bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship of the Severity of Citrus Greasy Spot, Caused by Mycosphaerella citri, to Ascospore Dose, Epiphytic Growth, Leaf Age, and Fungicide Timing
Authors: Mondal S. N. , Timmer L. W.
Published: May 2007

Greasy spot, caused by Mycosphaerella citri, produces leaf and fruit lesions and defoliates trees, resulting in reduced yields and fruit size. Techniques now available allow production of large numbers of ascospores and the quantification of epiphytic growth. The effects of ascospore dose, leaf age, and the timing of fenbuconazole sprays on epiphytic growth and disease severity was determined primarily on rough lemon seedlings in the greenhouse. Inoculation of leaves with 104 ascospores/ml resulted in rapid development of epiphytic growth and symptoms. At lower doses, epiphytic growth and symptoms developed more slowly and were less severe. There was a linear relationship between log10 of the ascospore dose and ratings of epiphytic growth and symptoms, and a linear relationship between the amount of epiphytic growth and symptom severity in greenhouse tests. On grapefruit trees treated with different fungicides in six field experiments, there also was a significant linear relationship between epiphytic growth of M. citri measured in August and symptom severity rated in February to March of the following year, but coefficients of determination were much lower than in greenhouse experiments. Leaf age from 10 to 60 days did not affect susceptibility of leaves to M. citri. Fenbuconazole applied up to 50 days prior to inoculation still reduced epiphytic growth and greasy spot severity under greenhouse conditions, but the postinoculation treatments were effective for only 30 days.
First Report of Puccinia puta on Ipomoea carnea subsp. fistulosa from Puerto Rico
Authors: Hernández J. R.
Published: May 2007

Leaves of Ipomoea carnea Jacq. subsp. fistulosa (Mart. ex Choisy) D. Austin (Convolvulaceae) with conspicuous, round, yellowish orange leaf spots measuring up to 8 mm in diameter were collected from a garden plant in Cabo Rojo, Miradero, Puerto Rico on 8 December 2004. Uredinia and telia were observed in the symptomatic areas. The uredinia were aecioid, amphigenous but mainly hypophyllous, cupulate, and grouped in the round chlorotic leaf spots. The peridial cells measured 24 to 36 × 18 to 25 μm with walls 4 to 6 μm thick, the outer wall was striate to verrucose and the inner wall was verrucose. Urediniospores were catenulate, globoid to ellipsoid, sometimes narrow at the apex, and measured 28 to 36 × 20 to 30 μm. The urediniospore walls were colorless to yellowish, verrucose, 2 to 3 μm at the sides, and as much as 15 μm at the apex. Telia were epiphyllous, in the same spots as the uredinia, rounded, chestnut brown, and subepidermal, becoming erumpent. Teliospores measured 42 to 57 × 28 to 36 μm and were pale to cinnamon brown when young, becoming chestnut brown at maturity. The teliospores were ellipsoid or oblong, rounded at the top and bottom, with no constriction at the septum, and with walls verrucose, 3 to 4 μm at the sides and 5 to 7 μm at the septum and apex. Each teliospore had a pedicel that was colorless except close to the spore it was pale brown. Pedicels measured as much as 70 μm long and 10 μm thick and were easily broken. The rust was identified as Puccinia puta H.S. Jacks. & Holw. ex F. Kern, Thurst. & Whetzel (2), as compared macroscopically and microscopically with specimens in the U.S. National Fungus Collection (BPI) and also with published descriptions. P. puta has been reported from South America and Mexico on species of Ipomoea (1). I. carnea subsp. fistulosa is cultivated as an ornamental plant and widely distributed mainly in wet areas in the Americas from Argentina to Florida and Texas. To my knowledge this is the first report of P. puta in Puerto Rico. It has not been reported in the continental United States. The voucher specimen has been deposited in the U.S. National Fungus Collection as BPI 872006.

References: (1) D. F. Farr et al. Fungal Databases. Systematic Botany and Mycology Laboratory. On-line publication. ARS, USDA, 2005. (2). F. D. Kern et al. Mycologia 25:448, 1933.
Weather-Based Fungicide Spray Programs for Control of Two Foliar Diseases on Carrot Cultivars Differing in Susceptibility
Authors: Rogers P. M. , Stevenson W. R.
Published: May 2007

Foliar diseases of carrot caused by Alternaria dauci and Cercospora carotae occur every year in Wisconsin, requiring repeated foliar fungicide applications to minimize defoliation and yield reduction. Improved timing of fungicide applications combined with the use of disease resistant cultivars offer growers a means to improve disease control with fewer fungicide inputs compared with the current strategy of weekly fungicide applications to a susceptible cultivar. Field experiments in 2002 to 2004 examined fungicide application schedules indicated by a disease forecasting model that calculated the duration of environmental conditions favorable for A. dauci and C. carotae (adaptation of TOM-CAST) on two carrot cultivars differing in susceptibility to these foliar diseases. All fungicide programs were initiated at a 1% disease severity threshold determined by scouting. Intervals for weather-based spray programs were based on in-canopy leaf wetness and temperature data. Fungicide sprays were applied according to 15 and 20 disease severity value (DSV) application thresholds, and were compared with a weekly spray program and an untreated control. Results of this trial demonstrated that fungicide sprays made according to weather data may reduce fungicide inputs in most years compared with current industry-standard, calendar-based spray programs. Host susceptibility affected the efficacy of weather-based spray programs, resulting in longer spray intervals and fewer fungicide applications on the resistant cultivar Bolero when compared with the susceptible cultivar Fontana. Fungicide spray programs based on TOM-CAST diminished fungicide inputs by 30 to 50%, compared with the weekly spray program, by lengthening intervals between applications without compromising disease control or root yield.
Wild Allium spp. as Natural Hosts of Iris yellow spot virus
Authors: Pappu H. R. , Hellier B. C. , Dugan F. M.
Published: May 2007

