Basidiospores of rust fungi ( Uromyces species) differentiate infection structures in vitro

Abstract

The effect of six different substrates on basidiospore germination and differentiation of infection structures was investigated in three species of Uromyces: U. appendiculatus var. appendiculatus, U. viciae-fabae, and U. vignae. Light and fluorescent microscopic observations were made after 3 days of incubation on the following substrates: 2 or 5% water agar, glass slide, collodion membrane, nitrocellulose sheet, and isolated host cuticle. Infection structure development up to the formation of a primary hypha was observed on hard substrates, such as 5% water agar, nitrocellulose sheet, and on isolated host cuticle. Addition of oil to the collodion membrane did not significantly increase the differentiation rate. The morphology and nuclear condition of these basidiospore infection structures were similar to those observed in host tissue. For the three directly penetrating species we studied, it appears that basidiospores respond to an unspecific stimulus, such as the thickness of host cuticle or the hardness of an artificial substrate.