bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Cabbage leaf curl virus (Family Geminiviridae) in Georgia
Authors: Mandal B. , Langston D. B. , Pappu H. R. , Beard G. H. , Kucharek T. A. , Flanders J. T. , Whiddon J. P. , Smith J. E. , Kelley W. T.
Published: May 2007

Cabbage and collard greens were inflicted with a previously undescribed virus-like disease during the fall 2000. Symptoms on leaves were yellow spots, vein clearing, mosaic, curling, and puckering. Symptomatic plants were widespread in Brooks, Colquitt, Grady, and Pierce counties in Georgia. Disease incidence ranged from 10 to 20% in the majority of the fields surveyed but some fields had 100% incidence. Fields were heavily infested by Bemisia argentifolii and the symptoms were suggestive of a whitefly-transmitted geminivirus infection. A polymerase chain reaction (PCR)-based diagnostic test for geminivirus was conducted. Total DNA was extracted from symptomatic cabbage and collard green plants collected from commercial fields. The two primers, 5'-GCCCACATYGTCTTYCCNGT-3' and 5'- GGCTTYCTRTACATRGG-3' (2,3), are “universal” for genus Begomovirus of family Geminiviridae. The primer pair could amplify a part of the replicase-associated protein and coat protein and the complete common region of DNA-A. The PCR gave a DNA band of expected size (1.1 kb) from both symptomatic cabbage and collard green samples, whereas no such product was obtained from healthy samples, suggesting that the causal agent could be a geminivirus. To establish the identity of the virus, the 1.1 kb PCR product was cloned into pGEM-T Easy (Promega) and sequenced. GenBank search showed that the geminivirus isolated in Georgia was most closely related (98% sequence identity) to Cabbage leaf curl virus (accession number U65529) reported from Florida (1). The virus was mechanically transmitted to healthy cabbage and collard green plants under experimental conditions. To our knowledge, this is the first report of Cabbage leaf curl virus from Georgia.

References: (1) A. M. Abouzid et al. Phytopathology 82:1070, 1992. (2) S. S. Pappu et al. Plant Dis. 84:370, 2000. (3) M. R. Rojas et al. Plant Dis. 77:340–347, 1993.
Karnal Bunt of Wheat Newly Reported from the African Continent
Authors: Crous P. W. , Van Jaarsveld A. B. , Castlebury L. A. , Carris L. M. , Frederick R. D. , Pretorius Z. A.
Published: May 2007

In December 2000 seed harvested from wheat (Triticum aestivum L.) cultivars SST 876 and SST 825 produced under sprinkler irrigation near Douglas, Northern Cape Province, South Africa, contained a substantial amount of partially bunted kernels. Kernel embryos contained black masses of teliospores, and in many instances the endosperm was partially degraded. Teliospores were brown to dark brown, densely echinulate, 25 to 45 μm in diameter with a short mycelial fragment on some of the spores. Hyaline, smooth-walled sterile cells were also present. Teliospores were soaked in sterile distilled water for 2 days, streaked on 2% water agar plates and incubated at 22°C in the dark. Teliospores germinated after 5 days, producing 50 to 250 filiform, nonconjugating, primary basidiospores and forcibly discharged allantoid, secondary basidiospores. Based on kernel appearance, a rotten fish odor in infected grain, teliospore morphology, and germination characteristics, the pathogen was identified as Tilletia indica Mitra, the cause of Karnal bunt (1). This morphological identification was confirmed at the USDA-ARS Systematic Botany and Mycology Laboratory, Beltsville, MD. Molecular verification of 12 South African isolates was provided by the Foreign Disease-Weed Science Research Unit at Fort Detrick, MD, using real-time polymerase chain reaction with the Tin3/Tin10 T. indica-specific primer set (2). Four additional isolates were confirmed as T. indica using the same primer set as well as ITS rDNA sequencing at the Beltsville laboratory. Reference specimens were deposited at the National Fungal Collection in Pretoria, South Africa (PREM 57214), and at Beltsville (BPI 748170). At present, the mode of introduction of T. indica into South Africa, as well as its precise distribution, is not known. It appears, however, that the pathogen is restricted to the Douglas production area in the Northern Cape where quarantine measures have been taken to contain and possibly eradicate the disease.

References: (1) L. A. Castlebury and L. M. Carris. Mycologia 91:121, 1999. (2) R. D. Frederick et al. Phytopathology 90:951, 2000.
Rice Blast Epidemics Initiated by Infested Rice Grain on the Soil Surface
Authors: Long D. H. , Correll J. C. , Lee F. N. , TeBeest D. O.
Published: May 2007

Field experiments were conducted in 1996 and 1997 with a marked strain of Pyricularia grisea to determine if inoculum from infested rice grain could cause primary infections and sustain a rice blast epidemic during the growing season by giving rise to leaf, collar, and neck symptoms. The marked strain, a sulfate nonutilizing (sul) mutant of P. grisea, was grown on autoclaved rice seed for 7 days at 25°C. Infested rice grains were applied to the soil surface at the time of plant emergence (approximately 10 days after planting) at densities of 0, 0.5, 5, 25, and 50 grains per 0.1 m2 in plots planted to the blast susceptible cv. M-201. Leaf blast symptoms were first detected in the plots containing infested grain 35 days after plant emergence in both 1996 and 1997. The sul mutant was isolated from more than 90% of the lesions sampled from rice seedlings 35 to 45 days after plant emergence. Leaf blast increased more rapidly in plots with 25 and 50 infested grains per 0.1 m2 than in plots with less inoculum pressure (0.5 and 25 infested grains per 0.1 m2), although in 1996, leaf blast incidence recorded at midseason in plots containing 0.5 and 5 infested grains per 0.1 m2 was 41 and 55%, respectively. At the end of both seasons, the sul mutant was recovered from over 90% of the leaf, collar, and neck blast lesions except for one sample date in 1996. Rice blast was not detected in the control plots (no infested grain) in 1997 and not until 65 days after planting in 1996. Comparisons of disease progress on leaves between the marked strain and the parental wild-type strain under field conditions indicated that development of disease caused by the sul mutant was similar to disease caused by the wild-type strain.
Effect of Wirestem Severity on Survival and Head Production of Transplanted Broccoli and Cabbage
Authors: Keinath Anthony P. , Farnham Mark W.
Published: May 2007

