Soil samples for isolation of antagonistic bacteria were collected
from potato field plots (located near Delhi, Ontario) that
had been treated multiple times with an organic product since
2007 to establish disease suppressive conditions against potato
diseases (Abbasi 2013). Soil samples from these plots were collected
in 2008 and 2009 after harvesting tubers. Total culturable
bacteria from soil samples were enumerated by dilution plating
onto nutrient agar and King’s B (KB) media as described by
Vidhyasekaran et al. (1997). Individual bacterial colonies from dilution plates were further purified on Luria–Bertani (LB) agar
plates. The purified bacterial isolates were evaluated for their
antagonistic activity against P. ultimum, Phytophthora capsici,
Fusarium oxysporum, and Rhizoctonia solani by dual culture technique as
described by Vidhyasekaran et al. (1997). The bacterial isolates
were streaked on one side of a Petri dish (1 cm in from the edge)
containing PDA medium, and a 6 mmmycelial disc from a 7-dayold
culture was placed on the opposite side of the Petri dish and
the plates were incubated at 24 °C for 3–5 days. The zone of inhibition
(mm) was recorded by measuring the distance between the
edges of the growing mycelium and the antagonistic bacterium.
Five replications were maintained for each isolate.