Molecular and Alkaloid Characterization of Claviceps purpurea Sensu Lato From Grass Seed Production Areas of the U.S. Pacific Northwest

Ergot, caused by Claviceps purpurea sensu lato, is an economically important seed replacement disease of Kentucky bluegrass (Poa pratensis) and perennial ryegrass (Lolium perenne) seed crops. C. purpurea sensu stricto is considered the primary Claviceps species responsible, but genetic diversity and cryptic species within C. purpurea sensu lato have previously been reported. Fifty-six C. purpurea sensu lato isolates collected from P. pratensis (n = 21) and L. perenne (n = 35) in Oregon and Washington between 2010 and 2014 were characterized via random amplified polymorphic DNA (RAPD), partial internal transcribed spacer (ITS), β-tubulin and elongation factor-1α (EF-1α) sequences, conidial size, and ergot alkaloid chemotype. Based on RAPD analysis, seven isolates from P. pratensis and 33 isolates from L. perenne collected in Oregon corresponded to C. purpurea sensu stricto, and 13 isolates collected from P. pratensis in Washington and Oregon were identified as C. humidiphila. Partial ITS, β-tubulin, and EF-1α sequences identified 10 isolates from P. pratensis as C. humidiphila, and seven isolates from P. pratensis and 33 isolates from L. perenne were identified as C. purpurea sensu stricto. Several isolates generated ambiguous RAPD bands or sequences that prevented identification. Ergot alkaloid chemotype profiling found that ergocornine and its epimer were predominant in sclerotia from P. pratensis, whereas ergotamine and its epimer were most abundant in sclerotia from L. perenne. This study confirms the presence of the C. purpurea sensu lato species complex in the U.S. Pacific Northwest and suggests that more research is needed to characterize and mitigate Claviceps spp. infection of grass seed crops in North America.

Detection and Quantification of Airborne Claviceps purpurea sensu lato Ascospores from Hirst-Type Spore Traps using Real-Time Quantitative PCR

The U.S. Pacific Northwest states of Oregon and Washington are major producers of cool-season grass seed. Ergot, caused by fungi in the Claviceps purpurea sensu lato group, is an important seed replacement disease of grass worldwide. Microscopic methods that are currently used to quantify airborne Claviceps ascospores captured by spore traps are not currently rapid enough to allow for detecting and reporting of spore numbers in a timely manner, hindering growers from using this information to help manage ergot. We developed a SYBR Green real-time quantitative polymerase chain reaction (qPCR)-based assay for fast and efficient detection and quantification of C. purpurea sensu lato ascospores from Hirst-type spore traps. Species-specificity of the qPCR assay was confirmed against 41 C. purpurea sensu lato isolates collected from six hosts and six other Claviceps spp. Significant relationships were observed between cycle threshold (Ct) values and standard curves of serial dilutions of DNA ranging from 1 pg to 10 ng (R² = -0.99; P = 0.0002) and DNA extracted from a conidial suspension representing 8 to 80,000 conidia (R² = -0.99; P = 0.0004). Ct values from qPCR were significantly correlated with results from microscopic examination of spore trap samples from the field (r = -0.68; P < 0.0001) and the procedure was able to detect a single ascospore from spore trap tape samples. The qPCR procedure developed in this study provided a means for quantifying airborne Claviceps ascospores that was highly specific and useful over a wide range of spore densities, and could be performed in a matter of hours instead of days. The qPCR assay developed in this study could be part of an integrated pest management approach to help grass seed growers make risk-based fungicide application decisions for ergot management in grass grown for seed.

Identification of Environmental Factors Related to Claviceps purpurea Ascospore Production in Perennial Ryegrass Seed Fields and Development of Predictive Models

Claviceps purpurea, the causal agent of ergot of perennial ryegrass seed crops, overwinters as sclerotia in the soil and releases airborne ascospores in the spring that infect flower ovaries and replace seed with sclerotia. Burkard spore traps were used to quantify the dispersal phenology and concentration of ascospores in perennial ryegrass seed fields in the Columbia Basin of Oregon. Weather factors were measured concurrently with spore trapping. Nonparametric regression, box-and-whisker plots, and univariate analysis were used to visualize and identify trends between ascospore concentrations and weather variables. Most ascospores (75.4%) were trapped when minimum soil temperatures were between 16.2 and 20.4°C. Over 67% of the total ascospores trapped were observed when minimum air temperatures were between 6.8 and 12.4°C and 64% of ascospores were trapped when daily mean dew point was between 3.7 and 8.2°C. Environmental favorability index (EFI) models were developed and validated based on their ability to predict ascospore occurrence. The EFI models were able to predict ascospore occurrence with an accuracy of 71.7 to 87.5% depending on the year. The models were up to 79.8% accurate when validated using three years of historical spore trap data not used in the EFI model development. Ninety-four percent of ascospores were trapped when cumulative air degree days, using lower and upper thresholds of 10 and 25°C, respectively, were between 230 and 403. These results suggest that weather parameters can be used to model C. purpurea ascospore occurrence and potentially improve the timing and efficacy of fungicide applications by identifying when plant protection is most needed.

Strain-Specific Resistance to Potato virus Y (PVY) in Potato and Its Effect on the Relative Abundance of PVY Strains in Commercial Potato Fields

Potato virus Y (PVY) is a serious threat to potato production due to effects on tuber yield and quality, in particular, due to induction of potato tuber necrotic ringspot disease (PTNRD), typically associated with recombinant strains of PVY. These recombinant strains have been spreading in the United States for the past several years, although the reasons for this continuing spread remained unclear. To document and assess this spread between 2011 and 2015, strain composition of PVY isolates circulating in the Columbia Basin potato production area was determined from hundreds of seed lots of various cultivars. The proportion of nonrecombinant PVY^O isolates circulating in Columbia Basin potato dropped ninefold during this period, from 63% of all PVY-positive plants in 2011 to less than 7% in 2015. This drop in PVY^O was concomitant with the rise of the recombinant PVY^N-Wi strain incidence, from less than 27% of all PVY-positive plants in 2011 to 53% in 2015. The proportion of the PVY^NTN recombinant strain, associated with PTNRD symptoms in susceptible cultivars, increased from 7% in 2011 to approximately 24% in 2015. To further address the shift in strain abundance, screenhouse experiments were conducted and revealed that three of the four most popular potato cultivars grown in the Columbia Basin exhibited strain-specific resistance against PVY^O. Reduced levels of systemic movement of PVY^O in such cultivars would favor spread of recombinant strains in the field. The negative selection against the nonrecombinant PVY^O strain is likely caused by the presence of the Ny_tbr gene identified in potato cultivars in laboratory experiments. Presence of strain-specific resistance genes in potato cultivars may represent the driving force changing PVY strain composition to predominantly recombinant strains in potato production areas.

Spatial Patterns of Ergot and Quantification of Sclerotia in Perennial Ryegrass Seed Fields in Eastern Oregon

Ergot, caused by Claviceps purpurea, is a major disease of perennial ryegrass grown for seed in eastern Oregon. The objective of this research was to quantify and describe the spatial patterns of ergot severity in each of three 50-ha commercial fields of perennial ryegrass grown for seed in 2012 and 2013. In total, 1,433 and 1,405 quadrats were sampled among the three fields in 2012 and 2013, respectively, and the percentage of quadrats with ergot ranged from 59 to 90%. The mean incidence of infected seed heads in each quadrat ranged between 13 and 29%, while mean severity in each quadrat ranged from 0.2 to 0.5 sclerotia per seed head. Significant autocorrelation and clustering were observed in all three fields in both years, as indicated by Moran's I and spatial analysis by distance indices of aggregation. The mean number of ergot sclerotia collected from each field after harvest ranged between 4 and 15 sclerotia m^-2 in 2012 and 18 and 119 sclerotia m^-2 in 2013. Sclerotia left in perennial fields after harvest are a significant source of inoculum that should be targeted for control. This is the first study to quantify spatial patterns of ergot in perennial ryegrass and provides insights into possible mechanisms that contribute to ergot etiology and epidemiology.

Afternoon Ascospore Release in Claviceps purpurea Optimizes Perennial Ryegrass Infection

In Kentucky bluegrass (Poa pratensis), Claviceps purpurea, the causal agent of ergot, typically releases ascospores during the early-morning hours, between about midnight and 10:00 a.m., corresponding to time of flowering, when the unfertilized ovaries are most susceptible to infection. During aeromycology studies of C. purpurea in perennial ryegrass (Lolium perenne) in northeastern Oregon during 2008 to 2010 and 2013, a strain of C. purpurea was found that released ascospores in the afternoon, coinciding with flowering in perennial ryegrass. Under controlled environmental conditions, sclerotia from perennial ryegrass and Kentucky bluegrass released spores in the afternoon and morning, respectively, consistent with timing of spore release under field conditions. Internal transcribed spacer (ITS) sequences of single sclerotial isolates from Kentucky bluegrass and perennial ryegrass were consistent with C. purpurea, although minor variations in ITS sequences among isolates were noted. Differences between Kentucky bluegrass and perennial ryegrass isolates were observed in random amplified polymorphic DNA. Evidence is provided for adaptation of C. purpurea to perennial ryegrass by means of delayed spore release that coincides with afternoon flowering in perennial ryegrass.

