A nearby transiting rocky exoplanet that is suitable for atmospheric investigation.

Spectroscopy of transiting exoplanets can be used to investigate their atmospheric properties and habitability. Combining radial velocity (RV) and transit data provides additional information on exoplanet physical properties. We detect a transiting rocky planet with an orbital period of 1.467 days around the nearby red dwarf star Gliese 486. The planet Gliese 486 b is 2.81 Earth masses and 1.31 Earth radii, with uncertainties of 5%, as determined from RV data and photometric light curves. The host star is at a distance of ~8.1 parsecs, has a J-band magnitude of ~7.2, and is observable from both hemispheres of Earth. On the basis of these properties and the planet's short orbital period and high equilibrium temperature, we show that this terrestrial planet is suitable for emission and transit spectroscopy.

A multiplanet system of super-Earths orbiting the brightest red dwarf star GJ 887.

The closet exoplanets to the Sun provide opportunities for detailed characterization of planets outside the Solar System. We report the discovery, using radial velocity measurements, of a compact multiplanet system of super-Earth exoplanets orbiting the nearby red dwarf star GJ 887. The two planets have orbital periods of 9.3 and 21.8 days. Assuming an Earth-like albedo, the equilibrium temperature of the 21.8-day planet is ~350 kelvin. The planets are interior to, but close to the inner edge of, the liquid-water habitable zone. We also detect an unconfirmed signal with a period of ~50 days, which could correspond to a third super-Earth in a more temperate orbit. Our observations show that GJ 887 has photometric variability below 500 parts per million, which is unusually quiet for a red dwarf.

A giant exoplanet orbiting a very-low-mass star challenges planet formation models.

Surveys have shown that super-Earth and Neptune-mass exoplanets are more frequent than gas giants around low-mass stars, as predicted by the core accretion theory of planet formation. We report the discovery of a giant planet around the very-low-mass star GJ 3512, as determined by optical and near-infrared radial-velocity observations. The planet has a minimum mass of 0.46 Jupiter masses, very high for such a small host star, and an eccentric 204-day orbit. Dynamical models show that the high eccentricity is most likely due to planet-planet interactions. We use simulations to demonstrate that the GJ 3512 planetary system challenges generally accepted formation theories, and that it puts constraints on the planet accretion and migration rates. Disk instabilities may be more efficient in forming planets than previously thought.

A candidate super-Earth planet orbiting near the snow line of Barnard's star.

Barnard's star is a red dwarf, and has the largest proper motion (apparent motion across the sky) of all known stars. At a distance of 1.8 parsecs1, it is the closest single star to the Sun; only the three stars in the α Centauri system are closer. Barnard's star is also among the least magnetically active red dwarfs known2,3 and has an estimated age older than the Solar System. Its properties make it a prime target for planetary searches; various techniques with different sensitivity limits have been used previously, including radial-velocity imaging4-6, astrometry7,8 and direct imaging9, but all ultimately led to negative or null results. Here we combine numerous measurements from high-precision radial-velocity instruments, revealing the presence of a low-amplitude periodic signal with a period of 233 days. Independent photometric and spectroscopic monitoring, as well as an analysis of instrumental systematic effects, suggest that this signal is best explained as arising from a planetary companion. The candidate planet around Barnard's star is a cold super-Earth, with a minimum mass of 3.2 times that of Earth, orbiting near its snow line (the minimum distance from the star at which volatile compounds could condense). The combination of all radial-velocity datasets spanning 20 years of measurements additionally reveals a long-term modulation that could arise from a stellar magnetic-activity cycle or from a more distant planetary object. Because of its proximity to the Sun, the candidate planet has a maximum angular separation of 220 milliarcseconds from Barnard's star, making it an excellent target for direct imaging and astrometric observations in the future.

A glycerophospholipid-specific pocket in the RVFV class II fusion protein drives target membrane insertion.

The Rift Valley fever virus (RVFV) is transmitted by infected mosquitoes, causing severe disease in humans and livestock across Africa. We determined the x-ray structure of the RVFV class II fusion protein Gc in its postfusion form and in complex with a glycerophospholipid (GPL) bound in a conserved cavity next to the fusion loop. Site-directed mutagenesis and molecular dynamics simulations further revealed a built-in motif allowing en bloc insertion of the fusion loop into membranes, making few nonpolar side-chain interactions with the aliphatic moiety and multiple polar interactions with lipid head groups upon membrane restructuring. The GPL head-group recognition pocket is conserved in the fusion proteins of other arthropod-borne viruses, such as Zika and chikungunya viruses, which have recently caused major epidemics worldwide.

