Effects of fungicides on physiology of phylloplane fungi

Abstract

Effects of Captan, Dicloran, Thiram and Verdasan on the growth, germination, cellulose decomposition and starch hydrolysis of some phylloplane fungi isolated from fungicidetreated leaves were studied. Radial growth rates were reduced with increasing concentrations of the fungicides; Captan and Dicloran were less inhibitory compared with Thiram and Verdasan. The fungi could tolerate lower concentrations of the fungicides in liquid media than on solid media : 0.05 ppm of Verdasan prevented the mycelial growth of Drechslern biseptata (Sacc. & Roum.) Richardson & Fraser and Trichoderma viride Pers. ex Fr. Spore germination and germ-tube elongation were retarded at lower concentrations of fungicides than was mycelial growth. Concentrations of Captan and Dicloran of up to 50 ppm were only fungistatic to the spores of Alternaria alternata (Fr.) Keissler, Cladosporium cladosporioides (Fres.) de Vries and T. viride . Thiram at 50 ppm and Verdasan at 10 ppm and higher were fungicidal after exposure of the spores to the fungicides for 24 h. Cellulose decomposition and starch hydrolysis were inhibited by increasing concentrations of the fungicides. The higher concentrations of Thiram and Verdasan prevented the cellulolytic abilities of even the strongly cellulolytic species. The physiological data are discussed in relation to ecological studies on the effects of fungicides on the occurrence of phylloplane fungi.