bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Acidovorax avenae subsp. citrulli Infecting Edible Seed Watermelon (Citrullus lanatus var. lanatus) in China
Authors: Ren Y. Z. , Li H. , Li G. Y. , Wang Q. Y. , Li J. Q.
Published: May 2007

Edible seed watermelon, Citrullus lanatus var. lanatus, is a type of watermelon from which only the seeds are consumed. Between 2003 and 2005, a bacterial disease was discovered on this type of watermelon in several regions of Xinjiang Province in western China, with a diseased area of 40,000 ha. The average disease incidence on fruit and seedlings was approximately 30 and 20%, respectively. Symptoms were most noticeable on fruit. Lesions on the fruit rind were first noticeable as small pinpoint water-soaked areas. As the lesions rapidly enlarged, black, starshaped cracks formed in the rind, and the rind along with the flesh around the spots hardened. If no secondary invaders or saprophytes entered through the cracks, the inside flesh often disintegrated into dry stiff cavities. The fruit with necrotic spots became markedly malformed. The pathogen also infected seedlings. First symptoms on the seedling appeared as dark, water-soaked lesions on the underside and edge of the cotyledons. As the cotyledon expanded, the lesions become necrotic and often extended along the length of the midrib and eventually merged into large, black, withered areas. To determine the causal agent of the disease, 54 bacterial strains were isolated from cotyledons, fruits, or seeds of edible seed watermelon. By spray inoculation, these strains were inoculated onto edible seed watermelon cv. Xinzigua1 at the two-true-leaf stage with bacterial concentrations at 107 CFU/ml. All strains were strongly virulent to cv. Xinzigua1, which is planted in large areas in Xinjiang, by forming many water-soaked spots on cotyledons and true leaves. There were no symptoms in the control that was sprayed with sterile deionized water. Through biological and biochemical characteristics, including Gram reaction and tests for catalase, oxidase, and oxygen requirement, all strains were identified as Acidovorax avenae subsp. citrulli. To verify pathogen identification, specific polymerase chain reaction was also carried out. One set of 16S primers, WFB1/WFB2 for A. avenae subsp. citrulli, was used (1). A single unique band of approximately 360 bp was amplified for all strains tested. To our knowledge, this is the first report of A. avenae subsp. citrulli infecting edible seed watermelon.

Reference: (1) R. R. Walcott and R. D. Gitaitis. Plant Dis.84:470, 2000.
First Report of Crown Rot of Gazania rigens Caused by Sclerotinia sclerotiorum in Louisiana
Authors: Holcomb G. E.
Published: May 2007

Gazania rigens (L.) (treasure flower, Asteraceae) is grown as a winter and summer annual bedding plant in Louisiana and the lower southern United States. In March 2006, cv. Kiss Mix was observed in a wholesale nursery with symptoms of leaf yellowing, wilt, crown rot, and death. White mycelia and black sclerotia were present on some infected and dead plants. The plants had been grown outdoors and approximately 2% of 1,120 plants had been lost. Petiole and crown tissue from infected plants were surface disinfected in 70% ethyl alcohol, and sections were placed on acidified potato dextrose agar (PDA). A fungus that produced white mycelia and black sclerotia consistently grew from tissue pieces. Other characteristics included production of numerous sclerotia (32 to 71 per dish from 10 dishes) that were oval to oblong and formed in a ring at the periphery of culture dishes. Sclerotia measured 3 to 7 mm long (mean = 4.4, standard error = 0.15, N = 50) × 2 to 4 mm wide (mean = 3.0, standard error = 0.06, N = 50). Cells of sclerotial rinds were globose and lacked erect tomentum hyphae (1). Growth rate of the fungus at 26°C on PDA ranged from 1.3 to 3.1 cm/day (mean = 2.2, standard error = 0.05, N = 45) and mycelia covered the dishes after 3 days (2). On the basis of these characteristics, the fungus was identified as Sclerotinia sclerotiorum (Lib.) de Bary. Fungal inoculum for pathogenicity tests was grown on twice-sterilized wheat grains and 1 g of 10-day-old inoculum, consisting of fungus mycelia and sclerotia, was placed at the base of six G. rigens cv. Daybreak Mix plants. Inoculated and noninoculated control plants were placed in a dew chamber held at 22°C for 48 h and then moved to a greenhouse where temperatures ranged from 20 to 25°C. Leaf yellowing, wilt, and crown rot developed after 3 to 4 days on all inoculated plants followed by death after 6 days. S. sclerotiorum was reisolated from all inoculated plants. Noninoculated plants remained healthy. Sclerotinia crown rot of G. rigens was first reported in the United States from California (3) and has also been reported from Italy and Argentina (4). To our knowledge, this is the first report of Sclerotinia crown rot on G. rigens in Louisiana.

References: (1) L. M. Kohn. Phytopathology 69:881, 1979. (2) G. Li et al. Mycol. Res. 104:232, 2000. (3) V. M. Muir and A. H. McCain. Calif. Plant Pathol. 16:1, 1973. (4) S. M. Wolcan. J. Plant Path. 86:263, 2004.
Efficacy of Fungicides for Control of Sclerotinia Stem Rot of Canola
Authors: Bradley C. A. , Lamey H. A. , Endres G. J. , Henson R. A. , Hanson B. K. , McKay K. R. , Halvorson M. , LeGare D. G. , Porter P. M.
Published: May 2007

