bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Lolium latent virus in Ryegrass in the United States
Authors: Maroon-Lango C. J. , Hammond J. , Warnke S. , Li R. , Mock R.
Published: May 2007

Initial reports of the presence of Lolium latent virus (LLV) in Lolium perenne L. and L. multiflorum Lam. breeding clones in Germany, the Netherlands, France (2), and recently the United Kingdom (3,4; described as Ryegrass latent virus prior to identification as LLV) prompted us to evaluate clonally propagated Lolium plants from the United States. Four genetically distinct plants (viz., MF22, MF48, MF125, and MF132) that have been maintained clonally for 5 years from a Lolium perenne × L. multiflorum hybrid population established in the United States exhibited either no symptoms or mild chlorotic flecking that coalesced to form chlorotic to necrotic streaking on the leaves. All four clonal plants tested positive using reverse transcription-polymerase chain reaction (RT-PCR) with the Potexvirus group PCR test (Agdia, Inc., Elkhart, IN), whereas all clones but MF48 tested positive using the Potyvirus group PCR test (Agdia, Inc.). No amplicons were obtained when the same plants were tested for tobamovirus, carlavirus, and closterovirus using appropriate virus group-specific primers. Cloning and sequencing of the potexviral amplicons revealed very high sequence identity with the comparable region of LLV-UK (GenBank Accession No. DQ333886), whereas those of the potyviral amplicons (GenBank Accession Nos. DQ355837 and DQ355838) were nearly identical with the comparable region of Ryegrass mosaic virus (RGMV), a rymovirus first reported from the United States in 1957 (1). Using indirect enzyme-linked immunosorbent assay (ELISA), extracts from all four Lolium clonal propagations tested positive for LLV using the antiserum raised to LLV-Germany (courtesy of Dr. Huth), whereas the potyvirus-positive results from RT-PCR of the three clones were confirmed using indirect ELISA with the broad spectrum potyvirus monoclonal antibody, PTY-1. LLV from singly or dually infected Lolium clones was transmitted to Nicotiana benthamiana Domin. but not to N. tabacum L. by mechanical inoculation. LLV was purified from infected N. benthamiana. Similar sized flexuous rods were observed using electron microscopy in leaf dip samples from Lolium clones and aliquots of the virions purified from N. benthamiana.

References: (1) G. W. Bruehl et al. Phytopathology 47:517, 1957. (2) W. Huth et al. Agronomie 15:508, 1995. (3) R. Li et al. Asian Conf. Plant Pathol. 2:89, 2005. (4) C. Maroon-Lango et al. Int. Congr. Virol. 13:63, 2005.
Approaches to Training Practitioners in the Art and Science of Plant Disease Diagnosis
Authors: Stewart Terry M. , Galea Victor J.
Published: May 2007

Allowing plant pathology students to tackle fictitious or real crop problems during the course of their formal training not only teaches them the diagnostic process, but also provides for a better understanding of disease etiology. Such a problem-solving approach can also engage, motivate, and enthuse students about plant pathology in general. This paper presents examples of three problem-based approaches to diagnostic training utilizing freely available software. The first provides an “adventure-game” simulation where students are asked to provide a diagnosis and recommendation after exploring a hypothetical scenario or “case”. Guidance is given on how to create these scenarios. The second approach involves students creating their own scenarios. The third uses a diagnostic template combined with reporting software to both guide and capture students' results and reflections during a real diagnostic assignment.
Biological and Serological Properties of Potato virus Y Isolates in Northeastern United States Potato
Authors: Baldauf P. M. , Gray S. M. , Perry K. L.
Published: May 2007

A survey of six potato viruses, Potato virus A (PVA), Potato virus M (PVM), Potato virus S(PVS), Potato virus X (PVX), Potato virus Y (PVY), and Potato leafroll virus (PLRV), was conducted in New York and Maine during 2002 and 2003. Leaf samples were tested by enzyme-linked immunosorbent assay and PVY-positive samples were further tested to determine whether a necrotic strain of PVY (PVYN) or a strain able to induce necrosis in tobacco and in potato tubers (PVYNTN) were present. In both years, PVY and PVS were identified in a majority of the samples, and mixed infections predominated in 83% of the symptomatic leaves in 2002. Of the total 394 PVY-positive samples, 3 reacted with monoclonal antibody (MAb) 1F5 and caused veinal necrosis (VN) in tobacco. Two of these isolates caused tuber necrosis in the potato cv. Yukon Gold. Three PVY isolates reacted with MAb 1F5 but did not cause VN in tobacco, and two caused VN but did not react with MAb 1F5. None of these eight isolates were able to overcome the Ry resistance gene in the potato cultivar Eva, but several were able to overcome the Ny resistance gene found in Allegany. PVYN isolates were not widespread in the northeastern United States; however, several PVY isolates differed from both PVYN and the ordinary strain of PVY and may represent strain recombinants.
Transmission of Xylella fastidiosa, Causal Agent of Citrus Variegated Chlorosis, by the Glassy-Winged Sharpshooter, Homalodisca coagulata
Authors: Damsteegt V. D. , Brlansky R. H. , Phillips P. A. , Roy Avijit
Published: May 2007

