bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Sclerotinia sclerotiorum on Coneflower
Authors: Chang K. F. , Howard R. J. , Gaudiel R. G. , Hwang S. F.
Published: May 2007

Purple coneflower (Echinacea purpurea (L.) Moench; Asteraceae), a perennial herb originating from North America, is used as a garden ornamental and is grown commercially for use in medicinal preparations as an immunostimulant. In October 1996, a previously undescribed stem rot disease was observed in a research plot of 6-month-old echinacea plants at Brooks. Seedlings had been raised in small rockwool cubes (2 × 2 × 5 cm3) in a greenhouse, then transplanted into the field in early June. By late August, dead and dying plants were observed throughout the stand. They had dark brown to black stem lesions above and at the soil level and dead leaves with bleached petiole lesions that extended ca. 15 cm above the axil. Diseased stems and petioles often disintegrated, leaving only fibrous tissues intact. Roots were rotted and black. Superficial white mycelium developed over the basal part of affected stems. Black, oblong to irregular-shaped sclerotia, 5.1 to 17.6 mm in size, formed externally on the crown areas after plant death. Sclerotinia sclerotiorum (Lib.) de Bary (1) was isolated from the diseased plants. Five isolates were selected to fulfill Koch's postulates with 3-month-old echinacea seedlings grown in 12-cm pots of soilless mix. Sclerotia from wilted, field-grown echinacea plants were transferred onto potato dextrose agar medium for 2 days at 20°C. Agar disks were cut with a 1-cm cork borer and two plugs containing sclerotial and mycelial tissues were inserted into the soilless mix 0.5 cm deep and 0.5 cm from the opposite sides of stems of test plants. Inoculated plants were enclosed in transparent plastic bags for 5 days and incubated in a growth chamber at 15/18°C (night/day) with a 12-h photoperiod. One to four lower leaves per plant wilted within 1 week after inoculation and aerial mycelia appeared on the petioles. Infected leaves quickly withered, dried, and dropped off the plant after the bags were removed. Plants often died 3 weeks after inoculation and S. sclerotiorum was reisolated from infected crown tissues. This disease was also found on 3-year-old plants of E. pallida (Nutt.) Nutt. var. angustifolia (DC.) Cronq. in Vernon, British Columbia, Canada, in May 1997. This is the first report of sclerotinia stem rot on Echinacea spp., a disease that could have a significant impact on the longevity and productivity of this crop in the field and greenhouse.

Reference: (1) L. H. Purdy. Phytopathology 69:875, 1979.
First Report of Powdery Mildew, Caused by Erysiphe cruciferarum, on Broccoli Raab in California
Authors: Koike S. T. , Saenz G. S.
Published: May 2007

Broccoli raab (Brassica rapa subsp. rapa), also known as rappini, is a leafy vegetable that is widely grown in Europe and has in recent years become an important crop in coastal California. During summer months in the Salinas Valley (Monterey County) in California, powdery mildew was observed on commercial field and greenhouse-grown plants. White ectophytic mycelial and conidial growth was present on leaves, causing chlorosis, and also developed on stems. Mycelia were amphigenous, in patches, often spreading to become effused. Appressoria were lobed and conidiophores were straight. Foot cells were cylindrical, measured 18 to 26 × 7 to 10 μm, and were followed by one to two cells of variable length. Conidia were produced singly, were cylindrical, and measured 35 to 50 × 12 to 21 μm with a length-to-width ratio greater than 2. No fibrosin bodies were observed in the conidia, and conidia germinated at the ends. Cleistothecia were not observed. The fungus was identified as Erysiphe cruciferarum Opiz ex Junell (1). Pathogenicity was demonstrated by gently pressing infected leaves having abundant sporulation onto leaves of potted broccoli raab (cv. Spring Raab), incubating the plants in a moist chamber for 48 h, and then maintaining plants in a greenhouse. After 10 to 13 days, powdery mildew colonies developed on the test plants. Uninoculated control plants did not develop powdery mildew. With the same inoculation procedure, potted broccoli (Brassica oleracea subsp. botrytis cv. Greenbelt) also became infected by the broccoli raab isolates. This is the first report characterizing this pathogen on broccoli raab in the state. Disease incidence and severity in field-planted crops were low, but greenhouse-grown plants became severely infected.

Reference: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987.
First Report of Banana Bunchy Top Virus in Malawi
Authors: Kenyon Lawrence , Brown Margaret , Khonje Patrick
Published: May 2007

Banana plants of the Cavendish subgroup (Musa AAA, locally known as “Kabuthu”) with classical banana bunchy top virus (BBTV) symptoms were observed to be widespread in Thiwi Valley, Salima Agricultural Development Division, Malawi. The symptoms included marginal yellowing of the younger leaves, dark green, dot-dash streaks along the veins, petioles, and midribs, and shortened internodes. The aphid vector of this virus, Pentalonia nigronervosa, was abundant on bananas in this area (H. Thindwa, personal communication). Young leaf and midrib samples from apparently healthy plants and plants with symptoms were transported to the United Kingdom for testing. In a triple antibody sandwich enzyme-linked immunosorbent assay (ELISA) with poly- and monoclonal antibodies specific for BBTV (1), the samples from symptomatic plants gave positive reactions (OD infected ≥ OD healthy + 3SE healthy). Polymerase chain reaction (PCR) amplification tests were performed for confirmation with oligonucleotide primers BBT1 and BBT2, which are homologous to conserved regions in BBTV DNA component 1. All ELISA-positive samples produced a PCR amplification product of about 349 bp, whereas the healthy control samples did not. The sizes of the DNA fragments produced following restriction enzyme digest of the PCR product suggest that the Malawi virus falls within the South Pacific group of BBTV isolates (2). The presence of both the virus and its vector has the potential for causing great economic damage to this important banana-growing region, and recommendations have been made to eradicate all plants with symptoms.

