Initiation and development of latent infections by Rhabdocline parkeri on Douglas-fir

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Abstract
Quantitative estimates of frequencies of latent infections by Rhabdocline parkeri Sherw. on Douglas-fir were obtained by direct microscopy of cleared needles from three half-sib trees. The infections are intracellular and are confined to a single epidermal cell until the onset of needle senescence, a period of 2=5 years. Infection frequencies varied widely among trees but increase logarithmically with needle age on all three trees. Differences in infection ferquencies among trees were not demonstrably related to levels of infestation by Contarinia spp., a needle-galling dipteran. Active colonization of the needle resumes at the onset of needle senescence, beginning with the production of haustoria in cells adjacent to the original infection sites. Rapid colonization of the needle and sporulation of R. parkeri coincide with needle abscission, occurring before substantial colonization of the needles by saprophytic fungi. Saprophytic fungi colonized needles rapidly following abscission, but R. parkeri was recoverable in culture from needles up to 35 days after abscission.