The incidence of Iris yellow spot virus (IYSV) of genus Tospovirus, family Bunyaviridae in a commercial onion crop was first confirmed in Washington state during 2003 (1). First found in Adams County, IYSV has rapidly spread to all onion-producing counties in the state, affecting seed and bulb crops. The USDA-ARS Western Regional Plant Introduction Station (WRPIS) collects, maintains, and distributes various Allium (garlic and onion) accessions. As part of the regeneration process, accessions are grown under field conditions at the WRPIS farms in two locations: Pullman and Central Ferry, WA. Symptoms indicative of viral infection, now known to be caused by IYSV, first appeared in field-grown accessions in 1999. In June 2005, leaf and scape tissues were collected from WRPIS accessions of wild onions (Allium pskemense, A. vavilovii, and A. altaicum) in Central Ferry that had symptoms indicative of IYSV infection (2). IYSV infection was confirmed using enzyme-linked immunosorbent assay with a commercially available kit (Agdia Inc., Elkhart, IN). Virus infection was further verified using reverse transcription-polymerase chain reaction (RT-PCR) with primers derived from the small (S) RNA of IYSV. The primers flanked the IYSV N gene (5′-TAA AAC AAA CAT TCA AAC AA-3′ and 5′-CTC TTA AAC ACA TTT AAC AAG CAC-3′). RT-PCR gave a PCR product of expected size (≈1.2 kb). The DNA amplicon was cloned and sequenced. Nucleotide sequence comparisons with known IYSV N gene sequences showed 95 to 98% sequence identity. The prevalence of the vector, onion thrips (Thrips tabaci), combined with the widespread incidence of IYSV in seed and bulb production areas of the state may have resulted in natural infection of wild relatives of cultivated onion. The potential role of wild Allium spp. in IYSV epidemiology remains to be determined. Information on the extent of IYSV infection of onion germplasm would be useful in identifying potential sources of host plant resistance to IYSV.

References: (1) L. J. du Toit et al. Plant Dis. 88:222, 2004. (2) B. Hellier et al. APSnet Image of the Week. Online publication, iw000049.asp, 2004.
First Report of Tomato yellow leaf curl virus in South Carolina
Authors: Ling K. S. , Simmons A. M. , Hassell R. L. , Keinath A. P. , Polston J. E.
Published: May 2007

Tomato yellow leaf curl virus (TYLCV), a begomovirus in the family Geminiviridae, causes yield losses in tomato (Lycopersicon esculentum Mill.) around the world. During 2005, tomato plants exhibiting TYLCV symptoms were found in several locations in the Charleston, SC area. These locations included a whitefly research greenhouse at the United States Vegetable Laboratory, two commercial tomato fields, and various garden centers. Symptoms included stunting, mottling, and yellowing of leaves. Utilizing the polymerase chain reaction (PCR) and begomovirus degenerate primer set prV324 and prC889 (1), the expected 579-bp amplification product was generated from DNA isolated from symptomatic tomato leaves. Another primer set (KL04-06_TYLCV CP F: 5′GCCGCCG AATTCAAGCTTACTATGTCGAAG; KL04-07_TYLCV CP R: 5′GCCG CCCTTAAGTTCGAAACTCATGATATA), homologous to the Florida isolate of TYLCV (GenBank Accession No. AY530931) was designed to amplify a sequence that contains the entire coat protein gene. These primers amplified the expected 842-bp PCR product from DNA isolated from symptomatic tomato tissues as well as viruliferous whitefly (Bemisia tabaci) adults. Expected PCR products were obtained from eight different samples, including three tomato samples from the greenhouse, two tomato plants from commercial fields, two plants from retail stores, and a sample of 50 whiteflies fed on symptomatic plants. For each primer combination, three PCR products amplified from DNA from symptomatic tomato plants after insect transmission were sequenced and analyzed. All sequences were identical and generated 806 nucleotides after primer sequence trimming (GenBank Accession No. DQ139329). This sequence had 99% nucleotide identity with TYLCV isolates from Florida, the Dominican Republic, Cuba, Guadeloupe, and Puerto Rico. In greenhouse tests with a total of 129 plants in two separate experiments, 100% of the tomato plants became symptomatic as early as 10 days after exposure to whiteflies previously fed on symptomatic plants. A low incidence (<1%) of symptomatic plants was observed in the two commercial tomato fields. In addition, two symptomatic tomato plants obtained from two different retail garden centers tested positive for TYLCV using PCR and both primer sets. Infected plants in both retail garden centers were produced by an out-of-state nursery; this form of “across-state” distribution may be one means of entry of TYLCV into South Carolina. To our knowledge, this is the first report of TYLCV in South Carolina.

Reference: (1) S. D. Wyatt and J. K. Brown. Phytopathology 86:1288, 1996.
First Report of Phakopsora pachyrhizi Telia on Kudzu in the United States
Authors: Harmon C. L. , Harmon P. F. , Mueller T. A. , Marois J. J. , Hartman G. L.
Published: May 2007

