bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of Resistance to Thielaviopsis basicola in Diploid Cotton
Authors: Wheeler T. A. , Gannaway J. R. , Keating K.
Published: May 2007

A screening program to find sources of resistance to Thielaviopsis basicola in cotton identified a diploid cotton (Gossypium arboreum, PI 1415) with apparent high resistance to this pathogen. Seedlings were obtained from self-pollinated seed taken from the resistant plant (PI 1415) and grown in growth chamber tests with the cultivars (tetraploid G. hirsutum) Paymaster HS-26 and Paymaster Tejas as controls. Seedlings were grown for 20 days in naturally infested field soil and evaluated for root growth and root necrosis. In all tests, PI 1415 had less (P = 0.001) root necrosis than the cultivars HS-26 and Tejas. A triadimenol seed treatment also resulted in less (P = 0.001) root necrosis for all three cotton genotypes, and the response was additive with level of disease resistance. Incorporation of the resistance factor from PI 1415 into tetraploid upland cotton may greatly reduce damage by black root rot, especially in combination with fungicide seed treatments.
Fruit Surface Colonization and Biological Control of Postharvest Diseases of Pear by Preharvest Yeast Applications
Authors: Benbow Jesse M. , Sugar David
Published: May 2007

The yeasts Cryptococcus infirmo-miniatus, Cryptococcus laurentii, and Rhodotorula glutinis, applied to Bosc and d'Anjou pear fruit in the field 3 weeks prior to harvest, maintained high population levels through harvest, while populations of Candida oleophila declined after 1 and 2 weeks, and by harvest were not significantly different from total yeast populations on untreated fruit. Yeasts were sprayed individually on fruit at concentrations of 1 to 3 × 108 CFU/ml, with approximately 2 ml applied per fruit. Initial population sizes for all four species averaged 5 × 106 CFU per fruit. C. infirmo-miniatus provided the most consistent decay control in fruit treated 3 weeks before harvest. C. infirmo-miniatus and R. glutinis also provided significant postharvest decay control in Bosc fruit treated 1 day before harvest.
Evaluation of Tactics for Managing Resistance of Venturia inaequalis to Sterol Demethylation Inhibitors
Authors: Köller Wolfram , Wilcox W. F.
Published: May 2007

The impact on the selection and control of subpopulations of V. inaequalis resistant to the sterol demethylation inhibitor (DMI) fenarimol or to dodine were evaluated with respect to several tactics of apple scab control. Experiments were conducted in an experimental orchard with elevated levels of DMI and dodine resistance over a period of three consecutive seasons. The DMI-resistant subpopulation was poorly (14%) controlled at a fenarimol rate of 15 mg/liter (sprayed to run-off), whereas control was significantly improved (54%) at twice that rate. Mancozeb mixed with the low rate of fenarimol also improved the control of DMI-resistant isolates, but the improvement was due to the indiscriminate control of both the DMI-sensitive and -resistant populations provided by mancozeb. The selection of fenarimol-resistant isolates resulting from poor control of the resistant subpopulation by the low rate of fenarimol was equivalent whether fenarimol was applied singly or in mixture with mancozeb. Consequently, the use of high DMI rates in mixture with a protective fungicide is expected to delay the build-up of resistant subpopulations by limiting their increase through two separate principles of control. For dodine in mixture with fenarimol, it was found that each mixing partner applied alone selected both fe-narimol- and dodine-resistant isolates. This selection pattern was partly explained by the possibility that one of the multiple genes underlying fenarimol and dodine resistance confers resistance to both fungicides, in addition to the selection of double-resistant isolates. Regardless, a mixture of fenarimol with dodine each employed at a low rate controlled both the fenarimol-and the dodine-resistant subpopulation at least as effectively as the individual components at twice their mixture rate, and an accelerated selection of double-resistant isolates was not detected. In commercial orchard trials, mixtures of DMIs with either a protective fungicide or with dodine provided equivalent control even when levels of DMI resistance, dodine resistance, or both were moderately elevated. With the exception of orchards with high levels of DMI or dodine resistance, dodine might be an alternative to protective fungicides as a mixing partner with DMIs.
Specificity of TAS-ELISA for Beet Necrotic Yellow Vein Virus and Its Application for Determining Rhizomania Resistance in Field-Grown Sugar Beets
Authors: Wisler G. C. , Lewellen R. T. , Sears J. L. , Liu H.-Y. , Duffus J. E.
Published: May 2007

Levels of beet necrotic yellow vein virus (BNYVV), as measured by triple-antibody sandwich-enzyme-linked immunosorbent assay (TAS-ELISA), were compared with biological evaluations in representative commercial and experimental sugar beet cultivars developed for production in the United States and ranging in their reactions to rhizomania from uniformly susceptible to highly resistant. TAS-ELISA was specific for BNYVV and did not react with related soilborne sugar beet viruses. Differences in absorbance (A405nm) values measured in eight cultivars closely correlated with the dosage and frequency of the Rz allele, which conditions resistance to BNYVV. A diploid (Rzrz) hybrid had a significantly lower absorbance value (less virus) than a similar triploid (Rzrzrz) hybrid. Cultivars that segregated (Rzrz:rzrz) had higher absorbance values than uniformly resistant (Rzrz) hybrids, as was expected. For all cultivars, absorbance values decreased as the season progressed. Absorbance value was significantly positively correlated with rhizomania disease index score and negatively correlated with individual root weight, plot root weight, and sugar yield. This information should be useful in resistance-breeding and -evaluation programs and in the sugar industry when considering cultivar choice, inoculum production, and future crop rotations.
First Occurrence of White Rust of Arugula, Caused by Albugo candida
Authors: Scheck H. J. , Koike S. T.
Published: May 2007

