Orientation of Germ Tubes of Puccinia hordei on the Hordeum chilense Leaf Surface

The directional growth of urediospores germ tubes along the transverse axis of a cereal's leaf is considered to be a response to stimuli from the plant surface. In order to find out if the germ tube growth is directed towards stomata, and if the cuticular wax layer plays a role in this orientated growth, several orientation parameters of Puccinia hordei Otth germ tube were measured on Hordeum chilense Roem. and Schult, leaves with and without the wax layer. Orientated growth of the germ tubes seems to start only upon contact with the epidermal cell junctions. The lateral growing of the germ tube over the first epidermal cell junction that it meets is longer than the subsequent lateral growings. These lateral growings, especially the first one, may help the germ tube to grow along the transverse axis of the leaf. No evidence was found of attraction of the germ tube by stomata. Removal of the cuticular wax layer did not result in poor germ tube orientation. This suggests that the leaf wax layer has no role on the orientation of the germ tube.