bluuebunny/crossref_metadata_2025 huggingface dataset:
Citrus and Coffee Strains of Xylella fastidiosa Induce Pierce's Disease in Grapevine
Authors: Li W.-B , Zhou C. -H. , Pria W. D. , Teixeira D. C. , Miranda V. S. , Pereira E. O. , Ayres A. J. , He C.-X. , Costa P. I. , Hartung J. S.
Published: May 2007

Xylella fastidiosa causes citrus variegated chlorosis (CVC) disease in Brazil and Pierce's disease of grapevines in the United States. Both of these diseases cause significant production problems in the respective industries. The recent establishment of the glassy-winged sharpshooter in California has radically increased the threat posed by Pierce's disease to California viticulture. Populations of this insect reach very high levels in citrus groves in California and move from the orchards into the vineyards, where they acquire inoculum and spread Pierce's disease in the vineyards. Here we show that strains of X. fastidiosa isolated from diseased citrus and coffee in Brazil can incite symptoms of Pierce's disease after mechanical inoculation into seven commercial Vitis vinifera varieties grown in Brazil and California. Thus, any future introduction of the CVC strains of X. fastidiosa into the United States would pose a threat to both the sweet orange and grapevine industries. Previous work has clearly shown that the strains of X. fastidiosa isolated from Pierce's disease- and CVC-affected plants are the most distantly related of all strains in the diverse taxon X. fastidiosa. The ability of citrus strains of X. fastidiosa to incite disease in grapevine is therefore surprising and creates an experimental system with which to dissect mechanisms used by X. fastidiosa in plant colonization and disease development using the full genome sequence data that has recently become available for both the citrus and grapevine strains of this pathogen.
Transmissibility of Field Isolates of Soybean Viruses by Aphis glycines
Authors: Clark A. J. , Perry K. L.
Published: May 2007

During the 2001 growing season, 191 symptomatic soybean (Glycine max (L.) Merr.) plants were dug from production plots in Indiana, Wisconsin, and Kentucky. Alfalfa mosaic virus (AMV), Bean pod mottle virus (BPMV), Bean yellow mosaic virus (BYMV), Peanut stunt virus (PSV), Tobacco ringspot virus (TRSV), and Soybean mosaic virus (SMV) were identified. No mixed infections were observed. The ability of the soybean aphid (Aphis glycines Matsamura) to transmit field isolates of these viruses was tested. Using naturally infected field- or greenhouse-grown soybean plants as sources, six isolates of SMV and two isolates of AMV were transmitted using a short feeding assay. One of two isolates of TRSV was transmitted by A. glycines in one of four experiments using an extended feeding transmission assay. BPMV was not transmitted by A. glycines in assays involving 11 field isolates and over 840 aphids. One field isolate each of BYMV and PSV were tested and no transmission by A. glycines was observed.
Use of Aeroponic Chambers and Grafting to Study Partial Resistance to Fusarium solani f. sp. glycines in Soybean
Authors: Mueller D. S. , Li S. , Hartman G. L. , Pedersen W. L.
Published: May 2007

Several plant introductions (PIs) and cultivars have been classified as partially resistant (PR) to sudden death syndrome. However, little is known about the nature of resistance to this disease. Seedlings of two PR PIs and two susceptible cultivars were inoculated with Fusarium solani f. sp. glycines in aeroponic chambers. Plants were inoculated by taping two sorghum seeds infested with F. solani f. sp. glycines to the main root. Foliar symptoms of the susceptible cultivars were higher than those on the PR PIs and were associated with lower root and plant dry weight. Root lesion lengths of the four soybean lines differed (P < 0.05), but did not correlate with foliar disease or any other variable. To better understand the resistance mechanism by distinguishing between root and plant resistance, three partially resistant PIs (PI 520.733, PI 567.374, and PI 567.650B) and one susceptible soybean cultivar (GL3302) were compared using different grafting combinations in aeroponic chambers. Results of sudden death syndrome evaluation indicated that resistance is conditioned by both the scion and the rootstock. All three PIs evaluated had resistance associated with the scion; resistance in PI 567.650B also was associated with the rootstock. Although the PR PIs used appear to have little or no root resistance, an aeroponic system and grafting may help identify new sources of resistance to F. solani f. sp. glycines with root- or whole-plant resistance.
Sensitivity of Sclerotinia homoeocarpa Isolates to Propiconazole and Impact on Control of Dollar Spot
Authors: Miller Gerald L. , Stevenson Katherine L. , Burpee Leon L.
Published: May 2007

In response to reports of reduced efficacy of propiconazole for control of dollar spot, isolates of Sclerotinia homoeocarpa were collected from several locations in Georgia and tested for sensitivity to propiconazole and other demethylation-inhibiting (DMI) fungicides. Two discriminatory concentrations of propiconazole (0.02 and 0.2 μg ml-1) were used to detect lower in vitro sensitivity in two populations that had been exposed repeatedly to propiconazole than in four nonexposed populations. Mean 50% effective concentration (EC50) values for a nonexposed population (baseline) and a DMI-exposed population were 0.0049 and 0.0283 μg ml-1, respectively. Positive correlations were significant among log10 EC50 values for propiconazole, fenarimol, and myclobutanil but not between triadimefon and any of the other three fungicides, indicating cross-resistance relationships in this pathogen may not be universal among the DMIs. In greenhouse experiments, propiconazole-treated bentgrass was inoculated with seven isolates of S. homoeocarpa differing in sensitivity to propiconazole. Incubation period decreased and relative area under the disease progress curve and disease severity 28 days after inoculation increased linearly with increasing log10 EC50 value of the isolate. Results of this study confirm a significant relationship between in vitro sensitivity of S. homoeocarpa and in planta control efficacy of propiconazole and provide evidence of field resistance to propiconazole in S. homoeocarpa in Georgia.
First Report of White Fir Dwarf Mistletoe on Mountain Hemlock
Authors: Mathiasen R.
Published: May 2007

