bluuebunny/crossref_metadata_2025 huggingface dataset:
Iris yellow spot virus in Onion in Chile
Authors: Rosales M. , Pappu H. R. , López L. , Mora R. , Aljaro A.
Published: May 2007

Iris yellow spot virus (IYSV) (genus Tospovirus, family Bunyaviridae) has become endemic in several parts of the world. Between 2000 and 2004, the virus was reported from several states in the United States and the most recent report was from Georgia (2). In South America, IYSV was first reported from Brazil (3). Symptoms indicative of IYSV infection (1), such as diamond-shaped and irregular chlorotic and necrotic lesions, were observed during 2004 and 2005 in onion fields in Colina and Tiltil (Chacabuco Province) and Rengo (Cachapoal Province) located in central Chile. In the sampled fields, as much as 50% of the crop showed symptoms. In all three locations, the crop was destined for bulb production and the cultivar was a long-day Valenciana-type. Approximately 50 and 5 ha in Chacabuco and Cachapoal provinces, respectively, were surveyed. Symptomatic plants were collected and tested in the laboratory for confirmation of IYSV infection. A commercially available IYSV-specific enzyme-linked immunosorbent assay kit was used (Adgen Limited, Ayr, Scotland, UK) that confirmed the samples were infected with IYSV. Total nucleic acids were extracted, and using primers flanking the nucleoprotein (NP) gene of IYSV, reverse transcription-polymerase chain reaction was used to verify virus identity. Primer sequences were 5′-TAA AAC AAA CAT TCA AAC AA-3′ and 5′-CTC TTA AAC ACA TTT AAC AAG CAC-3′. The resulting 1.2-kb DNA amplicons from five samples were cloned and sequenced (GenBank Accession No. DQ150107). Nucleotide sequence comparisons with known IYSV NP gene sequences showed 95 to 98% identity, confirming the virus as IYSV. The presence of IYSV in Brazil and now in Chile indicates its potential to become established in onion crops in the region.

References: (1) L. J. du Toit et al. APSnet Image of the Week. http://apsnet.org/online/archive/2003/IW000030.asp , 2003. (2) S. W. Mullis et al. Plant Dis. 88:1285, 2004. (3) L. Pozzer et al. Plant Dis. 83:345, 1999.
An Accurate In Vitro Assay for High-Throughput Disease Testing of Phytophthora infestans in Potato
Authors: Huang Sanwen , Vleeshouwers Vivianne G. A. A. , Visser Richard G. F. , Jacobsen Evert
Published: May 2007

An in vitro inoculation assay was developed as a routine disease testing method to study gene-for-gene interactions in the potato (Solanum tuberosum)-Phytophthora infestans pathosystem. The specificity and reliability of the new method was compared with the well-established detached-leaf assay. Four P. infestans isolates were tested for avirulence on a set of R gene differentials using tissue cultured plantlets and detached leaves. Both methods gave identical conclusions on avirulence profiles of all isolates. A population of 93 clones was phenotyped for segregation of two closely linked and functionally distinct genes—R3a and R3b—in the R3 locus. Both methods resulted in phenotypic scorings that were in perfect agreement for all clones. Furthermore, the phenotyping of the population was fully consistent with the genotyping obtained from analysis of molecular markers that flank each gene. This new assay is quick, space-effective, and accurate and can be used for investigation of the qualitative interaction between potato and P. infestans.
Isolation and Characterization of Burkholderia gladioli from Orchids in Hawaii
Authors: Keith Lisa M. , Sewake Kelvin T. , Zee Francis T.
Published: May 2007

Bacterial diseases of orchids continue to be serious problems. Bacterial strains were isolated from orchid plants exhibiting disease symptoms in Hawaii. Small to large leaf spots with or without water-soaking or soft rots were observed on various orchid genera, including Dendrobium, Oncidium, and Miltonia spp. and hybrids. Bacteria isolated and cultured from the lesions were tentatively identified using analytical profile index (API) strips and standard physiological and biochemical tests, and confirmed by species-specific polymerase chain reaction and sequencing of the 16S rRNA gene. The variation in pathogenic, morphological, cultural, and molecular characteristics of the orchid isolates also was evaluated. In our studies, a gramnegative, aerobic, rod-shaped bacterium that produced pale yellow, opaque, round colonies with entire margins on nutrient broth yeast extract agar (NBY) was isolated consistently from diseased orchid plants. On yeast dextrose calcium carbonate agar, the isolates produced brownishyellow, nonmucoid colonies, with the majority of the strains secreting a diffusible yellow or tan pigment into the media. The bacterium was identified as Burkholderia gladioli. Molecular analysis indicated very little diversity in the 16S rDNA gene. Testing B. gladioli isolates using media containing copper or streptomycin indicated varying levels of resistance (copper resistant = Cur; streptomycin resistant, Smr), with approximately 75% of the strains resistant to copper and 94% of the strains resistant to streptomycin. The minimum inhibitory concentration (MIC) of cupric sulfate among Cur strains ranged from 50 to 1,000 μg/ml and the MIC of streptomycin was 50 to 100 μg/ml for all Smr B. gladioli strains tested. Field and laboratory data suggest the frequent use of these chemicals in nurseries may have inadvertently resulted in the development of copper and streptomycin resistance in B. gladioli from orchids.
Influence of Epidemiological Factors on the Bioherbicidal Efficacy of Phomopsis amaranthicola on Amaranthus hybridus
Authors: Rosskopf E. N. , Yandoc C. B. , Charudattan R. , DeValerio J. T.
Published: May 2007