Sclerotinia stem rot (SSR), incited by Sclerotinia sclerotiorum, causes yield reductions to canola (Brassica napus) grown in North Dakota and Minnesota. Field trials were conducted in North Dakota and Minnesota from 2000 to 2004 to evaluate the effect of foliar fungicides on SSR and canola yield. Levels of SSR varied among years and location. In general, fungicides that consistently reduced SSR incidence compared with an untreated control were azoxystrobin, benomyl, boscalid, iprodione, prothioconazole, tebuconazole, thiophanate-methyl, trifloxystrobin, and vinclozolin. Significant reductions in SSR incidence with fungicides did not always translate into differences in canola yield, however. Inconsistent results were observed with different timings of applications based on percent bloom. This indicates that application timing should be based on factors in addition to percent bloom.
Discovery and Characterization of Xylella fastidiosa Strains in Southern California Causing Mulberry Leaf Scorch
Authors: Hernandez-Martinez R. , Pinckard T. R. , Costa H. S. , Cooksey D. A. , Wong F. P.
Published: May 2007

Mulberry leaf scorch (MLS), caused by Xylella fastidiosa, is a disease of mulberry trees in the United States that has largely been documented from locations in the eastern and central areas of the country. MLS was recently detected for the first time in white mulberry (Morus alba) trees in southern California. Four MLS-strains were isolated from two locations and confirmed as X. fastidiosa by enzyme-linked immunosorbent assay (ELISA), direct isolation of the pathogen, and use of the X. fastidiosa-specific PCR primers RST31-33. Isolated strains were characterized by the sequencing of their 16S-23S rDNA intergenic spacer regions (ISR) and random amplified polymorphic DNA (RAPD) analysis and subsequent comparison with a previously characterized MLS-strain (Mulberry-VA) and representatives of X. fastidiosa subsp. fastidiosa, X. fastidiosa subsp. multiplex, and X. fastidiosa subsp. sandyi. MLS-strains isolated from California were distinct from strains causing almond leaf scorch, oleander leaf scorch, and Pierce's disease and similar to the Mulberry-VA-strain. The ISR sequences of two MLS-strains, MLS063 and MLS059, were 100% identical to that of the Mulberry-VA sequence, whereas MLS012 and MLS024 were 99.8 and 99.6% identical to the Mulberry-VA-strain and 99.4% identical among themselves. Genomic analysis using RAPD revealed no differences among the four strains. The pathogenicity of one strain, MLS063, was confirmed by inoculation of glasshouse-grown white mulberry plants. Three months after inoculation, the pathogen was recovered from 21 of 25 inoculated plants, and 5 of 25 plants were dead within a year of inoculation. Inoculation of grapevines and oleanders with MLS063 did not result in any disease or recovery of the pathogen up to 1 year later, showing that this strain was not cross-infective to these hosts.
Geographical Distribution of Four Sugarcane yellow leaf virus Genotypes
Authors: Ahmad Youssef Abu , Royer Monique , Daugrois Jean-Henrich , Costet Laurent , Lett Jean-Michel , Victoria Jorge I. , Girard Jean-Claude , Rott Philippe
Published: May 2007

Specific primer pairs were designed to distinguish four genotypes (BRA for Brazil, CUB for Cuba, PER for Peru, and REU for Réunion Island) of Sugarcane yellow leaf virus (SCYLV) by reverse transcription-polymerase chain reaction (RT-PCR). A unique genome fragment was amplified from each genotype, with the exception of genotypes BRA and PER that are phylogenetically relatively close and were designated genotype BRA-PER. These RT-PCR primers were then used to identify the SCYLV genotype(s) present in 18 different sugarcane growing locations in the world, and 245 leaf samples infected by the virus were analyzed. Most samples were infected by only one of the three genotypes, but mixed infections occurred. Genotype BRA-PER was found in all sugarcane growing locations, whereas genotypes CUB and REU were each found in four geographical locations only. Genotypes BRA-PER, CUB, and REU were all three detected in locally bred sugarcane cultivars in Guadeloupe, indicating local transmission of these genotypes. In contrast, only genotypes BRA-PER and CUB were found in locally bred cultivars in Brazil, whereas genotype REU was detected in this country in cultivar R570 imported from Réunion. Similarly, genotypes BRA-PER and REU are both present in Réunion, but genotype BRA-PER has not, as of yet, spread on this island. Presence of several SCYLV genotypes in Brazil, Colombia, Guadeloupe, Mauritius, and Réunion suggests different virus introductions and/or different evolution histories of the virus after its introduction into a new environment.
Temporal and Spatial Epidemiology of Phytophthora Root Rot in Fraser Fir Plantations
Authors: Benson D. M. , Grand L. F. , Vernia C. S. , Gottwald T. R.
Published: May 2007

In 1999, 19 plots of Fraser fir (Abies fraseri) with a disease focus were established in commercial plantings grown for Christmas tree production in the mountains of five western North Caro-lina counties. Progress of Phytophthora root rot caused by Phytophthora cinnamomi as estimated by mortality was followed in each plot over 3 to 4 years in an attempt to understand dispersal of inoculum. Slope, aspect, and field production age at the time plots were established were recorded. Rainfall estimated from National Weather Service stations each growing season also was recorded. The relationship of site parameters and rainfall to dispersal and disease was investigated. Disease incidence and mortality were assessed in June and September each year for 3 or 4 years depending on plot. Phytophthora root rot as estimated by mortality counts over time in a logistic regression model progressed in only five of 19 plots over 3 years. None of the site parameters correlated with mortality data, although slightly more disease was found in plots with a north aspect. Rainfall was below normal in the 3 years of the study and did not correlate with mortality in any year. Lack of disease progress in the majority of plots was attributed to drought conditions in the region. In the five plots where mortality increased over time, spatial analysis suggested an aggregated pattern of diseased plants. Aggregation was apparent but not very strong among nearest neighbors, but was considerably stronger among groups of trees within a local area. This aggregation within groups was stronger when larger group sizes were examined by beta-binomial analysis. A spatial analysis by distance indices method (SADIE) indicated the presence of secondary clusters occurring several meters away from the main focus. A stochastic model also was employed that indicated a combination of spatial processes were likely involved, specifically a tendency toward spread within a local area, but not necessarily to the nearest neighboring trees, combined with an influence of background inoculum that could not be accounted for within local areas and may have come from external sources. Thus, all sources of inoculum including infected planting stock, inoculum in soil, infected trees, and contaminated equipment were equally important in epidemics of Phytophthora root rot in Fraser fir and dispersal of P. cinnamomi.
Optimum Sample Size for Determining Disease Severity and Defoliation Associated with Septoria Leaf Spot of Blueberry
Authors: Ojiambo P. S. , Scherm H.
Published: May 2007

