Multi-vendor multi-site T1ρ and T2 quantification of knee cartilage.

OBJECTIVE: To develop 3D T1ρ and T2 imaging based on the same sequence structure on MR systems from multiple vendors, and to evaluate intra-site repeatability and inter-site inter-vendor reproducibility of T1ρ and T2 measurements of knee cartilage. METHODS: 3D magnetization-prepared angle-modulated partitioned k-space spoiled gradient echo snapshots (3D MAPSS) were implemented on MR systems from Siemens, GE and Philips. Phantom and human subject data were collected at four sites using 3T MR systems from the three vendors with harmonized protocols. Phantom data were collected by means of different positioning of the coil. Volunteers were scanned and rescanned after repositioning. Two traveling volunteers were scanned at all sites. Data were transferred to one site for centralized processing. RESULTS: Intra-site average coefficient of variations (CVs) ranged from 1.09% to 3.05% for T1ρ and 1.78-3.30% for T2 in phantoms, and 1.60-3.93% for T1ρ and 1.44-4.08% for T2 in volunteers. Inter-site average CVs were 5.23% and 6.45% for MAPSS T1ρ and T2, respectively in phantoms, and 8.14% and 10.06% for MAPSS T1ρ and T2, respectively, In volunteers. CONCLUSION: This study showed promising results of multi-site, multi-vendor reproducibility of T1ρ and T2 values in knee cartilage. These quantitative measures may be applied in large-scale multi-site, multi-vendor trials with controlled sequence structure and scan parameters and centralized data processing.

First Report of Late Blight Caused by Phytophthora infestans Clonal Lineage US-23 on Tomato and Potato in Atlantic Canada.

Phytophthora infestans (Mont.) de Bary has produced significant losses in potato and tomato yield and quality during recent late blight epidemics in North America. During the 1990s, more aggressive and genetically diverse P. infestans genotypes migrated to Canada and the United States (2). For example, US-8 became predominant and was found to be more aggressive in potato than previous clonal lineages of P. infestans. Recent P. infestans genotypes in potato and tomato plants from the United States and Canada include US-22, US-23, and US-24 representing clonal lineages with unique epidemiological characteristics (2,3,4). Characteristic phenotypic traits have been described for P. infestans clonal lineages US-8, US-22, US-23, and US-24 based on the mating type, mefenoxam sensitivity, pathogenicity, and rate of germination suggesting an association between phenotypic variations and the genotype (1,4). Analysis of P. infestans isolates collected in Canada during 2010 revealed the presence of the US-23 clonal lineage in four different areas of western Canada but not in eastern Canada (4). Isolates of P. infestans collected from eastern Canada for several years prior to 2011 were all US-8 A2 mating type. Isolation and analysis of 98 P. infestans isolates in 2011 from New Brunswick and Prince Edward Island followed standard procedures (2,3,4). Results confirmed the presence of the US-23 clonal lineage in Atlantic Canada on potato and tomato leaves with late blight symptoms, increasing the genetic complexity of P. infestans in eastern Canada. Allozyme banding patterns at the glucose-6-phosphate isomerase (Gpi) locus showed a 100/100 profile in 10 P. infestans isolates, consistent with the US-23 clonal lineage (2,3,4). Furthermore, in vitro mefenoxam sensitivity was observed in all 10 P. infestans US-23 isolates from New Brunswick and Prince Edward Island. Mating type assays confirmed the isolates were of the A1 mating type. RFLP analysis of EcoR1-digested genomic DNA using the multilocus RG57 sequence as a probe produced the DNA pattern 1, 2, 5, 6, 10, 13, 14, 17, 20, 21, 24, 24a, 25, indicative of US-23 (2,4). Microsatellite analysis using polymorphic markers on New Brunswick and Prince Edward Island P. infestans isolates produced the Pi4B 213/217 bp, D13 134 bp, and PiG11 140/155 bp profile of P. infestans US-23 (1). These results show the presence of the P. infestans A1 and A2 mating types in New Brunswick and Prince Edward Island, which increases the probability of sexual recombination. To our knowledge, this is the first report of P. infestans clonal lineage US-23 causing late blight in New Brunswick and Prince Edward Island, increasing the genetic diversity from previous years in eastern Canada and underscoring the annual fluctuation occurring in the population composition. References: (1) G. Danies et al. Plant Dis. 97:873, 2013. (2) S. B. Goodwin et al. Phytopathology 84:553, 1994. (3) C. H. Hu et al. Plant Dis. 96:1323, 2012. (4) M. L. Kalischuk et al. Plant Dis. 96:1729, 2012.