Field experiments were conducted with transplants of Brassica oleracea with known severity levels of wirestem caused by Rhizoctonia solani anastomosis group 4. Seedlings of broccoli and cabbage were grown in steamed soil infested with R. solani at 5 to 25 sclerotia/kg. Two weeks after inoculation, plants were separated into five severity classes based on wirestem symptoms, then transplanted into fumigated field plots in the spring and fall of 1995. The percentage of plants with and without aboveground symptoms was assessed at 14 and 42 days after transplanting. Marketable-sized heads were harvested eight times. In both seasons, percentages of symptomless plants, surviving (symptomless plus symptomatic) plants, and plants producing a marketable-sized head decreased as wirestem severity increased. Only 33 and 29% of cabbage transplants with >75% of the stem circumference girdled survived and produced a marketable head, respectively, compared with 95 and 83% of healthy transplants, respectively. For broccoli, only 15% of transplants with girdled stems survived and produced heads in spring but, in the fall, 74 and 72% of transplants with girdled stems survived and produced heads, respectively. Percentage of plants producing a marketable-sized head was highly correlated (P = 0.0001) with percentage of symptomless plants at 14 days after transplanting and percentage of surviving plants at 42 days after transplanting.
Comparative Physical Modes of Action of Azoxystrobin, Mancozeb, and Metalaxyl Against Plasmopara viticola (Grapevine Downy Mildew)
Authors: Wong Francis P. , Wilcox Wayne F.
Published: May 2007

The physical modes of action of azoxystrobin, mancozeb, and metalaxyl were evaluated on grapevine seedlings using Plasmopara viticola as a model pathogen. The protectant, postinfection, postsymptom, translaminar, and vapor activities of azoxystrobin were evaluated at a rate of 250 μg/ml. Azoxystrobin provided 100% disease control when applied 1 to 5 days before inoculation. Postinfection applications of azoxystrobin had little effect on the incidence of disease, but colony area and sporulation from the resultant lesions was reduced by 47 and 96%, respectively, relative to the check treatment when applied up to 5 days after inoculation. Postsymptom applications (6 days after inoculation) of azoxystrobin resulted in an 85% mean reduction of resporulation from diseased tissue relative to the check when seedlings were evaluated 1 to 14 days after treatment. Translaminar activity was greatest when the upper surface of the leaf was treated 7 days before inoculation of the lower leaf surface (94% disease control). In contrast, control was <50% when leaves were similarly inoculated 1 and 3 days after treatment. Vapor activity was not pronounced, providing maximum reductions of 5, 11, and 37%, with regard to incidence, colony area, and sporulation, relative to the check when seedlings were treated 1 to 7 days before inoculating adjacent, untreated leaves. Comparatively, mancozeb (1,790 μg/ml) provided complete control of the disease when applied 1 to 5 days before inoculation, but showed little postinfection activity in reducing disease incidence, although it exhibited moderate to high antisporulant activity when applied in postinfection and postsymptom modes (mean reductions of 38 and 89%, respectively, compared with the check treatments). Metalaxyl (260 μg/ml) also provided complete control of the disease when used in protectant mode, and also when applied 1 day after inoculation. Applications at 3 to 5 days after inoculation provided substantial reductions in disease severity and sporulation (mean reductions of 46 and 94%, respectively, compared with the check treatments), and postsymptom applications resulted in a mean 84% reduction in resporulation. Collectively, the results of this study illustrate the unique physical modes of action for azoxystrobin in comparison to that of two traditional protectant and systemic fungicides, and provide information on how azoxystrobin and other strobilurin fungicides with similar physical modes of action should be best used in disease management programs.
Germination and Establishment of Infection on Grape Berries by Single Airborne Conidia ofBotrytis cinerea
Authors: Coertze S. , Holz G. , Sadie A.
Published: May 2007

Table grapes (cv. Dauphine) at different phenological stages were dusted in a settling tower with dry conidia of Botrytis cinerea. The berries were incubated for periods of 3 to 96 h at high relative humidity (RH; ±93% RH, moist berries), or were covered with a film of water (wet berries). Germination of the solitary conidia, appressorium formation, stilbene and suberin induction by germlings, and germling viability were examined by fluorescence microscopy after each incubation period. Isolation and freezing studies were conducted to determine surface colonization (berries left unsterile) and penetration (surface-disinfested berries). Symptoms were determined on berries incubated at a specific wetness regime, kept dry for 10 days, and then incubated for 4 days at high RH. Microscopic observations indicated that germination was delayed on immature berries, but proceeded at a high rate on mature berries. Growth was invariably restricted on moist berries. Attempted penetration was always direct. Stilbene and suberin were generally induced early and were intense on berries at the pea-size and bunch closure stages. Dieback of conidia and germlings occurred at a significantly higher rate on wet than moist berries, and was more pronounced on immature than on mature berries. The segment isolation and freezing studies showed that infections in grape berry cheeks established by this infection mode were few. Extended incubation periods did not lead to substantially higher rates of surface colonization and skin penetration. Disease symptoms did not develop during the 14-day period on the berries transferred to dry perspex chambers, irrespective of phenological stage, incubation period, or wetness regime. According to these findings, this mode of infection should not contribute to a gradual build-up of secondary inoculum in the vineyard, and to B. cinerea epiphytotics.
Occurrence and Pathogenicity of Puccinia hordei on Barley in South Africa
Authors: van Niekerk B. D. , Pretorius Z. A. , Boshoff W. H. P.
Published: May 2007

