Differentiation of aecidiospore-and uredospore-derived infection structures on cowpea leaves and on artificial surfaces by Uromyces vignae

Aecidiospores and uredospores are the two dikaryotic spore fonus of the cowpea rust fungus Uromyees vignae. After germination they can be induced to develop a series of infection structures including appressoria, infection hyphae, and haustorial mother cells. Haustoria are then fonned within host cells. The differentiation of infection structures was compared on polystyrene membranes with defined topographies, on-scratched polyethylene membranes, and in ·planta. On polystyrene membranes with defined topographies both sporelings showed highest rates of differentiation on ridges 0.3 μm high but aecidiosporelings responded less efficiently to this stimulus than uredosporelings. On scratched polyethylene membranes, almost 90% of both sporelings differentiated appressoria, but only 10% fonned haustorial mother ceUs; haustoria were not observed. On the host plant, by contrast, only 50% of the sporelings differentiated appressoria, but most of these fonned haustorial mother ceIls and haustoria. In planta haustorial mother cell development occurred approximately 6 h earlier than on inductive membranes. Infection structures fonned on artificial membranes and on host plants were similar in morphology and nuclear condition