bluuebunny/crossref_metadata_2025 huggingface dataset:
Response of Commercially Developed Soybean Cultivars and the Ancestral Soybean Lines to Fusarium solani f. sp. glycines
Authors: Mueller D. S. , Nelson R. L. , Hartman G. L. , Pedersen W. L.
Published: May 2007

Sudden death syndrome, caused by Fusarium solani f. sp. glycines, has caused severe damage to soybean production in recent years. One way to control sudden death syndrome is with resistant cultivars. Over a 3-year period, 2,335 publicly and privately developed soybean entries were inoculated and evaluated for their response to F. solani f. sp. glycines under greenhouse conditions. The entries were compared with the susceptible check, Great Lakes 3302 (GL3302), and the moderately resistant checks, plant introductions (PIs) 520733 and 567374. Thirty-eight entries were identified with moderate levels of resistance. Based on foliar ratings, there were no differences (P < 0.05) between the Roundup Ready and conventional cultivars. In all, 90 ancestral lines that represent 99% of the genes in modern U.S. cultivars and 55 lines found in the pedigrees of public cultivars reported to have some resistance were evaluated for their response to F. solani f. sp. glycines. Nine ancestral lines (Aoda, Kim, Jackson, Sioux, Mammoth Yellow, T117, PI 171450, PI 54615-1, and PI 71506) and 12 cultivars or experimental lines (Ina, D83-3349, LN98-4340, LN83-2356, Hartwig, Harosoy, Bedford, Merit, Cutler, Calland, Hill, and Evans) had disease ratings not significantly different (P < 0.05) from PI 520733 or PI 567374. PI 54610, a putative ancestral line, also was found to be moderately resistant.
Relationships Among Propagule Numbers of Botryosphaeria dothidea, Latent Infections, and Severity of Panicle and Shoot Blight in Pistachio Orchards
Authors: Ahimera N. , Driever G. F. , Michailides T. J.
Published: May 2007

Experiments were conducted between 1999 and 2001 to monitor the presence of propagules of Botryosphaeria dothidea and frequencies of latent infections on pistachio leaves and fruit clusters and to determine their relationships to panicle and shoot blight severity in commercial orchards. Numbers of B. dothidea propagules recovered from washing leaves and fruit clusters varied among the growing seasons and sampling dates. Lower numbers of B. dothidea propagules were obtained in 1999 and 2001 than in 2000. For the orchard in Glenn County, up to 75 propagules per leaf and 21 propagules per fruit cluster were recorded in 1999, compared with 365 and 248 propagules per leaf and fruit cluster, respectively, in 2000. Although more propagules were detected per leaf, the infection levels were higher on fruit clusters, suggesting that pistachio fruit is more susceptible to B. dothidea infection than leaves. Latent infections were detected as soon as leaves or fruit clusters started to expand and more infections were obtained in 2000 than 1999 or 2001. Significant (P < 0.05) relationships between propagules on leaves or frequency of infections on leaves (independent variables) and propagules on fruit clusters or frequency of infected fruit clusters (dependent variables) with r values ≥ 0.50 provide support for the role of latent infection in panicle and shoot blight later in the season. Propagules on leaves and fruit clusters were not significantly correlated to disease severity, but frequencies of latent infection on leaves and fruit clusters were positively correlated (P ≥ 0.05) with leaf and fruit disease severity under field conditions with r2 ranging between 0.25 and 0.42. Quantitative relationships between latent infections and disease severity may be incorporated in a prediction model for disease development or be used to develop a risk assessment method to guide growers in their effort to control panicle and shoot blight of pistachio.
Buckeye Rot of Tomato Caused by Phytophthora capsici in Michoacan, Mexico
Authors: Fernández-Pavía S. P. , Rodríguez-Alvarado G. , Sánchez-Yañez J. M.
Published: May 2007

The state of Michoacan is one of the main fresh pepper (Capsicum annuum L.) and tomato (Lycopersicon esculentum Mill.) producers in Mexico. During the last 5 years, pepper-producing areas in the state have become unproductive due to root-rotting pathogens, mainly Phytophthora capsici Leonian. Growers trying to overcome losses have increased tomato production in areas previously used for pepper production. Field-grown tomato plants with diseased green tomato fruits were observed in Tacambaro, Michoacan, during August 2002. Initially, brown-to-black lesions developed on fruits in contact with soil, followed by infection of the upper fruits in the raceme. Lesions enlarged and dark zonate “buckeye” bands were formed in the affected area. Diseased fruit turned mushy. Symptoms observed were similar to those described for buckeye rot of tomato (1). Diseased fruit were surface disinfested with 70% ethanol, cut into 0.5-cm slices, and incubated in a moist chamber to induce mycelial colonization. Isolation from mycelial tufts growing through the tomato slice was performed 3 days later, and mycelia was transferred to PARP selective medium (corn meal agar (CMA) plus ampicillin, pimaricin, rifampicin, and pentachloronitrobenzene). P. capsici was consistently isolated from diseased tomato fruits. Oomycete identification was based on sporangial and gametangial characteristics of cultures grown on CMA (1). Sporangia microscopically observed were spherical, broadly ellipsoid or obovoid with one papilla (occasionally two papillae), and deciduous with a long pedicel. Chlamydospores were not present (2). The isolates were heterothallic, and oogonia with amphigynous antheridia were observed in pairings with A1 and A2 isolates of P. capsici. Three isolates were A1 and two isolates were A2. To confirm pathogenicity, two experiments were performed using 20 healthy unwounded green tomatoes. One isolate of each mating type was tested. Isolates were grown for 5 days on CMA, and fruits were inoculated by placing P. capsici in contact with the fruit. Inoculated fruits were kept in a moist chamber at room temperature (17 to 20°C). Initial symptoms in the form of brown-to-black lesions appeared 24 h after inoculation. One week after inoculation, symptoms were similar to those observed in field-grown plants, and P. capsici was recovered from the margins of the diseased tissue. All inoculated fruits rotted. To our knowledge, this is the first report of P. capsici causing buckeye rot on tomato in Michoacan and of the presence of both mating types in the area.