In California, arugula (Eruca sativa) is grown commercially as a component of specialty mixed green salads. In 1999, white rust was observed on arugula in the central coast county of Santa Barbara. Symptoms consisted of white, blisterlike sori beneath the raised host epidermis on the underside of leaves from the seedling stage onward. Secondary infection of flower heads led to staghead development. Affected plantings were severely diseased and were not harvested. The pathogen was confirmed to be Albugo candida (Pers.) Kunze (2). Sporangia diameters ranged from 19.5 to 22.2 μm. Inoculum for pathogenicity tests was prepared by scraping sporangia from infected leaves and incubating them in sterile, distilled water for 12 h at 5°C to induce zoospore formation (1). The following plants were then spray inoculated: arugula, cauliflower (Brassica oleracea subsp. botrytis), Chinese cabbage (Brassica campestris subsp. pekinensis), Japanese mustard (Brassica campestris subsp. nipposinica), red mustard (Brassica juncea subsp. rugosa), and tah tsai (Brassica campestris subsp. narinosa). Twelve plants of each species were inoculated with 1.5 × 104 spores per ml at the six- to eight-leaf stage. Plants were incubated in a dew chamber for 48 h at 18°C and then maintained in a greenhouse at 20 to 24°C. After 10 to 12 days, white rust pustules similar to the original symptoms observed in the field developed only on arugula. The experiment was conducted three times and the results were the same. Distinct biological races of A. candida have been described for some Brassicaceae hosts of white rust (1). This is the first report of white rust of arugula in California caused by A. candida.

References: (1) R. S. Pidskalny and S. R. Rimmer. Can. J. Plant Pathol. 7:283, 1985. (2) G. S. Pound and P. H. Williams. Phytopathology 53:1146, 1963.
Coriander: A New Natural Host of Groundnut Ring Spot Virus in Brazil
Authors: Lima M. F. , de Ávila A. C. , da G. Wanderley L. J. , Nagata T. , da Gama L. J. W.
Published: May 2007

Coriander plants (Coriandrum sativum L. ‘Palmeira’), showing stunting, chlorotic ring spots, necrosis, and malformation of apical leaves were observed on 50-day-old-plants in July 1998 in one seed production field at Petrolina, State of Pernambuco, Brazil, but not in nearby fields. Leaf samples were collected and tested by double antibody sandwich-enzyme-linked immunosorbent assay (DAS-ELISA) with a panel of polyclonal antibodies made against the nucleocapsid protein (N) of tomato spotted wilt virus (TSWV), tomato chlorotic spot virus (TCSV), groundnut ring spot virus (GRSV), and impatiens necrotic spot virus (INSV) (1). All symptomatic samples reacted only with the GRSV antisera. Coriander leaf extracts from infected plants were mechanically inoculated onto potential indicator hosts. The virus induced systemic infection with vein clearing, chlorotic and necrotic spots, necrotic ring spots, mosaic, top distortion, and stunting within 21 days after inoculation on Capsicum annuum cv. Ikeda, C. chinense PI 159236, Physalis floridana, Nicandra physaloides, Nicotiana tabacum cv. TNN, N. benthamiana, Lycopersicon esculentum cv. Rutgers, Phaseolus vulgaris cv. BT2, and Gomphrena globosa. The symptomatic indicator plants tested positive for GRSV by DAS-ELISA. P. vulgaris, Chenopodium amaranthicolor, C. quinoa, and Cucurbita pepo (zucchini) cv. Caserta showed only small, necrotic, local lesions on inoculated leaves. Citrullus lanatus cv. Charleston Gray was asymptomatic. This is the first report of natural occurrence of GRSV on coriander in Brazil.

Reference: (1) A. C. de Ávila et al. J. Gen. Virol. 71:2801, 1990.
First Report of Soilborne Wheat Mosaic Virus in the United Kingdom
Authors: Clover G. R. G. , Wright D. M. , Henry C. M.
Published: May 2007

In April 1999, severe soilborne wheat mosaic virus (SBWMV) symptoms were observed in five fields of winter wheat (Triticum aestivum, cvs. Consort, Equinox, and Savannah) on one farm in Wiltshire, UK. Affected plants were markedly stunted and had a pale mosaic on their leaf sheaths that developed into bright yellow, parallel streaks on the leaves as they unfolded. Symptomatic plants were found in discrete, elliptical patches ranging in size from a few square meters to nearly a hectare. During May and June, symptoms became less marked as temperatures increased and were restricted to lower leaves. SBWMV was positively identified in all five fields (60 to 170 plants per field) by double (W. Huth, BBA-Braunschweig, Germany; Sanofi Phyto-Diagnostics, Paris) and triple (T. Wilson, SCRI, Dundee, UK) antibody sandwich enzyme-linked immunosorbent assay and by reversetranscription polymerase chain reaction (2). Identification was confirmed by immunoelectron microscopy, including protein-A gold labeling, which revealed bipartite, rod-shaped particles typical of SBWMV. Neither wheat spindle streak mosaic virus nor barley yellow dwarf virus was detected in the field samples, nor was SBWMV detected in any other field subsequently sampled, despite a survey of the surrounding area. Wheat is the most important economic crop in the United Kingdom (≈1.9 million hectares are grown annually, yielding ≈16 million tonnes), but its position is threatened by the economic impact of SBWMV, which has decreased yields by up to 50% in the United States (1).