References: (1) R. G. Dietzgen and J. E. Thomas. Australas. Plant Pathol. 20:161, 1991. (2) M. Karan et al. J. Gen. Virol. 75:3541, 1994.
Yellow Net of Triumffeta Is Caused by a Geminivirus: A First Report
Authors: Hallan Vipin , Saxena Sangeeta , Singh B. P.
Published: May 2007

Triumffeta rhomboidiaceae Jacq. (Tiliaceae family) is an annual rainy season weed that is commonly found throughout India. For the last 3 years, during the rainy season, several plants of T. rhomboidiaceae in and around the gardens of the National Botanical Research Institute have been found with vein yellowing symptoms. The initial symptoms were vein clearing but in later stages the veins became yellow and thickened. In severe cases, the chlorosis extends into interveinal areas, resulting in complete yellowing of the leaves. In a few cases, green leafy or thorny enations could be seen on the dorsal side of the leaf. The disease was investigated to identify the causal agent. Vector transmission studies showed that the causal agent is transmitted by the whitefly, Bemisia tabaci, from infected to healthy seedlings of T. rhomdoidiaceae. Since whitefly transmission of the disease is consistent with a geminivirus as the causal agent, the role of such a virus was investigated. DNA isolated from Triumffeta plants (both from the infected plants in the field as well as from those inoculated experimentally in the greenhouse) showing above mentioned symptoms was amplified with two sets of degenerate primers, PAL1v1978/PAR1c496 (set 1) and PAL1v1978/PCRc1 (set 2), that have been shown to be specific for DNA-A of whitefly transmitted geminiviruses (WTGs), in polymerase chain reaction (1). We could amplify DNA-A fragments of approximately 1.2 kb from set 1 and 0.7 kb from set 2, as expected (1). DNA isolated from healthy seedlings gave no amplification of such fragments. Identification of the amplified DNA fragments (from infected samples) to be of geminiviral in nature was confirmed by Southern blot hybridization carried out under high stringency conditions. DNA-A of Indian tomato leaf curl virus (2) was used as a general probe for WTGs for the above hybridization experiment. Therefore, Triumffeta yellow net disease is caused by a geminivirus. A review of literature revealed that there is no record of a viral disease affecting this weed and, therefore, this is the first report of a viral disease affecting this plant.

References: (1) M. R. Rojas et al. Plant Dis. 77:340, 1993. (2) K. M. Srivastava et al. J. Virol. Methods 51:297, 1995.
First Report of Powdery Mildew Caused by Oidium araliacearum on Ivy in California
Authors: Saenz G. S. , Koike S. T.
Published: May 2007

Powdery mildew was observed on English ivy (Hedera helix L.) in Berkeley, CA, in the spring of 1997. Fungal growth was ectophytic and amphigenous on leaves and petioles and caused slight reddening and buckling of leaves. The mycelium was white, effuse to dense, and had hyphal diameters of 3.5 to 6.9 μm. Appressoria were nipple-shaped to lobed, and sometimes were opposite. The foot cells of the conidiophores were cylindric, sometimes slightly flexuous, and were 18.5 to 30.0 × 6.9 to 9.2 μm in diameter. The foot cells were followed by 1 or 2 cells. When only one cell followed the foot cell, this cell was longer and slightly wider than the foot cell and measured 20.8 to 46.2 × 6.9 to 9.2 μm. When two cells followed the foot cell, these cells were of similar length to the foot cell, with the second cell usually shorter. Conidia were formed singly, were cylindric to slightly doliiform, and measured 32.0 to 44.0 × 11.5 to 19.0 μm. Fibrosin bodies were not observed. Conidia germinated at the ends and germ tubes terminated in lobed appressoria, placing this fungus in the Polygoni-type germination category (2). Cleistothecia were not observed. Based on these characters, the fungus was identified as Oidium araliacearum U. Braun & E. Oehrens B. A specimen was deposited with the University of California at Berkeley herbarium (accession number UC1713247). Pathogenicity was confirmed by gently pressing infected leaves onto leaves of various stages of maturity on ivy vines (3 to 4 vines per plant; 4 plants). Inoculated plants were kept in a moist chamber for 48 h, and then maintained in a greenhouse. Powdery mildew developed on inoculated plants, primarily on leaves of intermediate maturity, after 14 days, while uninoculated plants did not develop disease. Phyllactinia guttata is the only other powdery mildew recorded on English ivy (2). O. araliacearum differs from P. guttata in conidial shape (cylindric vs clavate), germination habit (end vs side of conidia), and asexual genus (Oidium vs Ovulariopsis) (2). Previous to this report, O. araliacearum was described only on Pseudopanax valdiviensis, another Araliaceae plant, in Chile (1). This is the first report of a powdery mildew disease of ivy in California, and the first report of Hedera helix as a host of O. araliacearum.