Reference: (1) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society. St. Paul MN, 1996. (2) M. Aragaki and J. Y. Uchida. Mycologia 93:137, 2001.
First Report of Typhula Blight on Agrostis stolonifera and Poa annua in Italy
Authors: Titone P. , Mocioni M. , Garibaldi A. , Gullino M. L.
Published: May 2007

During January 2002, Agrostis stolonifera and Poa annua turfgrasses on a golf course in Avigliana (northern Italy) exhibited 10- to 45-cm-diameter circular patches when the snow melted from the greens, tees, and fairways. Many patches coalesced to form large areas of strawcolored blighted turfgrass. At the patch margin, infected plants were covered with white-to-gray mycelium. Plants within patches were matted and appeared slimy with mycelium and sclerotia that were light pink, irregularly shaped, and less than 5 mm in diameter. Isolation from infected leaves on potato dextrose agar, supplemented with 100 mg/l of streptomycin sulfate, consistently yielded a fungus with mycelial, sclerotia, and cultural characteristics of Typhula incarnata (1). Pathogenicity tests were performed by spraying a suspension of mycelium and sclerotia, prepared by chopping mycelium and sclerotia produced in potato dextrose broth, onto 8-week-old A. stolonifera plants grown in plastic trays (45 × 30 cm). Trays were maintained at 0°C for 8 weeks in the dark. Blight symptoms developed on inoculated plants after 6 weeks. Non-inoculated plants remained healthy. The pathogen was reisolated from inoculated plants, and the pathogenicity test was repeated once. Typhula blight incited by T. incarnata was reported in Scandinavian countries and in several European countries including Holland, Germany, Austria, and Switzerland (1). To our knowledge, this is the first report of Typhula blight on turfgrass in Italy.

Reference: (1) J. D. Smith et al. 1989. Fungal Diseases of Amenity Turf Grasses. E & FN Spong Ltd, London.
Root Rot and Stunting of Hydroponically Grown Endive, Fennel, and Sorrel Caused by Pythium F-group in South Africa
Authors: Labuschagne N. , Gull C. , Wehner F. C. , Botha W. J.
Published: May 2007

Specialized vegetable crops such as endive (Cichorium endiva), fennel (Foeniculum vulgare), and sorrel (Rumex spp.) are being cultivated hydroponically in South Africa to be marketed as admixtures in salads. Stunted growth accompanied by browning and rotting of the root tips has been observed at a commercial recirculating gravel bed hydroponic system near Pretoria during the warm summer months. Root segments excised from symptomatic plants were rinsed in sterile water and plated on Pythium selective medium (1). Pythium F-group, characterized by the production of noninflated filamentous sporangia and no oospores (2), was isolated from 40% of endive, 60% of fennel, and 7% of sorrel root segments. Koch's postulates were confirmed by inoculating 4-week-old seedlings of each crop in the greenhouse with a Pythium F-group isolate from the particular crop. Inoculations were performed by adding 3 ml of suspension (105 zoospores per ml) to each liter of aerated nutrient solution. Control plants received no inoculum, and the experiment was repeated once. After 4 weeks, inoculated plants showed stunting of the foliage and slight to moderate root rot. Pythium F-group could readily be reisolated from roots of inoculated plants. To our knowledge, this is the first report of Pythium F-group on these crops in South Africa.

References: (1) W. J. Botha and R. L. J. Coetzer. S. Afr. J. Bot. 62:196, 1996. (2) M. W. Dick. Keys to Pythium. University of Reading Press, Reading, UK, 1990.
Occurrence of Barley mild mosaic virus on Barley in Spain
Authors: Achon M. A. , Ratti C. , Rubies-Autonell C.
Published: May 2007

Mosaic and yellowing symptoms were observed on winter barley during March of 2002 in northeastern Spain. Symptoms were similar to those caused by Barley yellow mosaic virus (BaYMV) and Barley mild mosaic virus (BaMMV), members of the genus Bymovirus (family Potyviridae). Leaves from 17 samples of barley were analyzed by enzyme-linked immunosorbent assay (ELISA) using antisera specific for BaYMV (Bio-Rad Laboratories, Hercules, CA) and BaMMV (Loewe Biochemica, Munich). Five samples tested positive with the BaYMV antiserum, and two samples were positive with the BaYMV and BaMMV antisera. Ranges of ELISA values were from 3.8 to 13 times higher than the negative controls with the BaYMV antiserum and from 18 to 21 times higher with the BaMMV antiserum. Mixed infections were further analyzed by reverse transcription-polymerase chain reaction (RT-PCR) using specific primers that amplify 433 bp of BaYMV (1) and 445 bp of BaMMV coat protein gene (primer 1: 5′GCG TCC GTT GCA ACT GA 3′ and primer 2: 5′GAA TTG CTT GTG CCA ACA 3′. A PCR product of the expected size was observed with BaMMV primers but not with BaYMV primers. The sequence of BaMMV PCR product was determined and compared with that of the equivalent regions of other BaMMV isolates (Genbank Accession Nos. AJ242725, AJ224872, D83410, D83408, L49381, Y10973, and Y10974). The greatest nucleotide identity (96 to 98%) was found with isolates from Germany and Italy, followed by those from France and the United Kingdom (89%), and the lowest identity being with isolates from Asia (85 to 88%). The BaYMV presence needs to be confirmed. To our knowledge, this is the first report of a bymovirus infecting barley in Spain, and illustrates the continuing spread within Europe of viruses vectored by Polymyxa graminis Led.

