bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Rhizoctonia solani AG-7 on Cotton in Mississippi
Authors: Baird R. , Batson W. , Carling D. , Scruggs M.
Published: May 2007

During a field study of the soilborne mycobiota on cotton (Gossypium hirsutum L.) roots, Rhizoctonia solani Kühn AG-7 was isolated from dark brown lesions present on the tap, feeder, and secondary roots onto potato-dextrose agar (PDA) (34 g of medium per liter of distilled water). Isolate identification was confirmed using tester R. solani AG-7 isolates (Carling, University of Alaska) for comparison during anastomosis pairing. To confirm pathogenicity, six AG-7 isolates (65, 66, 67, 68, 69, 70) obtained from cotton roots were tested in a plant growth incubator (18–24°C) by mixing 2.5 ml of 2-week-old cornmeal sand inoculum (3 g cornmeal, 100 g sand, and 20 ml distilled water) with 500 ml of autoclaved soil into each of five replicate polystyrene pots (15 cm wide × 20 cm long) per isolate. Five control pots containing noninfested soil were added for comparison. Five seed of cv. Deltapine 50 were sown into each pot. For all six isolates, mean stand counts (ranging from 0 and 1.3 plants per pot) were significantly lower (P ≤ 0.05) compared with those of plants in noninfested pots (3.8 plants per pot) at 21 days after planting. Furthermore, when the roots of surviving seedlings were evaluated for disease severity, brown, discolored lesions were observed at the base of stems and on roots in infested pots for all six isolates. Six AG-7 cultures of the pathogen were reisolated from symptomatic tissues onto PDA. The experiment was repeated with similar results. This is the first report of AG-7 occurring in Mississippi.
Evaluation of Methyl Iodide for Control of Peach Replant Disorder
Authors: Eayre C. G. , Sims J. J. , Ohr H. D. , Mackey B.
Published: May 2007

Peach replant soils were fumigated with methyl bromide (MB) or methyl iodide (MI) at rates of 392 to 448 kg/ha. In two trials, peach tree growth in fumigated soil or in untreated soil was evaluated by measuring trunk diameter and weight of branches removed by pruning. In both trials, trunk diameter of trees grown in MB- and MI-fumigated plots was greater than trees in control plots (P ≤ 0.01). In both trials, weight of branches pruned from trees grown in fumigated plots was greater than branch weights from trees grown in control plots (P ≤ 0.01). Plots fumigated with MI did not differ from plots fumigated with MB in trunk growth, weight of branch prunings, or reductions in population densities of the nematode Paratylenchus. MI and MB appeared to be equally effective in controlling replant disorder.
Oospore Survival and Pathogenicity of Single Oospore Recombinant Progeny from a Cross Involving US-17 and US-8 Genotypes of Phytophthora infestans
Authors: Mayton H. , Smart C. D. , Moravec B. C. , Mizubuti E. S. G. , Muldoon A. E. , Fry W. E.
Published: May 2007

Oospores of Phytophthora infestans produced in vitro and in planta, from a cross between US-17 and US-8 genotypes, were exposed to a variety of environments and their survival was assessed. Additionally, the pathogenic characteristics of some resultant progeny isolates were assessed. Viability of oospores as measured by plasmolysis declined slightly over a period of 18 months whether they were stored in water at 4°C, in soil at 18°C, or in soil under natural field conditions. In comparison, viability as measured by germination was lower overall but appeared to increase after storage in soil. Oospores produced in planta were buried in the field in the fall of 1998, and were capable of infecting both tomato and potato leaflets when recovered in May 1999. Single oospore progeny (n = 53) from the in vitro cross were analyzed individually for genetic and pathogenicity characteristics. All 53 progeny tested for restriction fragment length polymorphisms with probe RG57 were hybrids. All but one progeny produced sporulating lesions on detached potato or tomato leaflets in growth chamber tests, but most lesions were smaller and developed more slowly than those produced by either parental isolate. In a further test of pathogenicity, under field conditions, none of a subset of 10 A2 progeny was capable of initiating a detectable epidemic in small plots of either potatoes or tomatoes.
Molecular Characterization of Vegetative Compatibility Group 4A and 4B Isolates of Verticillium dahliae Associated with Potato Early Dying
Authors: Dobinson K. F. , Harrington M. A. , Omer M. , Rowe R. C.
Published: May 2007

Forty isolates of Verticillium dahliae, collected from potato seed tubers and potato plants from various regions in North America and previously assigned to vegetative compatibility groups (VCGs) 4A or 4B, were characterized using molecular markers. The VCG 4A isolates were previously shown to be a highly virulent pathotype of potato and to interact synergistically with the root-lesion nematode Pratylenchus penetrans to cause potato early dying. All but one of the VCG 4A isolates characterized in this study lacked the subspecies-specific repetitive DNA sequence E18 and could be differentiated from the remaining isolates by restriction fragment length polymorphisms (RFLPs) in the nuclear rDNA and Trp1 loci. The E18 RFLP patterns of several VCG 4B isolates from Maine and New York were highly similar to those of VCG 4B isolates previously collected from potato and tomato fields in Ontario. The data presented here suggest that the molecular markers will be useful for the detection and classification of isolates of V. dahliae associated with potato early dying.
Selecting Resistance to Bipolaris sorokiniana and Fusarium graminearum in Intermediate Wheatgrass
Authors: Krupinsky J. M. , Berdahl J. D.
Published: May 2007

