Foliar and Soilborne Fungal pathogens: Resistance to the bacterium Bacillus velezensis strain S4

• Kevin Chan, Plant Science, University of Delaware

• Nicole Donofrio, Plant and Soil Sciences, University of Delaware

The exudates derived from bacteria Bacillus velezensis strain S4 may contain potent compounds capable of inhibition for various economically important fungi and oomycetes. Of the compounds found in these exudates, one of which is suspected to be surfactin—a powerful antibiotic prominent for its surfactant-like properties. Species Bacillus velezensis is also known to create various other bioactive metabolites such as Fengycin, Bacillomycin D, Bacillibactin, Difficidin, Bacilysin, and Amylocycllicin. The functions of these various compounds have been identified as antifungal. The results from previously conducted research consisting of experiments using the exudate derived from B. velezensis strain S4 suggest that there may be varying levels of fungal inhibition depending on the pathogen’s preferred area of infection (foliar vs soilborne) as it seemed that the soilborne pathogens were more or less unaffected by the presence of the S4 exudate.

In this study, we assess the indirect inhibition produced by the bacterium in vitro against previously tested fungi such as Magnaporthe oryzae, Rhizoctonia solani, Colletotrichum graminicola, Diaporthe ueckerae, and Sclerotinia sclerotiorum, as well as the oomycetes Phytophthora nicotianae and Pythium dissotocum by growing both the bacteria and the respective plant pathogen within the vicinity of each other. Growth measurements and images were recorded and compared to determine if there was a correlation between resistance to the bacterium, and where the pathogens are normally located (foliar vs soilborne).