In Situ Production of Zoospores by Five Species of Phytophthora in Aqueous Environments for Use as Inocula.

The goal of this study was to develop a procedure that could be used to evaluate the potential susceptibility of aquatic plants used in constructed wetlands to species of Phytophthora commonly found in nurseries. V8 agar plugs from actively growing cultures of three or four isolates of Phytophthora cinnamomi, P. citrophthora, P. cryptogea, P. nicotianae, and P. palmivora were used to produce inocula. In a laboratory experiment, plugs were placed in plastic cups and covered with 1.5% nonsterile soil extract solution (SES) for 29 days, and zoospore presence and activity in the solution were monitored at 2- or 3-day intervals with a rhododendron leaf disk baiting bioassay. In a greenhouse experiment, plugs of each species of Phytophthora were placed in plastic pots and covered with either SES or Milli-Q water for 13 days during both summer and winter months, and zoospore presence in the solutions were monitored at 3-day intervals with the baiting bioassay and by filtration. Zoospores were present in solutions throughout the 29-day and 13-day experimental periods but consistency of zoospore release varied by species. In the laboratory experiment, colonization of leaf baits decreased over time for some species and often varied among isolates within a species. In the greenhouse experiment, bait colonization decreased over time in both summer and winter, varied among species of Phytophthora in the winter, and was better in Milli-Q water. Zoospore densities in solutions were greater in the summer than in the winter. Decreased zoospore activities for some species of Phytophthora were associated with prolonged temperatures below 13 or above 30°C in the greenhouse. Zoospores from plugs were released consistently in aqueous solutions for at least 13 days. This procedure can be used to provide in situ inocula for the five species of Phytophthora used in this study so that aquatic plant species can be evaluated for potential susceptibility.

Management of Daylily Rust with Different Fungicides and Application Methods.

The objectives of this study were to assess the efficacy of various fungicides applied as root dips, soil drenches, or foliar sprays to daylily plants grown in containers and planted in the field to manage rust caused by Puccinia hemerocallidis. Soil drenches and foliar sprays were evaluated in field experiments in Griffin, GA in 2010 and 2011. Dipping bare-root daylily plants for 5 min in azoxystrobin, tebuconazole, or thiophanate-methyl significantly reduced lesion development compared with nontreated control plants. Drenches with azoxystrobin, fluoxastrobin, or tebuconazole, each at three rates (0.06, 0.12, and 0.24 g of active ingredient [a.i.]/container), significantly reduced development of rust lesions on container-grown daylily plants for up to 9 weeks after treatment and 6 weeks after inoculation. One early-season drench of azoxystrobin at 0.12 g a.i‥/plant provided season-long reduction in disease incidence and disease progress that was comparable with foliar sprays with azoxystrobin or chlorothalonil applied at 14-day intervals. Dip or drench applications of fungicides would allow growers to diversify rust management options and could reduce the number of foliar fungicide applications.

Fungicides Used Alone, in Combinations, and in Rotations for Managing Gladiolus Rust in Mexico.

Gladiolus rust, caused by Uromyces transversalis, is a quarantine-significant pathogen in the United States. However, the fungus is endemic to commercial gladiolus-producing areas in Mexico and has been intercepted frequently on gladiolus plants entering the United States for the cut-flower market. The present study assessed 15 fungicide active ingredients (five quinone outside inhibitors: azoxystrobin, fluoxastrobin, kresoxim-methyl, pyraclostrobin, and trifloxystrobin; six triazoles: cyproconazole, difenoconazole, epoxiconazole, myclobutanil, propiconazole, and tebuconazole; three succinate dehydrogenase inhibitors: boscalid, flutolanil, and oxycarboxin; and one broad-spectrum protectant: chlorothalonil) and one plant activator, acibenzolar-S-methyl, applied alone, in combinations, and in various rotations for efficacy against U. transversalis on field-grown gladiolus plants in Mexico. Experiments were conducted in 2010, 2011, and 2012 in commercial fields in Atlixco and Santa Isabel Cholula in Puebla and Cuautla and Tlayacapan in Morelos. Fungicides were applied at 2-week intervals starting when plants had three full leaves. Disease severity was recorded each week for at least 7 weeks after the first application. Under high disease pressure in 2010, fungicides were less effective than in 2011 and 2012, when disease pressure was not as high. In all 3 years, most fungicide treatments significantly reduced disease severity. Triazoles were more effective than quinone outside inhibitors when applied as individual products in 2010, and combinations of two fungicides in different mode-of-action groups were more effective than fungicides applied individually in 2011. In 2012, rotations of fungicides, either with individual products or with combinations of two products, provided excellent rust management. Reducing disease development by U. transversalis on commercial gladiolus plants in Mexico will reduce the potential for introducing this pathogen on cut flowers into the United States.

