Three species of the Portulacaceae each infected by a Physoderma parasite were collected at several locations in Utah. The hosts have been identified as Claytonia lanceolata Pursh., Oreobroma pygmaeum (A. Gray) Howell, and Erocallis triphylla (S. Wats.) Rydb. Since our present knowledge of Physoderma on members of the Portulacaceae is meager, it seemed desirable to learn as much as possible about the parasite, its hosts, and the relationship between parasite and host. Plants of all three hosts activated from perennating organs were grown for extended periods of time under uniform conditions. Cold treatments were most successful in activating host perennating organs and scarifiacation of the seed coat was necessary to induce seed germination. From field and laboratory studies a description was made of the appearance and the effect of the parasite on each host species. Marked hypertrophy of host tissue and frequent distortion of plant organs were characteristic of infections on O. pygmaeum and the stems of E. triphylla. Discoloration and slight or no hypertrophy were characteristic of infections on C. lanceolata and the leaves of E. triphylla. Microscopic study of the endobiotic phase indicated similarities in the vegetative phase of the parasites on the three hosts. Comparative sporangial measurements, however showed differences in the size of resting sporangia from each host. The present report of the occurrence of Physoderma on C. lanceolata and E. triphylla are new records and extend our knowledge of the host range of this parasite. The report of vascular infection on O. pygmaeum and E. triphylla are additions to a limited number of such ingections reported for chytrid parasites. Various attempts to germinate resting sporangia of the parasites and make cross-inoculations on the three host species have been unsuccessful. Such information is important in the classification of the parasites here involved and will undoubtedly contribute to an evaluation of taxonomic characters in the genus Physoderma.



College and Department

Life Sciences; Plant and Wildlife Sciences



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