bluuebunny/crossref_metadata_2025 huggingface dataset:
Bacterial Canker Caused by Clavibacter michiganensis subsp. michiganensis on Tomato in the Baja California Peninsula of Mexico
Authors: Holguín-Peña R. J. , Vázquez-Juárez R. C. , Rueda-Puente E. O.
Published: May 2007

During the 2005 tomato-growing (Lycopersicon esculentum Mill.) season, an apparent bacterial disease with cankers on the stems and bird's eye lesions on the fruit appeared in commercial fields and greenhouses in the San Quintin and San Simon areas (a 60-mile long coastal plain) near the central region of the Baja California Peninsula of Mexico. The disease was found in midseason, especially when plants were flowering, and the mature and ripe stage. Incidence ranged from 4 to 46%, which represented an important loss in field and greenhouse production. Symptomatic plants showed reddish brown cavities in the stem, discoloration, and water soaking of vascular tissue. Diseased tissues were washed with phosphate buffer and placed on semiselective Clavibacter medium (SCM) (1), and a gram-positive, nonmotile, nonspore-forming, aerobic, curved rod bacterium was consistently isolated and morphologically characterized. Twenty-eight isolates were identified as Clavibacter michiganensis subsp. michiganensis by polymerase chain reaction (PCR) technology with primers CMM5/CMM6 to amplify a fragment of approximately 6.2 kb (2). The isolates were also identified by REP-PCR (repetitive extragenic palindromic PCR) genomic fingerprinting techniques (3) with REP and BOX primer sets (4). Pathogenicity tests consisting of three replicates of 4-week-old tomato seedlings (cv. Tequila) were performed by spraying (twice, 2 days apart) inocula at 108 CFU/ml. Control seedlings were sprayed with sterile water. Inoculated plants previously covered in polyethylene bags were incubated in a growth chamber at 25°C for 48 h. Within 3 weeks, symptoms of reddish-brown cavities, water-soaked lesions, and asymmetrical wilting appeared on inoculated plants and were similar to those symptoms observed in the field. No symptoms were observed on control plants. Confirmation of the causal agent was done by culturing the bacteria on SCM and PCR analysis. Occurrence of the disease in San Quintin Valley is relevant because the disease is one of the five most serious tomato diseases in the peninsula. Moreover, the potential spread of the pathogen by tomato seedlings represents a permanent risk to other pathogen-free areas in the peninsula. Although bacterial canker has been observed in Baja California (Punta Colonet, Vicente Guerrero, San Quintin, and San Simon), to our knowledge, this is the first confirmation of C. michiganensis subsp. michiganensis in Baja, Mexico.

References: (1). C. Alarcon et al. Phytopathology 88:306, 1998. (2) J. Dreier et al. Phytopathology 85:462, 1995. (3) F. J. Louws et al. Phytopathology 88:862, 1998. (4) J. Versalovic et al. Methods Mol. Cell. Biol. 5:25, 1994.
First Report of the Quarantine Brown Rot Pathogen Monilinia fructicola on Imported Stone Fruits in Switzerland
Authors: Bosshard E. , Hilber-Bodmer M. , Schärer H.-J. , Bünter M. , Duffy B.
Published: May 2007

Monilinia fructicola, causal agent of fruit brown rot, is a quarantine pathogen in Europe (1). It presents a significant threat because of its aggressivity on flowers, shoots, and wood at low temperatures and propensity for sexual reproduction that increases potential for evolutionarily adaptation to new environments, hosts, and fungicides. It is common in North America, Japan, Australia, and South America. It occurs in orchards in France, has been detected but eradicated from Austria and Spain, and has been found on imported peach in Hungary (1,2). In Switzerland, we recently detected M. fructicola in supermarkets on imported fruit with brown rot symptoms similar to those caused by endemic M. fructigena and M. laxa. Preliminary identification was based on distinctive colony and conidial morphology on potato dextrose agar of fruit isolates. Specific identification was determined by polymerase chain reaction (PCR) (3) and sequencing the internal transcribed spacer (ITS) region. Koch's postulates were fulfilled by reproducing brown rot on healthy inoculated fruit. Surveys of imported fruit in markets (n = 42) using PCR revealed M. fructicola on all imported apricot and nectarine from the United States and France, but none on apricot, peach, plum, and cherry from Spain, France, Italy, or Turkey. Field surveys of apricot, peach, plum, prune, nectarine, and cherry orchards in 13 Swiss cantons were all negative (n = 71 in 2003 and 164 in 2005). This report demonstrates that imported fruit is a weak link in quarantine efforts and poses a potential threat. Transmission to local trees via highly dispersible, profuse spores from recycled packaging and disposal sites for discarded fruit has thus far not occurred but the risk deserves attention. Revised regulations for fruit treatment at points of entry and/or scrutiny of origin orchards may be warranted.