Forage yield and persistence of intermediate wheatgrass and pubescent intermediate wheatgrass can be adversely affected by foot rot caused by Fusarium graminearum, Bipolaris sorokiniana, or both. Putative B. sorokiniana- and F. graminearum-resistant plants were selected from both Reliant and Manska cultivars of intermediate wheatgrass to produce four populations. When plants from half-sib families that were selected for resistance were intercrossed and progeny subjected to subsequent selection cycles for B. sorokiniana and F. graminearum resistance, progressively higher percentages of putative resistant seedlings were found for three of the four selected populations compared to the original base populations. In cycle 3 of three populations, 7 to 91% of half-sib families with statistically higher seedling survival rates than the base populations were considered more resistant than the base populations. Thus, progressive improvement in seedling survival was realized for three populations selected for resistance using three cycles of recurrent phenotypic selection among and within half-sib families.
First Report of Sugarcane yellow leaf virus in Peru
Authors: Alegría O. M. , Chatenet M. , Girard J. C. , Saldarriaga S. A. , Nuget A. , Rott P.
Published: May 2007

Two sugarcane cultivars, H 50-7209 and H 32-8560, have exhibited unusual, severe leaf yellowing for more than 18 years at Agro Industrial Paramonga S.A. (AIPSA) in Peru. In 1999, these varieties occupied about 4,600 ha (74% of the cultivated area), and almost all fields showed these symptoms. Symptoms first appear on the upper third of the leaf blades, which turns light green to light yellow in young canes up to 6 to 8 months of age. Between 10 and 16 months of age, the symptoms are visible on the spindle and first to third visible dewlap leaves. Tips and margins of older leaves become necrotic, and leaves can turn completely necrotic as the necrosis progresses down the leaves. The abaxial surface of leaf midribs is rarely bright yellow, which differs from the characteristic symptom of yellow leaf syndrome caused by the Sugarcane yellow leaf virus (ScYLV) (1). The most severe symptoms occur when the leaves of stalks that flower turn completely yellow and die. Samples from 98 plants exhibiting different types of yellowing were collected from six commercial fields of cultivars H 50-7209 and H 32-8560 and the germ plasm collection (cultivars PCG 59-1609, Trojan, CP 48-103, CP 72-2086, Q 87, and PR 908) at Paramonga. Tissue blot immunoassay was used to detect ScYLV in the midrib of the top visible dewlap leaf using antiserum provided by B. E. L. Lockhart (University of Minnesota) (2). ScYLV was detected in all 49 commercial field samples and in 35 out of 49 germ plasm samples. All six cultivars of the germ plasm collection were found to be infected, but ScYLV was detected in only a few leaves of Trojan and CP 72-2086. Eighteen cuttings from diseased stalks of cultivars H 50-7209 and H 32-8560 were grown in a greenhouse in Montpellier, France. Yellowing of the underside of the midribs and of the leaf tips appeared after 3 months in cultivar H 50-7209 but only after 9 months in cultivar H 32-8560. At 9 months, the top leaf with a visible dewlap and the four leaves immediately below it of cultivar H 50-7209 exhibited severe yellowing. Reverse transcription polymerase chain reaction with specific ScYLV primers, provided by M. S. Irey (U.S. Sugar Corp., Clewiston, FL) were used to detect ScYLV in the top visible dewlap leaf (1), and ScYLV was found in all nine samples taken from 6-month-old plants of the two cultivars. This is the first report of ScYLV in Peru.

References: (1) J. C. Comstock et al. Sugar Cane 4:21, 1998. (2) S. Schenck et al. Sugar Cane 4:5, 1997.
First Report of Leaf Blight of Dianthus chinensis Caused by Rhizoctonia solani
Authors: Holcomb G. E. , Carling D. E.
Published: May 2007

Dianthus chinensis (rainbow pink) is a popular seasonal bedding plant for the Gulf Coast of the United States and is primarily grown during the fall, winter, and early spring months. In August 1999, diseased plants were observed in a Baton Rouge, LA, propagation nursery with irregularly oval, tan leaf spots 3 to 10 mm in diameter. Heavily infected leaves became blighted and were killed, but plants survived and roots, crowns, and flowers were not affected. Infected leaf samples were surface-disinfected for 1 to 3 min in 70% ethyl alcohol, blotted dry, and sections were placed on 2% acidified water agar. A fungus that was identified as Rhizoctonia solani, and belonging to anastomosis group (AG)-1 IB, was consistently isolated from infected leaves. Inoculum was prepared by blending one 7-day-old plate culture, grown on acidified potato-dextrose agar, in 100 ml distilled deionized water. Pathogenicity tests were performed by dripping inoculum from a 10-ml pipette on leaf surfaces of healthy rainbow pink plants. Inoculated and noninoculated plants were held in a dew chamber at 26°C for 2 to 3 days and then removed to a greenhouse where temperatures ranged from 25 to 32°C. Inoculated plants developed water-soaked spots after 2 to 3 days that turned tan and became necrotic 5 to 10 days later. These symptoms were like those observed on the original diseased plants. R. solani was reisolated from inoculated plants, and noninoculated plants remained healthy. Although R. solani has been reported previously as a root and stem pathogen of D. chinensis (1), this is the first report of leaf blight disease caused by this fungus.

Reference: (1) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN.
First Report of Colletotrichum gloeosporioides on Chinese Rose in Argentina
Authors: Rivera M. C. , Wright E. R. , Carballo S.
Published: May 2007

Chinese rose (Hibiscus rosa-sinensis L.) is a shrub frequently planted in Argentina. In November 1999, dieback and anthracnose symptoms were detected on stems and leaves of plants cv. Hawaii cultivated in Buenos Aires. Disease prevalence was 50%. Pieces of infected tissues were surface-sterilized for 1 min in 2% NaOCl, plated on potato-dextrose agar and incubated at 24 ± 2°C. The isolate that was consistently recovered from diseased tissues was identified as Colletotrichum gloeosporioides (Penz.) Penz. and Sacc., based on morphological characteristics (1,2). Teleomorph stage was not observed. Inoculation for pathogenicity testing was carried out by spraying a conidial suspension (6.5 × 106 conidia per ml) on plants with previously punctured leaves and pruned stems. Inoculated plants with unwounded tissues, as well as noninoculated controls, were included. Five replications of each treatment were done. Plants were incubated in moist chambers at 24°C. Whitish areas of 0.3 to 0.5 cm diameter surrounded by a purple halo developed on all punctured leaves within 10 days. Stem blight and leaf drop were observed. The center of the lesions was covered by black acervuli 14 days after inoculation. Unwounded and noninoculated controls remained symptomless. The pathogen was reisolated from inoculated leaves, completing Koch's postulates. This is the first report of C. gloeosporioides causing disease on Chinese rose in Argentina.

