bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Brown Root Rot of Alfalfa Caused by Phoma sclerotioides in Wisconsin
Authors: Larsen R. C. , Grau C. R. , Vandemark G. J. , Hughes T. J. , Hudelson B. D.
Published: May 2007

Brown root rot (BRR) has been associated with winterkill of alfalfa (Medicago sativa L.) in the temperate regions of North America where winters are severe (1). Although suspected, BRR has not been associated with winterkill of alfalfa in the upper Midwestern United States. Alfalfa plants exhibiting symptoms resembling those induced by the causal agent Phoma sclerotioides G. Preuss ex Sacc. were collected from fields in Marinette, Pierce, and Marathon counties in Wisconsin during the spring and early summer of 2003. Symptoms included stunting and decline in 1- to 3-year-old plants that were slow to break dormancy in the early spring. Roots frequently exhibited dark brown lesions or were entirely decayed. Advanced lesions often formed dark bands around the circumference of tap and secondary roots. Beaked pycnidial structures typical of P. sclerotioides were also observed on many samples with advanced lesions. Plants with symptoms of BRR were also observed in Clark, Langlade, Lincoln, Oconto, Shawno, Taylor, and Wood counties. Several lesion areas of tissue on the tap and lateral roots of each sample were excised with a sterile scalpel. Total DNA was extracted using the Fast DNA kit (Bio 101, Carlsbad, CA). In addition, soil samples were collected in the root rhizosphere of symptomatic plants from four fields in two counties. Soil DNA was extracted with the Ultra-Clean DNA soil extraction kit (Mo Bio, Solana Beach, CA). DNA extractions were diluted 1:10 or 1:50, and samples were evaluated for the presence of P. sclerotioides using polymerase chain reaction (PCR)-based sequence-characterized amplified region (SCAR) markers according to the method described previously (4). Amplicons of the expected size (499 bp) were detected from alfalfa roots sampled from Marathon (4 of 4), Marinette (4 of 5), and Pierce (4 of 4) counties but not in roots from healthy controls produced in the greenhouse at Prosser, WA. PCR amplicons were also produced from all field soil samples in Marathon and Marinette counties. Proof of pathogenicity via Koch's postulates for this host-pathogen system was not attempted because of the extensive time period required (1). However, characteristic beaked pycnidia were present, and the pathogen was identified using PCR on DNA from roots symptomatic of BRR. Detection of BRR has been limited in the United States to Wyoming (2), but has been thought to occur in other states with severe winters (3). To our knowledge, this is the first report of P. sclerotioides in Wisconsin.

References: (1) J. G. N. Davidson. Brown root rot. Pages 29–31 in: Compendium of Alfalfa Diseases. 2nd ed. D. L. Stuteville and D. C. Erwin, eds. The American Phytopathological Society, St. Paul, MN, 1990. (2) F. A. Gray et al. Pages 27–28 in: Proc. 10th Western Alfalfa Improv. Conf., 1997. (3) C. R. Hollingsworth et al. Can. J Plant Pathol. 25:215, 2003. (4) R. C. Larsen et al. Plant Dis. 86:928, 2002.
First Report of Witches'-Broom Disease of Broussonetia papyrifera and Its Association with a Phytoplasma of Elm Yellows Group (16SrV)
Authors: Liu Qingzhong , Wu Tianqi , Davis Robert E. , Zhao Yan
Published: May 2007

Broussonetia papyrifera, commonly known as paper mulberry, is an ornamental tree that is native to northeastern Asia. Because of its fast-growing nature and tolerance of dust, smoke, and high temperatures, paper mulberry is an important component of the biological diversity in natural ecosystems as well as a favorable shade tree in the region. In September of 2003, a disease characterized by pronounced witches'-broom symptoms was observed in paper mulberry trees growing near a jujube (Ziziphus jujuba) orchard and in home gardens located in Taian, Shandong, China. The diseased trees developed dense clusters of highly proliferating branches with shortened internodes. Leaves on the affected branches were chlorotic and greatly reduced in size. Phytoplasma infection was first suspected in this paper mulberry witches'-broom (PMWB) disease because the disease occurred in an area where other phytoplasmal diseases, including jujube witches'-broom (JWB) disease and paulownia witches'-broom (PaWB) disease, are common (4). Results from nested polymerase chain reactions (PCR), performed using phytoplasma-universal 16S rDNA primers (P1/P7 and R16F2n/R16R2) (1,2,3), revealed that all seven diseased trees tested contained phytoplasma, whereas PCR assay of comparable leaf samples from three nearby symptomless paper mulberry trees were negative. Subsequent restriction fragment length polymorphism (RFLP) analysis of the PCR-amplified 16S rDNA indicated that all diseased trees contained the same phytoplasma and that the PMWB phytoplasma belongs to the subgroup B of the elm yellows (EY) phytoplasma group (16SrV-B). Nucleotide sequence analysis of the cloned PMWB phytoplasma partial rRNA operon (GenBank Accession No. AY576685), spanning a near full-length 16S rRNA gene, a 16S–23S rRNA intergenic spacer, a tRNA-Ile gene, and a partial 23S rRNA gene, suggested that PMWB phytoplasma is most closely related to JWB phytoplasma, a member of the subgroup16SrV-B. To our knowledge, this is the first report of a paper mulberry witches'-broom disease and the first report of its association with a phytoplasma. Further work is underway to determine whether the PMWB phytoplasma is distinct from previously characterized phytoplasmas included in group 16SrV and to assess impacts of the phytoplasma on the ecosystems in the region.