Although leaf rust, caused by Puccinia hordei, is considered an important disease of barley (Hordeum vulgare) and regularly reaches epidemic proportions, pathogenic variability has never been studied in South Africa. From 1994 to 1997, only one pathotype (SAPh 3231) was identified with virulence to resistance genes Rph1, Rph4, Rph5, Rph10, and Rph11. During 1998, a second pathotype (SAPh 7321) was identified, differing from pathotype SAPh 3231 only in virulence to Rph12. Pathotype SAPh 7321 increased rapidly in the area where it was first detected, resulting in localized epidemic outbreaks in 1999. The reactions of various South African cultivars and breeding lines toward these pathotypes were determined, and the presence of Rph12 was postulated for B93/4, Krona, Optic, Prisma, and SSG 532. Rph genes showed varying degrees of temperature sensitivity, with none of the known genes displaying major changes in their phenotypes except Rph8, which was less effective at higher temperatures. Eight accessions of two wild Hordeum spp. occurring abundantly in the barley growing regions were found to be either weak or nonhosts for P. hordei.
Disease Incidence—Inoculum Dose Relationships forBotrytis cinereaandPenicillium expansumand Decay of Pear Fruit Using Dry, Airborne Conidia
Authors: Spotts Robert A. , Cervantes Louis A.
Published: May 2007

The objective of this research was to determine quantitative relationships between incidence of pear fruit decay and inoculum dose of Botrytis cinerea and Penicillium expansum using dry conidia applied to wet or dry pears in a settling tower. On wet fruit, incidence of gray mold fruit rot increased from 0.1 to 83.1% as the airborne concentration of B. cinerea conidia increased from 0 to 8.6 spores per liter of air. Significantly less decay occurred in fruit inoculated dry compared to wet, particularly in fruit wounded after inoculation. Incidence of blue mold increased from 1 to 100% as the airborne concentration of P. expansum conidia increased from 0.1 to 803.5 spores per liter of air. Blue mold incidence was not affected by fruit wetness or time of wounding relative to inoculation. All regressions of decay incidence versus airborne and surface conidial concentrations were highly significant (P = 0.01).
A Blight Disease of Dill in California Caused by Itersonilia perplexans
Authors: Koike S. T. , Tjosvold S. A.
Published: May 2007

In 2000, a foliar disease was observed in commercial field plantings of dill (Anethum graveolens) in coastal California. Initial symptoms consisted of a gray-green discoloration and wilting of the tips of dill leaves. As disease developed, many of the leaves discolored and collapsed, which gave the foliage a blighted appearance and made the leaves unsuitable for harvest. A fungus was consistently isolated from symptomatic leaves. Slow growing colonies were cream-colored, velutinous, and flat with minimal aerial mycelium. Mycelium was hyaline and had clamp connections. Ovoid to subglobose sporogenous cells were abundant and measured 11 to 14 × 12 to 16 μm. Spores were ballistospores that were bilaterally symmetrical, lunate, 16 to 18 × 12 to 13 μm, and germinated with hyphae or secondary ballistospores. The fungus was identified as Itersonilia perplexans Derx (1,2). Pathogenicity was tested by preparing spore suspensions (1 × 104) and spray-inoculating potted dill plants. Plants were placed in a dew chamber for 24 h and then maintained in a greenhouse (23 to 25°C). After 10 days, leaves showed symptoms similar to those observed in the field and the same fungus was reisolated. Control plants sprayed with water did not develop symptoms. Inoculations were repeated and the results were the same. In another experiment, sets of dill plants and flowers of five cultivars of potted florist's chrysanthemum (Dendranthema × grandiflorum [= Chrysanthemum × morifolium]) and one cultivar of Leucanthemum paludosum (= C. paludosum) were spray-inoculated with several dill isolates and incubated as described previously. Dill plants developed symptoms and the fungus was reisolated. However, flowers of the six chrysanthemum cultivars did not develop any petal blight symptoms. Inoculations were repeated and the results were the same. These findings are consistent with previous studies that indicate I. perplexans consists of pathogenic forms that are host-specific to either chrysanthemum and closely related Compositae or to Apiaceae plants such as dill, carrot (Daucus carota subsp. sativus), parsley (Petroselinum crispum), and parsnip (Pastinaca sativa) (1,2,3). To our knowledge, this is the first report of I. perplexans on dill in California, and also appears to be the first record of this disease in North America.