In a 3-year field study, Premier rabbiteye blueberry plants were sampled at three hierarchical levels (leaf, shoot, and bush) to assess severity of Septoria leaf spot (caused by Septoria al-bopunctata) and incidence of defoliation. A positive linear relationship (R 2 = 0.977, P < 0.0001, n = 2127) was observed between the number of spots per leaf and percent necrotic leaf area, both assessed on individual leaves in mid- to late October. For data summarized at the shoot level, percent defoliation increased nonlinearly (R 2 = 0.729, P < 0.0001, n = 224) as disease severity increased, with a rapid rise to an upper limit showing little change in defoliation above 60 spots per leaf. Variance components were calculated for disease severity to partition total variation into variation among leaves per shoot, shoots per bush, and bushes within the field. In all cases, leaves per shoot and shoots per bush accounted for >90% of the total variation. Based on the variance components and linear cost functions (which considered the time required to assess each leaf and select new shoots and bushes for assessment), the optimum sample size for assessing disease severity as number of spots per leaf (with an allowable variation of 20% around the mean) was 75 leaves, one each selected from three shoots per bush on 25 bushes (total time required for assessment: 36.1 min). For disease severity expressed as percent necrotic leaf area, the corresponding values were 144 leaves, two each sampled from three shoots per bush on 24 bushes (total time required: 21.7 min). Thus, given the strong correlation between the two disease variables demonstrated in this study, visual assessment of percent necrotic area was the more efficient method. With an allowable variation of 10% around the mean, a sample of 27 shoots from nine bushes was the optimum sample size for assessing defoliation across the 3 years.
Physiologic Specialization of Puccinia triticina on Wheat in the United States in 2004
Authors: Kolmer J. A. , Long D. L. , Hughes M. E.
Published: May 2007

Collections of Puccinia triticina were obtained from rust-infected wheat leaves by cooperators throughout the United States and from surveys of wheat fields and nurseries in the Great Plains, Ohio Valley, southeast, California, and Pacific Northwest, in order to determine the virulence of the wheat leaf rust population in 2004. Single uredinial isolates (757 in total) were derived from the collections and tested for virulence phenotype on lines of Thatcher wheat that are near-isogenic for leaf rust resistance genes Lr1, Lr2a, Lr2c, Lr3a, Lr9, Lr16, Lr24, Lr26, Lr3ka, Lr11, Lr17a, Lr30, LrB, Lr10, Lr14a, Lr18, Lr21, and Lr28, and winter wheat lines with genes Lr41 and Lr42. In the United States in 2004, 52 virulence phenotypes of P. triticina were found. Virulence phenotype MCDSB, selected by virulence to resistance genes Lr17a and Lr26, was the most common phenotype in the United States and was found in all wheat growing areas. Virulence phenotype TBBGG, with virulence to Lr2a, was the second most common phenotype and was found primarily in the spring wheat region of the north-central states. Virulence phenotype MBDSB, which has virulence to Lr17a, was the third most common phenotype and was found in all wheat growing areas except California. Phenotype TNRJJ, with virulence to genes Lr9, Lr24, and Lr41, was the fourth most common phenotype and occurred in the southeastern states and throughout the Great Plains region. Virulence phenotypes avirulent to a second gene in the Thatcher differential line with Lr1 increased in frequency in the United States in 2004. The highly diverse population of P. triticina in the United States will continue to present a challenge for the development of wheat cultivars with effective durable resistance.
Interaction of Fungicide Physical Modes of Action and Plant Phenology in Control of Stem Rust of Perennial Ryegrass Grown for Seed
Authors: Pfender W. F.
Published: May 2007

Azoxystrobin provided protective and curative effects against stem rust (caused by Puccinia graminis subsp. graminicola) of inoculated perennial ryegrass under field conditions, significantly reducing disease severity compared with the nontreated check when applied as much as 15 days before infection or 14 days after infection. Propiconazole had a significant effect when applied 13, but not 15, days before infection or 7, but not 9, days after infection. Either fungicide was very effective when applied near the time of infection, and the effectiveness of each fungicide was well described by a second- or third-order polynomial with time (days or stem rust latent periods) as the independent variable. When symptomatic plants were sprayed with a fungicide, subsequent urediniospore production per pustule was reduced by 73% in propiconazole-treated plants and by 95% in azoxystrobin-treated plants. Azoxystrobin modestly but significantly reduced germinability of urediniospores from sprayed pustules, unlike propiconazole. These differences between the two fungicides in physical modes of action resulted in a marked difference in their effects on secondary, within-plant spread of the disease. In normal disease development, sporulation from the inner (adaxial) face of pustules on the flag-leaf sheath produces inoculum that leads to numerous contiguous secondary infections along the length of the emerging inflorescence, but only 7% of azoxystrobin-treated sheath pustules had sporulation from the adaxial surface compared with 72 and 90% of propiconazole-treated and nontreated pustules, respectively. Tillers treated with propiconazole early in the process of within-plant spread had significantly greater final stem rust severity than those treated with azoxystrobin at this time. Results of these experiments will allow effects of fungicide application to be incorporated into quantitative epidemic models that describe disease development as a function of environment and plant phenology.
First Report of Phytophthora citrophthora on Penstemon barbatus in Italy
Authors: Garibaldi A. , Bertetti D. , Minerdi D. , Gullino M. L.
Published: May 2007

