Drought resistance among genotypes of Port-Orford-cedar (Chamaecyparis lawsoniana (A. Murr.) Pan., Cupressaceae) seedlings was evaluated both in the field and in the greenhouse. Field water potentials (��) of 5-year-old seedlings were measured at two high-elevation plantation sites where summer drought occurs. Measurements of �� were compared to survival two years prior at the same site. The north coastal breeding zone 1 had significantly lower mid-day �� and lower survival than the southern interior breeding zone 6. Percent survival at 3 years was significantly correlated with mid-day ��. A second assessment of drought resistance was performed in the greenhouse on 1-0 seedlings. Root growth potential (RGP) was measured in the winter under non-stress conditions and following a drought in the summer. Differences among breeding zones were opposite in pattern from outplanting measurements of survival and water potential; therefore, RGP may not be a good predictor of drought resistance or survival among different genotypes within a single species. Low-elevation, coastal families had greater root growth than inland, high elevation sources. Greater root growth occurred in seedlings with more shoot mass. Little regional specialization in RGP across the species' range was indicated as there was greater variation among families than among breeding zones. In the summer RGP test following drought, only the two extremes of the range were evaluated; both north coastal and southern interior families showed decreased root growth compared to the winter RGP under non-stress conditions. Despite significantly higher predawn �� in inland, high elevation families, lower elevation coastal families had significantly more roots. Change in chlorophyll fluorescence yield measured on foliage of droughted plants was positively correlated with the absolute value of predawn ��; however, it was not a sensitive predictor of predawn �� (R��=0.06) at the levels used in this study. Lower levels of �� may be necessary to produce severe stress to damage Port-Orford-cedar foliage. / Graduation date: 2003

Breeding Port-Orford-cedar for resistance to Phytophthora lateralis, a causal agent of root disease, begins by screening, through artificial inoculation, phenotypically resistant trees selected from natural stands. The successful program selected tolerant or resistant POC parent trees for the purpose of disease management. Candidate resistant POCs were used in my dissertation to: 1. validate screening methods such as stem- and root-dip inoculation; 2. test for increased virulence of P. lateralis; and 3. evaluate detection techniques. The results showed that the established screening methods were appropriate, and no evidence of changed virulence was found. A PCR technique was more reliable than other techniques for detection of P. lateralis in seedlings. An additional test for foliar infection showed that initial penetration through wounds and natural openings was possible. POC seedlings and rooted cuttings from resistant and susceptible families were used to demonstrate resistance mechanisms. In order to explain the mechanisms at the cellular level, the susceptible response of POC seedlings to P. lateralis was first observed with light microscopy. Zoospores encysted on lateral roots, germinated, and penetrated by means of appressoria. Direct penetration between epidermal cells was common but penetration through epidermal cell walls was also observed. The hyphae colonized the root cortex inter- and intracellularly. Wound inoculation on stems resulted in inter- and intra cellular hyphal growth in cambial, sieve, and parenchyma cells in the secondary phloem. Several resistance mechanisms were observed: 1) there was a difference in zoospore attraction between susceptible and certain resistant POCs revealed by microscopic observation, direct count of encysted zoospores, and quantitative real-time PCR; 2) the frequency of encystment, penetration, and colonization of resistant seedlings was much lower than susceptible seedlings, but no differences in infection pathway were observed by means of light or electron microscopy; 3) collapsed cell walls were present in resistant POCs showing increased cell wall thickness, wall appositions, and electron dense materials. / Graduation date: 2005