White fir dwarf mistletoe (Arceuthobium abietinum Engelm. ex Munz f. sp. concoloris Hawksw. & Wiens) is a serious and common pathogen of white fir (Abies concolor (Gord. & Glend.) Hildebr.), grand fir (A. grandis (Dougl. ex D. Don) Lindl.), and Low's fir (A. lowiana (Gord.) A. Murr.) in the western United States (1). In August 2002, this dwarf mistletoe was observed parasitizing mountain hemlock (Tsuga mertensiana (Bong.) Carr.) growing among severely infected grand fir near the trailhead to Cabot Lake in the Mount Jefferson Wilderness Area, Oregon at 44°34′27″N, 121°43′43″W, elevation 1,340 m. Only 2 of 27 mountain hemlocks observed in this area were infected. One tree had four infections, and one tree had two infections. Several fully developed male plants were found on one of the infected branches of mountain hemlock and were morphologically similar to those growing on the nearby grand fir. Other dwarf mistletoes that commonly parasitize mountain hemlock (Arceuthobium tsugense subsp. mertensianae and Arceuthobium laricis) were not observed in the area. In addition, white fir dwarf mistletoe can be distinguished from these mistletoes by its larger, yellowish shoots (1). Specimens of the mistletoe from mountain hemlock have been deposited in the Deaver Herbarium, Northern Arizona University, Flagstaff. To my knowledge, this is the first report of white fir dwarf mistletoe on mountain hemlock (1).

Reference: (1) F. Hawksworth, and D. Wiens. Dwarf mistletoes: biology, pathology, and systematics. USDA Agric. Handb. 709, 1996
Key West Nightshade, a New Experimental Host for Plant Viruses
Authors: Adkins Scott , Rosskopf Erin N.
Published: May 2007

Key West nightshade (Solanum bahamense) is a perennial solanaceous weed found in the extreme southern portion of Florida. It can be propagated by seed and cuttings and is absent from the noxious weed lists of all U.S. states. Its susceptibility to five viruses common to Florida was evaluated by mechanical inoculation of leaves with Tomato spotted wilt virus (TSWV), Tobacco mosaic virus (TMV), Pepper mild mottle virus (PMMoV), Cucumber mosaic virus (CMV), and a putative tobamovirus recently isolated from hibiscus in Florida (HV). TSWV induced chlorotic rings on inoculated leaves and mosaic and malformation of uninoculated leaves. CMV induced necrotic local lesions on inoculated leaves. No symptoms were observed following inoculation with TMV, PMMoV, or HV. TSWV, TMV, and PMMoV systemically infected S. bahamense as determined by the use of enzyme-linked immunosorbent assay, reverse transcription-polymerase chain reaction, viral-associated double-stranded RNA analysis, and/or indicator hosts. Active growth of infected plants continued for 7 months following inoculation, making S. bahamense suitable for long-term maintenance of viruses in planta. We suggest that S. bahamense may be a useful host for virus culture collections and for studies involving large numbers of virus isolates where fresh, infected tissue is continuously required.
Influence of Formononetin and NaCl on Mycorrhizal Colonization and Fusarium Crown and Root Rot of Asparagus
Authors: Elmer Wade H.
Published: May 2007

Replanted asparagus fields commonly fail to produce a profitable stand due to alleopathic residues left behind from the previous asparagus crop, elevated densities of pathogenic Fusarium spp., and low densities of vesicular arbuscular mycorrhizae (VAM). Formononetin, a plant isoflavone that stimulates VAM spores to germinate, and sodium chloride (NaCl), a disease-suppressing amendment, were evaluated alone and in combination for their effect on reestablishing asparagus at two locations in abandoned asparagus fields. Greenhouse studies also were conducted with naturally and artificially infested soils. Formononetin was applied as a crown soak or soil drench, and NaCl was applied as a granular treatment. Feeder roots from soil cores sampled from field plots and from greenhouse transplants were assayed for colonization by VAM and for lesions caused by Fusarium oxysporum and F. proliferatum. Formononetin increased the number of VAM vesicles in roots from the field and greenhouse studies and reduced the percent root lesions caused by Fusarium spp. when compared with the nontreated controls. NaCl was more effective than formononetin in reducing the percentage of root lesions in both field and greenhouse experiment when compared with untreated plants but had no effect on VAM colonization. However, there was evidence that NaCl negated the effect of formononentin on VAM colonization. The NaCl treatment increased the May 2001 spear number by 15% and marketable spear weight by 23%. At one site, treatment with formononetin increased mean number of stalks per plant by 29% in 2000 and 14% in 2001. Both formononetin and NaCl improve growth and reduce disease of asparagus in replanted asparagus and may be useful in reestablishing asparagus in abandoned asparagus field.
Effect of Rice Root-Knot Nematode on Growth and Yield of Yellow Granex Onion
Authors: Gergon E. B. , Miller S. A. , Halbrendt J. M. , Davide R. G.
Published: May 2007