Greenhouse experiments were performed to determine the effect of dew period temperature and duration, plant growth stage, conidial concentration, and the addition of adjuvants on the bioherbicidal efficacy of Phomopsis amaranthicola on Amaranthus spp., using Amaranthus hybridus as test plant. P. amaranthicola infected A. hybridus at 20, 25, 30, and 35°C but the disease level achieved at 20°C may not be sufficient to cause high plant mortality. Plant mortality was also significantly lower in plants that were exposed to 4 h of dew. Plants at less than two- to two- to four-leaf stage were more easily killed than older plants, and increasing conidial concentration from 105 to 106 or 107 conidia ml-1 did not result in higher mortality levels. Among the adjuvants tested, polyalkyleneoxide-modified heptamethyltrisiloxane, algal polysaccharide, hyrdroxyethyl cellulose, and octylphenoxy polyethoxyethanol reduced conidial germination. Conidia applied with invert emulsion caused the highest plant mortality (74%) but invert emulsion alone caused 33% plant death due to phytotoxicity. Results indicate that P. amaranthicola can infect and kill Amaranthus spp. under a range of temperature, dew period, and inoculum levels and, therefore, has good potential as a bioherbicide agent.
First Report of the Stubby-Root Nematode, Paratrichodorus teres, from Potato in the Columbia Basin of Washington State
Authors: Riga E. , Neilson R.
Published: May 2007

Stubby-root nematodes of the genus Paratrichodorus are migratory ectoparasites that cause stunted and deformed roots. They also transmit Tobacco rattle virus, the causal agent of corky ringspot disease in potato. Thus, they are important to the potato industry in the Pacific Northwest, including the Columbia Basin of Washington state, which is one of the largest potato-producing regions in the United States. Stubby-root nematode species are difficult to identify because the morphological differences between the species are very small (4). Paratrichodorus teres is a morphologically similar species and has been reported mainly from temperate regions within Europe. P. teres has also been reported in potato fields in eastern Oregon (3). The morphological similarity between P. allius and P. teres creates problems for routine identification because trichodorid species have a conservative morphology and are separated by the following primary characteristics: females, type of genital system and vulva position; males, number of ventromedian precloacal supplements and cervical papillae and habitus (2). As with most soil nematodes, females are more prevalent than the males. Unfortunately, in the generic key (2), female P. allius and P. teres belong to subgroup 1–12 and are separated by a secondary characteristic, vaginal shape that could be affected by fixation or handling. Male P. allius and P. teres are separated by the former species having one fewer ventromedian precloacal supplement. Thus, the morphological similarity between P. allius and P. teres creates problems for routine identification. This might be one of the reasons that P. teres has not been diagnosed in Washington until now. Using nematode morphological diagnostic keys (1,2) and comparing 18S rDNA sequence data obtained from specimens with those listed on public sequence databases, e.g., NCBI GenBank, stubby-root nematodes from two potato fields close to Moses Lake, Grant County, WA, were diagnosed as P. teres. The two adjacent potato fields are irrigated and are situated approximately 100 miles from the eastern Oregon site where P. teres was first described (3). Soil samples were collected from several Columbia Basin potato fields that had corky ringspot disease and stubby-root nematodes. Corky ringspot disease is an emerging disease in Washington, and the presence of a new viruliferous nematode species might be of concern to the potato industry.

References: (1) W. Decraemer. Page 615 in: Manual of Agricultural Nematology. W. R. Nickle, ed. Marcel Dekker, Inc., New York, 1991. (2) W. Decraemer and P. Baujard. Fundam. Appl. Nematol. 21:37, 1998. (3) H. J. Jensen et al. Plant Dis. Rep. 58:269, 1974. (4) S. MacFarlane et al. Adv. Bot. Res. 36:169, 2002.
Population Dynamics of the Lance Nematode (Hoplolaimus galeatus) in Creeping Bentgrass
Authors: Settle D. M. , Fry J. D. , Todd T. C. , Tisserat N. A.
Published: May 2007

The effects of management practices and nematode population density on the seasonal fluctuationsin lance nematode (Hoplolaimus galeatus) populations in creeping bentgrass were studiedin a naturally infested experimental putting green and in artificially infested microplots. In general, H. galeatus populations increased from late spring through midsummer, declined in August, and increased again in the fall. Population increase in microplots was strongly density dependent, with final population densities inversely proportional to inoculum levels. Ectoparasitic populationsof H. galeatus in both studies were composed of adults and juveniles, whereas endoparasiticpopulations were almost exclusively juveniles. H. galeatus populations in the naturallyinfested site were aggregated spatially, but the aggregation was not temporally stable. Nematodepopulations were not affected by bentgrass cultivar selection or irrigation frequency.
Septoria Leaf Spot Reduces Flower Bud Set and Yield Potential of Rabbiteye and Southern Highbush Blueberries
Authors: Ojiambo P. S. , Scherm H. , Brannen P. M.
Published: May 2007