First Report of Phytophthora infestans Genotype US23 Causing Late Blight in Canada.

Late blight is caused by the oomycete Phytophthora infestans (Mont.) de Bary and is one of the most devastating diseases of potato and tomato. Late blight occurs in all major potato- and tomato-growing regions of Canada. Its incidence in North America increased during 2009 and 2010 (2). Foliar disease symptoms appeared earlier than usual (June rather than July) and coincided with the identification of several new P. infestans genotypes in the United States, each with unique characteristics. Prior to 2007, isolates collected from potato and tomato crops were mainly US8 or US11 genotypes (1). However, P. infestans populations in the United States have recently experienced a major genetic evolution, producing isolates with unique genotypes and epidemiological characteristics in Florida and throughout the northeastern states (2). Recent discoveries of tomato transplants with late blight for sale at Canadian retail outlets prompted an examination of the genotypes inadvertently being distributed and causing disease in commercial production areas in Canada. Analysis of isolates of P. infestans from across Canada in 2010 identified the US23 genotype for the first time from each of the four western provinces (Manitoba, Saskatchewan, Alberta, and British Columbia) but not from eastern Canada. Allozyme banding patterns at the glucose phosphate isomerase (Gpi) locus indicated a 100/100 profile consistent with US6 and US23 genotypes (4). Mating type assays confirmed the isolates to be A1 and in vivo metalaxyl sensitivity was observed. Restriction fragment length polymorphic analysis of 50 isolates from western Canada with the multilocus RG57 sequence and EcoRI produced the DNA pattern 1, 2, 5, 6, 10, 13, 14, 17, 20, 21, 24, 24a, 25 that was indicative of US23 (3). The recently described P. infestans genotype US23 appears to be more aggressive on tomato, and although isolates were recovered from both tomato and potato, disease symptoms were often more severe on tomato. Results indicate that movement and evolution of new P. infestans genotypes have contributed to the increased incidence of late blight and that movement of the pathogen on retail plantlets nationally and internationally may provide an additional early season source of inoculum. A major concern is that the introduced new A1 populations in western Canada have established a dichotomy with the endogenous A2 populations in eastern Canada, increasing the potential for sexual recombination producing oospores and additional genotypes should these populations merge. References: (1) Q. Chen et al. Am. J. Potato Res. 80:9, 2003. (2) K. Deahl. (Abstr.) Phytopathology 100(suppl.):S161, 2010. (3) S. B. Goodwin et al. Curr. Genet. 22:107, 1992. (4) S. B. Goodwin et al. Phytopathology 88:939, 2004.

Modal filtering for midinfrared nulling interferometry using single mode silver halide fibers.

We demonstrate the modal filtering properties of newly developed single mode silver halide fibers for use at midinfrared wavelengths, centered at 10.5 microm. The goal was to achieve a suppression of nonfundamental modes greater than a factor of 300 to enable the detection and characterization of Earthlike exoplanets with a space-based nulling interferometer. Fiber segments of 4.5 cm, 10.5 cm, 15 cm, and 20 cm lengths were tested. We find that the performance of the fiber was limited not by the modal filtering properties of the core but by the unsuppressed cladding modes present at the output of the fiber. In 10.5 cm and longer sections, this effect can be alleviated by properly aperturing the output. Exclusive of coupling losses, the fiber segments of 10.5-20 cm length can provide power suppression of undesirable components of the input field by a factor of 15,000 at least. The demonstrated performance thus far surpasses our requirements, such that even very short sections of fiber provide adequate modal filtering for exoplanet characterization.

