Pathogenicity of Phytophthora lateralis Lineages on Different Selections of Chamaecyparis lawsoniana.

Phytophthora lateralis, the cause of Chamaecyparis lawsoniana root disease, was introduced in North America about 1920, and has since killed trees along roads and streams throughout the tree's range. Recent results suggest an Asian origin for this oomycete and four genetic lineages were identified. This raised questions for the genetic exapted resistance demonstrated in 1989 within the wild population of C. lawsoniana but with only one P. lateralis lineage. The main goal of the present research was to test the durability of the demonstrated resistance and to compare the pathogenicity of isolates representing the four lineages. No breakdown of resistance was observed in five separate tests using different inoculation techniques, resistant and susceptible C. lawsoniana trees, and seedling families. Differences in mortality and lesion length were observed between the lineages. The higher aggressiveness of isolates of the TWJ and PNW lineages and the lower aggressiveness of the TWK lineage are discussed in view of the hypotheses on the history of spread and evolutionary history of the P. lateralis lineages.

Stream Monitoring for Detection of Phytophthora ramorum in Oregon Tanoak Forests.

Stream monitoring using leaf baits for early detection of Phytophthora ramorum has been an important part of the Oregon Sudden Oak Death (SOD) program since 2002. Sixty-four streams in and near the Oregon quarantine area in the southwest corner of the state were monitored in 2008. Leaves of rhododendron (Rhododendron macrophyllum) and tanoak (Lithocarpus densiflorus) were placed in mesh bags, and bags were floated in streams. Leaf baits were exchanged every 2 weeks throughout the year. Leaves were assayed by isolation on selective medium and by multiplex rDNA internal transcribed spacer polymerase chain reaction (ITS PCR). The two methods gave comparable results, but multiplex PCR was more sensitive. P. ramorum was regularly recovered at all seasons of the year from streams draining infested sites 5 years after eradication treatment. In streams with lower inoculum densities, recovery was much higher in summer than in winter. P. ramorum was isolated from streams in 23 watersheds. When P. ramorum was detected, intensive ground surveys located infected tanoaks or other host plants an average of 306 m upstream from the bait station. P. ramorum was isolated from stream baits up to 1,091 m from the probable inoculum source.

Phytophthora Species Causing Tanoak Stem Cankers in Southwestern Oregon.

Tanoak (Lithocarpus densiflorus) is a principal host of Phytophthora ramorum, cause of sudden oak death (SOD), in the western United States (1). In the course of SOD surveys in southwestern Oregon, other Phytophthora species were encountered to be causing stem cankers on tanoak that were indistinguishable from those caused by P. ramorum. In Oregon, SOD is subject to quarantine and eradication. Aerial surveys are flown two or more times a year to locate symptomatic tanoaks, which are then examined from the ground to determine the cause of death. Isolations on selective media were attempted from all trees with stem cankers typical of Phytophthora. Phytophthora species were identified by morphological features and DNA sequencing of either internal transcribed spacer (ITS) or the mitochondrial COX spacer region. ITS sequences were compared with validated GenBank records, and COX spacer sequences were compared with known reference isolates in the OSU collection. From 2001 through 2006, Phytophthora spp. were isolated from 482 of 1,057 tanoak stem cankers sampled. P. ramorum was isolated from 359 cankers, P. nemorosa was isolated from 102 cankers, P. gonapodyides was isolated from six cankers, P. cambivora was isolated from four cankers (all A1 mating type), P. siskiyouensis was isolated from four cankers, P. pseudosyringae was isolated from two cankers, P. cinnamomi was isolated from one canker (mating type A2), and P. taxon "Pgchlamydo" was isolated from one canker. Three cankers yielded isolates that were not identified but were closely related to P. pseudosyringae based on ITS sequence. No Phytophthora spp. were cultured from the remaining cankers. One isolate from each species identified (except P. ramorum and P. pseudosyringae) was tested for pathogenicity on tanoak stems (11.4 to 16.0 cm DBH) in the field. A 5-mm-diameter plug from the margin of a V8 agar culture was placed in a hole in the bark, covered with wet cheesecloth, and sealed with aluminum foil and duct tape. Each isolate was inoculated into five different stems. Each stem received three different isolates and an agar control. After 4 weeks, bark was removed to reveal lesion development. Lesions were measured (length by width), and pieces from four points on the lesion margin were plated in selective media to reisolate. P. cambivora, P. cinnamomi, P. gonapodyides, P. nemorosa, P. siskiyouensis and P. taxon "Pgchlamydo" all caused substantial lesions in inoculated tanoak trees (average area 11.5 to 18.6 cm2). In all cases, the species used for inoculation was recovered on reisolation from lesion margins. Control inoculations caused necrotic areas averaging 0.2 cm2. Isolations from these areas were clean. Prior to the recent SOD epidemic, no species of Phytophthora were known as pathogens of tanoak. The discovery of P. ramorum as a pathogen of tanoak in California was quickly followed by the discovery that P. nemorosa and P. pseudosyringae were also associated with tanoak cankers (2). Six years of diagnostic support for survey and detection of P. ramorum in tanoak forests of southwest Oregon has revealed the occurrence, at very low frequency, of at least five additional species of Phytophthora causing stem cankers in tanoak. References: (1) D. M. Rizzo et al. Ann. Rev. Phytopathol. 43:309, 2005. (2) A. C. Wickland et al. For. Pathol. Online publication. DOI:10.1111/j.1439-0329.2008.00552.x), 2008.