Diversity and Mefenoxam Sensitivity of Phytophthora spp. Associated with the Ornamental Horticulture Industry in the Southeastern United States.

Phytophthora isolates associated with ornamental plants or recovered from irrigation water in six states in the southeastern United States (Georgia, North Carolina, South Carolina, Tennessee, Texas, and Virginia) were identified and screened for sensitivity to mefenoxam. Isolates from forest and suburban streams in Georgia and Virginia were included for comparison. A new in vitro assay, utilizing 48-well tissue culture plates, was used to screen for mefenoxam sensitivity; this assay allowed high throughput of isolates and used less material than the traditional petri plate assay. In total, 1,483 Phytophthora isolates were evaluated, and 27 species were identified with Phytophthora nicotianae, P. hydropathica, and P. gonapodyides, the most abundant species associated with plants, irrigation water, and streams, respectively. Only 6% of isolates associated with plants and 9% from irrigation water were insensitive to mefenoxam at 100 µg a.i./ml. Approximately 78% of insensitive isolates associated with plants were P. nicotianae, and most of these (67%) came from herbaceous annual plants. Most of the insensitive isolates recovered from irrigation water were P. gonapodyides, P. hydropathica, P. megasperma, and P. pini, and 83% of the insensitive isolates from streams were P. gonapodyides. Overall, this study suggests that mefenoxam should continue to be a valuable tool in the management of Phytophthora diseases affecting ornamental plants in the southeastern United States.

Effects of Fuel Reduction Treatments on Incidence of Phytophthora Species in Soil of a Southern Appalachian Mountain Forest.

The National Fire and Fire Surrogate Study was initiated to study the effects of fuel reduction treatments on forest ecosystems. Four fuel reduction treatments were applied to three sites in a southern Appalachian Mountain forest in western North Carolina: prescribed burning, mechanical fuel reduction, mechanical fuel reduction followed by prescribed burning, and a nontreated control. To determine the effects of fuel reduction treatments on Phytophthora spp. in soil, incidences were assessed once before and twice after fuel reduction treatments were applied. Also, the efficiency of the baiting bioassay used to detect species of Phytophthora was evaluated, and the potential virulence of isolates of Phytophthora spp. collected from forest soils was determined. Phytophthora cinnamomi and P. heveae were the only two species recovered from the study site. Incidences of these species were not significantly affected by fuel reduction treatments, but incidence of P. cinnamomi increased over time. In the baiting bioassay, camellia leaf disks were better than hemlock needles as baits. P. cinnamomi was detected best in fresh soil, whereas P. heveae was detected best when soil was air-dried and remoistened prior to baiting. Isolates of P. heveae were weakly virulent and, therefore, potentially pathogenic-causing lesions only on wounded mountain laurel and rhododendron leaves; however, isolates of P. cinnamomi were virulent and caused root rot and mortality on mountain laurel and white pine plants.

Baseline and Differential Sensitivity to Two QoI Fungicides Among Isolates of Phytophthora cactorum That Cause Leather Rot and Crown Rot on Strawberry.