Penstemon barbatus (Cav.) Roth (synonym Chelone barbata), used in parks and gardens and sometimes grown in pots, is a plant belonging to the Scrophulariaceae family. During the summers of 2004 and 2005, symptoms of a root rot were observed in some private gardens located in Biella Province (northern Italy). The first symptoms resulted in stunting, leaf discoloration followed by wilt, root and crown rot, and eventually, plant death. The diseased tissue was disinfested for 1 min in 1% NaOCl and plated on a semiselective medium for Oomycetes (4). The microorganism consistently isolated from infected tissues, grown on V8 agar at 22°C, produced hyphae with a diameter ranging from 4.7 to 5.2 μm. Sporangia were papillate, hyaline, measuring 43.3 to 54.4 × 26.7 to 27.7 μm (average 47.8 × 27.4 μm). The papilla measured from 8.8 to 10.9 μm. These characteristics were indicative of a Phytophthora species. The ITS region (internal transcribed spacer) of rDNA was amplified using primers ITS4/ITS6 (3) and sequenced. BLASTn analysis (1) of the 800 bp obtained showed a 100% homology with Phytophthora citrophthora (R. & E. Sm.) Leonian. The nucleotide sequence has been assigned GenBank Accession No. DQ384611. For pathogenicity tests, the inoculum of P. citrophthora was prepared by growing the pathogen on autoclaved wheat and hemp kernels (2:1) at 25°C for 20 days. Healthy plants of P. barbatus cv. Nano Rondo, 6 months old, were grown in 3-liter pots (one plant per pot) using a steam disinfested substrate (peat/pomix/pine bark/clay 5:2:2:1) in which 200 g of kernels per liter of substrate were mixed. Noninoculated plants served as control treatments. Three replicates were used. Plants were maintained at 15 to 20°C in a glasshouse. The first symptoms, similar to those observed in the gardens, developed 21 days after inoculation, and P. citrophthora was consistently reisolated from infected plants. Noninoculated plants remained healthy. The pathogenicity test was carried out twice with similar results. A nonspecified root and crown rot of Penstemon spp. has been reported in the United States. (2). To our knowledge, this is the first report of P. citrophthora on P. barbatus in Italy as well as in Europe.

References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997 (2) F. E. Brooks and D. M. Ferrin. Plant Dis. 79:212, 1995. (3) D. E. L. Cooke and J. M. Duncan. Mycol. Res. 101:667, 1997. (4) H. Masago et al. Phytopathology 67:425, 1977.
First Report of Melon necrotic spot virus in Panama
Authors: Herrera J. A. , Cebrián M. C. , Jordá C.
Published: May 2007

Melon (Cucumis melo L.) represents an important crop in Panama where 1,449 ha were cultivated in 2005 with 920.4 ha of this crop planted in Los Santos Province (southeast region of Panama). During April 2005 and January 2006, several melon plants in commercial fields in that area showed stem necrosis at the crown level, and less frequently, small necrotic spots on leaves. In some cases, wilting and plant death were observed. Symptoms were similar to those caused by the carmovirus Melon necrotic spot virus (MNSV). Cysts of Olpidium bornovanus also were observed in the roots of all affected melon plants. Roots from eight symptomatic plants collected in seven fields were positive using doubleantibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) with an antiserum specific for MNSV (BIO-RAD, Life Sciences, Barcelona, Spain). To confirm these results, total RNA was extracted from symptomatic plants and used in one-step reverse transcription-polymerase chain reaction (RT-PCR) with Platinum Taq (Invitrogen Life Technologies, Barcelona, Spain). MNSV specific primers designed to amplify a region of the coat protein gene were used in the assays. Amplicons of the expected size (651 bp) were generated from symptomatic plant tissue, but were not produced from healthy plants or the water used as negative controls. To establish the authenticity of this virus, RT-PCR products were purified with the High Pure PCR Product Purification Kit (Roche Diagnostics, Mannheim, Germany) and directly sequenced. Nucleotide sequences were analyzed by using the basic local alignment search tool (BLAST) (1). The primers produced two amplicons with different but similar sequences. One sequence (GenBank Accession No. DQ443546) showed 92% identity to the coat protein gene of the MNSV Spanish isolate (GenBank Accession No. AY330700) and the MNSV Dutch isolate (GenBank Accession No. M29671) and 88% identity to the Japanese isolate (GenBank Accession No. AB189944). The second sequence (GenBank Accession No. DQ443547) was 93% identical with the Spanish and Dutch MNSV isolates, 88% identical with the Japanese isolate, and 100% identical with sequences from commercial melon seed previously isolated in our laboratory (GenBank Accession No. DQ443545). Infected seed may be a concern with regard to long distance spread of the virus independent of the vector (3) and should be considered in disease management strategies. MNSV has been previously reported in Japan, the Netherlands, the United Kingdom, the United States (2), Guatemala (4), Mexico, Honduras, and Uruguay (C. Jordá, unpublished). To our knowledge, this is the first report of MNSV in Panama.