References: (1) T. A. Kucharek and J. H. Walker. Plant Dis. Rep. 58:763, 1974. (2) R. E. Pennington et al. Plant Dis. 77:1202, 1993.
First Report of Rhizosis Caused by Ceratocystis radicicola on Date Palms in South Africa
Authors: Linde C. , Smit W. A.
Published: May 2007

During late summer (February to March) of 1997, a sudden loss of large date palms (Phoenix dactylifera L. ‘Medjool’) and adjacent suckers was observed in the Pofadder area of South Africa. The palms were planted in sandy soil, with flood irrigation from the adjacent Orange River. Initial symptoms included wilting of leaves, chlorosis of young leaves, and root necrosis. Ceratocystis radicicola (D.E. Bliss) C. Moreau (synamorph Ceratostomella radicicola; anamorph Chalara) was consistently isolated from necrotic roots and lower crown portions of diseased palms. Dark colored spores were observed in root sections. Pathogenicity studies were performed in a shadehouse on 5-year-old Medjool clones. Two experiments were conducted in which Medjool plants were inoculated with 2-week-old C. radicicola cultures grown on corn meal agar (CMA). In the first experiment, a 7-mm wound was made at the leaf base of 15 plants and inoculated with an agar plug of C. radicicola culture. The same number of control plants was inoculated with CMA. Wounds were sealed with Parafilm, and lesions were measured after 3 months. In the second experiment, conidial suspensions and pieces of mycelia from five C. radicicola cultures were harvested in 1.5 liters of water, and 100 ml of inoculum was added to each of 15 plants. Control plants (15 total) each received 100 ml of sterile water. Plants were examined after 3 months. In the first experiment, all leaves inoculated at the base with C. radicicola became necrotic at the point of inoculation, wilted rapidly, and died. In the second experiment, roots showed severe necrosis resembling rhizosis observed in the field. In each experiment, only three plants died, and C. radicicola was successfully isolated from all inoculated plants. No symptoms developed on control plants, and C. radicicola could not be isolated from them. Rhizosis of date palms caused by C. radicicola has been described in the United States (1) and differs from the disease of date palm stems, leaves, buds, and inflorescences caused by C. paradoxa (Dade) C. Moreau. This is the first report of rhizosis on date palms in South Africa.

Reference: (1) D. E. Bliss. Phytopathology 31:1123, 1941.
First Report of Pythium paroecandrum on Lupinus havardii
Authors: Fernández-Pavía S. P. , Valenzuela-Vazquez M.
Published: May 2007

Lupinus havardii Wats. (Big Bend Bluebonnet), a plant native to Texas, has been tested extensively for greenhouse production as a cutflower crop (1). Disease symptoms were observed on L. havardii plants grown in Las Cruces, NM, during two consecutive years. Plants were grown in Metro Mix 200 and watered by an automatic irrigation system every 3 days. During the growing season, which extended from September through February, 6% of mature plants (10-week-old plants) became chlorotic, wilted, and died. The first symptoms were observed during December 1998, when greenhouse temperatures were from 10 to 13°C. During the rest of the growing season, from February to July, only one plant became diseased, during May 1999, and the plant died within 1 week after greenhouse temperatures reached 20 to 25°C. Diseased plants were examined, and root, crown, and stem rot were found. Pythium paroecandrum Drechs. (2) was isolated routinely from infected tissues. Koch's postulates were fulfilled after plants were inoculated with oospores and mycelia of P. paroecandrum. Inoculum was applied next to the crown of 6-week-old plants in the form of water-agar plugs and a suspension that contained P. paroecandrum oospores and mycelia. Plants were maintained at 20 to 25°C. After 10 days, symptoms were similar to those previously observed, and the pathogen was reisolated from necrotic lesions observed on stems and crowns. Disease developed slower on 6-week-old plants (inoculated) than on 10-week-old plants (naturally infected). This is the first report of P. paroecandrum on L. havardii.

References: (1) W. A. Mackay and T. D. Davis. HortScience 33:348, 1998. (2) A. J. Van der Plaats-Niterink. Monograph of the genus Pythium. Studies Mycol. 21:1, 1981.
Outbreak of False Smut of Rice in Louisiana
Authors: Rush M. C. , Shahjahan A. K. M. , Jones J. P. , Groth D. E.
Published: May 2007

False smut, caused by Ustilaginoidea virens (Cooke) Takah., has been occurring in Louisiana rice since at least 1906 (4). A color plate (no. 69) of the disease was published in the Compendium of Rice Diseases published by the American Phytopathological Society (3). The slide for this plate was taken by M. C. Rush in 1976 of rice grown at the Rice Research Station at Crowley, LA. Since that time, the disease has been sporadic and light in Louisiana. In 1997, however, incidence was high. False smut was present on many germ plasms at the Rice Research Station in Crowley and was observed on commercial cultivars in several growers' fields in southwestern Louisiana. Incidence ranged from 1 to 15% of tillers infected with at least two to three spore balls per infected panicle. The disease occurred on both long- and medium-grain cultivars. False smut of rice occurs in the field at the hard dough to mature stages of the crop. A few spikelets in a panicle transform into globose, yellowish green, velvety spore balls that are 2 to 5 cm in diameter and covered by a thin orange membrane. The membrane bursts open and releases powdery dark green spores. The chlamydospores formed in the spore balls are spherical to elliptical, warty, olivaceous, and 3 to 5 × 4 to 6 μm in dimension. Some of the spore balls develop one or more sclerotia, which are the overwintering structure, in the center. False smut has been considered a minor disease of rice that occurs sporadically in Louisiana. The recent discovery of ustilotoxin, a phytotoxin and mycotoxin, produced by this pathogen on diseased tissues suggests that the fungus may be of concern as a contaminant on rice products consumed by livestock and humans (1,2). This increases the need to monitor the incidence of this disease.