Sensitivities of 89 isolates of Phytophthora cactorum, the causal agent of crown rot and leather rot on strawberry plants, from seven states (Florida, Maine, North Carolina, Ohio, Oregon, South Carolina, and New York) to the QoI fungicide azoxystrobin were determined based on mycelium growth and zoospore germination. Radial growth of mycelia on lima bean agar amended with azoxystrobin at 0.001, 0.01, 0.1, 1.0, 10, and 30 µg/ml and salicylhydroxamic acid (SHAM) at 100 µg/ml was measured after 6 days. Effect on zoospore germination was evaluated in aqueous solutions of azoxystrobin at 0.005, 0.01, 0.05, 0.1, 0.5, and 1.0 µg/ml in 96-well microtiter plates by counting germinated and nongerminated zoospores after 4 h at room temperature. SHAM was not used to evaluate zoospore sensitivity. The effective dose to reduce mycelium growth by 50% (ED50) ranged from 0.16 to 12.52 µg/ml for leather rot isolates and 0.10 to 15 µg/ml for crown rot isolates. The Kolmogorov-Smirnov test showed significant differences (P < 0.001) between the two distributions. Zoospores were much more sensitive to azoxystrobin than were mycelia. Differences between sensitivity distributions for zoospores from leather rot and crown rot isolates were significant at P = 0.05. Estimated ED50 values ranged from 0.01 to 0.24 µg/ml with a median of 0.04 µg/ml. Experiments with pyraclostrobin, another QoI fungicide, demonstrated that both mycelia and zoospores of P. cactorum were more sensitive to pyraclostrobin than to azoxystrobin. Sensitivities to azoxystrobin and pyraclostrobin were moderately but significantly correlated (r = 0.60, P = 0.0001).

Phytophthora tropicalis Isolated from Diseased Leaves of Pieris japonica and Rhododendron catawbiense and Found in Irrigation Water and Soil in Virginia.

An unidentified species of Phytophthora was isolated from irrigation water at a production nursery in Suffolk, VA in 2000 and 2001. Water samples were assayed using a filtration method (3). A similar species was recovered from soil samples collected in two mixed-hardwood forests in Fairfax County in 2002. Soil samples were air dried, remoistened, flooded, and then baited with rhododendron and camellia leaf pieces at room temperature (22 to 24°C) (2). A Phytophthora sp. was recovered from bait pieces cultured on PARPH-V8 selective medium (2). This same species also was isolated from symptomatic leaves of Pieris japonica cv. Temple Bells and Rhododendron catawbiense cv. Maximum Roseum at a garden center in Virginia Beach in 2004. On P. japonica, symptoms appeared as water-soaked, necrotic lesions and marginal necrosis on leaves and necrosis of shoot tips; on R. catawbiense, symptoms were wilting, dieback, and death of shoots. Representative isolates produced semipapillate to papillate sporangia with tapered bases that were caducous and had long pedicels (16 to 120 µm). Sporangia on four isolates were measured: mean lengths were 40.6 to 48.4 µm, mean widths were 26.9 to 31.4 µm, and length/width ratios consistently were 1.5. Sporangia occasionally were distorted and had dual apices, and they often contained a large globule after zoospore release. Chlamydospores ranged from 25 to 32 µm in diameter. All isolates were heterothallic; four isolates paired with known isolates of P. nicotianae were found to be mating type A1. Optimum temperature for mycelium growth on cornmeal agar was 25°C with slight growth at 35°C by some isolates and no growth at 4°C. These morphological characteristics were mostly consistent with those of P. tropicalis (1). P. tropicalis is reported to have sporangia that are papillate, have lengths of 40 to 55 µm, widths of 19 to 27 µm, and length/width ratios of 1.8 to 2.4 (1). The identity of these isolates as P. tropicalis was confirmed using single-strand conformational polymorphism analysis with comparison to a reference isolate (4). These isolates have been retained in permanent collections in the Hong and Jeffers labs. One isolate from each host plant and one isolate from irrigation water were tested for pathogenicity; agar blocks of mycelium (4 × 4 mm) were placed on wounded and nonwounded leaves of P. japonica cv. Mountain Fire and R. catawbiense cv. Olga plants and wrapped with Parafilm to prevent desiccation. Lesions formed on wounded and nonwounded leaves after 4 days at 20 to 30°C, and P. tropicalis was reisolated; no lesions formed on noninoculated control leaves. To our knowledge, this is the first report of P. tropicalis in the continental United States, in irrigation water systems, and as a cause of Phytophthora foliage blight on P. japonica and R. catawbiense (1). This study suggests that the host range of this pathogen is not limited to tropical plants. Although this pathogen did not cause significant economic loss in the garden center surveyed, it was isolated in irrigation water at the production nursery from late spring through fall. An investigation of its impact on nursery crops is warranted. References: (1) M. Aragaki and J. Y. Uchida. Mycologia 93:137, 2001. (2) A. J. Ferguson and S. N. Jeffers. Plant Dis. 83:1129, 1999. (3) C. X. Hong et al. Phytopathology 92:610, 2002. (4) P. Kong et al. Fungal Genet. Biol. 39:238, 2003.