Citrus variegated chlorosis (CVC) is an economically important disease of citrus in Brazil and Argentina. The causal pathogen is a strain of Xylella fastidiosa transmitted by several sharpshooter species. The glassy-winged sharpshooter (GWSS), Homalodisca coagulata, has become an important new pest of citrus and grapevines in California, where it transmits X. fastidiosa strains to several crops including grapes, oleander, and almonds. Transmission studies over a 3-year period at the USDA BSL3-P containment facility at Fort Detrick, MD, utilizing California field-collected GWSS, a Brazilian strain of CVC, and Madam Vinous sweet orange seedlings, have shown a consistent although low level of transmission of CVC. Test plants were observed for CVC symptoms, analyzed by polymerase chain reaction using species-specific primers for X. fastidiosa, membrane entrapment immunofluorescence, and scanning electron microscopy. X. fastidiosa was not detected in field-collected GWSS but was detected in GWSS following feeding on CVC-infected source plants. Transmission of the CVC strain of X. fastidiosa by GWSS increases the risk of establishment of CVC in the United States if it were introduced.
Genetic Characterization and Real-Time PCR Detection of Burkholderia glumae, a Newly Emerging Bacterial Pathogen of Rice in the United States
Authors: Sayler Ronald J. , Cartwright Richard D. , Yang Yinong
Published: May 2007

Panicle blight of rice (Oryza sativa), caused by the bacterium Burkholderia glumae, is one of the most important new diseases in rice production areas of the southern United States. In this study, pathogenic strains were isolated from diseased panicles in Arkansas rice fields and examined using the Biolog GN microplate system, whole cell fatty acid methyl ester analysis (FAME), rep-polymerase chain reaction (PCR) genomic DNA fingerprinting, and 16S–23S ribosomal DNA (rDNA) intergenic transcribed spacer (ITS) sequence analysis. The B. glumae isolates from Arkansas can be divided into two major groups, but their genetic diversity was relatively low as revealed by 16S–23S rDNA ITS sequence analysis. Since no practical method existed, up to now, for testing the presence of B. glumae in rice seeds, we have developed in this study a real-time PCR method that is effective in detecting and identifying the pathogen in seed lots and in whole plants. The specific PCR primers were designed based on the 16S–23S rDNA ITS sequence of several representative isolates from Arkansas and Japan. This method is highly sensitive, rapid, and reliable, and has great potential for analyzing large numbers of samples without the need for DNA extraction or agarose gel electrophoresis. Although vertical resistance has not been observed among tested rice cultivars, LM-1 and Drew exhibited considerable resistance to B. glumae infection based on disease lesion size and the bacterial growth in planta.
Role of Temperature and Moisture in the Production and Maturation of Gibberella zeae Perithecia
Authors: Dufault N. S. , De Wolf E. D. , Lipps P. E. , Madden L. V.
Published: May 2007

Fusarium graminearum (teleomorph Gibberella zeae) is the most common pathogen of Fusarium head blight (FHB) in North America. Ascospores released from the perithecia of G. zeae are a major source of inoculum for FHB. The influence of temperature and moisture on perithecial production and development was evaluated by monitoring autoclaved inoculated cornstalk sections in controlled environments. Perithecial development was assessed at all combinations of five temperatures (12, 16, 20, 24, and 28°C) and four moisture levels with means (range) -0.45 (-0.18, -1.16), -1.30 (-0.81, -1.68), -2.36 (-1.34, -3.53) and -4.02 (-2.39, -5.88) MPa. Moisture levels of -0.45 and -1.30 MPa and temperatures from 16 to 24°C promoted perithecial production and development. Temperatures of 12 and 28°C and moisture levels of -2.36 and -4.02 MPa either slowed or limited perithecial production and development. The water potential of -1.30 MPa had mature perithecia after 10 days at 20°C, but not until after 15 days for 24°C. In contrast, few perithecia achieved maturity and produced ascospores at lower moisture levels (-2.36 and -4.02 MPa) and low (12°C) and high (28°C) temperatures. In the future, it may be possible to use the information gathered in these experiments to improve the accuracy of FHB forecasting systems.
Tolerance in Cucumber to Cucurbit yellow stunting disorder virus
Authors: Eid Sahar , Abou-Jawdah Yusuf , El-Mohtar Choaa , Sobh Hana , Havey Michael
Published: May 2007

Cucurbit yellow stunting disorder virus (CYSDV), genus Crinivirus and family Closteroviridae, has emerged as a serious whitefly-transmitted virus of cucurbit crops, causing between 30 and 50% yield losses. Development of resistant cultivars represents an economically and environmentally sound approach to management of this disease. In all, 124 cucumber accessions were evaluated for reaction to CYSDV under high inoculum pressure over three growing seasons. Seven accessions showed delayed expression of symptoms, milder final symptoms, and lower percentages of infected plants compared with susceptible cucumbers. Although none of these accessions were immune to CYSDV, virus concentrations in the middle leaves of the tolerant accessions were significantly lower than those of susceptible accessions.
Tissue Necrosis of Sour Cherry Fruits, An Unusual Disease Occurrence Caused by a Phoma sp. in Serbia
Authors: Gavrilović V. , Arsenijević M.
Published: May 2007