Soybean rust caused by Phakopsora pachyrhizi H. Sydow & Sydow was first reported in the continental United States during 2004 (2). By 10 November 2005, the disease was confirmed in eight southern states (Florida, Georgia, Alabama, Mississippi, South Carolina, North Carolina, Louisiana, and Texas). Diagnoses have been based on visual observation of uredinia and urediniospores of the pathogen followed by polymerase chain reaction confirmation. On 10 November 2005, uredinia and telia were identified on leaves of kudzu (Pueraria lobata) in central Florida. Telia first were noted as dark brown-to-black flecks on the abaxial leaf surface intermingled with abundant tan-to-light brown uredinia. Of 200 leaves examined, 143 (72%) had telia. The number of telia ranged from a few (1/cm2) that were scattered to many (73/cm2). Telia were approximately the same diameter as uredinia, but were appressed to the leaf surface and pigmented. Twenty telia were excised from host tissue with the aid of a dissecting microscope and a 20 gauge hypodermic needle. Telia averaged 89 × 100 μm (n = 20, σ = 17 and 16 μm, respectively). Four telia were crushed and five teliospores from each averaged 4.3 × 8.3 μm (n = 20, σ = 0.5 and 0.9 μm, respectively). Pale yellowish brown-to-hyaline teliospores were similar in color to urediniospores. Observations matched descriptions by Ono et al. (1). To our knowledge, this is the first report of the telial stage of P. pachyrhizi in the United States.

References: (1) Y. Ono et al. Mycol. Res. 96:825, 1992. (2) R. W. Schneider et al. Plant Dis. 89:774, 2005.
Control of Benzimidazole- and DMI-Resistant Strains of Cercospora beticola with Strobilurin Fungicides
Authors: Karaoglanidis G. S. , Bardas G.
Published: May 2007

The control efficacy of two new strobilurin fungicides, trifloxystrobin and pyraclostrobin, against Cercospora beticola isolates resistant and sensitive to sterol demethylation-inhibiting (DMI) fungicides and benzimidazole fungicides and the effects on evolution of resistance were tested in the current study. Control efficacy of strobilurin fungicides was measured using three C. beticola isolates, one DMI-resistant (DMIR), one benzimidazole-resistant (BENR), and one of wild-type sensitivity (WCB). Both pyraclostrobin and trifloxystrobin provided satisfactory control of all the three isolates used in the study, when applied at 5 μg ml-1 and very high levels of control when applied at 10 μg ml-1. Control was independent of the isolate sensitivity to benomyl and difenoconazole. In contrast, benomyl applied at 10 μg ml-1 failed to control sufficiently the benzimidazole-resistant isolate, whereas difenoconazole applied at either 5 or 10 μg ml-1 failed to provide satisfactory control of the DMI-resistant isolate of the pathogen. The effects of strobilurin fungicide applications on the evolution of resistance to benzimidazole and DMI fungicides were tested under field conditions in a 2-year experiment (2003 to 2004). Applications of either trifloxystrobin or pyraclostrobin provided high levels of disease control during both years of the study, whereas applications of either benomyl or difenoconazole provided a moderate control efficacy. Measurements of resistance frequencies to benomyl and to difenoconazole showed that successive applications of benomyl tended to select for high frequencies of benzimidazole-resistant phenotypes, whereas successive applications of difenoconazole tended to select for high frequencies of DMI-resistant phenotypes. In contrast, applications of either trifloxystrobin or pyraclostrobin prevented an increase of benzimidazole- or DMI-resistant phenotypes compared with the plots treated with benomyl or difenoconazole, respectively, and decreased frequency of resistance compared with untreated control plots.
Cryopreservation of Synchytrium solstitiale In Planta
Authors: Widmer T. L.
Published: May 2007

The fungus Synchytrium solstitiale is a candidate for use as a biocontrol agent against Centaurea solstitialis. This obligate parasite can be propagated only in planta, which necessitates development of a method for preserving cultures for longer periods of time for routine biological studies and shipment to other laboratories. Normally, sporangia embedded within the plant tissue release zoospores when submersed in water at temperatures above freezing. To examine what chemicals might inhibit zoospore release, infected tissue was exposed to different suspensions of fungicides. Cycloheximide and benomyl completely inhibited zoospore release or immediately induced encystment from tissue stored in these two chemicals, respectively. A few zoospores were released in suspensions of iprodione and propionic acid but were not motile. However, when tissue stored in iprodione or propionic acid was transferred to fresh distilled water, abundant active zoospores were released. Freezing the infected tissue at different temperatures in different cryoprotectants also affected the release of motile zoospores. Infected C. solstitialis tissue was immersed in water, water plus iprodione, methanol, ethylene glycol, dimethyl sulfoxide, glycerol, skim milk, trehalose, or sucrose and subjected to different temperatures for various periods of time. Some treatments protected the viability of the fungus for a shorter period of time whereas other treatments completely inhibited release. The best results were obtained when infected tissue was stored at -2°C in 0.5 M sucrose where active zoospores were released after 12 weeks of storage. Overall, results obtained from this study demonstrate a technique for long-term storage of S. solstitiale.
Bacterial Leaf Spot of Lettuce: Relationship of Temperature to Infection and Potential Host Range of Xanthomonas campestris pv. vitians
Authors: Robinson P. E. , Jones J. B. , Pernezny Ken
Published: May 2007

Epidemiological aspects, including optimum temperature for infection and host range of Xanthomonas campestris pv. vitians, causal organism of bacterial leaf spot (BLS) of lettuce, were investigated. The optimum temperature for infection was determined to be 22.7°C based on growth chamber studies. Internal populations were monitored over time in lettuce, tomato, pepper, parsley, cilantro, and beet. Each plant species was infiltrated with the bacterium at 105CFU/ml. Highest populations developed in lettuce (108CFU/cm2) followed by pepper with 106CFU/cm2, whereas the other plant species harbored much lower populations (105 to 103CFU/cm2). Infectivity titration endpoints were similar in pepper and lettuce (103 to 104CFU/ml). For other plant species tested, infectivity titration endpoints were 106 to 107 CFU/ml. Electrolyte leakage data and corresponding internal population data support the conclusion that fresh-market tomato is not a host of X. campestris pv. vitians but, instead, interacts in an incompatible response. Electrolyte leakage from cells of tomato plants inoculated with X. campestris pv. vitians or a pepper strain of X. axonopodis pv. vesicatoria peaked at 48 h, suggesting that tomato is not a host for the BLS pathogen. Both electrolyte leakage and population dynamics results point to pepper as a potential host of X. campestris pv. vitians.
Use of Entomopathogenic Nematodes and Thyme Oil to Suppress Plant-Parasitic Nematodes on English Boxwood
Authors: Pérez Enrique E. , Lewis Edwin E.
Published: May 2007