References: (1) S. Deng and C. Hiruki. J. Microbiol. Methods 14:53, 1991. (2) D. E. Gundersen and I.-M. Lee. Phytopathol. Mediterr. 35:144, 1996. (3) C. D. Smart et al. Appl. Environ. Microbiol. 62:2988, 1996. (4) S. Zhu et al. Acta Hortic. 472:701, 1998.
First Report of the Pitch Canker Fungus (Fusarium circinatum) in the Sierra Nevada of California
Authors: Vogler D. R. , Gordon T. R. , Aegerter B. J. , Kirkpatrick S. C. , Lunak G. A. , Stover P. , Violett P.
Published: May 2007

The pitch canker fungus, Fusarium circinatum (teleomorph Gibberella circinata), was isolated from a branch originating from rootstock of a Douglas-fir (Pseudotsuga menziesii) graft in a breeding orchard at 1,000m elevation in El Dorado County, California. We visited the orchard after the New Zealand Ministry of Agriculture and Forestry reported in November 2003 that a Douglas-fir scion (branch cutting) shipped from there in January—and subsequently grafted and held in a quarantine facility near Christchurch—was infected with the pitch canker fungus. We took samples throughout the orchard of any branches that appeared unhealthy. In addition, asymptomatic branches from the tree alleged to be the source of the New Zealand infestation were collected to assay for propagules of F. circinatum. Wash water from these branches was negative for the pathogen. Likewise, F. circinatum was not recovered from water washings of 20 branches collected randomly throughout the orchard. Fifteen branch samples collected from symptomatic Douglas-fir grafts were cultured on water agar and only one yielded a colony with an appearance consistent with F. circinatum. A single spore subculture of this isolate was confirmed as F. circinatum on the basis of colony morphology and the structure of the microconidiophores (1). The virulence of this isolate was evaluated by inoculating susceptible 2-year-old Monterey pine (Pinus radiata) seedlings with a toothpick to wound the main stem and insert potato dextrose agar colonized by the fungus. Twenty-four days later, pitching and yellow needles were evident at the site of inoculation, and removal of the bark revealed resin-soaked and discolored tissue. Concurrent with the pathogenicity test described above, a culture of the putative F. circinatum isolated in New Zealand was inoculated into Monterey pines with an identical outcome. The fungus was reisolated from lesions from both sets of inoculations and confirmed as F. circinatum based on morphological criteria. Isolates GL285 and GL286 are available from T. R. Gordon upon request. Prior to its discovery in the Sierra Nevada, pitch canker in California was known only from counties on or near the coast. Our report indicates the pathogen can survive and infect trees 110 km east of the previous most-inland site of infestation. It remains to be seen how extensively pitch canker will develop in the Sierra Nevada. Douglas-fir is only moderately susceptible to F. circinatum, which has not been observed to cause significant damage to this species. On the other hand, low-elevation Sierra Nevada pines including P. sabiniana, P. coulteri, and P. ponderosa are substantially more susceptible than are Douglas-fir in greenhouse tests (2).

References: (1) T. R. Gordon et al. Mycol. Res. 100:850, 1996. (2) T. R. Gordon et al. Plant Dis. 85:1128, 2001.
Biological and Molecular Variability Among High Plains virus Isolates
Authors: Seifers Dallas L. , She Y.-M. , Harvey Tom L. , Martin T. J. , Haber S. , Ens W. , Standing K. G. , Louie Raymond , Gordon D. T.
Published: May 2007

The High Plains virus (HPV), vectored by the wheat curl mite (WCM) (Aceria tosichella), causes a severe disease of maize (Zea mays) in the U. S. High Plains. In the present study, five HPV isolates from five states were separated from co-infecting Wheat streak mosaic virus and their molecular and biological variability studied. Molecular studies involved time-of-flight mass spectrometry (TOFMS) to determine amino acid sequence variability of the 32-kDa nucleoprotein (32 np) of the isolates. Biological studies involved testing the ability of the five HPV isolates to infect a maize line previously shown to have resistance. Inoculations of the HPV isolates were conducted using vascular puncture inoculation (VPI) and viruliferous WCM. TOFMS analyses demonstrated an 18-amino acid sequence in the isolates at the N-terminus of the 32 np, the presence of amino acid sequence differences among the isolates, and variability among amino acid sequences of the 32 np of some isolates. Three of the five HPV isolates infected the resistant maize inbred, B73, using VPI, and two of the same three HPV isolates infected this line using WCM inoculation, albeit low numbers of plants were infected by each technique.
Disease Progression of Phytophthora ramorum and Botryosphaeria dothidea on Pacific Madrone
Authors: Maloney P. E. , Lynch S. C. , Kane S. F. , Rizzo D. M.
Published: May 2007

Infection by Phytophthora ramorum was associated with stem and leaf lesions of Pacific madrone (Arbutus menziesii) seedlings and saplings. In addition, a common and native pathogen, Botryosphaeria dothidea, caused similar leaf and stem lesions. When exposed to natural levels of inoculum in forests infested with P. ramorum, 50 to 66% of madrone saplings used as bait died. Recovery of P. ramorum from colonized plant tissue on culture media was generally low. From initial infection, P. ramorum was not culturable from leaf tissue after a mean of 3.5 weeks or from stem tissue after a mean of 8 weeks. Generally, B. dothidea was recovered more frequently from necrotic stems and leaves than was P. ramorum. Experimental inoculations of madrone seedlings showed that leaf and stem lesion lengths were, on average, greater on tree seedlings inoculated with P. ramorum than on those inoculated with B. dothidea. P. ramorum and B. dothidea appear to coexist in stem and leaf tissue, forming a novel pathogen complex, affecting growth and reproduction of Pacific madrone.
Relationship Among Concentrations of Sphaerotheca macularis Conidia in the Air, Environmental Conditions, and the Incidence of Powdery Mildew in Strawberry
Authors: Blanco C. , de los Santos B. , Barrau C. , Arroyo F. T. , Porras M. , Romero F.
Published: May 2007