Port-Orford-cedar (Chamaecyparis lawsoniana) is a forest tree native to a small area of Oregon and California. A root disease caused by Phytophthora lateralis causes widespread mortality of Port-Orford-cedar. This dissertation examines three important elements of the Port-Orford-cedar P. lateralis pathosystem related to breeding for disease resistance: use of resistant rootstocks to maintain genotypes of Port-Orford-cedar for breeding; the heritability and genetic basis of disease resistance; and variability in virulence and DNA fingerprint among a sample of P. lateralis isolates. Port-Orford-cedar was reciprocally grafted to western redcedar (Thuja plicata), incense cedar (Calocedrus decurrens), and Alaska yellow-cedar (Chamaecyparis nootkatensis). Port-Orford-cedar scion graft success was moderate with western redcedar and incense cedar, but extreme overgrowth of the rootstock by the scion indicated incompatibility. Xylem union was good, but phloem union was incomplete or lacking. Nearly all Port-Orford-cedar rootstocks and seedlings exposed to P. lateralis died of root disease. Four percent of the Alaska yellow-cedar exposed also died, confirming this tree as a host for P. lateralis. Resistance of Port-Orford-cedar to P. lateralis is rare. A small number of trees have been identified exhibiting resistance. A number of families were tested to determine the genetic basis for resistance. Estimates of narrow-sense and family mean heritability of resistance, as exhibited by restriction of lesion length after inoculation, were determined. Both narrow-sense and family mean heritabilities were between 0.61 and 0.98 in most tests. Between 21% and 32% of the variance was due to differences among families. Thirteen isolates of P. lateralis were collected from three hosts throughout the geographic range of the fungus. Variation in growth rate on artificial media at three temperatures, virulence when used to inoculate Port-Orford-cedar, and DNA fingerprint were compared. There were significant differences in growth rate among isolates at 24C, but fewer differences at lower temperatures and on a rich medium. One isolate produced significantly shorter lesions in three different inoculation tests. Isolates differed at only two of 189 bands produced by Inter Simple Sequence Repeat (ISSR) DNA primers, indicating very little genetic variation among isolates. / Graduation date: 2001

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 128-132). Also available on the World Wide Web.

Phytophthora lateralis is the causal agent of cedar root rot, a fatal forest pathogen whose principal host is Chamaecyparis lawsoniana (Port-Orford-cedar), a predominantly riparian-restricted endemic tree species of ecological, economical, and cultural importance to coastal Oregon and California. Local scale distribution of P. lateralis is thought to be associated with timber harvest and road-building disturbances. However, knowledge of the landscape-scale factors that contribute to successful invasions of P. lateralis is also important for effective land management of Port-Orford-cedar. P. lateralis is able to infest in wet conditions via stream networks (zoospore) and dry conditions via road networks (resting spore). This study tested the hypothesis that vehicles spread P. lateralis by relating its distribution to traffic intensive, anthropogenic disturbances (i.e. a road network, timber harvest) over a 31-yr period in a 3,910-km² portion of the Rogue River-Siskiyou National Forest in the Siskiyou Mountains of Oregon. Indices of road disturbance (presence/absence, configuration, length, density, road-stream network connectivity) and timber harvest (presence/absence, area, density, frequency) were related to locations of infested cedar populations from a USFS survey dataset using a geographic information system (GIS). About 40% of 934 7th-field catchments were infested with the pathogen. Total road length of the study site was 5,070 km; maximum road density was 8.2 km/km2 and averaged 1.6 km/km² in roaded catchments (n = 766). Timber activities extracted 17,370 ha (2,338 cutting units) of forest across 509 catchments; 345 catchments were cut ≥ twice. Maximum harvest density was 0.92 km²/km² ([mean] = 0.04). Both road networks and timber harvest patchworks were significantly related to cedar root rot heterogeneity. Chi-squared contingency tables showed that infestation rates were 2.2 times higher in catchments with roads compared to roadless catchments and 1.4 times higher in catchments with road-stream intersections compared to those that were unconnected. Infestation was twice as likely in catchments with both harvest and road presence than road presence alone. Single-variable logistic regression showed that a one percent increase in harvest density increased infestation odds 25% and a one-unit (km/km²) increase in road density increased infestation odds 80%. Road and stream network configuration was also important to pathogen distribution: 1) uninfested catchments are most likely to be spatially removed from infested, roaded catchments, 2) only 11% of 287 roaded catchments downstream of infested, roaded catchments were uninfested, and 3) only 12% of 319 catchments downstream of infested catchments were uninfested. Road networks and timber harvest patchworks appear to reduce landscape heterogeneity by providing up-catchment and down-catchment access to host populations by linking pathogenic materials to the stream network. Timber harvest data suggest that while infestation risk to Port-Orford-cedar populations remains high, management policies may have curbed infestation risk in timber-harvested catchments; if this is a result of specific P. lateralis mitigation policies adopted in the late 1980's or broader, region-wide conservation policies (i.e. the Northwest Forest Plan) is yet unclear. / Graduation date: 2012