References: (1) U. Braun. Mycotaxon 25:259, 1986. (2) U. Braun. Nova Hedwigia 89:1, 1987.
Natural Occurrence of Fumonisins in Rice with Fusarium Sheath Rot Disease
Authors: Abbas H. K. , Cartwright R. D. , Shier W. T. , Abouzied M. M. , Bird C. B. , Rice L. G. , Ross P. Frank , Sciumbato G. L. , Meredith F. I.
Published: May 2007

Twenty samples of rough rice (Oryza sativa) (unpolished kernels) collected during the 1995 harvest season from Arkansas (seven samples) and Texas (13 samples) were obtained from rice fields known to include plants with symptoms of Fusarium sheath rot putatively caused by Fusarium proliferatum. Samples were analyzed for fumonisin B1 (FB1) at three laboratories using three different extracting solvents by high-performance liquid chromatography (HPLC) or enzyme-linked immunosorbent assay (ELISA) methods. Forty percent of the samples were positive for FB1 at levels ≤4.3 μg/g by HPLC. The same samples contained FB1 at ≤3.6 μg/g when measured by an ELISA method. Most samples that were positive for FB1 were positive for fumonisin B2 (FB2) and fumonisin B3 (FB3) by HPLC at levels ≤1.2 μg/g. Very good agreement was obtained among the two laboratories using HPLC methods and the third using ELISA. Shelling of the unpolished rice results in hull and brown rice fractions. In a sample that contained 4.3 μg/g in whole kernels, the fumonisin level was very high in hulls (≤16.8 μg/g) and low in brown rice (≤0.9 μg/g). Milling of brown rice results in bran and white rice fractions. Fumonisins were found in bran at a level of ≤3.7 μg/g but were below the level of detection by HPLC in white rice. The presence of fumonisins (FB1, FB2, and FB3) was confirmed by fast atom bombardment/mass spectrometry. This is the first report of fumonisins in naturally contaminated rice in the United States.
Virulence of Blumeria graminis f. sp. tritici on Winter Wheat in the Eastern United States
Authors: Niewoehner A. S. , Leath S.
Published: May 2007

Samples of perithecia of Blumeria graminis f. sp. tritici from senescing wheat leaves were collected by cooperators from 17 states. Ascospores were discharged from perithecia and single-spore isolates were characterized for virulence genes using a differential host series containing 15 known resistance genes. A total of 520 isolates from 17 states were characterized in 1993 and 1994. Virulence frequencies and complexity and racial composition were examined. The data were analyzed for associations among sets of virulence genes and the geographical distribution of phenotypes. Virulence to Pm3c, Pm3f, pm5, Pm6, and Pm7 was present in all states surveyed. Since 1990, virulence to Pm3a has increased in the northeast, and virulence to Pm1, Pm4b, Pm8, and Pm17 has increased across the area surveyed. The resistance genes Pm12 and Pm16 remain highly effective in the southeastern United States. An increase in virulence frequencies and complexity of isolates was observed.
Detection of the Cassava Bacterial Blight Pathogen, Xanthomonas axonopodis pv. manihotis, by Polymerase Chain Reaction
Authors: Verdier V. , Mosquera G. , Assigbétsé K.
Published: May 2007

Cassava bacterial blight, caused by Xanthomonas axonopodis pv. manihotis, is of significant concern wherever cassava is grown. The movement of infected, asymptomatic stems is a major means of pathogen dispersal. A reliable and sensitive diagnostic procedure is necessary for the safe movement of cassava planting material. We used a cloned and sequenced pathogenicity gene of X. axonopodis pv. manihotis to develop a polymerase chain reaction (PCR) test for this pathogen. A set of primers directed the amplification of an 898-bp fragment in all 107 pathogenic strains of X. axonopodis pv. manihotis tested. PCR products were not observed when genomic DNA was tested for 27 strains of other xanthomonads, for saprophytic bacteria, or for five nonpathogenic strains of X. axonopodis pv. manihotis. The primers worked well for pathogen detection in direct PCR assays of X. axonopodis pv. manihotis colonies grown on liquid medium and in PCR assays of extracts from leaf and stem lesions. The minimum number of cells that could be detected from cassava stem and leaf lesions was 3 × 102 to 104 CFU/ml. The PCR assays proved to be relativyel sensitive and could become very useful in detecting the pathogen in cassava planting material.
Comparison of Diagnostic Techniques for Detecting Tomato Infectious Chlorosis Virus
Authors: Li R. H. , Wisler G. C. , Liu H.-Y. , Duffus J. E.
Published: May 2007

A polyclonal antiserum prepared against purified virions of tomato infectious chlorosis virus (TICV) was used to evaluate serological tests for its detection, to determine its distribution in infected plants, to study relationships among isolates of this virus, and to detect it in field samples. A cRNA probe representing TICV RNA 1 and RNA 2 was used in dot blot hybridization tests. A reverse transcriptase-polymerase chain reaction (RT-PCR) assay was also developed for detection of TICV isolates. The comparative study of these four techniques indicated that RT-PCR was 100-fold more sensitive than enzyme-linked immunosorbent assay (ELISA), Western blot, and dot blot hybridization assays for TICV detection. TICV was detected in leaf, stem, flower, and root tissues of the infected tomato plants. However, the virus was not uniformly distributed throughout the infected tomato plants, and the highest viral concentration was observed in fully developed young tomato leaves at the onset of yellowing symptoms. The virus was detected by indirect ELISA, Western blot, dot blot hybridization, and RT-PCR assays in laboratory-infected tomato, tomatillo, potato, and Nicotiana clevelandii and in naturally infected tomato, petunia, and Ranunculus sp. plants obtained from commercial sources. These tests indicate that there are apparently no detectable serological or nucleic acid differences among four TICV isolates obtained from Orange and Yolo Counties of California or from North Carolina or Italy.
Occurrence and Distribution of Ergot and Estimates of Seed Loss in Kentucky Bluegrass Grown for Seed in Central Oregon
Authors: Alderman Stephen C. , Coats Dale D. , Crowe Fred J. , Butler Marvin D.
Published: May 2007