References: (1) J. A. Bailey and M. J. Jeger, eds. 1992. Colletotrichum. CAB International, Surrey, England. (2) B. C. Sutton. 1980. The Coelomycetes. CMI, Kew.
Aspergillus Colonization and Aflatoxin Contamination in Peanut Genotypes with Reduced Linoleic Acid Composition
Authors: Holbrook C. Corley , Wilson David M. , Matheron Michael E. , Hunter John E. , Knauft David A. , Gorbet Daniel W.
Published: May 2007

Aspergillus flavus and A. parasiticus can contaminate several agricultural crops with the toxic fungal metabolite aflatoxin. Previous research has indicated that resistance may be conferred by altering the fatty acid composition of these crops. Recently, peanut breeding lines with reduced linoleic acid content have been developed. The purpose of this study was to examine the effect of reduced linoleic acid composition on preharvest aflatoxin contamination of peanut. Seven breeding lines with relatively low linoleic acid and two check genotypes were grown in a randomized complete block design with 10 replicates for 4 years in Georgia and for 3 years in Arizona. The plots were inoculated with a mixture of A. flavus and A. parasiticus about 60 days after planting and subjected to drought and heat stress for the 40 days immediately preceding harvest. Differences were observed in only one environment. Low linoleic acid composition had no measurable effect on preharvest aflatoxin contamination in peanut when data were combined across years and locations. Products of the lipoxygenase pathway that have been shown to affect aflatoxin biosynthesis in vitro may not be present in sufficient quantities in peanut.
Occurrence of a Strain of Texas pepper virus in Tabasco and Habanero Pepper in Costa Rica
Authors: Lotrakul Pongtharin , Valverde Rodrigo A. , De La Torre Rodolfo , Sim Jeonggu , Gomez Alvaro
Published: May 2007

A viral disease causing severe leaf malformation and yellow mottle on Tabasco (Capsicum frutescens) and Habanero (C. chinense) pepper plants was observed in 1997 on farms in southwestern Costa Rica. Whiteflies (Bemisia tabaci) were present on affected farms and transmitted the putative virus. Total DNA was extracted from a whitefly-transmitted isolate, and polymerase chain reaction (PCR) was performed using degenerate primers. The expected PCR product (550 bp) was obtained, suggesting the presence of a geminivirus. This was confirmed by Southern analysis using a geminivirus-specific probe. The virus was mechanically transmitted from pepper to pepper. Electron microscopy of ultrathin sections from infected Tabasco pepper plants revealed fibrillar rings and viruslike particles in the nucleus of the vascular parenchyma cells. The sequence of DNA A was obtained from three overlapping PCR fragments amplified using three pairs of degenerate primers; PAL1v1978/PAR1c496, PCRc1/AV494, and PCRv181/ AC1048. The complete sequence of DNA A of this begomovirus consisted of 2,619 bp (GenBank accession number: AF149227) containing four open reading frames (ORF). The nucleotide sequence of the virus was 92.3% identical to DNA A of the Tamaulipas strain of Texas pepper virus (TPV-TAM). Phylogenetic analyses using AC1 and AV1 nucleotide sequences also indicated a close relationship between this virus and TPV. Based on the biological characteristics, the high percentage of nucleotide and derived amino acid sequence identities, and phyloge-netic analyses, we concluded that this virus is a distinct strain of TPV, and designated it as the Costa Rica strain. This is the first report of TPV in Costa Rica.
Effect of Fenarimol Application Timing on Fruit Shape of Bartlett Pear
Authors: Sugar David , Spotts R. A. , Gubler W. D. , McGourty Glenn T.
Published: May 2007

Plots were established at Ukiah and Davis, California, and Medford and Hood River, Oregon, to evaluate the effect of fenarimol (Rubigan 1 EC), applied at various stages of bloom development, on fruit shape of Bartlett pear. At each location, 10 different treatment schedules were applied at various combinations of bud burst (BB), green cluster (GC), white bud (WB), and full bloom (FB). In schedules that included an application at FB, the fruit length:diameter (L/D) ratio was significantly reduced in at least three of four locations when compared to untreated controls. When fenarimol was applied at BB, GC, WB, and FB, the L/D ratio was reduced at all locations. Treatment at BB only did not affect L/D ratio. Schedules involving GC or WB, but not FB, resulted in reduced L/D ratios at only one or two locations. When data from all four locations were combined, L/D ratios were significantly reduced by all fenarimol treatments except BB alone, and the smallest L/D ratios resulted from treatments which included applications at both WB and FB. Fruit stem length was significantly reduced by all timings of fenarimol application except GC at Medford, and all timings except BB and GC at Ukiah. Fruit weight did not differ among treatments.
First Report of Sclerotium rolfsii on Catharanthus roseus
Authors: Holcomb G. E.
Published: May 2007