Following frequent rains during May and June of 1999, a high incidence of an unknown disease on sour cherry (Prunus cerasus) fruits was observed in western Serbia (Šabac). Initially, small, water-soaked, dark green spots appeared on the fruit tissue similar to infections caused by Pseudomonas syringae or a Colletotrichum sp. (1,2). Later, spots enlarged, coalesced, and became necrotic and covered most of the fruit surface. The diseased tissue was slightly depressed and fruit shriveled and dried. Approximately 60 to 80% of the total yield was affected. Numerous hyaline, unicellular, and ellipsoidal conidia were observed with a microscope. Orange spore masses often occurred on the necrotic tissue following rain. Symptoms of the disease were not expressed during the dry spring of 2000, but were observed in rainy 2001. The most susceptible cultivar was Haiman's Rubin. Disease symptoms were absent on the domestic cultivar Oblačinska. Placing small necrotic fragments on potato dextrose agar (PDA) resulted in grayish fungal colonies that produced black, globose pycnidia with hyaline, unicellular, and ellipsoidal conidia under daylight conditions that were similar to those formed on necrotic sour cherry fruit in the orchard. At 25°C, colonies covered the entire 9-cm diameter surface of PDA after 5 to 6 days. No teleomorph was observed. Bacterial isolations on nutrient agar were unsuccessful. Unripe sour cherry fruits were punctured with a sterile needle and small colony fragments of the fungus were placed over the wound. Symptoms typical of those on fruit found in orchards were observed after 7 days of incubation at 25°C. No symptoms developed on control fruits punctured with a sterile needle. The fungus was reisolated from the inoculated fruits and shown to be identical to the original strains. On the basis of pathogenicity and morphological characteristics of the strains investigated, the fungus was determined to be a Phoma sp. (3), also known as sour cherry necrosis in other fruit-tree-growing regions. To our knowledge, this is the first report of the fungus on sour cherry fruit in Serbia.

References: (1) J. Balaž and M. Arsenijević. Proc.Int. Conf. Plant. Path. Bact. 7:515, 1990. (2) M. Ivanović and D. Ivanović. Zašt. Bilja 201:211, 1992. (3) B. C. Sutton. Pages 379–391 in: Coelomycetes. CMI, Kew, Surrey, England, 1980.
First Report of Alternaria Leaf Spot on Cherry Trees in Greece
Authors: Thomidis T. , Tsipouridis C.
Published: May 2007

Cherry leaf spot disease caused by Alternaria spp. has been reported in China (1) but never in Greece. The fungus Alternaria alternata (Fr.:Fr.) Keissler (CBS 119115) was isolated on acidified potato dextrose agar (2.5 ml of 85% lactic acid per liter of nutrient medium) from the leaves of cherry cv. A1/5 (hybrid of Prunus avium (L.) L.) at the Pomology Institute Naoussa, Greece in 2005. Microscopic morphology showed acropetal chains of multicellular conidia (dictyoconidia) produced sympodially from simple, sometimes branched, short or elongate conidiophores. Conidia are obclavate, obpyriform, sometimes ovoid or ellipsoidal, often with a short conical or cylindrical beak, pale brown, smooth-walled or verrucose. The percentage of diseased leaves was approximately 30 to 40%. Lesions first appeared on leaves in late spring as small, round, blackish spots and gradually enlarged to 2 to 5 mm in diameter with a brownish purple border. Some spots turned grayish brown, but most underwent a secondary enlargement and become irregular and much darker, acquiring a frogeye appearance. Similar symptoms were also observed on the leaves of cherry hybrids A1/3 and A5 established in the same cherry orchard. Zhu and Chang (1) reported that infected leaves of cherry trees by Alternaria seraci showed holes and resulted in early leaf fall. Symptoms were reproduced in the laboratory by spraying 2-year-old plants (20 plants) at the stage of fullleaf development, planted in pots, of the same cherry hybrid with conidia of the fungus. Aqueous suspension was adjusted to 3 × 10-6 conidia per ml (approximately 100 ml per plant) collected from an isolation of the fungus. Control plants were sprayed with distilled water without conidia. Plants were then placed in a growth chamber at 25°C for 3 months. After the incubation period, some leaves of the inoculated plants developed similar to those previously observed. No disease symptoms were observed in control leaves. Koch's postulates were satisfied after reisolating the fungus. To our knowledge, this is the first report of the occurrence Alternaria leaf spot on cherry trees in Greece.

Reference: (1) J. Zhu and Y. Chang. China Fruits 3:9, 2004.
First Report of Root Rot and Stem Canker Caused by Phytophthora cambivora on Noble Fir (Abies procera) for Bough Production in Norway
Authors: Talgø V. , Herrero M. , Toppe B. , Klemsdal S. , Stensvand A.
Published: May 2007

In 2004, damages resembling those caused by Phytophthora spp. were observed in a 15-year-old bough plantation of noble fir (Abies procera). When removing bark upward from the roots and base of a diseased tree, a reddish brown discoloration with distinct borders to surrounding wood appeared. The discoloration extended approximately 1.5 m above ground, but only on one side of the stem. This resulted in dead basal branches (flagging) on the cankered side of the tree. Other dying trees in the same field did not show flagging symptoms but turned chlorotic to brown after being girdled by the expanding stem canker. Approximately 25% of the trees were dead or dying. Isolations were carried out from the area between healthy and diseased tissue both from roots and base of the stem of the tree with flagging symptoms. Samples were rinsed in running tap water and plated on the Phytophthora selective medium PARP (17 g of cornmeal agar, 10 mg of pimaricin, 250 mg of ampicillin, 10 mg of rifampicin, and 100 mg of pentachloronitrobenzene (PCNB) in 1 liter of water), with and without hymexazol added (50 mg/l). Morphological characters of the isolated Phytophthora sp. included nonpapillate sporangia (37 to 64 μm), internal proliferation, and characteristic hyphal swellings. The isolate was heterothallic and produced amphigynous antheridia when crossed with tester strains of P. cryptogea. The mating type was A2. The internal transcribed spacer (ITS) rDNA sequences were identical to P. cambivora (GenBank Accession No. AY880985). Thus, both morphological characters and DNA analysis supported the species identification. A pathogenesis test to fulfill Koch's postulate was carried out during 2005. Inoculation was done by placing agar with culture in the growth medium close to the roots of noble fir seedlings. Eleven weeks after inoculation, clearly visible stem canker symptoms were observed. The ITS sequences of the reisolated Phytophthora sp. were determined and found identical to P. cambivora. P. cambivora was reported to cause root rot and stem canker in a noble fir Christmas tree plantation in the United States (1). P. citricola and P. citrophthora are known to cause problems on Lawson Falsecypress/Port-Orford-cedar (Chamaecyparis lawsoniana) in Norway, but damages by Phytophthora spp. have never been reported in Abies spp. plantations or forest stands in Norway. Currently, we are also working on Phytophthora problems discovered in two different Christmas tree plantations (A. lasiocarpa and A. nordmanniana).

