Chemical induction of infection structures in rust fungi: II. Inorganic ions

Abstract

Cations and anions incorporated into agar-containing media were screened for their effects on induction of infection structures in germinating urediospores of three rust fungi. K + and Mg 2+ strongly induced differentiation in bean rust and sunflower rust fungi, while Ca 2+, Mn 2+, and Na + were only weak inducers. Differentiation frequency increased with increasing concentration of K +, and up to 70% of germinated spores formed infection structurs. Most potassium salts gave similar induction frequencies indicating that anion effects were relatively unimportant. However, iodide and nitrate anions appeared to interfere with the induction process and virtually eliminated infection structure formation even though they permitted good germ tube growth. Induction by salts was sensitive to total buffer concentration and to surface phenomena possibly related to aeration or humidity factors. Combinations of low levels of K + and Ca 2+ or K + and sucrose showed synergistic effects and in the latter case resulted in differentiation frequencies in excess of 80% for the sunflower rust fungus. Infection hyphae developed from the infection structures and the average length increased slightly between 24 and 48 hr.