CARBOHYDRATES, INVERTASE ACTIVITY, GROWTH AND DIMORPHISM IN SPORISORIUM-REILIANUM

Sporisorium reilianum, the fungus that causes sorghum head smut, was g rown with sucrose, lactose, trehalose or raffinose in liquid suspensio n or on a solid medium. Liquid culture media were analyzed for hydroly sis products of these carbohydrates to determine extracellular enzyme activity of the fungus. Increased amounts of glucose and fructose in t he culture medium of S. reilianum grown with sucrose or raffinose indi cated that invertase (beta-fructofuranosidase, 3.2.1.26) activity was present. No evidence of extracellular galactosidase or trehalase activ ity was found. Enhanced sporidial colony formation on carbohydrates th at can be hydrolyzed to hexoses, and specific forms of mycelial growth on lactose, trehalose or on a carbohydrate-deficient medium might sug gest that mycelial growth is a way of foraging for food sources. Howev er, the rapid and profuse mycelial growth on the host cell wall glycop rotein appears to be in response to abundant food supply (probably of a different type). Therefore availability of different kinds of carbon sources in the environment of the growing fungus might determine dimo rphism and associated pathogenesis by S. reilianum.