Toxicity of Fungicides to Urediniospores of Six Rust Fungi That Occur on Ornamental Crops.

The recent introduction and rapid spread of rust on daylilies, caused by Puccinia hemerocallidis, suggested a need for fungicide treatments that reduce urediniospore viability on plant surfaces. Twelve fungicides in seven chemical classes were evaluated in vitro for toxicity to urediniospores of rust fungi that occur on daylily (P. hemerocallidis), geranium P. pelargonii-zonalis), iris (P. iridis), oxalis (P. oxalis), mint (P. menthae), and Florida azalea (Pucciniastrum vaccinii). Germination of urediniospores of all six rust fungi on potato dextrose agar in the absence of fungicides ranged from 54 to 88%. Germination of urediniospores of all rust species during and after exposure to azoxystrobin, chlorothalonil, copper sulfate pentahydrate, mancozeb, and trifloxystrobin was less than or near 1%. Germination during exposure to fenhexamid, iprodione, myclobutanil, propiconazole, thiophanate-methyl, triadimefon, and triflumizole ranged from 0 to 60% and usually was greater (0 to 75%) after fungicide residues had been removed. Germination of urediniospores of P. pelargonii-zonalis decreased when exposed to azoxystrobin, copper sulfate pentahydrate, and mancozeb for 1 min and was nearly eliminated after a 30-min exposure, while exposure to trifloxystrobin and chlorothalonil eliminated germination after 4 and 8 h, respectively. Urediniospores that had been allowed to imbibe water for 4 h had no further germination or germ tube growth after a 24-h exposure to azoxystrobin, chlorothalonil, copper sulfate pentahydrate, mancozeb, and trifloxystrobin. Less than one lesion per plant developed on seedlings inoculated with urediniospores of P. pelargonii-zonalis that had been sprayed with azoxystrobin, chlorothalonil, copper sulfate pentahydrate, and mancozeb, whereas seedlings inoculated with spores not exposed to fungicides developed 148 lesions per plant. The strobilurin (azoxystrobin and trifloxystrobin), broad-spectrum protectant (chlorothalonil and mancozeb), and inorganic copper (copper sulfate pentahydrate) fungicides were fungicidal to urediniospores of the six rust fungi. However, the benzimidazole (thiophanate-methyl), dicarboximide (iprodione), hydroxyanilide (fenhexamid), and demethylation-inhibiting (myclobutanil, propiconazole, triadimefon, and triflumizole) fungicides were only fungistatic to rust urediniospores.

Effect of Pathogen Aggressiveness and Vinclozolin on Efficacy of Rhodotorula glutinis PM4 Against Botrytis cinerea on Geranium Leaf Disks and Seedlings.

Efficacy of the yeast Rhodotorula glutinis isolate PM4 as a biological control agent against 29 isolates of Botrytis cinerea obtained from greenhouse-grown ornamentals was assessed in vitro on geranium leaf disks. Isolates of B. cinerea varied in aggressiveness in the absence of either biological or chemical controls; diameters of lesions produced on leaf disks ranged from 0.8 to 12.3 mm. Efficacy of R. glutinis PM4 against the different isolates of B. cinerea varied greatly; lesion diameters ranged from 0.2 to 10.3 mm when the yeast was present. The yeast significantly reduced lesion development by 16 B. cinerea isolates in each of two replicate trials and by 9 isolates in one of the trials; however, 3 isolates were not inhibited by the yeast on geranium leaf disks. The yeast significantly reduced lesion development by B. cinerea isolate 01, used as a standard for comparison, in four of six trials. Fourteen of the B. cinerea isolates were inoculated onto geranium seedlings and produced a range of lesion sizes (2.9 to 16.4 mm), similar to that produced on leaf disks. Efficacy of the yeast in combination with a reduced rate (0.1×) of the fungicide vinclozolin (50 µg of active ingredient ml-1) was evaluated on geranium seedlings against 10 isolates of B. cinerea that were resistant to vinclozolin. Addition of vinclozolin to the yeast significantly reduced lesion diameter by five of the isolates compared with diameters of lesions produced in the presence of the yeast alone. Lesions produced by nine of the resistant isolates were 2.6 mm or smaller in both trials on plants treated with the mixture of yeast and vinclozolin. The effect of vinclozolin concentration (0 to 500 µg a.i. ml-1) on biocontrol efficacy of R. glutinis PM4 was evaluated using three resistant isolates of B. cinerea and geranium seedlings. Disease control was significantly better at higher concentrations of fungicide for two of the isolates. Linear regression of lesion diameter against vinclozolin concentration showed a significant effect on yeast biocontrol efficacy with B. cinerea isolate FL-2-b (y = 6.20 - 0.63x; r2= 0.74) and isolate BR-1 (y = 4.10 - 0.32x; r2 =0.28) but there was no significant effect with isolate GG-2-b. Overall, PM4 exhibited biocontrol activity on both geranium leaf disks and seedlings against a number of isolates of B. cinerea that varied in aggressiveness. Variability in biocontrol efficacy against isolates resistant to vinclozolin usually was reduced by the addition of vinclozolin.