First Report of Natural Infection by 'Candidatus Liberibacter solanacearum' in Bittersweet Nightshade (Solanum dulcamara) in the Columbia Basin of Eastern Oregon

Potatoes are a major crop in the Columbia Basin of Oregon and Washington, representing an annual farm gate value of almost $750 million. Zebra chip disease (ZC), a new and economically important disease of potato, was first reported in Oregon and Washington in 2011 (1). The disease is caused by the bacterium 'Candidatus Liberibacter solanacearum' (Lso, also referred to as 'Ca. L. psyllaurous'), which is vectored by the potato psyllid (Bactericera cockerelli Sulc) (1,2). Identifying alternative hosts for Lso may facilitate management of ZC disease, which has increased potato production costs in the region. The perennial weed, bittersweet nightshade (Solanum dulcamara L.), is a year-round host of the potato psyllid (3) and is also a suspected host of Lso. However, little is known about the role of this weed in ZC epidemiology. Naturally occurring bittersweet nightshade plants (n = 21) were sampled at six different locations near Hermiston, Oregon, between May and October in 2012. These plants exhibited several symptoms associated with Lso, ranging from asymptomatic to slight purpling, chlorosis, or scorching of the foliage. However, S. dulcamara exhibits similar symptoms under a variety of environmental conditions (drought stress, etc.); therefore, it was difficult to identify potentially infected plants based solely on symptomology. Leaf and stem tissue (n = 21) was analyzed with high-fidelity PCR using species-specific primers for the 16S rDNA gene, CLipoF, and OI2c (2,4). Approximately 27.3% of the plants tested positive for Lso using these primers, including plants from the following locations on 16 April, 16 May, and 24 May, respectively: Hat Rock, OR (45°55.033' N, 119°10.495' W), Irrigon, OR (45°54.560' N, 119°24.857' W), and Stanfield, OR (45°46.971' N, 119°13.203' W). Three plants were selected for further PCR analysis with primers for the outer membrane protein gene, 1482f and 2086r (1). Amplicons obtained with both sets of PCR primers were directly sequenced. A BLAST analysis showed that the 16S rDNA gene sequence (993 to 1,000 bp) shared 99 to 100% identity with several Lso accessions, including JN848751.1 (from Washington) and JN848753.1 (from Oregon). Likewise, the outer membrane protein gene sequence (600 to 601 bp) shared 99 to 100% identity with 'Ca. L. solanacearum' accession KC768330.1 (from Honduras). All six sequences were deposited in GenBank (Accession Nos. KJ854199 to KJ854204). According to these findings, bittersweet nightshade may be an important annual source of Lso in the region, particularly since it serves as a host for the potato psyllid. Potato psyllids were also detected at two of the locations with infected S. dulcamara: Irrigon, OR, and Stanfield, OR. A subsample of the psyllids collected in 2012 were analyzed with PCR and Lso was detected in a sample from Stanfield, OR (5). Identifying perennial hosts of Lso promotes a better understanding of both ZC disease epidemiology and management. To our knowledge, this is the first report of Lso causing natural infections in S. dulcamara in the United States. References: (1) J. M. Crosslin et al. Plant Dis. 96:452, 2012. (2) S. Jagoueix et al. Mol. Cell. Probes 10:43, 1996. (3) A. F. Murphy et al. Am. J. Pot. Res. 90:294, 2013. (4) G. A. Secor et al. Plant Dis. 93:574, 2009. (5) K. D. Swisher et al. Am. J. Pot. Res. 90:570, 2013.

First Report of Ustilago cynodontis Causing Smut of Cynodon dactylon in Washington State, United States

Bermudagrass (Cynodon dactylon) is an important warm-season perennial turf and forage grass that is typically grown in warm, tropical and subtropical climates. Smutted inflorescences of bermudagrass were observed and collected in Benton County, Washington, United States, in October of 2012 in an unmanaged, naturalized area located near the banks of the Columbia River and adjacent to large expanses of managed turf containing bermudagrass. The climate in this area is favorable to bermudagrass due to the relatively mild winters and hot, dry summers that usually occur in this region. The infected plants occurred in patches alongside healthy plants and several disease foci were observed along a 100-m transect of non-contiguous bermudagrass. The disease was severe wherever it occurred. Diseased inflorescences were covered with black-brown teliospores, distorted, and frequently failed to fully emerge and develop. Teliospores (n = 80) were irregularly globose to subglobose, 5.3 to 7.0 × 4.5 to 6.2 μm (mean 6.4 × 5.9 μm) and 6.2 to 8.8 × 5.3 to 7.0 μm (mean 7.0 × 6.5 μm), with a smooth wall approximately 1 μm thick, and were consistent with previous descriptions of Ustilago cynodontis teliospores (1,3). Teliospores germinated within 24 h when plated on 0.2% malt agar at 16°C and produced 4-celled basidia in a 3+1 arrangement, also consistent with U. cynodontis (3). Basidia gave rise to lateral and terminal, ovoid to long ellipsoidal basidiospores. Basidiospores budded or germinated by hyphae from which lateral or terminal aerial sporidia developed as previously described (3,4). DNA was extracted from sporidia of three single-spored isolates grown in malt extract broth. Complete nucleotide sequences of the 5.8S ribosomal RNA coding region and partial sequences of the internal transcribed spacer (ITS) regions 1 and 2 were obtained from the three isolates using ITS1 and ITS4 primers. The corresponding regions of the three aligned sequences (GenBank Accession Nos. KC920742 to KC920744) were identical and exhibited 99 to 100% identity with U. cynodontis strains previously deposited in GenBank (HM143013, AY740168, AF038825, and AY345000). Representative specimens were deposited in the WSU Mycological Herbarium as WSP 72345 to WSP 72348. This is the first report of U. cynodontis causing smut on bermudagrass in Washington State and represents the northernmost record of this fungus in North America (2). The occurrence of U. cynodontis in Washington State suggests that the pathogen may exist in other hot and dry areas of northwestern North America where bermudagrass is found associated with turf in recreational, landscape, or natural settings. References: (1) S. D. Brook. Trans. R. Soc. N. Z. 84:643, 1957. (2) D. F. Farr and A. Y. Rossman. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Online. Retrieved from http://nt.ars-grin.gov/fungaldatabases , April 18, 2013. (3) C. T. Ingold. Trans. Br. Mycol. Soc. 83:251, 1984. (4) C. T. Ingold. Trans. Br. Mycol. Soc. 89:471, 1987.

Incidence and impact of Verticillium dahliae in soil associated with certified potato seed lots

Verticillium dahliae causes Verticillium wilt of potato and can be found in soil associated with potato seed tubers. The purpose of this research was to quantify V. dahliae in soil associated with certified seed tubers and determine if this potential inoculum source is related to disease development in the field. Approximately 68% of seed lots assayed contained V. dahliae-infested soil on seed tuber surfaces (seed tuber soil). Over 82% of seed lots contained V. dahliae in loose seed lot soil obtained from bags and trucks used to transport seed tubers. Most samples contained ≤50 CFU/g but some contained >500 CFU/g. Most isolates (93%) were vegetative compatibility group 4A. Populations of V. dahliae in stem sap increased with increasing inoculum densities in field soils only when V. dahliae concentrations in seed tuber soil were low. High concentrations of V. dahliae in seed tuber soil resulted in greater stem sap colonization when V. dahliae inoculum densities in field soil were low (P < 0.01) and resulted in greater pathogen inoculum densities in postharvest field soils (P = 0.04). Seed tubers contaminated with V. dahliae-infested soils may introduce the pathogen into fields not previously cropped to potato or recontaminate those which have received preplant management practices. Long-term management of V. dahliae requires reducing propagules in soil associated with seed lots.

First Report of Zebra Chip Disease and "Candidatus Liberibacter solanacearum" on Potatoes in Oregon and Washington State

In August of 2011, potato (Solanum tuberosum) tubers grown in the lower Columbia Basin of southern Washington State and northern Oregon were observed with internal discolorations suggestive of zebra chip disease (ZC). Symptoms included brown spots, streaks, and stripes in and near the vascular tissue, typical of ZC (1). Symptoms were observed in cvs. Alturas, Russet Norkotah, Pike, Ranger Russet, Umatilla Russet, and Russet Burbank. Foliar symptoms on plants that produced symptomatic tubers included purple discoloration in upper leaves, leaf rolling, axial bud elongation, chlorosis, leaf scorch, and wilt. Tissue was taken from two symptomatic tubers each of cvs. Alturas and Russet Norkotah, three tubers of cv. Umatilla Russet, and one tuber of cv. Pike. These tubers were tested by PCR for "Candidatus Liberibacter solanacearum", an unculturable alphaproteobacterium associated with ZC (1,4). Primers specific for the 16S rDNA were CLipoF (4) and OI2c (3), and primers OMB 1482f and 2086r were specific for the outer membrane protein (2). All of these samples, except one Umatilla tuber, were positive for the bacterium. The 16S rDNA and OMB amplicons from one symptomatic tuber each of Alturas (from Washington) and Pike (from Oregon) were cloned and three clones of each were sequenced. BLAST analysis of the consensus sequences confirmed "Ca. L. solanacearum". The 16S sequences (1,071 bp) from the two tubers were identical and showed 99 to 100% identity to a number of 16S rDNA sequences of "Ca. L. solanaceaum" in GenBank (e.g., Accession Nos. HM246509 and FJ957897). The 16S rDNA sequences were deposited in GenBank as Accession Nos. JN848751 and JN848753. Consensus sequences of the two OMB clones (605 bp; deposited in GenBank as Accession Nos. JN848752 and JN848754) were identical and showed 97% identity to the two "Ca. L. solanacearum" OMB sequences in GenBank (Accession Nos. CP002371 and FJ914617). Potato psyllids (Bactericera cockerelli Sulc), the vector of "Ca. L. solanacearum", were present in ZC-affected fields in Oregon and Washington and the bacterium was confirmed by PCR in 5 to 10% of 128 adult psyllids collected from two fields. On the basis of foliar and tuber symptoms, specific PCR amplification with two primer pairs, sequence analyses, and the presence of Liberibacter-infected potato psyllids, ZC and "Ca. L. solanacearum" are present in potatoes in Oregon and Washington State. Washington and Oregon together grow ~80,000 ha of potatoes. ZC has caused significant economic damage to potatoes in Texas, Mexico, Central America, and New Zealand (1). Therefore, ZC may pose a risk to agriculture in Oregon, Washington, and neighboring states. However, the potential for development of widespread and serious disease will depend upon the arrival time and number of infective potato psyllids entering the region. References: (1) J. M. Crosslin et al. Online publication. doi:10.1094/PHP-2010-0317-01-RV, Plant Health Progress, 2010. (2) J. M. Crosslin et al. Southwest. Entomol. 36:125, 2011. (3) S. Jagoueix et al. Mol. Cell. Probes 10:43, 1996. (4) G. A. Secor. Plant Dis. 93:574, 2009.