First Report of Reduced Sensitivity to a QoI Fungicide in Isolates of Alternaria solani Causing Early Blight of Potato in Canada.

Early blight of potato (Solanum tuberosum L.) caused by Alternaria solani Sorauer is a frequent concern for potato growers in Canada. Management of early blight has relied on foliar fungicides that often include quinone outside inhibitor (QoI) fungicides such as azoxystrobin. In recent years, isolates of A. solani with reduced sensitivity to QoI fungicides, conferred by the presence of the F129L mutation (in the cytochrome b gene causing amino acid substitution of phenylalanine with leucine at position 129), have become widespread in potato-production areas of the United States, leading to a reduced efficacy of these products (3). Observations of reduced fungicide efficacy, following application of QoI fungicides to commercial fields in Manitoba, Canada in 2007, prompted an examination of the fungicide sensitivity of isolates of A. solani collected from fields in this province. Nine isolates of A. solani were obtained from potato foliage with typical early blight symptoms from four fields in Manitoba using standard protocols (2). Isolates were maintained on clarified V8 agar (1) and identified to species level based on conidial morphology (4). The sensitivity of each isolate to azoxystrobin was determined by assessing conidial germination on water agar plates amended with 0, 0.001, 0.01, 0.1, 1.0, or 10.0 mg/liter of azoxystrobin with protocols described previously (1). Two reference isolates of A. solani from North Dakota with known sensitivities to azoxystrobin and one isolate from Prince Edward Island (PEI), Canada, (a province yielding only isolates sensitive to azoxystrobin in previous surveys; R. D. Peters, unpublished data) were included in the assays. Calculated effective concentration (EC50) values (azoxystrobin concentration inhibiting conidial germination by 50%) were determined for each isolate response from two replications of the assays. The reference isolates of A. solani from North Dakota were sensitive or had reduced sensitivity to azoxystrobin with mean EC50 values of 0.02 and 0.2 mg/liter, respectively. The isolate from PEI was sensitive to azoxystrobin with a mean EC50 value of 0.04 mg/liter. By contrast, isolates of A. solani from Manitoba had reduced sensitivity to azoxystrobin with mean EC50 values from 0.2 to 0.8 mg/liter. Real-time PCR analysis of each isolate was performed (2) and confirmed the presence of the F129L mutation in the Manitoba isolates and the isolate with reduced sensitivity to azoxystrobin from North Dakota. The F129L mutation was absent in the azoxystrobin-sensitive wild-type isolates from PEI and North Dakota. To our knowledge, this is the first report of isolates of A. solani with reduced sensitivity to azoxystrobin in Canada. Since cross resistance among QoI fungicides has been demonstrated in A. solani isolates with the F129L mutation (3), adoption of resistance management strategies, including alternating QoI fungicides with fungicides having different modes of action and further monitoring pathogen populations for QoI sensitivity in Canadian production areas, is recommended. References: (1) J. S. Pasche et al. Plant Dis. 88:181, 2004. (2) J. S. Pasche et al. Plant Dis. 89:269, 2005. (3) J. S. Pasche and N. C. Gudmestad. Crop Prot. 27:427, 2008. (4) J. Rotem. The Genus Alternaria: Biology, Epidemiology, and Pathogenicity. The American Phytopathological Society, St. Paul, MN, 1994.

First Report of Fludioxonil-Resistant Isolates of Fusarium spp. Causing Potato Seed-Piece Decay.