AFLP Analysis of Phytophthora cactorum Isolates from Strawberry and Other Hosts: Implications for Identifying the Primary Source of Inoculum.

Forty-seven isolates of Phytophthora cactorum from North America and Germany were subjected to amplified fragment length polymorphism (AFLP) analysis to investigate genetic diversity among isolates and geographical populations; 42 isolates were recovered from cultivated strawberry plants (Fragaria × ananassa), and five isolates had been recovered from plants in four other genera (Syringa, Abies, Malus, and Panax). From all isolates evaluated, 226 out of 264 markers (85.6%) were polymorphic and provided 42 unique AFLP profiles. The genetic diversity among isolates of P. cactorum from strawberry was greater than that among isolates from the other hosts. Isolates collected during recent crown rot epidemics in strawberry fields in South Carolina were genetically diverse and scattered among isolates from other geographical areas in an unweighted pair-group mean analysis (UPGMA) dendrogram. Isolates collected during recent crown rot epidemics in North Carolina also were genetically diverse, but most isolates clustered with isolates collected in 1997 from Florida strawberry fields. These data suggest that recent outbreaks of Phytophthora crown rot in the southeastern United States resulted from use of transplants already infected or infested with P. cactorum rather than from endemic populations of this pathogen, which would affect recommendations for disease management.

Effect of Timing of Fungicide Applications on Development of Rusts on Daylily, Geranium, and Sunflower.

Integrated disease management should provide the most effective means of controlling rusts on ornamental crops over time, and fungicides are an important component of an integrated rust management program. Proper timing of fungicide applications is critical for effective disease management; however, information about application timing is lacking for rusts on ornamental crops. The objective of this study was to determine how fungicides affected rust development on daylily, geranium, and sunflower plants when applied several days before or after inoculation. Five fungicides registered for use against rusts on ornamental crops were evaluated: the strobilurin azoxystrobin; three sterol biosynthesis inhibiting fungicides-myclobutanil, propiconazole, and triadimefon; and the broad spectrum protectant chlorothalonil. All five fungicides significantly reduced lesion development by rust pathogens on daylily, geranium, and sunflower plants when these compounds were applied preventatively up to 15 days before inoculation and infection with a few exceptions (e.g., propiconazole on geranium and triadimefon on sunflower). Curative activity, which resulted from fungicide application after inoculation, was observed for the three rusts with some products (azoxystrobin on all three plants and myclobutanil, propiconazole, and triadimefon on geranium) when applied up to 7 days postinoculation. In general, fungicide efficacy with several of the products decreased as the time from application to inoculation (preventative activity) or inoculation to application (curative activity) increased.

First Report of Resistance to Mefenoxam in Phytophthora cactorum in the United States and Elsewhere.

