Efficiency and mechanisms of action of pelletized compost loaded with Bacillus velezensis CE 100 for controlling tomato Fusarium wilt

Abstract

The objective of this study was to determine the control efficacy of pelletized compost containing high number of the biocontrol agent, Bacillus velezensis CE 100, for tomato Fusarium wilt. Pelletizing had no serious effects on the cell numbers and quality of strain CE 100 in producing lytic enzymes although antifungal activities of reisolated strain CE 100 from pellet against Fusarium oxysporum f. sp. lycopersici was slightly reduced compared to the original strain. However, culture filtrates of two B. velezensis CE 100 strains not only induced abnormal mycelial development with pigment reduction but also caused hyphal deformations with swelling and bugling of the fungal pathogen. Moreover, cyclo(prolyl-valyl), an antifungal dipeptide, was isolated from B. velezensis CE 100 culture and identified by HR-ESI-MS and 1D- and 2D-NMR experiments. The dipeptide limited conidial germination of F. oxysporum f. sp. lycopersici in a concentration-dependent pattern. Long incubation period triggered irregular hyphal morphologies with swollen septa and disorganized cell contents in treatments with the dipeptide. Under in vivo conditions, supplementation of soil with strain CE 100-pelletized compost significantly controlled Fusarium wilt and resulted in the lowest disease incidence rate, consequently promoting tomato growth. The soil amendment with strain CE 100-pelletized compost could be used as a potential approach for a better fungal disease control, promoting sustainable agriculture.