Potato (Solanum tuberosum L.) diseases incited by Fusarium spp. include postharvest dry rot and seed-piece decay. Fusarium seed-piece decay is commonly controlled by preplant applications of chemical seed treatments. However, isolates of Fusarium spp. resistant to benzimidazole fungicides have been reported (2,4). In the spring of 2007, samples of cut seed tubers (cvs. Shepody and Russet Burbank) showing extensive symptoms of decay were received from three seedlots in Prince Edward Island (PE) and one seedlot in Saskatchewan (SK), Canada. All seed tubers had been treated with fludioxonil (Maxim Potato Seed Protectant [PSP], 0.5% fludioxonil) following cutting and then stored for 10 to 14 days prior to planting. Using standard isolation protocols (4), the 19 potato tuber pieces examined from PE and 2 from SK yielded 21 Fusarium isolates for further study. Five isolates (including both isolates from SK) were identified as Fusarium sambucinum Fuckel and the remaining 16 isolates were identified as F. coeruleum (Libert) Sacc. (3). To confirm identifications, isolates were compared with two known standards of each of F. sambucinum and F. coeruleum identified by K. Seifert (Agriculture and Agri-Food Canada, Ottawa, ON) by DNA sequencing of the partial ß-tubulin gene or the translation elongation factor 1-α ( http://fusarium.cbio.psu.edu ; [1]). These standard isolates were also used as fludioxonil-sensitive controls in amended agar assays for chemical sensitivity. Agar plugs (5 mm in diameter) taken from the margins of 7-day-old cultures of the Fusarium isolates were transferred to petri dishes containing ½-strength potato dextrose agar amended with 0, 0.1, 1.0, 10.0, or 100.0 mg/liter of fludioxonil. Fludioxonil (Maxim PSP, 0.5% a.i.) was prepared as a stock solution in sterile distilled water and added to the molten agar after autoclaving. Culture incubation and mycelial growth measurements were performed as described previously (4). Measurements from four replicate petri dishes per concentration of fludioxonil were taken. Calculated EC50 values (fludioxonil concentration inhibiting pathogen growth by 50%) were obtained. The trial was repeated three times. The two standard isolates of F. sambucinum were sensitive to fludioxonil, with mean EC50 values of 0.002 (±0.002 standard error [SE]) and 0.005 (±0.002 SE) mg/liter. The two standard isolates of F. coeruleum were also sensitive to fludioxonil, with mean EC50 values of 0.17 (±0.005 SE) and 0.19 (± 0.005 SE) mg/liter. All other tested isolates of F. sambucinum and F. coeruleum were resistant to fludioxonil and showed no growth inhibition even at 100 mg of fludioxonil per liter. To our knowledge, this is the first report of resistance to fludioxonil in isolates of Fusarium spp. causing potato seed-piece decay. Since the isolates of F. sambucinum were also resistant to thiophanate-methyl and thiabendazole (data not shown), multiclass (benzimidazole and pyrrole) resistance was also documented. References: (1) D. M. Geiser et al. Eur. J. Plant Pathol. 110:473, 2004. (2) L. M. Kawchuk et al. Am. Potato J. 71:185, 1994. (3) P. E. Nelson et al. Fusarium Species: An Illustrated Manual for Identification. Pennsylvania State University Press, 1983. (4) R. D. Peters et al. Plant Dis. 85:1030, 2001.

Magnetic resonance imaging of temperature changes during interstitial microwave heating: a phantom study.

Changes in magnetic resonance (MR) signals during interstitial microwave heating are reported, and correlated with simultaneously acquired temperature readings from three fiber-optic probes implanted in a polyacrylamide gel phantom. The heating by a MR-compatible microwave antenna did not interfere with simultaneous MR image data acquisition. MR phase-difference images were obtained using a fast two-dimensional-gradient echo sequence. From these images the temperature-sensitive resonant frequency of the 1H nuclei was found to decrease approximately by 0.008 ppm/ degree C. The method and results presented here demonstrate that noninvasive MR-temperature imaging can be performed simultaneously with interstitial microwave thermal treatment.

