia flexa as the most prevalent species. The most frequent PGP traits were phosphate solubilization (80.65%), proteolytic activity (70.97%), siderophore production (67.74%), and nitrogenase activity (64.52%). The highest phosphate solubilization indices were observed for strain R3 (3.41), R6 (3.39) and S6 (3.21), whilst the highest indole-3-acetic acid yields were recorded for C9 (172.88 µg/mL), R11 (96.22 µg/mL) and C3 (90.94 µg/mL), and the strongest siderophore production for C3 (30.37 mm), C7 (27.96 mm) and S7 (27.88 mm). These findings highlight O. dillenii-associated coastal bacteria as promising resources for plant growth and plant stress resilience.

Endophytic and rhizosphere bacteria have considerable potential as bioinoculants for enhancing plant growth and improving soil health. However, despite their agricultural importance, their antibiotic resistance profiles remain poorly documented. This study assessed the antibiotic resistance of 31 bacterial strains isolated from the roots, cladodes, and rhizosphere of O. dillenii growing in the coastal zone of Benin. Antibiotic susceptibility was evaluated using the Kirby–Bauer disk diffusion method according to CA-SFM/EUCAST guidelines. Depending on the bacterial genus, each strain was tested against 7 to 12 antibiotics selected from a panel of 19 antibiotics representing 14 antimicrobial classes. The results showed moderate resistance of 40–60% for linezolid and clindamycin. Low resistance of 10–39% was recorded for erythromycin and vancomycin. In contrast, the bacterial resistance to Tetracycline, Amoxicillin, Ciprofloxacin, Fusidic Acid, Gentamicin, Quinupristin–dalfopristin, Rifampicin, and Trimethoprim–Sulfamethoxazole remained extremely low (<10%). No bacterial resistance was detected against Ampicillin, Amoxicillin–clavulanic Acid, Ceftriaxone, Cefoxitin, Cefotaxime, Norfloxacin, or Imipenem. Overall, 9 out of 31 endophytic strains (29.03%) exhibited multidrug resistance. Therefore, this finding provides valuable biosafety data for the selection and registration of bacterial biofertilizers and identifies several promising strains for future agricultural applications.

Tomato production is severely affected by bacterial wilt caused by Ralstonia solanacearum. This study assessed the biocontrol potential of bacterial strains isolated from the cladodes, roots, and rhizosphere of Opuntia dillenii for the sustainable management of bacterial wilt in tomato. An in vitro screening identified antagonistic strains, which were subsequently assessed under greenhouse conditions. Among the isolates, Priestia flexa C10 and Bacillus subtilis R6 showed the strongest antagonistic activity against R. solanacearum, with inhibition zones of 22.5 and 20.0 mm, respectively. Under pathogen pressure, the inoculated control exhibited a wilt incidence of 47.5%, whereas B. subtilis R6 and P. flexa C10 reduced disease incidence to 40% and 45%, respectively. Both strains also improved plant growth. Under non-inoculated conditions, B. subtilis R6 showed the greatest growth-promoting effect, increasing plant height (35.9%), leaf number (24.6%), root biomass (94.5%), and root length (59.4%). Under pathogen pressure, P. flexa C10 notably enhanced root biomass (49.8%) and root length (30.6%), while B. subtilis R6 increased root biomass by 80.4%. These findings indicate that while P. flexa C10 and B. subtilis R6 offer limited direct suppression of bacterial wilt, they significantly promote tomato vegetative growth and could serve as valuable plant growth-promoting inoculants to mitigate disease-induced stress.

High soil salinity constrains global agricultural productivity, necessitating effective mitigation strategies. Plant growth-promoting bacteria (PGPB) offer a promising approach to enhance crop salt tolerance. This study evaluated halotolerant bacteria from O. dillenii to improve tomato (Solanum lycopersicum L.) growth under salinity. Bacteria from plant organs and rhizosphere were screened at 0–3 M NaCl; 52.38% grew above 1.5 M, and six strains—P. flexa S4, S6, R7, C5; B. amyloliquefaciens R4; and M. yunnanensis C11—tolerated up to 2.5 M. Under 120 mM NaCl, biopriming with P. flexa S6 and C5 increased germination to 75% and vigor index by 149.2%. Under 200 mM NaCl, P. flexa S6 boosted root biomass by 167.5%, C5 improved root length and diameter by 25.6% and 30.98%, and R7 enhanced shoot growth while reducing leaf proline by 78%. These selected strains effectively alleviate salt stress and promote tomato growth, promising an application in sustainable agricultural systems. Graphical abstract