In field trials on Premier rabbiteye blueberry, individual shoots were selected and tagged in the fall of 2001, 2002, and 2003 to quantify the effects of Septoria leaf spot severity and disease-induced premature defoliation on flower bud set and return yield. Experiments were carried outsimilarly on Bluecrisp southern highbush blueberry using shoots tagged after fruit harvest in the summer of 2002 and 2003. Leaves on the distal 20-cm segments of these shoots were monitored for disease severity (number of spots per leaf) through the remainder of the growing season; at the same time, defoliation (expressed as the proportion of nodes with missing leaves) was recorded for each of the shoot segments. Flower bud set was assessed subsequently in winter or early spring, and berries were harvested as they matured the following summer to determine return yield. For both cultivars, higher flower bud numbers were more likely to occur on shoots with lower disease levels the previous fall (P ≤ 0.0462 based on a Kolmogorov-Smirnov test). The data further showed that flower bud set potential (i.e., the maximum number of buds on shoots within a given disease severity range) decreased linearly as disease severity increased (r2≥ 0.926, P ≤ 0.0005). Based on the slope of this relationship, flower bud set potential decreased by one bud per shoot as disease severity the previous fall increased by 18 and 12 spots per leaf for Premier and Bluecrisp, respectively. Relationships between yield and disease variables were similar to those of flower bud numbers and disease, except that the decrease in yield potential (i.e., the maximum fruit weight per shoot within a given disease severity range) was less gradual than for flower bud set potential. On Premier, yield potential dropped markedly and significantly as disease severity the previous fall exceeded about 50 to 60 spots per leaf on average (P < 0.0001 based on a Kruskal-Wallis test). Evidence for such a threshold effect was weaker on Bluecrisp, presumably because of the lower number of data points for this cultivar combined with lower yields due to poor pollination.
Lignin Degradation by Fusarium solani f. sp. glycines
Authors: Lozovaya V. V. , Lygin A. V. , Zernova O. V. , Li S. , Widholm J. M. , Hartman G. L.
Published: May 2007

Sudden death syndrome (SDS), caused by the soilborne fungal pathogen Fusarium solani f. sp. glycines, is one of the most important diseases of soybean. Lignin degradation may play a role in the infection, colonization, and survival of the fungus in root tissue. Lignin degradation by F. solani f. sp. glycines was shown by the catalyzed release of 14CO2 from purified 14C-labeled Klason lignin, the degradation of polymeric aromatic dyes in culture (a method commonly used to test the ligninolytic capacity of microorganisms), and the production of laccase and lignin peroxidase (the major fungal lignin degrading enzymes). The laccase and lignin peroxidase activities and the amount of decolorization of aromatic polymeric dyes (Poly R-478 and Remazol Brilliant Blue R) by F. solani f. sp. glycines were intermediate or greater than that found with two known lignin-degrading fungi, Polyporus tulipifera and Schizophyllum commune. Studies of lignin synthesis from [14C]phenylalanine with soybean hairy root cultures showed that F. solani f. sp. glycines treatment stimulated lignin synthesis in 2 h, and by 24 h, some lignin degradation had occurred. These results indicate that F. solani f. sp. glycines was capable of degrading lignin which may be important in infection, colonization, and survival of the fungus.
A One-Day Sensitive Method to Detect and Distinguish Between the Citrus Black Spot Pathogen Guignardia citricarpa and the Endophyte Guignardia mangiferae
Authors: Meyer L. , Sanders G. M. , Jacobs R. , Korsten L.
Published: May 2007

If South African citrus exporters wish to retain their competitive edge in the European market and access new markets such as the United States of America, it is of quarantine importance to distinguish between the citrus black spot pathogen, Guignardia citricarpa, and the harmless endophyte, G. mangiferae. The endophyte is not a sanitary or phytosanitary concern. This paper describes the design of species-specific primers that are able to detect and distinguish between these two Guignardia species. Application of the primer set CITRIC1 and CAMEL2 in conjunction with the ITS4 primer yielded polymerase chain reaction (PCR) amplicons of approximately 580 bp and 430 bp for G. citricarpa and G. mangiferae, respectively. Results obtained with these primers are in accordance with sequence data, and repeated tests verified accuracy and sensitivity. A BLAST search revealed no matches other than G. citricarpa and G. mangiferae, and no positive PCR results were obtained with Colletotrichum gloeosporioides, which is the most common contaminant in black spot lesions. We are, therefore, able to distinguish G. citricarpa and G. mangiferae unequivocally using a PCR-based method. This method was further improved to directly isolate DNA from fruit lesions by means of the DNeasy Plant Mini Kit (Qiagen). This eliminates the prior need for culturing the slow-growing organism, thereby shortening the time required to one day to test for and verify the presence or absence of the pathogenic G. citricarpa in export consignments.
First Report of Sudden Death Syndrome of Soybean Caused by Fusarium solani f. sp. glycines in Nebraska
Authors: Ziems A. D. , Giesler L. J. , Yuen G. Y.
Published: May 2007

During August of 2004, soybean (Glycine max (L.) Merr.) plants exhibiting symptoms typical of sudden death syndrome (SDS) caused by Fusarium solani (Mart.) Sacc. f. sp. glycines (= Fusarium virguliforme Akoi, O'Donnell, Homma, & Lattanzi) (1) were observed in Nemaha and Pierce counties in eastern Nebraska. Leaf symptoms ranged from small chlorotic spots to prominent interveinal necrosis on plants at R5-R6 growth stages. Taproots of symptomatic plants were plated on potato dextrose agar (PDA) amended with hymexazol, ampicillin, and rifampicin (HAR). Resulting fungal isolates grew slowly and developed masses of blue macroconidia, characteristic of F. solani f. sp. glycines. Sorghum seed infested with the isolates were placed 1.5 cm below soybean seeds of the susceptible cv. Sloan planted in clay pots (3). Noninfested sorghum seed and sorghum seed infested with F. oxysporum were controls. Plants were maintained for 32 days at 27.5 ± 2.5°C in the greenhouse. Small cholorotic spots were observed on leaves of F. solani f. sp. glycines-inoculated plants within 21 days followed by the development of interveinal chlorosis. Roots of symptomatic plants were plated on PDA with HAR and F. solani f. sp. glycines was recovered. Identification of the fungal cultures was further confirmed as F. solani f. sp. glycines by a real-time quantitative polymerase chain reaction (qPCR) assay described by Gao et al. (2). During 2005, SDS symptoms were also reported in early planted soybeans from Jefferson and Seward counties and the presence of SDS was confirmed by qPCR. The confirmation of SDS at multiple locations suggests that the pathogen is widely distributed in the eastern one-third of Nebraska. SDS could be a serious threat to soybean production in this area since spring weather conditions favor SDS infection and many producers plant soybean early in cool soils.

