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Abstract
Concepts of fractal geometry have been used to describe the branching patterns of a variety of organisms ranging from microorganisms to trees. The fractal dimension is a measure of branching density. The fractal dimension was used to investigate the hyphal branching patterns of young colonies of the soil-borne phytopathogen Macrophomina phaseolina. The temporal development of branching density was examined by assembling composite photomicrographs of 17 entire thalli (representing three test isolates) at 2-hour time intervals. These photomicrographic images were digitized, and the fractal dimension was determined using a box-count algorithm. Analysis of 90 images revealed patterns of thallus development which were remarkably radially asymmetric. The fractal dimension ranged from 1.21 to 1.84, indicating a wide range of branching density. The temporal development of branching density was investigated by regression of fractal dimension on time. Branching density increased with time at rates characteristic of each isolate. Further, the magnitude of fractal dimension together with the rate of temporal increase of the fractal dimension permitted clear distinction among the three test isolates of M. phaseolina. These results suggest that quantitative description of branching density using the fractal dimension might become a novel supplement to the morphological criteria traditionally used in fungal taxonomy.