Stepwise-Selected Bacillus amyloliquefaciens and B. subtilis Strains from Composted Aromatic Plant Waste Able to Control Soil-Borne Diseases

Abstract

In the present study, 133 bacterial isolates from 11 composted aromatic plant wastes were selected for their ability to inhibit the mycelial growth of the soil-borne phytopathogenic fungi Sclerotinia minor and Rhizoctonia solani. Successively, a subset of 35 from them were further characterized for their ability to control, in vivo, rocket damping-off caused by the two fungi. Moreover, the isolates were characterized for morphology of the colonies, Gram reaction, siderophore production, P-solubilization and for the presence of antimicrobial lipopeptide genes in the genome. The screening for the in vitro antagonisms showed a mycelial growth reduction ranging between 31.7% and 56.1% for R. solani and 34.4% and 59.4% for S. minor. All the isolates were not able to produce siderophores and some of them were able to solubilize P. The isolates contained two or more of the five lipoproteins coding genes investigated in this study. The most promising isolates were identified at species level by 16S-rRNA partial gene sequence analysis and were grouped in two main clusters related to Bacillus subtilis and Bacillus amyloliquefaciens reference strains. Results indicated that Bacillus isolates from compost are good candidates for application in the biocontrol of cultivated plants.