Download (PDF 188 KB): https://research.fs.usda.gov/download/treesearch/40878.pdf
Abstract
Twenty-five plant species (21 genera, 14 families), which comprise a portion of the understory in forests of the Eastern United States, were evaluated for susceptibility to infection by
Phytophthora ramorum. The degree to which
P. ramorum is able to form sporangia and chlamydospores was also assessed on these hosts. Seedlings were spray-inoculated with a mixture (4,000 sporangia/ml) of four
P. ramorum isolates followed by incubation in a dew chamber at 20°C in darkness for 5 days. Percent infection on individual leaves/leaflets was assessed visually. Mean percent leaf area infected ranged from 0.7% for
Smilax rotundifolia to 93.8% for
Kalmia latifolia. Eight plant species tested developed significantly larger lesion areas than those found on susceptible control
Rhododendron 'Cunningham’s White'. Fourteen species in addition to the susceptible control exhibited infection of over 90% of their leaves. Sporangia production by
P. ramorum varied considerably among plant species, ranging from 36 per cm² lesion area on
Myrica pennsylvannica to 2,001 per cm² lesion area on
Robinia pseudoacacia. Numbers of chlamydospores produced per 6-mm-diameter leaf disk incubated in a
P. ramorum sporangia suspension ranged from 25 on
Ilex verticillata to 493 on
Rhus typhina. The results indicate that many common understory species in Eastern U.S. forests are susceptible to
P. ramorum and capable of providing ample sources of inoculum (sporangia and chlamydospores) for forest epidemics should the pathogen be introduced and should temperature and moisture conditions exist that are conducive to disease development. [
Partially funded by PSW, UESD, Agreement 08-IA-11272138-060
Citation
Tooley, Paul W.; Browning, Marsha. 2009. Susceptibility to Phytophthora ramorum and inoculum production potential of some common eastern forest understory plant species. Plant Disease: The American Phytopathological Society. 93(3):249-256.