Reference: (1) G. A. Chastagner et al. Plant Dis. 79:290, 1995.
Evaluation of Virulence of Phakopsora pachyrhizi and P. meibomiae Isolates
Authors: Bonde M. R. , Nester S. E. , Austin C. N. , Stone C. L. , Frederick R. D. , Hartman G. L. , Miles M. R.
Published: May 2007

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi and recently discovered for the first time in continental United States, has been of concern to the U.S. agricultural industry for more than 30 years. Since little soybean rust resistance is known, and resistance is often difficult to detect or quantitate, we initiated a project to develop a better, more quantitative, method. The methodology determined the average numbers and diameters of uredinia in lesions that developed on leaves of inoculated plants 14 days after inoculation. It was used to compare virulence of P. pachyrhizi isolates from Asia and Australia and P. meibomiae from Puerto Rico and Brazil, collected as many as 30 years earlier, with isolates of P. pachyrhizi recently collected from Africa or South America. Susceptible reactions to P. pachyrhizi resulted in tan-colored lesions containing 1 to 14 uredinia varying greatly in size within individual lesions. In contrast, on these same genotypes at the same time of year, resistance to other P. pachyrhizi isolates was typified by 0 to 6 small uredinia in reddish-brown to dark-brown lesions. Using appropriate rust resistant and rust susceptible genotypes as standards, examination of uredinia 14 days after inoculation allowed quantitative comparisons of sporulation capacities, one measure of susceptibility or resistance to soybean rust. The study verified the presence and ability to detect all known major genes for resistance to soybean rust in the original sources of resistance. It demonstrated that soybean lines derived from the original PI sources, and presumed to possess the resistance genes, in actuality may lack the gene or express an intermediate reaction to the rust pathogen. We suggest that a determination of numbers and sizes of uredinia will detect both major gene and partial resistance to soybean rust.
Timing Fungicide Applications for Managing Sclerotinia Stem Rot of Potato
Authors: Johnson Dennis A. , Atallah Zahi K.
Published: May 2007

Fungicides were applied to potato foliage at row closure (between rows) and at full bloom of primary inflorescences to control Sclerotinia stem rot during replicated trials in 2003, 2004, and 2005. Application at row closure followed labeled recommendations from manufacturers. Incidence of Sclerotinia stem rot did not vary significantly among fungicides when full labeled rates of thiophanate-methyl, fluazinam, and boscalid were applied at full bloom of primary inflorescences. Incidence of Sclerotinia stem rot was significantly less when fungicides thiophanatemethyl, fluazinam, or boscalid were applied to potato foliage at full bloom of primary inflorescences than at row closure or when fungicides were not applied in 2004 and 2005, and when thiophanate-methyl or fluazinam was applied to potato foliage at full bloom of primary inflorescences than at row closure or when fungicides were not applied in 2003. Mean percentage of control for the fungicides combined, relative to the nontreated control, was 43, 48, and 20% in 2003, 2004, and 2005, respectively, when application was made at row closure; whereas, it was 77, 83, and 80% in 2003, 2004, and 2005, respectively, when application was at full bloom of primary inflorescences. Mean disease incidences of infected stem were significantly less when fluazinam was applied at 100% bloom of primary inflorescences than at 20% drop of blossoms from primary inflorescences in 2004 and 2005. In summary, control of Sclerotinia stem rot was significantly better when fungicides were applied at full bloom of primary inflorescences than at row closure during all 3 years of the study.
Population Dynamics of Phialophora gregata in Stem Residue of a Resistant and a Susceptible Soybean Cultivar
Authors: Impullitti A. E. , Grau C. R.
Published: May 2007

Previous studies on the saprophytic survival of Phialophora gregata were conducted with soybean residue derived from a susceptible cultivar and did not address genotypes of P. gregata. This current study monitored the saprophytic population density of P. gregata in stem residue derived from a susceptible and a resistant soybean cultivar placed in the field. A second phase of the study followed the frequencies of genotypes A and B of P. gregata in stem residue derived from a susceptible cultivar. The population density of P. gregata declined 10-fold in stem residue from the initiation of sampling to the end of this 16-month study, regardless of cultivar or whether residue was positioned on the soil surface or buried. The population density of P. gregata was greater in buried residue of the resistant cultivar compared with the susceptible cultivar after 12 to 14 months, but equalized after 16 months. The population density of P. gregata was similar in residue derived from the susceptible and resistant cultivars if positioned on the soil surface. Genotype B was detected more frequently than genotype A of P. gregata at each sampling date regardless of residue placement.
Mutation at β-Tubulin Codon 200 Indicated Thiabendazole Resistance in Penicillium digitatum Collected from California Citrus Packinghouses
Authors: Schmidt Leigh S. , Ghosoph Jennifer M. , Margosan Dennis A. , Smilanick Joseph L.
Published: May 2007

