Growth promotion potential of Bacillus spp. isolates on two tomato (Solanum lycopersicum L.) varieties in the West region of Cameroon

Abstract Inoculation of plants with plant growth-promoting bacteria (PGPB) is an ecological approach to improve plants growth and yield. The objective of this study was to screen native PGPBs in tomato root rhizosphere and evaluate their performance in germination and growth of seedlings in the greenhouse in the western region of Cameroon. Isolates were selected based on their ability to solubilize phosphate, produce indole-3-acetic acid, and improve seed germination and seedling growth under laboratory conditions. Following this screening, eight bacteria were selected (S1, S4, S13, S14, S16, B9, B11, and B15) to assess their performance on seedling growth in greenhouse. Seeds of two tomato varieties (one improved, Raja, and the local one, Foolewouh) were used in this study. The experiment was performed in sterilized and non-sterilized soils. Phylogenetic analysis of the 16S rRNA sequence showed that these bacteria belong to the genus Bacillus, including B. thuringiensis, B. cereus, B. pacificus, and B. aerius. The bacterial performance depended on the variety and conditions of soil treatment. Isolates improved seed germination (up to 31.93%) and seeding strength (up to 78.59%) in vitro. In greenhouse, inoculation with PGPB significantly increased stem height, root length, and weight of fresh and dry stems and roots. Raja variety was more sensitive to bacteria and performed better than the Foolewouh variety. Bacterial isolates on sterilized soil allowed to better seedling growth compared to non-sterilized soil. The study showed that B. thuringiensis (strain B9), B. pacificus (strain B11), and Bacillus sp. (strain B15) can be used as inoculant formulations to improve seedling growth of tomato plant.