Atmospheric concentrations of Sphaerotheca macularis conidia were monitored for 2 years on a strawberry crop in Huelva (southwestern Spain). The presence of airborne conidia was determined to assess the role of weather conditions on conidial release. The relationship between airborne conidia and incidence of powdery mildew on fruit was also studied. Concentrations of conidia were estimated with a Burkard volumetric spore sampler. The presence of conidia was related to temperature, relative humidity, and rainfall, with a positive correlation for the first factor and a negative correlation with the other two. The presence of conidia in the air was positively correlated with disease incidence. A diurnal pattern of conidia release was observed.
Wheat Stripe Rust Epidemic and Virulence of Puccinia striiformis f. sp. tritici in China in 2002
Authors: Wan Anmin , Zhao Zhonghua , Chen Xianming , He Zhonghu , Jin Shelin , Jia Qiuzhen , Yao Ge , Yang Jiaxiu , Wang Baotong , Li Gaobao , Bi Yunqing , Yuan Zongying
Published: May 2007

In China, wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most destructive diseases of wheat and can cause severe yield losses when susceptible cultivars are grown and weather conditions are favorable for the disease. Wheat stripe rust most frequently affects the winter wheat growing areas in Northwest, Southwest, and North China, and the spring wheat growing areas in Northwest China. In the 2001-2002 growing season, a widespread stripe rust epidemic affected about 6.6 million hectares of wheat in 11 provinces: Si-chuan, Chongqing, eastern Gansu, southern and western Shaanxi, southern and central Ningxia, Yunnan, Guizhou, Hubei, Henan, southern and central Hebei, and Shandong. The epidemic could be attributed to relatively warm weather from November 2001 to March 2002, high frequencies of stripe rust races CYR31 and CYR32, and widely grown susceptible cultivars. Race CYR31 was virulent on the Chinese differential cultivars Trigo Eureka, Fulhard, Lutescens 128, Mentana, Virgilio, Abbondanza, Early Premium, Funo, Danish 1, Fengchan 3, Lovrin 13, Shui-yuan 11, Lovrin 10, and Hybrid 46. Race CYR32 had all the virulence factors of CYR31, plus virulences on Chinese differential cultivars Jubilejina 2 and Kangyin 655, i.e., CYR32 was virulent on all differential cultivars, except Zhong 4. When tested on the world and European differential and some other resistant genotypes, CYR32 was virulent on Chinese 166 (Yr1), Heines VII (Yr2, Yr25, and YrHVII), Vilmorin 23 (Yr3a and Yr4a), Heines Kolben (Yr6 and YrHK), Lee (Yr7, Yr22, and Yr23), Clement (Yr9, Yr25, YrCle), VPM1 (Yr17), Selkirk (Yr27), Anza (YrA), Carstens V (YrCV1, YrCV2, and YrCV3), Gaby (YrG), Strubes Dickkopf (Yr25), and Suwon 92/Omar (YrSO). Resistance genes in Triticum spelta album (Yr5), Zhong 4, and Moro (Yr10 and YrMor) were effective against all races identified.
Black and Hairy Nightshade, the First Weedy Hosts of Potato virus A in the United States
Authors: Thomas P. E.
Published: May 2007

Potato virus A (PVA; genus Potyvirus, family Potyviridae) occurs wherever potatoes are grown and may reduce tuber yields as much as 40%. Its host range consists of six experimental hosts (Lycopersicon pimpinellifolium (Jusl.) P. Mill., Nicandra physalodes (L.) Gaertn., Nicotiana tabacum L., Solanum demissum Lindl., S. demissum × S. tuberosum, and Nicotiana debneyi Domin.) and two natural hosts (S. tuberosum L. and S. betaceae (Cav.) Sendt.) (1). N. physalodes and Nicotiana tabacum sometimes grow in nature in the eastern and southern United States (2) but have not been reported to be PVA sources in nature. PVA is known to survive winter in temperate climates only in tubers used for potato propagation and potato volunteers. We detected PVA in all six Black Nightshade (S. nigrum L.) and all six Hairy Nightshade (S. sarrachoides Sendt.) weeds expressing mild mosaic symptoms and growing in PVA-infected potato fields near Prosser, WA in September of 2002. PVA was not detected in any of the 24 Cutleaf Nightshade (S. trifolium) plants selected from the same fields. The virus was detected using double antibody sandwich enzyme-linked immunosorbent assay with a test kit obtained from Agdia, Inc. (Elkhart, IN) and by reverse transcription-polymerase chain reaction using primers designated 3 (gta-ctg-aac-tgg-aaa-agt-act) and 4 (ccc-tga-cag-ttg-aaa-cat-aag) (3). One positive control for these assays was a PVA virus isolate from the “Shultz Collection” provided by Robert Goth (USDA, ARS, Beltsville, MD) in 1986. The Agdia, Inc. test kit also provided a positive control. We also transmitted PVA from one of the Black Nightshade and one of the Hairy Nightshade weeds to greenhouse-produced Nicotiana megalosiphon Van Heurck & Mull. Agr., Nicotiana tabacum cv. Samsum NN, S. tuberosum cv. Russet Burbank, S. sarrachoides, and S. nigrum plants by Myzus persicae Sulzer in a stylet-borne manner. The virus was transmitted from the greenhouse test plants back to S. sarrachoides and S. nigrum plants where it produced mild mosaic symptoms identical to virus from the original sources. PVA was not transmitted from weedy sources to Datura tatula L., Physalis floridana Rydb., or S. trifolium. M. persicae readily colonized S. sarrachoides, S. nigrum, and S. trifolium in the field and greenhouse. Since black and hairy nightshade are frequently found in potato fields (4) and our findings show these weeds to be hosts of PVA, their role in the epidemiology of this disease should be more fully evaluated.