Reducing tuber damage by potato tuberworm (Lepidoptera: Gelechiidae) with cultural practices and insecticides

Cultural practices and insecticide treatments and combinations were evaluated for effect on tuber damage by potato tuberworm, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) in the Columbia basin of eastern Oregon and Washington. A range of intervals between initial application of several insecticides and vine-kill were tested to determine how early to implement a program to control potato tuberworm tuber damage. Esfenvalerate, methamidophos, and methomyl were applied at recommended intervals, with programs beginning from 28 to 5 d before vine-kill. All insecticide treatments significantly reduced tuber damage compared with the untreated control, but there was no apparent advantage to beginning control efforts earlier than later in the season. Esfenvalerate and indoxacarb at two rates and a combination of the two insecticides were applied weekly beginning 4 wk before and at vine-kill, and indoxacarb was applied at and 1 wk postvine-kill as chemigation treatments. Application of insecticides at and after vine-kill also reduced tuberworm infestation. 'Russet Norkotah' and 'Russet Burbank' plants were allowed to naturally senesce or were chemically defoliated. They received either no irrigation or were irrigated by center-pivot with 0.25 cm water daily from vine-kill until harvest 2 wk later. Daily irrigation after vine-kill reduced tuber damage, and chemical vine-kill tended to reduce tuber damage compared with natural senescence. Covering hills with soil provides good protection but must be done by vine-kill. Data from these trials indicate that the most critical time for initiation of control methods is immediately before and at vine-kill.

Spatial and temporal dynamics of potato tuberworm (Lepidoptera: Gelechiidae) in the Columbia Basin of the Pacific Northwest

A landscape-scale study from 2004 to 2006 investigated the spatial and temporal dynamics of a new pest to the Columbia Basin of the Pacific Northwest, the potato tuberworm, Phthorimaea operculella (Zeller). Male P. operculella were monitored in spring, summer, and fall each year with a pheromone-baited trapping network in Oregon and Washington. The objectives of the study were to (1) describe the temporal and spatial dynamics of the recent outbreak of P. operculella in the region and (2) examine the relationship of the spatial and temporal distribution of the outbreak and weather (air temperature, precipitation, and dew point) and geographic variables (elevation and latitude). Weather data during the P. operculella outbreak were compared with a reference period (1993-1999) that occurred before the outbreak. The outbreak in 2004, which caused the first widespread tuber damage in the region, was positively associated with warmer temperatures in the preceding fall and in the spring, summer, and fall of the growing season. October and November 2003 and March 2004 were also drier than the reference period. However, the winter of 2003/2004 was colder than the reference period and thus mild winter conditions did not explain the outbreak. The importance of environmental variables on the seasonal spatial distribution of the pest each year was examined using nonparametric multiplicative regression. Locations with higher spring, summer, or fall temperatures were associated with increased trapping rates in most seasons. Elevation and latitude seemed to play a constraining role, because low trapping rates of P. operculella were associated with higher elevations and latitudes.

First Report of Garlic virus B and Garlic virus D in Garlic in the Pacific Northwest

With the recent report of several viruses infecting garlic (Allium sativum L.) grown in the Pacific Northwest (1-3), studies were initiated on cloves planted in the fall of 2006 to determine the presence of additional viruses infecting plants exhibiting mosaic and/or chlorotic leaves. Cloves from symptomatic plants of the cultivar 'Early' from two seed production fields in Benton County, WA and two seed production fields in Morrow County, OR were tested by two-step reverse transcription (RT)-PCR using primers specific to the coat protein (CP) of the allexiviruses (4), since garlic infected with this group had similar symptoms in Asia and South America (4). Of the 87 cloves tested, 84 were positive, and four representative samples of the RT-PCR amplicons from each location were cloned and sequenced. Sequence comparisons indicated that the cloves from both locations were infected with Garlic virus D (GarV-D), also known as Japanese garlic virus (JGV), since they shared 98% identity with known isolates (GenBank Accession Nos. L388922.1, AF519572.1, and AB010303.1). In addition, sequences of isolates from the Oregon cloves shared a 96% identity with a known isolate of Garlic virus B (GarV-B; GenBank Accession No. AF543829.1). Because no antiserum specific to these viruses was available, primers specific to the CP genes of GarV-D (JGV-F2/JGV-R2 5'-GCTCACTCRGATGTGTTAGC-3' and 5'-CGCGTGGACATAAGTTGTTG-3') and GarV-B (GVB-F1/GVB-R2 5'-GAGGAGAACTAACGCCACAC-3' and 5'-ACGACCTAGCTTCCTACTTG-3') were designed and the cloves were retested by RT-PCR using these virus-specific primers. With the GarV-D specific primers, 98 and 63% of the cloves were positive from Washington and Oregon, respectively, and 52% of the cloves from Oregon were positive using the GarV-B specific primers. None of the cloves tested from Washington were positive for GarV-B. The identity of the amplicons was verified by cloning and sequencing (GarV-D, GenBank Accession No. FJ643476; GarV-B, GenBank Accession No. FJ643475). Incidence of the two viruses differed between Oregon and Washington was likely due to the expansion of the seed lots in two different locations (California and Nevada) prior to planting in 2006. With such high infection rates, studies should be conducted to determine the impact of these viruses on yield when plants are singly infected as well as in combination with the other viruses known to infect garlic in this region. These and the other viruses (1) are likely to impact yield. To our knowledge, this is the first report of GarV-D (JGV) and GarV-B in garlic in the Pacific Northwest. References: (1) S. L. Gieck et al. Plant Dis. 91:461, 2007. (2) H. R. Pappu et al. Plant Dis. 89:205, 2005 (3) H. R. Pappu et al. Online publication. doi:10.1094/PHP-2008-0919-01-RS. Plant Health Progress, 2008. (4) T. Tsuneyoshi et al. Phytopathology 86:253, 1996.

Detection, Quantification, and Vegetative Compatibility of Verticillium dahliae in Potato and Mint Production Soils in the Columbia Basin of Oregon and Washington

Soil samples from 87 fields intended for potato production in the Columbia Basin of Washington and Oregon and 51 fields intended for mint production in Washington were assayed on a semiselective medium to quantify populations of Verticillium dahliae. The pathogen was isolated from 77 (89%) of the fields intended for potato production and 41 (80%) of the fields intended for mint production. Population densities ranged from 0 to 169 propagules/g of air-dried soil in fields intended for potato production and 0 to 75 propagules/g of air-dried soil in fields intended for mint production. Isolates of V. dahliae were recovered from soil assay plates and pure cultures were prepared to provide a collection of isolates for vegetative compatibility analysis. Among fields intended for potato production from which isolates of the fungus were assigned to a vegetative compatibility group (VCG), 93% of the fields were found to contain one or more isolates assigned to VCG 4A, nine (23%) contained one or more isolates assigned to VCG4B, and only one (3%) contained any isolates assigned to VCG 2B. In the case of fields planned for mint production in 1999 from which isolates of the fungus were assigned to a VCG, 13 fields (81%) were found to contain one or more isolates assigned to VCG 4A, 7 (44%) contained one or more isolates assigned to VCG 4B, and 5 (31%) contained one or more isolates assigned to VCG 2B. VCG 4A isolates of V. dahliae are widespread and numerous, particularly following potato production, but cause only mild to moderate symptoms in mint; therefore, this pathotype is unlikely to seriously endanger subsequent plantings of mint. However, planting potato in a field recently used to produce mint may pose a significant risk to the potato crop if high populations of the VCG4A pathotype (highly aggressive to potato) predominate. Preplant assessment of soil populations of V. dahliae without regard for the relative populations of various pathotypes present in a particular sample may lead to information not fully useful in integrated pest management systems.

First Report of Corky Ringspot Caused by Tobacco rattle virus on Potatoes (Solanum tuberosum) in Michigan

Potato is the fourth most important agricultural commodity in Michigan and is grown for table stock, chip processing, and seed. Tubers are either processed or fresh packed immediately following harvest or sent to storage. Tubers of potato cv. FL1879 representing two separate fields in Huron County were removed from separate storage facilities in February and March of 2007, and substantial internal necrosis was observed in 1 to 2% of the tubers. Symptoms included arcs similar to those caused by Tobacco rattle virus (TRV). This virus is a member of the genus Tobravirus and is transmitted by a number of species of stubby-root nematodes (Paratrichodorus or Trichodorus spp.). Stubby-root nematodes have been reported previously from Michigan (1). To confirm the presence of TRV, nucleic acid extractions were made from these symptomatic tubers (3). Samples were initially tested for TRV by reverse transcription (RT)-PCR using primers specific to the 16 kDa open reading frame on genomic RNA-1 (2). Samples from both storage facilities were positive. The 463-bp RT-PCR product, amplified with these primers, was sequenced (GenBank Accession No. EU315227) and was 99.6% identical to the corresponding region of two TRV isolates from Florida and Washington (GenBank Accession Nos. AF055912 and EU315226, respectively). In addition, sap from cv. FL1879 tuber samples was used to transmit the virus mechanically to tobacco cv. Samsun NN, which produced typical TRV symptoms following inoculation, and sap extracts from the tobacco leaves also tested positive with antiserum specific to TRV upon subsequent ELISA testing. Corky ringspot can result in substantial losses, with entire potato fields being rejected because of internal tuber damage. Once found, fields must be considered permanently at risk to this disease due to the large host range of both the virus and the nematode vector. This disease has been previously found in the United States in California, Colorado, Florida, Idaho, Washington, Oregon, and it is likely present in Indiana. To our knowledge, this is the first report of corky ringspot and TRV on potato in Michigan. References: (1) G. W. Bird and N. Knobloch. Plant Dis. Rep. 60:76, 1976. (2) J. M. Crosslin and P. E. Thomas. Am. Potato J. 72:605, 1995. (3) G. G. Presting et al. Phytopathology 85:436, 1995.

