Phosphate-solubilizing and siderophore-producing andosol rhizobacteria suppress potato Phytophthora infestans

Abstract

Beneficial interactions between plants and rhizosphere microorganisms are a major lever for sustainable agriculture in Cameroon. This study evaluated in vitro the potential for promoting plant growth and the antagonistic activity of bacterial strains isolated from the rhizosphere in 12 major districts of western Cameroon where potato ( Solanum tuberosum ) is cultivated. Initially, 169 bacteria were isolated and purified. Eighty-two isolates were screened based on their phosphate solubilization index in solid medium, and 20 isolates were screened for their performance in producing significant amounts of phosphorus in liquid medium. Three isolates were selected based on their overall plant growth-promoting (PGP) performance. These were Corynebacterium sp. (K1, 145 ± 0.2 mg/g of phosphorus solubilized in liquid medium and 12.33 ± 2.30 mm of chitin digestion halo), Bacillus subtilis (K13, 6.49 ± 0.19 mg/ml of IAA biosynthesis and 13.12 ± 0.75 mm of cellulose degradation halo), and Pseudomonas aeruginosa (K5, high production of siderophores with a discoloration ratio of 5.17 ± 2.19 in solid medium, a siderophore production unit of 18.43 ± 0.03 in liquid medium, and a potassium solubilization index of 2.29 ± 0.5). Although all three strains selected at the end of the screening process exhibited in vitro antifungal activity against Phytophthora infestans , K13 achieved total inhibition, as did the synthetic fungicide based on Chlorothalonil 30% and Cymoxanil 6% (100% inhibition). Analysis of the bacterial cultures by gas chromatography coupled with mass spectrophotometry confirmed the presence of compounds with potential plant growth-promoting properties including 1,2-butadiene, para-trifluoromethylbenzoic acid, glycyl-L-proline and 4-hydroxy-6-methyl-3-nitro-2-pyridone. This study highlights the significant biotechnological potential of the isolated strains, particularly Bacillus subtilis K13, as a sustainable alternative to synthetic fungicides. These findings open up promising prospects for the development of indigenous biofertilizers aimed at optimizing potato productivity and disease control in tropical regions.