Rice root-knot nematode, Meloidogyne graminicola, infects all commercially grown onion cultivars in rice-onion cropping systems in the Philippines, but its economic importance has not been established. The effects of different preplant population levels (Pi) of M. graminicolaon Yellow Granex onion in pots and of different percentages of galled roots in a naturally infested field were evaluated. Leaf weight and root length of ‘Yellow Granex 429’ seedlings decreased with increasing Pi, while low Pi mildly stimulated plant height at the vegetative growth stage. Age of transplant and Pi influenced growth and yield of onion at maturity. Onion yield and root and leaf weights decreased as the age of the transplants increased. Growth and yield decreased with increased Pi. Bulb weight was reduced by 7 to 82% and diameter by 10 to 62% when plants were inoculated with 50 to 10,000 second-stage juveniles. Onion bulbs from the field were reduced by 16, 32, and 35% in weight and by 6, 17, and 18% in diameter when the percentage of roots galled was 10, 50, and 100%, respectively. Management of M. graminicolapopulations at the start of the growing season must be part of onion culture in rice-onion systems to reduce onion yield losses and to prevent economic loss.
First Report of the Cyst Nematode (Globodera tabacum) Complex on Flue-Cured Tobacco in Spain
Authors: Espárrago G. , Blanco I.
Published: May 2007

The Globodera tabacum complex infects tobacco (Nicotiana tabacum L.) fields in the United States. In August 2001, plants of flue-cured tobacco cv. K326 from a field of the La Vera Region of Spain displayed a premature wilting and yellowing of foliage, but the roots looked healthy. In the laboratory under the microscope, nematode cysts were observed on the roots. At harvest in September 2001, soil and root samples were collected to identify the nematode and to quantify the population in the soil. Identification of the nematode was based on morphological characteristics of second-stage juveniles collected from cysts and perineal patterns of cysts recovered from the roots (2). Cysts were collected from roots, and second-stage juveniles were extracted from crushed cysts. The nematode population was extracted from the soil and quantified as described by Barker (1). The nematode population was identified as Globodera tabacum. Soil density of the nematode was 5,307 cysts per liter of soil, 64,286 eggs per liter of soil, and 16,071 second-stage juveniles per liter of soil. To our knowledge, this is the first report of G. tabacum complex in Spain.

References: (1) K. R. Barker. Nematode extraction and bioassays. Page 19 in: An Advanced Treatise on Meloidogyne. Vol II, Methodology. K. R. Barker, C. C. Carter, and J. N. Sasser, eds. North Carolina State University Graphics, Raleigh, 1985. (2) R. H. Mulvey and A. Morgan Golden, J. Nematol. 15:1, 1983.
Polygala myrtifolia as a New Natural Host of Cucumber mosaic virus
Authors: Tessitori M. , Reina A. , Catara V. , Polizzi G.
Published: May 2007

Cucumber mosaic virus (CMV), Tomato spotted wilt virus (TSWV), and Impatiens necrotic spot virus (INSV) are among the most important viral pathogens of ornamental plants (1). Polygala myrtifolia L. (myrtle-leaf milkwort), originating from South Africa, and a member of the Polygalaceae, was recently introduced in Italy as a cultivated ornamental shrub for its fast and attractive free-flowering growth and drought-resistant characteristics. It can become an invasive plant and is now considered a serious problem in coastal areas of Australia where it was introduced as a garden plant. In Italy, P. myrtifolia is propagated by cuttings in commercial nurseries during the summer. In the winter of 2002, plants of P. myrtifolia growing in pots in an ornamental nursery in Sicily showed virus-like mosaic and malformation of leaves that appeared lanceolate with a lack of flowering. Leaf tissue was analyzed by double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) with polyclonal antisera to CMV, TSWV (Lettuce type), and INSV. Positive ELISA results were obtained only with the CMV polyclonal antisera. Complete remission of symptoms was observed on new flushes after pruning and incubation of infected plants at warm temperatures (30 and 20°C, day and night, respectively). This evidence led to the hypothesis that the disease or virus was disseminated by transportation and propagation of plants without visible symptoms during the hot season. A survey was also performed in two historical gardens of Catania (Sicily) where a group of apparently healthy P. myrtifolia plants, from the previously mentioned ornamental nursery in Sicily, were introduced as a single specimen or to form a hedge. These plants showed the same leaf malformations and mosaic symptoms observed in the nursery. DAS-ELISA confirmed the presence of CMV but not TSWV and INSV. To our knowledge, this is the first report of CMV on P. myrtifolia and it adds a new host to over 1,000 species (85 plant families) infected by this virus.

Reference: (1) M. L. Daughtrey et al. Plant Dis. 81:1220, 1997.
First Report of Gaeumannomyces graminis var. graminis on Seashore Paspalum in the United States
Authors: Elmore W. C. , Gooch M. D. , Stiles C. M.
Published: May 2007