Wilt, blight, and stem necrosis were observed on Catharanthus roseus (L.) G. Don ‘Mediterranean Deep Rose’ (MDR) plants (Madagascar or rose periwinkle) in August 1999 at Burden Research Plantation in Baton Rouge, LA. MDR was the only prostrate-form cultivar and the only cultivar of 11 that was diseased. Twelve of twenty-four plants of cv. MDR were killed in the trial planting. White mycelia and small (1 mm diameter) light brown sclerotia were present at the base of infected plants. The suspect fungus was isolated consistently on acidified water agar and maintained on acidified potato dextrose agar (APDA). Pathogenicity tests were done by pipetting 1 ml of blended inoculum (contents of one 7-day-old plate culture grown on APDA in 100 ml of deionized water) at the base of nine 15-cm-tall Madagascar periwinkle plants. Inoculated and noninoculated plants were held in a dew chamber for 3 days at 28°C and placed in a greenhouse where temperatures ranged between 25 and 31°C. All inoculated plants showed wilt, blight, and basal stem rot after 3 days and were dead after 10 days. Noninoculated plants remained symptomless. The fungal pathogen was identified as Sclerotium rolfsii Sacc. and was reisolated from inoculated plants. The fungus was previously reported on Lochnera rosea (L.) Rchb. (=C. roseus) from Taiwan (1). This is the first report of the occurrence of S. rolfsii on Madagascar periwinkle in the United States.

Reference: (1) K. Goto. Trans. Nat. Hist. Soc. Formosa 23:37, 1933.
First Report of Petunia vein clearing virus in Israel
Authors: Gera A. , Sikron N. , Cohen J. , Zeidan M.
Published: May 2007

Petunia vein clearing virus (PVCV), a possible member of the cauli-movirus group, was detected in several cultivars of vegetatively propagated petunias grown in commercial nurseries in Israel. Symptoms associated with PVCV infection in petunia cv. Chaplin consisted of stunted young shoots, leaf yellowing, and severe vein clearing. Virus incidence within this cultivar was 40 to 60%. Symptoms were most frequently expressed when plants were subjected to temperatures above 20°C and nutrient deficiencies. The virus was transmitted to petunia only by grafting, however, not by aphids or mechanical inoculation. Leaf dip preparations and thin sections of leaf tissue were analyzed by transmission electron microscopy. Spherical virus particles (45 to 50 nm diameter) were observed in samples from symptomatic petunia plants. In immunoelectron microscopy, the virus particles produced a distinct pattern with the specific antiserum against PVCV provided by D. Lesemann (Biologische Bundesanstalt, Braunschweig, Germany). Infection with PVCV also was confirmed by polymerase chain reaction with total nucleic acid extract preparations. Two primer pairs—5′-GAGGTCAGAGCAAGTCAGAGG-3′ (nucleotides 4339 to 4359) and 5′-GTAATGATTTGACTTGTTGAG-3′ (nucleotides 5055 to 5075)—were designed to flank a 736-bp sequence in the RNA-dependent RNA polymerase gene of the PVCV genome (GenBank Accession no. U95208). A DNA fragment of the predicted size was visualized in agarose gels. Authenticity of the amplified DNA fragment was confirmed by restriction analysis. The virus has been detected in the past in Germany (1) and recently in the United States (2). This is the first report of PVCV in commercial nurseries in Israel.

References: (1) D. Lesemann and R. Casper. Phytopathology 63:1118, 1973. (2) B. Lockhart and D. Lesemann. Plant Dis. 82:262, 1998.
Expansion of the European Race of Gremmeniella abietina in Newfoundland, Canada
Authors: Harrison K. J. , Hurley J. E. , Warren G. R. , Laflamme G.
Published: May 2007

Since its detection on ornamental pines in St. John's, Newfoundland, Canada, in 1979 (3), the European race causing Scleroderris canker (Gremmeniella abietina (Lagerb.) Morelet) has been detected throughout the Avalon Peninsula at the eastern end of the province. A quarantine was established on the Avalon Peninsula in 1980 to reduce the risk of introducing the disease to the natural red pine (Pinus resinosa Aiton) stands on the remainder of the island. Scots, red, and jack pines were examined at 34 locations in Newfoundland in 1998 and 1999. Infected trees were detected at four locations outside the quarantine zone. In the fall of 1998, the disease was found in plantations at three locations outside the quarantine zone: on Scots pine (P. sylvestris L.) at Bonavista and Catalina (≈135 km north-northeast of the quarantine) and on jack pine (P. banksiana Lamb.) and Scots pine at Sunnyside on Trinity Bay (≈45 km northwest of the quarantine). In 1999, the disease was detected at a fourth location on planted Scots pine in Come By Chance, near the Sunnyside location. Cultures of the pathogen were recovered from branch samples collected at each location and submitted for race determination at the Laurentian Forestry Centre, Sainte-Foy, QB. All isolates were determined based on the polymerase chain reaction diagnostic technique (1) to be the European race of G. abietina. This is a significant range extension from that reported by Laflamme et al. (2). The infected trees originated from the former Back River tree nursery at Salmonier Line that provided planting stock for a provincial reforestation program between 1937 and 1952. Evidence suggests that this nursery was the source of infected stock for plantations at nine locations within the Avalon Peninsula quarantine zone and the four new locations detected during the 1998 and 1999 surveys. This is similar to the pattern described for other nurseries in eastern Canada and the United States (2). The presence of the European race of G. abietina outside of the Avalon Peninsula increases the risk that the disease will become established in the rare natural red pine stands on the rest of the island of Newfoundland.

