Host surface tissues and basidiospore-derived infection strategies of some rust fungi

Abstract

-Some Authors belief that the basidiospore germ tubes of rust fungi penetrate angiosperms directly and gymnosperms indirectly, hypothesizing that the different strategies of basidiospore-derived penetrations could be ascribed to the heavily cutinized and thick walled epidermal cells of the leaves of gymnosperms. In this paper the surface tissues of the organs of some angiosperms and gymnosperms -which are directly and/or indirectly penetrated by basidiospore germlings of Melampsora spp., Cronartium flaccidum and Crysomyxa abietis -were examined, in order to: (i) evaluate the role of the cuticular and epidermal cell-wall thickness, still considered a barrier to a direct penetration, and (ii) search for other possible cyto-histological aspects of surface tissues which could explain the different penetration strategies of rust basidiospore germlings. The results show that the thickness of cuticle and epidermal cell walls of the organs onto which the monokaryotic phase of each rust species has fitted itself during evolution to penetrate is not important in determining the penetration strategy, whereas it seems that it is the presence of lignin in the surface tissues of these organs which probably limits the direct penetration of rust basidiospore germlings.