References: (1) A. Brunt. Potyviruses. Pages 77–86 in: Virus and Virus-Like Diseases of Potatoes and Production of Seed Potatoes. G. Loebenstein et al., eds. Kluwer Academic Publishers, Boston, 2001 (2) A. Ogg and B. S. Rogers. Rev. Weed Sci. 4:25, 1989. (3) M. Rajamaki et al. Virology 88:311, 1998. (4) USDA, NTPD, National Plant Data Center, Version 3.5 On-line Publication, 2004.
First Report of Strawberry latent ringspot virus in a Mentha sp. from North America
Authors: Postman J. D. , Tzanetakis I. E. , Martin R. R.
Published: May 2007

Yellow veinbanding symptoms have been observed in several mint clones at the U.S. Department of Agriculture, Agricultural Research Service, National Clonal Germplasm Repository (NCGR) mint collection in Corvallis, Oregon. The most dramatic symptoms are in a “variegated” clone of Mentha × gracilis Sole (NCGR Accession No. MEN-454), which is marketed widely in the nursery industry under cultivar names such as Golden Ginger Mint and Green and Gold. Tucker and Fairbrothers (2) proposed the name Mentha gentilis (= M. × gracilis) L. ‘Variegata’ for forms of this species with a graft transmissible variegation. Doublestranded RNA (dsRNA) was extracted from three mint clones with veinbanding symptoms of varying intensity. The dsRNA from MEN-454 was cloned, and sequences from several clones corresponded to RNA 2 of Strawberry latent ringspot virus (SLRSV), a tentative member of the family Sequiviridae. Sequences of additional cDNA clones suggested that two previously unknown viruses and the satellite RNA of SLRSV were also present in MEN-454. On the basis of the sequences of the SLRSV clones, primers F (5′ CCTCTCCAACCTGCTAGACT 3′) and R (5′ AAGCGCATGAAGGTGTAACT 3′) were developed and used in reverse transcription-polymerase chain reaction (RT-PCR) to amplify a 497-bp fragment of RNA 2 of SLRSV from MEN-454. No amplicons in RT-PCR tests or dsRNA was obtained from a clone of MEN-454 that was freed of the yellow vein symptom by heat therapy and apical meristem culture. The consensus sequence of cloned dsRNA and sequenced PCR products for SLRSV from MEN-454 has been deposited in GenBank (Accession No. AY 438666). Chenopodium quinoa, inoculated mechanically with leaf extracts from MEN-454, developed chlorosis and apical necrosis that were similar to symptoms reported for SLRSV infection (1). The presence of SLRSV in C. quinoa was confirmed using RT-PCR. Variegated M. × gracilis clones were obtained from wholesale and mail-order nurseries in Maryland, Ohio, and Nebraska. Samples were assayed using RT-PCR utilizing the F and R primers for presence of SLRSV. All samples tested positive for the virus using RT-PCR. Because of the presence of additional viruses, we cannot attribute yellow vein symptoms solely to SLRSV, however the presence of this virus in clones of M. × gracilis ‘Variegata’ from different regions throughout the United States demonstrates that SLRSV is distributed widely in the United States. To our knowledge, this is the first report of SLRSV in mint in North America.

References: (1) K. Schmelzer. Phytopathol. Z. 66:1, 1969. (2) A. O. Tucker and D. E. Fairbrothers. Taxon 21:209, 1972.
Diaporthe perjuncta Does Not Cause Phomopsis Cane and Leaf Spot Disease of Grapevine in Australia
Authors: Rawnsley B. , Wicks T. J. , Scott E. S. , Stummer B. E.
Published: May 2007

In Australia, Diaporthe perjuncta (formerly known as Phomopsis taxon 1) and Phomopsis viticola (Phomopsis taxon 2) have been associated with Phomopsis cane and leaf spot of grapevine. Although P. viticola causes distinct leaf spots, as well as lesions on shoots and canes, the pathogenicity of D. perjuncta is relatively unknown. The pathogenicity of D. perjuncta and P. viticola was studied in relation to symptom expression and bud loss. Only P. viticola caused brown-black, longitudinal, necrotic lesions on stem tissue and leaf spots characteristic of the disease, whereas both D. perjuncta and P. viticola induced bleaching of dormant canes. Inoculation of dormant buds with D. perjuncta did not cause bud death. D. perjuncta and P. viticola were reisolated from inoculated tissue and into pure culture. D. perjuncta colonized the epidermis and cortex of the grapevine shoot but not the vascular tissue. D. perjuncta appears to be an endophyte, rather than a pathogen of grapevine.
Virulence of Pythium Species Isolated from Wheat Fields in Eastern Washington
Authors: Higginbotham R. W. , Paulitz T. C. , Kidwell K. K.
Published: May 2007