References: (1) Koiso et al. Ustiloxin: A phytotoxin and a mycotoxin from false smut balls on rice panicles. Tetrahedron Lett. 33:4157, 1992. (2) Koiso et al. Ustiloxins, antimitotic cyclic peptides from false smut balls on rice panicles caused by Ustilaginoidea virens. J. Antibiot. 47:765, 1994. (3) F. N. Lee and P. S. Gunnel. 1992. Compendium of Rice Diseases. The American Phytopathological Society, St. Paul, MN. p. 28. (4) W. A. Orton. 1907. Plant diseases of 1906. Yearbook U.S. Department of Agriculture. U.S. Government Printing Office, Washington, DC, pp. 499–508.
First Report of Cucurbit Yellow Stunting Disorder Virus (Genus Crinivirus) in North America
Authors: Kao J. , Jia L. , Tian T. , Rubio L. , Falk B. W.
Published: May 2007

In late summer 1999, field- and greenhouse-grown melon plants (Cucumis melo) showing severe stunting and yellowing symptoms were observed near Donna in southern Texas and near the town of Reynosa in northern Mexico. Symptoms were typical of those caused by viruses in the genus Crinivirus, family Closteroviridae. High populations of Bemisia spp. whiteflies were associated with these plantings, with many plants showing heavy infestation. Laboratory analyses showed that melon plants from both locations were infected by the whitefly-transmitted Cucurbit yellow stunting disorder virus (CYSDV). Positive hybridization reactions with digoxigenin-UTP-labeled transcript probes corresponding to the CYSDV heat shock protein 70 (HSP70) homolog coding region (1) were obtained for RNAs extracted from symptomatic plants. Similar probes for the related Lettuce infectious yellows virus (LIYV) and Beet pseudo-yellows virus (BPYV), two whitefly-transmitted viruses previously reported from North America (2), did not hybridize with the RNAs. Definitive confirmation of CYSDV was obtained by performing reverse-transcription polymerase chain reaction (RT-PCR) analyses for two distinct CYSDV coding regions. RT-PCR with primers corresponding to CYSDV, but not LIYV or BPYV HSP70 homolog coding regions, gave specific (≈500 bp) products from corresponding test plants. RNAs from healthy control plants gave no RT-PCR product. Because the HSP70 coding region is highly conserved (2), we also performed RT-PCR with primers designed for the Spanish CYSDV capsid protein gene (GenBank accession AJ243000). Positive RT-PCR products of ≈700 bp were obtained only from the Texas and Mexico melon plants. CYSDV is a widespread and damaging virus of cucurbits in southern Europe and the Middle East (2). This is the first report of this important virus in North America.

References: (1) Tian et al. Phytopathology 86:1167, 1996. (2) Rubio et al. Phytopathology 89:707, 1999.
Evidence that Watermelon Leaf Curl Disease in Pakistan Is Associated with Tomato Leaf Curl Virus-India, a Bipartite Begomovirus
Authors: Mansoor S. , Khan S. H. , Hussain M. , Mushtaq N. , Zafar Y. , Malik K. A.
Published: May 2007

Whitefly-transmitted geminiviruses (begomoviruses) have emerged as major constraints on food and fiber crops worldwide, and there are several examples of begomovirus mobilization in previously unknown host plants. Here we report on evidence that leaf curl disease of watermelon in Pakistan is caused by Tomato leaf curl virus-India (TLCV-India). Leaf curl disease of watermelon, characterized by leaf curling and mottling and stunted plant growth, was observed at several locations in the Punjab Province of Pakistan. Symptomatic and asymptomatic leaf samples were collected from three locations, and total DNA was isolated by the cetyltrimethylammoniumbromide method and resolved in agarose gel. A full-length clone of Cotton leaf curl virus DNA A was labeled with [32P]dCTP and used as a general probe in Southern hybridization. The probe detected characteristic geminivirus DNA forms in infected watermelon plants, whereas no signal was detected in asymptomatic plants. The association of a begomovirus was confirmed further by polymerase chain reaction (PCR) amplification with degenerate primers PAL1V and pAR1c (2). Samples were screened for infection by TLCV-India, because of symptom similarity. A full-length clone of DNA B of TLCV-India (1) was labeled with [32P]dCTP by random priming and was used as a specific probe in Southern hybridization. The probe detected geminivirus DNA forms, showing that the disease is associated with TLCV-India. Primers TLCV1 (GAGGTACCAAAACTTGTCGTTTTGATTCGG), in the virion-sense, and TLCV2 (GCCCATGGTTCTTTGCTCGGAGAACAAGAA), in the complementary-sense, were designed based on the sequence of DNA A of TLCV-India. These primers were used in PCR and amplified a product of the expected size from infected plants. Similarly, primers TLCVBC1 (GCGGATCCTTATTCCGTAATTATATCTGCA), in the virion-sense, and TLCV BC2 (CACCATGGCAATAGGAAATGATGGTATGGG), in the complementary-sense, were designed based on the sequence of DNA B of TLCV-India (1). These primers amplified a product of expected size when used in PCR. The results show that watermelon leaf curl disease in Pakistan is associated with TLCV-India. This the first report of detection of a begomovirus in watermelon in Pakistan and the first report of detection of TLCV-India on a plant other than tomato from Southeast Asia.