References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) A. A. Brunt et al. Plant Viruses Online: Descriptions and Lists from the VIDE Database. Online Publication, 1996. (3) R. N. Campbell et al. Phytopathology 86:1294, 1996. (4) C. Jordá et al. Plant Dis. 89:338, 2005.
Types A and B of Beet necrotic yellow vein virus Occur in Poland
Authors: Borodynko N.
Published: May 2007

Beet necrotic yellow vein virus (BNYVV) is the type member of the genus Benyvirus and the causal agent of rhizomania disease of sugar beet. Since 1999, BNYVV is becoming one of the most important viruses of sugar beet in Poland. BNYVV is represented by three types, frequently A and B and rarely P, however, in Poland, type A only was recorded (2). In 2005, a survey was conducted to determine the incidence of types A and B of BNYVV in Poland. Thirty samples of sugar beet plants with rhizomania-like symptoms were collected from six fields in the western, southern, and northern areas of Poland. All samples were analyzed by double antibody sandwich-enzyme linked immunosorbent assay (DAS-ELISA) with commercial antiserum (Bio-Rad, Hercules, CA). Infection of BNYVV was found in 26 samples. The presence of the virus in these samples was confirmed by reverse transcription-polymerase chain reaction (RT-PCR). The total RNA extracted from sugar beet was tested with specific primers designed to amplify a fragment of the RNA2 for BNYVV (1). Multiplex (m) RT-PCR with two sets of primers, rhizo AF/rhizo AR and rhizo BF/rhizo BR (2), was used to distinguish A and B types of BNYVV. Two obtained mRT-PCR products were sequenced and compared with other sequences available in GenBank. A 121-nt amplicon sequence (GenBank Accession No. DQ 228872) had 100% nucleotide and amino acid sequence identity with all BNYVV type B sequences (e.g., Stourton-GenBank Accession No. AY682695) (2). A 171-nt amplicon sequence (GenBank Accession No. DQ228871) had 100% nucleotide and amino acid sequence identity with all BNYVV type A sequences (e.g., Ravenna-GenBank Accession No. AY 654282) (2). Type A was detected in 23 BNYVV-infected sugar beet plants from five fields located in western and southern Poland while type B was found in three samples from one field in northern Poland. To my knowledge, this is the first report of the natural occurrence of BNYVV type B in Poland.

References: (1) A. Maunier et al. Appl. Environ. Microbiol. 69:2356, 2003. (2) C. Ratti et al. J. Virol. Methods 124:41, 2005.
First Report of Colletotrichum acutatum Causing a Leaf Spot on Myrica cerifera in Florida
Authors: Mackenzie S. J. , Takahashi L. M. , Mertely J. C. , Seijo T. E. , Peres N. A.
Published: May 2007

Wax myrtle (Morella cerifera (synonym Myrica cerifera) (L.) Small) is a native tree used in Florida landscapes. In the summer of 2005 and spring of 2006, small necrotic spots were observed on young leaves in two commercial nurseries in central Florida. Lesions were dark brown-to-black and eventually coalesced to form large, irregular necrotic areas. Leaves with large lesions abscised prematurely, defoliating the entire plant. Conidia formed on acervuli were observed on the surface of the largest lesions and were tentatively identified as a Colletotrichum sp. Isolations from the edges of lesions were made on potato dextrose agar (PDA) after surface disinfestation of leaf pieces in 0.6% NaOCl for 30 sec. Red chromogenic colonies developed after 5 days of incubation at 24°C. Colonies produced hyaline, oblong conidia with pointed ends averaging 14 × 4 μm and were identified as Colletotrichum acutatum J.H. Simmonds (1). The sequence from internal transcribed spacer regions 1 and 2 and the 5.8s rRNA gene of the rDNA repeat for an isolate (GenBank Accession No. DQ839609) was 100% identical to sequence from the same region of 36 C. acutatum isolates in the NCBI database. These isolates came from at least 16 different hosts, including seven ornamental hosts. There were three isolates from blueberry among the matches (Accession Nos. AB219029, AJ301911, and AJ301905), and the rDNA sequence was also identical to the sequence obtained in our laboratory for a chromogenic C. acutatum isolate from blueberry. Three single-spore isolates were tested for pathogenicity on potted plants in the greenhouse. Two young shoots were spray inoculated with a suspension (1 × 106 conidia/ml) of each isolate. Shoots were covered with a plastic bag for 24 h and maintained at 26.5°C. Two shoots were sprayed with sterile water as a control and similarly covered. All isolates produced brown spots on the youngest leaves 3 to 5 days after inoculation; no symptoms developed on control shoots. The fungus was reisolated from all inoculated shoots. To our knowledge, this is the first report of C. acutatum on wax myrtle in Florida. The disease has a potential to spread and become a significant problem for the cultivation of this species in ornamental nurseries in Florida.

