Occurrence of antimicrobial activities of bacteria from soybean leaf spots

Bacteria were isolated from leaf spots of field grown soybeans during two growing seasons. The leaf spots yielded up to 4 different species and a total population size of about 107–108 bacteria/cm2. The majority of the 192 isolates belonged to the species Pseudomonas syringae pv. glycinea (55%), causing leaf spots of bacterial blight on soybeans, and Erwinia herbicola (22%). The remaining isolates included bacteria from other genera, but occurred occasionally. The determination of biological activity of the isolates demonstrated that a high percentage of strains from the group Erwinia/Enterobacter produced biological active substances against Escherichia coli (69%) and against Chlorella pyrenoidosa (88%). The majority of P. syringae pv. glycinea strains failed to do so. None of the isolates affected the growth of Geotrichum candidum. The E. herbicola strains showed clear antagonistic properties against a wide range of isolated bacteria. Four E. herbicola strains inhibited the growth of nearly all other E. herbicola isolates and 6 other strains were active against most of the P. syringae pv. glycinea isolates. However, antagonistic interactions among strains isolated from a distinct leaf spot were very rarely.