References: (1) R. C. Hamelin et al. Appl. Environ. Microbiol. 59:1752, 1993. (2) G. Laflamme et al. For. Chron. 74:561, 1998. (3) P. Singh et al. Plant Dis. 64:1117, 1980.
First Report of St. John's-Wort Anthracnose Caused by Colletotrichum gloeosporioides in Switzerland
Authors: Debrunner N. , Rauber A.-L. , Schwarz A. , Michel V. V.
Published: May 2007

In Switzerland, the increase in St. John's-wort (Hypericum perforatum L.) production was accompanied by the appearance of anthracnose caused by Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. The disease was first observed in 1995. In 1999, most of the 20 ha of St. John's-wort planted in Switzerland were grown organically, at an average gross income per hectare per year of 30,000 U.S. dollars. Anthracnose can destroy this perennial crop in the first year of cultivation, especially when it is grown in more humid areas and heavy soils. The restriction of fungicide use in organic farming can lead to a complete loss of the crop in such cases. Typical symptoms observed in the field were brown, sunken stem-girdling lesions and the reddish color of infected plants. In a later stage, aerial plant parts dried completely causing death. Acervuli that formed on stem lesions were sparsely setose. No saete occurred when the pathogen was grown on potato dextrose agar and ascospores of the teleomorph Glomerella cingulata (Stoneman) Spauld. & Schrenk were observed. Strain AN16 was sent to CABI Bioscience Identification Services (Egham, U.K.) who confirmed our identification. A conidial suspension (107 spores per ml) of AN16 was prepared and used to inoculate two St. John's-wort accessions, Hp 7 and Hp 9. Inoculation occurred under highly conducive conditions in the greenhouse. Symptoms developed on all infected plants 1 week after inoculation. One week later, the more susceptible Hp 9 was killed, whereas the more resistant Hp 7 showed only occasional stem lesions. Koch's rules were completed by reisolating the pathogen from infected plants.
Occurrence and Pathogenicity of Fungi Associated with Melon Root Rot and Vine Decline in California
Authors: Aegerter B. J. , Gordon T. R. , Davis R. M.
Published: May 2007

The occurrence of fungi associated with root rot and vine decline of melon (Cucumis melo) in commercial fields in California was surveyed over 3 years. The fungi most frequently isolated from discolored vascular tissue or root rot were Acremonium cucurbitacearum, Rhizopycnis vagum, Monosporascus cannonballus, Fusarium solani, Macrophomina phaseolina, Pythium spp., and Verticillium dahliae. The frequency of isolation of the various fungi varied with root symptomology. Pythium spp., and M. phaseolina were frequently associated with a wet, brownish root rot, while A. cucurbitacearum, R. vagum, and Rhizoctonia solani were generally associated with a dry, corky root rot. Presence of Monosporascus cannonballus was associated both with a wet, brownish rot as well as with discrete, reddish, corky lesions. The frequency of isolation of a given pathogen varied with geographic location, with M. cannonballus present only in the southern production areas, while A. cucurbitacearum and Rhizopycnis vagum were most common in the northern production areas. In pathogenicity tests in field microplots, M. cannonballus caused vine collapse and severe root rot of cantaloupe, reducing root length density by 93%. California isolates of R. vagum and A. cucurbitacearum, although only weakly pathogenic in field microplots, caused root discoloration and reduced vine growth in greenhouse tests. Reduction in dry weight of greenhouse-grown cantaloupe was 40, 23, and 39% for R. vagum, A. cucurbitacearum, and M. cannonballus, respectively.
Application of Candida saitoana and Glycolchitosan for the Control of Postharvest Diseases of Apple and Citrus Fruit Under Semi-Commercial Conditions
Authors: El-Ghaouth Ahmed , Smilanick Joseph L. , Brown G. Eldon , Ippolito Antonio , Wisniewski Michael , Wilson Charles L.
Published: May 2007

The efficacy of the combination of Candida saitoana with 0.2% glycolchitosan (the bioactive coating) as a biocontrol treatment of postharvest diseases of apple and citrus fruit was evaluated in tests with natural inoculations that simulated commercial packinghouse conditions. The growth of C. saitoana in apple wounds and on fruit surfaces was not affected by glycolchitosan. The bioactive coating was more effective in controlling decay of several cultivars of apples (Red Delicious, Rome, Golden Delicious, and Empire) than either C. saitoana or 0.2% glycolchitosan alone. Depending on the apple cultivar used, the bioactive coating was comparable or superior to thiabendazole in reducing decay. The bioactive coating was also superior to C. saitoana in controlling decay of oranges (cvs. Washington navel, Valencia, Pineapple, and Hamlin) and cv. Eureka lemons, and the control level was equivalent to that with imazalil. The bioactive coating and imazalil treatments offered consistent control of decay on Washington navel oranges and Eureka lemons in early and late seasons, while C. saitoana or 0.2% glycolchitosan were most effective on early-season fruit. The combination of C. saitoana with 0.2% glycolchitosan also reduced the incidence of stem-end rot of cv. Valencia oranges, but control was less effective than treatment with imazalil.
Condition of Green Ash, Incidence of Ash Yellows Phytoplasmas, and Their Association in the Great Plains and Rocky Mountain Regions of North America
Authors: Walla J. A. , Jacobi W. R. , Tisserat N. A. , Harrell M. O. , Ball J. J. , Neill G. B. , Reynard D. A. , Guo Y. H. , Spiegel L.
Published: May 2007

About 50% of 1,057 green ash (Fraxinus pennsylvanica) systematically sampled in the Great Plains and Rocky Mountain regions had substantial dieback (>10% of crown branches with dieback), and the average growth ring width during the last 20 years was 2.9 mm. The overall condition of the population was rated fair. Ash yellows phytoplasmas were identified at 102 of 106 sites throughout six U.S. states (North Dakota, South Dakota, Wyoming, Nebraska, Colorado, Kansas) and three Canadian provinces (Alberta, Saskatchewan, Manitoba). These phytoplasmas had not previously been known in Alberta, Saskatchewan, Manitoba, Wyoming, Colorado, or Kansas. Incidence of phytoplasmal detection ranged from 16% in Wyoming to 71% in South Dakota. Incidence varied in the range 41 to 67% across site types and crown dieback classes. Incidence was highest in rural plantings, in trees with the most crown dieback, and in larger diameter trees. No significant relationships were detected between presence of ash yellows phytoplasmas and radial growth rates of trees.
Stability in Population of Phytophthora infestans Attacking Tomato in Ecuador Demonstrated by Cellulose Acetate Assessment of Glucose-6-Phosphate Isomerase
Authors: Erselius Lynn J. , Vega-Sánchez Miguel E. , Forbes Gregory A.
Published: May 2007

