Biological control of damping-off and root rot caused by Pythium aphanidermatum on greenhouse cucumbers

Abstract

Damping-off and root rot of greenhouse cucumbers grown in rock wool, caused by Pythium aphanidermatum, is a recurring problem for growers throughout the major production areas of Canada. Four commercially formulated biocontrol agents, Streptomyces griseoviridis strain K61 (Mycostop®), Trichoderma harzianum strain T-22 (RootshieldTM Drench), Trichoderma virens strain GL-21 (SoilGardTM 12G), and Gliocladium catenulatum strain J1446 (PrestopTM WP, Prestop mix) were evaluated in growth-chamber and greenhouse trials conducted over 2 years for efficacy against this disease. The agents were applied twice, once at seeding time and again 11 days later, as a drench (or incorporated into the sawdust medium for SoilGard). This was followed by inoculation with a P. aphanidermatum mycelial suspension 12 days after seeding. In growth-chamber trials conducted at 28–30 °C and 90% relative humidity, seedling mortality in the treatment receiving P. aphanidermatum alone was over 80%. Only G. catenulatum (Prestop WP) significantly reduced disease incidence and enhanced plant height and fresh mass under these conditions. In greenhouse experiments conducted in the fall seasons of 2001 and 2002, mortality in the treatments receiving P. aphanidermatum alone was about 60%. The most effective biocontrol agent was G. catenulatum (Prestop WP, Prestop mix), followed by S. griseoviridis (Mycostop), which both significantly reduced plant mortality and increased plant height. These results indicate that G. catenulatum, when applied as a preventative treatment, has the potential to significantly reduce root rot and damping-off caused by P. aphanidermatum on greenhouse cucumbers, under conditions of high disease pressure.