Evaluation of biological control agents for Fusarium wilt in Hiemalis begonia

Five laboratory-isolated Bacillus subtilis strains: CB1, CGB, JHB1, SSB1 and WW4; and five commercial biocontrol agents: Actinovate (R) (Stretomyces lydicus strain WYEC108), Serenade (R) MAX (Bacillus subtilis strain QST713), Mycostop (R) (Streptomyces griseoviridis strain K61), RootShield (R) (Trichoderma harzianum strain T-22), and Prestop (R) WP (Gliocladium catenulatum strain J1446) were evaluated for their potential to inhibit Fusarium foetens both in vitro in Petri dishes and in the greenhouse using potted begonia plants. Bacillus subtilis strain JHB1 inhibited F. foetens mycelial growth by 76% compared with the untreated dishes after seven days of dual culturing; and also provided significant protection to potted begonia plants against F. foetens under greenhouse conditions (two trials) when applied as two soil drenches prior to pathogen inoculation. Compared with the pathogen-inoculated control, disease severity (DS) was reduced by 33% and 50% by JHB1 in trial one and two, respectively. All of the commercial biocontrol agents significantly reduced DS compared with the control when applied as soil drenches prior to pathogen inoculation. Most of the commercial products delayed plant disease symptom development by seven or more days. Moreover, Mycostop, Prestop, Actinovate, RootShield and Serenade all significantly reduced the DS, and increased the shoot dry weights and chlorophyll content index for over 28 days after inoculation compared with the control.