Cellulose acetate electrophoresis was used to examine glucose-6-phosphate (Gpi) isomerase banding patterns of the population of Phytophthora infestans attacking tomato in Ecuador. All but two of 160 sporulating lesions from tomato leaflets collected from 25 tomato fields between January 1998 and March 1999 produced the 86/100 Gpi isozyme electromorph. This isozyme type is characteristic of the US-1 clonal lineage, indicating that no change in the population of P. infestans attacking tomato in Ecuador has occurred since a more exhaustive study was done using isolates collected between 1993 and 1995. The two lesions that produced a different Gpi electromorph in the current study came from a field that was located approximately 80 m from a potato field that had been severely affected by late blight. These two isolates produced a single large band for Gpi with a relative migration distance of 100. This electromorph is characteristic of the clonal lineage EC-1, which was shown previously to be the predominant clonal lineage attacking potato in Ecuador. Therefore, we assume that the two tomato lesions with the EC-1 phenotype were caused by inoculum originating from the potato field. During the current study, 34 infected potato leaflets were collected from five potato fields found in close proximity to blighted tomato fields. All of the potato leaflets produced banding patterns characteristic of EC-1. Our data are consistent with earlier studies indicating that, in Ecuador, tomato and potato are attacked by separate populations of P. infestans, which belong to two different clonal lineages.
First Report of Pseudomonas syringae pv. tomato Race 1 on Tomato in California
Authors: Arredondo C. R. , Davis R. M.
Published: May 2007

Symptoms of bacterial speck have occurred sporadically in California since 1993 on tomato (Lycopersicon esculentum) cultivars that possess the PTO gene for resistance to Pseudomonas syringae pv. tomato race 0. In 1998, the disease was found on numerous cultivars resistant to race 0 in fields throughout the Sacramento Valley. In several fields, it caused severe defoliation of tomato seedlings. Symptoms included dark brown to black leaf and stem lesions surrounded by yellow halos. Seven isolates were identified as P. syringae pv. tomato based on analysis of whole cell fatty acids (MIDI, Newark, DE; similarity indices of 0.746 to 0.710), carbon utilization profile (Biolog, Hayward, CA; similarity indices of 0.556 to 0.840), and LOPAT results: levan production (+), oxidase reaction (-), potato soft rot (-), arginine dihydrolase production (-), and tobacco hypersensitivity (+) (2). The isolates were identified as race 1 by inoculating greenhouse-grown tomato plants of cv. Ontario 7710, which possesses the PTO gene, and cv. H1916, which is susceptible to both known races of P. syringae pv. tomato. At least eight plants of each cultivar were inoculated with each isolate. Plants were inoculated by spraying leaves with a bacterial suspension mixed with Carborundum or puncturing leaves with needles dipped in the bacterial suspension (107 cells per ml). Controls were inoculated with water. All plants inoculated with the bacteria developed speck symptoms in 6 days. The bacteria were reisolated from all inoculated plants and confirmed as strains of P. syringae pv. tomato. This is the first documentation of P. syringae pv. tomato race 1 in California. This race was previously reported in Canada in 1986 (1).

References: (1) M. B. Lawton and B. H. MacNeill. Can. J. Plant Pathol. 8:85, 1986. (2) R. A. Lelliott et al. J. Appl. Bacteriol. 29:470, 1966.
First Report of Trunk Blight and Canker of Morus alaba var. pendula Caused by Fusarium lateritium f. sp. mori in Hungary
Authors: Vajna L.
Published: May 2007

Morus alba var. pendula (mulberry) is a favorite ornamental tree in Hungary. In 1998 and 1999, a canker disease was observed on this species in a western Hungarian ornamental tree nursery in Köszeg. Bark necrosis and cankers exposing the xylem were observed on the trunks of 1-, 2-, and 3-year-old trees. Pink sporodochia 200 to 400 μm in diameter were found in the necrotic bark. The fungus associated with the trunk cankers was identified as Fusarium lateritium Nees:Fr. f. sp. mori (Desmaz.) Matuo & K. Sato (1) from sporodochia and fungal isolates recovered from necrotic tissues. Isolations on potato dextrose agar yielded white colonies with a slight pink discoloration. Radial colony growth rate at 22°C and 12 h of light daily was 5 mm. Macroconidia were typical of F. lateritium, with three to eight septa. Microconidia were not observed. Intercalary chlamidospores (7 to 8 μm) rarely formed. Pathogenicity of the fungus was confirmed with a monoconidial culture. Three-year-old mulberry tree stems were inoculated with mycelial agar plugs. After 10 days, sunken necrotic lesions with a brownish discoloration, similar to naturally occurring cankers, developed. F. lateritium was successfully recovered from these lesions. No necrosis developed around control wounds. Mulberry Fusarium stem blight and canker is found in many temperate regions (2) but was not recorded as a disease of M. alba var. pendula in nurseries. This is the first record of the disease in Hungary.