First Report of A1 Mating Type of Phytophthora ramorum in North America.

Phytophthora ramorum is known in Europe and the western United States (1). In Europe, it is found in nurseries and landscape plantings. In the United States, it has been confined to coastal forests, and in California, it is found in a few horticultural nurseries. All European isolates tested have been A1 mating type, while all North American isolates were A2 mating type (2). Amplified fragment length polymorphism markers also indicated that the populations on the two continents are distinct, and nearly all North American isolates are from one clone (Kelly Ivors, unpublished). In June 2003, P. ramorum was isolated from diseased Viburnum and Pieris spp. cultivars from a Clackamas County nursery in northern Oregon and diseased Camellia sp. cultivar from a Jackson County nursery in southern Oregon. Representative isolates were submitted to the American Type Culture Collection, Manassas, VA. As part of the effort to determine the origin of these new infestations, we tested the nursery isolates for mating type. Seven Oregon nursery isolates, three Oregon forest isolates (from the predominant North American clone), and two European isolates were paired. Agar plugs from 3-day-old colonies were placed in close proximity on carrot agar plates, and then the plates were examined for oogonia after 3 and 10 days as advised by C. M. Brasier (personal communication). Oogonia and antheridia typical of P. ramorum (2) formed when isolates from the Clackamas County nursery were paired with the Oregon forest isolates and also when isolates from the Jackson County nursery were paired with the European isolates. Gametangia also formed in pairings between Oregon forest isolates and European isolates, but not in any other combinations. We developed polymerase chain reaction (PCR) primers for four microsatellite loci and determined allele sizes for the same set of isolates (unpublished). Microsatellite alleles of the Clackamas County isolates were identical to the European tester isolates, and alleles of the Jackson County isolates were identical to the Oregon forest isolates. These results indicate that the recent Oregon nursery infestations are of separate origins. The Clackamas County isolates are A1 mating type and have microsatellite alleles like the European testers, but according to shipping records, the nursery has received no host nursery stock directly from Europe. However, host nursery stock has been received from a Canadian nursery. The Jackson County isolates are of A2 mating type and have microsatellite alleles like the forest isolates of Oregon, which is consistent with the reported origin of these plants from a California nursery. These preliminary microsatellite results need to be validated against a larger isolate set but are congruent with the mating type results. The Oregon nursery infestations highlight the dangers of unregulated or underregulated transport of host nursery stock from infested areas to noninfested areas. All host plants from infested nursery blocks at the affected Oregon nurseries have been destroyed by incineration, and a monitoring program has been implemented. Other host nursery stock on site has been taken "off-sale" pending verification that it is disease free, per the United States Department of Agriculture, APHIS requirements. References: (1) J. M. Davidson et al. On-line publication. doi:10.1094/PHP-2003-0707-01-DG. Plant Health Progress, 2003. (2) S. Werres et al. Mycol. Res. 105:1155, 2001.

The Use of Soil Solarization for the Management of Soilborne Plant Pathogens in Strawberry and Red Raspberry Production.