In 1991 to 1993, ergot was detected in 36, 44, and 62%, respectively, of fields of Kentucky bluegrass grown for seed in central Oregon. Relatively few fields (2 to 13%) had a high (more than 20 sclerotia/gm seed) level of ergot. Ergot severity (percent sclerotia by weight) in 1991 to 1993 was estimated at 0.85, 0.07, and 0.34%, respectively. Percent seed replaced by ergot in 1991 to 1993 was estimated at 0.22, 0.02, and 0.08, respectively. Recleaning of seed to reduce ergot contamination and to meet purity standards resulted in a 7.8% reduction in marketable seed weight. Estimated value of seed replaced by ergot in 1991, 1992, and 1993, was $75,625, $4,758, and $17,076, respectively. Estimated value of seed lost during recleaning in 1991, 1992, and 1993, was $37,669, $8,171, and $21,964, respectively. Weed grasses supporting ergot at the time of harvest of Kentucky bluegrass were species of Bromus, Secale, Festuca, and Poa. However, very few seed heads of weed grasses were infected, and they appeared to contribute little to ergot development in central Oregon. Most infested fields (with more than one sclerotium/gm seed prior to recleaning) or weed grass sites with ergot were located in the southern range of the area of study.
Coffee Leaf Scorch Bacterium: Axenic Culture, Pathogenicity, and Comparison with Xylella fastidiosa of Citrus
Authors: de Lima J. E. O. , Miranda V. S. , Hartung J. S. , Brlansky R. H. , Coutinho A. , Roberto S. R. , Carlos E. F.
Published: May 2007

Symptoms of coffee leaf scorch (CLS) appear on young flushes of field plants as large marginal and apical scorched areas on recently mature leaves. Affected leaves drop, shoot growth is stunted, and apical leaves are small and chlorotic. Symptoms may progress to shoot dieback. Only scorched leaves which could not be related to other known agents consistently contained bacteria and bacterial agglomerates when observed with light microscopy. Only plants with these symptoms were positive in enzyme-linked immunosorbent assay (ELISA) tests using antiserum to Xylella fastidiosa Wells et al. The bacterium Xylella fastidiosa Wells et al. was isolated in November 1995 from coffee (Coffea arabica) leaves with scorch symptoms on supplemented periwinkle wilt medium. Colonies were circular, dome-shaped, white, and 0.5 to 1.5 mm in diameter. Two of 10 young coffee seedlings stem-inoculated with a suspension of the isolated X. fastidiosa in January 1996 showed leaf scorch symptoms 3 to 5 months later, contained bacteria in xylem extracts, and reacted positively in ELISA using antiserum to the citrus variegated chlorosis (CVC) strain of X. fastidiosa. ELISA-positive bacteria were reisolated from this plant. None of the symptomless plants, including controls, revealed bacteria on microscopic examinations, ELISA, or isolation attempts. Antisera developed against cultured bacteria from both CLS and CVC plants reacted positively against plant extracts of both diseases in dot immunobinding assays (DIBA). The level of detection was about 5 × 105 bacteria ml-1 for both homologous and heterologous reactions. The polymerase chain reaction amplification products produced by CLS and CVC strains of X. fastidiosa were indistinguishable. Geographical distribution of these strains is not the same. CLS is widespread and usually occurs if coffee is adjacent to CVC-affected citrus. However, CVC does not always occur when citrus is grown adjacent to CLS-affected coffee. The bacteria are closely related, if not identical.
A New Strain of Potato Carlavirus M
Authors: Cavileer T. D. , Clarke R. C. , Corsini D. L. , Berger P. H.
Published: May 2007

In 1994, potato samples for certification from Idaho seed fields reacted in enzyme-linked immunosorbent assay (ELISA) tests to a polyclonal potato carlavirus M (PVM) antiserum. Sample affinity to the antiserum was lower than control samples. Furthermore, ELISA-positive samples were obtained from both symptomatic as well as asymptomatic plants. A complementary DNA library was prepared using both reverse transcription-polymerase chain reaction and primers based on published PVM sequences, or oligo d(T) primed reverse transcribed sequences. The nucleotide sequence was determined for the 3′-terminus of the genome. Putative coat protein amino acid sequence was compared to published PVM and potato virus S coat protein sequences. While this new isolate is likely a strain of PVM, it is significantly different from known PVM coat protein sequences in the amino terminus region. These differences may explain the poor reactivity to other PVM antisera and suggest that it is a new strain of PVM, which we have designated PVM-ID.
Soil Solarization in Established Avocado Trees for Control of Dematophora necatrix
Authors: López-Herrera C. J. , Pérez-Jiménez R. M. , Zea-Bonilla T. , Basallote-Ureba M. J. , Melero-Vara J. M.
Published: May 2007

Four field experiments on the control of Dematophora necatrix in avocado orchards affected by white root rot were conducted in the Mediterranean coastal area of southern Spain during 1991 to 1994. In the unshaded locations of solarized plots, the maximal temperatures were 35 to 42°C, depending upon the year and soil depth (15 to 60 cm). Temperature increases attributable to soil solarization ranged between 4 and 8°C in unshaded areas, whereas for shaded areas they were approximately 4°C. Inoculum recovery was decreased in root samples buried at 15 to 30 cm in unshaded locations of both solarized and unsolarized plots after 3 to 5 weeks, whereas 4 to 8 weeks of solarization were required for the elimination of the pathogen buried at depths of 45 to 60 cm. In contrast, inoculum recovery ranged from 30 to 60% for samples in shaded locations of unsolarized plots. D. necatrix was not recovered from roots of infected trees in solarized plots sampled 9 months after solarization, whereas recovery from roots in unsolarized plots was similar to levels before solarization. Soil solarization in established orchards was successful in reducing viability of inoculum buried in soil and eliminated inoculum in infected roots of live trees.
Control of Brown Rot and Blue Mold of Sweet Cherry with Preharvest Iprodione, PostharvestCryptococcus infirmo-miniatus, and Modified Atmosphere Packaging
Authors: Spotts R. A. , Cervantes L. A. , Facteau T. J. , Chand-Goyal T.
Published: May 2007

