Assessing the severity of damping-off caused by Pythium ultimum and Rhizoctonia solani in peat-based greenhouse substrates amended with pine wood chip aggregates

Processed pine wood has potential as a greenhouse substrate component to replace perlite. However, there is limited information regarding processed pine wood’s suppressiveness to soilborne diseases. A series of experiments were conducted to evaluate pine wood chips (PWC) suppressiveness to Pythium ultimum and Rhizoctonia solani on cucumber (Cucumis sativus L. ‘Straight Eight’) seedling growth. In Experiment 1, cucumber seeds were sown in substrates formulated to contain either 10, 20, or 30% perlite or PWC aggregates and were inoculated with no pathogen (control), 0.1 g L-1 Pythium ultimum, or 0.05 g L-1 Rhizoctonia solani isolates. Fourteen-day-old cucumber seedlings were evaluated to determine disease severity. P. ultimum inoculum concentration of 0.1 g L-1 did not cause damping-off in substrates amended with perlite or PWC aggregates. Regardless of aggregate amendment rate, R. solani severity of damping-off was generally similar among substrates amended with perlite. In general, less disease was observed with PWC aggregates than with perlite across all amendment volumes. In Experiment 2, cucumber seedlings were sown in substrates formulated to contain either 20, 30, or 40% perlite or PWC aggregates and were inoculated with 0 (control), 1.2, 2.4, or 3.6 g L-1 P. ultimum isolates. Disease severity of cucumber seedlings were similar among all substrates amended with 20 to 40% PWC aggregates. In Experiment 3, cucumber seedlings were sown in substrates formulated to contain either 20, 30, or 40% perlite or PWC aggregates and were inoculated with 0 (control), 1.2 g L-1 of P. ultimum, or 0.05 g L-1 R. solani inoculum isolates. Results found potential suppressiveness of P. ultimum and R. solani when peat-based substrates were amended with PWC.