References: (1) M. Padidam et al. J. Gen. Virol. 76:25, 1995. (2) M. R. Rojas et al. Plant Dis. 77:340, 1993.
Management of Dollar Spot on Creeping Bentgrass with Metabolites of Pseudomonas aureofaciens (TX-1)
Authors: Powell J. F. , Vargas J. M. , Nair M. G. , Detweiler A. R. , Chandra A.
Published: May 2007

Antifungal extracts from four strains of bacteria that were selected for their ability to inhibit fungal turfgrass pathogens were compared for in vitro activity. The cell extract from Pseudomonas aureofaciens Tx-1 (ATCC 55670) exhibited the greatest antifungal activity against selected turfgrass pathogens. Purification of the extract yielded a single active component that was identified as phenazine-1 carboxylic acid (PCA). Minimum inhibitory concentrations of PCA to tested fungal pathogens ranged from 10 to 25 µg/ml. In greenhouse studies, PCA provided management of dollar spot on creeping bentgrass equal to that of the commercial fungicides triadimefon and chlorothalonil at equivalent rates of active ingredient. Phytotoxic effects were observed on creeping bentgrass in greenhouse but not field evaluations of PCA at the rate of 0.48 g/m2. At the end of 2 years of field study, PCA applied every 14 days at 0.15 g/m2 provided dollar spot management on creeping bentgrass equal to that of chlorothalonil applied every 10 days at the label rate of 0.48 g/m2.
Lack of Relationship Between Susceptibility to Common Root Rot and Drought Tolerance Among Several Closely Related Wheat Lines
Authors: Piccinni G. , Rush C. M. , Vaughn K. M. , Lazar M. D.
Published: May 2007

Common root rot caused by Bipolaris sorokiniana is a disease of wheat associated with plant stress. Three cultivars (Siouxland, TAM 200, and TAM 107) and several hard red winter wheat lines closely related to TAM 107, but known to differ with respect to drought tolerance, were included in a 2-year dryland field study to evaluate whether observed variation in drought tolerance was associated with susceptibility to B. sorokiniana. Untreated seed of each entry or seed treated with imazalil was planted in soil naturally infested with B. sorokiniana. Plants were evaluated at jointing and at harvest. Disease incidence and severity, number of plants, number of heads, and grain weight per meter were evaluated. Grain weight and number of heads of individual plants were recorded in order to correlate disease rating of each plant with yield components. Plot yield and test weight also were measured. There were significant entry by seed treatment interactions for number of heads per plant, grain weight per plant, and grain weight per meter. A year by treatment interaction was found for the jointing disease index, and plants grown from seed treated with imazalil had a significantly lower disease index than those grown from nontreated seed. Observed drought tolerance among the three varieties and eight closely related plant introductions was not associated with disease susceptibility to common root rot.
The Effect of Stand Density on the Development of Puccinia graminis f. sp. tritici in Barley
Authors: Dill-Macky R. , Roelfs A. P.
Published: May 2007

The progress of stem rust epidemics caused by race Pgt-QCCJ of Puccinia graminis f. sp. tritici was examined in field plots of the six-rowed barley cvs. Robust and Steptoe at four stand densities, and in short rows and hill plots. Cv. Robust carries Rpg1, which confers resistance to most races of P. graminis f. sp. tritici, other than Pgt-QCCJ, while cv. Steptoe lacks any reported genes for resistance to P. graminis f. sp. tritici. The stand-density treatments established were approximately double, the equivalent of, half of, and one quarter of the planting rate recommended for commercial barley. Stem rust caused by race Pgt-QCCJ spread more rapidly in cv. Steptoe than in cv. Robust, irrespective of the stand-density treatment. The effect of stand density on rust severity was, however, greater than the effect of cultivar. Rust severity was 18 to 36% greater in sparse stands than in dense stands of both cultivars. Reductions in kernel size were most severe in sparse stands where rust development was greatest. Knowledge that reduced stand densities may promote the development of stem rust in barley may be useful in refining procedures for screening breeding material for resistance to stem rust, and in allaying concern over the high levels of stem rust occasionally reported in lightly seeded seed increases and in commercial fields where sparse stands are encountered.
Dynamics of Ascospore Release by Apiosporina morbosa from Sour Cherry Black Knots
Authors: McFadden-Smith W. , Northover J. , Sears W.
Published: May 2007

Ascospore discharge was monitored from black knots excised from sour cherry trees in May 1992 and 1993, and March, April, and May 1994 and 1995. Rain, temperature, and wetness duration were monitored and a regression model was developed to describe the relationship between environmental conditions and ascospore discharge. Regardless of the date of excision, the peak period for ascospore release occurred from late May (shuck split) through the end of June (shoots 20 cm long), considerably later than previously reported from knots on plum. Fewer ascospores were released from knots excised in early March compared to later dates in 1994. In 1995, the spring was much warmer than in 1994 and ascospore release from March-excised knots was comparable to that from knots excised later in the spring. The period of release and total number of ascospores released was similar from non-excised knots and from knots excised in April or May 1994. Release of ascospores was dependent on rainfall and temperature, but not on the duration of wetness.
Inheritance of Adult Plant Leaf Rust Resistance in the Brazilian Wheat Cultivar Toropi
Authors: Barcellos A. L. , Roelfs A. P. , de Moraes-Fernandes M. I. B.
Published: May 2007

Adult plant resistance to leaf rust in the Brazilian wheat cultivar Toropi (Triticum aestivum) was studied in crosses with the susceptible cultivar IAC 13. Cvs. Toropi and IAC 13 are susceptible at the seedling stage to race LCG-RS of Puccinia triticina Erikss., and to all other known Brazilian leaf-rust races. Thus, the resistance observed in Toropi in the field was due to adult plant-resistance genes. In the greenhouse at the adult plant stage, resistance segregated in a 7:9 ratio for two complementary recessive genes. Additionally, two recessive genes for leaf-tip necrosis were identified in the greenhouse environment. Necrosis was expressed when the two homozygous recessive genes occurred together in the F2, independently of the response to leaf rust. The resistance and leaf-necrosis genes differ from those previously reported in wheat. Segregation for leaf-rust resistance in the field at Passo Fundo, Brazil, fit a 1:3 ratio for a single recessive gene. With a different pathogen race, and in crosses of cvs. Toropi and ThatcherLr34, two recessive genes and a dominant gene for resistance were detected in the field in Mexico. The dominant gene was likely Lr34 from cv. ThatcherLr34 and the two recessive genes were likely those detected in the greenhouse adult plants tests at Passo Fundo.
Single and Mixed Phytoplasma Infections in Phyllody- and Dwarf-Diseased Clover Plants in Lithuania
Authors: Staniulis Juozas B. , Davis Robert E. , Jomantiene Rasa , Kalvelyte Audrone , Dally Ellen L.
Published: May 2007