Reference: (1) J. H. Simmonds. Qld. J. Agric. Anim. Sci. 22:437, 1965.
Evaluation of Elite Wheat Germ Plasm for Resistance to Tan Spot
Authors: Singh P. K. , Mergoum M. , Ali S. , Adhikari T. B. , Elias E. M. , Anderson J. A. , Glover K. D. , Berzonsky W. A.
Published: May 2007

Tan spot, caused by Pyrenophora tritici-repentis, is a serious foliar disease of wheat (Triticum aestivum) in North America. Control of tan spot through management practices and fungicide application is possible; however, the use of resistant varieties is the most effective and economical means of controlling tan spot. This study was conducted to determine the disease reaction of 126 elite hard red spring, white, and durum wheat varieties and advanced breeding lines collected from the northern Great Plains of the United States and Canada to individual races/toxins of P. tritici-repentis. Seedling evaluation of the 126 genotypes was done under controlled environmental conditions with virulent races 2, 3, and 5 of P. tritici-repentis and toxins Ptr ToxA and Ptr ToxB. Based on disease reactions, two resistant varieties and two advanced breeding lines adapted to the northern Great Plains were found to be resistant to all the races and insensitive to the toxins tested. Additionally, six genetically diverse lines/varieties were identified to be resistant to tan spot; however, these sources may not be well adapted to the northern Great Plains. These results suggest that the wheat germ plasm contains a broad genetic base for resistance to the most prevalent races of P. tritici-repentis in North America, and the resistant sources identified in this study may be utilized in wheat breeding programs to develop tan spot resistant varieties.
Epidemiology of Strawberry pallidosis-associated virus and Occurrence of Pallidosis Disease in North America
Authors: Tzanetakis Ioannis E. , Wintermantel William M. , Cortez Arturo A. , Barnes Janelle E. , Barrett Stephanie M. , Bolda Mark P. , Martin Robert R.
Published: May 2007

Strawberry pallidosis-associated virus (SPaV) was found closely associated with pallidosis disease. The modes of transmission of the virus were studied, including pollen, seed (achene), and whitefly transmission. Three whitefly species were tested for their ability to transmit SPaV, but only the greenhouse whitefly, Trialeurodes vaporariorum, was identified as a vector of the virus. Testing strawberries for SPaV and Beet pseudo yellows virus (BPYV), a second crinivirus associated with pallidosis disease, in strawberry-producing areas in North America confirmed a high incidence of both viruses in areas where high populations of whiteflies were present. Infection rates as high as 90% for SPaV and 60% for BPYV were observed when plants exhibiting decline symptoms were tested. Lower rates of infection were found in regions where whiteflies were absent or found in low numbers. The role of these criniviruses in the strawberry decline observed over the past few years along the western coast of North America was examined.
Interactions AmongSweet potato chlorotic stunt virusand Different Potyviruses and Potyvirus Strains Infecting Sweetpotato in the United States
Authors: Kokkinos C. D. , Clark C. A.
Published: May 2007

Sweet potato virus disease (SPVD) is the most serious viral disease of sweetpotato globally. This disease is caused by the synergistic interaction between the aphid-transmitted potyvirus Sweet potato feathery mottle virus (SPFMV) and the whitefly-transmitted crinivirus Sweet potato chlorotic stunt virus (SPCSV). In sweetpotato, titers of SPFMV have been shown to be significantly enhanced when coinfecting with SPCSV. In this study, the effect of SPCSV on titers of different potyviruses and potyvirus strains infecting sweetpotato in the United States was investigated using real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). No significant difference was observed in titers of the russet crack strain of SPFMV (SPFMV-RC), Ipomoea vein mosaic virus (IVMV), and Sweet potato virus G (SPVG) between single and mixed infections. Titers of all potyviruses and potyvirus strains evaluated were enhanced in the presence of SPCSV, suggesting that a conserved mechanism may underlie these interactions. Titers of the common strain of SPFMV (SPFMV-C), which did not cause SPVD-like symptoms when coinfecting with SPCSV, were also significantly enhanced in the presence of SPCSV. Furthermore, titers of SPCSV were found to be lower in treatments involving pairwise infections compared with plants infected by SPCSV alone. The degree of potyvirus titer enhancement did not correspond to the severity of symptoms observed in certain treatments involving pairwise infections.
First Report of Iris yellow spot virus on Onion (Allium cepa) in Texas
Authors: Miller M. E. , Saldana R. R. , Black M. C. , Pappu H. R.
Published: May 2007

Iris yellow spot virus (IYSV; family Bunyaviridae, genus Tospovirus) has emerged as a potentially devastating and widespread virus of onion. IYSV was first reported in the United States from Idaho in 1993 and has since spread to many of the onion-producing areas (1). In South America, the most recent reports of the virus on onion were from Peru and Chile (2,4). In 2005, onion plants in Uvalde County, Texas exhibited necrotic lesions on leaves typical of IYSV and disease incidence approached 100% in some fields with yield loss and quality problems. Five of six plants tested were positive for IYSV with double antibody sandwich-enzyme linked immunosorbent assay (DAS-ELISA; Agdia Inc., Elkhart, IN). In 2006, similar lesions were observed on onion plants in Uvalde County and approximately 400 km south in Hidalgo and Cameron counties. Infection points generally started as a single plant near the edge of fields and spread to plants in a 3- to 4-m area after 1 to 2 weeks. Early-season disease incidence was low in onions grown for bulbs and transplants, <10% in 2006. Disease incidence increased in some fields until the crop was harvested. Leaves of symptomatic plants were tested for IYSV and Tomato spotted wilt virus (TSWV) using DAS-ELISA, and 18 of 23 samples from the Hidalgo County area and 12 of 21 samples from the Uvalde County area were positive for IYSV. All samples tested for TSWV from these counties were negative. Virus infection in some ELISA-positive plants was verified by reverse transcription-polymerase chain reaction (RT-PCR) using primers derived from the small RNA of IYSV. The primers flanked the IYSV nucleocapsid (N) gene (5′-TAA AAC AAA CAT TCA AAC AA-3′ and 5′-CTC TTA AAC ACA TTT AAC AAG CAC-3′ (3). RT-PCR gave a PCR product of expected size (approximately 1.2 kb). The DNA amplicon was cloned and sequenced (GenBank Accession No. DQ658242). Nucleotide sequence analysis confirmed the identity of the amplicon as that of IYSV N gene and sequence comparisons with known IYSV N gene sequences showed 95 to 98% sequence identity. The primary vector of IYSV, onion thrips (Thrips tabaci), is a widespread and destructive pest of onion in south Texas. The year-to-year incidence of IYSV and the severity of the disease will probably depend on the onion thrips population levels. Bulb yield reduction could be severe during years with high thrips populations. More research is needed to determine the impact of IYSV on bulb yield in Texas, the relationship between IYSV incidence and T. tabaci population levels, and oversummering hosts. To our knowledge, this is the first known report of IYSV in Texas.