References: (1) T. Boekhout. Mycol. Res. 95:135, 1991. (2) T. Boekhout et al. Can. J. Microbiol. 37:188, 1991. (3) A. G. Channon. Ann. Appl. Biol. 51:1, 1963.
First Report of a Phytoplasma Disease of Almond (Prunus amygdalus) in Lebanon
Authors: Choueiri E. , Jreijiri F. , Issa S. , Verdin E. , Bové J. , Garnier M.
Published: May 2007

During a survey conducted in October 1999 to establish the sanitary status of stone fruits in Lebanon, almond trees with symptoms of leaf yellowing, shoot proliferation, and dieback were observed in the Bekaa region. Because such symptoms are often associated with phytoplasma infections, samples were collected for analysis by PCR using universal primers for amplification of phytoplasma ribosomal RNA genes (2). DNA was extracted from the leaf midveins and/or bark phloem tissue from nine symptomatic trees and one symptomless tree in four different orchards as well as from healthy almond trees collected in France. PCR resulted in amplification of an expected 1.8 kbp rDNA fragment from all symptomatic samples but not from the healthy or symptomless samples. For characterization, the amplified DNA was analyzed by RFLP. Even though the restriction profiles were different from those published for other phytoplasmas and in particular from those infecting almond trees in Western Europe (1), sequence analysis of the amplified DNA revealed that it belongs to the pigeon pea witches' broom cluster (PPWB) (2). This is the first report of a phytoplasma infection in Lebanon and the first report for a PPWB group phytoplasma in almond trees.

References: (1) W. Jarausch et al. J. Plant Pathol. 104:17–27, 1998. (2) B. Schneider et al. 1995. Molecular and diagnostic procedures in Mycoplasmology Vol. 1, 369–380, S. Razin and J. G. Tully, eds.
Distribution and Transmission of Iris yellow spot virus
Authors: Kritzman A. , Lampel M. , Raccah B. , Gera A.
Published: May 2007

Iris yellow spot virus (IYSV), a new tospovirus associated with a disease in onion (Allium cepa) that is known to growers in Israel as “straw bleaching,” was identified and further characterized by host range, serology, electron microscopy, and molecular analysis of the nucleocapsid gene. The transmissibility of IYSV by Thrips tabaci and Frankliniella occidentalis was studied. IYSV was efficiently transmitted by T. tabaci from infected to healthy onion seedlings and leaf pieces. Two biotypes of F. occidentalis, collected from two different locations in Israel, failed to transmit the virus. Surveys to relate the incidence of thrips populations to that of IYSV were conducted in onion fields. They revealed that the onion thrips T. tabaci was the predominant thrips species, and that its incidence was strongly related to that of IYSV. Forty-five percent of the thrips population collected from IYSV-infected onion and garlic fields in Israel transmitted the virus. IYSV was not transmitted to onion seedlings from infected mother plants through the seed, and was not located in bulbs of infected plants.
Chlorine Concentration and the Inoculation of Tomato Fruit in Packinghouse Dump Tanks
Authors: Bartz J. A. , Eayre C. G. , Mahovic M. J. , Concelmo D. E. , Brecht J. K. , Sargent S. A.
Published: May 2007

Chlorine concentrations (pH 6 to 7 and 22 to 27°C) that killed arthrospores (spores) of Geotrichum candidum or sporangioles (spores) of Rhizopus stolonifer, causal agents of sour rot and Rhizopus rot, respectively, in moving water within 30 to 45 s did not prevent these pathogens from inoculating wounded tomatoes (Lycopersicon esculentum) in a water flume containing chlorine and spores. Free chlorine concentrations of 20 or 25 mg/liter were lethal to spores of G. candidum within 30 s in most in vitro tests, whereas spores of R. stolonifer were slightly less sensitive. Wounded tomatoes placed in a flume with free chlorine at 30 mg/liter and then exposed to spores for 1 min developed about 50% less decay incidence during storage at 24°C for 6 days than did fruit exposed to spores and water alone. In the absence of chlorine, incidence averaged 57% (range, 15 to 95%) for R. stolonifer and 38% (range, 17 to 58%) for G. candidum. Sporadic sour rot lesions were observed among fruit that had been treated with free chlorine at 75 mg/liter, whereas chlorine at up to 180 mg/liter failed to completely protect fruit from Rhizopus rot. A water-soluble dye rapidly penetrated wounds on tomato fruit. The dye framed the outlines of cells at the wound surface and appeared to penetrate into a few intercel-lular spaces. Application of 1% sodium hypochlorite decolorized the dye on the wound surface, whereas deposits located below the wound surface remained blue. Thus, spores suspended in moving water can escape the action of chlorine if carried into intercellular spaces by diffusion or by capillary movement of cell sap and water.
First Report of Turnip mosaic virus in Watercress in Mauritius
Authors: Gungoosingh A. , Beni Madhu S. P. , Dumur D.
Published: May 2007

In July 1999, leaf mosaic and distortions were observed on watercress in the region of Camp de Masque, in the eastern part of Mauritius. Electron microscopy of crude sap preparations revealed the presence of 720 nm, flexuous filamentous particles. Virus detection by reverse-transcription polymerase chain reaction (RT-PCR) and virus sequencing by A. Mackenzie (Research School of Biological Sciences, Australian National University) confirmed the identity of the causal pathogen as Turnip mosaic virus (TuMV) in November 1999. A survey was initiated in January 2000, covering the 44 major watercress ponds across the island. Two hundred seventy-five samples (231 symptomatic; 44 symptomless) were collected from 22 localities. TuMV was detected by double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) using commercial antisera (Agdia Inc.). Plant extracts were prepared by cutting approximately 20 g of leaf samples into small pieces, from which 1.0 to 1.5 g were used in the evaluation. Eighty-one percent of symptomatic samples (187 out of 231) were TuMV positive; all of the symptomless samples were TuMV negative. Symptoms on infected watercress included leaf mosaic, mottling, distortions, general yellowing, and plant stunting. TuMV has since been detected on all three commonly grown watercress varieties in Mauritius: Brède Doux, Brède Blanc, and Constance. Under local conditions, TuMV affects the quality and thus the commercial value of the crop. Additional hosts of TuMV among local brassicas are also being determined, and to date the virus has been detected in turnip (Brassica campestris spp. rapa), pak choi (Brassica campestris spp. chinensis), and petsai (Brassica campestris spp. pekinensis).
Stemphylium botryosum Pathogenic on Spinach Seed Crops in Washington
Authors: du Toit L. J. , Derie M. L.
Published: May 2007

