Role of surface films in the germination of rust uredospores

Abstract

An association of rust uredospores with materials which form films on water surfaces was demonstrated. One milligram of spores of Puccinia graminis tritici and 3.5 mg of Uromyces phaseoli spores released about 100 cm2 of film within 1 min of coming into contact with a large water surface. Oxidative reactions within these films, which were accelerated by light, formed products which inhibited spore germination. When spores were germinated on a large volume of water, germination varied with the surface area, which indicated that inhibitor was formed and retained at the water surface.Hydration of spores resulted in an increased germination, a decreased film area and a delay or prevention of film reactions. Storage of spores at lower humidities resulted in decreased germination, decreased film area, and film reactions which began as soon as the spores came into contact with the water surface. These results suggest that the effects of light and of storage conditions on germination may be mediated by surface film materials.The amount of surface film material released by wheat and bean rust spores may be correlated with the wetability of the host cuticle and also with the ability of rusts to differentiate infection structures in vitro on artificial membranes. On plastics which supported the formation of infection structures, spores acquired spherical infection droplets when exposed to a humid atmosphere. The surface area of these droplets was correlated with the area of surface film. It is suggested that surface film material may interact with the appropriate host cuticle to determine the size and configuration of infection droplets. This would provide a water surface of defined area upon which film reactions occur resulting in a sequence of products which control germination, directed growth of the germ tube and differentiation of infection structures.