Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: 4/30/2008
Publication Date: 6/15/2008
Citation: Shishkoff, N. 2008. Sporulation on plant roots by Phytophthora ramorum. Phytopathology. 98:S145
Technical Abstract: Phytophthora ramorum has been shown to infect the roots of many of the pathogen’s foliar hosts. Methods of detecting inoculum in runoff and of quantifying root colonization were tested using Viburnum tinus, Camellia oleifera, Quercus prinus, Umbellularia californica, and Epilobium ciliatum. Plants grown from seed or cutting in Turface monmorillonite clay granules were inoculated with a sporangial suspension (15 mL per pot at 500 sporangia/mL) and after 24 hours, uprooted, washed, and transplanted to fresh Turface (100 mL volume). Runoff was collected periodically and aliquots plated on selective media to quantify inoculum of P. ramorum; at the end of the assay (after 8-14 d) roots were plated on selective media to determine colonization. In some trials, plant roots were carefully examined at the end of the experiment, and in Viburnum, it was easy to see sporulation on root tips. Dissection of Viburnum roots revealed embedded chlamydospores. Other host roots, however, could be heavily pigmented or extremely fine, and signs of the pathogen were not often seen, even in heavily infected material. P. ramorum was commonly detected from runoff of all tested plants. In 32 Viburnum trials over the course of a year, an average of 41 propagules per pot (4 propagules per mL of runoff) were recovered from runoff from plants seven days after inoculation, with a high of 358 propagules/pot (24 propagules/mL runoff). The significance of such sporulation in the epidemiology of the pathogen needs further study.