First Report of Soilborne wheat mosaic virus on Wheat (Triticum aestivum) in the Columbia Basin of Oregon

The Columbia Basin of Oregon consists of six counties (Gilliam, Hood River, Morrow, Sherman, Wasco, and Umatilla) and is the major wheat-producing region in the state. In 2005, these counties produced 300,277 ha of mostly fall-planted wheat. While primarily a dryland production area, wheat (approximately 8,094 ha) is also grown as a rotational crop under irrigation. Stunted and chlorotic winter wheat plants with leaves exhibiting a mosaic pattern consistent with that caused by Soilborne wheat mosaic virus (SBWMV) were observed in March 2005. These plants originated from four center-pivot irrigated fields in Umatilla County with each field approximately 50.6 ha. One-half of one field was planted with cv. Western Breeders 470 (WB470) and the other half with cv. Tubbs, while the three other fields were planted to Tubbs. In the split-planted field, symptoms were widespread in the WB470 half but only observed in low-lying areas planted with Tubbs. ELISA with a monoclonal antibody (Agdia Inc., Elkhart, IN) confirmed the presence of SBWMV, which is transmitted by the soilborne organism Polymyxa graminis. Electron microscopy confirmed rigid, rod-shaped particles that were 19 nm wide and of two size classes, 138 to 222 and 416 to 471 nm long. Presence of SBWMV was further verified by reverse transcription (RT)-PCR using SBWMV RNA-2 specific primers (sense 5'-AAAGAGTCTIGCGTRTARCAYTC-3' and antisense 5'-AACGGTGTTAGTAARYTRGGKGA-3'), which amplified the predicted 338-bp product from the coat protein gene (1). Additional positive samples were found in 2006 from fall-planted wheat cvs. WB 528 and MJ9 from two additional 50.6-ha fields in Umatilla County. In 2005, yield of WB470 in the split-planted field was reduced by approximately 15% compared with yields obtained in similar fields planted with WB470 not exhibiting symptoms. SBWMV has been reported previously in Oregon (2) but nearly 322 km to the west in an area that is not the major wheat-producing region in Oregon. Because of the apparent reduced susceptibility of Tubbs, which is an older cultivar, as compared with WB470, WB528, and MJ9, which are three new high-yielding cultivars, additional research is needed to identify the reaction to SBWMV of cultivars adapted for production in the Pacific Northwest, particularly if this disease becomes widely distributed in both irrigated and dryland production areas. References: (1) G. R. G. Clover et al. Plant Pathol. 50:761, 2001. (2) M. L. Putman et al. Plant Dis. 78:102, 1994.

Control of Paratrichodorus allius and Corky Ringspot Disease in Potato with Shank-injected Metam Sodium

Corky ringspot disease (CRS) of potato produces necrotic areas in tubers that are considered quality defects that can lead to crop rejection. CRS is caused by tobacco rattle virus that is vectored by stubby-root nematodes (Paratrichodorus spp., Trichodorus spp.) at very low population densities, making disease management difficult and expensive. Fumigation with metam sodium (MS) is a common practice to control soil-borne fungi and increase potato yield. MS is generally applied in water via chemigation (water-run, WR) but is ineffective at controlling CRS when WR-applied, even at high rates. Therefore, WR MS is often used in combination with 1,3-dichloropropene (1,3-D), aldicarb or oxamyl to attain adequate CRS control. Between 1996 and 2000, fields with a history of CRS were treated with WR MS, shank-injected MS, and/or 1,3-D, and tubers were evaluated for symptoms of CRS. Shank injection of MS (SH MS) at depths of 41 cm, 15 and 30 cm, or 15, 30 and 45 cm controlled CRS over 3 years of testing. All rates of 280 liters/ha or greater were effective. Shank injection of metam potassium (MP) at rates of 448 liters/ha was also effective. 1,3-D controlled CRS alone or in combination with WR or SH MS. Proper shank application of MS or MP may adequately control CRS without the additional cost of other nematicides at low (<10 P. allius/250 g soil) to moderate (10 to 30 P. allius/250 g soil) populations of the nematode vector. Although SH MS was superior to WR MS, additional research is necessary to determine if this practice would be sufficient at higher CRS disease pressure or if addition of other nematicides would be necessary.

Control of Meloidogyne chitwoodi in Potato with Shank-injected Metam Sodium and other Nematicides

Metam sodium (MS) is often applied to potato fields via sprinkler irrigation systems (water-run, WR) to reduce propagules of soil-borne pathogenic fungi, particularly Verticillium dahliae, to prevent yield loss from potato early dying disease. However, this procedure has not been effective for controlling quality defects in tubers caused by Columbia root-knot nematode (Meloidogyne chitwoodi). In five trials from 1996 to 2001, application of MS by soil shank injection (SH) provided better control and tuber quality than that generally obtained by WR MS, in three of five trials. Results were similar when SH MS was injected at one (41-45 cm), two (15 and 30 cm) or three (15, 30 and 45 cm) depths. In the two trials where SH metam potassium was tested, culls were reduced to 3% and 0% and were equivalent to those resulting from a similar rate in kg a.i./ha of SH MS. A shank-injected tank mix of MS plus ethoprop EC and SH MS plus in-season chemigation applications of oxamyl provided acceptable control in trials where SH MS alone was inadequate. In-furrow application of aldicarb at planting following SH MS did not appear to increase performance. Most consistent control (0-2% culled tubers in five trials) occurred when SH MS at 280 liters/ha was used together with 1,3- dichloropropene (140 liters/ha), applied simultaneously or sequentially. This was similar to combinations of 1,3-D and WR MS, but SH MS may be preferred under certain conditions.

First Report of Onion yellow dwarf virus, Leek yellow stripe virus, and Garlic common latent virus in Garlic in Oregon

A general mosaic and yellowing of leaves of three cultivars of garlic (Allium sativum L., Late, Early, and Germinador) were observed in two seed-production fields in Morrow County, OR in June 2005. Approximately 50% of plants within the 50-ha fields were symptomatic. With recent findings of Onion yellow dwarf virus (OYDV), Leek yellow stripe virus (LYSV), and Garlic common latent virus (GCLV) in Washington (2), 45 composite samples of 10 leaves each from symptomatic (mosaic and yellowing) and nonsymptomatic plants were analyzed with a GCLV-specific antiserum (Agdia Inc., Elkhart, IN). All samples of 'Germinador' were infected regardless of symptoms, whereas 6.7% of all 'Late' and 'Early' samples were positive. GCLV infection was verified by reverse transcription (RT)-PCR using primers specific to the coat protein gene of GCLV followed by cloning and sequencing of the cloned amplicon. To determine the presence of a potyvirus, all composite samples were also tested with a general potyvirus antiserum (Agdia) and all samples from symptomatic plants were found to be positive. Representative positive samples from each cultivar were then tested by RT-PCR using degenerate, potyvirus group specific primers (3), and an amplicon of the expected size was obtained. To confirm which potyvirus was present, amplicons were cloned and sequenced, and sequence comparisons indicated that the representative samples were infected with OYDV. All symptomatic samples from the three cultivars were positive for OYDV when tested by RT-PCR using primers specific to its coat protein gene (1). Additionally, 53.3 and 6.7% of 'Early' and 'Late' samples, respectively, were also positive when tested with LYSV-specific primers (4). LYSV infection was further verified through cloning and sequencing of the cloned amplicon. Because this garlic is grown for seed, studies are being initiated to determine if current season spread occurs and yields are reduced. To our knowledge, this is the first report of OYDV, LYSV, and GCLV in garlic in Oregon. References: (1) P. Lunello et al. J. Virol. Methods 118:15, 2004. (2) H. R. Pappu et al. Plant Dis. 89:205, 2005. (3) S. S. Pappu et al. J. Virol. Methods 41:9, 1993. (4) T. Tsuneyoshi et al. Phytopathology. 86:253, 1996.

Potato Silver Scurf Affected by Tuber Seed Treatments and Locations, and Occurrence of Fungicide Resistant Isolates of Helminthosporium solani

The effectiveness of various seed-tuber treatments was evaluated for control of silver scurf on potato (Solanum tuberosum), caused by Helminthosporium solani, at four locations in Washing-ton and Oregon using seed-tubers from the same source. Disease incidence was determined at harvest and following storage, and differed significantly among locations. The highest incidence of disease was observed at Redmond, OR and the lowest was at Hermiston, OR. Significantly less silver scurf occurred on progeny-tubers, regardless of location, when seed was treated with the fungicide treatments fludioxonil, fludioxonil + quintozene, azoxystrobin, or thiophanate-methyl + mancozeb compared with the nontreated control. A sample of H. solani from seed planted in the Columbia Basin of Washington and Oregon was assessed for resistance to thia-bendazole (TBZ) and thiophanate-methyl (TPM). Sensitivity of 20 isolates of H. solani to TBZ was determined on V8 media amended with TBZ. Four isolates, selected as a subset from the 20 isolates tested for TBZ sensitivity, were tested for resistance to TPM, mancozeb, and TPM + mancozeb on amended V8 media. Isolates differed significantly in sensitivity to both chemicals. Thirteen isolates out of the 20 tested were resistant to TBZ. One out of the four subsets of isolates was resistant to both TBZ and TPM. TBZ sensitivity was not related to geographic origin of the isolates. Variation in resistance was evident on a small scale as seen with one resistant and one sensitive isolate collected from the same tuber. This is the first report that silver scurf incidence is affected by location despite the same tuber-seed source and also the first report of TBZ and TPM resistant isolates of H. solani from the Columbia Basin (Oregon and Washington) production area.

