Development of Leptographium wageneri on root surfaces and other substrata

Summary Conidia of Leptographium wageneri var. ponderosum, Leptographium wageneri var. pseudotsugae and Leptographium wageneri var. wageneri germinated on wounded roots of ponderosa pine (Pinus ponderosa) , Douglas fir (Pseudotsuga menziesii) , and pinyon (Pinus edulis) , but not on unwounded roots. On wounds, germination occurred regardless of the combination of pathogen variety and plant species. When wounded roots of ponderosa pine and Douglas fir seedlings were inoculated with conidia of L. w. var. ponderosum and L. w. var. pseudotsugae , respectively, 87‐100% of the seedlings became infected. When unwounded roots were inoculated with wooden blocks colonized with L. wageneri , 60‐66% of the seedlings became infected. The development of L. w. var. ponderosum and L. w. var. pseudotsugae on agar was compared with their development on agar overlaid with either cellophane or Nucleopore membranes. Undulating hyphae were found commonly in and on the agar, but less frequently on the membranes. On both membranes, mycelia formed mats which were tightly appressed to the surface; mats were not formed on the agar. On both agar and the membranes, two or more hyphae often formed a strand. When L. w. var. ponderosum mycelia were allowed to colonize the surface of an unwounded pine root, strands, undulating hyphae and poorly formed mats were seen.