Bibliometric Analysis of Scientific Output and Experimental Evidence on Bacillus spp. as Plant Growth-Promoting Bacteria Under Combined Salinity and Drought Stress Conditions

Salinity and drought are major abiotic stresses responsible for substantial losses in global agricultural productivity, particularly in arid and semi-arid regions. Although Bacillus spp. are widely studied as plant growth-promoting rhizobacteria (PGPR) capable of enhancing plant tolerance to abiotic stress, the extent to which this research has addressed combined salinity and drought stress remains underexplored. This study conducted a bibliometric analysis of scientific output and experimental evidence available in the Scopus-indexed literature published between 2016 and 2024 on Bacillus spp. as PGPR under combined salinity and drought stress conditions. A total of 479 documents were analyzed using the Bibliometrix R package v. 5.4.1 in R v. 4.5.3 and VOSviewer v. 1.6.20, applying Bradford’s and Lotka’s laws, keyword co-occurrence analysis, and citation analysis. Scientific output exhibited a compound annual growth rate of 24.5%, reaching 103 publications in 2024. China, India, and Pakistan were the leading contributors. Among the 495 eligible studies, only 2 studies identified through the primary Scopus search experimentally evaluated Bacillus spp. as PGPR under combined salinity and drought stress conditions. A third study was identified through a complementary external search, revealing a critical gap in experimental in vivo evidence under combined stress conditions. Addressing this gap is essential for advancing effective bioinoculant development for sustainable agriculture under combined abiotic stresses.