Gaeumannomyces graminis var. graminis is an ectotrophic, root-infecting fungus found on some warm-season turfgrass species (1). A sample of seashore paspalum (Paspalum vaginatum) exhibiting rotted roots and stolons was taken from dying patches of turf in a home lawn in Hernando County, FL, and submitted to the Florida Extension Plant Disease Clinic, Gainesville, in October 2001. The lawn had been established within the previous year. Strongly lobed hyphopodia typical of G. graminis var. graminis (3,4) were present on diseased roots and stolons, and no other fungal plant pathogens were detected in the sample. Diseased roots and stolons with lobed hyphopodia were surface-sterilized and placed on one-quarter-strength potato dextrose agar (PDA) amended with rifampicin and streptomycin. One isolate produced structures characteristic of G. graminis var. graminis (3,4), including dark, strongly lobed hyphopodia, and perithecia and ascospores in PDA after incubation. The isolate (PDC 2965) was grown on a sterile ryegrass seed substrate at 25°C for 4 weeks to produce inoculum (2). The isolate was used to inoculate pots of ‘Sea Isle 1’ seashore paspalum grown in sterile soil from sprigs. An inoculum layer, 1 to 2 cm deep, was placed 2 to 4 cm below each sprig and covered with an overlay of sterile soil prior to sprigging (2). Following 4 weeks of plant growth in a greenhouse, dark, necrotic lesions appeared on leaf bases. Very dark lesions developed on roots, and brown runner hyphae and strongly lobed hyphopodia were observed on root and shoot tissues. Selected pieces of symptomatic root and shoot tissue were surface-sterilized and placed on PDA. One week later, dark mycelia and deeply lobed hyphopodia were observed growing from roots and shoots on the PDA. After 1 month, black, flask-shaped perithecia, 156 to 234 μm in body width, developed in cultures. Hyaline, filiform, septate ascospores ranged from 75 to 100 μm (mean = 89 μm; n = 250) long and were approximately 2.5 μm wide. Hyphopodia, perithecia, and ascospores were characteristic of G. graminis var. graminis (3,4). To our knowledge, this is the first report of take-all root rot disease due to G. graminis var. graminis on seashore paspalum in the United States.

References: (1) L. E. Datnoff et al. Plant Dis. 81:1127, 1997. (2) M. L. Elliott. Plant Dis. 79:699, 1995. (3) M. L. Elliott and P. J. Landschoot. Plant Dis. 75:238, 1991. (4) P. J. Landschoot. Taxonomy and biology of ectotrophic root-infecting fungi associated with patch diseases of turfgrasses. Pages 41–71 in: Turfgrass Patch Diseases. B. B. Clarke and A. B. Gould, eds. American Phytopathological Society, St. Paul, MN, 1997.
Characterization of Tobacco mosaic virus Isolated from Potato Showing Yellow Leaf Mosaic and Stunting Symptoms in Korea
Authors: Jung H. W. , Yun W. S. , Hahm Y. I. , Kim K.-H.
Published: May 2007

Four isolates of Tobacco mosaic virus (TMV-potato 1 to 4) were obtained from potato plants (Solanum tuberosum) in cultivated potato plantings in Korea. These isolates were differentiated based on biological properties, symptomatology, and nucleotide sequence analysis of the coat protein (CP) gene. TMV potato isolates caused typical symptoms on 20 inoculated plant species as compared to the type (U1) TMV strain. The four isolates each produced distinctly different symptoms on Gomphrena globosa. In contrast to the type strain of TMV, infections with two of the isolates reported here were not restricted to inoculated leaves of G. globosa but moved systemically through the plants. In addition, three additional systemic hosts (Chenopodium amaranticolor, C. quinoa, and C. murale) for TMV were revealed. Sequence analysis of the CP gene differentiated TMV-potato isolates. The CP gene sequence exhibited significant identity (83.1 to 99.2%) among TMV-potato isolates while showing 88.1 to 99.4% identities on predicted amino acid sequences. Based on a comparison of the CP gene nucleotide and deduced amino acid sequences between TMV-potato isolates and other TMV strains, TMV-potato 1, 3, and 4 were closely related to TMV strains U1, U2, V-FAVA, and NC82 with 98.8 to 100% identity. In contrast, TMV-potato 2 was closely related to TMV strains L, KP, KO-TOB, K1, and K2 with 93.8 to 98.8% identity.
Biological Control of Gray Mold with Ulocladium atrum in Annual Strawberry Crops
Authors: Boff P. , Köhl J. , Jansen M. , Horsten P. J. F. M. , Lombaers-van der Plas C. , Gerlagh M.
Published: May 2007

The efficacy of the fungal antagonist Ulocladium atrum to control gray mold in annual strawberry crops using waiting-bed transplants under field conditions was investigated. Seven field experiments were conducted with strawberry cv. Elsanta during the summer seasons of 1996-99 in the Netherlands. Treatments included untreated controls, fungicide programs, U. atrum spray programs, and crop sanitation. Under low disease pressure, U. atrum spray programs effectively reduced gray mold at harvest in four of seven experiments. Sprays of U. atrum starting at transplanting resulted in better control of gray mold than sprays starting at the beginning of flowering in only one of five experiments. Removal of necrotic leaves did not affect the level of gray mold, which demonstrated that strawberry leaves were not a significant inoculum source for Botrytis cinerea in this annual cropping system. These results suggest that U. atrum can be effective in reducing gray mold in strawberry crops, and further studies on the use of the antagonist in annual systems should consider flowering time as the best period to apply this antagonist.
The Use of Hierarchical Sampling in the Surveillance Program for Plum pox virus Incidence in the United States
Authors: Hughes G. , Gottwald T. R. , Levy L.
Published: May 2007