In September 2000, symptoms typical of leaf spot caused by Cladosporium variabile were observed on a spinach (Spinacea oleracea L.) seed crop in western Washington. Dry, bleached spots (1 to 20 mm) were most abundant on lower leaves. Two isolates of C. variabile and three isolates of Stemphylium were recovered by plating surface-sterilized (0.1% sodium hypochlorite) sections of symptomatic leaf tissue onto water agar and acidified potato dextrose agar (PDA). Transfers of each isolate were made to PDA, and cultures were kept at 24 ± 2°C on a lab bench (natural day/night cycle) for 10 to 14 days. Spore suspensions (105/ml) of the isolates of C. variabile were prepared in a 0.01% solution of Tween 80. Isolates of Stemphylium produced few spores, so mycelial suspensions (105 fragments/ml) were prepared. Five 8-week-old seedlings of each of the cultivars Winter Bloomsdale and Ozarka II were inoculated per fungal isolate by atomizing the inoculum onto each seedling until all leaves were covered with a thin film of droplets (4 to 5 ml of inoculum per seedling). Plants were enclosed in plastic bags on a greenhouse bench (24 ± 3°C) for 72 h (8 h/16 h day/night). Symptoms developed within 80 h of inoculation for both isolates of C. variabile and two isolates of Stemphylium. Small (1 to 2 mm) sunken spots turned white 24 to 48 h later and became dry and bleached. Lesions caused by isolates of Stemphylium enlarged and coalesced more rapidly than lesions caused by C. variabile, and were more irregular and usually not delimited by the thin brown margin typical of lesions caused by C. variabile. The differences in symptoms were consistent on both spinach cultivars. Symptoms were not observed on non-inoculated control plants nor on plants inoculated with the third isolate of Stemphylium. C. variabile and Stemphylium were reisolated from symptomatic leaf tissue. Colony morphology, conidiophores, and conidia of the pathogenic Stemphylium isolates were similar to those of pathogenic isolates of Stemphylium botryosum obtained from spinach plants in California (2). This is the first report of S. botryosum as a foliar pathogen of spinach seed crops in Washington. Although Correll et al. (1) noted Stemphylium to be damaging on mature spinach plants grown for seed production, S. botryosum may not have been diagnosed previously on spinach seed crops in Washington because of the similarity of symptoms caused by S. botryosum and C. variabile. S. botryosum was recently reported as a foliar pathogen of spinach in California (2).

References: (1) J. C. Correll et al. Plant Dis. 78:653, 1994. (2) S. T. Koike et al. Plant Dis. 85:126, 2001.
First Report of Cryptocline taxicola Infecting Pacific Yew (Taxus brevifolia) in Eastern North America
Authors: Vujanovic Vladimir , St-Arnaud Marc
Published: May 2007

To our knowledge, this is the first report of Cryptocline taxicola (Allesch.) Petrak (Coelomycetes) on Pacific yew (Taxus brevifolia Nuttall) and the first observation of the fungus infecting living needles. C. taxicola is known to occur on needles of Taxus baccata in Europe (on T. baccata var. fastigiata) and North America (Vermont) (on T. baccata var. canadensis) (2). In August 1999 and 2000, chlorotic and necrotic current and second-year needles of Pacific yew were observed to have fruiting bodies, sometimes greater than 400 per needle, on the upper surface. Acervuli were circular to subcircular, yellowish, surrounded by brown circles, subcuticular to intraepidermal, at first covered, later exposed by the fissure of the cuticule, and 150 to 350 μm wide. Hyphae in host tissue were septate, brownish, and 3 to 4.5 μm in diameter. Conidiophores were phialidic, cylindrical, hyaline, 10 to 20 × 2.5 to 4.5 μm. Mature conidia were ellipsoidal to oval, truncate at the base, obtuse at the apex, hyaline to slightly pigmented, 8 to 17 × 4 to 5 μm. From these symptomatic needles, C. taxicola was often isolated (>85%) on potato dextrose agar. Koch's postulates were completed for C. taxicola by spraying current-year living needles, on one twig of each of separate plants (five) of T. brevifolia with a conidial suspension of 4 × 103 conidia per ml. Five control twigs were sprayed with sterile, distilled water. Twigs were covered with black sterile plastic bags and incubated outdoors for 24 h, when the bags were removed. Within 3 weeks, inoculated needles exhibited chlorotic and necrotic symptoms similar to those originally observed, but symptoms were never observed on control twigs. The fungus was reisolated (91%) only from the symptomatic needles. T. brevifolia trees growing in the Montreal Botanical Garden (Quebec, Canada) are clones originating from the Pacific Coast of the United States. We found that Pacific yew was colonized more frequently on the dry rock outcrops in the Alpine and Chinese Garden tree plantations. We believe that inappropriate stand selection, unfavorable humid conditions, and a thin organic soil layer may predispose Pacific yew to infection by this fungal species. A similar effect has been reported in Europe (1) for Cryptocline pseudotsugae causing serious levels of disease in a Pseudotsuga menziesii plantations.