Reference: (1) D. Hariri et al. Eur. J. Plant Pathol. 106:365, 2000.
Susceptibility of Mefenoxam-Treated Cucurbits to Isolates of Phytophthora capsici Sensitive and Insensitive to Mefenoxam
Authors: Lamour K. H. , Hausbeck M. K.
Published: May 2007

The susceptibility of mefenoxam-treated cucurbit plants to infection by isolates of Phytophthora capsici that were sensitive (S), intermediately sensitive (IS), and fully insensitive (I) to mefenoxam in vitro was investigated to determine if in vitro screening will accurately predict the response of mefenoxam-treated cucurbit plants to infection by P. capsici. Isolates were recovered from a cross between IS parents or from naturally infected cucumbers, squash, pumpkins, and peppers in Michigan, New York, and North Carolina. Pumpkin or yellow squash seedlings were treated with water or mefenoxam at either 19.17 μg/ml or 57.51 μg/ml 24 h prior to inoculation. Four days after inoculation, all of the isolates of P. capsici exhibited similarly high virulence on the water-treated seedlings. The diameter of the lesions produced by S, IS, and I isolates on mefenoxam-treated seedlings ranged from no visible lesions for S isolates to lesions indistinguishable from those produced on water-treated plants for I isolates. These findings are consistent with the expectations based on in vitro screening and suggest that in vitro screening of mefenoxam sensitivity using a single high rate of mefenoxam (100 ppm) provides useful information for predicting the response of natural populations of P. capsici to mefenoxam.
Distribution and Virulence Phenotypes of Heterodera glycines in Missouri
Authors: Niblack T. L. , Wrather J. A. , Heinz R. D. , Donald P. A.
Published: May 2007

The soybean cyst nematode, Heterodera glycines, is the most economically important pathogen of soybean in Missouri. Knowledge of the nematode's distribution and ability to adapt to resistant varieties is important for determining crop losses and establishing research priorities. No previous surveys of Missouri have provided reliable population density and phenotypic diversity data; therefore, we conducted a random survey to obtain both. Two samples from each of 200 fields were collected; 392 samples were processed for extractions of cysts and eggs. Two hundred and forty seven (63%) of the samples had detectable cyst nematode populations, which ranged from 15 to 149,700 eggs per 250 cm3 of soil. The lowest average population densities were observed in the east-central region of Missouri (2,260 eggs per 250 cm3 of soil), and the highest were observed in the northeast (9,238 eggs per 250 cm3 of soil), but among the eight regions sampled, mean population densities did not differ significantly. These population densities were potentially responsible for losses worth over $58 million in 1999 in Missouri. Race tests were conducted on populations from 183 samples. In order of frequency, races 3, 1, and 2 accounted for 86% of H. glycines populations. Nearly 60% of the populations were virulent (able to produce females) on plant introduction (PI) 88788, which is the source of resistance for most H. glycines-resistant cultivars. More than a third of the populations were virulent on cv. Peking, another common resistance source. Very few populations were virulent on PI 90763 or PI 437654, suggesting that these sources of resistance should be exploited more frequently.
Serratia marcescens, a Phloem-Colonizing, Squash Bug -Transmitted Bacterium: Causal Agent of Cucurbit Yellow Vine Disease
Authors: Bruton B. D. , Mitchell F. , Fletcher J. , Pair S. D. , Wayadande A. , Melcher U. , Brady J. , Bextine B. , Popham T. W.
Published: May 2007

Cucurbit yellow vine disease (CYVD), which can inflict heavy losses to watermelon, pumpkin, cantaloupe, and squash in U.S. production areas from the midwest to northeastern states, causes phloem discoloration, foliar yellowing, wilting, and plant decline. Bacteria were cultured from the phloem of crown sections of symptomatic plants of Citrullus lanatas and Cucurbita pepo. Those bacteria testing positive in CYVD-specific polymerase chain reaction (PCR) were all gram negative and appeared morphologically identical, producing creamy white, smooth, entire, convex colonies on Luria-Bertani or nutrient agar. Characterized cucurbit-derived strains of Serratia marcescens were introduced into greenhouse-grown squash plants by puncture inoculation and into field-grown squash plants by enclosure with S. marcescens-fed squash bugs, Anasa tristis. Up to 60% of the bacteria-inoculated plants in the greenhouse and up to 17% of field plants caged with inoculative squash bugs developed phloem discoloration and tested positive for S. marcescens by CYVD-specific PCR. None of the controls developed phloem discoloration or tested positive by PCR. Of the diseased field plants, 12% (2 of 35) also yellowed, wilted, and collapsed, exhibiting full symptom development of CYVD. However, neither plant collapse nor decline was observed in the greenhouse-grown, puncture-inoculated plants. The morphology, growth habit, and PCR reaction of bacteria cultured from crown tissue of a subset of plants in each experimental group were indistinguishable from those of the inoculum bacteria. Evidence presented from our studies confirms that the squash bug can transmit S. marcescens, the CYVD causal bacterium. The S. marcescens-A. tristis relationship described here is the first instance in which the squash bug has been identified as a vector of a plant pathogen. Our experiments represent a completion of the steps of Koch's postulates, demonstrating that S. marcescens is the causal agent of CYVD and that the squash bug, A. tristis, is a vector of the pathogen.
Evaluation of Electrolyzed Oxidizing Water for Management of Powdery Mildew on Gerbera Daisy
Authors: Mueller D. S. , Hung Y.-C. , Oetting R. D. , van Iersel M. W. , Buck J. W.
Published: May 2007