The Occurrence of PVYO, PVYN, and PVYN:O Strains of Potato virus Y in Certified Potato Seed Lot Trials in Washington and Oregon

Totals of 960 and 286 certified potato seed lots from locations across North America were planted in trials in Washington and Oregon, respectively, in 2001 to 2003 and tested for strains of Potato virus Y (PVY). The incidence of PVY^O-infected lots averaged 16.4 and 25.9% in the Washington and Oregon trials, respectively. There was a general trend of increasing incidence of the PVY^O, PVY^N:O, and PVY^N strains during this period, as evidenced by more infected cultivars, sites of seed origin, and number of seed growers providing infected seed lots. In particular, there was a dramatic increase in seed lots with the PVY^N:O strain from 2002 to 2003. PVY^N:O, in contrast to PVY^O, which only causes yield reduction, also causes internal and external damage to tubers, making them unmarketable. In 2003, PVY^N:O occurred in seed lots originating in eight states and three Canadian provinces. The increased incidence of PVY^N:O was likely due to the difficulty in differentiating this strain from PVY^O. The prevalence of PVY in potato seed lots documented herein poses a threat to potato production in the United States and suggests that current measures to reduce the incidence of this virus are inadequate.

Whole genome characterization of Potato virus Y isolates collected in the western USA and their comparison to isolates from Europe and Canada

Potato virus Y (PVY) is a serious potato pathogen that affects potato seed and commercial production crops. In recent decades, novel PVY strains have been described that cause necrotic symptoms on tobacco foliage and/or potato tubers. The major PVY strains that affect potato include PVY(O) and PVY(N), which have distinct serotypes that can be differentiated by immunoassay. Other economically important strain variants are derived from recombination events, including variants that cause tuber necrotic symptoms (PVY(NTN)) and PVY(O) serotypes that cause tobacco veinal necrosis (PVY(N)-W, PVY(N:O)). Although the PVY(NTN) and PVY(N)-W variants were first reported in Europe, apparently similar strains have been appearing in North America. Confirmation of the existence of these recombinant strains in North America is important, as is whether they spread from a common source or were derived by independent recombination. Whole genome sequencing can be used to positively identify strain variants and begin to address the issue of origins. Symptomology, serology, RT-PCR, and partial sequencing of the coat protein region were used to identify isolates of the PVY(NTN), PVY(N), PVY(NA-N), and PVY(N:O) for whole-genome sequencing. Sequencing confirmed the presence of PVY(NTN) and PVY(N) isolates that were >99% identical to European sequences deposited in GenBank in the 1990's. Sequences of the PVY(NA-N) and PVY(N:O) types were 99.0% and 99.5% identical to known sequences, respectively. There was no indication that recombinant strains PVY(NTN) or PVY(N:O) had different parental origins than recombinant strains previously sequenced. This is the first confirmation by whole-genome sequencing that "European"-type strain variants of PVY(N) and PVY(NTN) are present in North America, and the first reported full-length sequence of a tuber necrotic isolate of PVY(N:O).

Association of beet leafhopper (Hemiptera: Cicadellidae) with a clover proliferation group phytoplasma in Columbia basin of Washington and Oregon

At least 16 taxa of cicadellids and delphacids were tested by polymerase chain reaction (PCR) for the presence of a phytoplasma in the clover proliferation group, designated 16SrVI. Nucleic acid extracts from individual insects or groups of 5-10 were tested using PCR primers designed from the DNA sequence of 16S-23S rRNA or ribosomal protein genes of the pathogen. The beet leafhopper, Circulifer tenellus (Baker), was most often associated with the phytoplasma, with approximately 16% of the insects testing positive. The phytoplasma was occasionally found associated with Ceratagallia spp. Leafhopper species that were not associated with the phytoplasma included Macrosteles spp., Dikraneura spp., Colladonus montanus (Van Duzee), Circulifer geminatus (Van Duzee), Ballana spp., Amplysellus spp., Paraphlepsius spp., Texananus spp., Balclutha spp., Latalus spp., Erythroneura spp., Exitianus exitiosus (Uhler), and unidentified delphacids. The detected phytoplasma was similar to, or synonymous with, the beet leafhopper-transmitted virescence agent that is associated with the potato purple top disease in the Columbia Basin region of Washington and Oregon. This is in contrast to the phytoplasma associated with potato purple top disease in Mexico that is related to aster yellows (group 16SrI). The association of the group 16SrVI phytoplasma almost exclusively with the beet leafhopper suggests that this insect is the major vector of the phytoplasma in this region.

First Report of Stunting and Root Rot of Potato Associated with Pratylenchus penetrans in the Columbia Basin of Washington

The root-lesion nematode, Pratylenchus penetrans (de Man, 1880) Filipjev, 1936, is a common pathogen of potato in the United States east of the Rocky Mountains and frequently interacts with Verticillium dahliae to aggravate early dying disease (4). West of the Rocky Mountains, P. penetrans is associated with numerous crops including mint, tree, and small fruits but is rarely recovered from potato fields. Pratylenchus neglectus is a common plant-parasitic nematode on potato in the west, but causes little loss in yield and does not usually interact with V. dahliae (1). Management of P. neglectus is generally unnecessary; although a population of P. neglectus from Ontario, Canada appears to be more pathogenic and does interact with V. dahliae (1). During May 2003 (6 weeks after planting), large areas of stunted plants were observed in field inspections and in aerial photographs of two fields (50.6 ha) of cv. Ranger Russet in Benton County, Washington. Lower roots and stolons had numerous, dark lesions that are typical of P. penetrans damage and were severely stunted, while long, white roots had formed abnormally near the soil surface. In early May 2003, lesion nematodes (65 nematodes per 250 g of dry soil and 810 nematodes per g of fresh root weight) recovered from these potato fields were identified as P. penetrans on the basis of morphological characters (2,3). The crop responded to oxamyl (four applications at 1.1 kg of a.i. per ha between early May and mid-July), but the grower estimated that yields were 1.62 tons/ha (4 tons/acre) less than in comparable unaffected fields. To our knoweldge, this is the first report of severe damage to potato from P. penetrans in the Colombia Basin potato-production area. Soil fumigation with Telone II (1,3-dichloropropene) is commonly used in the Columbia Basin to control root-knot (Meloidogyne chitwoodi and M. hapla) and stubby-root (Paratrichodorus allius) nematodes, and metam sodium is used to control V. dahliae. However, since the only nematode recovered from preplant samples was assumed to be P. neglectus, and because cv. Ranger Russet is relatively tolerant to V. dahliae, no fumigant was used in these fields. An increase in mint production in this area may be responsible for introducing P. penetrans into previously uninfested fields since mint is propagated vegetatively and lesion nematodes are commonly associated with mint and could be easily spread in planting material and adhering soil. Identification of P. penetrans in stunted corn from two nearby fields during 2004 suggests that this nematode may be a new and emerging problem in this area. The Columbia Basin is one of the largest potato-producing regions in the United States, and widespread introduction of P. penetrans could add substantial cost to potato production in this area. References: (1) K. Mukerji. No. 458 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1975. (2) H. Scheck and S. Koike. Plant Dis. 83:877, 1999.

Soil Fumigant Effects on Three Genera of Potential Soilborne Pathogenic Fungi and Their Effect on Potato Yield in the Columbia Basin of Oregon

During three years of trials in commercial production fields, populations of three genera of potato pathogens, Fusarium spp, Pythium spp, and Verticillium dahliae, were followed before and after the single or combination use of 1,3-dichloropropene (1,3-D), 1,3-D + 17% chloropicrin (1,3-D + chloropicrin), or metam sodium (MS). Populations of these fungi did not always increase during the growing season but the relative population at a soil depth of 0 to 30 cm was nearly always higher than at 30 to 60 cm, regardless of year, sampling time, or fungal pathogen. The use of MS alone or in combination with 1,3-D generally suppressed recovery of all three genera and also increased yields. 1,3-D or 1,3-D + chloropicrin did not reduce fungal populations, but 1,3-D increased yield in 1 of 3 years. Reduced rates of MS and 1,3-D used in combination were as effective as higher rates of MS used alone. Multiple regression analysis comparing yield with fungal populations before planting indicated that population size was correlated negatively with yield. Propagules of V. dahliae had the greatest impact in reducing yield, but propagules of Pythium spp. and Fusarium spp. may have been important when populations of V. dahliae were low. Soil populations of Fusarium spp. and Pythium spp. have not been reported previously to be associated with yield reductions in potato grown in the Columbia Basin. Threshold estimates suggested that yield of number one tubers was reduced by 1 metric ton/ha for each 0.6 to 3.0 V. dahliae CFU/g dry soil present at planting.

Aerial photography used for spatial pattern analysis of late blight infection in irrigated potato circles

ABSTRACT Spatial and temporal dynamics of late blight were investigated from color, infrared aerial photographs of five commercial potato fields in the Columbia Basin during epidemics in 1993, 1995, and 1998. Aerial photographs were taken one to four times at 6- to 21-day intervals. Photographs were scanned and pixels, representing approximately 1 m(2) in the field, were used in the analysis. Late blight-infected plants were aggregated as indicated by runs analysis. Significant z-tests were computed for four directions during each sampling date in each of the five fields. Absolute z-values for runs analysis increased, indicating increasing aggregation in the four directions, as disease incidence increased in the early and midphases of the epidemics in each field. Variograms indicated the existence of autocorrelation among infected plants in four directions; the range of influence increased as disease incidence increased except at the highest levels of disease. Late blight was observed to spread in fields as foci. Late blight foci enlarged in size, produced distinct daughter foci, and coalesced. A field where initial inoculum likely originated from infected seed tubers exhibited less initial aggregation than the other fields, perhaps due to a different source of primary inoculum. Aerial photography coupled with spatial analyses of late blight-infected plants was an effective technique to quantitatively assess disease patterns in relatively large fields and was useful in quantifying an intensification of aggregation during the epidemic process on a large scale.

