A stimulus for sporulation of axenically grown flax rust

Abstract

Flax rust ( Melampsora lini) grown axenically on a chemically defined medium sporulates only sparsely. The presence of an impermeable film on top of the mycelium stimulates sporulation where it touches the mycelium. The density of spores (as measured by the concentration of carotenoids) can increase tenfold and more. The increase in strictly localized to the area in contact with the film. If the film is applied after a certain critical age the effect drops off rapidly. The nature of the film seems to be unimportant as long as it is relatively impermeable to volatile substances. The effect is also persistent: if the film is removed after a number of days, the tissue at that location will still produce more spores.