DIFFERENTIATION OF AECIDIOSPORE-DERIVED AND UREDOSPORE-DERIVED INFECTION STRUCTURES ON COWPEA LEAVES AND ON ARTIFICIAL SURFACES BY UROMYCES-VIGNAE

Aecidiospores and uredospores are the two dikaryotic spore forms of th e cowpea rust fungus Uromyces vignae. After germination they can be in duced to develop a series of infection structures including appressori a, infection hyphae, and haustorial mother cells. Haustoria are then f ormed within host cells. The differentiation of infection structures w as compared on polystyrene membranes with defined topographies, on scr atched polyethylene membranes, and in planta. On polystyrene membranes with defined topographies both sporelings showed highest rates of dif ferentiation on ridges 0.3 mum high but aecidiosporelings responded le ss efficiently to this stimulus than uredosporelings. On scratched pol yethylene membranes, almost 90% of both sporelings differentiated appr essoria, but only 10% formed haustorial mother cells; haustoria were n ot observed. On the host plant :by contrast, only 50% of the sporeling s differentiated appressoria, but most of these formed haustorial moth er cells and haustoria. In planta haustorial mother cell development o ccurred approximately 6 h earlier than on inductive membranes. Infecti on structures formed on artificial membranes and on host plants were s imilar in morphology and nuclear condition.