Selection of bacterial antagonists for the biological control of Rhizoctonia solani in oilseed rape (Brassica napus)

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.