Plum pox virus (PPV) was first reported in North America in late 1999. As part of the eradication effort mounted in response to this finding, a Plum Pox Virus National Surveillance Program has been implemented in the United States. The survey method adopted for this program is a form of “group testing” that utilizes relationships between disease incidence at two levels in a spatial hierarchy, known as hierarchical sampling. Leaf material is collected from groups of four trees and tested by enzyme-linked immunosorbent assay (ELISA) for PPV infection without distinguishing between the individual trees in a group. PPV incidence at the scale of the individual tree is then calculated by means of a formula. Incidence data were collected during an initial survey conducted by the Pennsylvania Department of Agriculture from nine PPV-infected orchards in the fall of 1999 and from an additional 11 PPV-infected orchards during the spring and summer of 2000. The pattern of PPV-infected trees at the within-group scale was weakly aggregated. As a result, an effective sample size of v = 3.2, rather than the nominal group size of four, should be used in the formula to calculate an estimate of incidence at the scale of the individual tree from observations of incidence collected at the group scale.
Quantifying Alfalfa Yield Losses Caused by Foliar Diseases in Iowa, Ohio, Wisconsin, and Vermont
Authors: Nutter F. W. , Guan J. , Gotlieb A. R. , Rhodes L. H. , Grau C. R. , Sulc R. M.
Published: May 2007

Although foliar diseases of alfalfa occur throughout the United States wherever alfalfa is grown, little work has been done to quantify yield losses caused by foliar pathogens since the late 1980s. To quantify the yield losses caused by foliar diseases of alfalfa, field experiments were performed in Iowa, Ohio, Vermont, and Wisconsin from 1995 to 1998. Different fungicides and fungicide application frequencies were used to obtain different levels of foliar disease in alfalfa. Visual disease and remote sensing assessments were performed weekly to determine the relationships between disease assessments and alfalfa yield. Visual disease assessments of percentage of defoliation, disease incidence, and disease severity were performed weekly, approximately five to six times during each alfalfa growth cycle. Remote sensing assessments also were obtained weekly by measuring the percentage of sunlight reflected from alfalfa canopies using handheld, multispectral radiometers. Yield loss estimates were calculated as the yield difference between the fungicide treatment with the highest yield and the nonfungicide control, divided by the yield obtained from the highest yielding fungicide treatment × 100. Over the 4-year period, significant alfalfa yield losses (P ≤ 0.05) occurred on 22 of the 48 harvest dates for the four states. The average significant yield loss for the 22 harvests was 19.3%. Both visual and percentage of reflectance assessments were used as independent variables in linear regression models to quantify the relationships between assessments and alfalfa yield. From 1995 to 1998, visual disease assessments were performed for a total of 209 dates and remote sensing assessments were performed on 198 dates from the four states. Yield models were developed for each of these assessment dates. There were 26/209, 26/209, and 17/209 significant yield models based on percentage of defoliation, disease incidence, and disease severity, respectively. Most of the significant models were for disease assessments performed on or within 1 or 2 weeks of the date of alfalfa harvest. When the significant models were averaged, percentage of defoliation, disease incidence, and disease severity explained 51, 55, and 52% of the variation in alfalfa yield, respectively. There were a total of 68/198 significant alfalfa yield models based on remote sensing assessments, and the significant models (averaged) explained 62% of the variation in alfalfa yield. Alfalfa foliar diseases continue to have a significant negative impact on alfalfa yields in the United States and remote sensing appears to offer a better means to quantify the impact of foliar diseases on alfalfa yield compared with visual assessment methods.
Dynamics and Pattern of Latent Infection Caused byBotryosphaeria dothideaon Pistachio Buds
Authors: Ntahimpera N. , Driever G. F. , Felts D. , Morgan D. P. , Michailides T. J.
Published: May 2007

A study was conducted in four commercial pistachio orchards to monitor the presence and pattern of external contamination and latent infections of buds by Botryosphaeria dothidea between 1998 and 2000. Symptomless buds were sampled every 2 to 3 weeks and analyzed either by a washing/crushing method or by direct plating of split (half) or intact buds on lactic acid potato dextrose agar. The proportion of infected buds varied among orchards over time. Levels of latent infections were highest in February and March when they reached as much as 60% in orchards of Glenn and Yolo counties. This period corresponded to the months with the highest rainfall. Buds collected from orchards in Glenn and Yolo counties had, in general, higher incidence of infection than buds from San Joaquin and Merced counties. Buds became infected in June immediately after their formation. Infection incidence on basal segments of buds from male trees was approximately twice (19%) that of apical or middle segments (11%). Plating of split buds resulted in similar levels of incidence as the plating of intact buds. The number of B. dothidea propagules on bud surfaces varied over time and among orchards. In general, the number of propagules per bud was highest in February and March (approximately seven propagules per bud) when the rainfall amount was highest.
Puccinia abrupta var. partheniicola on Parthenium hysterophorus in Southern Africa
Authors: Wood A. R. , Scholler M.
Published: May 2007

