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Survival of Macrophomina phaseolina Sclerotia in Soil: Effects of Soil Moisture, Carbon:Nitrogen Ratios, Carbon Sources, and Nitrogen Concentrations. O. D. Dhingra, Research Associate, Department of Plant Pathology, University of Illinois, Urbana 61801; J. B. Sinclair, Professor, Department of Plant Pathology, University of Illinois, Urbana 61801. Phytopathology 65:236-240. Accepted for publication 11 September 1974. DOI: 10.1094/Phyto-65-236.

Sclerotium populations of Macrophomina phaseolina declined rapidly under high soil moisture and in soils amended with glucose and NaNO₃ in different C:N ratios. At soil moisture of 60-100% moisture holding capacity, sclerotium populations declined 96-99% as compared with populations in dry soil (control). Sclerotium populations declined rapidly within 2-3 weeks in soils amended with glucose, sucrose, starch, or cellulose with the greatest reduction (81%) occurring with the addition of sucrose. In soils amended with sodium nitrate, M. phaseolina sclerotium populations decreased for 2-3 weeks after treatment, then increased until at 7 weeks, populations exceeded the controls. Sclerotium populations declined more rapidly when soils were amended with glucose (1%, w/w air dry soil) and NaNO₃ mixtures giving C:N ratios of 10 and 20, than at 40 and 80. The sclerotium populations for all C:N ratios decreased by 58-61% compared with the control during the first week after treatment. Among all amendments the decrease in M. phaseolina populations was significantly correlated with increase in total microbial population in the soil.