References: (1) D. H. Gent et al. Plant Dis. 88:446, 2004, (2) S. W. Mullis et al. Plant Dis. 90:377, 2006, (3) H. Pappu et al. Arch. Virol. 151:1015, 2006. (4) M. Rosales et al. Plant Dis. 89:1245, 2005.
First Report of Tomato yellow leaf curl virus in China
Authors: Wu J. B. , Dai F. M. , Zhou X. P.
Published: May 2007

Tomato yellow leaf curl virus (TYLCV) is a devastating pathogen of tomato that causes significant yield losses in many tropical and subtropical regions (2). In China, however, there has as yet been no report of this virus, although other begomoviruses have been reported infecting tomato (1,3). A yellow mosaic disease was observed on tomato with 90% disease incidence during March 2006 in fields of Sunqiao, Shanghai Province, China. Triple-antibody sandwich enzyme-linked immunosorbent assay (TAS-ELISA) tests indicated that tomato plants were not infected by Tomato mosaic virus or Cucumber mosaic virus. Tomato plants were found to be infested with Bemisia tabaci, suggesting a begomovirus etiology. The disease agent was transmitted to tomato by whiteflies and produced yellow mosaic and stunting symptoms that were identical to those observed in the field. Total DNA was isolated from eight collected leaf samples. Polymerase chain reaction (PCR) was performed with begomovirus degenerate primers PA and PB (3), and an amplicon of the expected size (~500 bp) was obtained in all eight samples but not from healthy leaf samples. The PCR products from two samples (SH1 and SH2) were cloned and sequenced. All residues in the sequences were confirmed by comparison of duplicate clones. Alignment of the sequences showed that they shared 97.4% nucleotide sequence identity (GenBank Accession No. AM282874–75), suggesting that they were infected by an identical virus. Overlapping primers Full/F (5′-AGCCCAATACATTGGGCC ACGA-3′) and Full/R (5′-CGTAAGTTTCCTCAACGGACTGC-3′) were then designed to amplify the full length DNA-A of SH2. The sequence was determined to be 2,781 nucleotides long (GenBank Accession No. AM282874). A comparison with other begomoviruses shows SH2 DNA-A has the highest nucleotide sequence identity (99.8%) with TYLCV isolate Tosa from Japan (GenBank Accession No. AB192966). The above results indicate that the virus associated with yellow mosaic disease of tomato in Shanghai is an isolate of TYLCV. To our knowledge, this is the first report of TYLCV in China and the first report of a begomovirus in Shanghai.

References: (1) X. F. Cui et al. J. Virol. 78:13966, 2004. (2) E. Moriones and J. Navas-Castillo. Virus Res. 71:123, 2000. (3) Z. H. Li et al. Arch. Virol. 149:1721, 2004.
First Report of Phytoplasmas in Grapevine in South Africa
Authors: Botti S. , Bertaccini A.
Published: May 2007

In April 2006, grapevine plants with typical symptoms of yellows (GY) were observed in some South African vineyards. The affected plants showed premature yellowing or reddening and downward rolling of leaves. In some cases, these symptoms were associated with extensive lack of cane lignification that was undistinguishable from yellows symptoms reported in grapevine in the major viticultural areas of the world. Nucleic acids were extracted separately from 0.1 g of fresh leaf midribs and cane phloem scrapes from three symptomatic and three asymptomatic grapevine plants, cv. Shiraz, and from three symptomatic plants, cv. Cabernet, collected from three different locations using Qiagen (Milan, Italy) DNAeasy Plant Mini Kit. A nested polymerase chain reaction (PCR) assay was employed for phytoplasma detection with 2.5 μl of the extracted DNA. Direct and nested PCR assays were performed with P1/P7 (2) and R16F2/R2 (1) universal primer pairs, respectively, obtaining the expected products only from phloem scrapes of the symptomatic plant samples cv. Shiraz. Restriction fragment length polymorphism (RFLP) analyses of R16F2/R2 amplicons with TruI and Tsp509I restriction enzymes, discriminating among phytoplasma ribosomal group and subgroups, showed profiles corresponding to those of “Candidatus Phytoplasma aurantifolia” (ribosomal subgroup 16SrII-B) in all three positive samples. A Stolbur phytoplasma profile (ribosomal subgroup 16SrXII-A) was also observed in one of those samples, indicating the presence of mixed phytoplasma infection (1). Sequencing of the obtained amplicons confirmed the RFLP phytoplasma identification; in particular 16SrXII-A could be the same phytoplasma associated with the ‘Bois Noir’ disease reported in grapevine; the 1601-bp sequence of 16SrII-B phytoplasma showed 98% similarity to U15442, i.e., to the phytoplasma associated with lime witches'-broom disease in Oman (“Ca. P. aurantifolia”) confirming RFLP results. To our knowledge, this is the first report of phytoplasmas in grapevine in South Africa.