References: (1) OEPP/EPPO. List of A2 pests regulated as quarantine pests in the EPPO region. Version 2005-09. Online publication with distribution map at http://www.eppo.org , 2005. (2) M. Petróczy and L. Palkovics. Plant Dis. 90:375, 2006. (3) K. J. D. Hughes et al. EPPO Bull. 30:507, 2000.
Incidence and Significance of Iprodione-Insensitive Isolates of Botrytis squamosa
Authors: Carisse O. , Tremblay D. M.
Published: May 2007

Botrytis leaf blight, caused by Botrytis squamosa, is an economically important disease of onion. The principal means of controlling the disease is by applying fungicides. Typical fungicide programs include applications of dithiocarbamates, chloronitriles, carboxamides, and dicarboximides such as iprodione (Rovral). Onion fields were surveyed in 2002, 2003, and 2004 for insensitivity to iprodione. Tests for insensitivity to iprodione were conducted on 62, 58, and 60 monoconidial field isolates using the automated quantitative (AQ) method with a discriminatory dose of 1.78 ppm of iprodione active ingredient (a.i.) in 2002, 2003, and 2004, respectively. Overall, insensitive isolates were detected in 51% of the fields, and the proportions of insensitive isolates were 8.1, 20.7, and 18.3% in 2002, 2003, and 2004, respectively. The aggressiveness of 10 insensitive and 18 sensitive isolates and the efficacy of iprodione was tested in planta. Onion leaves were inoculated with 750 μl of a conidial suspension of 75,000 conidia per ml and incubated in a growth chamber at 15°C. Aggressiveness was measured as lesion density (average number of lesions per cm2 of onion leaf). Lesion density varied from 2.82 to 8.04 lesions per cm2 of leaf. There was a significant effect (P < 0.0001) of isolates on lesion density. However, there was no significant correlation between lesion density and sensitivity to iprodione (r = 0.08). When onion leaves were sprayed with 1,875, 3,750, and 7,500 ppm of iprodione, percent inhibition of lesion density was higher for sensitive isolates with means of 43.04, 61.42, and 74.59, respectively. Accordingly, percent inhibition was lower for insensitive isolates with means of 13.81, 28.26, and 44.37 for iprodione concentrations of 1,875, 3,750, and 7,500, respectively. It was concluded that the incidence of insensitive isolates was relatively low, but insensitive isolates were capable of infecting onion leaves. There was a good relationship between insensitivity to iprodione in B. squamosa populations measured in vitro with the AQ method, and the reduced efficacy of iprodione in controlling Botrytis leaf blight.
An IPM Program for Managing Fungal Leaf Blight Diseases of Carrot in New York
Authors: Gugino B. K. , Carroll J. E. , Widmer T. L. , Chen P. , Abawi G. S.
Published: May 2007

Fungal leaf blight diseases caused by Cercospora carotae and Alternaria dauci occur annually on processing carrot in New York, with growers applying up to eight fungicide sprays to manage these diseases. An integrated pest management (IPM) program involving the use of a 25% disease incidence threshold to prompt the first fungicide application and timing subsequent sprays by monitoring for increases in disease severity and weather forecasts in conjunction with a 10- to 14-day spray interval was evaluated in grower fields in 1997 and 1998. The IPM plots, compared with the grower plots, required two to six fewer fungicide applications but showed no yield reduction. From 1999 to 2004, the IPM program was validated and the effect of crop rotation and carrot cultivar susceptibility also were assessed. Carrot plants growing in fields with 2-year or longer crop rotation intervals reached the 25% disease incidence threshold later in the season and required fewer fungicide applications. The less-susceptible carrot cultivars also reached the 25% disease incidence threshold later, required fewer fungicide applications, and were less severely diseased than more susceptible cultivars. Validation of the IPM program in New York showed that both fungal leaf blights can be managed effectively using a 25% incidence threshold to prompt the first fungicide spray and making the subsequent fungicide applications based on increases in disease severity, weather forecasts, and a 10- to 14-day spray interval.
First Report of Leaf Rust by Puccinia triticina on Wheat in Oman
Authors: Deadman M. L. , Al Sa'di A. , Al Maqbali Y. , Aime M. C.
Published: May 2007