The effectiveness of preharvest iprodione and postharvest Cryptococcus infirmo-miniatus treatments alone and in combination for control of decay of sweet cherry fruit was studied. Also, the effect of a modified atmosphere on brown rot control was evaluated as a part of the iprodione–C. infirmo-miniatus combinations. A single preharvest application of iprodione at 1.13 kg a.i./ha reduced brown rot in stored sweet cherry fruit in both years of this study. Significantly better control of brown rot was obtained when cherry fruit that received a preharvest iprodione application also were treated with a postharvest dip in a suspension of C. infirmo-miniatus containing 0.5 to 1.5 × 108CFU/ml. Brown rot was reduced by modified atmosphere packaging (MAP) alone and further reduced as a result of a C. infirmo-miniatus–MAP synergism. Incidence of brown rot was reduced from 41.5% in the control to 0.4% by combining preharvest iprodione and postharvest C. infirmo-miniatus treatments with MAP.
First Report of Alternaria cassiae on Cowpea
Authors: la Grange N. , Aveling T. A. S.
Published: May 2007

A destructive foliar disease was observed during field surveys of cowpea (Vigna unguiculata (L.) Walp.) in the Mpumalanga and Gauteng provinces in South Africa. Foliar symptoms begin as semicircular water-soaked lesions at the leaf margins. Lesions enlarge toward the center of the leaf, becoming necrotic. Sporulation is visible with the naked eye on the leaf surface as a black velvet mass. Occasionally, circular lesions are observed in the center of the leaf. Lesions begin as small brown spots, surrounded by a yellow halo. The lesions enlarge and become water-soaked, and black masses of conidia are visible on the brown, necrotic tissue surface. Alternaria cassiae (A. M. M. Juriar & A. Khan) was consistently isolated from the diseased leaf material. An isolate of the causal pathogen was identified by and deposited with the National Collection of Fungi, Plant Protection Research Institute, Pretoria, South Africa, and designated with the number PPRI 6393. Koch's postulates were proven by inoculating the leaves of cowpea seedlings with a 106 conidia ml-1suspension. Inoculated plants were maintained in a humidity chamber for 48 h and then returned to the greenhouse. After approximately 7 days, symptoms resembling those observed in the field were apparent. A. cassiae was reisolated from diseased tissue. The same foliar disease was observed on cowpea in Botswana. A. cassiae was isolated and identified from the characteristic lesions.
Pseudomonas syringae Leaf Blight, a New Disease of Kalmia latifolia
Authors: Putnam M. L.
Published: May 2007

In spring and fall of 1997, and in February 1998, Kalmia latifolia cv. Olympic Fire plants with severe leaf blight symptoms were submitted to the Oregon State University Plant Clinic from a commercial nursery. The primary symptom was a dark purple leaf blight, often associated with the leaf mid-rib. Disease progressed down the petioles and into twigs, causing blackening of affected tissues and leaf drop. Abundant bacterial streaming was observed oozing from the margins of affected tissue when examined at ×100. Isolations from affected tissues were made onto King's medium B (KB). A fluorescent bacterium was recovered and identified as Pseudomonas syringae by the Biolog system of identification. Identity was confirmed by fatty acid methyl ester analysis performed by Larry Barnes (Texas A&M University, College Station). Attempts to determine the pathovar were unsuccessful. A single colony isolate of the bacterium was raised on KB. Koch's postulates were completed by the following procedures. A bacterial suspension was made from a 24-h-old agar culture of this isolate with phosphate buffer with 0.2% gelatin (PBG). The concentration of the suspension was adjusted to 8 × 107 cells per ml by direct enumeration. Five milliliters of the suspension was atomized onto young leaves on six twigs of Kalmia latifolia. Controls consisted of young leaves on four twigs atomized with 5 ml of PBG. Twigs receiving the inoculum or the PBG were enclosed in plastic bags and maintained at room temperature near a north-facing window. Symptoms appeared 6 days later: dark purple spots on the margins of inoculated leaves and blight symptoms near the leaf mid-rib. Symptoms did not appear on PBG-sprayed leaves. Pseudomonas syringae was successfully reisolated from surface-disinfested inoculated leaves but not from leaves sprayed with PBG. This is the first report of Pseudomonas syringae causing a leaf blight of Kalmia.
Detection of Chlorothalonil in Dew Water Following Aerial Spray Application and Its Role in the Control of Black Sigatoka in Banana
Authors: Washington J. R. , Cruz J. , Fajardo M.
Published: May 2007

A standardized bioassay measuring the growth inhibition of Aspergillus niger in vitro allowed the detection of small concentrations (0.1 to 20 μg/ml) of chlorothalonil present in dew water on both the adaxial and abaxial surface of banana leaves in a commercial plantation receiving aerial sprays. Chlorothalonil concentrations detected in dew water on the banana leaf surface were within the range of concentrations required to prevent Mycosphaerella fijiensis (causal agent of black Sigatoka) ascospore germination in laboratory bioassays. When 9-cm-diameter banana leaf disks inoculated with M. fijiensis ascospores were immersed for 4 h in water containing 0.1 to 0.6 μg of chlorothalonil per ml, ascospore germination was inhibited by 96.9%. The EC50 values for inhibition of ascospore germination were between 0.01 and 0.03 μg/ml for chlorothalonil and between 3.2 and 3.7 μg/ml for mancozeb. Following a 4-h exposure to chlorothalonil and mancozeb, and subsequent removal of the fungicides by a washing step, ascospores failed to germinate, indicating that both fungicides are fungicidal to M. fijiensis, not fungistatic. Recovery analysis of chlorothalonil spray droplet deposits and active ingredient on deposition cards in the field during aerial spray applications indicated that detectable fungicide deposition on the abaxial leaf surface occurs only when the banana leaf-target is vertical or nearly so. The significance of this observation in relation to the control of black Sigatoka with protectant fungicides is discussed.
Effects of Oxygen Deprivation and Pythium Root Rot on Sugarcane Red Rot
Authors: Yin Zhi , Hoy J. W.
Published: May 2007

