Macrophomina phaseolina in the Sonoran Desert

The relationship between microsclerotial populations of Macrophomina phaseolina (Tassi) Goid. and selected perennial species was investigated at five native Sonoran Desert sites. The population level of M. phaseolina was found to have an inverse relationship with the presence of several plant species, including Acacia constricta and Larrea tridentata, as measured by canopy cover, plant counts, and proximity of the soil sampling point to the nearest individual. Microsclerotia of M. phaseolina were detected in 45% of the 500 quadrats (3.3 m2) sampled, with a maximum observed population of 233 microsclerotia per 20 g soil. The microsclerotial populations of the five study sites showed significant aggregation as measured by Morisita's index of dispersion. No relationship was found between microsclerotial populations and soil pH, soil nitrate, or total soil nitrogen. The frequency of detection and population level of this agriculturally important pathogen raises questions concerning the role of the fungus in t...