Wheat (Triticum aestivum L.), cultivated for forage and grain production, is an important crop in the Sultanate of Oman. In April 2005, leaf samples of an unknown local variety showing rust symptoms were collected from Rustaq, 100 km southwest of Muscat. Circular-to-oval, red-brown pustules, typical of uredinia, occurred mostly on the upper surface of leaves on plants nearing maturity. Telia with teliospores were observed on leaf sheaths. The disease was widespread in many fields and was likely to be limiting the yield. Urediniospores typical of Puccinia triticina Erikss. (=P. recondita Rob. ex Desm. f. sp. tritici) were roughly subglobose, measuring 18 to 28 × 20 to 25 μm, echinulate, with 3 to 8 scattered germ pores; teliospores were 2-celled, 34 to 50 × 15 to 17 μm, apex is chestnut brown, lower cell is light yellow, no germ pores (1,2). Pathogen identity was confirmed by nuclear ribosomal large subunit and internal transcribed spacer region-2 DNA analysis (voucher sequence deposited in GenBank, Accession No. DQ664194, voucher specimens deposited in the U.S. National Fungus Collections, BPI 872158 and 872159). Wheat is grown during the winter months in Oman and harvested in May. Although the disease was observed again in 2006, pathogen survival mechanisms are not presently clear, and current research is attempting to confirm its presence on alternate hosts, including grass weeds, and determine the distribution of the pathogen on local wheat land races and imported varieties. To our knowledge, this is the first documented report of P. triticina on wheat in Oman.

Reference: (1) D. B. O. Savile. Fungi Can. 309:1, 1986. (2) M V Wiese. Compendium of Wheat Diseases. The American Phytopathological Society, St Paul, MN, 1987.
Maturation of Thyriothecia of Schizothyrium pomi on the Reservoir Host Rubus allegheniensis
Authors: Cooley Daniel R. , Lerner Susan M. , Tuttle Arthur F.
Published: May 2007

Flyspeck disease caused by the Ascomycete fungus Schizothyrium pomi is a major component of a summer disease complex that has become an increasing problem on apple in the northeastern United States. This study describes the development of thyriothecia of S. pomi on one of its major reservoir hosts, wild blackberry, and suggests that temperature drives thyriothecium maturation. An empirical model relating thyriothecium maturity to degree-days from apple leaf budbreak in Massachusetts had a high coefficient of determination, R2 = 0.90. Ninety percent of thyriothecia matured between 540 and 1,625 degree-days from the budbreak biofix. S. pomi produced one generation of asci per year on blackberry. This discrete maturation period occurred well before signs of disease developed on apple fruit and before production of conidia. Considering that fungicide applications for scab management in commercial apple orchards also will protect fruit from flyspeck during early fruit development, it is unlikely that ascospores produced on reservoir hosts directly infect fruit. Instead, they probably initiate infections in reservoir hosts adjacent to commercial orchards, which produce conidia that are the inoculum which infects apple fruit in commercial production.
The Relative Influence of Diseases and Other Small-Scale Disturbances on Fuel Loading in the Black Hills
Authors: Lundquist J. E.
Published: May 2007

Disturbances that kill trees in forests often co-occur in time and/or space. This process results in changes in the fuel loading for wildfire. Determining specific causes of changing fuel loads can be complex. Path analysis was used to estimate the relative importance and the strength of interaction of each of nine small-scale disturbances affecting forest stands in the Black Hills. Different disturbances were partitioned according to their indirect and direct effects on fuel loads. Fire and wind had the greatest indirect effects; stem rots had the smallest. Root rots had the largest direct effects. Root rots, strong wind, stem rots, suppression, human disturbances, and tree cutting all caused fuel loads to increase. Treeless meadows, stem cankers, fire, ice/snow damage, failed regeneration, and shallow soil were associated with decreasing fuel loads. Grazing, lightning, bark beetles, and competition had null impacts. Disease control has two aims: reducing fire hazard and enhancing restoration. Understanding the biology and ecology of the agents that create dead wood is as fundamental to restoration ecology as it is to forest pathology. Management and control both begin by first determining the cause.
Genetic Analysis of Pyricularia grisea Population by rep-PCR During Development of Resistance to Scytalone Dehydratase Inhibitors of Melanin Biosynthesis
Authors: Suzuki Fumihiko , Arai Michiyoshi , Yamaguchi Junichiro
Published: May 2007

