BIOLOGICAL-CONTROL OF RHIZOCTONIA STEM ROT OF POINSETTIA IN POLYFOAM ROOTING CUBES WITH PSEUDOMONAS-CEPACIA AND PAECILOMYCES-LILACINUS

A strain of Pseudomonas cepacia (ex Burkholder) Pallerni and Holmes, s train 5.5B, and an isolate of Paecilomyces lilacinus (Them) Samson, is olate 6.2F, were evaluated for biocontrol of Rhizoctonia stem rot of p oinsettia in polyfoam rooting cubes after preliminary screenings of co llected bacteria, fungi, and actinomycetes. In repeated experiments co nducted over 2-week periods, no disease developed on cuttings in cubes treated with P. cepacia as opposed to the nontreated, pathogen-infest ed controls (73 to 100% infection). Control with P. lilacinus was less effective but remained significant compared to the pathogen-infested controls. During 3-week trials, some infection (18%) occurred on cutti ngs in cubes treated with P. cepacia but the level of infection was si gnificantly less than that in the pathogen-infested controls (100% inf ection). The P. lilacinus isolate provided similar levels of stem rot control over 2- and 3-week periods. Root development on poinsettia cut tings typically was not affected by P. cepacia but, in some experiment s, was less on cuttings in cubes treated with P. lilacinus. These expe riments demonstrate the significant potential of these antagonists as biocontrol agents for Rhizoctonia stem rot of poinsettia. P. lilacinus has not been previously reported as an antagonist of R. solani. (C) 1 995 Academic Press, Inc.