Comparison of thermal damage calculated using magnetic resonance thermometry, with magnetic resonance imaging post-treatment and histology, after interstitial microwave thermal therapy of rabbit brain.

Clinical application of high-temperature thermal therapy as a treatment for solid tumours requires an accurate and close to real-time method for assessing tissue damage. Imaging methods that detect structural changes during heating may underestimate the extent of thermal damage. This is due to the occurrence of delayed damage manifested at tissue locations exposed to temperatures lower than those required to cause immediate structural changes. An alternative approach is to measure temperature and then calculate the expected damage based on the temperature history at each tissue location. Magnetic resonance (MR) imaging methods now allow temperature maps of the target and surrounding tissues to be generated in almost real-time. The aim of this work was to evaluate whether thermal damage zones calculated on the basis of MR thermometry maps measured during heating correspond to actual tissue damage as measured after treatment by histological methods and MR imaging. Four male rabbits were treated with high-temperature thermal therapy delivered in the brain by a single microwave antenna operating at 915 MHz. MR scanning was performed before, during and after treatment in a 1.5 T whole-body scanner. Temperature maps were produced using the proton resonance frequency (PRF) shift method of MR thermometry. In addition, conventional T1-weighted and T2-weighted spin-echo images were acquired after treatment. Thermal damage zones corresponding to cell death, microvascular blood flow stasis and protein coagulation were calculated using an Arrhenius analysis of the MR temperature/time course data. The calculated zones were compared with the lesions seen on histopathological examination of the brains which were removed within 6-8 h of treatment. The results showed that calculated damage zones based on MR thermometry agreed well with areas of damage as assessed using histology after heating was completed. The data suggest that real-time calculations of final expected thermal damage based on an Arrhenius analysis of MR temperature data may provide a useful method of real-time monitoring of thermal therapy when combined with conventional T2-weighted images taken after treatment.

A Rapid Technique for the Evaluation of Potato Germ Plasm for Susceptibility to Pink Rot.

Disease-free plantlets of 20 potato cultivars commonly grown in Prince Edward Island were inoculated with zoospore suspensions of Phytophthora erythroseptica, the causal agent of pink rot, to determine disease response. All inoculated cultivars developed disease symptoms relative to noninoculated controls, but disease severity differed significantly (P = 0.05) among cultivars. Plantlets of the cultivars Goldrush and Yukon Gold were consistently the most susceptible to the disease, whereas plantlets of cultivars Butte and Russet Burbank were the least susceptible. Most of the cultivars assessed were moderately susceptible to disease. Plantlets of potato cultivars with late-season field maturity were more resistant to disease than those with early or mid-season maturity. Isolates of P. erythroseptica from diverse regions of Prince Edward Island and Maine did not differ significantly (P = 0.05) in pathogenicity. The screening protocol described was a reliable technique to determine the relative resistance of nontuber potato germ plasm to disease, resulting from infection with P. erythroseptica.

Inoculation with Nonpathogenic Fusarium solani Increases Severity of Pea Root Rot Caused by Aphanomyces euteiches.

Aphanomyces euteiches is an important root-rotting pathogen of pea. When recovering isolates of A. euteiches from infested soils in Wisconsin using pea as a bait host, isolates of Fusarium solani often were recovered. Experiments were established to compare disease symptoms of pea seedlings inoculated with isolates of A. euteiches and F. solani alone or in combination. Inoculation of pea seedlings with either of two isolates of A. euteiches produced typical root rot symptoms. However, inoculation of pea seedlings with an isolate of F. solani resulted in no disease symptoms, indicating that the isolate was nonpathogenic to pea. Co-inoculation of pea seedlings with A. euteiches and the nonpathogenic isolate of F. solani resulted in significantly (P = 0.05) greater disease severity than inoculation with A. euteiches alone. Both A. euteiches and F. solani could be reisolated, individually or together, from pea seedlings following individual or co-inoculations, respectively. Although the mechanisms of interaction between these two species are unknown, the synergism documented in this study indicates that the interactions of pathogens with nonpathogens may affect development of disease symptoms.