Thiabendazole (TBZ) is commonly applied to harvested citrus fruit in packinghouses to control citrus green mold, caused by Penicillium digitatum. Although TBZ is not used before harvest, another benzimidazole, thiophanate methyl, is commonly used in Florida and may be introduced soon in California to control postharvest decay of citrus fruit. Isolates from infected lemons and oranges were collected from many geographically diverse locations in California. Thirty-five isolates collected from commercial groves and residential trees were sensitive to TBZ, while 19 of 74 isolates collected from 10 packinghouses were resistant to TBZ. Random amplified polymorphic DNA analysis indicated that the isolates were genetically distinct and differed from each other. Nineteen TBZ-resistant isolates and a known TBZ-resistant isolate displayed a point mutation in the β-tubulin gene sequence corresponding to amino acid codon position 200. Thymine was replaced by adenine (TTC → TAC), which changed the phenylalanine (F) to tyrosine (Y). In contrast, for 49 TBZ-sensitive isolates that were sequenced, no mutations at this or any other codon positions were found. All of the isolates of P. digitatum resistant to TBZ collected from a geographically diverse sample of California packinghouses appeared to have the same point mutation conferring thiabendazole resistance.
Transmission ofPotato virus Yin Tobacco Plants byMyzus persicae nicotianaeandM. persicaes.str.
Authors: Kanavaki Olympia M. , Margaritopoulos John T. , Katis Nikolaos I. , Skouras Panagiotis , Tsitsipis John A.
Published: May 2007

The transmission efficiency of Potato virus YN(PVYN) from and to tobacco plants by Myzus persicae nicotianae, a tobacco specialist, and M. persicae s.str. (Hemiptera: Aphididae), a generalist, was evaluated. In direct transmission tests, 1,004 spring migrants collected as nymphs from peach and 1,434 wingless females from 12 clonal lineages of both taxa were examined. Both the winged and wingless females were starved before being transferred individually for a 3-min acquisition period on infected plants and then moved to healthy plants for a 10-min inoculation access period. Little variation in transmission efficiency was observed. Although not statistically significant, M. persicae nicotianae was slightly more effective. This may suggest similar genetic properties (e.g., virion receptors in mouthparts) between the taxa in relation to virus transmission. M. persicae s.str. transmitted the virus less efficiently when a shorter inoculation period was given. This may indicate differences in probing behavior during the early phase of host selection. Nevertheless, behavioral differences related to host selection have been found using arena tests with infected and healthy tobacco plants where 180 winged females from each taxon were tested. M. persicae s.str. had significantly higher propensity to transmit PVYNthan M. persicae nicotianae (31.9 versus 15.3%).
Seed Transmission of Cephalosporium gramineum in Winter Wheat
Authors: Murray Timothy D.
Published: May 2007

Although isolation of Cephalosporium gramineum from wheat (Triticum aestivum) seed has been reported, development of Cephalosporium stripe in plants from infected seed has not been demonstrated experimentally. Winter wheat seed was collected from three experimental field plots where Cephalosporium stripe was present, and C. gramineum was isolated from the seed following surface-disinfection and incubation on a semi-selective medium. C. gramineum was isolated from 0.10 to 0.88% of seed from 11 of 12 cultivars in a field experiment at Pullman, WA, and from 0.10 to 0.30% of seed from 3 of 4 genotypes in a field experiment at Fort Hall, ID; differences among cultivars were not significant in either experiment. C. gramineum was isolated from 0.35 and 0.55% of cv. Stephens plants with no symptoms and severe symptoms, respectively, from a uniform seeding in Pullman. Seed of the four genotypes from Fort Hall and Stephens from Pullman were grown under controlled environment in a soilless potting mix with no added inoculum and in which C. gramineum was not detected. Symptoms of Cephalosporium stripe developed in 0.08 and 0.17% of Stephens and breeding line 87-00314A plants, respectively, from Fort Hall, and from 0.18 and 0.55% of Stephens plants with no symptoms and severe symptoms, respectively. Although development of Cephalosporium stripe in plants grown from seed lots harvested from diseased plants was low, infected seed can provide an important source of inoculum for introducing the pathogen and initiating epidemics in areas where the pathogen did not occur previously.
Vector Specificity, Host Range, and Genetic Diversity of Tomato chlorosis virus
Authors: Wintermantel William M. , Wisler Gail C.
Published: May 2007

Tomato chlorosis virus (ToCV), family Closteroviridae, genus Crinivirus, causes interveinal chlorosis, leaf brittleness, and limited necrotic flecking or leaf bronzing on tomato leaves. ToCV can cause a decline in plant vigor and reduce fruit yield. It is emerging as a serious production problem for field and greenhouse tomato growers, and has been increasing in prevalence in many parts of the world. The virus is unique among known whitefly-transmitted viruses, due to its ability to be transmitted by four whitefly vectors from two genera. Studies demonstrated that transmission efficiency and virus persistence in the vector varies significantly among the different whitefly vectors. Trialeurodes abutilonea and Bemisia tabaci biotype B are highly efficient vectors of ToCV. B. tabaci biotype A and T. vaporariorum are less efficient vectors, but are fully capable of transmission. ToCV persists for up to 5 days in T. abutilonea, 2 days in B. tabaci biotype B, and only 1 day in B. tabaci biotype A and T. vaporariorum. ToCV has a moderately wide host range, infecting 24 host plant species in seven families. A portion of the coat protein coding region of five geographically diverse ToCV isolates was compared and found to be highly conserved. This information, coupled with existing information on conservation within the heat shock protein 70 homologue coding region, suggests that many ToCV isolates throughout the world are related very closely, and may have been distributed on plant material.
First Report of Cotton Leaf Curl Disease in Central and Southern Sindh Province in Pakistan
Authors: Mansoor S. , Amrao L. , Amin I. , Briddon R. W. , Malik K. A. , Zafar Y.
Published: May 2007