References: (1) T. Akoi et al. Mycologia 95:660, 2003. (2) X. Gao et al. Plant Dis. 88:1372, 2004. (3) K. W. Roy et al. Plant Dis. 81:259, 1997.
Dasylirion serratifolium as a New Host of Botrytis cinerea, the Causal Agent of Leaf Spots and Blight in Italy
Authors: Polizzi G. , Vitale A.
Published: May 2007

Sandpaper sotol (Dasylirion serratifolium Zucc.), native to Mexico, has green leaves with margins highlighted by whitish yellow prickles like a fine sandpaper. During the spring of 2004 and 2005, necrotic lesions were observed in the middle of leaf blades and near prickles on 2- to 5-year-old, container-grown sandpaper sotol plants from two nurseries in eastern Sicily (Italy). Symptoms were detected on 20 to 30% of plants and consisted of reddish lesions that developed a reddish brown stripe surrounded by a yellow halo. As lesions enlarged, the center turned yellow and expanded rapidly causing blight of young leaves. Occasionally, symptomatic tissues had masses of gray fungal conidia and/or sclerotia. Botrytis cinerea was isolated consistently from infected tissues disinfected for 1 min in 1% NaOCl and rinsed in sterile distilled water and grown on potato dextrose agar (PDA). Hyaline, ovoid conidia (average 6.4 × 9.7 μm) and conidiophores were similar to those described of B. cinerea, and 5- to 8-day-old cultures developed black sclerotia that were round or irregular in shape (average 1.55 × 1.02 mm) that is typical of gray mold (1). Koch's postulates were performed by spraying 6-week-old sandpaper sotol plants grown in 12-cm pots with a spore suspension (1 × 106 CFU per ml) obtained from 12-day-old cultures grown on PDA. Eight plants were naturally wounded by scratching leaf blades among themselves and were subsequently inoculated, while eight plants were inoculated without wounding. An equal number of noninoculated plants sprayed with sterile water served as controls. All plants were maintained in high humidity conditions (90 to 95% relative humidity) at 20 ± 2°C. Leaf spots similar to the ones observed in nurseries were evident on all naturally wounded and nonwounded plants within 2 to 3 weeks after inoculation. Noninoculated control plants were symptomless. B. cinerea was reisolated from affected tissues. The pathogen has reduced commercial value of sandpaper sotol plants and may represent a limiting factor for the cultivation of this plant in eastern Sicily. To our knowledge, this is the first report in the world of leaf spot and blight caused by B. cinerea on D. serratifolium.

Reference: (1) M. B. Ellis. Dematiaceous Hyphomycetes. CAB International Mycological Institute, Kew, Surrey, England, 1971.
Infection of Rice Seed Grown in Arkansas by Pyricularia grisea and Transmission to Seedlings in the Field
Authors: Guerber C. , TeBeest D. O.
Published: May 2007

Rice blast, caused by Pyricularia grisea, is an important and serious disease of rice (Oryza sativa) in the southeastern United States. The disease sporadically reaches epidemic proportions on susceptible cultivars within fields and over large areas within Arkansas. The main overwintering sources of inoculum reportedly include infected rice stubble, related host species, and infected seed. The objectives of the research were to (i) determine whether rice seed grown in Arkansas were infected with P. grisea, (ii) investigate the relationship between seed infection and seedling disease, and (iii) determine if planting naturally infected seed could lead to the subsequent development of rice blast on seedlings in the field. The results of seed assays showed that P. grisea was detected in samples of foundation, certified, and production seed. Estimated levels of infection by P. grisea of rice seed from 66 samples of rice seed grown in Arkansas ranged from 0 to 10.5%. Planting infected seed in the greenhouse and the field resulted in seedling infection. Planting naturally infected seed may result in disease development (i) from seedlings grown from infected seed planted beneath the soil surface, (ii) from seedlings grown from germinating seed left on the soil surface, (iii) from seed coats, or (iv) from nongerminated seed left on the soil surface after planting. Additional research is necessary to establish the mechanisms of infection of seedlings and to establish disease thresholds for this important fungal pathogen of rice.
Wettability of Poplar Leaves Influences Dew Formation and Infection by Melampsora larici-populina
Authors: Pinon Jean , Frey Pascal , Husson Claude
Published: May 2007