Parthenium weed (Parthenium hysterophorus L., family Asteraceae), an annual herb of neotropic origin, is an invasive noxious weed with a pantropical distribution (1). It is particularly undesirable because of the serious health risks it poses to people living close to infestations (1). In January 1995, S. Neser (ARC-Plant Protection Research Institute, Pretoria, South Africa) collected a rust fungus on this plant near Brits, Northwest Province, South Africa (25°35′S, 27°46′E). Only uredinia were present. The same rust fungus was collected in the same area in January, March, and June of 2001, and again only uredinia were observed. In its native range, P. hysterophorus is infected by two rust fungus species, Puccinia abrupta Diet. & Holw. var. partheniicola (Jackson) Parmelee and Puccinia melampodii Diet. & Holw., but the latter species is microcyclic with telia only. The morphology of the urediniospores in the South African collections corresponds to Puccinia abrupta var. partheniicola (3): obovoid to almost triangular, 22 to 27 × 18 to 25 µm, echinulate, two subequatorial and one apical germ pores, spines absent around germ pores, wall 1 to 2.5 µm thick. The native range of Puccinia abrupta var. partheniicola is Mexico and northern South America (3). In addition, it has been recorded from Mauritius (3), Kenya, and India (H. C. Evans and C. A. Ellison, International Institute of Biological Control, CAB, 1987, unpublished data). It was intentionally introduced into Australia for the biological control of P. hysterophorus (2). Thirteen specimens in the Arthur Herbarium were examined, and only two had telia in addition to uredinia. The other 11 had only uredinia, indicating that nonformation of telia is common. Telia and uredinia are produced in high altitude, semiarid areas of Mexico, whereas in low altitude, more humid areas only uredinia are produced (1). The production of telia appears to depend on environmental conditions, and their absence is not unexpected at the Brits site, which is a high altitude (1,120 m) area with high summer rainfall (400 to 600 mm per year from November to February) and dry winters. Voucher specimens were deposited at the National Collection of Fungi, Plant Protection Research Institute, Pretoria (PREM 57298) and the Arthur Herbarium, West Lafayette, IN (PUR N1117). To our knowledge, this is the second report of this rust fungus in Africa and the first in southern Africa.

References: (1) H. C. Evans. Trans. Br. Mycol. Soc. 88:105, 1987. (2) A. Parker et. al. Plant Pathol. 43:1, 1994. (3) J. A. Parmelee. Can. J. Bot. 45:2267, 1967.
First Report of Powdery Mildew on Azalea Cv. Mollis (Rhododendron japonicum × R. molle) in Italy
Authors: Garibaldi A. , Gilardi G. , Bertetti D. , Gullino M. L.
Published: May 2007

Rhododendron cultivation has a long history in northern Italy, where a wide selection of varieties and hybrids are grown. In summer 2001, a previously unknown powdery mildew was observed on azalea cv. Mollis (Rhododendron japonicum × R. molle) grown in several gardens in the province of Biella. Initial symptoms included chlorotic spots, followed by white fungal mycelia on both leaf surfaces. Eventually, infected leaves turned reddish and dropped prematurely. Fruit were also infected. On infected tissues, dark brown-to-black spherical cleistothecia developed, alone or in groups. The teleomorph was identified by light microscopy examination of cleistothecia. Cleistothecia measured 110 to 140 µm and were dark brown. They contained four to eight stalked or sessile asci that measured 35 to 45 µm × 40 to 55 µm, each containing six to eight ascospores. Ascospores were ellipsoid to ovoid and measured 12 to 18 µm × 20 to 25 µm. Cleistothecial characteristics were consistent with those described for Microsphaera azaleae but were different from those of the recently described species M. digitata reported in Belgium (1). The presence of conidia was rare in the specimens, so the anamorph could not be identified. To our knowledge, this is the first report of M. azaleae in Italy, but three outbreaks of powdery mildew on rhododendron were first reported in the United Kingdom on plants grown in glasshouses in the mid-1950s, 1969 and 1973 (1). Outdoors, powdery mildew was first reported on rhododendron in Europe in 1981. M. azaleae has been identified as the causal agent of rhododendron powdery mildew in the United Kingdom, Germany, and Switzerland (1). In most cases the disease is readily controlled by regular application of fungicides commonly used against powdery mildews of other crops.

Reference: (1) A. J. Inman et al. J. Phytopathol. 148:17, 2000.
Survey Methods for Assessment of Citrus tristeza virus Incidence in Urban Citrus Populations
Authors: Hughes G. , Gottwald T. R. , Yamamura K.
Published: May 2007

This article concerns survey methodology for pathogens in urban citrus populations, motivated in particular by the need for assessments of Citrus tristeza virus (CTV) incidence. We envisage a large area R not devoted primarily to the commercial cultivation of citrus, that nevertheless has a substantial population of citrus trees. It is desired to sample the citrus population of area R in order to be able to make a statement about the level of infection of the population with CTV, or with particular isolates thereof. We describe a two-stage acceptance sampling scheme in which area R is divided into N sampling units, of which n are inspected. The size of the sampling units, while much smaller than R, is still large, so subsampling is carried out, introducing the possibility of misclassification of sampling units. To account for misclassification of sampling units, a larger number must be inspected than if it were assumed that there were no misclassifications. We describe the calculation of sample sizes required for subsampling within sampling units and for the total number of sampling units to be inspected, using parameters that can be adjusted to meet different specified regulatory scenarios.
Control of Root and Stem Rot of Cucumber, Caused byFusarium oxysporumf. sp.radicis-cucumerinum, by Grafting onto Resistant Rootstocks
Authors: Pavlou G. C. , Vakalounakis D. J. , Ligoxigakis E. K.
Published: May 2007

