Biological and fungicidal antagonism of Sclerotium cepivorum for controlling onion white rot disease

The action of some microbial isolates and Topsin-M against the most pathogenic isolate (Sc-2) of Sclerotium cepivorum causing onion white rot was tested. Bacillus subtilis B-4, B. subtilis B-5, Trichoderma koningii and Trichoderma harzianum were the most antagonistic isolates of the causal fungus. Mycelia of sclerotial germination of S. cepivorum (Sc-2) were completely inhibited in vitro by application of 2.0 g L-1 Topsin-M. In pots, disease incidence was decreased to 8.33 % by the use of Topsin-M followed by T. koningii (29.17 %) compared with 95.83 % for the control, i.e., a remarkable reduction in severity was obtained. Under field conditions, disease incidence was decreased to 2.78 % by Topsin-M and to 11.11 % by T. harzianum. Both agents caused a sharp reduction in disease severity, reaching 1.39 % and 9.72 %, respectively, with 11.80 % being achieved by T. koningii and B. subtilis B-5. A close link between the biological action and enhancement of the enzyme activities of polyphenol oxidase and peroxidase with ability of onion to resist S. cepivorum was found, indicating induction of systemic acquired resistance. Accordingly, chlorophyll, root and foliage lengths, foliar, bulb dry matter and bulb productivity were also enhanced upon application of this biological control strategy.