Oospore Germination of Aphanomyces euteiches in Root Exudates and on the Rhizoplanes of Crop Plants.

A technique was developed that allows prolific production, easy collection, and increased germination frequency of single oospores of Aphanomyces euteiches. The influence of root exudates and roots of various plant species, including pea, bean, alfalfa, oat, soybean, corn, and tomato, on germination of A. euteiches oospores also was studied. Compared with a sterile, deionized water control, root exudates from several hosts were only slightly effective in stimulating oospore germination, since only 0 to 11.1% of oospores exposed to various exudates germinated. By contrast, oospores placed directly on plant roots germinated at higher frequencies. Oospores of pea pathotype isolates P30 and P46 germinated at a greater frequency (30.6 to 61.1%) on pea, bean, and oat roots than on roots of any of the other plant species tested. Oospores of bean pathotype isolates GB33 and GB71 had a higher germination frequency (47.2 to 52.8%) on bean roots than on the roots of the other plant species tested. A higher percentage of oospores germinated if placed on lateral roots as opposed to taproots of pea and bean. A higher percentage of oospores of bean pathotype isolates and one pea pathotype isolate germinated on 10-day-old rather than on 20-day-old roots of bean. Therefore, pea and bean roots can be used effectively to germinate oospores of pea and bean isolates of A. euteiches, respectively. This technique will be valuable for studies of sexual reproduction and genetics of A. euteiches.

First Report of Thiabendazole-Resistant Isolates of Fusarium sambucinum Infecting Stored Potatoes in Nova Scotia, Canada.

Fusarium dry rot is a significant postharvest disease of potato (Solanum tuberosum L.) and is often controlled by applying thiabendazole to tubers prior to storage. However, thiabendazole-resistant isolates of Fusarium spp. have been reported from Europe (2), the United States (1), and Canada (1,4). To address concerns, samples of potato tubers showing symptoms of dry rot caused by Fusariumspp. were collected from three storage bays in a commercial storage facility in Nova Scotia, Canada, in February 2001. All tubers had been treated with thiabendazole after harvest and prior to storage. Tubers were cut longitudinally, and small tissue samples (10 × 5 × 3 mm) were taken from the margins of internal necrotic regions with a sterile scalpel, surface-sterilized in 0.6% sodium hypochlorite for 15 s, rinsed twice in sterile distilled water (SDW), and blotted dry on sterile filter paper. Tissue pieces were plated on 0.5-strength potato dextrose agar (PDA) amended with tetracycline (0.05 g/liter) and streptomycin sulfate (0.1 g/liter). Petri dishes were incubated in the dark at 22°C for 4 to 7 days. After incubation, hyphal tips from the margins of actively growing isolates were removed with a sterile probe and plated on 0.5-strength PDA to generate pure cultures. Of 35 potato tubers examined, 10 (29%) yielded Fusarium isolates for further study. All 10 isolates were identified as F. sambucinum Fuckel according to Nelson et al. (3). Agar plugs (5 mm diameter) taken from the margins of 7- to 10-day-old cultures of F. sambucinum isolates were transferred to petri dishes containing 0.5-strength PDA amended with thiabendazole at 0, 1, 5, 10, 20, 50, or 100 mg/liter. Thiabendazole was prepared as a stock solution in SDW and added to molten agar after autoclaving. Cultures were grown in the dark for 7 days at 22°C, after which mycelial growth diameter was measured using digital calipers. Two measurements, along orthogonal diameters, were taken from each of three replicate plates for a total of six measurements per thiabendazole concentration. Means were calculated, and the diameter of the inoculation plug was subtracted from each mean. Calculated EC50 values (thiabendazole concentration inhibiting pathogen growth by 50%) were obtained by regression of the log of the chemical concentration against the corresponding probit of percent fungal inhibition. All isolates of F. sambucinum were resistant to thiabendazole, with EC50 values ranging from 7 to 82 mg/liter. Six isolates had EC50 values between 40 and 82 mg/liter. Control isolates of F. sambucinum, F. avenaceum, F. solani, and F. oxysporum were sensitive to thiabendazole, with EC50 values of <1 mg/liter. Although isolates of F. sambucinum resistant to thiabendazole have been recovered from eastern Canada (1,4), this is the first report of thiabendazole resistance in F. sambucinum isolates from tubers in commercial storage in the Annapolis Valley of Nova Scotia, Canada, a production region that concentrates on growing processing potatoes for the potato chip industry and is several hundred kilometers from other potato-growing regions of Prince Edward Island and New Brunswick. References: (1) A. E. Desjardins. Am. Potato J. 72:145, 1995. (2) G. A. Hide et al. Plant Pathol. 41:745, 1992. (3) P. E. Nelson et al. 1983. Fusarium Species: An Illustrated Manual for Identification . Pennsylvania State University Press, University Park, PA. (4) H. W. Platt. Phytoprotection 78:1, 1997.

