VIEW ARTICLE

Isolation and Quantitative Determination of Macrophomina phaseolina from Soil. G. C. Papavizas, Microbiologist, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland 20705; N. G. Klag, Biological Aid, Soilborne Diseases Laboratory, Plant Protection Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland 20705. Phytopathology 65:182-187. Accepted for publication 26 August 1974. DOI: 10.1094/Phyto-65-182.

Selective media and a method were developed for the direct isolation of Macrophomina phaseolina from soil, and for the quantitative estimation of its inoculum density in soil. The selective basal agar contained commercial potato-dextrose agar and 25 and 100 mg/liter of chlortetracycline hydrochloride and streptomycin sulfate, respectively. The best combinations of other antimicrobial agents added to the basal medium were p-(dimethylamino) benzenediazo sodium sulfonate (DASS) + oxgall + rose bengal and DASS + oxgall + pentachloronitrobenzene. The isolation method involved wet-sieving of soil and exposure of selected sieve residues to NaClO solution for 8 minutes before aliquots were pipetted from the final dilutions onto the surface of the selective media. The method was used with naturally and artificially infested soils. Recovery of sclerotia from artificially infested soils was between 70 and 80 percent. Numbers of sclerotia in naturally infested soils ranged from none to more than 1,000/g soil. Most colonies from naturally infested soils originated from free sclerotia in soil.