ARS | Publication request: DIRECT SPORE COUNTS VS. COLONY FORMING UNIT COUNTS AS METHODS FOR QUANTI- FYING VIABLE BEAUVERIA BASSIANA CONIDIA

Submitted to: Society for Invertebrate Pathology Annual Meeting Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: May 18, 2000
Publication Date: August 13, 2000
Citation: JARONSKI, S., LIEBMANN, J. DIRECT SPORE COUNTS VS. COLONY FORMING UNIT COUNTS AS METHODS FOR QUANTIFYING VIABLE BEAUVERIA BASSIANA CONIDIA. PROCEEDINGS OF THE ANNUAL MTG OF THE SOCIETY FOR INVERTEBRATE PATHOLOGY. 2000.

Technical Abstract: Two different methods are generally used to quantify spores in fungal preparations. One technique is based on colony forming units (CFU) resulting from the plating of diluted spore suspensions on some agar medium. The second method uses direct counts of conidia in a diluted spore suspension with a hemocytometer. The counts are then adjusted by conidial viability determined by the percent spore germination after a standard incubation time on an agar medium. The purpose of this study was to determine the relative accuracy and precision of the two methods in estimating the viable conidial count of Mycotech technical grade Beauveria bassiana spore powder (TGAI) and two end product formulations,wettable powder (Mycotrol 22WP) and an emulsifiable suspension (Mycotrol ES). Direct conidial counts, adjusted for conidial viability,were ecompared with a CFU method.Three replicate determinations were performed o each of three replicate samples of each formulation.CFU-based data consist- ly underextimated the true viable conidial count of all three materials,as low as 16% of the direct count methods(TGA) suspended in.05% Tween 80).With 22wp & ES the CFU method underestimated true count by 58%&50%,respectively, In addition,the precision & reproducibility of the CFU method,as indicated by the Coefficient of Variation of replicate determinations & replicate samples,was poorer for the CFU method, then for the adjusted direct count. Based on our observations were strongly advise against the use of CFU meth- odology to est.viable conidial count, such as in shelf life studies or quality control.If circumstances require the CFU method, then allowance should be made for considerable underestimation and reduced precision.