Variation in Aggressiveness of Canadian Isolates of Phytophthora infestans as Indicated by Their Relative Abilities to Cause Potato Tuber Rot.

Studies were conducted in 1995, 1996, and 1997 to determine the ability of Canadian isolates of Phytophthora infestans to cause tuber disease in a variety of potato cultivars. Most isolates of recently introduced multilocus genotypes (US-7, US-8, g11, g26, g29, and g40) were more aggressive on tuber tissue than isolates of the traditional US-1 genotype, based on surface necrosis (SN), lesion depth (LD), and compound aggressiveness index (CAI = SN × LD) components. Other multilocus genotypes (g30, g41, g42, and UN-3) were similar in aggressiveness to US-1. The g11 (US-11) genotype consistently displayed aggressiveness that was intermediate to that of the US-8 and US-1 genotypes. Variation also occurred within a multilocus genotype, and an isolate of the US-8 genotype from New Brunswick was consistently less aggressive than other US-8 isolates. Cvs. Dorita and Island Sunshine were consistently the most resistant to infection, regardless of isolate, relative to the more susceptible responses of Green Mountain, Russet Bur-bank, Kennebec, Superior, Shepody, Red Pontiac, Sebago, and Bintje. Even so, isolates of the newly introduced US-8 genotype were able to cause significantly more disease on these resistant cultivars than isolates of the US-1 genotype. The predominant genotypes currently found in potato production areas in Canada (US-8 and g11) have higher fitness on tuber tissue than displaced, preexisting strains (US-1).

First Report of Aster Yellows Phytoplasma in Alfalfa.

