INTERACTION OF BEAN LEAF PUBESCENCE WITH RUST UREDINIOSPORE DEPOSITION AND SUBSEQUENT INFECTION DENSITY

The role of dense straight trichomes on bean leaves associated with race-nonspecific resistance to rust was studied using a settling tower method for uniform inoculation. Abaxial leaf trichomes, which occur only on adult leaves, trapped significant numbers of urediniospores, especially those deposited in clusters, and resulted in reduced effective inoculum reaching the leaf surface. In the field where infection conditions are often less than optimum, leaf pubescence would partially explain the observed resistance. However, the observed increase in total number of spores as well as similar infection densities on fully expanded leaves of glabrous and pubescent genotypes cannot be explained by the trichomes. Other physical or chemical features of the leaf surface such as waxes or cations may play a role. The ecological fit of leaf pubescence is discussed.