Although Pythium root rot in wheat (Triticum aestivum) is well documented, limited information is available concerning which species of Pythium are most responsible for disease damage. The objective of this study was to examine the variation in virulence on wheat among isolates of Pythium collected from cereal grain fields in eastern Washington. Isolates of nine Pythium species were tested for virulence on spring wheat cultivars Chinese Spring and Spillman. Cultivars were planted in pasteurized soil infested with Pythium isolates and placed in a growth chamber maintained at a constant 16°C and ambient humidity. Plant height, length of the first true leaf, and number of seminal roots were recorded, and roots were digitally scanned to create computer files that were analyzed using WinRhizo software. Pythium isolates caused a significant reduction (P < 0.05) in the number of root tips, root length, and length of the first leaf. Differences in virulence were detected among species and among isolates within species. Isolate Pythium debaryanum 90136 and P. ultimum 90038 were the most virulent and may prove useful in future disease screening assays of Triticum germ plasm.
Evaluation of Sclerotinia Stem Rot Resistance in Oilseed Brassica napus Using a Petiole Inoculation Technique Under Greenhouse Conditions
Authors: Zhao J. , Peltier A. J. , Meng J. , Osborn T. C. , Grau C. R.
Published: May 2007

A petiole inoculation technique was adapted for evaluating resistance of oilseed Brassica napus seedlings to Sclerotinia sclerotiorum. In the first of four experiments, four isolates of S. sclerotiorum were tested, two originating from soybean and two from B. napus. In all, 10 to 47 B. napus accessions were inoculated in the seedling stage and responses to isolates were evaluated using days to wilt (DW) and a lesion phenotype index (LP). There were no significant differences in virulence among the four isolates for DW and only slight differences for LP. However, significant differences (P < 0.0001) were observed among the B. napus accessions for DW and LP in this experiment and in subsequent experiments using one isolate. The responses of accessions were consistent among experiments and among evaluation criteria. Higher levels of resistance were found among winter-type than spring-type accessions, and among rapeseed-quality compared with canola-quality accessions. The most resistant accessions identified also were the most resistant when inoculated at the flowering stage. Terminal stems were inoculated immediately below the lowest flower and stem lesion length (SLL) was used to characterize the interaction phenotype of each accession. The petiole inoculation technique can be used successfully to differentiate oilseed B. napus germ plasm for response to S. sclerotiorum. This inoculation technique and the sources of resistance identified in this study may be used to determine inheritance resistance to S. sclerotiorum and for improving oilseed B. napus cultivars for resistance to this important pathogen.
First Report of White Mold Caused by Sclerotinia sclerotiorum on Hutchinsia alpina in Italy
Authors: Garibaldi A. , Minuto A. , Gullino M. L.
Published: May 2007

Hutchinsia alpina (Chamois cress), a plant belonging to the Brassicaceae family, is cultivated as a potted ornamental plant in Italy. In the winter of 2002, leaves and stems of plants grown in pots (14-cm diameter) in commercial farms near Albenga (northern Italy) developed soft and watery tissues covered with whitish mycelium at the soil line. As necrosis progressed, infected plants wilted and died. Dark sclerotia developed on infected tissues. Because of high planting density, the infection spread very rapidly. Sclerotinia sclerotiorum was consistently recovered from infected stem pieces of H. alpina disinfested 1 min in 1% NaOCl and plated on potato dextrose agar (PDA) amended with 100 ppm of streptomycin sulfate. Sclerotia produced on PDA were ellipsoid and measured 1.3 to 9.3 × 1.3 to 4.5 mm (average 3.9 × 2.8 mm) (1). Pathogenicity of three isolates obtained from infected plants grown in a single greenhouse was confirmed by inoculating 90-day-old plants grown in pots (14 cm). Inoculum that consisted of wheat kernels infested with mycelium and sclerotia of each isolate were placed on the soil surface around the base of each of 10 plants. Plants treated with plain wheat kernels served as controls. The inoculation trial was repeated once. All plants were kept at temperatures ranging between 5 and 26°C and watered as needed. Inoculated plants developed symptoms of leaf yellowing, followed by the appearance of white mycelium within 15 days, and eventually wilted while control plants remained symptomless. White mycelium and sclerotia developed on infected tissues, and S. sclerotiorum was reisolated only from inoculated plants. To our knowledge, this is the first report of white mold on Hutchinsia alpina caused by S. sclerotiorum.

Reference: (1) N. F. Buchwald. Den. Kgl. Veterin.er-og Landbohojskoles Aarsskrift, 1949.
First Report of Alternaria alternata Causing Stem Blight of Compass Plant (Silphium laciniatum) in Poland
Authors: Wagner A. , Jamiolkowska A.
Published: May 2007

Compass plant (Silphium laciniatum), like other Silphium species, is a new horticultural plant in Poland. It is grown in gardens and farms as a medicinal, ornamental, and forage crop. For medicinal purposes, leaves, flowers, and rhizomes are harvested. During the summer of 2003, stunted plants with yellowing leaves and reduced inflorescence were observed on fields near Lublin in eastern Poland. Oblong, brown-purplish spots developed on the stems during the month of July. The disease was noticed on approximately 15% of plants. Alternaria alternata was isolated from affected stems onto potato dextrose agar medium. Sterilized seeds of compass plant were sown in sterilized pots with autoclaved soil and maintained at 24°C in a growth chamber with 12 h of light per day. When the plants attained the height of 50 cm, they were artificially inoculated with five isolates of A. alternata obtained from diseased plants collected from the fields near Lublin. Conidial suspensions (1 × 105 per ml) with 0.1% amendment of Tween 20 were brushed on one side of the stems with a beaver hairbrush (20 plants per each isolate). Twenty control plants were treated in the same way but with sterile distilled water with Tween 20. Plants were arranged in a completely randomized design. Symptoms of stem necrosis were first detected after 10 days, and after 20 days, all inoculated plants were affected. Control plants remained healthy. A. alternata was reisolated from infected stems. The fungal isolates are deposited in our laboratory. Diseased plants of S. laciniatum have no value as ornamentals and cannot be used for medicinal purposes because of fungal infection. To our knowledge, this is the first report of Alternaria stem blight of compass plant.
First Report of Fusarium Crown and Root Rot Caused by Fusarium solani on St. John's-Wort in Argentina
Authors: Gaetán S. , Madia M. , Cepeda R.
Published: May 2007