A 2-year experiment was conducted to test suppression of plant-parasitic nematodes on English boxwood using entomopathogenic nematodes and 3.5% thyme oil formulated as Promax. Treatments were Steinernema riobrave formulated as BioVector and S. feltiae formulated as Nemasys, both applied at a rate of 2.5 billion infective juveniles/ha, thyme oil at rate of 9.3 liters/ha, and nontreated control. In the 2001 season, treatment with S. feltiae reduced (P ≤ 0.05) the population growth of Tylenchorhynchus sp. 7 days after treatment and Hoplolaimus sp. 30 and 60 days after treatment. Treatment with S. riobrave reduced (P ≤ 0.05) the population growth of all plant-parasitic nematode species at all sampling dates, with the exception of Mesocriconema sp. 30 days after treatment and Tylenchorhynchus sp. and Rotylenchus buxophilus 60 days after treatment. Treatment with thyme oil reduced (P ≤ 0.05) the population growth of all plant-parasitic nematode genera at all sampling dates except Tylenchorhynchus sp. and R. buxophilus 60 days after treatment. In the 2002 season, treatment with S. feltiae had no effect on nematode population growth. Treatment with S. riobrave reduced (P ≤ 0.05) the population growth of R. buxophilus 7 days after treatment, and all plant-parasitic nematodes 30 and 60 days after treatment except Hoplolaimus sp. 30 days after treatment and Mesocriconema sp. 60 days after treatment. Treatment with thyme oil reduced (P ≤ 0.05) the population growth at all sampling dates of plant-parasitic nematodes except Mesocriconema sp. 60 days after treatment.
Resistance in U.S. Wheat to Recent Eastern African Isolates of Puccinia graminis f. sp. tritici with Virulence to Resistance Gene Sr31
Authors: Jin Y. , Singh R. P.
Published: May 2007

The stem rust resistance gene Sr31 derived from rye has been used as an important source of stem rust resistance in many wheat cultivars worldwide. Isolates of Puccinia graminis f. sp. tritici with virulence to Sr31 were identified from Uganda in 1999. Stem rust susceptibility in wheat lines with Sr31 was observed in Kenya in 2003 and 2004. An isolate collected from Uganda in 1999 and an isolate collected from Kenya in 2004, identified to be race TTKS, were used in the rust evaluations. Selected cultivars and advanced breeding lines (450 in total) of wheat from the United States were tested against these two stem rust isolates. Resistance to race TTKS was detected in major classes of wheat with the following frequencies: 16% of hard red spring wheat, 48% of hard red winter wheat, and 27% of soft winter wheat. The genes that conferred resistance in the spring wheat have not been conclusively identified. Resistance in cultivar Ivan was likely due to Sr24. Resistance in hard red winter wheat was postulated to be primarily due to Sr24, and resistance in soft winter wheat was postulated to be primarily due to Sr36. The 1AL.1RS translocation present in many U.S. winter wheat cultivars and breeding lines appears to carry an effective resistance gene different from Sr31. The presence of resistance to race TTKS in the adapted germ plasm presents an opportunity to improve stem rust resistance in wheat.
Population Dynamics of Plant-Parasitic Nematodes in Golf Course Greens Turf in Southern New England
Authors: Jordan K. S. , Mitkowski N. A.
Published: May 2007

The distribution, frequency, and population levels over time of plant-parasitic nematodes were surveyed on 114 greens from 38 different golf courses throughout southern New England. Sampling took place in the spring, summer, and fall of 2003 and 2004. The predominant genera of phytoparasitic nematodes recovered from soil samples were Tylenchorhynchus, Helicotylenchus, Criconemella, Hoplolaimus, and Heterodera. Tylenchorhynchus and Helicotylenchus spp. were the most common, found in all 38 golf courses sampled. Population levels were significantly higher (α = 0.05) in 2004 than in 2003 for Criconemella, Tylenchorhynchus, and Heterodera juveniles. There was a significant effect of season on population levels of Criconemella, Tylenchorhynchus, and Heterodera juveniles in the 2003 sampling year, and on Helicotylenchus, Tylenchorhynchus, and Heterodera juveniles in 2004. Population levels were highest in the fall for all genera except for Tylenchorhynchus, which were highest in the summer for both years. The results of this study suggest that parasitic nematodes are present in relatively high numbers in golf course turf soils in southern New England, and that there are variations in the dynamics of population levels among the different genera found in the area.
Fungicide Sensitivity and Phylogenetic Relationship of Anthracnose Fungi Isolated from Various Fruit Crops in Japan
Authors: Chung Wen-Hsin , Ishii Hideo , Nishimura Kumiko , Fukaya Masako , Yano Kazutaka , Kajitani Yuji
Published: May 2007

