Antigenic relationship of Dactylaria gallopava to Scolecobasidium constrictum

Dactylaria gallopava and Scolecobasidium constrictum were reduced to varietal status under the new combination of Dactylaria constricta (Abbott) Dixon et Salkin var. gallopava (Cooke) Salkin & Dixon, and D. constricta (Abbott) Dixon et Salkin var. constricta, primarily on the basis of the morphologic similarity of their two-celled, dematiaceous, blastic conidia. To appraise this taxonomic change, we studied the antigenic relationship of D. gallopava to S. constrictum using the exoantigen procedure. Exoantigens were prepared from 20 isolates of D. gallopava, seven isolates of S. constrictum and two isolates of S colecobasidium tschawytschae and were tested against reference rabbit anti-D. gallopava and anti-S. constrictum antisera in the presence of their homologous antigens using the micro-immunodiffusion technique. All D. gallopava isolates produced two to three distinct, identical exoantigens. The seven isolates of S. constrictum also produced two to three distinct exoantigens. None of the seven isolates of S. constrictum was reactive against the D. gallopava reference system. Three of the 20 D. gallopava culture filtrate antigens produced one or two precipitin bands of nonidentity with the S. constrictum reference reagents. Both isolates of S. tschawytschae were nonreactive with the D. gallopava and S. constrictum reference reagents. In addition, D. gallopava differed from S. constrictum in the production of a reddish-brown diffusible pigment, growth up to 45°C, and sensitivity to cycloheximide. Based on these physiologic differences and little or no antigenic relatedness between D. gallopava and S. constrictum, we conclude that these two species should be retained as separate entities rather than be considered as varieties of a single species.