References: (1) C. Booth. 1971. The Genus Fusarium. Commonwealth Mycological Institute, Kew, England. (2) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN.
Impact of Azoxystrobin, Dimethomorph, Fluazinam, Fosetyl-Al, and Metalaxyl on Growth, Sporulation, and Zoospore Cyst Germination of Three Phytophthora spp.
Authors: Matheron M. E. , Porchas M.
Published: May 2007

In vitro activity of azoxystrobin, dimethomorph, and fluazinam on growth, sporulation, and zoospore cyst germination of Phytophthora capsici, P. citrophthora, and P. parasitica was compared to that of fosetyl-Al and metalaxyl. The 50% effective concentration (EC50) values for)inhibition of mycelial growth of the three pathogens usually were lowest for dimethomorph and (metalaxyl, ranging from <0.1 to 0.38 μg/ml. However, the 90% effective concentration (EC90) levels for dimethomorph always were lower than the other four tested compounds, with values ranging from 0.32 to 1.6 μg/ml. Mycelial growth of P. capsici, P. citrophthora, and P. parasitica was least affected by azoxystrobin and fluazinam, with estimated (EC90) values >3,000 μg/ml. Reduction of sporangium formation by P. capsici, P. citrophthora, and P. parasitica in the presence of dimethomorph at 1 μg/ml was significantly greater than that recorded for the same concentration of azoxystrobin, fluazinam, and fosetyl-Al. For the three species of Phytophthora, zoospore motility was most sensitive to fluazinam (EC50 and EC90 values of <0.001 μg/ml) and (least sensitive to fosetyl-Al, with (EC50 and EC90 values ranging from 299 to 334 and 518 to 680 μg/ml, respectively). Germination of encysted zoospores of P. capsici, P. citrophthora, and P. parasitica was most sensitive to dimethomorph (EC50 and EC90 values ranging from 3.3 to 7.2 and 5.6 to 21 μg/ml, respectively), intermediate in sensitivity to fluazinam (EC50 and EC90 from 18 to 108 and 67 to >1,000 μg/ml, respectively) and metalaxyl (EC50 and EC90 from 32 to 280 and 49 to 529 μg/ml, respectively), and lowest in sensitivity to azoxystrobin and fosetyl-Al (EC50 and EC90 from 256 to >1,000 μg/ml). The activity of azoxystrobin, dimethomorph, and fluazinam on one or more stages of the life cycle of P. capsici, P. citrophthora, and P. parasitica suggests that these compounds potentially could provide Phytophthora spp. disease control comparable to that of the established fungicides fosetyl-Al and metalaxyl.
Differentiation and Detection of Sugar Beet Fungal Pathogens Using PCR Amplification of Actin Coding Sequences and the ITS Region of the rRNA Gene
Authors: Weiland John J. , Sundsbak Jamie L.
Published: May 2007

The DNA sequences of the actin genes of several fungi were compared and highly conserved regions in the coding sequence were identified. Deoxyoligonucleotide primers were synthesized based on conserved sequence blocks in the 5′ and 3′ ends of the open reading frame encoding the actin protein. In addition, primers (internal transcribed spacer [ITS] regions 1 and 4) based on conserved regions of the ribosomal RNA (rRNA) genes of fungi were synthesized. Use of the primers in the polymerase chain reaction (PCR) resulted in the amplification of DNA products from the genomes of sugar beet fungal pathogens of a size consistent with the amplification of the actin gene and rRNA gene sequences, respectively, in these fungi. With one primer pair (5FWDACT and MIDREVACT) directed to the actin gene, the major products amplified from the DNA of Aphanomyces cochlioides, Pythium ultimum, Cercospora beticola, Phoma betae, Fusarium oxysporum, and Rhizoctonia solani were of the sizes of 0.9, 0.9, 1.1, 1.1, 1.2 and 1.7 kilobase pairs (kbp), respectively, whereas no product was generated from the DNA of sugar beet (Beta vulgaris L.). Restriction endonuclease digestion of products amplified using 5FWDACT and MIDREVACT permitted the differentiation of A. cochlioides from A. euteiches. Use of ITS1 and ITS4 in PCR reactions employing the same template DNAs and reaction conditions yielded single products of 0.7, 0.8, 0.5, 0.5, 0.6, and 0.7 kbp, respectively, as well as a 0.7-kbp product from DNA of sugar beet. The data indicate that actin and rRNA gene sequences are appropriate targets for the development of PCR-based strategies for distinguishing sugar beet fungal pathogens at the genus level. The presence of A. cochlioides DNA in extracts of diseased sugar beet seedlings was detected using PCR with primers 5FWDACT and MIDRE-VACT.
First Report of Downy Mildew (Caused by Peronospora destructor) of Onion in Georgia
Authors: Langston D. B. , Sumner D. R.
Published: May 2007

In February 1999, localized areas in a commercial field of Vidalia sweet onions in Toombs County, GA, exhibited symptoms that included elongated pale to light tan lesions on older leaves as well as some totally collapsed leaves. A dark, sooty to purple-gray fungal growth also was observed on affected leaves. Both symptoms and signs were observed during a period of wet, cool weather. Microscopic observation of affected tissues revealed nonseptate mycelia and dichotomously branched sporangiophores, which tapered to short sterigmata, giving rise to pyriform to fusiform sporangia. Based on these observations, the disease was determined to be downy mildew of onion caused by Peronospora destructor (Berk.). The dimensions of 25 sporangia averaged 25.1 ± 3.8 × 64.2 ± 4.3 μm, falling within the range of those currently reported for P. destructor (1). The disease was isolated to the field in which it was initially reported and did not cause extensive damage. Its failure to progress and spread may have been due to the warm, dry conditions that prevailed subsequent to symptom detection. This is the first report of P. destructor in Georgia.