References: (1) I.-M. Lee et al. Phytopathology 85:728, 1995. (2) B. Schneider et al. Pages 369–380 in: Molecular and Diagnostic Procedures in Mycoplasmology Vol. I. Academic Press Inc., 1995.
A New Subgroup of Rhizoctonia AG-D, AG-D III, Obtained from Japanese Zoysia Grass Exhibiting Symptoms of a New Disease
Authors: Hayakawa Toshihiro , Toda Takeshi , Ping Qu , Mghalu Joseph M. , Yaguchi Shigeharu , Hyakumachi Mitsuro
Published: May 2007

Isolates of an unidentified Rhizoctonia sp. (UN isolates) were obtained from Japanese zoysia grass (Zoysia japonica Steud) that exhibited symptoms of a new sheath rot disease. UN isolates were binucleate and showed hyphal fusion with tester isolates of Rhizoctonia anastomosis group (AG)-D. Those isolates were compared with isolates of subgroups I and II of Rhizoctonia AG-D based on cultural morphology, hyphal growth rate at different temperatures, anastomosis frequency, pathogenicity, and sequence analysis of the internal transcribed spacer (ITS) region of ribosomal DNA genes (rDNA-ITS region). The mycelial color of UN isolates was light yellow which differs from AG-D I but is similar to AG-D II. Sclerotia of UN isolates were dark brown in color and larger in size (1 to 3 mm in diameter) than those of AG-D subgroup I (1 mm in diameter), whereas isolates of AG-D II produced white mycelial clamps 4 to 5 mm in size. Hyphal growth rate of UN isolates was slower than that of two AG-D subgroups at several temperatures, especially 25°C. In pathogenicity tests on Japanese zoysia grass, UN isolates showed moderate disease severity and lower pathogenicity than isolates of AG-D subgroups I and II. Sequences of the rDNA-ITS region within UN isolates were almost homologous, but had lower homology with subgroups AG-D I or II. Phylogenetic trees constructed using ITS sequences showed that UN isolates formed an individual cluster that differed from the clusters of the two subgroups. We propose that UN isolates are a new subgroup of Rhizoctonia AG-D, subgroup III, and the name of the disease is “spring-rot” on Japanese zoysia grass.
Yield Loss in Sweet Corn Caused by Puccinia sorghi: A Meta-Analysis
Authors: Shah Denis A. , Dillard Helene R.
Published: May 2007

Data sets meeting established criteria were included in a meta-analysis of the relationship between percent common rust severity and percent relative yield loss in sweet corn (processing: 20 data sets; fresh market: 14 data sets). The slope of the linear, zero intercept relationship was estimated from each data set. Overall slopes and their respective 95% confidence intervals for the processing and fresh market situations were estimated by a random effects meta-analysis. Results indicated that for processing sweet corn, every 10% increase in rust severity reduced yield by 2.4 to 7.0%; the corresponding reduction for fresh market sweet corn was between 3.0 and 6.2%. A meta-regression analysis did not identify any factors that could account for the observed variability between data sets. An expression was then obtained for Δs, the reduction in rust severity a single strobilurin fungicide spray ought to cause for the cost of the treatment to be offset by the value of the resulting yield improvement. The empirical distribution of Δs,was derived by stochastic simulation, which showed that fungicide usage could be cost effective 90% of the time when rust severity is reduced by 12% in processing sweet corn and by 5% in fresh market sweet corn.
Spatial Heterogeneity of the Incidence of Powdery Mildew on Hop Cones
Authors: Gent David H. , Mahaffee Walter F. , Turechek William W.
Published: May 2007

The spatial heterogeneity of the incidence of hop cones with powdery mildew (Podosphaera macularis) was characterized from transect surveys of 41 commercial hop yards in Oregon and Washington from 2000 to 2005. The proportion of sampled cones with powdery mildew ( p) was recorded for each of 221 transects, where N = 60 sampling units of n = 25 cones assessed in each transect according to a cluster sampling strategy. Disease incidence ranged from 0 to 0.92 among all yards and dates. The binomial and beta-binomial frequency distributions were fit to the N sampling units in a transect using maximum likelihood. The estimation procedure converged for 74% of the data sets where p > 0, and a loglikelihood ratio test indicated that the beta-binomial distribution provided a better fit to the data than the binomial distribution for 46% of the data sets, indicating an aggregated pattern of disease. Similarly, the C(α) test indicated that 54% could be described by the beta-binomial distribution. The heterogeneity parameter of the beta-binomial distribution, θ, a measure of variation among sampling units, ranged from 0.01 to 0.20, with a mean of 0.037 and a median of 0.015. Estimates of the index of dispersion ranged from 0.79 to 7.78, with a mean of 1.81 and a median of 1.37, and were significantly greater than 1 for 54% of the data sets. The binary power law provided an excellent fit to the data, with slope and intercept parameters significantly greater than 1, which indicated that heterogeneity varied systematically with the incidence of infected cones. A covariance analysis indicated that the geographic location (region) of the yards and the type of hop cultivar had little effect on heterogeneity; however, the year of sampling significantly influenced the intercept and slope parameters of the binary power law. Significant spatial autocorrelation was detected in only 11% of the data sets, with estimates of first-order autocorrelation, r1, ranging from -0.30 to 0.70, with a mean of 0.06 and a median of 0.04; however, correlation was detected in only 20 and 16% of the data sets by median and ordinary runs analysis, respectively. Together, these analyses suggest that the incidence of powdery mildew on cones was slightly aggregated among plants, but patterns of aggregation larger than the sampling unit were rare (20% or less of data sets). Knowledge of the heterogeneity of diseased cones was used to construct fixed sampling curves to precisely estimate the incidence of powdery mildew on cones at varying disease intensities. Use of the sampling curves developed in this research should help to improve sampling methods for disease assessment and management decisions.