The effects of oxygen deprivation or poor drainage and Pythium root rot on development of red rot, caused by Colletotrichum falcatum, and spring shoot population of sugarcane were evaluated under controlled and field conditions. Detached stalks of five cultivars were exposed to low atmospheric oxygen (0.5 to 2.7%), created by enclosing stalks in sealed chambers through which humidified nitrogen gas was passed for 0, 1, or 2 weeks. Stalks were then inoculated with C. falcatum and maintained for 6 weeks with humidified air flow. Red rot severity, assessed as four disease traits, was not increased by previous oxygen deprivation. In field experiments, inoculation of stalks of three cultivars with C. falcatum before planting resulted in a reduction in shoot populations the following spring. Poor drainage resulted in an additional reduction in shoot populations developing from inoculated stalks. Soil atmospheric oxygen was reduced in the root zone below planted stalks under poor drainage conditions. However, only minor reductions in oxygen were detected in the zone of elevated rows in which planted stalks were located. The detrimental effect of poor drainage on shoot populations from inoculated stalks was alleviated by metalaxyl application. Pythium root rot, caused by Pythium arrhenomanes, reduced the initial root system and growth of shoots in greenhouse experiments. The combination of P. arrhenomanes and C. falcatum inoculation increased dead bud percentage in one of two cultivars and red rot severity for both. The results suggest that spring shoot populations developing from red rot-affected stalks exposed to poor drainage can be reduced by the combined effects of red rot and Pythium root rot.
Germination Stimulation of Striga gesnerioides Seeds by Hosts and Nonhosts
Authors: Berner D. K. , Williams O. A.
Published: May 2007

Cowpea (Vigna unguiculata) is an important source of protein in Africa, but production is hindered by the parasitic plant Striga gesnerioides. Crop rotation with nonhost cultivars, selected to stimulate parasite seed germination, is being used successfully to control other Striga spp. and may have potential to control S. gesnerioides. Little information has been available on nonhosts of S. gesnerioides that are capable of stimulating germination of parasite seeds. A laboratory procedure was used to evaluate species and cultivars for their ability to stimulate S. gesnerioides seed germination. Genotypes of all Vigna spp. tested stimulated parasite seed germination. Some genotypes of the nonhost species Cajanus cajan, Lablab purpureus, stenocarpa, and Sorghum bicolor also stimulated parasite seed germination. One cultivar of Sorghum bicolor stimulated significantly more germination than any other cultivar or species. Control of S. gesnerioides through rotation with selected nonhost cultivars has potential if selection is done with the parasite isolate(s) from the locality of intended use. When seeds of single-plant isolates of S. gesnerioides were tested against roots of seedlings from Sorghum bicolor landraces and from a susceptible cowpea cultivar, only specific isolate and plant combinations resulted in parasite seed germination. These specific interactions have broader implications for parasite survival.
Physiochemical Characterization and Field Assessment of Lettuce Chlorosis Virus
Authors: McLain Jennifer , Castle Steven , Holmes Gerald , Creamer Rebecca
Published: May 2007

Lettuce chlorosis virus (LCV) was purified and partially characterized, and polyclonal antisera were produced and used to assess disease in the field. The antisera reliably detected LCV by indirect enzyme-linked immunosorbent assay (ELISA) in Nicotiana benthamiana. In Western blots, the LCV antisera distinguished between LCV and lettuce infectious yellows virus (LIYV)-infected plants. LCV particle lengths in partially purified preparations, as observed by transmission electron microscopy, were variable, with the majority between 750 and 950 nm long. A single, high molecular weight dsRNA and several lower molecular weight dsRNAs were isolated from LCV-infected N. benthamiana. A single RNA isolated from purified virion preparations was estimated to be 8,625 nucleotides long and was suspected to be the genomic RNA of LCV. LCV was present in experimental field plots in Holtville, California, during the lettuce growing seasons of 1995 to 1997. The percentage of symptomatic plants and yield of lettuce heads treated with insecticide, as well as dsRNA and ELISA reactions for the plots, are reported. A dsRNA consistent in size with LCV was isolated from four weed species in the Imperial Valley of California.
Effect of Tillage Practices on Vertical Distribution of Phytophthora sojae
Authors: Workneh F. , Yang X. B. , Tylka G. L.
Published: May 2007

