Formation of aerial hyphae in Saprolegnia ferax

Abstract

During colony development on solid media aerial hyphae of Saprolegnia ferax never formed at the colony margin, but developed from the tip region of surface-growing lateral branches, from initiation of lateral branches from a dorsal position on surface-growing hyphae, and by submerged hyphae growing upwards and penetrating the medium surface. There was a gradient in production of aerial hyphae with numbers increasing towards the colony centre. When colonies were superimposed almost all marginal hyphae of the top colony ceased growth temporarily before resuming growth as aerial hyphae. Aerial hyphae were also induced in blocks cut from young cultures and inserted in older colonies in a position just proximal to the colony margin. Other fungal species induced formation of aerial hyphae in S. ferax . The formation of aerial hyphae is discussed in relation to negative autotropism and evidence is presented for self-produced metabolites which induce formation of aerial hyphae.