Cotton leaf curl is a devastating disease of cotton that has resulted in severe losses (estimated at more than US$87 million per annum) in Pakistan. The epidemic is centered in Punjab, the province that contributes approximately 80% of Pakistan's cotton. Previously, the disease had been observed sporadically on single plants in the northern Sindh Province but did not cause economically significant damage. During the years 2004 and 2005, a high incidence (approximately 20%) of the disease was observed in Shahdadpur and parts of District Sanghar, located in central Sindh Province. The disease was also observed at low incidence (<1%) in southern Sindh. To confirm the identity of the causal agent of the disease, 18 samples from three districts in central southern Sindh (Sanghar, Hala, and Hyderabad) were collected, and total DNA was extracted using cetyltrimethylammoniumbromide (2). Universal primers for begomoviruses based on conserved sequences as follows were used in polymerase chain reaction (PCR): BegomoF (5′-CCGTGCTGCTGCCCCCATTGTCCGCGTCAC-3′) and BegomoR (5′-CTGCCACAACCATGGATTCACGCACAGGG-3′). Universal primers for amplification of DNA β with PCR were also used (1). A full-length clone of Cotton leaf curl Multan virus (CLCuMV) was labeled with alpha-32PdCTP by the oligo-labeling method and used as a probe in Southern hybridization for the detection of geminivirus DNA forms (2). Similarly, cotton leaf curl disease associated DNA β was also labeled and used as a probe in Southern hybridization. The use of universal primers for begomoviruses resulted in amplification of viral DNA of the expected size from all samples while no PCR product was obtained from healthy plants. PCR results confirmed that all plants were infected with begomoviruses. Southern hybridization with CLCuMV and DNA β probes detected begomovirus DNA forms associated with virus replication when washed at medium stringency, further confirming that the plants were infected with the cotton leaf curl geminivirus complex (2). Our results indicate that cotton leaf curl complex has become established in central and southern districts of Sindh Province and it poses a major threat to cotton grown in the region.

References: (1) R. W. Briddon et al. Mol. Biotechnol. 20:315, 2002. (2). S. Mansoor et al. Arch. Virol. 148:1969, 2003.
First Report of a Begomovirus Infecting Sweetpotato in Kenya
Authors: Miano D. W. , LaBonte D. R. , Clark C. A. , Valverde R. A. , Hoy M. W. , Hurtt S. , Li R.
Published: May 2007

Previous surveys for viruses in sweetpotatoes (Ipomoea batatas) in Africa did not assay for the presence of begomoviruses such as Sweet potato leaf curl virus (SPLCV), which have been found recently in the Americas and Asia. Symptomatic sweetpotato plants, including some with leaf curling symptoms similar to those observed in SPLCV-infected sweet-potato plants (2), were collected from a germplasm collection plot at Kakamega Research Station in Western Kenya during February 2005. Whiteflies, the vectors for begomoviruses, were observed in the same plots. Ipomoea setosa plants graft-inoculated with scions from the symptomatic sweetpotato developed leaf curl, leaf roll, interveinal chlorosis, and stunting symptoms similar to those caused by infection with SPLCV alone or in combination with Sweet potato feathery mottle virus. Total DNA was isolated from 10 I. setosa plants using the GenElute Plant Genomic DNA Kit (Sigma-Aldrich Inc., St. Louis, MO). Sweetpotato cuttings from 39 clones, selected from the Kenyan germplasm collection for their resistance or susceptibility to sweetpotato virus disease (SPVD), were sent to the Plant Germplasm Quarantine Office of USDA-ARS. The cuttings were planted in a greenhouse. Total DNA was extracted from sweetpotato leaves 1 month later using a cetyltrimethylammoniumbromide (CTAB) extraction method (1). Degenerate primers SPG1/SPG2, developed for PCR detection of begomoviruses (1), amplified a 912-bp DNA fragment from 3 of 10 DNA extracts from I. setosa and 5 of 39 sweetpotato plants held in quarantine. The primers anneal to regions of open reading frame (ORF) AC2 and ORF AC1 that are highly conserved in begomoviruses infecting sweetpotato. SPLCV-specific primers PW285-1/PW285-2 (2) amplified a 512-bp DNA fragment of ORF AC1 from seven samples (two from I. setosa and five from I. batatas). Amplicons from three independent PCR assays of two samples and single PCR assays of four additional samples were cloned into the pGEM-T Easy vector. Clone inserts were sequenced, and compared with sequences deposited in GenBank using the basic local alignment search tool (BLAST). Sequences were closely related to SPLCV (GenBank Accession No. AF104036) with nucleotide sequence identities varying from 93% (GenBank Accession No. DQ361004) to 97% (GenBank Accession No. DQ361005). The presence of the virus poses a challenge to the dissemination of planting materials in the region because begomovirus-infected plants often do not show symptoms. To our knowledge, this is the first report of a begomovirus infecting sweetpotato in Kenya or the East African Region.

References: (1) R. Li et al. Plant Dis. 88:1347, 2004. (2) P. Lotrakul et al. Plant Dis. 82:1253, 1998.
First Report of Soybean Rust Caused by Phakopsora pachyrhizi on Kudzu (Pueraria montana var. lobata) in Kentucky
Authors: Hershman D. E. , Bachi P. R. , Harmon C. L. , Harmon P. F. , Palm M. E. , McKemy J. M. , Zeller K. A. , Levy L.
Published: May 2007