Since 2001, 15 to18% of commercial plantings of the medicinal plant St. John's-wort (Hypericum perforatum L.) in Buenos Aires Province, Argentina were affected by a new disease. Disease symptoms of crown and root rot, wilting, chlorosis, and necrosis of the leaves appeared in circular-to-irregular shaped sectors of 12- to 14-month-old plants. Symptoms began with foliage turning yellow followed by an irregular, brown necrosis of the leaf margins. Lesions coalesced to form large necrotic areas causing a severe defoliation of the basal and upper leaves. A soft rot affected the crown and roots causing a complete maceration of these tissues. Infected plants broke off easily because the crown region and the roots were destroyed. As the disease developed, a dark brown discoloration girdled the stems that progressed above the soil line to the apex. The infected stems became dry and breakable. Finally, the affected plants died. Segments (1 cm long) were taken from roots and rotted crowns of diseased plants, dipped in 70% ethanol, surface sterilized with NaOCl (1%) for 1 min, and rinsed in sterile water. Each segment was blotted dry and placed on potato dextrose agar. Plates were incubated in the dark at 26°C for 4 to 7 days. The predominate fungus isolated from the diseased tissue was identified as Fusarium solani (Mart.) Sacc. (1). Koch's postulates were completed by dipping the roots of seedlings in a 2 × 106 conidia per ml suspension of a single spore isolate for 45 min. Plants were repotted (20 inoculated and 10 controls) in a sterilized soil mix (soil/sand 2:1) and held in the greenhouse at 23 to 26°C. Characteristic symptoms identical to the original developed on 90% of inoculated plants within 2 weeks after inoculation. Symptoms included wilt and collapse, crown and root rot, and death of the plants. The fungus was recovered from symptomatic tissues. Control plants dipped into distilled water remained healthy. The experiment was repeated, and the results were identical to the first inoculations. To our knowledge, this is the first report of St. John's-wort as a susceptible host of F. solani.

Reference: (1) P. E. Nelson et al. Fusarium species. An Illustrated Manual for Identification. Pennsylvania State University Press, University Park, 1983.
Resistance of Soybean Cultivars to Field Populations of Heterodera glycines in North Carolina
Authors: Koenning S. R.
Published: May 2007

The soybean cyst nematode (SCN), Heterodera glycines, is the most important pathogen of soybean, Glycine max, in North Carolina. Cultural practices are the most effective means of managing this pathogen because a majority of cultivars are susceptible to the races of this nematode that predominate in the state. Resistant and susceptible cultivars were evaluated in 14 H. glycines-infested fields from 1992 to 1999. Resistance in cvs. Hartwig and Delsoy 5710, and line S92-1603 derived from plant introduction (PI) 437654, was highly effective against all populations of H. glycines evaluated in these experiments. Numbers of cysts (cysts and white females) per three plants 28 days after planting and final egg population densities (Pf) were lower than on other cultivars evaluated. Cultivars with SCN resistance derived from PI 90763 were moderately resistant in many of the test fields, but cultivars with Peking-derived resistance were effective at only two locations. Some cultivars with resistance derived from PI 88788 were highly to moderately resistant to races 9 or 14 of SCN, but were not consistently effective against other populations. Hartwig and Delsoy 5710 had low SCN reproductive factors (Rf = egg density at harvest/mean egg density at planting for site) of 0.16 and 0.23 compared with an Rf of 1.9 and 2.19 on the susceptible cvs. Essex and Hutcheson, respectively. In contrast, the Rf on cultivars derived from Peking generally was greater than on susceptible cultivars. Resistant cvs. Hartwig and Delsoy 5710 generally yielded more than susceptible cultivars or cultivars derived from other sources of resistance. The initial inoculum level (Pi) was negatively correlated with soybean seed yield, but cysts 28 days after planting proved to be better at predicting seed yield than Pi. Due to the genetic diversity of H. glycines populations with regard to the ability to parasitize resistant cultivars, cultivars with resistance derived from PI 437654 or other genotypes are needed to manage this nematode in North Carolina.
Distribution ofXylella fastidiosain Sycamore Associated with Low Temperature and Host Resistance
Authors: Henneberger T. S. M. , Stevenson K. L. , Britton K. O. , Chang C. J.
Published: May 2007

Experiments were conducted in the field and laboratory to determine effects of low temperatures on Xylella fastidiosa populations in American sycamore. Roots and shoots from naturally infected trees at two locations were collected monthly. Sap extracted from the samples was tested by enzyme-linked immunosorbent assay for presence of X. fastidosa and was diluted and plated on periwinkle wilt medium to determine populations of viable bacteria. Cumulative rainfall and hours below temperature thresholds (-5 to 10°C) were recorded at each site. Bacterial populations in shoots were negatively correlated with cumulative hours below -5°C air temperature (r= -0.96). In roots, bacterial populations were only weakly correlated with cumulative hours below soil temperature thresholds (-0.61 < r <-0.25). Bacterial populations were not correlated with monthly rainfall. In the laboratory, resistant and susceptible sycamore trees were inoculated with X. fastidiosa and held in the dark at 5°C or 22°C. After 12 weeks, inoculated stem sections were collected and sap was extracted and tested as described previously. Stems that tested positive for X. fastidiosa were divided into additional samples and tested as described above. Results of the laboratory study indicated no significant effects of low-temperature treatment (5°C) or host resistance on viable bacteria. Bacterial detection frequency and population size were greatest near the inoculation point and the primary direction of early bacterial spread was acropetal.
Genetic Diversity Among Alternaria solani Isolates from Potatoes in South Africa
Authors: van der Waals Jacquie E. , Korsten Lise , Slippers Bernard
Published: May 2007