Anthracnose diseases of fruit crops are mainly caused by Colletotrichum gloeosporioides and C. acutatum. In these Colletotrichum species, intra- and interspecific variation in fungicide sensitivity has been reported; however, the relationship between fungicide sensitivity and molecular phylogeny has not been analyzed. Fifty-one isolates from 10 fruit crops, acacia, and tea were tested for their sensitivities to thiophanate-methyl, diethofencarb, and iminoctadine-triacetate, and their internal transcribed spacer (ITS) and 5.8S regions of rDNA were analyzed. C. gloeosporioides isolates were divided into sensitive, less sensitive, intermediate resistant, or resistant to the three fungicides. In contrast, C. acutatum isolates were all less sensitive. In molecular phylogenetic analyses, C. gloeosporioides isolates fell into the same genetic group, whereas C. acutatum isolates were placed into two genetic groups. Although phylogenetic relationship was not closely related to fungicide sensitivity, the isolates of C. gloeosporioides most resistant to iminoctadine-triacetate were found in the same phylogenetic subgroup.
First Report in Argentina of Plum pox virus Causing Sharka Disease in Prunus
Authors: Zotto A. Dal , Ortego J. M. , Raigón J. M. , Caloggero S. , Rossini M. , Ducasse D. A.
Published: May 2007

Sharka disease, caused by Plum pox virus (PPV), is probably the most important disease of stone fruits crops worldwide because of tremendous yield losses from infected trees (1). During November 2004, symptoms resembling sharka disease were observed in a plum and apricot orchard consisting of 5,000 trees in Pocito, San Juan Province, Argentina. Apricot leaves showed chlorotic spots while plum leaves showed chlorotic rings, spots, and irregular edges. Plum fruits were deformed and much smaller than those from symptomless trees. Samples collected from 70 symptomatic trees were tested using double-antibody sandwich enzyme-linked immunosorbent assays with a polyclonal antiserum anti-PPV from BIOREBA (Reinach BL1, Switzerland), and immunosorbent electron microscopy with a polyclonal antiserum from our laboratory made against a recombinant PPV capsid protein (CP). The samples were also tested using double-antibody sandwich indirect enzyme-linked immunosorbent assay using the REAL kit (Durviz, Valencia, Spain) with two different monoclonal antibodies including Mab 5b that recognizes all strains of PPV and Mab 4DG5 that is specific for PPV strain D. Samples were positive with both antibodies in 80% of the cases. Leaf extracts from symptomatic plum samples were also analyzed by immuno-capture reverse-transcription polymerase chain reaction. A 1,209-bp fragment was amplified with specific primers that anneal at the 5′ end of the coat protein coding region and the viral 3′ end poly A tail. The amplified fragment was cloned and the nucleotide sequence was determined for two of the resulting clones (Gen-Bank Accession Nos. DQ299537 and DQ299538). The sequences were 98% identical with the PPV-strain D from the United States (GenBank Accession No. AF360579) and Germany (GenBank Accession No. X81081). The restriction sites for AluI and RsaI, previously described (2) as typical for the PPV-D strain, were present in the expected positions. To our knowledge, this is the first report of PPV-D in Argentina.

Reference: (1) M. Németh. Virus, Mycoplasma, and Rickettsia Disease of Fruit Trees. Martinus Nijhoff Publishers, Dordrecht, the Netherlands, 1986. (2) T. Wetzel et al. J. Virol. Methods 33:355, 1991.
First Report of Tomato spotted wilt virus in Soybean (Glycine max) in Georgia
Authors: Nischwitz C. , Mullis S. W. , Gitaitis R. D. , Csinos A. S.
Published: May 2007

Tomato spotted wilt virus (TSWV) is a member of the family Bunyaviridae and has a wide host range including important crops such as tomato, pepper, tobacco, peanut, and onion. In areas of Georgia, soybean (Glycine max) is double cropped between two onion crops and as a rotation crop with peanuts. Soybeans do not show any TSWV symptoms, and therefore, have not been tested on a large scale for the virus. However, because symptomless weed and crop plants provide a reservoir for TSWV and the thrips vectors (2), a survey was conducted during the summer of 2005 to evaluate the occurrence of TSWV in soybean. The survey took place in seven counties in southern Georgia with field sizes ranging between 0.4 and 20 ha (1 and 50 acres). Soybean cultivars included Haskell, DP7220, DP6770, Pioneer 97B52, and Vigoro V622NRR. Of 848 randomly selected plants tested using the double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) (Agdia, Inc., Elkhart, IN), 6.6% tested positive for TSWV. Plants testing positive ranged from seedling to the pod-setting stages. Leaves and roots of several plants tested positive, indicating a systemic infection. Soybean plants testing positive using ELISA were blotted onto FTA cards (Whatman Inc., Brentford, UK) to bind viral RNA for preservation, and the blotted samples were processed according to the manufacturer's protocol. Reverse transcription-polymerase chain reaction using punch-outs from the FTA cards and TSWV nucleocapsid gene specific forward and reverse primers (5′-TTAAGCAAGTTCTGTGAG-3′ and 5′-ATGTCTAAGGTTAAGCTC-3′), respectively (4), confirmed the identity of TSWV. TSWV has been found in soybean in other parts of the world (1) but has only been reported in the United States in a survey from Tennessee (3). To our knowledge, this is the first report of the occurrence of TSWV in soybean in Georgia. The role soybean plays as a reservoir or green bridge for thrips and TSWV is currently unknown.