Phytophthora cactorum causes crown rot of strawberry (Fragaria × ananassa) (2), a disease that has been particularly severe during the last 5 years in the southeastern United States. In the fall of 2001, strawberry plants (cv. Camarosa) in a field in Lexington County, South Carolina exhibited typical crown rot symptoms (2) 1 to 2 weeks after transplanting, even though plants had been drenched with mefenoxam (Ridomil Gold; Syngenta Crop Protection, Greensboro, NC) immediately after transplanting. Initially, we observed leaves that had marginal necrosis, were smaller than normal, and were discolored. Soon after, diseased plants appeared stunted and unthrifty compared with other plants in the field, and some of these plants eventually wilted and died. Severely affected plants had necrotic roots and decayed crowns. Ten symptomatic plants were collected for isolation. In the laboratory, root and crown tissues were rinsed in running tap water and blotted dry, small pieces of necrotic tissue were placed aseptically on PAR-V8 selective medium (1), and isolation plates were placed at 20°C in the dark for up to 7 days. P. cactorum was recovered from six plants. Isolates produced characteristic asexual and sexual structures directly on the isolation plates (i.e., papillate sporangia on sympodial sporangiophores and oospores with paragynous antheridia) (2). A single hypha of an isolate from each plant was transferred to fresh PAR-V8, and pure cultures were stored on cornmeal agar in glass vials at 15°C in the dark. All six isolates from the Lexington County field and nine other isolates of P. cactorum from strawberry (three from South Carolina, three from North Carolina, and three from Florida) were tested for sensitivity to mefenoxam on fungicide-amended medium. Mefenoxam was added to 10% clarified V8 juice agar (cV8A) after autoclaving so the concentration in the medium was 100 ppm. Agar plugs from active colonies were transferred to mefenoxam-amended and nonamended cV8A (three replicates per treatment), plates were placed at 25°C in the dark for 3 days, and linear mycelium growth was measured. All six isolates from Lexington County were highly resistant to mefenoxam with mycelium growth relatively unrestricted on mefenoxam-amended medium (73 to 89% of that on nonamended medium). In comparison, the other nine isolates were sensitive to mefenoxam with mycelium growth severely restricted by 100 ppm of mefenoxam (0 to 7% of that on nonamended medium). To our knowledge, this is the first report of mefenoxam resistance in P. cactorum on strawberry or any other crop in the United States and elsewhere. Because mefenoxam is the primary fungicide used to manage Phytophthora crown rot in the southeastern United States, resistance may limit use of this fungicide in strawberry production. References: (1) A. J. Ferguson and S. N. Jeffers. Plant Dis. 83:1129, 1999. (2) E. Seemüller. Crown rot. Pages 50-51 in: Compendium of Strawberry Diseases, 2nd ed. J. L. Maas, ed. The American Phytopathological Society, St. Paul, MN, 1998.

A single p450 allele associated with insecticide resistance in Drosophila.

Insecticide resistance is one of the most widespread genetic changes caused by human activity, but we still understand little about the origins and spread of resistant alleles in global populations of insects. Here, via microarray analysis of all P450s in Drosophila melanogaster, we show that DDT-R, a gene conferring resistance to DDT, is associated with overtranscription of a single cytochrome P450 gene, Cyp6g1. Transgenic analysis of Cyp6g1 shows that overtranscription of this gene alone is both necessary and sufficient for resistance. Resistance and up-regulation in Drosophila populations are associated with a single Cyp6g1 allele that has spread globally. This allele is characterized by the insertion of an Accord transposable element into the 5' end of the Cyp6g1 gene.

Effects of Cultural Practices and Temperature on Fusarium Root and Crown Rot of Container-Grown Hostas.

Fusarium root and crown rot of hosta plants grown in containers is caused primarily by Fusarium hostae. In an effort to develop an integrated strategy for managing this disease at nurseries, the effects of wounding, container mix content, watering schedule, and temperature on disease development were investigated. Plants were not wounded or were wounded by severing the roots, severing the roots and making incisions in the crown, or severing the roots and removing a small piece of the crown. Plants were inoculated by dipping roots and crowns into a suspension of conidia from one of two isolates of F. hostae. In addition, some plants were inoculated by wounding crowns with a scalpel dipped in a conidium suspension. Disease development was examined on plants grown at different temperatures (18, 25, or 32°C), grown in different container mixes (100% Canadian sphagnum peat, 100% aged and processed pine bark, or a mixture of 50% peat and 50% bark), and watered on different schedules (which kept the container mix wet, moist, or dry). Significant levels of disease occurred only on plants that were wounded when inoculated. Fusarium root and crown rot was more severe when both the roots and crowns were wounded than when only the roots were wounded. Disease symptoms developed when crowns of plants were wounded with a scalpel infested with conidia, suggesting that contaminated tools used for vegetative propagation may transfer F. hostae. Disease development also was affected significantly by container mix content, watering schedule, and temperature. In separate experiments, disease was most severe on plants grown in 100% aged pine bark, in dry container mix, or at 18 to 25°C. Disease development was significantly less when plants were grown in 100% peat, in wet container mix, or at 32°C. These results suggest that altering or manipulating cultural practices used to produce hostas in containers at nurseries can reduce the impact from Fusarium root and crown rot.