Observations on the Cultural and Pathogenic Habits of Thielaviopsis basicola (Berk. & Br.) Ferraris

Abstract

It is now common knowledge that many species of pathogenic fungi possess physiologic races that differ in one or more of such factors as cultural characters, morphology, pathogenicity, physiologic and ecologic relations, and biochemical effects. Stakman ('36) has suggested four principal explanations of the origin of races of fungi: (1) adaptation of an existing form, (2) hybridization of two existing forms, (3) mutations, and (4) heterocaryosis. Although new forms may arise through adaptation these changes are usually more satisfactorily explained by other means. Many investigators have shown conclusively that new forms do arise from hybridization-especially well demonstrated in the Uredinales and Ustilaginales. There seems to be some conflict of evidence regarding the origin of new forms by heterocaryosis, but it must be conceded that this phenomenon would satisfactorily explain some of the sectoring that has occurred in cultures. Results of many experiments, notably by Stakman and his students, seem to prove that mutations do occur in fungi. Results of investigations indicate that many physiologic races exist undiscovered today. Furthermore, considering the modes of origin of these races, it becomes painfully apparent that new forms are continually arising. Their importance can hardly be over-estimated. Any attempt to combat the ravages of a disease caused by such a variable fungus, in order to be successful, must be based on a comprehensive knowledge of the specialization or variation exhibited by the causal organism in various regions.