Characterising resistance at different levels of expression is important in understanding host defence mechanisms and the improvement of durable disease resistance in crop plants. Histological reactions of the lentil cultivars EL-142 (susceptible) and Gudo (resistant) to infection by Uromyces viciae-fabae, were investigated by means of fluorescence and confocal laser microscopy. Components of resistance included the proportion of successful penetrations, early abortion, host cell necrosis and colony size. The percentage of germinated urediniospores that had not penetrated was significantly higher for Gudo than for EL-142. Furthermore, Gudo had a higher percentage of early aborted colonies, frequently associated with host cell necrosis, than the susceptible cultivar. The host cell necrosis index for Gudo was 1.13, indicating an excessive hypersensitive response to lentil rust. At the macroscopic level, rust pustules on Gudo were surrounded by chlorotic and necrotic flecks. Results indicated that the resistance to lentil rust in Gudo is the result of prehaustorial and posthaustorial mechanisms. However, resistance to rust may not be durable because of its hypersensitive nature.

S OME YEASTS PRODUCE SEXUAL SPORES (ascospores) in a variety of shapes and surface ornamentations. These intriguing structures have hitherto been used only in yeast classification. Here, we propose the likely primary function of spore shape and ornamentations, in water-driven movement, as aiding the dispersal of the spores from enclosed containers (asci). This interpretation of the mechanics involved might find application in nano-, aero-and hydro-technologies with the re-scaling of these structures.