Genetic diversity among isolates of Alternaria solani, the causal agent of early blight of potato, from various potato-growing regions in South Africa (SA), was determined using virulence assays, vegetative compatibility (VC) tests, and random amplified microsatellite (RAMS) primers. The virulence assays showed low virulence levels for the largest part of the population, but failed to otherwise characterize the population diversity. The VC tests revealed 19 VC groups (VCGs), indicating a relatively high level of diversity among the isolates. There was little correlation between geographic origin of isolates and VCGs. Analysis of RAMS profiles revealed 27% genetic diversity among 46 isolates. This value is relatively high for an asexually reproducing fungus, but is similar to values obtained previously by authors studying A. solani. Distance analysis of the RAMS profiles also provided no evidence for geographical clustering of isolates. VCG and RAMS profiles indicated that isolates are randomly spread across SA. This fact, together with the high diversity of A. solani in SA, indicates that the fungus has a high potential to adapt to resistant cultivars or fungicides. This information can aid in the breeding and deployment of A. solani-resistant potato varieties, and in early blight disease management in SA.
Susceptibility of Selected Ericaceous Ornamental Host Species to Phytophthora ramorum
Authors: Tooley P. W. , Kyde K. L. , Englander L.
Published: May 2007

We assessed disease reactions of 51 species or varieties of ericaceous ornamental hosts to two isolates of Phytophthora ramorum, the causal agent of sudden oak death. Inoculation was performed with an A2 mating type U.S. isolate from rhododendron and the P. ramorum type culture of A1 mating type from Germany. For only one host were statistically significant differences in disease observed between the two isolates. Several different inoculation methods were compared. The 51 hosts tested varied widely in susceptibility, ranging from 0% to over 90% leaf area infected. Two cultivars of Vaccinium macrocarpon (cranberry) showed no disease, while three cultivars of Kalmia latifolia (mountain laurel) were all highly susceptible. The results indicate that many ornamental hosts grown in the United States are susceptible to P. ramorum under artificial inoculation conditions. Inoculum density studies with two susceptible host species showed that P. ramorum is capable of producing disease symptoms over sporangium concentrations ranging from 100 to 5,000 sporangia per ml. Mean numbers of chlamydospores forming in host tissue of 21 hosts ranged from 2 to over 900 chlamydospores per 6-mm-diameter leaf disk. Whether hosts showing susceptiblity under the experimental conditions used in this study would become infected with P. ramorum in the presence of inoculum under natural conditions is unknown.
Development and Comparison of Symptom Indices for Quantifying Grapevine Resistance to Pierce's Disease
Authors: Krivanek A. F. , Stevenson J. F. , Walker M. A.
Published: May 2007

Symptoms of Pierce's disease (PD) were assessed under greenhouse conditions on field-resistant and field-susceptible grapevines in order to characterize the PD resistance phenotype in the genus Vitis. A cane maturation index (CMI) was developed to quantify the green-islands symptom, which was measured at 12 weeks post-bacterial inoculation, along with leaf scorch and percentage of xylem vessels blocked by occlusions. Canes of resistant genotypes matured normally and had a significantly lower CMI score of 0.9 (on a 0-to-6 scale) compared with 5.1 for the susceptible genotypes. The CMI scoring method had a high correlation (R2= 0.91) with previously characterized field performance, whereas leaf scorch had only a moderate correlation (R2= 0.51) with field performance. Average scorched area on leaves of the susceptible and resistant genotypes was 80 and 48%, respectively, demonstrating that leaf scorch can be extensive in resistant genotypes under the presented screening conditions, and suggesting that systemic infection can occur in all evaluated genotypes. Occlusions within both stem and petiole vessels were composed principally of tyloses and were significantly higher in petioles than in stems of either resistant or susceptible backgrounds. Susceptible genotypes displayed a higher level of stem tylose occlusions relative to resistant genotypes, but correlation to field performance was low (R2= 0.13). Ease of use and high correlation to field performance makes CMI scoring a better choice for PD resistance evaluations relative to other phenotypic symptom assessments.
Frequency of the Ht1 Gene in Populations of Sweet Corn Selected for Resistance to Exserohilum turcicum Race 1
Authors: Campaña Andrea , Pataky J. K.
Published: May 2007