Powdery mildew has been a major concern for greenhouse growers. Acidic electrolyzed oxidizing (EO) water was evaluated for the management of powdery mildew on gerbera daisy. EO water significantly reduced percent powdery mildew when sprayed twice a week and when sprayed every other week, alternating with fungicides. Studies were completed to determine if EO water could be used in an integrated management system. EO water was compatible with several fungicides and insecticides in an in vitro assay. However, EO water was not compatible with thiophanate methyl at the full rate and acephate at both the half and full rates. EO water is a viable option for controlling powdery mildew on gerbera daisies and provides growers an additional tool to reduce the use of traditional fungicides in greenhouses.
Classifying the Relative Host Reaction in Potato Cultivars and Breeding Lines to the US-8 Strain of Phytophthora infestans in Minnesota
Authors: Jenkins J. C. , Jones R. K.
Published: May 2007

A total of 32 commercial cultivars grown in the United States and 15 potato breeding lines and non-U.S. cultivars were evaluated at Rosemount, MN for their reaction to the US-8 strain of Phytophthora infestans. Commercial red-, russet-, and white-skinned cultivars tested in the commercial cultivar trial (COMC) in 1996 and 1997 were susceptible (S) to moderately susceptible (MS) to this organism, except for Elba, which ranked as moderately resistant (MR). Yellow-fleshed cvs. Hertha, Santé, and Agria were screened in the late blight nursery (LB1) in 1997 and 1998 and classified as S to MS while Island Sunshine, Brador, and Aziza were classified as MR. The Scottish breeding line G6582-3 and U.S. breeding lines A90586-11, AWN86514-2, AWN85624-5, B0692-4, B0718-3, and B0767-2 were classified as resistant (R). Comparison among entries was based on the area under the disease progress curve (AUDPC). Spearman rank correlation for AUDPC in the 1996 and 1997 COMC trials at 14 to 18 days after inoculation (r = 0.65, P < 0.01) was greater than any other interval tested. The Spearman rank correlation for AUDPC in the 1997 and 1998 LB1 trials at 14 to 18 days after inoculation was r = 0.87, P < 0.01 and increased only slightly in successive assessment dates, suggesting that, in Minnesota, effective evaluation of the foliar infection of late blight can occur at 18 days after inoculation or later. The average tuber blight incidence for the COMC trials at harvest was 10.0% in 1996 and 9.7% in 1997. The average tuber blight incidence for the LB1 trials at harvest was 4.3% in 1997 and 14.6% in 1998. Pearson correlations between tuber blight incidence and foliar disease for the COMC trials was very low; however, for the LBl trials, it was significant in both 1997 (r = 0.53, P < 0.01) and 1998 (r = 0.53, P < 0.01). Asymptomatic tubers harvested from the COMC trials developed additional tuber blight when stored 28 days at ambient temperatures and still more when stored for another 5 months at 5°C. Surviving tubers of nine entries were planted in field trials during 1997 and 1998 to determine if plants that develop from tubers exposed to P. infestans could manifest late blight in the subsequent season. Late blight failed to develop throughout the trials in either year.
Effect of Organic Amendments on Soilborne and Foliar Diseases in Field-Grown Snap Bean and Cucumber
Authors: Stone A. G. , Vallad G. E. , Cooperband L. R. , Rotenberg D. , Darby H. M. , James R. V. , Stevenson W. R. , Goodman R. M.
Published: May 2007

Several paper mills in Wisconsin have programs for spreading paper mill residuals (PMR) on land. A growing number of vegetable farmers recognize the agronomic benefits of PMR applications, but there have been no investigations on the use of PMR for control of vegetable crop diseases. Our objective was to determine the effect of PMR amendments on soilborne and foliar diseases of cucumber and snap bean grown on a sandy soil. Raw PMR, PMR composted without bulking agent (PMRC), or PMR composted with bark (PMRBC) were applied annually in a 3-year rotation of potato, snap bean, and pickling cucumber. Several naturally occurring diseases were evaluated in the field, along with in situ field bioassays. All amendments suppressed cucumber damping-off and Pythium blight and foliar brown spot of snap bean. Both composts reduced the incidence of angular leaf spot in cucumber. In a separate field experiment planted with snap bean for two consecutive years, all amendments reduced common root rot severity in the second year. In a greenhouse experiment, the high rate of PMRBC suppressed anthracnose of snap bean. These results suggest that the application of raw and composted PMR to sandy soils has the potential to control several soilborne and foliar diseases.
Evaluation of Resistance to Ergot, Caused by Claviceps purpurea, in Kentucky Bluegrass, Based on Incidence and Severity Estimates
Authors: Alderman Steve C. , Barker Reed E.
Published: May 2007

Ergot, caused by Claviceps purpurea, is an important disease of Kentucky bluegrass grown for seed. Resistance is a preferred means of disease control, although approaches to evaluating ergot resistance in Kentucky bluegrass are not well established. A large scale disease assessment trial was established to compare within-year and year-to-year variability among measures of ergot incidence or severity in Kentucky bluegrass and to determine the most efficient approaches for cultivar evaluation. The susceptibility of 104 Kentucky bluegrass cultivars (78 commercial and 26 experimental) to ergot was assessed, based on percentage of panicles with sclerotia (incidence), sclerotia per panicle (severity), percentage of seeds replaced by sclerotia, or percentage of sclerotia among seed by weight. Cultivar ranking for susceptibility within years was similar for all methods of ergot assessment. Yearly mean incidence of ergot among cultivars ranged from 1.0 to 97.5% for susceptible cv. HV102 to 0.0 to 2.5% for resistant cv. Huntsville, with remaining cultivars distributed between the extremes. Yearly mean values of ergot incidence and severity differed among years. Much of this variability was due to days with rain during the period from flower initiation to maturity (period of susceptibility). Disease incidence was correlated (P ≤ 0.05) with days with rain in 22 of the cultivars. Duration of flowering was correlated (P ≤ 0.05) with ergot incidence in 11 cultivars. Results from this study suggest that variability in host and environment would likely offset any gain in precision of severity data. In large trials in particular, collection of incidence data (percentage of panicles with ergot) would provide the most timely and efficient means for ergot assessment.
The Role of Autumn Infections in the Progression of Fire Blight Symptoms in Perennial Pear Branches
Authors: Blachinsky D. , Shtienberg D. , Oppenheim D. , Zilberstaine M. , Levi S. , Zamski E. , Shoseyov O.
Published: May 2007