First Report of the Necrotic Strain of Potato virus Y (PVYN) on Potatoes in the Northwestern United States

More than 50 isolates of Potato virus Y (PVY) with characteristics of strains that cause tobacco veinal necrosis (PVY^N) were obtained from potatoes (Solanum tuberosum L.) grown in the northwestern United States. These isolates are being characterized at the biological and molecular levels. Isolate RR1 was obtained from leaves of potato cv. Ranger Russet showing distinct mottling and leaf deformity, which is in contrast to the leaf-drop and necrosis usually observed with ordinary strains of PVY (PVY^O) in this variety. Isolate AL1 was obtained from tubers of potato cv. Alturas showing distinct internal light brown rings and blotches. When RR1 and AL1 were transmitted to tobacco (Nicotiana tabacum L. cvs. Samsun NN and 423), they caused systemic veinal necrosis, including stem and petiole lesions typical of PVY^N strains (2). Symptoms induced by RR1 and AL1 on tobacco appeared 9 to 11 days after inoculation, whereas some other isolates caused delayed veinal necrosis. All isolates that produced veinal necrosis on tobacco were detectable with PVY polyclonal antisera. Potato virus X was not detected by enzyme-linked immunosorbent assay in tobacco plants showing veinal necrosis. Some isolates, including AL1, failed to react in serological tests using PVY^N-specific monoclonal antibodies obtained from three commercial sources. Other isolates, including RR1, were detectable with these monoclonal antibodies. Reverse transcription-polymerase chain reaction (RT-PCR) products obtained with primers specific for the coat protein (CP) open reading frame (ORF) were cloned and sequenced. AL1 possesses a CP more closely related to PVY^O type isolates, which would account for its failure to react with PVY^N monoclonal antibodies. In this regard, AL1 is similar to the PVY^N-Wilga isolate (1). Other isolates that are detectable with the PVY^N monoclonal antibodies possess a CP more consistent with N strains of the virus. Results of RT-PCR tests using primers derived from the P1 ORF sequence (3), and the restriction enzyme analysis and sequencing of the RT-PCR products, all suggest that AL1 and RR1 are related to European-type members of PVY tuber necrotic (NTN) or N strains. However, other isolates under investigation appear to be more closely related to previously reported North American NTN types (3). The symptomatology of these viruses on tobacco and potato, and the serological and molecular data clearly show that at least two distinct variants of PVY^N have been found for the first time in a major potato production area of the United States, and pose a potential threat to the potato industry. References: (1) B. Blanco-Urgoiti et al. Eur. J. Plant Pathol. 104:811, 1998. (2) J. A. de Bokx and H. Huttinga. Potato virus Y. Descriptions of Plant Viruses. No. 242, CMI/AAB, Surrey, England, 1981. (3) R. P. Singh et al. Can J. Plant Pathol. 20:227, 1998.

First Report of Rhizomania of Sugar Beet in the Columbia River Basin of Washington and Oregon

Rhizomania, caused by Beet necrotic yellow vein virus (BNYVV) and vectored by the soilborne fungus, Polymyxa betae Keskin, is one of the most economically damaging diseases affecting sugar beet (Beta vulgaris L.) worldwide and has been found in most sugar beet-growing areas of the United States (2). During harvest in October 2000, sugar beet plants exhibiting typical symptoms of rhizomania (1) were found in a field near Paterson, WA. Sugar beet had been planted in the field in 1999 and 2000, but prior to this, the field had not been planted with sugar beet for approximately 20 years. Symptomatic roots from the field exhibited stunting, vascular discoloration, and proliferation of lateral rootlets. Leaves of affected plants were chlorotic. Four soil samples were taken from symptomatic areas of the field and diluted with an equal amount of sterile sand. Seeds of rhizomania-susceptible sugar beet cv. Beta 8422 were planted in the soil and sand mix and maintained in a controlled environment at 24°C and 12 h of daylight at one location and in the greenhouse at another. After 8 weeks, enzyme-linked immunosorbent assay (ELISA) was performed on roots of plants grown at each location. Triple-antibody sandwich (TAS) ELISA (Agdia, Inc., Elkhart, IN) was conducted at the University of Idaho, Twin Falls, ID and double-antibody sandwich (DAS) ELISA was performed at USDA-ARS, Salinas, CA, with antiserum specific for BNYVV (2). Two of four samples were positive for BNYVV in the ELISA tests at both locations based on absorbance values at least three times those of healthy controls. TAS-ELISA tests were conducted on roots collected in July 2001 from a field in Washington, 12.9 km from the first field, as well as from a field across the Columbia River near Boardman, OR. Samples from both fields tested positive for BNYVV. All three fields are within 24 km of one another. Four additional fields have subsequently been confirmed to be infected with BNYVV in this region, based on symptomology and ELISA. There are approximately 3,240 ha of sugar beet grown in the region, and growers have been advised as a result of this confirmation to plant resistant cultivars and increase the sugar beet rotation interval with nonhost crops to a minimum of 4 years. References: (1) J. E. Duffus. Rhizomania. Pages 29-30 in: Compendium of Beet Diseases and Insects. E. D. Whitney and J. E. Duffus, eds. The American Phytopathological Society, St. Paul, MN, 1986. (2) G. C. Wisler et al. Plant Dis. 83:864, 1999.

Control of Paratrichodorus allius and Corky Ringspot Disease of Potato in the Columbia Basin of Oregon

Corky ringspot disease (CRS) of potato, caused by tobacco rattle virus that is vectored by stubby-root nematodes (Paratrichodorus spp.), is often controlled by aldicarb. When use of aldicarb on potato was suspended in 1989, an increase in crops rejected due to CRS in the Columbia Basin of the U.S. Pacific Northwest occurred. During 1992-94, several fumigant and nonfumigant nematicides were tested alone and in combination for control of P. allius and CRS. Aldicarb alone significantly reduced CRS but not to acceptable levels. Metam sodium or ethoprop alone did not control CRS, but metam sodium plus ethoprop provided adequate control under light disease pressure. Two or three postemergence applications of oxamyl, either with or without metham sodium, appeared to control CRS at low pressure. Fosthiazate reduced CRS incidence when used alone but not in combination with metam sodium. At low P. allius population densities, 1,3 dichloropropene (1,3-D) controlled CRS at 94 liters/ha, and rates of 140 liters/ha or greater were adequate at higher population densities. Treatment with 1,3-D plus chloropicrin was no better than 1,3-D alone and did not always control CRS. Combinations of 1,3-D at 94 liters/ha or greater plus metam sodium at 374 liters/ha or greater controlled CRS. Paratrichodorus allius numbers were higher and severity of CRS greater after wheat than after field corn, but P. allius declined rapidly after potato was planted and remained at low levels until harvest.

Control of Meloidogyne chitwoodi in Potato with Fumigant and Nonfumigant Nematicides

During 1993-94, several fumigant and nonfumigant nematicides were tested alone and in combination at various rates for control of Columbia root-knot nematode (Meloidogyne chitwoodi) in potato. Ethoprop, oxamyl, or metam sodium alone did not adequately reduce tuber infection. Metam sodium plus ethoprop reduced culled tubers to 3%, and metam sodium plus 2 or 3 foliar applications of oxamyl reduced culls to </=10% in all but one instance. Fosthiazate provided excellent control of tuber infection with or without metam sodium. Rates of 1,3-dichloropropene (1,3-D) below 234 liters/ha did not always adequately control tuber damage, but 140 liters/ha of 1,3-D plus ethoprop reduced the percentage of culled tubers to zero. 1,3-Dichloropropene plus chloropicrin did not provide better control than 1,3-D alone. Combinations of 1,3-D at 94 liters/ha or greater plus metam sodium at 374 liters/ha or greater consistently provided excellent control of tuber damage by M. chitwoodi and would be the treatment of choice where soilborne fungal pathogens are also present.

Thyroid function changes related to use of iodinated water in the U.S. Space Program

BACKGROUND

The National Aeronautics and Space Administration (NASA) has used iodination as a method of microbial disinfection of potable water systems in U.S. spacecraft and long-duration habitability modules. A review of thyroid function tests of NASA astronauts who had consumed iodinated water during spaceflight was conducted.

METHODS

Thyroid function tests of all past and present astronauts were reviewed. Medical records of astronauts with a diagnosis of thyroid disease were reviewed. Iodine consumption by space crews from water and food was determined. Serum thyroid-stimulating hormone (TSH) and urinary iodine excretion from space crews were measured following modification of the Space Shuttle potable water system to remove most of the iodine.

RESULTS

Mean TSH significantly increased in 134 astronauts who had consumed iodinated water during spaceflight. Serum TSH, and urine iodine levels of Space Shuttle crewmembers who flew following modification of the potable water supply system to remove iodine did not show a statistically significant change. There was no evidence supporting association between clinical thyroid disease and the number of spaceflights, amount of iodine consumed, or duration of iodine exposure.

CONCLUSIONS

It is suggested that pharmacological doses of iodine consumed by astronauts transiently decrease thyroid function, as reflected by elevated serum TSH values. Although adverse effects of excess iodine consumption in susceptible individuals are well documented, exposure to high doses of iodine during spaceflight did not result in a statistically significant increase in long-term thyroid disease in the astronaut population.

Implications of Sexual Reproduction for Phytophthora infestans in the United States: Generation of an Aggressive Lineage

Phytophthora infestans isolates (n = 26) collected in the Columbia Basin of Oregon and Washington in 1993, which had been characterized previously for mating type, metalaxyl sensitivity, and alleles at the glucose-6-phosphate isomerase locus, were analyzed for nuclear restriction fragment length polymorphism (RFLP) bands detected by probe RG57 and mitochondrial haplotype. Analyses involving the larger set of markers indicated that this group of isolates satisfied expectations of a sexual progeny: they contained much greater genetic diversity than has been reported for most other epidemic populations of P. infestans in the United States and Canada (16 unique multilocus genotypes); both mating types were present in proximity; all possible combinations of alleles occurred at many pairs of polymorphic loci; and two distinct mitochondrial haplotypes were distributed among the isolates. An in vitro laboratory cross involving the putative parents (US-6 and US-7) as parental strains produced progeny with the same general characteristics as the field isolates. Among the field progeny were two genotypes, US-11 and US-16, that had been described previously but from subsequent and largely clonal collections. Isolates obtained from tomatoes (n = 40) and potatoes (n = 7) in 24 counties in California in 1998 were analyzed as described above, and all except one US-8 isolate from potatoes were of the US-11 clonal lineage, consistent with the hypothesis that the US-11 lineage is an especially fit clonal lineage that has survived over time and can dominate pathogen populations over a large area. We conclude that the 1993 Columbia Basin collection represents a sexual progeny that generated the US-11 lineage, and that this lineage is particularly fit when tomatoes are part of the agroecosystem.