The vertical distribution of Phytophthora sojae was investigated in soil samples collected in the spring of 1994 from soybean fields at 62 locations in Illinois, Indiana, Iowa, and Minnesota. In the fall of 1995, soil samples were collected from 18 additional locations in Illinois and Iowa. Each location consisted of a pair of no-till and conventional-till fields, and soil samples were collected from arbitrarily selected locations in each field at 0- to 7.5-cm and 7.5- to 15-cm depths. Separate intensive sampling was made in the spring of 1995 from two pairs of adjacent no-till and conventional-till fields at the Iowa State University Northeast Research Farm, in which samples were collected from 0- to 30-cm depth in increments of 5 cm. Samples were assayed for P. sojae with the use of a leaf-disk bioassay. In the 1994 regional samples, there was greater recovery of P. sojae (P ≤ 0.05) at 0- to 7.5-cm depth in the no-till samples than in the conventional-till samples for all states except Minnesota. The fall 1995 samples from Illinois followed a similar trend (P = 0.05); whereas samples from Iowa showed no significant difference between tillage systems. At depths greater than 7.5 cm, there was generally no difference in detection frequency of P. sojae between tillage systems. Samples from the Northeast Research Farm followed patterns of vertical distribution similar to those of the regional samples. In no-till fields, the detection frequency of P. sojae was greatest near the soil surface; two to three times greater than that of the conventional-till fields at this depth. In the conventional-till fields, however, the frequency of recovery peaked at 20 cm and was comparable at these depths to those of no-till fields. There was a positive correlation between the percentage of leaf disks colonized and residue dry weights in the no-till fields (r = 0.84, P = 0.04; and r = 0.86, P = 0.03) but not in the conventional-till fields (r = -0.06, P = 0.90; and r = -0.60, P = 0.17). The recovery of P. sojae in greater frequency near the soil surface in no-till fields than in conventional-till fields suggests that the potential for damping-off may be greater in no-till fields than in conventional-till fields.
Instability of a pEA29 Marker in Erwinia amylovora Previously Used for Strain Classification
Authors: Schnabel E. L. , Jones A. L.
Published: May 2007

We examined the use of previously observed restriction fragment length polymorphisms (RFLPs) of a polymerase chain reaction (PCR)-amplified fragment of plasmid pEA29 for differentiating strains of Erwinia amylovora. The PCR fragment from E. amylovora strain CA11 contains a region of 8-bp tandem repeats which is predicted to cause the RFLPs. Examination of a collection of 93 strains revealed the repeat sequence GATTACA(GAATTACA)nGAATTACA in pEA29 with n ranging from 3 to 14. Selected strains were examined after growth in liquid culture to establish the stability of this character. Four strains originally with n = 14, 13, 7, and 3 repeats were grown overnight in liquid culture and streaked onto agar plates to produce individual colonies. Respectively, 4, 10, 1, and 0 out of 17 colonies per strain had an altered copy number when retested. Considering the instability in the number of repeats, it is concluded that the polymorphism in this region of pEA29 is not useful as a marker for following the migration of E. amylovora.
Comparative Virus Resistance and Fruit Yield of Transgenic Squash with Single and Multiple Coat Protein Genes
Authors: Fuchs Marc , Tricoli David M. , Carney Kim J. , Schesser Mike , McFerson James R. , Gonsalves Dennis
Published: May 2007

Five transgenic squash lines expressing coat protein (CP) genes from cucumber mosaic cucumovirus (CMV), zucchini yellow mosaic potyvirus (ZYMV), and watermelon mosaic virus 2 potyvirus (WMV 2) were analyzed in the field for their reaction to mixed infections by these three viruses and for fruit production. Test plants were exposed to natural inoculations via aphids in trials simulating the introduction of viruses by secondary spread from mechanically infected susceptible border row plants. Plants of transgenic line CZW-3 expressing the CP genes from CMV, ZYMV, and WMV 2 displayed the highest level of resistance with no systemic infection, although 64% exhibited localized chlorotic dots which were mainly confined to older leaves. CZW-3 plants had a 50-fold increase in marketable yield compared to controls and the highest predicted cash returns. Plants of transgenic line ZW-20 expressing the CP genes from ZYMV and WMV 2 displayed high levels of resistance to these two potyviruses, but 22% became infected by CMV. However, ZW-20 plants provided a 40-fold increase in marketable yield relative to controls and good estimated cash returns. Three transgenic lines expressing single CP genes from either ZYMV (line Z-33), WMV 2 (line W-164) or CMV (line C-14) developed systemic symptoms similar to those of controls but showed a delay of 2 to 4 weeks before the onset of disease. Plants of transgenic line Z-33 were highly resistant to ZYMV but not to WMV 2 and CMV. Interestingly, Z-33 plants had a 20-fold increase in marketable yield compared to controls and some predicted cash returns if market sale prices were high. This study indicates that virus-resistant transgenic lines are economically viable even if they are affected by viruses other than those to which they are resistant.
First Report of Tobacco Streak Ilarvirus from Honeysuckle
Authors: Waterworth H. E.
Published: May 2007

A honeysuckle (Lonicera fragrantissima) shrub on the grounds of the former Plant Quarantine Station, Glenn Dale, MD, had chlorotic leaves on some shoot tips and a mild veinal chlorosis. Young leaves were triturated in buffer and rub-inoculated onto a series of potential indicator hosts. The virus incited necrotic local lesions and necrosis of the growing point in Chenopodium quinoa, etched ringspots on inoculated leaves of Nicotiana tabacum Xanthi nc, mosaic in Zinnia violacea, and chlorotic local lesions in Tetragonia tetragonioides. It did not infect any of 46 other herbaceous genera in families Cucurbitaceae, Fabaceae, Asteraceae, Solanaceae, or Brassicaceae. In gel diffusion tests with symptomatic leaves from tobacco, this virus reacted with antiserum to tobacco streak virus (TSV) HR strain, but did not react with antisera to alfalfa mosaic or with antisera to 12 viruses in the NEPO or Sobemovirus groups. Virus in leaves directly from the source shrubs, tested by enzyme-linked immunosorbent assay (ELISA), also reacted with TSV strain HF antiserum. Examination by electron microscopy of leaf dips revealed isometric particles 27 nm in diameter. The now 12-ft tall shrubs were grown from seed imported from China in 1914 (PI 40689). This species is now widely commercially available in the U.S. and grown for its fragrant late winter flowers (2). Viral-infected Lonicera spp. have been reported from Europe, Russia, Japan, and Canada (1). TSV is reported to be seed-borne in several other genera. Among other viruses reported from honeysuckle are Lonicera latent carlavirus, tobacco leaf curl geminivirus, alfalfa mosaic virus, tomato bushy stunt virus, a rhabdovirus, and an aphid transmitted virus.

