Biocontrol of Rhizoctonia stem and root rot of poinsettia with Burkholderia cepacia and binucleate Rhizoctonia

Strategies for applying Burkholderia cepacia (strain 5.5B) and Pesta formulations of binucleate Rhizoctonia (BNR) isolates (BNR621 and P9023) were evaluated for biocontrol of Rhizoctonia stem and root rot of poinsettia caused by R. solani. During propagation, one application of B. cepacia suppressed stem rot, while application of either isolate of BNR did not. In contrast, after transplanting rooted poinsettias, one application of either BNR isolate was more effective for suppression of stem and root rot than application of B. cepacia. Sequential application of B. cepacia at propagation followed by a BNR isolate at transplanting was more effective over the crop production cycle than multiple applications of one biocontrol agent or combination application of both biocontrol agents. Root colonization by both biocontrol agents after transplanting rooted poinsettias was affected by application strategy. The least root colonization by both biocontrol agents occurred in the combination application. The highest root colonization by the BNR isolates was observed in the sequential application that provided the most effective disease control. Application of different biocontrol agents during the different production phases of poinsettia was effective for disease control, but understanding the interaction between biocontrol agents and root colonization was important to develop the best application strategy.