Phakopsora pachyrhizi, the causal organism of soybean rust, was first observed in the continental United States on 6 November 2004 (2). On 11 November 2005, as part a national soybean rust monitoring effort, 75 leaves of kudzu (Pueraria montana var. lobata) were arbitrarily collected from a patch growing in Princeton, Caldwell County, Kentucky (37.106650°N, 87.886120°W) that had been periodically scouted for the presence of the disease since May 2005. Upon microscopic examination of the nonincubated sample, a small (˜2.0 cm2) area of one leaf exhibited lesions, uredinia, and urediniospores characteristic of those reported for P. pachyrhizi (the Asian species) and P. meibomiae (the New World species) (2). No other infected leaves were observed despite repeated visits to the site and collection and observation of nearly 200 leaves. On 16 November 2005, one-half of the symptomatic tissue was sent by overnight courier to the USDA/APHIS/PPQ/NIS Laboratory, Beltsville, MD and the other half was sent to the Southern Plant Diagnostic Network Laboratory (SPDN), University of Florida, Gainesville. Both laboratories confirmed that the rust was a Phakopsora spp. on the basis of morphological examination. The preliminary polymerase chain reaction (PCR) testing conducted by the SPDN according to Harmon et al. (1) indicated the presence of P. pachyrhizi that was confirmed by the USDA/NPGBL using the validated modified real-time PCR assay described previously (2). The field diagnosis of P. pachyrhizi and preliminary PCR results were officially confirmed by USDA/APHIS on 18 November 2005. To our knowledge, this is the first report of P. pachyrhizi on kudzu or any host in Kentucky, and currently, the northernmost report of soybean rust on any host in the continental United States.

References: (1) P. F. Harmon et al. On-line publication, doi:10.1094/PHP-2005-0613-O1-RS. Plant Health Progress, 2005. (2) R. W. Schneider et al. Plant Dis. 89:774, 2005.
Effect of Chinese Herb Extracts on Spore Germination of Oidium murrayae and Nature of Inhibitory Substance from Chinese Rhubarb
Authors: Chu Y. L. , Ho W. C. , Ko W. H.
Published: May 2007

More than 21% of the Chinese herbs tested contained substances in their aqueous extracts inhibitory to conidial germination of the powdery mildew fungus Oidium murrayae. Extracts from Chinese rhubarb and Japanese knotweed were very effective in controlling powdery mildew on cucumber, pumpkin, and eggplant. The inhibitory substance in Chinese rhubarb was soluble in polar solvents and less soluble in nonpolar solvents. The inhibitor in the aqueous extract was not dialyzable in the membrane tubing with molecular weight cut-off of 14,000, but was exchangeable by anion but not cation exchange resins, indicating that the inhibitor has a molecular weight larger than 14,000 and negative charge on its molecule.
Evaluation of Cotton Germ Plasm for Resistance to the Whitefly and Cotton Leaf Crumple (CLCr) Disease and Etiology of CLCr in California's Imperial Valley
Authors: Seo Y.-S. , Zhou Y.-C. , Turini T. A. , Cook C. G. , Gilbertson R. L. , Natwick E. T.
Published: May 2007

Cotton (Gossypium hirsutum) entries were evaluated for resistance to the whitefly (Bemisia tabaci biotype B) and cotton leaf crumple (CLCr) disease during the 1999 to 2001 growing seasons in the Imperial Valley of California. Entries were evaluated for densities of whitefly adults and nymphs, and for CLCr, by visual rating and squash/dot blot hybridization analyses. Differences in whitefly densities were detected among entries, but none were highly resistant, nor was there any correlation with CLCr disease severity. Entries AP 4103 and AP 6101 had relatively low whitefly densities and were highly susceptible (high CLCr disease severity ratings and viral titers), whereas NK 2387C and DPX 1883 also had low whitefly densities but were highly resistant (no symptoms or detectable viral titers). Other entries showed moderate CLCr resistance, which was independent of whitefly density. Geminivirus DNA-A and DNA-B components were consistently detected in cotton leaves with CLCr symptoms by polymerase chain reaction (PCR) with degenerate begomovirus primers, and full-length DNA-A and DNA-B clones were obtained. Cotton seedlings inoculated with these cloned DNAs by particle bombardment developed CLCr symptoms, and progeny virus was whitefly-transmissible. Sequence analysis revealed that these clones comprised the genome of a California isolate of the bipartite begomovirus Cotton leaf crumple virus (CLCrV-CA). Thus, CLCr disease in the Imperial Valley is caused by CLCrV-CA, and cotton entries with high levels of resistance were identified.
Response of a Maize Synthetic to Selection for Components of Partial Resistance to Exserohilum turcicum
Authors: Carson M. L.
Published: May 2007

A synthetic population of maize (Zea mays) was created from five inbred lines of varying levels of partial resistance to northern leaf blight (NLB). This synthetic was subjected to three cycles of recurrent phenotypic selection with pollen control for either increased latent period or decreased lesion length. A selection intensity of ca. 10% was used in each selection cycle. The original synthetic and three advanced selection cycles for each of the two components of partial resistance were evaluated in field trials in the summers of 1999 and 2001, and in greenhouse trials. Selection for increased latent period was more effective in improving resistance to NLB (20 to 27% gain/cycle) (as measured by area under the disease progress curve [AUDPC]) than was selection for decreased lesion length (14 to 18% gain/cycle). Responses in AUDPC to selection for either component of resistance were linear in the 1999 field trial, but were quadratic (decreased response in advanced cycles) in the 2001 trial. Selection for increased latent period in the field resulted in a 0.6-day increase in latent period per selection cycle when measured in the greenhouse and a 2-day increase per selection cycle when measured in the field. Selection for decreased lesion length in the field did not significantly alter latent period in the greenhouse. These results support using selection for increased latent period as an effective means of improving partial resistance to NLB in maize populations. Decreased lesion length was more difficult to measure and selection based on this criterion was less effective in improving partial resistance.
First Report of Meloidogyne arenaria Parasitizing Lettuce in Southern Spain
Authors: Castillo P. , Landa B. B. , Navas-Cortés J. A. , Vovlas N. , Jiménez-Díaz R. M.
Published: May 2007