The role of autumn infections in the progression of fire blight (caused by Erwinia amylovora) symptoms in perennial pear branches was studied in orchard-grown trees in Israel. The extent of symptom progression and the final length of fire blight cankers in perennial branches were variably affected by the vigor of the trees and the season of infection. Following spring infections, when all trees supported active shoot growth, fire blight symptoms progressed more rapidly and to longer distances in trees that exhibited high vigor (i.e., with numerous annual shoots on most terminal branches) than in low-vigor trees (i.e., few or no annual shoots on terminal branches). Irrespective of the vigor of the trees, the progression of fire blight symptoms in perennial branches ceased between mid-May and mid-July, and only a small proportion (0 to 14.2%) of the infections had invaded main limbs or trunks of trees. Progression of fire blight symptoms following autumn infections was related to the preceding summer (August to No-vember) shoot regrowth: in trees in which the shoots did not restore their growth in the summer, the rate of symptom progression in perennial branches was higher in trees with a low vigor than in those with a high vigor, whereas for those with summer regrowth the relationship between rates of symptom expression was reversed. Irrespective of the vigor group and of whether there was summer regrowth, symptoms in perennial branches continued to progress through the winter until the following spring. Most of the autumn infections (50 to 78.5%) that developed in susceptible trees had invaded main limbs or trunks of trees. The results of this study indicate that factors related to host phenology and physiology, rather than factors related to environmental influences (such as temperature), govern the extent, rate, and duration of fire blight progression in perennial pear branches. Furthermore, it turned out that autumn infections play a substantial role in fire blight epidemiology in Israel.
Phytotoxicity of the Fungicide Metalaxyl and Its Optical Isomers
Authors: Singh M. , Mersie W. , Brlansky R. H.
Published: May 2007

Metalaxyl is a systemic fungicide commonly used in citrus production to control Phytophthora root rot and foot rot. When applied as a drench, injury was observed on newly planted, young citrus trees. The visual injury symptoms ranged from light- to bright-yellow leaves. It was learned that the commercial formulation of metalaxyl contained various isomers and that these isomers may vary in phytotoxic effects on citrus leaves. The objective of this study was to determine the difference in herbicidal activity between the two optical isomers of metalaxyl on pepper plants and citrus leaves. The phytotoxicity of the fungicide metalaxyl and its optical isomers (CGA76538, S+; CGA76539, R-) was determined using a pepper seedling growth bioassay and by measuring protein synthesis as estimated by the incorporation of 14C-leucine by citrus mesophyll cells. The two isomers and metalaxyl differed in their herbicidal activity to pepper plants and citrus cells. Pepper seedlings treated with R- had significantly higher mean fresh weight than plants treated with metalaxyl or S+ at 0.1, 1.0, 10.0, and 100 ppm. Protein synthesis, as measured by the inhibition of 14C-leucine incorporation by citrus mesophyll cells, also was inhibited more by metalaxyl and the S+ isomer than by the R- isomer. After 30 min of incubation at 100 μM, the R- isomer inhibited 14C-leucine incorporation by 29%, whereas incorporation of 14C-leucine in the metalaxyl and the S+ isomer treatments was higher (46 and 81%, respectively). Similarly, the highest 14C-leucine uptake at 60 min was obtained by R- at all concentrations. The assays showed that the R- and S+ isomers differ in their biological activity as expressed by weight loss of pepper plants and inhibition of protein synthesis and that the S+ isomer is responsible for the phytotoxicity of metalaxyl. The findings in this study show that the phytotoxicity of metalaxyl was due to the presence of the S+ optical isomer. Removal of this isomer from metalaxyl has enabled the continued use of this fungicide for control of foot rot and root rot in citrus.
Effect of Formulated Plant Extracts and Oils on Population Density of Phytophthora nicotianae in Soil and Control of Phytophthora Blight in the Greenhouse
Authors: Bowers John H. , Locke James C.
Published: May 2007

Formulated plant extracts and oils were investigated for control of diseases caused by Phytophthora spp. Soil infested with chlamydospores of Phytophthora nicotianae was treated by incorporating 1, 5, and 10% aqueous emulsions of formulations containing clove oil, neem oil, pepper extract and mustard oil, cassia extract, synthetic cinnamon oil, or the fungicide metalaxyl. Population densities of P. nicotianae were determined at 0 (before treatment), 1, 3, 7, 14, and 21 days after treatment. Treatment of the soil with 5 and 10% aqueous emulsions resulted in significant (P < 0.05) differences among treatment mean values at each assay date. After 1 day, population densities were reduced to below the limit of detection (<0.04 CFU/cm3) in soil treated with 10% aqueous emulsions of two pepper extract-mustard oil formulations and two cassia extract formulations, and near the limit of detection for a synthetic cinnamon oil formulation. Over time, populations of P. nicotianae were detected in the assay; however, after 21 days, populations of P. nicotianae in soil treated with one of the pepper extract-mustard oil formulations still were not detected. Formulations of clove oil, another pepper extract-mustard oil combination, the two cassia extracts, and the synthetic cinnamon oil reduced populations 98.4 to 99.9% after 21 days compared with the nontreated control soil. The neem oil formulation and metalaxyl did not reduce pathogen populations at any rate tested. In the greenhouse after 35 days, 10% aqueous emulsions of a pepper extract-mustard oil formulation, a cassia extract, and the synthetic cinnamon oil formulation suppressed disease development in periwinkle 93.0 to 96.7% compared with the nontreated infested soil. The observed reduction in the pathogen population and significantly more healthy plants in the greenhouse indicates that these formulations of plant extracts and oils could have important roles in biologically based management strategies for control of diseases caused by P. nicotianae.
Genetic Diversity of Ascochyta rabiei in Canada
Authors: Chongo G. , Gossen B. D. , Buchwaldt L. , Adhikari T. , Rimmer S. R.
Published: May 2007

