Sapindus saponaria L. (Sapindaceae) as a reservoir of plant-growth-promoting endophytes: Diversity, phosphate solubilization, enzymatic activity, and biocontrol potential

Endophytic bacteria from the medicinal plant Sapindus saponaria were comprehensively characterized for their plant growth promotion potential, enzymatic activities, and biocontrol capabilities against phytopathogens. Through 16S rRNA gene sequencing of 126 isolates, 58 strains belonging to 17 genera were identified, with Staphylococcus (25.8 %), Acinetobacter (13.7 %), Enterococcus (12.0 %), and Bacillus (10.3 %) as the most abundant. Phosphate solubilization screening revealed that 16 of 39 tested strains (41 %) possessed this trait, with Pseudomonas aeruginosa SS93 showing exceptional activity (solubilization index = 7.07). Remarkably, 97.4 % of strains produced at least one hydrolytic enzyme, with high frequencies of proteases (79.5 %), lipases (61.5 %), and pectinases (46.2 %) production. The strain Paenibacillus sp. SS73 demonstrated particularly broad enzymatic capabilities, actively secreting seven different enzyme types. In biocontrol assays against six phytopathogens, Bacillus amyloliquefaciens SS13, and P. aeruginosa SS93 showed outstanding antagonism, inhibiting Alternaria alternata , Fusarium solani , and Colletotrichum sp. by 74–89 %. Notably, SS13 alone inhibited Sclerotinia sclerotiorum by 76.8 %. Inhibition occurred even without physical contact, suggesting antibiotic compound production. These results establish S . saponaria as a valuable source of multifunctional endophytes, with selected strains exhibiting phosphate solubilization, diverse enzymatic activities with industrial potential, and significant biocontrol capacity against economically important plant pathogens. The combined traits of these endophytes make them promising candidates for developing sustainable agricultural inputs and biotechnological applications. • Diversity of endophytic bacteria studied in Sapindus saponaria leaves. • 16 strains showed phosphate solubilization, led by Pseudomonas aeruginosa (SS93). • 97.44 % of strains produced at least one enzyme, highlighting their biotechnological use. • Strains SS13 and SS93 showed > 74 % inhibition of critical phytopathogenic fungi. • Promising application in sustainable agriculture and biocontrol strategies.