During the 2005-2006 autumn to winter lettuce-growing (Lactuca sativa cv. Iceberg) season, severely stunted and yellowing lettuce plants with disease incidence ranging from 80 to100% were observed in four commercial, fall-sown fields at Almodóvar del Río (Córdoba Province) in southern Spain. Early symptoms consisted of severely reduced growth of the plants that continued with extensive leaf yellowing and the absence of tight-head formation. Attacks by the disease were estimated to cause near complete loss of the crop yields since the lettuce head produced in affected fields were unmarketable. Observations of affected lettuce plants revealed high parasitism of the root system by a root-knot nematode (Meloidogyne sp.) in the main and feeder roots as well as heavy soil infestations by the nematode. The nematode was identified by the female perineal pattern, esterases phenotype, and a sequence-characterized amplified region polymerase chain reaction (SCAR-PCR) technique (1,2,4). Measurements and morphological observations of 20 second-stage juveniles (J2s) (body length = 463 ± 28 μm, dorsal gland orifice from stylet base = 2.8 ± 0.6 μm, stylet length = 10.4 ± 0.5 μm, tail length = 54.4 ± 0.6 μm; hyaline tail terminus = 9.4 ± 0.6 μm) and 10 adult females (stylet length = 14.5 ± 0.7 μm, dorsal gland orifice from stylet base = 4.7 ± 0.5 μm, and perineal pattern with low and rounded dorsal arch with coarse striae) conformed to the description of Meloidogyne arenaria (3). On the basis of the characteristics of the perineal pattern, the 2-band esterase phenotype, and the 420-bp SCAR fragment, the causal agent was identified as the peanut root-knot nematode M. arenaria. Nematodes were extracted from soil and root samples by standard procedures and their populations quantified. M. arenaria was detected in nearly all soil and root samples assessed, with nematode population densities ranging from 206 to 1,072 eggs and J2s per 5 g of fresh roots. Different Meloidogyne spp. have been reported parasitizing lettuce roots, especially M. hapla in northern areas (2); however, to our knowledge this is the first time that M. arenaria is reported parasitizing lettuce roots in Spain and elsewhere.

References: (1) P. R. Esbenshade and A. C. Triantaphyllou. J. Nematol. 22:10, 1990. (2) N. A. Mitkowski et al. Plant Dis. 86:840, 2002. (3) K. J. Orton Williams. Meloidogyne arenaria. CIH Descriptions of Plant-Parasitic Nematodes. Set 5, No. 62. Commonwealth Institute of Helminthology, St. Albans, 1975. (4) C. Zijlstra et al. Nematology 2:847, 2000.
Colonization of Potato Plants after Aerial Infection by Colletotrichum coccodes, Causal Agent of Potato Black Dot
Authors: Nitzan N. , Evans M. , Johnson D. A.
Published: May 2007

Colonization of potato plants by Colletotrichum coccodes after artificial inoculation of stems was modeled in relation to the severity of chlorosis and necrosis on foliage using logistic regression. C. coccodes internally colonized the stems up to 24 cm above the inoculation court (mean of 11.3 ± 7.7 cm and 14.1 ± 9.3 cm in 2003 and 2004, respectively), and completely colonized the stem below the inoculation court including the roots (mean of 13.2 ± 3.1 cm and 12 ± 2.3 cm in 2003 and 2004, respectively). C. coccodes grew significantly faster from the inoculation court toward the roots, stolons, and tubers than toward the plant apex. Internal stem colonization was restricted before senescence but rapidly increased as the plants started to senescence, suggesting that physiological events associated with plant senescence activated fungal growth and plant colonization. The results showed no relationship between C. coccodes growth and plant colonization and the development of chlorosis and necrosis severity of leaves. The severity of chlorosis and necrosis on foliage in this study was the outcome of natural plant senescence, and was not caused by the fungal colonization. Therefore, chlorosis and necrosis severity is an inaccurate tool to diagnose infection in potato by C. coccodes and does not indicate the presence or amount of C. coccodes in potato plants. Disease assessment for C. coccodes in potato plants should not rely on severity of chlorosis and necrosis. Black dot assessment should be carried out by isolation and quantification of the fungus from stem and root tissues or by polymerase chain reaction techniques before plant senescence.
Identification of Small Grains Genotypes Resistant to Soilborne wheat mosaic virus
Authors: Cadle-Davidson L. , Sorrells M. E. , Gray S. M. , Bergstrom G. C.
Published: May 2007

Soilborne wheat mosaic virus (SBWMV) was detected in New York in 1998 for the first time and has been associated with yield loss where identified. We assessed 115 regionally adapted small grains genotypes for resistance to SBWMV over four growing seasons. Resistance to SBWMV reduces the percentage of plants that develop detectable viral titer and symptoms. Logistic regression was used to analyze disease incidence data and was compared with a general linear model for categorizing relative resistance to SBWMV. Logistic regression facilitated assessment of the effects of small sample size, low disease incidence, and nonuniform disease distribution. By increasing sample size from 20 to 30 stems per replicate, the number of resistance categories was increased through improved resolution of intermediate resistance classes. In environments with low disease incidence, the number of genotypes categorized as susceptible decreased while intermediate genotypes appeared to be resistant in the analysis. Inclusion of disease distribution data as covariates in a spatially balanced experiment did not increase the power of the logistic analysis. No genotype assessed in multiple years was immune to infection. However, 41 of the regionally adapted genotypes tested repeatedly expressed strong resistance to SBWMV, providing growers a choice of cultivars resistant to SBWMV.