Naturally diseased plants of clover (Trifolium spp.) exhibiting symptoms of clover phyllody (virescence and phyllody of flowers) or of clover dwarf (abnormally small leaves, shortened internodes, proliferation of shoots, and dwarf growth habit) were observed in fields in Lithuania. Phytoplasma group-specific polymerase chain reactions (PCRs) and restriction fragment length polymorphism (RFLP) analysis of 16S rDNA revealed that the plants were infected by two mutually distinct phytoplasmas. Clover phyllody-diseased plants were infected by a subgroup 16SrI-C (subgroup I-C) phytoplasma (CPh-L) related to clover phyllody (CPh-C) phytoplasma in Canada. Clover dwarf-diseased plants were infected by both CPh-L and a phytoplasma (CYE-L) related to clover yellow edge (CYE-C) phytoplasma (subgroup 16SrIII-B = III-B) in Canada. A 1.8-kbp fragment of rRNA operon from CYE-L was amplified, cloned, and sequenced, and putative restriction sites mapped. This sequence shared high similarity (99.7%) with that of CYE-C and exhibited no differences from CYE-C in RFLP patterns of 16S rDNA; therefore, we tentatively classified CYE-L in subgroup 16SrIII-B (type strain, CYE = CYE-C phytoplasma) of the X-disease phytoplasma group. These findings extend the known geographical ranges of subgroup I-C and subgroup III-B taxa to the region of northern Europe including Lithuania and suggest a role of the subgroup III-B phytoplasma in clover dwarf disease.
Biocontrol of Cucumber Diseases in the Field by Plant Growth-Promoting Rhizobacteria With and Without Methyl Bromide Fumigation
Authors: Raupach G. S. , Kloepper J. W.
Published: May 2007

Field trials were conducted in 1996 and 1997 to determine the effect of plant growth-promoting rhizobacteria (PGPR) strains, which previously were found to induce systemic resistance in cucumber, on cucumber plant growth and on naturally occurring cucumber diseases with and without methyl bromide fumigation. Seven PGPR seed treatments included single-strain treatments and mixtures of Bacillus pumilus strain INR7, Curtobacterium flaccumfaciens strain ME1, and Bacillus subtilis strain GB03. In both years, in the absence of methyl bromide, all seven PGPR treatments significantly promoted plant growth, compared to the non-treated control, while with methyl bromide fumigation, only 3 and 1 of the same PGPR treatments promoted growth significantly in 1996 and 1997, respectively. In 1996, main runner length of plants in all seven PGPR treatments without fumigation was statistically equivalent to the main runner length of the nontreated control with methyl bromide fumigation. Naturally occurring foliar diseases were angular leaf spot, caused by Pseudomonas syringae pv. lachrymans in 1996, and a mixed infestation of angular leaf spot and anthracnose, caused by Colletotrichum orbiculare in 1997. In both years, all PGPR treatments significantly reduced severity of foliar disease, compared to the nontreated control, with and without methyl bromide. Mixtures of PGPR strains showed a higher level of disease protection in both years with and without methyl bromide. The results indicate that attempts to develop PGPR-mediated induced systemic resistance into components of vegetable integrated pest management should not be negatively impacted by the planned withdraw of MeBr from standard vegetable production and that PGPR may help compensate for reduced plant growth often seen without methyl bromide fumigation.
Factors that Affect Development of Collar Rot on Tobacco Seedlings Grown in Greenhouses
Authors: Gutierrez W. A. , Shew H. D.
Published: May 2007

Collar rot, caused by Sclerotinia sclerotiorum, is an important disease of tobacco transplants produced under greenhouse conditions. Factors that affect the development of the disease were studied, including age of seedlings, presence of an external source of nutrients (leaf extract), clipping (leaf removal) practices, exposure to low temperature, and leaf injury caused by heat and a chemical. Flue-cured tobacco seedlings, cultivar K-326, were grown in polystyrene cell trays floating on a nutrient solution. Trays were maintained in a phytotron growth chamber with a 28/18°C day/night temperature regime. Seedlings were inoculated with ascospores of S. sclerotiorum at the desired stage of growth by placing mature apothecia in the growth chamber and inducing ascospore release and deposition. Disease incidence was determined by examining seedlings for the presence of stem lesions over the next 15 to 21days. Seedlings between 35 and 53 days old were more susceptible to collar rot than younger or older seedlings. Inoculum efficiency was highest and disease was most severe when an external source of nutrients was present on leaf surfaces. Clipping of leaf tips did not increase disease, but if the leaf pieces created by clipping were left on seedlings, collar rot development was enhanced compared with treatments where debris was removed. Heat and chemical injuries that resulted in necrotic tissue provided highly susceptible infection courts for ascospores of S. sclerotiorum, but exposure to low temperature, which caused no visible injury, did not enhance infection. Adoption of cultural practices that minimize accumulation of leaf debris and eliminate factors that cause necrotic injury on leaves should greatly reduce the severity of collar rot of tobacco seedlings.
First Report of Gray Leaf Spot Caused by Pyricularia grisea on Lolium perenne in Illinois
Authors: Pedersen D. K. , Kane R. T. , Wilkinson H. T.
Published: May 2007