Design and current status of the longitudinal study of astronaut health

BACKGROUND

Information has been collected regarding the immediate physiological effects of spaceflight on humans. However, little is yet known regarding long-term effects. The purpose of this paper is to describe the Longitudinal Study of Astronaut Health (LSAH) and report current mortality data.

METHODS

All astronauts selected for the United States Space Program are followed from selection throughout their lifetime or until the end of the study. Comparisons are ground-based Johnson Space Center (JSC) employees matched to the astronauts at a 3:1 ratio by sex-specific age and body mass index. They are followed in the same manner as astronauts. Morbidity and mortality data are obtained from medical records supplemented with study questionnaires. Checks for death certificates are made to ascertain death of participants who miss routine examinations.

RESULTS

Current cause-specific mortality rates for astronauts selected from 1959 through 1991 are not statistically different from rates for comparison participants for cardiovascular (p = 0.8112), cancer (p = 0.2382), or other disease (p = 0.5040) mortality. Astronauts have a significantly higher mortality rate due to accidents and injuries (p < 0.0001).

CONCLUSIONS

Astronauts have a similar risk of death due to chronic diseases as ground-based participants, but are at greater risk for occupational-related accidental death.

Cost of Fungicides Used to Manage Potato Late Blight in the Columbia Basin: 1996 to 1998

The cost of managing potato late blight with fungicides in the Columbia Basin of Washington and Oregon in 1996 to 1998 was documented and compared with the cost of managing the epidemic in 1995. Mean number of fungicide applications on late-season potatoes from 1996 to 1998 ranged from 5.3 to 8.8 in the north Columbia Basin of Washington and 8.5 to 12.3 in the southern basin of Washington and Oregon. Mean cost per hectare of fungicides and application on late-season potatoes in 1998 was $316 per hectare ($128 per acre) in Washington's north basin and $472 per hectare ($191 per acre) in Washington's south basin. Even though the price of most fungicides had increased since 1995, total cost of control per hectare over the season was less during 1996 to 1998 than in 1995 because of altered management practices. These included fewer fungicide applications, a shift toward lower cost fungicides, substitution of aerial application by chemigation, and a reduction in the number of fields chemically desiccated before harvest. Total cost of managing late blight and tuber rot loss was $22.3 million in 1998, whereas it was $30 million in 1995. The 1998 cost included $19.8 million for fungicide applications and materials, $1.1 million for canopy desiccation, and $1.4 million loss due to tuber rot in storage.

Effects of Seedborne Potato Leafroll Virus on Russet Norkotah Potato

Tuber yield and quality of cv. Russet Norkotah potato plants grown from seed infected with potato leaf roll virus (PLRV) were compared with tuber yield and quality of adjacent plants grown from virus-free seed. Plants from PLRV-infected seed produced at least 60% less total yield and 88% less marketable yield (tubers >85 g) than plants grown from healthy seed. PLRV-infected seed also produced plants with fewer and smaller tubers than plants grown from healthy seed. No compensatory yield was measured in plants grown from PLRV-free seed growing adjacent to plants from PLRV-infected seed.

Management of Paratrichodorus allius Damage to Onion in the Columbia Basin of Oregon

Production of storage and dehydration (dehy) onions is increasing rapidly in the northcentral Oregon region of the Columbia Basin. Roughly circular patches of stunted onions have been observed in many fields and are often numerous and (or) extensive in area. Onions in these patches often exhibit symptoms typical of stubby-root nematodes, and Paratrichodorus allius has been collected from several damaged areas. This study examined the relationship of P. allius densities to onion yield reduction and benefit from oxamyl application. Transect samples and onions harvested across areas with varying P. allius densities revealed that the total number of onions was not affected by P. allius but that onions were in smaller, less valuable size classes. Yield of the largest size class of storage onions (colossals) declined substantially (57-61%) even at low (5-16/250 g soil) nematode densities. Treatment with oxamyl at 1.1 kg a.i./ha mitigated most of the damage, and the value of both storage and dehy onions was increased by more than $1,200/ha. Early applications were superior to later applications, whereas treatment at both times was no better than the early treatment alone. Damage at low (<10/250 g soil) nematode densities, low treatment cost ($86-172/ha), and high crop values suggest an economic benefit from treatment at population densities of four or more P. allius/250 g soil. However, stunted patches of onions may occur for reasons other than nematodes, and the presence of P. allius should be confirmed before treating fields. This is the first report of stubby-root nematode damage to dehy onions and to storage onions in the Columbia Basin.

Fungicide Application for Late Blight Management: A Boom Attached to a Center Pivot Irrigation System

Chlorothalonil was applied to commercial potato fields of cvs. Russet Norkotah and Russert Burbank in replicated trials through either a center-pivot irrigation system or a spray-boom-attached-to-the-pivot system. Water rates were 26,192 and 675 liters/ha for the center pivot and attached boom, respectively. Three crop canopy levels were sampled within 2 h and again after 6 days following fungicide applications made at 7-day intervals. Efficacy of the two application methods was tested by inoculation of individual excised leaves with an isolate of strain US-1 or US-8 of Phytophthora infestans and by chemical residue analysis. Severity of late blight did not differ between the two fungicide application methods 2 h after application but, after 6 days, disease severity was significantly less on leaves where chlorothalonil was applied by the attached boom. Fungicide residues were three times higher on leaves where chlorothalonil was applied by the attached boom than with the center-pivot system. Significantly more disease occurred on fungicide-treated and non-treated leaves inoculated with the US-8 than the US-1 strain. Severity of late blight on inoculated leaves was inversely related to the amount of chlorothalonil residue on leaves.

Comparison of Application Methods on Deposition and Redistribution of Chlorothalonil in a Potato Canopy and Potential for Control of Late Blight

The effect of application method by aircraft (fixed wing), ground, and chemigation on deposition of chlorothalonil in a potato canopy was compared over 2 years. Initial chlorothalonil deposition was greatest with ground application, less by aircraft, and least with chemigation. After application by aircraft or ground, the upper canopy had more chlorothalonil than the middle, and the lower canopy had the least. With chemigation, the upper canopy also had more chlorothalonil, but amounts in the lower and middle canopy were similar. Redistribution occurred with time as material from the upper canopy moved downward. With a 9-day application frequency using ground or aircraft methods, residue levels throughout the treated potato canopy were maintained, even if distribution of the fungicide within the canopy was poor from the initial application. With chemigation, low initial chlorothalonil levels were further decreased due to redistribution, increasing the likelihood that levels could fall below that which may be needed to adequately control late blight, particularly beyond 7 days after application.

Effects of Seedborne Potato Virus Y Infection in Two Potato Cultivars Expressing Mild Disease Symptoms

The effects of seedborne potato virus Y (PVY) in Shepody and Russet Norkotah, two new cultivars that express mild disease symptoms, were determined by comparing tuber yield and specific gravity of plants grown from PVY-infected seed with those of adjoining plants grown from virus-free seed. Seedborne PVY-infected Shepody plants produced 28.7% less total yield in 1994, and 41.1 and 47.3% less in two trials in 1995. Marketable yield was reduced 55.8 and 79.4% in 1995 trials. PVY infection did not affect specific gravity in Shepody. Seedborne PVY infections in Russet Norkotah reduced total yield by 45.5 and 48.8% in the 1994 and 1995 trials, respectively. During the 1995 trial, marketable yield from seedborne infected plants was reduced 65.1% compared with adjacent plants grown from noninfected seed. Additionally, specific gravity was lower for tubers from seedborne infected Russet Norkotah plants than from plants grown from noninfected seed in 1994. Seedborne infected plants of both varieties had fewer and smaller tubers than did plants grown from virus-free seed. No compensatory yield increase was measured for plants originating from PVY-free seed and growing adjacent to seedborne infected plants for either variety. Rather, yield reduction was observed in Russet Norkotah plants growing adjacent to seed infected plants in 1995. Enzyme-linked immunosorbent assay (ELISA) on Shepody in 1995 showed most plants grown from PVY-free seed became infected within 6 weeks of emergence.

Expansion of Potato Late Blight Forecasting Models for the Columbia Basin of Washington and Oregon

A regional potato late blight forecasting system for irrigated potatoes in the semiarid environment of the Columbia Basin was expanded by developing specific forecasting models for four vicinities throughout the Basin. Relationships between weather and outbreaks of late blight at the locations over a 27-year period were examined using logistic regression analysis. The response variable was a year either with or without a late blight outbreak. An indicator variable representing the occurrence of an outbreak during the preceding year (Yp) and number of days of rain during April and May (Ram) correctly classified the disease status (presence or absence of late blight) of 89, 82, 78, and 78% of the years at Prosser, Washington, Hermiston, Oregon, and Hanford and Othello, Washington, respectively. The percentage of years with disease outbreaks correctly classified was 93, 85, 79, and 79% at the four respective locations. All years with late blight outbreaks and 96% of the total years were correctly classified using data from at least one of the four locations. These predictors are particularly important early in the growing season and can be used to make area forecasts. A second set of predictors, Yp and number of days of rain in July and August (Rja), for Hermiston and Hanford, and a third set, Yp, Ram, and Rja, for Prosser and Othello were found effective for making additional late blight forecasts later in the growing season.