References: (1) A. R. Golnaraghi et al. Plant Dis. 88:1069, 2004. (2) R. L. Groves et al. Phytopathology 91:891, 2001. (3) B. S. Kennedy and B. B. Reddick. Soybean Genet. Newsl. 22:197, 1995. (4) H. R. Pappu et al. Tob. Sci. 40:74, 1996.
First Report of Cucurbit aphid-borne yellows virus in Iran Causing Yellows on Four Cucurbit Crops
Authors: Bananej K. , Desbiez C. , Wipf-Scheibel C. , Vahdat I. , Kheyr-Pour A. , Ahoonmanesh A. , Lecoq H.
Published: May 2007

A survey was conducted from 2001 to 2004 in the major cucurbit-growing areas in Iran to reassess the relative incidence of cucurbit viruses. Severe yellowing symptoms were observed frequently on older leaves of cucurbit plants in various regions in outdoor crops, suggesting the presence of Cucurbit aphid-borne yellows virus (CABYV, genus Polerovirus, family Luteoviridae) (1,2). Leaf samples (n = 1019) were collected from plants of melon (Cucumis melo L.), cucumber (C. sativus L.), squash (Cucurbita sp.), and watermelon (Citrullus lanatus L.) showing various virus-like symptoms (mosaic, leaf deformation, yellowing). All samples, collected from 15 provinces, were screened for the presence of CABYV by double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) with IgGs and alkaline phosphatase-conjugated IgGs against a CABYV reference isolate (1). Of the 1,019 samples tested, 471 were positive for CABYV using DAS-ELISA. Some of the positive samples had typical severe yellowing symptoms while symptoms in other samples were masked by mosaic or leaf deformations caused by other viruses frequently found in mixed infections (data not shown). During the entire survey, CABYV was detected by DAS-ELISA in 201 of 503 melon samples, 72 of 129 cucumber samples, 158 of 249 squash samples, and 40 of 138 watermelon samples. These results indicate that CABYV is widely distributed on four cucurbit species in the major growing areas of Iran. In order to confirm CABYV identification, total RNA extracts (TRI-Reagent, Sigma Chemical, St Louis, MO) were obtained from 25 samples that were positive using DAS-ELISA originating from Khorasan (n = 4), Esfahan (n = 6), Teheran (n = 3), Hormozgan (n = 4), Azerbaiejan-E-Sharqi (n = 4), and Kerman (n = 4). Reverse transcription-polymerase chain reactions (RT-PCR) were carried out using forward (5′-CGCGTGGTTGTGG-TCAACCC-3′) and reverse (5′-CCYGCAACCGAGGAAGATCC-3′) primers designed in conserved regions of the coat protein gene according to the sequence of a CABYV reference isolate (3) and three other unpublished CABYV sequences. RT-PCR experiments yielded an expected 479-bp product similar to the fragment amplified with extracts from the reference isolate. No amplification of the product occurred from healthy plant extracts. To our knowledge, this is the first report of the occurrence of CABYV in Iran on various cucurbit species. The high frequency (46.2%) with which CABYV was detected in the samples assayed indicates that this virus is one of the most common virus infecting cucurbits in Iran.

References: (1) H. Lecoq et al. Plant Pathol. 41:749, 1992 (2) M. A. Mayo and C. J. D'Arcy. Page 15 in: The Luteoviridae. H. G. Smith and H. Barker, eds. CAB International Mycological Institute, Wallingford, UK, 1999. (3) H. Guilley et al. Virology 202:1012, 1994.
Status of Cassava Begomoviruses and Their New Natural Hosts in Nigeria
Authors: Ogbe F. O. , Dixon A. G. O. , Hughes J. d'A. , Alabi O. J. , Okechukwu R.
Published: May 2007

A diagnostic survey was conducted in 2002-03 to determine the status of cassava mosaic begomoviruses in Nigeria and to ascertain if the virulent Ugandan variant of East African cassava mosaic virus (EACMV-Ug2) was present. Of the 418 farms visited, 48% had cassava with moderately severe or severe symptoms, whereas 52% had cassava with mild symptoms. These distributions were at random. Of the 1,397 cassava leaf samples examined, 1,106 had symptoms. In polymerase chain reaction tests, 74.1% of the symptom-bearing samples tested positive for African cassava mosaic virus (ACMV) alone, 0.3% for EACMV alone, 24.4% for mixed infections by the two viruses, and 1.2% did not react with any of the primers used. The two viruses also were detected in 32% of the 291 symptomless plants and in the whitefly vector samples. EACMV-Ug2, Indian cassava mosaic virus, and South African cassava mosaic virus were not detected in any of the whitefly or leaf samples. Most farms had ACMV in single infection as well as in mixed infections with EACMV. Most doubly infected plants showed severe symptoms. Two biological variants of ACMV were identified based on symptom expression on cassava in the field. ACMV and EACMV were detected in the leguminous plant Senna occidentalis (L.) Link and the weed Combretum confertum Lams.; these are new natural hosts of the viruses. Although the virulent EACMV-Ug2 was not detected, the occurrence of variants of ACMV and a high proportion of mixed infections by ACMV and EACMV, which could result in recombination events such as the one that produced EACMV-Ug2, demands appropriate measures to safeguard cassava production in Nigeria.
A Quantitative Assay of Puccinia coronata f. sp. avenae DNA in Avena sativa
Authors: Jackson E. W. , Avant J. B. , Overturf K. E. , Bonman J. M.
Published: May 2007

Crown rust, caused by Puccinia coronata f. sp. avenae, is the most damaging disease of oat. Quantification of the disease can be done by visual or digital assessments of diseased leaf area, lesion number, lesion size, and latent period. Laborious measurements of sporulation can also be made. As an alternative to these methods, a new quantitative assay was developed. The method employs simple inoculum application, quantitative sampling from inoculated areas, a closed tube DNA extraction method restricting loss of tissue, and real-time polymerase chain reaction (PCR) using a pathogen-specific TaqMan primers/probe set. Image analyses of genotypes with varying levels of crown rust resistance were compared to fungal DNA (FDNA) estimations by the new assay. The moderately resistant genotype IA98822-2 was distinguished from susceptible genotypes at the seedling stage, and the moderately resistant genotype O × T 107 was distinguished from the resistant cultivar TAM-O-301 at seedling and adult plant stages using FDNA. These separations were not evident with digital image analysis. The new assay also detected fungal development earlier and more rapidly in genotypes with lower levels of resistance. The assay can consistently estimate disease and should be useful for studying many aspects of the crown rust host-pathogen interaction where precise assessment of pathogen development is needed.
Forecasting Site-Specific Leaf Wetness Duration for Input to Disease-Warning Systems
Authors: Kim K. S. , Gleason M. L. , Taylor S. E.
Published: May 2007