References: (1) T. L. Cech. Forstschutz Aktuell. 25:13, 2000. (2) G. Morgan-Jones. Can. J. Bot. 51:309, 1973.
First Report of Meloidogyne partityla on Pecan in New Mexico
Authors: Thomas S. H. , Fuchs J. M. , Handoo Z. A.
Published: May 2007

For several years, decline was observed in mature pecan (Carya illinoensis (F.A. Wangenheim) K. Koch) trees in an orchard in Dona Ana County, New Mexico despite normal fertilization and irrigation practices. Affected trees were growing in sandy soil in two widely separated irrigation terraces and exhibited chlorosis of foliage and substantial die-back of branches in the upper canopy. Examination of feeder roots revealed the presence of numerous small galls and egg masses, with root-knot nematode females often visibly protruding from root tissue. Attempts to culture the nematode on tomato (Lycopersicon esculentum Mill. ‘Rutgers’) were unsuccessful. Females and egg masses were collected from fresh pecan roots and sent to the USDA Nematology Laboratory in Beltsville, MD, in October 2000, where specimens were identified as Meloidogyne partityla Kleynhans (1) based on morphological examination. This is the first report of M. partityla from New Mexico, and the second report of this nematode outside South Africa. Starr et al. (2) first reported M. partityla from pecan in the United States in 1996, after recovering the nematode from five orchards in Texas. In their study, the host range of M. partityla was limited to members of the Juglandaceae, which may explain the inability of the New Mexico population to reproduce on tomato. Additional information is needed regarding distribution of this nematode within pecan-growing regions throughout North America.

References: (1) K. P. N. Kleynhans. Phytophylactica 18:103, 1986. (2) J. L. Starr et al. J. Nematol. 28:565, 1996.
Detection of Cucurbit Yellow Vine Disease in Squash and Pumpkin in Massachusetts
Authors: Wick R. L. , Lerner J. , Pair S. D. , Fletcher J. , Mitchell F. , Bruton B. D.
Published: May 2007

Commercial plantings of summer squash in Charlemont, Franklin County, MA, were decimated in 1999 by 100% incidence of a yellowing disease resembling cucurbit yellow vine disease (CYVD) (1). Both plantings were established in the same field during the third week of May, one with transplants and the second by direct-seeding. Each planting consisted of four 30-m rows each of yellow zucchini (Cucurbita pepo cv. Gold Rush), summer squash (C. pepo cv. Seneca Prolific), and zucchini (C. pepo cv. Condor). Crops were produced organically and pyrethrum was used to control a high infestation of squash bugs, Anasa tristis (De Geer) (Heteroptera:Coreidae), a putative vector of CYVD (3). Just prior to fruit set, during the first two weeks of June, plants began showing symptoms of foliar chlorosis, plant stunting, or both. All of the plants in the field eventually wilted and collapsed. Cross-sections of the below-ground stem and primary root revealed a honey-brown phloem discoloration and healthy appearing xylem, symptoms characteristic of CYVD. Plants yielded marketable fruit for only about 1 week. When plant samples were tested by polymerase chain reaction (PCR) with CYVD bacterium specific primers (2), a band of the expected size for the CYVD bacterium, identified as Serratia marcescens based on 16s rDNA and groE sequence analyses (4), was amplified in every case. Since all plant samples collected were symptomatic and PCR positive for S. marcescens, asymptomatic greenhouse plants were run simultaneously as a control. All control plants tested negative. A third planting, similar to the two disease-affected plantings and containing the same three squash cultivars from the same seed lot, was established at about the same time approximately 3 km away. No symptoms of CYVD occurred at this site, further evidence that the pathogen is not seed-borne (1). Furthermore, squash bugs were not observed in this field. In 2000, the disease was observed in a planting of ‘Atlantic Giant’ pumpkin in Erving, Franklin County, MA, and confirmed by PCR. Until now, CYVD has been reported only in the states of Oklahoma, Texas, and Tennessee. Confirmation of the disease in Massachusetts significantly increases the known geographical range of CYVD to include the New England area.

References: (1) B. D. Bruton et al. Plant Dis. 82:512–520, 1998. (2) U. Melcher et al. Phytopathology 89:S95, 1999. (3) S. D. Pair et al. Pages 145–148 in: Proc. 19th Ann. Hort. Conf., Okla. State Univ. (4) J. Rascoe et al. Phytopathology 90:S63, 2000.
First Report of Aflatoxin in Dried Yam Chips in Benin
Authors: Bassa S. , Mestres C. , Champiat D. , Hell K. , Vernier P. , Cardwell K.
Published: May 2007

Dried yam (Dioscorea spp.) chips are widely consumed in Bénin but are often attacked by molds. Invasion of food by Aspergillus flavus may lead to aflatoxin contamination. We report here the result of a survey on the sanitary quality of dried yam chips in Bénin. During July and August 2000, 50 dried yam chips samples were collected from different points in the marketing chain; 10 samples were collected from each of 5 stages: producers, wholesalers, retailers, dried yam-based food sellers and consumers. Aflatoxin content was assayed by the bio-luminescence method (1) after methanol/water extraction. Aflatoxins were detected in all dried yam chip samples, with levels ranging from 2.2 to 200 ppb and a mean value of 14 ppb. An aflatoxin concentration higher than the European Union's maximum residue limit (MRL) of 4 ppb was found in 98% of the samples (N = 50), while 6% had an aflatoxin concentration higher than the World Health Organization's MRL of 20 ppb. Molds were analyzed from two samples, each with aflatoxin levels around 5 ppb, on colony unit medium specific for A. flavus (2). Aspergillus spp. were detected in the inner part of dried yam chips of both samples, with a mean level of 9,000 CFU/g. Fusarium colonies were also present but were not identified to species.