Root and stem rot of cucumber (Cucumis sativus), caused by Fusarium oxysporum f. sp. radicis-cucumerinum, is a new catastrophic disease of greenhouse crops in Greece and some other countries. No effective disease control methods are available, apart from soil disinfestation by fumigation with methyl bromide and disinfection of internal space of greenhouses with a formaldehyde solution. However, it is anticipated that the use of methyl bromide will be phased out in Greece by 1 January 2005. Therefore, alternative measures for disease management are urgently required. In this study, the efficacy of grafting commercial Dutch type cucumber hybrids onto various cucurbits, used as rootstocks, was examined in growth chamber and greenhouse experiments. Of the nine commercial Cucurbita spp. evaluated, six, A27, Cucurbita Ficifolia, Patron F142.91 F1, TS-1358 F1, and TZ-148 F1, found resistant to F. oxysporum f. sp. radicis-cucumerinum, were selected to serve in subsequent greenhouse experiments as root-stocks for grafting the susceptible cv. Brunex F1. Of these, Peto 42.91 F1, TS-1358 F1, and TZ-148 F1were found to be superior to the others due to their horticultural performance under the climatic conditions prevailing in Crete during the cucumber crop season, late October to late May. This study shows that grafting commercial Dutch type cucumber hybrids onto various resistant Cucurbita rootstocks could be used as an alternative control method to methyl bromide for root and stem rot.
Inoculation with Nonpathogenic Fusarium solani Increases Severity of Pea Root Rot Caused by Aphanomyces euteiches
Authors: Peters R. D. , Grau C. R.
Published: May 2007

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.
In Situ Immunoassay (ISIA) of Field Grapefruit Trees Inoculated with Mild Isolates of Citrus tristeza virus Indicates Mixed Infections with Severe Isolates
Authors: Lin Youjian , Rundell Phyllis A. , Powell Charles A.
Published: May 2007

Ten grapefruit trees that had been inoculated with a mild isolate of Citrus tristeza virus (CTV) and maintained in the field for 18 years were found in a previous study to be declining and infected with severe isolates of CTV, or symptomless and infected with mild isolates of CTV, using enzyme-linked immunosorbent assay (ELISA). They were assayed with an in situ immunoassay (ISIA) procedure using monoclonal antibodies 17G11 (reacts with most Florida isolates of CTV) and MCA13 (reacts with severe, but not Florida mild isolates of CTV). All the grapefruit trees were 17G11 positive by ELISA and ISIA. The five trees that showed moderate decline symptoms were MCA13 positive by ELISA and ISIA. The five symptomless trees were MCA13 negative by ELISA. However, four of the five symptomless trees were MCA13 positive by ISIA, which showed that ISIA with MCA13 had greater sensitivity in detecting severe CTV isolates than ELISA. These results suggested that the cross-protected grapefruit trees, regardless of symptoms, were infected with both mild and severe isolates of CTV.
Etiology of Bronze Leaf Disease of Populus
Authors: Smith Jason A. , Blanchette R. A. , Ostry M. E. , Anderson N. A.
Published: May 2007

Bronze leaf disease is a potentially destructive disorder of the Populus section of the genus Populus. The causal agent has been reported to be Apioplagiostoma populi (anamorph: Discula sp.). Based on etiological and symptomological studies, field observations of symptom development suggest that the pathogen moves systemically in the host. This was verified by graft experiments where symptoms progressed from the scion into the elongating stem. A bronze-pigmented vascular discoloration was observed in symptomatic leaves and branches. Dieback of affected stems also was common. Spore-trap studies elucidated the timing and necessary weather conditions of A. populi ascospore dispersal in relation to infection and symptom development. Exposure-tree experiments revealed that ascospores of A. populi are the primary inoculum and resulting infection causes distinctive disease symptoms on affected trees. Perithecia of A. populi were observed on overwintered symptomatic leaves, but were not observed on asymptomatic leaves. Acervular conidiomata were observed on symptomatic leaves during August and September. Although A. populi ascospores germinated in vitro, A. populi was not recovered from symptomatic tissue. Isolations from diseased leaves consistently yielded Epicoccum nigrum, but the role of this species is unclear. Inoculations of susceptible plants with E. nigrum conidia failed to reproduce symptoms, but inoculations with ascospores of A. populi produced symptoms typical of bronze leaf disease and Koch's postulates were performed.
An Epidemic of Almond Witches'-broom in Lebanon: Classification and Phylogenetic Relationships of the Associated Phytoplasma
Authors: Abou-Jawdah Yusuf , Karakashian Armig , Sobh Hana , Martini Marta , Lee Ing-Ming
Published: May 2007

An epidemic of almond witches'-broom has devastated almond production in Lebanon. Thousands of almond trees have died over the past 10 years due to the rapid spread of the disease. The symptoms, which include early flowering, stunted growth, leaf rosetting, dieback, off-season growth, proliferation of slender shoots, and witches'-brooms arising mainly from the main trunk and roots, resemble those caused by phytoplasmal infections. For the detection of the putative causal agent, nested polymerase chain reaction (PCR) was performed using universal primers (P1/P7, R16mF2/R16mR1, and R16F2n/R16R2) commonly used for the specific diagnosis of plant pathogenic phytoplasmas. Phytoplasmas were readily detected from infected trees with witches'-broom symptoms collected from three major almond growing regions in Lebanon. Restriction fragment length polymorphism (RFLP) analysis of PCR products amplified by the primer pair R16F2n/R16R2 revealed that the phytoplasma associated with infected almonds is similar to, but distinct from, members of the pigeon pea witches'-broom phytoplasma group (16SrIX). A new subgroup, 16SrIX-B, was designated. Sequencing of the amplified products of the phytoplasma 16S rRNA gene indicated that almond witches'-broom (AlmWB) phytoplasma is most closely related to members of the pigeon pea witches'-broom phytoplasma group (with sequence homology ranging from 98.4 to 99.0%). Phylogenetic analysis of 16S rDNA sequences from AlmWB phytoplasma and from representative phytoplasmas from GenBank showed that the AlmWB phytoplasma represents a distinct lineage within the pigeon pea witches'-broom subclade. The same phytoplasma appears also to infect peach and nectarine seedlings.
Evolution of Physiologic Races and Virulence of Puccinia striiformis on Wheat in Syria and Lebanon
Authors: Yahyaoui A. H. , Hakim M. S. , Naimi M. El , Rbeiz N.
Published: May 2007