Assessment of variability of Ascochyta rabiei (teleomorph: Didymella rabiei) was based on virulence tests of 40 isolates and on random amplified polymorphic DNA (RAPD) analysis of 39 isolates from Canada. In addition, isolates of A. rabiei from other countries were assessed in the virulence (18 isolates) and RAPD (20 isolates) analyses. Seven isolates of A. lentis (teleo-morph: Didymella lentis) and two of A. pinodes (teleomorph: Mycosphaerella pinodes) also were included in the RAPD analysis. Significant line-isolate interactions in the virulence tests indicated that certain isolates were virulent only on certain lines. Canadian isolates were grouped into 14 pathotypes using eight chickpea differentials. These groupings also encompassed 17 of the 18 isolates from other countries. RAPD analysis of all 68 isolates using 8 primers produced 112 fragments, of which 96% were polymorphic. Similarities among A. rabiei isolates from Canada ranged from 20 to 100%. In the RAPD dendrogram, all five A. rabiei isolates from Australia, three of six from Syria, three of five from the United States, and one of two from India clustered within the major groups of Canadian isolates. There was a weak association between RAPD and pathotype groups. A. rabiei was 45% similar to A. lentis and only 14% similar to A. pinodes. The levels of DNA variability and virulence among isolates show that the population of A. rabiei in Canada is highly diverse.
Comparison of Media for Recovery of Verticillium dahliae from Soil
Authors: Kabir Z. , Bhat R. G. , Subbarao K. V.
Published: May 2007

Polygalacturonic acid (PGA) is an important constituent of Sorensen's NP-10 medium (NP-10) for estimating the population density of Verticillium dahliae in soil. Different types of PGA are available, but not all of them favor the growth of V. dahliae. Unavailability of PGA sodium salt from orange (P-1879) has created an unprecedented problem for the quantification of microscle-rotia (MS) of V. dahliae in soil. The PGA from orange (P-3889) that is now available does not support the growth of V. dahliae. Therefore, experiments were conducted to optimize the use of NP-10 prepared with P-3889 and various concentrations of NaOH. NP-10 with P-3889 amended with eight concentrations of NaOH were compared with NP-10 prepared from PGA sodium salt from orange (P-1879, now discontinued) and citrus (P-3850) along with cellophane and Na-pectate media for recovery of MS from soil and growth of V. dahliae on the media. Seven soils were assayed for MS, and eight isolates of V. dahliae were evaluated for growth and production of MS. Concentrations of NaOH >0.035N and <0.02N in NP-10 with P-3889 reduced mycelial growth, microsclerotial production, and recovery of MS from soils. Similarly, NP-10 with P-3850 alone, cellophane, and Na-pectate media had significantly reduced growth on media and recovery of V. dahliae from soils. The NP-10 with P-3889 and 0.025N NaOH consistently yielded numbers of V. dahliae MS from soil samples and supported the growth and production of MS similar to the NP-10 with P-1879. The medium developed in this study can serve as a direct replacement for the original NP-10 that was developed nearly three decades ago, an important component of which is no longer available.
A Reevaluation of the Host Range and Geographical Distribution of Claviceps Species in the United States
Authors: Alderman Stephen C. , Halse Richard R. , White James F.
Published: May 2007

A listing of host and state reports and distribution maps for 11 taxa of Claviceps occurring in the United States, including C. africana, C. cinerea, C. grohii, C. nigricans, C. paspali, C. pusilla, C. purpurea var. purpurea and var. spartinae, C. tripsaci, C. yanagawensis, and C. zizaniae, was prepared based on literature citations and examination of specimens from herbaria. The occurrence of C. ranunculoides is questioned based on examination of conidia and sclerotia from archived specimens. Collections of C. purpurea var. purpurea from grasses in the Pani-coideae were referred to other Claviceps spp. based on occurrence of macroconidia and micro-conidia. C. purpurea var. purpurea was found on 165 grass species within the continental United States and Alaska. The size of conidia of C. purpurea var. purpurea was found to be relatively stable across host and geographical regions. However, conidia of C. purpurea var. purpurea from hosts in the Aveneae and Meliceae (generally associated with wet habitats) were more variable in size and generally larger than those from other tribes in the Pooideae. Claviceps spp. in the continental United States occurred in diverse habitats, including temperate grasslands of the middle to northern latitudes (C. purpurea var. purpurea, C. nigricans) to the middle to southern latitudes (C. pusilla), coastal habitats (C. purpurea var. spartinae, C. ziza-niae), northern wetlands (C. grohii), southern temperate to subtropical grasslands (C. africana, C. paspali, C. tripsaci, C. yanagawensis), and arid southwestern grasslands (C. cinerea).
Pumpkin (Cucurbita maxima and C. pepo), a new host of Beet pseudo yellows virus in California
Authors: Wintermantel W. M.
Published: May 2007