Each year from 1991 to 1999, a disease matching the description of gray leaf spot (1) was observed in the central and north central regions of Illinois. Disease severity was low (<10% blight) from 1991 to 1994 and 1999 and was severe (>50% blight in some areas) from 1995 to 1998. The disease was observed on Lolium perenne (perennial ryegrass) golf course fairways and sports fields. Isolations of Pyricularia grisea were made from L. perenne collected from golf courses in Bloomington, Decatur, Kankakee, Pekin, Urbana, and Moline, IL. All isolates were collected from surface-sterilized, symptomatic leaves. Cultures were maintained on one-fifth strength potato-dextrose agar (PDA) and induced to sporulate on full-strength oatmeal agar. All isolates in culture displayed vegetative and conidial characteristics similar to those previously described for P. grisea (1). Twenty-five different L. perenne germ plasms were inoculated with isolate WF9826 (Kankakee) using a suspension of 1 × 105 conidia per milliliter. The 4-week-old lawns (100 plants per 3-cm-diameter cone-tainer) of each ryegrass germ plasm were inoculated by spraying foliage with the conidial suspension until runoff. Inoculated and uninoculated lawns were enclosed in plastic bags and placed in an incubator (16 h light; 28°C) for 7 days. Disease severity was rated using a scale of 0 to 10 (10 = 100% blight). Each treatment was replicated three times, and all experiments were repeated four times. Small blue-gray, water-soaked lesions with dark brown borders were observed on leaves of all inoculated ryegrass germ plasms. Advanced symptoms included blighting of much of the leaves. The mean disease severity rating was 3.8 (range 2 to 7) for all experimental units and all 25 germ plasms. P. grisea was isolated from leaves that were inoculated with WF9826. This is the first report of gray leaf spot of perennial ryegrass caused by P. grisea in Illinois.

Reference: (1) P. J. Landschoot et al. Plant Dis. 76:1280, 1992.
Gaeumannomyces graminis var. graminis Isolated from Emerald Zoysiagrass in Texas
Authors: Tomaso-Peterson M. , Trevathan L. E. , Gonzalez M. S. , Colbaugh P. F.
Published: May 2007

Wilkinson and Kane (3) previously reported diseased zoysiagrass infected by Gaeumannomyces graminis (Sacc.) Arx & Olivier var. graminis in the spring in Illinois. Emerald zoysiagrass (Zoysia japonicum Steud. × Zoysia matrella (L.) Merr var. tenufolia (Willd. ex Thiele) established by sod in a home lawn for one year in Austin, TX, developed irregular, chlorotic, and, subsequently, necrotic patches 30 cm in diameter and larger in late summer of 1999. Patches were restricted to areas of the lawn receiving full sun. The lawn was fertilized, mowed at 2.5 cm, and watered daily during active growth. A thatch layer in excess of 1.9 cm was present. Tillers within diseased patches were removed easily from stolons. Crowns were rotted and colonized by dark brown septate hyphae (4.5 µm wide) and olivaceous brown lobed hyphopodia (25 × 21 µm). Diseased tillers were desiccated and newly developed leaves were chlorotic. Stolons were also chlorotic and developed water-soaked lesions adjacent to crowns. Diseased roots appeared light brown and brittle with strands of dark brown septate runner hyphae along the surface of the root axis and olivaceous brown growth cessation structures within the cortical tissue. Overall, symptoms were more severe on crowns and nodes than roots. A Gaeumannomyces fungus was isolated from root, sheath, and bud tissues. Taxonomy of the fungus was consistent with the description of G. graminis var. graminis by Walker (1,2). Diseased plants were washed free of soil and other debris and maintained in a moist chamber for 14 days. Perithecia were formed on leaf sheaths. Morphology of perithecia, asci, and ascospores was consistent with Walker's description of perithecia, asci, and ascospores of G. graminis var. graminis (2). Leaf buds and root tissue, colonized by G. graminis var. graminis, were plated directly onto potato-dextrose agar containing streptomycin sulfate and rifampicin (100 ppm, respectively). Colonies of sparse white, slightly aerial mycelium turning olive brown with age and producing lobed hyphopodia, developed from plated plant material. Hyphae at the margin of colonies curled back, characteristic of G. graminis var. graminis. Symptoms reported here are similar to those described by Wilkinson and Kane (3); however, the season and prevailing environmental conditions were different.

References: (1) J. Walker. Trans. Br. Mycol. Soc. 58:427, 1972. (2) J. Walker. Mycotaxon 11:1, 1980. (3) H. T. Wilkinson and R. T. Kane. Plant Dis 77:100, 1993.
First Outbreak of Banana Streak Badnavirus Infection in Commercial Export Bananas in Costa Rica
Authors: Pasberg-Gauhl C. , Lockhart B. E. , Duran S.
Published: May 2007

Banana streak badnavirus (BSV) is the most widely occurring virus in banana and plantain (1) but has not been reported to be a significant problem in commercial export bananas. In early 1999, the first severe outbreak of BSV infection in commercial export bananas (Musa AAA cv. Grand Nain) was recorded at Siquirres on the Atlantic coast of Costa Rica. Disease incidence in the plantation was 60% and symptoms included foliar chlorotic streaks, stunting of plants, splitting and internal necrosis of pseudostems and fruits, cigar leaf necrosis, and bunch emergence through the pseudostem. Diseased plants within a 0.8 ha area were eliminated to prevent possible further spread of the disease. The presence of BSV in diseased plants was confirmed by enzyme-linked immunosorbent assay and immunosorbent electron microscopy (1). Cucumber mosaic virus and Banana mild mosaic virus, which also occur in banana and plantain in Latin America (2), were not detected in the plants tested. Other recent accounts of BSV occurrence in commercial banana plantations in South America (our unpublished results) suggest that BSV occurrence in export bananas may be more significant than previously thought.

