Melanin Deficiency and its Effect on Pathogenicity in Alternaria alternata

Many plant fungal pathogens produce dark brown to black pigments; melanins. These pigments are thought to contribute to longevity, survival and pathogenicity of their producers. In an attempt to test the role of melanin in the pathogenicity of the fungus Alternaria alternata, three melanin-deficient (white) isolates, SW1, SW2 and SW3 were compared with their wild type (black) parent for some parameters that are considered essential to disease development. These included colony radial growth rate, number of viable conidia produced, rate of growth of leaf spot, and efficiency of producing the pathogenicity- associated enzymes, cellulase and pectinase. In none of these parameters did the melanin-deficient (white) isolates significantly differ from their wild type (black) parent indicating a lack of direct effect of melanin in pathogenicity of this fungal species.