In the summer of 2002, pumpkin plants (Cucurbita pepo L. and C. maxima Duchesne) with extensive leaf chlorosis similar to those observed in crinivirus infections were found in fields at two locations in Monterey County, California. Leaves of diseased plants were observed to have large populations of the greenhouse whitefly (Trialeurodes vaporariorum) present. Double-stranded RNA was extracted from symptomatic leaves of these plants and tested by northern hybridization for numerous criniviruses. A positive signal was identified exclusively with probes against the HSP70h gene of Beet pseudo yellows virus (BPYV) and confirmed by reverse transcription-polymerase chain reaction (RT-PCR) amplification of a 335-nucleotide section of the BPYV minor coat protein (CPm) gene (3). Similar symptoms were observed in additional fields in 2003, and BPYV was again confirmed. In addition, the CPm RT-PCR product was cloned into a TOPO pCR2 vector (Invitrogen, Carlsbad, CA) and sequenced. BLAST analysis of the cloned CPm RT-PCR product sequence corresponded to the published sequence of the CPm gene of BPYV (98%) (3) and Cucumber yellows virus (CuYV), a recently sequenced crinivirus considered to be a strain of BPYV (97%) (2). Incidence of BPYV in pumpkin appears to be variable and probably corresponds to the incidence of viruliferous whiteflies. On the basis of foliar symptoms, BPYV incidence varied from less than 50% in these fields in 2002 to nearly 100% infection of a large commercial field in 2003. BPYV is transmitted semipersistently by the greenhouse whitefly and has an extensive host range (1). The virus causes economic losses worldwide for greenhouse vegetable production and is becoming an increasing problem for field crops in areas of high greenhouse whitefly incidence (3). The impact of BPYV on pumpkin production remains to be determined; however, grower data suggests an increased incidence of fruit abortion and a substantial decrease in fruit weight. To our knowledge, this is the first report of BPYV infecting pumpkin.

References: (1) J. E. Duffus. Phytopathology 55:450, 1965. (2) S. Hartono et al. J. Gen. Virol. 84:1007, 2003. (3) I. E. Tzanetakis et al. Plant Dis. 87:1398, 2003.
Anastomosis Grouping of Rhizoctonia solani Associated with Black Scurf and Stem Canker of Potato in South Africa
Authors: Truter M. , Wehner F. C.
Published: May 2007

Rhizoctonia disease (black scurf of tubers and stem canker) of potato (Solanum tuberosum L.) caused by Rhizoctonia solani Kühn was first recorded in South Africa in 1918 (3). Although the sclerotial form on tubers is one of the most common potato diseases in the country, it is not known which anastomosis groups (AGs) of R. solani are involved. Between 1999 and 2001, R. solani was isolated from 28 plant and 56 soil samples collected in 7 (Eastern Free State, Gauteng, KwaZulu-Natal, Limpopo, Mpumalanga, Northern Cape, and Sandveld) of the 14 potato-production regions of South Africa and screened for hyphal anastomosis with tester strains of R. solani AG-1 to AG-10 according to Carling et al. (1). Of the 411 isolates from tubers with black scurf symptoms, 408 were AG-3 and three were AG-5. Symptomless tubers yielded two AG-3 isolates and three AG-5 isolates. Of 39 isolates from symptomatic stems and roots, 32 were AG-3, five were AG-4, and two were AG-5. Of the 127 isolates obtained from soil, 86, 28, 7, 3, and 3 were AG-3, AG-4, AG-5, AG-7, and AG-8, respectively. More than one AG was isolated from five of the seven regions. Virulence of 40 isolates representative of the above AGs was determined in triplicate on sprouts growing from seed tubers of potato cultivar Up-to-Date in a sand/soil mixture as described by Carling and Leiner (2) but using cultures grown in cornmeal/sand instead of colonized agar disks as inoculum. Damage to sprouts (lesions, girdling, and death) was assessed after 28 days at 16 to 28°C according to the 0 to 4 rating scale (2). Chi-square analysis of the data indicated that AG-3 was the most virulent, with isolates from sclerotia on tubers and lesions on stems more aggressive than those from symptomless tubers or soil. AG-4 and AG-5 caused significantly less disease than AG-3, but none of the AG-7 and AG-8 isolates showed any virulence to potato sprouts.

References: (1) D. E. Carling et al. Phytopathology 77:1609, 1987. (2) D. E. Carling and R. H. Leiner. Phytopathology 80:930, 1990. (3) E. M. Doidge. S. Afr. Fruit Growers 5:6, 1918.
First Report of Monosporascus cannonballus on Melon in Brazil
Authors: Sales R. , Bezerra do Nascimento I. J. , de Souza Freitas L. , Beltrán R. , Armengol J. , Vicent A. , García-Jiménez J.
Published: May 2007