Virulence-avirulence phenotypes of Puccinia striiformis isolates collected in Lebanon and Syria were determined on seedlings of the wheat-yellow rust differential genotypes. We found 25 and 11 physiologic races over 6 years (1994 to 1999) in Syria and Lebanon, respectively. The composition of physiologic races found in Syria and Lebanon differed greatly between 1994 and 1999. Races identified in 1999, such as 230E150 and 230E134, have wider spectra of virulence on resistant genotypes than races collected in 1994. In Lebanon, three races were found in 1994 compared with six races in 1999. Yellow rust differential genotypes were used in a trap nursery to monitor yellow rust populations under natural conditions. Races identified from cultivars in the trap nursery in Syria and Lebanon, and from land race cultivars in Iraq, were recovered among the races identified from farm fields. Yellow rust samples were collected from Yemen, and none of the races identified from Yemen samples were identical to those in Syria and Lebanon. Virulence frequencies in the yellow rust population on the differential genotypes tested in the trap nurseries were above 70% for some resistance genes. Yellow rust populations in Syria and Lebanon have diverse virulence phenotypes. P. striiformis populations appear to be changing over, and this would be an important consideration for wheat breeding programs in the region.
First Report of Albugo tragopogonis on Cultivated Sunflower in North America
Authors: Gulya T. J. , Viranyi F. , Appel J. , Jardine D. , Schwartz H. F. , Meyer R.
Published: May 2007

White rust, caused by Albugo tragopogonis (Pers.) S.F. Gray, was observed on a few plants of both oilseed and confection sunflowers (Helianthus annuus L.) in northwestern Kansas (Cheyenne County) in 1992. The disease was observed again from 1993 to1995 in nine counties in western Kansas, with incidence per field ranging up to 35%. White rust was found only on late-planted fields in 1996 and 1997 and was not found at all from 1998 to 2001. White rust was also observed on cultivated and wild sunflower (H. annuus) for the first time in eastern Colorado (Kit Carson and Yuma counties) from 1994 to 1997, but was absent from 1998 to 2001. Leaf pustules on both cultivated and wild sunflowers were similar in appearance. Pustules were convex, chlorotic on the upper side of the leaf, and concave and dull white on the under side of the leaf. Pustules on cultivated sunflower were generally limited to three to six leaves in the middle of the plant and affected 10 to 40% of the leaf area. Sporangial dimensions fell within the reported dimensions for A. tragopogonis (2). In 1997, water-soaked lesions 1 to 2 cm long containing oospores of A. tragopogonia were observed on the lower to middle portions of stems of cultivated sunflower in western Kansas and the adjacent area of Colorado. Stem lesions were observed much less frequently than foliar lesions and only in 1997. Sporangia were not observed in stem lesions, nor were any other fungi isolated from these lesions. To our knowledge, this is the first report of white rust occurring on cultivated sunflower in any production area of North America; the disease has not been observed in the major U.S. sunflower production area of North Dakota, South Dakota, and Minnesota. Foliar white rust lesions generally have little economic impact on sunflower, but the presence of stem lesions is significant because stem lesions may lead to lodging (3). Lodging due to A. tragopogonia was not observed in either Kansas or Colorado. White rust has previously only been reported on wild H. annuus in Wisconsin and on perennial Helianthus spp. in Missouri and Illinois (1).

References: (1) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN 1989. (2) K. G. Mukeri. Description of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK 1976. (2) P. S. van Wyk et al. Helia 22:83, 1995.
Iris yellow spot virus on Onion in Colorado
Authors: Schwartz H. F. , Brown W. M. , Blunt T. , Gent D. H.
Published: May 2007

A new disease was found in September 2001 on greenhouse-produced onion transplants of cv. Colorado 6 grown in a field in Larimer County in northern Colorado. Symptoms included straw-colored, dry, tan, spindle- or diamond-shaped lesions on the leaves and scapes of onion plants. Infected plants were scattered (less than 5% incidence) throughout the outer perimeter of the sprinkler-irrigated field. Iris yellow spot virus (IYSV) in two collections each with 4 to 6 symptomatic onion plants was confirmed with western blot assays by James Moyer of North Carolina State University. Western blot showed a faint band from protein extracts of infected Nicotiana benethimiana. Western blot assay is the most definitive method of identification. IYSV can be mechanically transmitted to N. benethimiana, but it cannot be recovered and transmitted back to onion, and it is difficult to detect in infected onion plants. IYSV is a tospovirus that is transmitted by various species of thrips, including onion thrips and western flower thrips (1). The host range for this disease includes onion, leek, and iris. IYSV has been reported previously on onion in Israel, Brazil, and Idaho (2). There are no reports that this disease affects bulb quality or marketability; however, heavy losses of onion bulb production are reported (1). University and industry personnel in other onion-growing areas of the country are encouraged to monitor onion and other host fields for evidence and distribution of IYSV.

References: (1) A. Kritzman et al. Plant Dis. 85:838, 2001. (2) L. Pozzer et al. Plant Dis. 83:345, 1999.