Empirical models based on classification and regression tree analysis (CART model) or fuzzy logic (FL model) were used to forecast leaf wetness duration (LWD) 24 h into the future, using site-specific weather data estimates as inputs. Forecasted LWD and air temperature then were used as inputs to simulate performance of the Melcast and TOM-CAST disease-warning systems. Overall, the CART and FL models underpredicted LWD with a mean error (ME) of 2.3 and 3.9 h day-1, respectively. The CFL model, a corrected version of the FL model using a weight value, reduced ME in LWD forecasts to -1.1 h day-1. In the Melcast and TOM-CAST simulations, the CART and CFL models predicted timing of occurrence of action thresholds similarly to thresholds derived from on-site weather data measurements. Both models forecasted the exact spray dates for approximately 45% of advisories derived from measurements. When hindcast and forecast estimates derived from site-specific estimates provided by SkyBit Inc. were used as inputs, the CART and CFL models forecasted spray advisories within 3 days for approximately 70% of simulation periods for the Melcast and TOM-CAST disease-warning systems. The results demonstrate that these models substantially enhance the accuracy of commercial site-specific LWD estimates and, therefore, can enhance performance of disease-warning systems using LWD as an input.
Sugar Beet Performance with Curly Top Is Related to Virus Accumulation and Age at Infection
Authors: Wintermantel William M. , Kaffka Stephen R.
Published: May 2007

Resistance to curly top disease caused by Beet curly top virus (BCTV) and related curtoviruses has been important to sustainable sugar beet (Beta vulgaris) production in the western United States for most of the last century. Recent advances in sugar beet genetics have led to the development of high-yielding cultivars, but these cultivars have little resistance to curly top disease. These cultivars are highly effective when disease management practices or environmental factors minimize curly top incidence, but can result in significant losses in years with early infection or abundant curly top. A greenhouse assay has been developed to rapidly test cultivars for a broad array of factors affecting performance in the presence of curly top. Previous studies have shown that sugar beet plants were more susceptible and losses more severe when seedlings were infected by BCTV, but less severe when plants were larger at the time of infection. To evaluate more precisely the relationship between age at infection, disease severity, virus accumulation, and yield loss in modern cultivars that were not bred for curly top resistance, individual sugar beet plants varying in degree of resistance and susceptibility to curly top were inoculated by viruliferous beet leafhoppers (Circulifer tenellus) when plants had two, four, or six true leaves, and maintained in a greenhouse for 6 weeks. When plants were inoculated at the two-leaf stage, all cultivars became severely stunted, with high disease ratings and similar rates of symptom development, regardless of resistance or susceptibility of the cultivar. Plants inoculated at four-and six-leaf stages exhibited increasing separation between resistant and susceptible phenotypes, with highly resistant cultivars performing well with low disease ratings and increased plant weights relative to susceptible cultivars. High-yielding cultivars performed only slightly better than the susceptible control cultivar. Results from greenhouse trials matched those from field trials conducted under heavy curly top pressure. Importantly, low virus concentration was directly correlated with lower disease ratings and higher plant weight, while elevated virus concentrations corresponded to higher disease ratings and lower weights. This demonstrates that a rapid greenhouse assay involving multiple traits can provide a rapid and effective means of selecting cultivars with improved curly top control, and could lead to more rapid incorporation of resistance into high-yielding sugar beet.
Prereaction of Citrus tristeza virus (CTV) Specific Antibodies and Labeled Secondary Antibodies Increases Speed of Direct Tissue Blot Immunoassay for CTV
Authors: Lin Youjian , Rundell Phyllis A. , Xie Lianhui , Powell Charles A.
Published: May 2007

An improved direct tissue blot immunoassay (DTBIA) procedure for detection of Citrus tristeza virus (CTV) within 1 h is described. Prints of fresh young stems of citrus plants that were infected or not infected with CTV were made by gently and evenly pressing the fresh-cut surface of the stems onto a nitrocellulose membrane. The tissue blots were air-dried for 5 min, incubated with prereaction solutions of CTV-specific antibodies and labeled secondary antibodies, goat anti-mouse Ig (H+L)-alkaline phosphatase conjugate or goat anti-rabbit IgG alkaline phos-phatase conjugate, for up to 20 min, rinsed with PBST buffer for 5 min, and immersed into an NBT-BCIP substrate solution for 15 to 20 min. Then the blots were rinsed in water for a few seconds to stop the reactions, and the results were observed and recorded under a light microscope. All samples from greenhouse plants that were infected with CTV decline inducing isolate T-36 were positive to CTV-specific polyclonal antibody 1212 (PCA 1212) and monoclonal antibodies 17G11 (MAb 17G11) and MCA13 (MAb MCA13), whereas samples from greenhouse plants infected with non-decline-inducing isolate T-30 were positive to PCA 1212 and MAb 17G11, but not to MAb MCA13. The noninfected greenhouse plants were negative to all of the antibodies. The improved DTBIA was at least as reliable as other immunological procedures and almost as reliable as polymerase chain reaction for detecting CTV in field trees. The improved DTBIA enables the detection of CTV within 1 h by having a prereaction of CTV-specific antibodies and labeled secondary antibodies in solutions before they are applied to the tissue blots. This DTBIA procedure may be useful in detecting other plant viruses and other pathogens such as bacteria and fungi.
First Report of Pyricularia grisea (Gray Leaf Spot) on Perennial Ryegrass (Lolium perenne) in Nevada
Authors: Wong F. P. , de la Cerda K. A.
Published: May 2007