Aggressiveness of Isolates of Phytophthora infestans from the Columbia Basin of Washington and Oregon

ABSTRACT The aggressiveness of 22 isolates of Phytophthora infestans collected from naturally infected potato plants in the Columbia Basin of Washington and Oregon was determined on detached potato leaflets at 18 degrees C in an incubator. Selected isolates were evaluated on whole plants in a greenhouse. Aggressiveness was measured by using the area under the lesion expansion curve (AULEC), incubation period, latent period, sporulation capacity, and lesion size on detached leaflets and the area under the disease progress curve and sporulation capacity on whole plants. The detached-leaflet assay was useful in that a large number of isolates were tested, several components of aggressiveness were studied, and significant differences were found among isolates. Significant variation for components of aggressiveness was found within and among isolates classified according to genotype. Significant interactions among isolates and cultivars were found for some components of aggressiveness, so results were pooled according to cultivar. On average, US-8 and US-11 isolates had higher AULEC scores, indicating aggressiveness higher than that of US-7, US-6, and US-1 genotypes. One US-8 genotype isolate had a higher standardized sporulation capacity than isolates of the other genotypes. US-6 genotype isolates were the least aggressive group, as indicated by low AULEC, sporulation capacity, and lesion size values. The replacement of the US-1 genotype by the US-8 genotype in the Columbia Basin may be partially explained by the increased aggressiveness of US-8 isolates. Additionally, potato growers may need to shorten intervals between fungicide applications and begin applications earlier.

Risk of cancer mortality among the Longitudinal Study of Astronaut Health (LSAH) participants

BACKGROUND

The potential for occupational radiation exposures in the U.S. Space Program makes cancer risk a major health concern.

METHODS

The NASA Medical Operations Branch and KRUG Life Sciences Epidemiology Section at the Johnson Space Center (JSC) investigated the rate of cancer mortality among the astronauts and the comparison participants of the Longitudinal Study of Astronaut Health (LSAH). Medical records are maintained by the JSC Flight Medicine Clinic, JSC Occupational Medicine Clinic, and LSAH. Cause of death data from death certificates were reviewed for cancer mortality. These data were compared with cancer mortality data for the general population residing in the Texas Gulf Coast area.

RESULTS

The astronauts had a higher age-specific risk of cancer mortality than the comparison group (SMR = 345; 95% CI = 69.5-756.2), but the difference did not reach statistical significance. Both the astronauts and the comparison group had lower age-specific rates than the general population (SMR = 47, 95% CI = 9.6-105.1; SMR = 17, 95% CI = 3.5-37.9, respectively).

Characterization of the Phytophthora infestans Population in the Columbia Basin of Oregon and Washington from 1992 to 1995

ABSTRACT Isolates of Phytophthora infestans collected from 1992 to 1995 from potato fields in the Columbia Basin of Oregon and Washington were analyzed for compatibility type, metalaxyl sensitivity, and glucose-6-phosphate isomerase (Gpi) genotype. In 1992, 30 of 31 isolates were of the US-1 multilocus genotype. A single metalaxyl-resistant isolate of the US-6 (A1 Gpi 86/100) genotype was found near the end of the growing season. In 1993, only 2 of the 59 isolates collected were A1 isolates with Gpi 86/100. Ten isolates were of the A2 compatibility type, seven with Gpi 100/111, two with Gpi 100/100, and one was undetermined. The remaining isolates were metalaxyl-resistant A1 compatibility types with either Gpi 100/100 or 100/111. The first A2 isolates in the Columbia Basin were found in 1993. In 1994, 10 of 18 isolates were of the US-1 genotype. The remaining isolates were US-6 and US-8 genotypes. In 1995, 97% of 268 isolates tested were of the US-8 genotype. Five isolates were A2 compatibility type with Gpi 100/122. One A2, metalaxyl-resistant isolate was Gpi 100/100/111, and two A1 isolates were Gpi 100/111/122. The population of P. infestans quickly changed between 1992 and 1995, from a population comprised almost exclusively of the US-1 genotype to a population represented by new or recombinant genotypes.

Potato Late Blight in the Columbia Basin: An Economic Analysis of the 1995 Epidemic

The cost of managing late blight in potatoes during a severe epidemic caused by new, aggressive strains of Phytophthora infestans in the Columbia Basin of Washington and Oregon in 1995 was documented. The mean number of fungicide applications per field varied from 5.1 to 6.3 for early- and midseason potatoes, and from 8.2 to 12.3 for late-season potatoes in the northern and southern Columbia Basin, respectively. In 1994, a year when late blight was not severe, the mean number of fungicide applications per field made to early- and midseason potatoes was 2.0; whereas late-season potatoes received a mean of 2.5 applications. The mean per acre cost of individual fungicides applied varied from $4.90 for copper hydroxide to $36.00 for propamocarb + chlorothalonil. Total per acre expenses (application costs plus fungicide material) for protecting the crop from late blight during 1995 ranged from $106.77 to $110.08 for early and midseason potatoes in different regions of the Columbia Basin and from $149.30 to $226.75 for lateseason potatoes in the northern and southern Columbia Basin, respectively. Approximately 28% of the crop was chemically desiccated before harvest as a disease management practice for the first time in 1995, resulting in an additional mean cost of $34.48/acre or $1.3 million for the region. Harvested yields were 4 to 6% less than in 1994. The total cost of managing late blight in the Columbia Basin in 1995 is estimated to have approached $30 million.

First Report of Bacterial Fruit Blotch of Watermelon in Oregon

Most of the watermelons, Citrullus lanatus (Thunb.) Matsum. & Nakai, consumed in the Pacific Northwest during the summer months are grown in the southern Columbia Basin under dry (<5 cm rainfall), low relative humidity (46 to 57%), and high temperature (29 to 41°C) conditions, using transplants, plastic mulch, and drip irrigation. During May 1996, irregularly shaped, water-soaked lesions were observed on cotyledons and first true leaves of watermelon cv. Sangria transplants growing in a greenhouse. Similar lesions were observed later on older leaves in a commercial field of cv. Millionaire. Microscopic examination of symptomatic tissue revealed bacterial streaming, and isolation on nutrient agar consistently yielded numerous creamy to off-white bacterial colonies. Bacteria from purified, single colonies were Gram negative and rod shaped. Physiological characterization by the Biolog GN Bacterial Identification System (version 3.5) showed a similarity of 0.971 to the Biolog description for Acidovorax avenae subsp. citrulli. Pathogenicity of two strains was confirmed in three separate tests by hypodermic needle infiltration of cotyledons or by stab inoculation into hypocotyls of 12 to 24 21-day-old cv. Crimson Sweet seedlings with aqueous suspensions of bacteria containing approximately 6.0 × 10⁸ CFU/ml. Inoculum was prepared from 48-h-old nutrient agar cultures. Test plants were incubated in the greenhouse at 21°C, under a 16-h photoperiod. Hypocotyl and cotyledon inoculations produced water-soaked lesions within 24 to 48 h on both the hypocotyl and cotyledons or just the cotyledon, respectively, on plants inoculated by either method. No symptoms developed on control plants infiltrated or stabbed with sterile water only. Isolations from three symptomatic seedlings yielded colonies similar in morphology to those used for inoculation. Tests of two purified cultures by Biolog indicated the bacteria were A. avenae subsp. citrulli. The symptomatic test plants were transplanted to fields, and the maturing melons developed large, dark green, water-soaked lesions with irregular margins. Similar fruit symptoms were seen in commercial fields. Labels on seed used in commercial production and in our tests warned of risks related to fruit blotch. This is the first report of bacterial fruit blotch of watermelon in Oregon. This disease may have a significant impact on watermelon production in the Columbia Basin.

Perception of the medical risk of spaceflight

We conducted an opinion survey to improve the characterization of medical risk during spaceflight, using a questionnaire designed to elicit space medicine experts' perceptions of the probability, health effect, and mission impact of selected medical events occurring during spaceflight missions of 30-90 d. This questionnaire was directed toward those events about which little data currently exist, therefore medical events that have occurred during spaceflights with some frequency, such as space motion sickness, were excluded from the questionnaire. The questionnaire was mailed to 99 clinical and research professionals involved with NASA medical programs; 65 responses were returned, of which 60 could be analyzed. The experts rated skin disorders as the most likely to occur, but which would have little effect on mission completion or astronaut health. Circulatory diseases were rated as having the lowest probability of occurrence, but the highest effect on the mission or on a crewmember's health. The results of this survey will be combined with data from analogous populations and existing astronaut health data to establish a data set to support decisions about allocation of health care resources.

Longitudinal study of astronaut health: mortality in the years 1959-1991

We conducted a historical cohort study of mortality among 195 astronauts who were exposed to space and medical sources of radiation between 1959 and 1991. Cumulative occupational and medical radiation exposures were obtained from the astronaut radiation exposure history data base. Causes of death were obtained from obligatory death certificates and autopsy reports that were on file in the medical records. There was a total of 20 deaths that occurred during the 32-year follow-up period of which 16 were due to accidents. The all-cause standardized mortality ratio (SMR) was 181 (95% confidence interval 110, 279). There was 1 cancer death in the buccal cavity and pharyngeal ICD-9 rubric whose occurrence was significantly beyond expectation. Mortality for coronary disease was 53% lower than expected (2 deaths; SMR = 47; 95% confidence limits 5, 168). The crude death rate for 12 occupationally related accidents was 445 deaths per 100,000 person-years and was an order of magnitude greater than accidental death rates in the mining industries. The SMR of 1346 for fatal accidents was significantly beyond expectation (16 deaths; 95% confidence limits 769, 2168) and was similar to SMRs for accidents among aerial pesticide applicators. The 10-year cumulative risk of occupational fatalities based on the exponential, Weibull, Gompertz, and linear-exponential distributions was 10%. Mortality from motor vehicle accidents was slightly higher than expected, but was not significant (1 death; SMR = 165; 95% confidence limits 2,922). Radiation exposures from medical procedures accounted for a majority of cumulative dose when compared with space radiation exposures. Overall, it was found that astronauts are at a health disadvantage as a result of catastrophic accidents.