Reference: (1) H. F. Schwartz and S. K. Mohan. 1995. Diseases of aerial parts caused by fungi. Pages 20–24 in: Compendium of Onion and Garlic Diseases. The American Phytopathological Society, St. Paul, MN.
Bean Anthracnose: Virulence of Colletotrichum lindemuthianum Isolates from Burundi, Central Africa
Authors: Bigirimana J. , Fontaine R. , Höfte M.
Published: May 2007

The diversity of Colletotrichum lindemuthianum is a major limiting factor in control of anthracnose on bean (Phaseolus vulgaris), and race characterization of this pathogen is an important tool in breeding programs. Race characterization has been carried out on isolates from North, Central, and South America; Europe; and Asia, but little or no information exists on the diversity of C. lindemuthianum in Africa. In this work, 12 isolates from the major bean-growing areas of Burundi, Central Africa, were characterized. Their virulence was tested on 12 bean differential cultivars (1) and on 4 bean cultivars commonly grown in Burundi: 2 from local germ plasm (Muyinga-1 and Urubonobono) and 2 from Colombia (A 321 and Calima). Detached unifoliate bean leaves from 8-day-old plants were placed on a humid surface in trays and sprayed until runoff with a suspension of 106 spores ml-1. Trays covered with transparent plastic sheets to keep a minimum relative humidity of 92% were incubated at 20°C. Seven days after inoculation, symptoms were evaluated for severity on a scale of 1 to 9. Leaves scored as 1 to 3 were considered resistant. Races were characterized according to a numerical binary system (1). Nine races were identified: 9, 69, 87, 384, 385, 401, 448, 449, and 485. Seven of these races (9, 69, 87, 384, 401, 448, and 485) were described for the first time in Africa. Races 401 and 485 have not yet been reported in the literature. The most susceptible differential cultivars were Michelite, PI 207262, To, and Mexico 222. Muyinga-1, Urubonobono, and A 321 were sensitive to nine, six, and five races, respectively. There is a high diversity of C. lindemuthianum in Burundi, and the local germ plasm tested is very susceptible to the characterized races. Breeding programs in Burundi should focus on lines and cultivars, such as Tu, AB 136, G 2333, and Calima, that are resistant to all the races characterized in this study.

Reference: (1) M. A. Pastor-Corrales. Phytopathology 81:694, 1991.
Visual and Infrared Assessment of Root Colonization of Apple Trees by Phymatotrichopsis omnivora
Authors: Watson W. T. , Kenerley C. M. , Appel D. N.
Published: May 2007

Root systems of 5-year-old, trellised apple trees (Malus domestica Borkh) on cv. M.7a root-stocks were assessed for the presence of fungal strands of Phymatotrichopsis omnivora (Duggar) Hennebert in two orchards in central Texas. Fungal advance within each orchard was assessed in five directions. Pathogen growth (P < 0.01) occurred beyond symptomatic trees along and perpendicularly across rows. In one orchard, 80% of the first asymptomatic trees were infected along rows, followed by 60% infection perpendicularly across rows. In the other orchard, there was 100% infection of the first asymptomatic trees along rows and 60% infection perpendicularly across rows. No growth was observed diagonally across rows in either orchard. Infrared readings of canopy temperature and differences between canopy temperature and air temperature were significant (P < 0.01) for predicting infection of asymptomatic, infected trees in one orchard. Trees were shown to have extensive taproot decay and infection of lateral roots before canopy symptoms began to develop. Root diameter appeared to have no effect on the growth of the fungus.
Influence of Gibberellic Acid on Carrot Growth and Severity of Alternaria Leaf Blight
Authors: Santos P. , Nunez J. J. , Davis R. M.
Published: May 2007

Applications of gibberellic acid (GA) to carrot foliage consistently reduced the percentage of leaf area affected by Alternaria dauci compared with nontreated plants. The degree of leaf blight reduction with two applications of GA was similar to that achieved with four applications of the fungicide iprodione. At the rates examined (GA at 2.5 to 250 mg/liter), foliage dry weights were generally increased by GA. Although root weight was significantly reduced by rates of 250 mg/liter, applications of lower rates (40 mg/liter or less) reduced leaf blight severity without affecting root quality. Applications of GA usually resulted in plants with longer leaves, wider petioles, and a more upright growth habit. In one trial, leaf length and petiole diameter increased linearly with increasing rates (20, 30, and 40 mg/liter). When applied twice at 30 mg/liter, GA did not affect cuticle, epidermal, or leaf thickness. In general, the initial timing of two applications of 20 to 40 mg/liter (4, 6, or 8 weeks after plant emergence) did not influence the effects of GA. However, in one trial, there was a greater incidence of core separation from the root cortex when 40 mg/liter was applied initially at 4 weeks. GA at 30 mg/liter slightly but significantly decreased inner root color in one of two trials.
Sensitive Method for Testing Peanut Seed Lots for Peanut stripe and Peanut mottle viruses by Immunocapture-Reverse Transcription-Polymerase Chain Reaction
Authors: Gillaspie A. G. , Pittman R. N. , Pinnow D. L. , Cassidy B. G.
Published: May 2007

An immunocapture-reverse transcription-polymerase chain reaction (IC-RT-PCR) method was developed for testing peanut (Arachis hypogaea) seed lots for infection by Peanut stripe virus (PStV) and Peanut mottle virus (PeMV). A small slice was removed from each seed distal to the radicle of a random 100-seed sample, the slices were extracted in buffer and centrifuged, and a portion of the supernatant was incubated in a tube that had been coated with antiserum to either PStV or PeMV. Following immunocapture of the virus, the tube was washed, the RT-PCR mix (with primers designed from conserved sequences within the capsid region of each virus) was placed in the same tubes, and the test completed. Results obtained on 15 previously untested seed lots from the collection indicated good correlation between virus detected by the IC-RT-PCR method and virus detected from the same seed lots by enzyme-linked immunosorbent assay (ELISA). The IC-RT-PCR method detected three lots infected with PeMV and none with PStV from 106 seed lots grown in Ecuador (results confirmed by ELISA). The IC-RT-PCR method is more sensitive than ELISA (currently used on samples consisting of five seeds), is useful for testing large numbers of seed lots of peanut germ plasm, and could be adapted to test other plants and detect other viruses.