References: (1) D. Champiat and J. Larpent. Bio-chimie-luminescence: Principes et Applications. Masson, Paris, France. 1993. (2) P. J. Cotty. Mycopathologia 125:157, 1994.
Root Characteristics in Pea in Relation to Compaction and Fusarium Root Rot
Authors: Kraft John M. , Boge W.
Published: May 2007

Differences in pea root length, root surface area, and diameter were rapidly determined using the WinRhizo computer program. Repeatable differences were measured both in the laboratory and in the field. Large-rooted lines, as measured in the laboratory, also were the largest-rooted lines in the field. Large-rooted lines produced more roots and had more root surface area when exposed to a 1.6 g cm-3 bulk density compacted layer with the presence of the Fusarium root rot pathogen (Fusarium solani f. sp. pisi). Also, large-rooted lines regenerated more roots when one-third or two-thirds of the root system was removed or when one cotyledon was removed from 5-day-old plants. Large-rooted pea lines should have an advantage in growing under adverse conditions of compaction and the presence of Fusarium root rot.
Female Fertility and Single Nucleotide Polymorphism Comparisons in Cylindrocladium pauciramosum
Authors: Schoch Conrad L. , Crous Pedro W. , Polizzi Giancarlo , Koike Steven T.
Published: May 2007

Cylindrocladium pauciramosum is well established in South America, and has recently been collected from nurseries in South Africa, Italy, and the United States. Isolates were compared with respect to the percentages of hermaphrodites and the respective mating types in the different samples. Based on these data, the effective population size could be determined for the different areas studied. All nurseries had mating type ratios significantly different from an idealized 1:1 ratio. In the South African nursery, the MAT-1 mating type was dominant, while the MAT-2 mating type dominated in other samplings. This is consistent with an introduction of a small starter population. High percentages of hermaphrodites also agreed with recent introductions into nurseries in Italy and the United States. Variability of DNA sequences of the 5′ end of the β-tubulin gene from a set of C. pauciramosum isolates from different geographic regions was low to high. Isolates from South Africa, the United States, and Australia had identical β-tubulin DNA sequences; this sequence was also found in the Italian sample, along with another unique group. Finally, a group of isolates obtained from South and Central America had the highest variation of all isolates investigated, and also included isolates that shared single nucleotide variations with another species, C. candelabrum. These findings suggest that C. pauciramosum most likely has a Central or South American center of origin.
Effect of Microsphaeropsis sp. on the Production of Perithecia and Ascospores of Gibberella zeae
Authors: Bujold I. , Paulitz T. C. , Carisse O.
Published: May 2007

The potential of Microsphaeropsis sp. (isolate P130A) as an antagonist of Gibberella zeae was tested under in vitro and field conditions. Firstly, an in vitro method of ascospore production was developed on wheat and corn residues. The plant type (corn or wheat), residue type (straw/stalk or grain), and incubation conditions (closed or open) had a significant effect on ascospore production. Perithecia were more abundant on wheat and corn grain incubated under open conditions. On these two substrates, the application of Microsphaeropsis sp. significantly reduced ascospore production. On wheat, the antagonist had a significant effect when applied 2 weeks before (-2), at the same time (0), and 4 weeks after (+4) inoculation with G. zeae, with 1.73, 0.31, 1.11, and 1.36 log ascospores per cm2 for the control, -2, 0, and +4 weeks treatments, respectively. On corn, Microsphaeropsis sp. had a significant effect when applied 2 weeks before, at the same time, 4 weeks after, and 6 weeks after inoculation with G. zeae with 3.02, 0.23, 1.29, 2.35, and 2.22 log ascospores per cm2 for the control, -2, 0, +4, and +6 weeks treatments, respectively. When applied to crop residues in the field as postharvest or preplanting applications, Microsphaeropsis sp. had no effect on the pattern of perithecia maturation, but significantly reduced the number of perithecia produced on two sampling dates, May 1998 and July 1999. There is a potential to biologically reduce the initial inoculum of G. zeae; however, more work is needed to optimize the efficacy of the biocontrol agent.
Differentiation of Peanut Seedborne Potyviruses and Cucumoviruses by RT-PCR
Authors: Dietzgen Ralf G. , Callaghan Ben , Higgins Colleen M. , Birch Robert G. , Chen Kunrong , Xu Zeyong
Published: May 2007

Seedborne peanut viruses pose important constraints to peanut production and safe movement of germ plasm. They also pose a risk of accidental introduction into previously disease-free regions. We have developed reverse transcription-polymerase chain reaction (RT-PCR) assays based on identical cycling parameters which identified peanut stripe, Peanut mottle, Peanut stunt, and Cucumber mosaic viruses through production of specific DNA fragments of 234 bp, 327 bp, 390 bp, and 133 bp, respectively. Assay sensitivity in the picogram range was achieved. The two potyviruses and two cucumoviruses could be differentiated using duplex RT-PCR assays. These assays should be useful for testing peanut leaves or seeds for virus identification in epidemiological studies, seed testing or in post-entry quarantine.
First Report of Alfalfa mosaic virus in Physostegia virginiana
Authors: Cardin L. , Onesto J.-P. , Moury B.
Published: May 2007