The wettability of leaves of 60 poplar (Populus spp.) clones from sections Aigeiros (black) and Tacamahaca (balsam) and their hybrids was assessed by measuring the contact angle of calibrated water droplets on their abaxial leaf surface. The frequency and duration of dew on these clones were recorded in two nurseries. Black poplar leaves had the highest wettability, with relatively flat-shaped water droplets and a short drying time, in both the laboratory and nursery. Conversely, round-shaped water droplets on balsam poplars dried more slowly in the laboratory. In the nursery, dew was more frequent and persisted longer. First-generation intersectional hybrids behaved like balsam poplars, but successive backcrosses with black poplar (P. deltoides) resulted in clones with leaves that were more wettable and possessed less frequent and persistent dew. Infection by Melampsora larici-populina on two hybrid clones (‘Robusta’ and ‘Beaupré’), assessed by the number of uredinia in the laboratory, was dependent on the duration of leaf moisture. Maximum infection occurred when water was present on the leaves for 12 h. Leaf wettability should be considered as an additional trait when breeding poplar for durable resistance to M. larici-populina, as this characteristic is likely to be a useful defense against all pathotypes of the pathogen.
Field Application of Dilophospora alopecuri to Manage Annual Ryegrass Toxicity Caused by Rathayibacter toxicus
Authors: Barbetti Martin J. , Riley Ian T.
Published: May 2007

Field experiments were conducted in three consecutive years to determine the effect of Dilophospora alopecuri inoculation on the incidence of galls with Rathayibacter toxicus in annual ryegrass (Lolium rigidum). R. toxicus is carried into the grass by the seed gall nematode, Anguina funesta, and colonizes the ovules, displacing the nematodes, and producing the toxin responsible for annual ryegrass toxicity. Treatments included three types of D. alopecuri inoculum (naturally colonized ryegrass, cultures grown on sterilized wheat grain, and spore suspension) applied at different application rates and times. In the first year, naturally colonized ryegrass (30 kg ha-1), applied 1 week after the break of season, colonized wheat grain (150 kg ha-1) applied once at 1, 4, or 8 weeks or applied three times at 1, 4, and 8 weeks after the break of season, and spore suspension at heading, all significantly reduced the numbers of bacterially colonized galls (by 85 to 96%). In the second and third years, inoculum was applied at various rates and times. There were no significant treatment effects in the second year. In the third year, colonized wheat (450 kg ha-1) reduced the number of bacterially colonized galls by 73% and there was a significant negative relationship between inoculation rate of colonized wheat (5.5 to 450 kg ha-1) and the number of bacterially colonized galls (r = 0.86, P < 0.01). D. alopecuri has potential as a biopesticide for the management of annual ryegrass toxicity, but efficacy could be highly variable depending upon season or site, and uneconomic application rates might be needed.
Regional Development of Orchardgrass Choke and Estimation of Seed Yield Loss
Authors: Pfender W. F. , Alderman S. C.
Published: May 2007

A survey for choke, caused by Epichloë typhina, in orchardgrass seed-production fields in Oregon was conducted annually from 1998 to 2003. In all, 99 fields were inspected, 57 in more than 1 year, to produce a set of 217 observations on disease incidence. There was a significant increase in disease incidence in 38% of the revisited fields, and a significant reduction of incidence in 3%. Yearly increases in disease incidence were as high as 29% in individual fields, but the average yearly increase from 1999 to 2003 was 5 to 8%. In 1998, 60% of all surveyed fields were infested with choke and, by 2003, 90% were infested. Average disease incidence in fields in their first year of production was <2%, and average disease incidence in older fields was approximately 10%, in 2003. Seed yield loss was equal to disease incidence (percentage of tillers diseased), and we found no significant yield compensation in diseased stands. An observed correlation of disease incidence with disease prevalence (proportion of sampled sites infested w ithin a field) may permit simple estimation of incidence and, thus, of potential economic loss in an affected field. We estimate regional loss to the 2004 orchardgrass seed crop due to choke o be approximately $0.8 million.
First Report of Bacterial Leaf Spot of Italian Dandelion (Cichorium intybus) Caused by a Pseudomonas syringae Pathovar in California
Authors: Koike S. T. , Bull C. T.
Published: May 2007

Italian dandelion (Cichorium intybus) is a leafy, nonhead forming chicory plant that is eaten as a fresh vegetable in salads. During the late summer (August through October) of 2002, in the Salinas Valley (Monterey County) in California, a previously unreported disease was found in commercial Italian dandelion fields. Early symptoms were angular, vein delimited, dark, water-soaked leaf spots that measured 2 to 7 mm in diameter. As disease developed, spots retained angular edges but exhibited various irregular shapes. Spots commonly formed along the edges of the leaves; in some cases these spots developed into lesions that measured between 10 and 30 mm long. Spots were visible from adaxial and abaxial sides and were dull black in color. A cream-colored pseudomonad was consistently isolated from leaf spots that were macerated and streaked onto sucrose peptone agar. Fungi were not recovered from any of the spots. Recovered strains were blue-green fluorescent when streaked onto King's medium B agar. Bacterial strains were levan positive, oxidase negative, and arginine dihydrolase negative. Strains did not rot potato slices but induced a hypersensitive reaction on tobacco (Nicotiana tabacum cv. Turk). These data indicated that the bacteria belonged to LOPAT group 1 of Pseudomonas syringae (1). Pathogenicity of six strains was tested by growing inoculum in nutrient broth shake cultures for 48 h, diluting to 106 CFU/ml, and spraying onto 12 6-week-old plants of Italian dandelion cv. Catalogna Special. Untreated control plants were sprayed with sterile nutrient broth. After 10 to 12 days in a greenhouse (24 to 26°C), leaf spots similar to those observed in the field developed on all inoculated plants. Strains were reisolated from the spots and identified as P. syringae. Control plants remained symptomless. These inoculation experiments were done twice and the results were the same. Amplification of repetitive bacterial sequences (repetitive sequence-based polymerase chain reaction [rep-PCR]) demonstrated that all Italian dandelion strains had the same rep-PCR fingerprint, which differed from fingerprints of P. syringae pv. tagetis and P. syringae pv. tabaci. Additionally, toxin specific primers did not amplify tagetitoxin or tabtoxin biosynthesis genes from Italian dandelion strains. To our knowledge, this is the first report of bacterial leaf spot of commercially grown Italian dandelion in California caused by a P. syringae pathovar. Because fields were irrigated with overhead sprinklers, the disease was severe in several fields and as much as 30% of those plantings were not harvested.

