Use of Bacillus subtilis as biocontrol agent. V. Biological control of diseases on maize and sunflowers

The effect of different environmental conditions on plant growth-promoting and antifungal activities of two different Bacillus subtilis strains were s tudied. For this purpose, the bacteria isolated and commercialized by FZB B iotechnik GmbH Berlin were tested for their in vitro and in vivo performanc es. First, the strains were screened for their antagonistic abilities again st phytopathogenic fungi of maize and sunflowers. It was found that antifun gal activities varied according to the composition of the assay medium, pH and temperature value. Low iron availability in the assay medium increased bacterial competition for this element and resulted further in a higher ant ifungal activity. Further, it was found that different nitrogen sources aff ected differently growth and spore production by B. subtilis strains. Highe r growth and spore production rates were observed when the bacteria were in cubated in Landy medium or in nitrate-nitrogen rather than in ammonium-nitr ogen broth. Then the efficacy of the bacteria to promote plant health and g rowth was evaluated. These studies were conducted in culture solution and i n soil under different ecological factors. The results suggest that these b acterial strains may produce substances that enhance plant growth and yield on maize and sunflowers. However, the results also showed that in vitro an tibiotic activity did not always correlate with disease reduction on maize in greenhouse and field trials. Only in the case of the biological control of Sclerotinia sclerotiorum on sunflowers in field trials, a satisfying eff ectiveness was achieved. The results are discussed with regard to the gener al effect of plant growth and health-promoting substances produced by Bacil lus subtilis.