The possibility that the Ht1 gene or genes tightly linked to Ht1 convey general resistance to races of Exserohilum turcicum that are virulent against Ht1 (i.e., residual resistance) could be useful in sweet corn where the Ht1 gene is present in many commercial hybrids and breeding populations. The objective of this study was to determine if the frequency of the Ht1 gene changed in populations of sweet corn selected for general resistance to E. turcicum race 1, thus conveying residual resistance. Four populations were developed with theoretical initial frequencies of the Ht1 gene of 0, 0.25, 0.25, and 0.5. The populations were advanced by recurrent mass selection with parental control through four or five cycles of selection following inoculation with an Ht-virulent race of E. turcicum (i.e., race 1). Plants from each cycle of each population were evaluated for severity of northern corn leaf blight (NCLB) and chlorotic lesion reactions following inoculation in field and greenhouse trials with either race 0 or 1 of E. turcicum. Recurrent mass selection for general resistance to E. turcicum race 1 reduced the severity of NCLB in all four populations of sweet corn, although the change in the most susceptible population was minimal. Percent gain per cycle was 14.5, 12.3, 14, and 3.7% for populations I, II, III, and IV, respectively. The Ht1 gene did not convey levels of general resistance to E. turcicum race 1 that were substantial enough to be selected for in this population improvement program. There was no apparent selection advantage for resistance to E. turcicum race 1 in the populations that contained the Ht1 gene. The frequency of the Ht1 gene did not differ among cycles of selection within any of the populations in response to improved levels of general resistance to NCLB. The lack of change in frequency of Ht1 in these populations and the similarity in gain per cycle among populations with and without Ht1 lead us to conclude that the Ht1 gene itself did not have a residual effect on resistance.
A Simple Generic Infection Model for Foliar Fungal Plant Pathogens
Authors: Magarey R. D. , Sutton T. B. , Thayer C. L.
Published: May 2007

In this study, a simple generic infection model was developed for predicting infection periods by fungal foliar pathogens. The model is designed primarily for use in forecasting pathogens that do not have extensive epidemiological data. Most existing infection models require a background epidemiological data set, usually including laboratory estimates of infection at multiple temperature and wetness combinations. The model developed in this study can use inputs based on subjective estimates of the cardinal temperatures and the wetness duration requirement. These inputs are available for many pathogens or may be estimated from related pathogens. The model uses a temperature response function which is scaled to the minimum and optimum values of the surface wetness duration requirement. The minimum wetness duration requirement (Wmin) is the number of hours required to produce 20% disease incidence or 5% disease severity on inoculated plant parts at a given temperature. The model was validated with published data from 53 controlled laboratory studies, each with at least four combinations of temperature and wetness. Validation yielded an average correlation coefficient of 0.83 and a root mean square error of 4.9 h, but there was uncertainty about the value of the input parameters for some pathogens. The value of Wminvaried from 1 to 48 h and was relatively uniform for species in the genera Cercospora, Alternaria, and Puccinia but less so for species of Phytophthora, Venturia, and Colletotrichum. Operationally, infection models may use hourly or daily weather inputs. In the case of the former, information also is required to estimate the critical dry-period interruption value, defined as the duration of a dry period at relative humidities <95% that will result in a 50% reduction in disease compared with a continuous wetness period. Pathogens were classified into three groups based on their critical dry-period interruption value. The infection model is being used to create risk maps of exotic pests for the U.S. Department of Agriculture's Animal Plant Health and Inspection Service.
The Complete Nucleotide Sequence and Biotype Variability of Papaya leaf distortion mosaic virus
Authors: Maoka Tetsuo , Hataya Tatsuji
Published: May 2007

The complete nucleotide sequence of the genome of Papaya leaf distortion mosaic virus (PLDMV) was determined. The viral RNA genome of strain LDM (leaf distortion mosaic) comprised 10,153 nucleotides, excluding the poly(A) tail, and contained one long open reading frame encoding a polyprotein of 3,269 amino acids (molecular weight 373,347). The polyprotein contained nine putative proteolytic cleavage sites and some motifs conserved in other potyviral polyproteins with 44 to 50% identities, indicating that PLDMV is a distinct species in the genus Potyvirus. Like the W biotype of Papaya ringspot virus (PRSV), the non-papaya-infecting biotype of PLDMV (PLDMV-C) was found in plants of the family Cucurbitaceae. The coat protein (CP) sequence of PLDMV-C in naturally infected-Trichosanthes bracteata was compared with those of three strains of the P biotype (PLDMV-P), LDM and two additional strains M (mosaic) and YM (yellow mosaic), which are biologically different from each other. The CP sequences of three strains of PLDMV-P share high identities of 95 to 97%, while they share lower identities of 88 to 89% with that of PLDMV-C. Significant changes in hydrophobicity and a deletion of two amino acids at the N-terminal region of the CP of PLDMV-C were observed. The finding of two biotypes of PLDMV implies the possibility that the papaya-infecting biotype evolved from the cucurbitaceae-infecting potyvirus, as has been previously suggested for PRSV. In addition, a similar evolutionary event acquiring infectivity to papaya may arise frequently in viruses in the family Cucurbitaceae.
Serological, Molecular, and Pathotype Diversity of Pepper veinal mottle virus and Chili veinal mottle virus
Authors: Moury Benoît , Palloix Alain , Caranta Carole , Gognalons Patrick , Souche Sylvie , Selassie Kahsay Gebre , Marchoux Georges
Published: May 2007

Variability within the pepper-infecting potyviruses Pepper veinal mottle virus (PVMV) and Chili veinal mottle virus (ChiVMV) in Africa and Asia was investigated. Coat protein (CP) gene sequence diversity revealed three clades that corresponded to three geographic locations and there was no evidence of presence of the ChiVMV/Asian group in western or central Africa. These clades included closely related isolates that potentially belong to two viral species, which is consistent with current nomenclature. These clades could not be unambiguously identified with polyclonal antisera; however, reverse transcription-polymerase chain reactions allowed differentiation of the isolates into two species based on a large indel in the CP gene. PVMV and ChiVMV isolates were classified into three and two pathotypes, respectively, in relation to pepper genotypes carrying different resistance factors. Specificity of resistance only partially corresponded to molecular diversity of the isolates. Only one isolate of PVMV could infect pepper genotypes carrying the two recessive genes pvr6 and pvr2 2; however, these genotypes were not infected by PVMV in field trials in Senegal, despite a high prevalence of PVMV in the surrounding pepper plants.