Samples of alfalfa (Medicago sativa L.) leaves and stems showing symptoms of inter-veinal chlorosis and purpling, commonly associated with insect feeding, were collected from 8 sites in central and southern Wisconsin in autumn of 1998. Samples were frozen within 24 h of collection. Approximately 0.3 g of plant tissue from each sample was used for total DNA extraction according to the protocol of Zhang et al. (4), with minor modifications in grinding procedures and reagent volumes to optimize results. Nested polymerase chain reaction (PCR) was carried out by amplification of 16S rDNA with the universal primer pairs R16mF2/R16mR1 followed by R16F2n/R16R2 as described by Gunder-sen and Lee (1). Undiluted total sample DNA was used for the first amplification; PCR products were diluted (1:30) in sterile water prior to final amplification. Alfalfa DNA and sterile water were used as negative controls; DNA from phytoplasma causing X-disease in peach (CX) served as a positive control. Fragments of 16S rDNA from putative phytoplasmas amplified by PCR with the primer pair R16F2n/R16R2 were characterized by restriction endonuclease digestion (3). The resulting restriction fragment length polymorphism (RFLP) patterns were compared with patterns for known phytoplasmas described by Lee et al. (3). Products of nested PCR were also purified and sequenced with primers R16F2n/R16R2 and an automated DNA sequencer (ABI 377XL; C. Nicolet, Biotechnology Center, University of Wisconsin-Madison). Of 51 samples of alfalfa assessed, one sample from Evansville, WI, yielded a nested PCR product of the appropriate size (1.2 kb), indicating the presence of phytoplasma. Digestion of this product with various restriction enzymes produced RFLP patterns that were identical to those for phytoplasmas in the aster yellows phytoplasma subgroup 16SrI-A (3). Alignment of the DNA sequence of the nested PCR product from the positive sample with sequences found in the GenBank sequence data base (National Center for Biotechnology Information, Bethesda, MD) with the BLAST sequence similarity function confirmed this result. Although other phytoplasma strains (particularly those causing witches'-broom) have been reported to infect alfalfa (2), this is the first report of the presence of the aster yellows phytoplasma in the alfalfa crop. Vectors involved in transmission and the potential agronomic impacts of aster yellows phytoplasma in alfalfa are topics of current investigation. References: (1) D. E. Gundersen and I.-M. Lee. Phytopathol. Mediterr. 35:144, 1996. (2) A.-H. Khadhair et al. Microbiol. Res. 152:269, 1997. (3) I.-M. Lee et al. Int. J. Syst. Bacteriol. 48:1153, 1998. (4) Y.-P. Zhang et al. J. Virol. Methods 71:45, 1998.

Physically abusive and nonabusive mothers' perceptions of parenting and child behavior.

Physically abusive and nonabusive mothers were studied for differences in perceptions of the parenting role and of child behavior problems. Findings suggested systematic differences in attributional style of the abusive mothers, supporting the hypothesis that such mothers are hyperreactive to their children's misbehavior. These mothers also tended to minimize both their own contribution to negative parent-child interactions and their children's role in positive ones.

Better Beginnings, Better Futures: a community-based approach to primary prevention.

Better Beginnings, Better Futures is a 25-year primary prevention policy research demonstration project. Its major purpose is to assess the extent to which community-based primary prevention programs can be effective in preventing emotional, behavioural, physical and cognitive problems in children from economically disadvantaged communities. The project grew out of a number of primary prevention initiatives introduced by the Ontario Ministry of Community and Social Services (MCSS) since the late 1970s. Eleven sites, four of them located on native reserves, received funding in January, 1991 to establish programs in their communities. From the beginning, a qualitative, naturalistic research approach has been utilized to document and understand the ways in which the programs have developed in the various Better Beginnings communities.

The role of head and neck squamous cell carcinoma cancer stem cells in tumorigenesis, metastasis, and treatment failure.

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide. Despite advances in diagnostic and therapeutic methods, survival of HNSCC remains unchanged over the last 30 years with treatment failure and metastases being the strongest indicators of poor outcome. Cancer stem cells (CSC) have been identified in multiple other solid tumors, including breast, prostate, and pancreatic carcinoma. Recently, a subpopulation of tumor cells has been identified in HNSCC based on the overexpression of the cellular marker CD44 and increased activity of aldehyde dehydrogenase. These cells have been designated CSC based on their stem cell-like properties: self-renewal, tumorigenesis, and the ability to recapitulate a heterogeneous tumor. Recent work looking at the role of HNSCC CSC in tumorigenesis has shown that CSC have a greater capacity for tumor growth, increased motility, and invasive characteristics; in vivo experiments confirm greater metastatic potential in CSC compared to non-CSC. Clinically, CSC enrichment has been shown to be enhanced in recurrent disease, treatment failure, and metastasis. CSC represent a novel target of study given their slow growth and innate mechanisms conferring treatment resistance. Further understanding of their unique phenotype may reveal potential molecular targets to improve therapeutic and survival outcomes in patients with HNSCC.