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Histopathology and Cytology of Cronartium ribicola in Tissue Cultures of Pinus monticola. A. E. Harvey, Plant Pathologist, USDA Forest Service, Intermountain Forest and Range Experiment Station, Ogden, Utah 84401, stationed in Moscow, Idaho, at the Forestry Sciences Laboratory, which is maintained in cooperation with the University of Idaho; J. Y. Woo, Biological Laboratory Technician, USDA Forest Service, Intermountain Forest and Range Experiment Station, Ogden, Utah 84401, stationed in Moscow, Idaho, at the Forestry Sciences Laboratory, which is maintained in cooperation with the University of Idaho. Phytopathology 61:773-779. Accepted for publication 3 February 1971. DOI: 10.1094/Phyto-61-773.

Intercellular ramification by mycelia of the blister rust fungus (Cronartium ribicola) was pronounced in 12-week-old host tissue cultures of western white pine (Pinus monticola). Individual hyphal cells were mononucleate and generally uniform in diameter. Constrictions of the haustoria were observed at points of entrance into host cells. Haustorial morphology varied widely. The numbers of nuclei within individual haustorial cells also varied. Mononucleate haustoria were the most common, but binucleate haustoria were rarely observed. Haustoria had well-developed encapsulation layers, and were usually associated with the hostís nuclei. Host cell damage increased as the age of the infection advanced.

Additional keywords: Obligate parasitism, histology, nucleation.