In August of 2005, a golf course in Las Vegas, NV reported turf loss from an unknown disease on perennial ryegrass fairways. Samples from this course were examined, and diseased plants were found covered with lesions and sporulation typical of gray leaf spot as caused by Pyricularia grisea (Cooke) Sacc. With petroleum jelly, sporulating leaves were attached to the inside top surface of 100-mm petri dishes filled with 15 ml of 1.5% water agar. Conidia were allowed to drop onto the agar surface and 24 h later, individual germinating pyriform conidia were transferred to petri dishes containing one-quarter-strength potato dextrose agar (¼-PDA) with the aid of a fine needle and stereomicroscope. Isolates of the fungus were maintained at 28°C with constant fluorescent light. Isolates were examined 7 to 10 days later, and morphology and conidia production were consistent with that described previously for P. grisea (1). Koch's postulates were performed using a single isolate (SSGC-1.1) grown for 14 days on ¼-PDA. The petri dish was flooded with 15 ml of sterile distilled water plus 0.05% Tween 20 and conidia dislodged into the solution with a rubber policeman to obtain a solution of approximately 5 × 103 conidia per ml. Using a modified thin-layer chromatography plate sprayer, the solution was misted onto six pots of 6-week-old perennial ryegrass (a mixture of approximately 33% each of varieties ‘Kokomo’, ‘Cabo’ and ‘Secretaria’), seeded at a density of 2 kg per 93 m2 grown in 4- × 4-cm plastic pots filled with University of California soil mix. As a control treatment, six pots of perennial ryegrass (grown as previously described) were treated with water plus 0.05% Tween 20 only. Pots of plants were placed into closed, translucent, plastic containers lined with wet paper towels to provide a moist environment and held at 30°C for 48 h. Pots of plants were transferred to an incubator set at 30°C and 80% relative humidity with 12 h of alternating light and dark cycles. Four days after inoculation, plants misted with conidia developed symptoms typical of gray leaf spot. Plants were again placed into closed plastic containers lined with wet paper towels for 24 h, at which time, lesions on symptomatic plants developed abundant conidia characteristic of P. grisea. Water-only treated plants did not show any symptoms or signs of disease. P. grisea was reisolated from sporulating leaves as described above. The disease has been spreading in the midwestern and northeastern United States since first reported in 1991 on perennial ryegrass in Pennsylvania. It has only recently been found on turfgrass in California (2), and to our knowledge, this is the first report of this pathogen on perennial ryegrass in Nevada.

References: (1) M. B. Ellis. Dematiaceous Hyphomycetes. CMI, Kew, Surrey, UK, 1971. (2) W. Uddin et al. Plant Dis. 86:75, 2002.
Mycosphaerella fijiensis, Causal Agent of Black Sigatoka of Musa spp. Found in Puerto Rico and Identified by Polymerase Chain Reaction
Authors: Irish B. M. , Goenaga R. , Ploetz R. C.
Published: May 2007

Black Sigatoka, also known as black leaf streak, is caused by Mycosphaerella fijiensis Morelet (anamorph Pseudocercospora fijiensis (Morelet) Deighton). It is the most significant disease of bananas and plantains (Musa spp.) because most of the economically important cultivars of exported and staple commodities are highly susceptible. The Caribbean is one of the few regions of the world where black Sigatoka is not widespread. Black Sigatoka has been reported in the Bahamas, Cuba, Hispaniola, and Jamaica (2). Yellow Sigatoka, caused by M. musicola Leach (anamorph P. musae (Zimm.) Deighton), has been recognized in Puerto Rico since 1938-1939 (3). In August 2004, symptoms resembling black Sigatoka were first observed in Añasco, Puerto Rico by extension personnel from the University of Puerto Rico. Since black and yellow Sigatoka produce similar disease symptoms, a survey was conducted in the western banana- and plantain-production region of Puerto Rico to confirm the presence of black Sigatoka. Leaf samples were collected from production fields near the towns of Las Marias, Maricao, and Añasco. Single-ascospore isolates were recovered using the discharge technique from moistened pseudothecia in necrotic lesions that were inverted over water agar, and ascospores were transferred to potato dextrose agar. The isolates were subcultured in potato dextrose broth for mycelium production. DNA was isolated from mycelium with the FastDNA kit (Q-Biogen, Irvine, CA) for 19 isolates. Internal transcribed spacer as well as the 5.8s rDNA regions were polymerase chain reaction amplified with primers specific to M. fijiensis or M. musicola (1). Amplification products (˜1,100 bp) were observed for 18 of the 19 isolates, 6 of which were M. fijiensis and the remaining 12 were M. musicola, while the positive controls for both species were also amplified with the respective primer pairs. M. fijiensis was recovered from production fields close to all three towns. The source of M. fijiensis in Puerto Rico is unclear, but it may have originated from introduced leaf material and/or wind dispersed ascospores from neighboring countries. The presence of black Sigatoka in Puerto Rico will most likely increase production costs where fungicide applications will be needed to maintain yields. The USDA-ARS, Tropical Agriculture Research Station is the official Musa spp. germplasm repository for the National Plant Germplasm System. As such, efforts are underway to introduce and evaluate black Sigatoka disease-resistant clones that can satisfy local and export market criteria.

References: (1) A. Johnasen. Detection of Sigatoka leaf spot pathogens of banana by the polymerase chain reaction. Chatman, UK, Natural Resource Institute, 1997. (2) R. C. Ploetz. Plant Dis. 88:772, 2004. (3) R. H. Stover. Trop. Agric. Trinidad. 39:327, 1962.