References: (1) F. Gauhl et al. Int. J. Pest Management 45:167, 1991. (2) D. R. Jones, ed. 1999. Diseases of Banana, Abacá and Enset. CABI Publishing, Wallingford, U.K.
First Report of Tobacco vein banding mosaic virus in China (Xian, Shaanxi Province) in Datura stramonium and Tobacco
Authors: Roggero P. , Accotto G. P. , Ciuffo M. , Lenzi R. , Desbiez C. , Lecoq H. , Bosco D. , Huang X. , Gu Q.
Published: May 2007

Tobacco vein banding mosaic virus (TVBMV) has been reported in Taiwan (1), North America (Tennessee) (2), and Japan (3) and induces a severe disease of tobacco. During surveys on viruses of vegetables in China, TVBMV was isolated from a Datura stramonium weed plant in July 1998 in Shaanxi Province. It showed severe mosaic with blistering of the leaves. The plant was also infected by Cucumber mosaic virus (CMV). When sap from D. stramonium was frozen, thawed, and mechanically inoculated, only TVBMV was recovered. The 3′-end of the viral genome was amplified by reverse transcription-polymerase chain reaction (RT-PCR) using primers derived from the potyviridae primers (4) and cloned in pBlueScript. The sequence of 1,630 bp (GenBank AF274315) was determined on both DNA strands and found to have approximately 94% homology with other TVBMV sequences (L 28816 from Tennessee, X77637 from Taiwan, and AB020524 from Japan). The host range of the Chinese isolate was similar to that reported for the U.S. isolate. D. stramonium, Nicotiana benthamiana, N. clevelandii, N. glutinosa, N. tabacum Samsun, White Burley type and Xanthi, Lycopersicon esculentum cv. Marmande, and Petunia hybrida were systemically infected. A local infection developed in N. rustica, Chenopodium amaranticolor, C. quinoa, and Ocimum basilicum. The Chinese isolate did not infect Capsicum annuum cv. Quadrato d'Asti, Solanum melongena, or several Cucurbitaceae and Leguminosae species. Myzus persicae transmitted the Chinese TVBMV in a non-persistent mode from both D. stramonium and tobacco to the same plants and to tomato. No seed transmission occurred in experimentally infected D. stramonium (20 seedlings), tobacco White Burley type (200 seedlings), and tomato cv. Marmande (100 seedlings). The virus was found in the roots of D. stramonium and tobacco. Since the virus was not seed-transmissible, overwintering rootstocks may provide sites for winter survival of the virus. An antiserum was produced against the virus and an enzyme-linked immunosorbent assay survey was carried out in solanaceous crops including D. stramonium collected in July 1999 in Shaanxi, Shanxi, Henan, and Hebei provinces and Beijing surroundings. TVBMV was found only in the same field as in 1998 in four D. stramonium plants in association with CMV and in a tobacco plant 200 m from D. stramonium. TVBMV was not found in the closest tomato crops, where infection of CMV was severe. This is the first report of TVBMV in China, and Xian is the most northern location in which this virus has been found.

References: (1) J. K. Chiang et al. Bull. Tobacco Res. Inst. 32:39, 1990. (2) B. B. Reddick et al. Plant Dis. 76:856, 1992. (3) H. Tochihara. Rev. Plant Prot. Res. 13:122, 1980. (4) A. Gibbs and A. Mackenzie. J. Virol. Meth. 63:9, 1997.
First Report of Tomato spotted wilt virus in Habanero and Tabasco Peppers in Florida
Authors: Momol M. T. , Pappu H. R. , Dankers W. , Rich J. R. , Olson S. M.
Published: May 2007

In spring 2000, symptoms similar to thrips-vectored spotted wilt disease caused by Tomato spotted wilt virus (TSWV) were observed on habanero (Capsicum chinense) and tabasco (Capsicum frutescens) peppers in north Florida. Habanero peppers were from commercial fields grown for specialty markets and tabasco peppers were from research plots. Symptoms observed were leaf necrosis, fruit drop, necrotic stem lesions, and stunting. Fruit symptoms included chlorotic and necrotic spotting and distinct ring pattern and distortion. The incidence of symptomatic habanero peppers was 7 to 8% in one of the three production fields visited, and a lower incidence in two other fields (all in Jackson County). In tabasco pepper, TSWV was detected in spring and fall 1999, and spring 2000 seasons in 10 to 15% of the plants (Gadsden County). Adjacent tomato fields contained scattered plants exhibiting symptoms of TSWV. Diagnosis of TSWV from symptomatic stems, leaves, and fruit of habanero and tabasco peppers was confirmed by a double antibody sandwich enzyme linked immunosorbent assay (ELISA) using a commercially available kit (Agdia Inc., Elkhart, IN). ELISA values ranged from 1.57 to 1.95 for habanero pepper and 0.80 to 0.95 for tabasco pepper. The mean ELISA value of the negative controls was 0.001. To further verify TSWV infection, immunocapture reverse transcription-polymerase chain reaction (IC-RT-PCR) was performed (1). The primer pair 5′-ATGTCTAAGGTTAAGCTC-3′ and 5′-TTAAGCAAGTTCTGTGAG-3′ represented the first and last 18 bases of the coding region of the nucleocapsid gene of TSWV, respectively, and produces approximately 800 bp PCR product (1). IC-RT-PCR gave a single DNA band of expected size in both habanero and tabasco samples, while no amplification was found in an uninfected pepper sample. This is the first report of TSWV on habanero and tabasco peppers in Florida. TSWV continues to be an economically important disease constraint to the production of tomato, pepper (C. annuum), peanut, and tobacco in the southeastern United States (observations from Georgia and Florida). Meanwhile, the known host range is expanding to include new species of cultivated vegetables.

References: (1) R. K. Jain et al.. Plant Dis. 82:900, 1998.