Biochar and Trichoderma Reduce Containerized Poinsettia Root Rot Caused by Pythium aphanidermatum

Poinsettia (Euphorbia pulcherrima) root rot disease caused by Pythium apha-nidermatum is a significant problem for poinsettia production. Biochar can replace peatmoss, a commonly used substrate, and has many benefits, including reducing soil -borne diseases. A greenhouse study was conducted to test the suitability of mixed hardwood biochar (HB) for greenhouse potting mix and its potential to reduce poin-settia root rot disease. Mixed HB was blended with the commercial substrate (CS) at 0%, 20% and 40% [CS100 (control), HB20, HB40, respectively, by volume]. Half of the poinsettia plants were inoculated with P. aphanidermatum, and the other half were not. Trichoderma spp. were inoculated to half of the pathogen-inoculated and pathogen-free plants. The plant growth index (GI), shoot dry weight (SDW), disease severity (DS), and disease incidence (DI) were measured. In the absence of the patho-gen, plant growth in HB20 and HB40 had similar GI and SDW with the control. In the presence of the pathogen, plants grown in HB20 had significantly higher SDW but lower DS and DI than the control. HB20 could replace peatmoss-based substrate to reduce poinsettia root rot disease caused by P. aphanidermatum.