Approximately 15,000 ha of melon (Cucumis melo L.) are grown in the northeastern section of Brazil, mostly for export to Europe during the winter months. Surveys for melon vine decline diseases were carried out in farms in the municipalities of Mossoró (Rio Grande do Norte) and Quixeré (Ceará) during 2002 and 2003. Symptoms typical of vine decline were observed in several fields and included yellowing of crown leaves just prior to harvest and collapse of many of the vines. Affected plants exhibited necrotic root systems and lacked most of the secondary and tertiary feeder roots. Numerous perithecia were observed on roots which, when examined with a microscope, showed characteristic asci and ascospores of the fungus Monosporascus cannonballus Pollack & Uecker (2). Isolations were made from the crown region and primary and secondary roots of affected plants by excising 4- to 6-mm pieces that were surface sterilized for 30 to 60 s with 1.5% active chlorine solution. Seven tissue pieces from each plant part were placed on potato dextrose agar (PDA) containing 0.5 g liter-1 of streptomycin sulfate. Plates were examined daily for fungal growth for 7 days, and hyphal tips from all colonies were transferred to PDA for subsequent growth and sporulation. M. cannonballus was isolated from 50% of the root sections. All isolates produced only one ascospore per ascus. Pathogenicity of four isolates was confirmed in the greenhouse on the muskmelon cv. Temprano Rochet. Inoculum was produced in a sand-oat hulls (Avena sativa L.) medium (0.5 liter of sand, 46 g of ground oat hulls, and 37.5 ml of distilled water) and incubated at 25°C for 1 month. Colony forming units (CFU) were quantified by serial dilution using 1% hydroxyethyl cellulose. A sterilized mixture of equal portions (vol/vol) of sand and peat moss was used to fill plastic pots (17 cm in diameter), and inoculum was added to produce an inoculum concentration of 20 CFU g-1. Five melon seeds were planted in each pot and after germination, were thinned to one seedling per pot. There were five replicated pots for each treatment with an equal number of uninfested pots. Plants were evaluated for disease 45 days after sowing. Roots were exposed by carefully washing the potting mix away. All isolates of M. cannonballus tested were highly aggressive and caused severe root necrosis compared with the noninoculated control plants. M. cannonballus was reisolated from symptomatic plants, confirming Koch's postulates. Double cropping in the same fields for several years has created serious problems in Brazil, which are related to this soilborne pathogen that also causes root rot and vine decline of watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) worldwide (1). To our knowledge this is the first report of M. cannonballus in Brazil and South America.

References: (1) R. D. Martyn and M. E. Miller. Plant Dis. 80:716, 1996. (2) F. G. Pollack and F. A. Uecker. Mycologia 66:346, 1974.
Bacterial Spot of Tomato and Pepper Caused by Xanthomonas axonopodis pv. vesicatoria in the Western Mediterranean Region of Turkey
Authors: Basim H. , Basim E. , Jones J. B. , Minsavage G. V. , Dickstein E. R.
Published: May 2007

Xanthomonas axonopodis pv. vesicatoria, causal agent of bacterial spot of tomato (Lycopersicon esculentum L.) and sweet pepper (Capsicum annuum L.) was isolated from tomato and pepper plants in greenhouse production in the Province of Antalya, in southwestern Turkey. Disease incidence was less than 4% of plants observed in 2001 and ranged from 1 to 20% in 2002. Eleven seedling-producing companies and 26 greenhouses that produce tomato and pepper were surveyed during the rainy seasons of 2001 and 2002. The increase in disease incidence in 2002 is an indication that this disease is becoming more prevalent on tomato and pepper plants grown in greenhouses in southwestern Turkey. A gram-negative bacterium producing yellow-pigmented colonies on nutrient agar was consistently isolated from brown, circular spots on leaflets of tomato and sweet pepper seedlings. Five isolates were pathogenic on commercial cultivars of tomato and pepper when bacterial suspensions (108 CFU/ml) were infiltrated into the intercellular spaces of leaves to determine race by using procedures described by Bouzar et al. (1). All the isolates produced hypersensitive reaction responses on tomato genotype cv. Hawaii 7998 and pepper genotype cvs. 20 R and 30 R and were designated tomato race 1 pepper race 1 (T1P1) (1). Fatty acid analysis of the strains identified them as X. axonopodis vesicatoria with similarity index values of 0.872 to 0.933. In addition, the strains were tested with X. axonopodis vesicatoria-specific polymerase chain reaction primers (RST 2/3 and RST 9/10) (2). The isolates were determined to be X. axonopodis vesicatoria. Although bacterial spot of tomato has been suspected in Turkey for a number of years, to our knowledge, this is the first report of the bacterium on tomato.

References: (1) H. Bouzar et al. Phytopathology 84:663, 1994. (2) R. P. Leite, Jr. et al. Appl. Env. Microbiol. 60:1068, 1994.
Screening Triploid Hybrids of ‘Lakeland’ Limequat for Resistance to Citrus Canker
Authors: Viloria Z. , Drouillard D. L. , Graham J. H. , Grosser J. W.
Published: May 2007

Resistance of citrus genotypes to Xanthomonas axonopodis pv. citri, the cause of Asiatic citrus canker (ACC), was evaluated by injection infiltration of 103 and 104 CFU/ml through stomates on the abaxial surface of immature leaves. Citrus genotypes for screening comprised two autotetraploids and nine triploid hybrids of ‘Lakeland’ limequat (Citrus aurantifolia × Fortunella japonica) and their progenitors (‘Lakeland’ limequat, the autotetraploids ‘Femminello’ lemon (Citrus limon) and ‘Giant Key’ lime (C. aurantifolia), and the somatic hybrids ‘Key’ [also known as ‘Mexican’] lime + ‘Valencia’ orange and ‘Hamlin’ orange + ‘Femminello’ lemon). ‘Meiwa’ kumquat (Fortunella crassifolia) and ‘Pineapple’ sweet orange (C. sinensis) were used as known resistant and susceptible standards, respectively. Lesion number per inoculation site and bacterial population per lesion were recorded 15 to 19 days after inoculation. The assay was performed four times during a spring-summer-fall period under greenhouse conditions. Canker lesions were consistently produced by stomatal inoculation with 104 but not 103 CFU/ml. Susceptible and resistant genotypes were separated based on lesion number per inoculation site and bacterial population per lesion. Spearman's rank correlation analysis for lesion numbers on 15 genotypes common to all four assays showed significant correlations among the genotype rankings. Genotype rankings were also significantly correlated between the two bacterial population assays. Lesion number per inoculation site is sufficient for assessment of resistance of citrus genotypes to ACC without the necessity of conducting bacterial population assays. ‘Lakeland’ limequat is a promising seed parent for breeding acid citrus fruit that is resistant to ACC.