Biocontrol of Rhizoctonia solani Damping-Off of Tomato with Bacillus subtilis RB14

Abstract

Bacillus subtilis RB14, which showed antibiotic activities against several phytopathogens in vitro by producing the antibiotics iturin A and surfactin, was subjected to a pot test to investigate its ability to suppress damping-off of tomato seedlings caused by Rhizoctonia solani. To facilitate recovery from soil, B. subtilis RB14-C, a spontaneous streptomycin-resistant mutant of RB14, was used. Damping-off was suppressed when the culture broth, cell suspension, or cell-free culture broth of RB14-C was inoculated into soil. Iturin A and surfactin were recovered from the soils inoculated with the cell suspension of RB14-C, confirming that RB14-C produced them in soil. The gene lpa-14, which was cloned from RB14 and required for the production of both antibiotics, was mutated in RB14-C, and a mutant, R⌬1, was constructed. The level of disease suppressibility of R⌬1 was low, but R⌬1(pC115), a transformant of R⌬1 with the plasmid pC115 carrying lpa-14, was restored in suppressibility. These results show that the antibiotics iturin A and surfactin produced by RB14 play a major role in the suppression of damping-off caused by R. solani. RB14-C, R⌬1, and R⌬1(pC115) persisted in soil during the experimental period and were recovered from the soil, mostly as spores.

Natural functions of lipopeptides fromBacillusandPseudomonas: more than surfactants and antibiotics

“…However, several studies suggest that LPs are susceptible to enzymatic degradation. For Bacillus, Asaka & Shoda (1996) showed that surfactin levels remained stable for 25 days in sterile soil. Similar observations were made for Pseudomonas LPs: when viscosinamide, tensin and amphisin were introduced in sterile soil, their concentrations remained stable during a 2-week incubation period, but declined after 1-2 days in nonsterile soil, and only minimal amounts could be recovered after 2 weeks (Nielsen & Sørensen, 2003).…”

Antimicrobial peptides and plant disease control

“…Iturin synthesis by Bacillus subtilis B-3 was related to the control of peach brown rot caused by Monilinia fructicola (Gueldner et al, 1988). The production of surfactin was also involved in the control of Pseudomonas syringae infections in Arabidopsis by Bacillus subtilis 6051 (Bais et al, 2004) and of Rhizoctonia solani by Bacillus subtilis RB14 (Asaka & Shoda, 1996). Secretion of bacillomycin, fengycin or iturin by different strains of Bacillus subtilis has been implicated in the biocontrol of powdery mildew of melon caused by Podosphaera fusca (Romero et al, 2007).…”

Viscosinamide, a new cyclic depsipeptide with surfactant and antifungal properties produced by Pseudomonas fluorescens DR54

“…As suggested by Shanahan et al (1992b), antibiotics against pathogenic fungi may be grouped into phenazines (Gurusiddaiah et al 1986; Thomashow et al 1990), pyo compounds (Takeda 1958), pyrrols (Howell and Stipanovic 1979), and other compounds such as phloroglucinols (Keel et al 1992;Nowak-Thompson et al 1994). Antibiotics with surfactant properties (Asaka and Shoda 1996;Stanghellini and Miller 1997) have also been found.…”