Physostegia virginiana Benth. (false dragon head) is a perennial plant from the family Lamiaceae cultivated as an ornamental in gardens and for cut-flower production. In 2000, stunting of plants and yellow-to-brown ringspots on leaves were observed in cut-flower production in the Alpes Maritimes Department (southeast France). These symptoms greatly decreased the commercial value of the stems. The disease was attributed to Alfalfa mosaic virus (AMV) because extracts of infected plant tissues revealed typical bacilliform particles by electron microscopy, produced symptoms typical of AMV after inoculation of a range of previously described test plants (1), and reacted positively in enzyme-linked immunosorbent assays (ELISA) with antibodies raised to a tomato strain of AMV (from G. Marchoux, INRA, France). After isolation from single local lesions on Vigna unguiculata, the AMV isolate was multiplied in cv. Xanthinc tobacco, where it induced local and systemic ringspot symptoms. Infected Xanthinc plants served as sources of inocula for subsequent mechanical- and aphid (Myzus persicae)-transmission tests to healthy seedlings of P. virginiana (seeds from the botanic garden of Nancy, France; 36 plants for each inoculation procedure). Chlorotic and necrotic local lesions were observed in 25% of mechanically inoculated plants. Three months after inoculation, uninoculated leaves of all mechanically inoculated plants and 30.5% of aphid-inoculated plants tested positive for AMV based on ELISA. During the first year after inoculation, less than 10% of infected plants showed typical systemic symptoms. This proportion reached 40% during the second year. Recently, we observed similar symptoms in P. virginiana plants cultivated in public gardens in Intercourse (Pennsylvania), Toronto (Ontario, Canada) and Montreal (Quebec, Canada). Using ELISA, AMV was detected in symptomatic plants from these three additional locations.

Reference: (1) L. Cardin and B. Moury. Plant Dis. 84:594, 2000.
Prevalence and Ecological Association of Foliar Pathogens of Cucumber in North Carolina, 1996-1998
Authors: Peterson P. D. , Campbell C. L.
Published: May 2007

During the fall growing seasons of 1996-98, 5,400 leaves exhibiting leaf spots were collected from cucumber (Cucumis sativus L.) fields and microscopically examined to identify the organisms associated with these symptoms. Five fungal pathogens were associated with leaf lesions: Alternaria cucumerina, Colletotrichum orbiculare, Corynespora cassiicola, Didymella bryoniae, and Pseudoperonospora cubensis; D. bryoniae and C. orbiculare occurred most frequently. When pathogens were paired on five or more leaves, associations between pathogen pairs were tested for independence via a 2-by-2 contingency table χ2 analysis. In all, 66 two-way pathogen associations were tested. Of these, 39 associations were negative (occurred together less often than expected at random), 1 was positive (occurred together more often than expected at random), and, in 16 cases, the pathogens were not associated. An association between C. orbiculare and D. bryoniae occurred 24 times and, each time, the relationship was negative. This result, combined with different environmental requirements for infection, suggests that these pathogens either occupy different niches in the plant canopy or are antagonistic. No relationship between the cultivars grown or the fungicides applied and the pathogens isolated from specific field sites was found. Information on the dominant pathogens responsible for leaf spot epidemics in North Carolina's cucumber fields will be useful to target breeding and disease control strategies.
Reduced Fungicide Applications and Host Resistance for Managing Three Diseases in Pumpkin Grown on a No-Till Cover Crop
Authors: Everts Kathryne L.
Published: May 2007

Two recent changes in Maryland pumpkin production are (i) planting no-till into a cover crop with soil surface residue (70% of acreage) and (ii) adoption of cultivars with moderate resistance to powdery mildew. Pumpkin cultivar resistance to powdery mildew, planting method (no-till cover crop or conventional tillage bare ground), and fungicide schedules were examined for development of powdery mildew (caused primarily by Podosphaera xanthii), Plectosporium blight (Plectosporium tabacinum), and black rot (Didymella bryoniae), and pumpkin yield and quality. Fungicide application intervals were (i) nontreated, (ii) 7 days, (iii) 14 days, or (iv) 7 days early and 14 days late season. Pumpkin grown no-till on hairy vetch and hairy vetch plus rye cover crops had an average 36% less Plectosporium blight and 50% less black rot than those grown conventional tillage on bare ground. Powdery mildew was less severe on cv. Magic Lantern, which is moderately resistant to this disease, than on susceptible cv. Wizard. Regression equations to describe the impact of disease and treatment on pumpkin fruit number, weight, and peduncle quality (healthy, intact peduncles) were developed using three-stage least squares procedure. Powdery mildew caused the greatest reduction on fruit number, weight, and peduncle quality compared with other diseases. Plectosporium blight reduced fruit number in 1999 and 2000, and fruit weight and peduncle quality in 2000. Hairy vetch and hairy vetch plus rye cover crops resulted in greater fruit number (1,033 and 858 more marketable fruit/ha, respectively) than bare ground in 2000. Powdery mildew resistance (Magic Lantern) combined with pumpkin production on a cover crop resulted in lower levels of powdery mildew (average areas under the disease progress curve 1,474 versus 2,379), Plectosporium blight (average 5 versus 16% severity), and black rot (average 153 versus 217 symptomatic fruit/ha) compared with conventional production (Wizard on bare ground). A reduced fungicide schedule resulted in acceptable disease management, yield, and peduncle quality of Magic Lantern grown on a cover crop; Magic Lantern grown on a cover crop and sprayed every 14 days yielded the same as or more than Wizard grown on bare ground and sprayed weekly.