Fungal Phytohormones in Pathogenic and Mutualistic Associations

Abstract

Phytohormones are a naturally occurring group of organic substances that at low concentration control several stages of plant growth and development such as cell elongation, cell division, tissue differentiation, and apical dominance (Costacurta and Vanderleyden 1995) and occur in all major groups of flowering plants and gymnosperms. Five major groups of phytohormones regulate plant growth and development (Table 1), and all have been found in microorganisms. Both indole-3acetic acid (Thimann 1936) and the gibberellins (Kurosawa 1926) were found very early in the study of plant growth regulators, long before their recovery in flowering plants. Abscisic acid is produced in large amounts by fungi of the genera Cercospora and Botrytis (Assante et al. 1977) and ethylene also by some fungal groups (Arshad and Frankenberger 1988). Cytokinins have been isolated from the bacterium Pseudomonas syringae, the causal organism of olive knot, and from some fungi as well (Mandahar and Suri 1983; Gulati and Mandahar 1986).