VIEW ARTICLE

Mode of Penetration of Needles of Eastern White Pine by Cronartium ribicola. Robert F. Patton, Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706; David W. Johnson, Former Project Assistant, now Graduate Research Assistant, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 60:977-982. Accepted for publication 23 January 1970. DOI: 10.1094/Phyto-60-977.

Labeling basidiospores of Cronartium ribicola with a fluorescent brightener facilitated detection of penetration sites of eastern white pine needles by the germ tubes. Entry of the fungus was through the stomata. The germ tube of a basidiospore on the needle surface grew into the outer stomatal pit, penetrated between the guard cells as a very thin strand, and then characteristically formed a sub-stomatal vesicle and an infection hypha from which a mycelium developed in the mesophyll. Germ tubes that grew over the surface of the needle were brightly fluorescent for their entire length. All fluorescence imparted by the fluorescent brightener was quenched at the point of entry between the guard cells, indicating some host-parasite interaction at this point.