Reference: (1) R. A. Lelliott et al. J. Appl. Bacteriol. 29:470, 1966.
Molecular Characterization of Pepper yellow leaf curl Indonesia virus in Leaf Curl and Yellowing Diseased Tomato and Pepper in Indonesia
Authors: Tsai W. S. , Shih S. L. , Green S. K. , Rauf A. , Hidayat S. H. , Jan F.-J.
Published: May 2007

Yellowing and leaf curl symptoms were observed in tomato and pepper fields near Bogor, Java, Indonesia in 2000. Samples were collected from one diseased tomato (Lycopersicum esculentum) and three diseased chili pepper (Capsicum annuum) plants. Viral DNA was extracted (2) and tested for the presence of geminiviral DNA-A, DNA-B, and associated satellite DNA using polymerase chain reaction (PCR) with previously described primers (1,3,4). The begomovirus DNA-A general primer pair PAL1v1978/PAR1c715 amplified the predicted 1.4-kb DNA fragment from the tomato and two of the chili samples. DNA-B and satellite DNA were not detected using PCR with DNA-B general primer pairs (DNABLC1/DNABLV2 and DNABLC2/DNABLV2) and satellite detection primer pair (Beta01/Beta02). The amplicons from the tomato and from one of the chili samples were cloned and sequenced. On the basis of the 1.4-kb DNA sequences, specific primers were designed to complete the DNA-A sequences. Following sequence assembly, the full-length DNA-A nucleotide sequences were determined as 2,744 nt (GenBank Accession No. DQ083765) for the tomato- and 2,743 nt (GenBank Accession No. DQ083764) for the chili-infecting begomoviruses. Sequence comparisons and analyses were conducted using the DNAMAN sequence analysis software (Lynnon Corporation, Quebec, Canada). The DNA-A of both begomoviruses contained six open reading frames, including two in the virus sense and four in the complementary sense, and the geminivirus conserved nanosequence-TAATATTAC in the loop of the hairpin structure of the intergenic region. Because of their high nucleotide sequence identities of 99%, the tomato- and chili-infecting begomovirus are considered the same virus. When compared by using BLAST with available gem-iniviral sequences in the GenBank database, the DNA-A sequences of the tomato and the chili isolates showed highest nucleotide sequence identity (95%) with the partially sequenced Pepper yellow leaf curl Indonesia virus (GenBank Accession No. AB189849) in the 1,842 nt to 660 nt region and in the 1,841 nt to 659 nt region, respectively. Comparisons with full-length DNA-A sequences of begomoviruses available in the GenBank database indicated high sequence identities of 76 and 77% for the tomato and chili isolates, respectively, with an eggplant isolate of Tomato yellow leaf curl Kanchanaburi virus (GenBank Accession No. AF511530) from Thailand. According to our knowledge, this is the first report of full-length DNA-A sequence of the Pepper yellow leaf curl Indonesia virus and its natural occurrence in tomato and pepper in the Bogor area of Indonesia.

References: (1) R. W. Briddon et al. Virology 312:106, 2003. (2) R. L. Gilbertson et al. J. Gen. Virol. 72:2843, 1991. (3) S. K. Green et al. Plant Dis. 85:1286, 2001. (4) M. R. Rojas et al. Plant Dis. 77:340, 1993.
A New Phytoplasma Infecting Lettuce in Iran
Authors: Salehi M. , Izadpanah K. , Nejat N.
Published: May 2007

Lettuce phyllody (LP) is an economically important disease of romaine lettuce (Lactuca sativa) in vegetative crop and seed crop fields in the Fars Province of Iran. Wild lettuce phyllody (WLP) occurs also in epidemic proportions in wild lettuce (L. serriola) during the fall in Iranian central and southern provinces, especially in Fars. Among various leafhopper species tested, Neoaliturus fenestratus successfully transmitted agents of LP and WLP to lettuce, wild lettuce, periwinkle, and sowthistle directly after field collection or after 5 to 7 days of feeding on diseased source plants. With primer pair P1/P7 in polymerase chain reaction (PCR), target DNA fragments (1.8 kbp) were amplified from total nucleic acid samples extracted from diseased lettuce and wild lettuce plants, but not from healthy counterparts. On the basis of disease symptoms, leafhopper transmission, and positive reaction in phytoplasma-specific PCR, Iranian lettuce and wild lettuce phyllodies agents have phytoplasmal etiology. Phylogenetic and putative restriction site analysis of 16S/23S rDNA spacer region (SR) indicated that LP and WLP phytoplasmas are members of pigeon pea witches'-broom (16SrIX) group and are closely related. Reciprocal transmission of LP phytoplasma to wild lettuce and WLP phytoplasma to lettuce by the same leafhopper species and induction of similar symptoms in common hosts are other evidences that agents of LP and WLP may be related or identical phytoplasmas. This is the first report of lettuce as a new host in pigeon pea witches'-broom group and N. fenestratus as a vector of a pigeon pea witches'-broom group phytoplasma. In other countries, phytoplasmas of aster yellows group (16SrI) are commonly associated with phytoplasmal lettuce diseases (2) and Macrosteles quadrilineatus leafhopper is reported as the vector (1). Relatedness of WLP phytoplasma to 16SrIX group was previously reported (3). On the basis of the results of this study, wild lettuce and sowthistle are two reservoirs of LP phytoplasma.

