Phytophthora pini Leonian, recently re-established from P. citricola
I, is a pathogen with a wide range of forest and nursery hosts. It causes foliar
infections in horticultural nurseries in Oregon, where recirculating irrigation
systems are common. Increased use of recirculating irrigation systems may
contribute to disease caused by waterborne plant pathogens.
Simulated nursery chamber experiments were utilized to investigate the
relationship between Phytophthora pini zoospore inoculum dose and disease on
Rhododendron. Disease incidence in this system was unexpectedly low despite
high inoculum levels tested, so further experiments under lab conditions were
conducted to explore possible causes.
Detached leaf assays were conducted to determine how inoculum dose,
leaf wounding, and agitation of zoospore inoculum affected foliar infection of
Rhododendron. Wounded and nonwounded leaves were dipped into suspensions
of zoospores that were either untreated, mechanically agitated by vortexing to
cause encystment, or pumped through an irrigation sprayer system. Disease
severity (lesion area) and incidence (number of lesions per leaf area) were
measured over seven days.
At inoculum levels of ���10,000 propagules/mL, motile zoospores infected
both wounded and nonwounded leaves. Vortexing or pumping resulted in
zoospore encystment, and inoculation with these treatments caused disease
almost exclusively on wounded leaves. No disease symptoms were observed
following inoculation with any inocula at ��� 2,000 propagules/mL.
Scanning electron microscopy of leaves inoculated with encysted
propagules showed germinated cysts with hyphae growing over and around
stomata without entering leaf tissue until reaching a wound site. Nonwounded
leaves inoculated with motile spores showed stomata penetrated by hyphae.
These findings indicate the importance of zoospore motility in reaching
suitable infection sites, and demonstrate the impact of zoospore encystment on
disease development. This has implications for disease management in
nurseries where pruning wounds are common and the pumping of infested
irrigation water may influence zoospore motility and infectivity. / Graduation date: 2013
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33940 |
| Date | 31 August 2012 |
| Creators | Shay, Sarah D. |
| Contributors | Parke, Jennifer L. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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