S S A L L . 1993. A strain of Bacillus subtilis which produces an antibiotic metabolite was also found to produce a volatile compound(s) which was antifungal to Rhizoctonia solani and Pythium ultimum.abnormalities of the hyphae were observed, including hyphal distortion and vacuolation. A range of media were tested for volatile production and potato dextrose agar (PDA) was found to be the most active. Temperature had a considerable effect on antifungal volatile activity with the greatest inhibition occurring at 30°C. Addition of iron (111) chloride to Sabouraud's glucose agar (SGA) also enhanced the antifungal effect. The volatiles were found to be water soluble and remained active when trapped in SGA.

Aims: Five bacterial strains belonging to Bacillus subtilis, Pseudomonas fluorescens and Ps. corrugata and two fungal strains belonging to Trichoderma viride and Gliocladium virens were evaluated for their efficacy in controlling sugar beet and cucumber damping‐off caused by Pythium ultimum. Methods and Results: The in vitro antagonistic activity of bacteria against various Pythium spp. was evaluated with dual cultures in various media. Pseudomonas strains inhibited the pathogen better than Bacillus strains. To identify potentially useful antagonist combinations, dual compatibility of antagonists was also evaluated, based on growth in two liquid media containing substrate previously used by other antagonists. Four pairs of bacteria were selected. Sugar beet damping‐off biocontrol was attempted with bacterial seed treatments (individually and in pairs). Cucumber damping‐off biocontrol was attempted with bacterial seed treatments and bacterial and fungal compost treatments. In sugar beet, satisfactory biocontrol was only achieved with Pseudomonas antagonists. Antagonist combinations did not show any superior biocontrol ability to individual antagonists and compatibility of bacteria in vitro did not correlate with compatibility in vivo. Bacterial seed treatments and fungal compost treatments failed to control cucumber damping‐off. Better biocontrol in cucumber was achieved when bacterial antagonists were applied by drenching or by coating seed with bacteria in a peat carrier. Conclusions: Pseudomonas antagonists were superior to Bacillus antagonists in controlling damping‐off in cucumber and sugar beet. Pseudomonas peat inocula maintained a good shelf‐life 2 years after preparation. Significance and Impact of the Study: Pseudomonas peat formulations have the potential for development into commercial biopesticides.

An antibiotic-producing strain of Bacillus subtilis has been shown to produce potent antifungal volatiles (AFV). These volatiles are active against a range of fungal species and are produced on a range of growth media and in loam-based compost. In vitro antifungal volatile activity on nutrient agar is enhanced with the addition of D-glucose, complex carbohydrates and peptones. The addition of L-glucose led to significantly less AFV activity than comparable levels of D-glucose. Growth studies in liquid culture revealed that B. subtilis failed to grow in response to L-glucose. Further growth studies on solid media showed no clear correlation between enhanced bacterial growth and increases in in vitro AFV activity in response to supply of substrates. Low level AFV activity was also detected from oilseed rape roots inoculated with B. subtilis. Gas chromatography mass spectrometry headspace analysis of B. subtilis cultures grown on various substrates revealed common similarities between substrates promoting AFV activity, although it was not possible to isolate individual antifungal compounds.

Spore‐forming bacteria isolated from oilseed rape (OSR) roots were tested for biological control activity against Rhizoctonia solani damping‐off of OSR, using a simple slurry coat formulation. From a total of 239 strains which were tested, Bacillus subtilis 205 was selected as the most promising biocontrol agent (BCA). A known isolate of B. subtilis (NCIMB 12376), which had previously shown activity against R. solani in cotton, was used as a standard comparison throughout. In an in vivo screening, pre‐emergence damping‐off disease control by B. subtilis 205 was excellent, with plant stands being almost as high as non‐diseased controls. However, post‐emergence survival was less good, although the surviving plants exhibited significantly reduced hypocotyl rot. Growth‐room trials which assessed the effect of ambient temperature on the biological control efficacy of B. subtilis strains 12376 and 205 showed that isolate 205 was more effective at lower temperatures. Disease control by isolate 205 at 15°C/10°C (day/night) suggests that this bacterium could operate under autumn sowing field conditions. Further investigations also indicated that the addition of iron (III) to the BCA formulation may enhance disease control by both bacilli. The potential of bacterial BCAs for the control of seedling diseases is discussed.

Two leaf disc bioassays were developed for screening bacteria as putative biological control agents of Botrytis cinerea and Rhizoctonia solani on lettuce. Aerobic spore and non-spore forming bacteria were isolated from the phylloplane, rhizoplane and rhizosphere of symptom-free lettuce plants grown in the presence and absence of chitin or composted bark soil amendments. Bacteria, previously isolated from other plants, were also included in the primary screen initially against B. cinerea. One hundred and twentyseven of 700 isolates reduced botrytis rotting of lettuce leaves by more than 50% in the primary screen. Following a secondary screen against B. cinerea, the lead 50 isolates were also tested for suppression of R. solani infection. Four isolates significantly reduced both botrytis and rhizoctonia leaf rotting. Eleven and five isolates gave control of botrytis and rhizoctonia, respectively, equal to that given by the standard fungicides Rovral WP (iprodione) and Basilex (tolclofos methyl). The two most effective isolates against B. cinerea and R. solani were both identified as Bacillus subtilis. Use of soil amendments did not increase the proportion of efficacious isolates recovered. Effective isolates were originally recovered from roots of oilseed rape and lettuce leaves. In general, it was found that bacteria which controlled one disease effectively did not control the second disease nearly as well. The bioassay protocols developed in this study were used successfully in screening a large number of bacterial isolates in a short time.