References: (1) D. Errampalli et al. Phytopathology 76:1084, 1986. (2) I.-M. Lee et al. Ann. Rev. Microbiol. 54:221, 2000. (3) E. Verdin et al. Int. J. Syst. Bacteriol. Evol. Microbiol. 53:833, 2003.
First Report of 16S rDNA II Group Phytoplasma on Polygala mascatense, a Weed in Oman
Authors: Livingston S. , Al-Azri M. O. , Al-Saady N. A. , Al-Subhi A. M. , Khan A. J.
Published: May 2007

Polygala mascatense Boiss. (family Polygalaceae) is a common weed found in neglected farms, under date palm trees, and in stony locations throughout the Sultanate of Oman (1). It is a perennial herb approximately 30 to 40 cm tall, has slender branches, is woody at the base, and has linear leaves with purple flowers. Recently (November 2004), in the interior region of Oman (210 km south of Muscat), some polygala plants were found stunted with small leaves, bushy growth, and the floral parts were showing phyllody symptoms. Total genomic DNA extracted from asymptomatic and symptomatic plants with modified cetyltrimethylammoniumbromide (CTAB) buffer method (4) was used as a template for direct polymerase chain reaction (PCR) amplification of phytoplasma 16S rDNA with P1/P7 primers. Direct PCR product was used as template DNA for nested PCR with primers R16F2n/R16R2. DNA from plants infected with alfalfa and lime witches'-broom phytoplasma was used as positive controls, and DNA from healthy plants and water was used as negative controls. Products from nested PCR (1.2 kb) were analyzed by using single endonuclease enzyme digestion (restriction fragment length polymorphism [RFLP]) with Tru9I, HaeIII, HhaI, TaqI, AluI, and RsaI (3). The results showed the presence of a 1.8-kb product amplified with direct PCR and a 1.2-kb product of the nested PCR from infected polygala and the positive controls, whereas no PCR products were observed in the negative controls. The PCR assay confirmed the presence of phytoplasma causing witches'-broom disease in polygala. The RFLP results showed the polygala phyto-plasma to be most similar to the alfalfa phytoplasma, a member of 16SrII group (2). Infected polygala weeds may serve as a reservoir for alfalfa witches'-broom phytoplasma that causes annual losses over $25 million to alfalfa cultivation in Oman (2). A detailed investigation needs to be carried out to establish transmission of phytoplasma from polygala to alfalfa. To our knowledge, this is the first report of phytoplasma infecting polygala weeds in Oman.

References: (1) S. A. Ghazanfar. Pages 95–96 in: An Annotated Catalogue of the Vascular Plants in Oman. Scripta Botanica Belgica Meise, National Botanic Garden of Belgium, 1992. (2) A. J. Khan et al. Phytopathology 92:1038, 2002. (3) I. M. Lee et al. Int. J. Syst. Bacteriol. 1153, 1998. (4) M. A. Saghai-Maroof et al. Proc. Natl. Acad. Sci. USA 81:8014, 1984.
Fieberiella florii (Homoptera: Auchenorrhyncha) as a Vector of “Candidatus Phytoplasma mali”
Authors: Tedeschi Rosemarie , Alma Alberto
Published: May 2007

Laboratory trials were carried out to transmit “Candidatus Phytoplasma mali” to healthy apple seedlings with the leafhopper Fieberiella florii. Experiments on serial inoculation access period and molecular analyses performed on test plants and insects confirmed the ability of the leaf-hopper to carry and transmit the phytoplasma. Field surveys by means of yellow sticky traps were conducted in northwestern Italy to verify the abundance and the natural infectivity of F. florii in apple orchards and in wild vegetation in areas surrounding apple orchards. Despite the high percentages of infected specimens obtained in the apple orchards (5.7%) and in the wild vegetation areas (20.0%), the risk of apple tree infection by F. florii in nature is probably low because of the very low insect density recorded. In spite of the low number of specimens collected, the presence of the leafhopper in apple orchards in summer, when the main vector, the psyllid Cacopsylla melanoneura, feeds on alternative hosts, is meaningful. Moreover, the high degree of polyphagy of the leafhopper opens up new interesting prospects for the epidemiology of apple proliferation.
Factors Affecting Infection of Yellow Starthistle (Centaurea solstitialis) by Synchytrium solstitiale, Causal Agent of False Rust Disease
Authors: Widmer T. L. , Guermache F.
Published: May 2007