References: (1) R. W. Fulton. CMI/AAB Descriptions of Plant Viruses No. 307, 1985. (2) C. J. Perkin. Plantsman 12:215, 1991.
Control of Papaya Ringspot Virus-Type W in Zucchini Squash by Cross-Protection in Brazil
Authors: Rezende J. A. M. , Pacheco D. A.
Published: May 2007

Two mild strains of papaya ringspot virus-type W (PRSV-W) were tested under greenhouse and field conditions to study the potential of cross-protection for control of zucchini squash mosaic. Protected plants of zucchini squash cultivars Caserta and Clarinda were challenged with three severe strains from different geographic regions of the country in tests carried out in the greenhouse. Challenge inoculations were done mechanically 10 and 20 days after the protective inoculation. The mild strains did not have a visible negative effect on the development of the plants and offered effective protection against the severe strains. Field tests of protected Caserta plants were carried out in Piracicaba County, São Paulo. Comparative evaluation based on the symptoms and development of protected and unprotected plants of zucchini squash showed that both mild strains effectively protected the plants against the effects of the severe strain present in the field. Yield of marketable fruits harvested from protected plants was only 10% less than that of the healthy plants in one field trial. Compared with the yield from plants infected with the severe strains, protected plants showed an increase of 511 and 633% in the number and weight of marketable fruits, respectively, in a test in 1994. In a second experiment in 1995, an increase of 327% in the number and 344% in the weight of marketable fruits was recorded. These studies demonstrate the effectiveness of cross-protection for the control of the mosaic disease caused by PRSV-W in zucchini squash and offer growers a method for large-scale application of this technology.
Seasonal Patterns of Spore Dispersal of Phaeosphaeria spp. and Stagonospora spp.
Authors: Arseniuk E. , Góral T. , Scharen A. L.
Published: May 2007

The spatial and temporal patterns of discharge and dissemination of airborne spores of Phaeosphaeria spp. and Stagonospora spp. were studied. Both ascospores and pycnidiospores of the pathogens were deposited at various densities on microscope slides used as spore samplers. The maximum deposition of the spores was observed during the period of August to October. A multiple regression analysis was used to determine which weather factors significantly explained the variation measured in the numbers of ascospores that settled on microscope slides. Rainfall, air temperature, and relative air humidity were influential in the release of Phaeosphaeria spp. ascospores into the air. The amount of airborne ascospores was a function of the variables and remained largely under their control. The liberation of ascospores was favored by air temperature above 0°C, rainfall greater than 1 mm, and high relative humidity. The range of atmospheric conditions stimulating air dispersal of ascospores was wider than that for pycnidiospores. Pycnidiospores were sampled only during rainy days. Their release was affected adversely by air temperature below 5°C. Multiple regression models based on weather data were developed and verified for their predictive ability and accuracy by jackknife and cross-validation procedures, as well as by comparisons of observed and predicted mean numbers of deposited ascospores per microscope slide after a substitution of each period data set with a set of data of the other respective time interval. The numbers of airborne ascospores predicted by the regression models were in a good agreement with the observed values. The jackknife and cross-validation techniques allowed use of the limited data sets for both the parameter estimation and validation processes in a development of simulation models. The airborne inoculum appeared to be omnipresent over cereal areas year round, except during periods with freezing temperatures and a snow cover. Such an omnipresence of inoculum of the pathogens poses a danger to crops and could be of importance in the epidemiology of Stagonospora (= Septoria) blotches under the climatic conditions of central Poland.
First Report of Inonotus tomentosus, the Cause of Tomentosus Root Disease, from the Yukon Territory
Authors: Hunt R. S. , White T.
Published: May 2007

During forest pest surveys in the Watson Lake area (60°N 129°W) of the Yukon Territory (YT), sporocarps, tentatively identified as Inonotus tomentosus (Fr.:Fr.) S. Teng, were observed in association with old mortality (25+ years) and root rot of old (200 to 275 years) white spruce (Picea glauca (Moench) Voss) growing in riparian zones. I. tomentosus primarily attacks spruce throughout North America (1). Cultures from collected sporocarps and from a decayed root of a living tree produced chlamydospore-like hyphal swellings typical of I. tomentosus(2). Although three of the collected sporocarps were bracketlike, none bore hooked hymenial setae, typical of I. circinatus (Fr.) R. L. Gilbertson. All sporocarps collected possessed straight setal hyphae and were confirmed as I. tomentosus (1). These specimens are filed at the Pacific Forestry Centre herbarium as DAVFP 25375 and DAVFP 25376. This is the first western Canadian report of this major conifer root disease north of about 55°N latitude. Sporocarps have been collected at about the same latitude as Watson Lake, but from 21° farther west, near Fairbanks and Anchorage, AK (L. Trummer, USDA For. Serv. Anchorage, AK, personal communication). For several years, other stump and root decay samples have been collected in the YT as far west as Haines Junction (about halfway between Anchorage and Watson Lake), but the pathogen has never been successfully cultured nor sporocarps collected. Because the decay pattern can be confused with that caused by Phellinus pini (Thore:Fr.) A. Ames, and other diagnostic features were lacking, there has been a reluctance to accept that I. tomentosus is present in the YT. However, it seems likely that I. tomentosus is much more widespread north of 55°N in western Canada than has previously been recognized.

References: (1) R. L. Gilbertson and L. Ryvarden. North Am. Polypores. Fungiflora 1:403, 1986. (2) R. S. Hunt. Can. J. Plant Pathol. 19:307, 1997.