Biocontrol potential of endophytic Bacillus spp. associated to wild solanaceous species and their secondary metabolites against various potato (Solanum tuberosum L.) storage diseases.

Fusarium dry rot, Pythium leak and Southern blight diseases caused by various Fusarium species, Pythium aphanidermatum, and Agroathelia rolfsii, respectively, are responsible for important losses of tuber at the post-harvest stage in Tunisia. In the present study, six Bacillus strains, isolated from wild solanaceous plants, were screened for their abilities to inhibit potato pathogens in vitro and on potato tubers. Based on the dual culture assays, the whole cell suspensions of B. tequilensis SV39 and SV104, B. subtilis SV41, B. methylotrophicus SV44 and B. amyloliquefaciens subsp. plantarum SV65 exhibited potent antifungal activity against target pathogens. Significant inhibitory effects were also induced by their cell-free culture filtrates, butanolic and chloroform extracts depending on target pathogens, concentration used and bacterial strains tested. The gas chromatography-mass spectrometry (GC-MS) analysis of B. tequilensis SV39 butanolic extract revealed the highest relative abundance of phthalic acid and derivatives as major volatile compounds. The current study sheds light on the ability of all bacterial strains to reduce the lesion diameter or rot penetration by about 59-61 % and 51-58 %, respectively. Furthermore, B. tequilensis SV104 and SV39 were the most effective bio-agents in reducing the lesion diameter by 64.06 and 57.31 %, respectively, while SV104 (B. tequilensis), SV41 (B. subtilis) and SV65 (B. amyloliquefaciens subsp. plantarum) based treatments were the most effective in decreasing the rot penetration by 54-63 %. The application of these Bacillus strains constitutes a promising alternative for an efficient and safe control of potato storage diseases.