Yellow starthistle (Centaurea solstitialis) is an annual invasive weed in the United States with Mediterranean origins. The expense of chemical control and the vast area of invasion make this weed an appropriate target for classical biological control. Observations of a field site in southern France revealed small orange galls on the leaves of yellow starthistle seedlings caused by the fungus Synchytrium solstitiale. Inoculation of yellow starthistle seedlings with a suspension of zoospores released from infected tissue resulted in infection. Ten days after inoculation, typical orange galls appeared on the exposed tissue. Preliminary host range testing showed up to 100% infection of C. solstitialis seedlings from both France and the United States and infection of Carthamus tinctorius, Centaurea americana, C. diffusa, C. rothrockii, C. squarrosa, and Helianthus annuus seedlings. No symptoms were observed on seedlings of Centaurea calcitrapa, C. maculosa, C. sulfurea, Cirsium californica, C. occidentale, Cynera cardunculus, and Taraxacum officinale. Zoospores were released in a pH range between 4.45 and 8.25 and optimally at temperatures between 5 and 15°C. Infection of yellow starthistle seedlings occurred after a minimum 1-h exposure to a zoospore suspension at 20°C.
Discovery of the Canker Pathogen Chrysoporthe austroafricana on Native Syzygium spp. in South Africa
Authors: Heath R. N. , Gryzenhout M. , Roux J. , Wingfield M. J.
Published: May 2007

Chrysoporthe canker is one of the most important diseases of plantation-grown Eucalyptus spp. in tropical and subtropical regions worldwide. For many years, the disease was reported to be caused by the fungal pathogen Cryphonectria cubensis. Recent DNA-based studies have shown that the fungus in South Africa is not conspecific with Chr. cubensis and it was recently described in the new genus Chrysoporthe as Chrysoporthe austroafricana. Chr. austroafricana is known only from South Africa, where it causes severe cankers on Eucalyptus spp. and on ornamental Tibouchina trees, both of which have been introduced into South Africa. The origin of Chr. austroafricana is unknown, but it is possible that it expanded its host range from native trees related to Eucalyptus and Tibouchina spp. to these exotic hosts. Subsequent surveys of some indigenous South African Myrtales led to the discovery of fruiting structures resembling those of Chr. austroafricana on native Syzygium cordatum and S. guineense. The fungus from these Syzygium spp. was identified as Chr. austroafricana based on morphological characteristics and β-tubulin gene sequences. Pathogenicity trials showed that Chr. austroafricana is more virulent on exotic Eucalyptus spp. than on native S. cordatum. This study represents the first report of Chr. austroafricana from native hosts in South Africa and adds credence to the view that the fungus could be native to this country.
Development and Evaluation of PCR-Based Diagnostic Assays for the Bacterial Speck and Bacterial Spot Pathogens of Tomato
Authors: Cuppels Diane A. , Louws Frank J. , Ainsworth Teresa
Published: May 2007

Bacterial speck and bacterial spot lesions can easily be confused with each other and with those formed by other tomato pathogens. To facilitate disease diagnosis, we developed and evaluated polymerase chain reaction (PCR)-based lesion assays using crude DNA extracts and primer sets COR1/2 (bacterial speck) and BSX1/2 (bacterial spot). All 29 pathogenic Pseudomonas syringae pv. tomato strains tested produced a 689-bp amplicon with COR1/2; 28 of the 37 geographically diverse bacterial spot-causing xanthomonad (BSX) strains that were tested generated the 579-bp BSX1/2 amplicon. The detection limit with plant samples was 30 to 50 CFU/reaction. In a 6-year study, the COR1/2 PCR assay diverged from the culture-based classical assay for only 3 of 70 bacterial speck lesion samples collected from Ontario greenhouses and tomato fields; the BSX1/2 assay was positive for 112 of the 124 confirmed bacterial spot lesions sampled. The majority (66%) of the BSX strains isolated from these lesions belonged to group D; the 12 strains that were BSX1/2-negative belonged to group C. Group D strains produced a 425-bp PCR product with crude DNA extracts but a 579-bp product with purified DNA; the former was identical to the latter except that it was missing 150 bp from the middle of the 579-bp sequence.
First Report of Globodera tabacum Infecting Tobacco Plants in Quebec, Canada
Authors: Bélair G. , Miller S.
Published: May 2007

The tobacco cyst nematode Globodera tabacum (Lownsbery & Lowns-bery) Behrens is a damaging soilborne pathogen of shade and broadleaf tobacco in the United States (2). Nematode infection of roots can cause dramatic stunting, yield loss, and reduce leaf quality. G. tabacum is considered a complex of three cyst nematodes not distinguishable morphologically including G. tabacum tabacum, G. tabacum virginiae, and G. tabacum solanacearum. During 1998, infested flue-cured tobacco plants were harvested in the Lanaudière Region near Montreal, Quebec. Cysts recovered from roots and soil were identified by morphological and morphometric analysis of mature cysts and unhatched juveniles. Although multiple interceptions on nursery stock entering Quebec from infested nurseries in Hartford County, Connecticut from 1974 to 1986 have been recorded (1), to our knowledge, this is the first record of G. tabacum established in Canadian soil. On the basis of historic nematode infestations in this county, it could be inferred that it was G. tabacum tabacum, but further analysis is necessary for definitive subspecies determination. The infested tobacco plants were stunted in the field when compared with noninfested plants. Recently, the production in that area has been abandoned. Because cysts may survive for years in absence of host and also because potato, also a host of G. tabacum, is being introduced on these tobacco farms, it is believed that the distribution of this nematode could expand in the future in this part of the country.

References: (1) Agriculture Canada Canadian Plant Quarantine Annual Reports. Intercepted Plant Pests. Publisher (Ottawa): Plant Protection Division, Department of Agriculture, 1967-2000. (2) J. G. Baldwin and M. Mundo-Ocampo. Heteroderinae, cyst- and non-cyst forming nematodes. Page 275 in: Manual of Agricultural Nematology. W. R. Nickle ed. Marcel Dekker Inc., New York, 1991.