Root rot caused by Phytophthora fragariae var. fragariae and P. fragariae var. rubi are major concerns in strawberry and raspberry production in the Pacific Northwest. Of lesser importance is black root rot of strawberry, caused by a complex of fungi and nematodes. Soil solarization was evaluated in 1997 in a strawberry planting and in 1998 in a raspberry planting for: (i) enhancing plant health and growth, and (ii) reducing population densities of root-destroying pathogens. Plots were solarized from mid-July to mid-September. Maximum and mean soil temperatures in solarized plots recorded at 10 cm depth were 48 and 33°C in the strawberry plots and 46 and 29°C in the raspberry plots. These temperatures were 7 to 17°C higher than temperatures recorded in nonsolarized plots. Soil collected after solarization was assayed by growing bait plants, cv. Totem strawberry or cv. Qualicum raspberry, at 15°C for 6 weeks in saturated soil to promote infections. Root health and plant growth were evaluated after 6 weeks. Solarization significantly reduced (P < 0.05) root necrosis and increased root weight of bait plants compared to plants grown in soil from nonsolarized plots. Infection of strawberry roots by P. fragariae, Pythium, Rhizoctonia, and Cylindrocarpon spp. was reduced (P < 0.05) by solarization in sampled soil. Disease was reduced in cv. Hood strawberries and Qualicum and Skeena red raspberries planted in solarized field plots. In the second growing season, total number and number of healthy primocanes of Qualicum plants were greater (P < 0.05) in solarized plots compared to nonsolarized plots. Solarization combined with applications of mefenoxam was no more effective in controlling diseases than solarization alone, but better than mefenoxam alone. Skeena plants responded similarly, but the differences were not significant. Red raspberry plants growing in solarized soil yielded more fruit than plants growing in nonsolarized soil in the third year after solarization. Solarization has potential as a component in an integrated pest management program of root diseases in raspberry and strawberry production, particularly within the first 2 years following planting.

Pleural fluid: accuracy of computed tomography in differentiating exudates from transudates.

PURPOSE: To determine the accuracy of computed tomography in differentiating pleural exudates from transudates when reviewed subjectively by two experienced radiologists in a community hospital. METHODS: Computed tomography scans of 55 consecutive patients who had a thoracenteses within 10 days of the study were retrospectively reviewed independently by two experienced staff radiologists. They were asked to evaluate subjectively parietal pleural thickness (anterior, lateral, posterior), attenuation of extra-pleural fat, and categorize pleural fluid as loculated or free flowing. Radiographic findings were correlated with biochemical results of thoracentesis (Light's criteria) to assess the accuracy of computed tomography in differentiating pleural exudates from transudates. RESULTS: For the diagnosis of an exudate, pleural thickening alone had the best sensitivity and specificity (50%, 100%, respectively) with an accuracy of 55%. CONCLUSION: Subjective evaluations for increased pleural thickness have a high accuracy for diagnosing pleural exudates.

Virulence for guinea pigs of tubercle bacilli isolated from the sputum of participants in the BCG trial, Chingleput District, South India.

This study, conducted in Madras, India and in Madison, Wisconsin, USA, was concerned with the virulence of isolates of Mycobacterium tuberculosis obtained from the sputum of individuals living in the Chingleput district of south India. The following results were obtained. 1. The findings of Mitchison with respect to the predominance of low virulence for guinea pigs among isolates from persons living Madras, were confirmed on isolates from the sputum of residents of the Chingleput district. 2. A high correlation was found between the log10 number of tubercle bacilli recovered from the spleen of guinea pigs infected intramuscularly with 1.0 mg of tubercle bacilli and the root index of virulence. 3. A high correlation was found between the log10 number of tubercle bacilli recovered from the spleen of guinea pigs infected intramuscularly with 1.0 mg of tubercle bacilli and the number recovered from the spleen of guinea pigs infected by the respiratory route with 5-10 tubercle bacilli. 4. Relatively low correlations were found between RIV and the susceptibility of isolates to thiophene-2 carboxylic acid hydrazide or to hydrogen peroxide.

Does infection with environmental mycobacteria suppress the protective response to subsequent vaccination with BCG?

Using a guinea pig model of experimental airborne tuberculosis, we were unable to find evidence to support the hypothesis that infection with environmental mycobacteria (M. simiae or M. avium-intracellulare) interferes with the induction of a protective response in animals subsequently vaccinated with BCG.

Does trypsin extract soluble antigen meet the criteria of immunogenicity without allergenicity?

We were unable to confirm the finding of Crowle that TESA possesses the attribute of immunogenicity and absence of allergenicity which are desired in a non-living antituberculosis vaccine. This disagreement could be a function of the particular lot of TESA examined and/or differences in the animal test systems used for the assay of protective potency. The relative contribution of these two possibilities could be determined by the simultaneous assay of a potent TESA product in different laboratories using different animal models.