In 2001, field isolates of Pyricularia grisea resistant to scytalone dehydratase inhibitors of melanin biosynthesis (MBI-D) were reported in Saga prefecture, Kyushu. Among 1,175 isolates collected from six prefectures of Kyushu in 2002 and 2003, 647 were resistant to MBI-D fungicides, each due to a single point mutation of the scytalone dehydratase (SDH) gene. On the basis of repetitive element-based polymerase chain reaction (rep-PCR) fingerprint data, the haplotypes of the resistant isolates showed high genetic diversity, indicating that the resistance existed in a multigenetic background. Three predominant haplotypes mainly contributed to the widespread resistance in Kyushu; haplotype Sa4 was observed frequently in Saga, Sa18 was predominant in Oita and Miyazaki, and Sa5 was widely distributed among all four prefectures. Also, phylogenetic analysis showed that both the resistant and sensitive isolates were clustered together in a closely related group. These results suggest that isolates possessing the SDH mutation would have been selected and then multiplied rapidly in each region of Kyushu as a result of the widespread introduction of MBI-D fungicides in a short period.
First Report of Witches'-Broom Disease in a Cannabis spp. in China and Its Association with a Phytoplasma of Elm Yellows Group (16SrV)
Authors: Zhao Y. , Sun Q. , Davis R. E. , Lee I.-M. , Liu Q.
Published: May 2007

Hemp fiber plants (Cannabis spp.) spread naturally in almost every climate zone in China and have a long history of cultivation in the country (1). While hemp stalks provide high-quality fibers for making ropes, clothes, and paper products, hemp seeds are a rich source of edible oil. During the summer of 2004, a disease characterized by witches'-broom symptoms was observed in wild hemp fiber plants growing in suburban Taian, Shandong, China. The diseased plants developed clusters of highly proliferating branches with much shortened internodes and leaves on the affected branches were significantly reduced in size. Phytoplasma infection was suspected in this hemp fiber witches'-broom (HFWB) disease because of the typical symptoms and because of its geographic location where other phytoplasmal diseases such as jujube witches'-broom (JWB), paulownia witches'-broom (PaWB), paper mulberry witches'-broom (PMWB), and Chinese wingnut witches'-broom (CWWB) diseases were previously reported (3,4). Total DNA was extracted from leaves of four diseased and four nearby healthy looking hemp fiber plants. Nested PCR were carried out on the DNA samples using phytoplasma universal 16S rDNA primers (P1A/16S-SR and R16F2n/R16R2) (2). Results revealed that all examined diseased plants were infected by phytoplasma, whereas nearby healthy looking plants were phytoplasma free. Subsequent restriction fragment length polymorphism (RFLP) analysis of the PCR-amplified 1.25-kb 16S rDNA R16F2n/R16R2 fragment indicated that the phytoplasma associated with HFWB disease belongs to subgroup 16SrV-B of the elm yellows (EY) phytoplasma group. Nucleotide sequence analysis of the cloned HFWB phytoplasma partial rRNA operon (GenBank Accession No. EF029092), spanning a near full-length 16S rRNA gene and a partial 16S-23S rRNA intergenic spacer, suggested that HFWB phytoplasma is most closely related to JWB and PMWB phytoplasmas, both members of subgroup16SrV-B. To further characterize the HFWB phytoplasma, a genomic segment covering full-length ribosomal protein genes rplV and rpsC was PCR-amplified using primer pair rp(V)F1A/rp(V)R1A (2), cloned, and sequenced (GenBank Accession No. EF029093). The nucleotide sequence of the HFWB phytoplasma rplV and rpsC locus is nearly identical (99.9%) to that of JWB phytoplasma. To our knowledge, this is the first report of a phytoplasmal disease in Cannabis spp. Since HFWB and JWB phytoplasmas share extremely high sequence identity and share the same eco-geographic location, further investigation is warranted to determine whether these two phytoplasmas are actually one species that can infect both plants, an issue having important implications in managing both diseases.

References: (1) S. Hong and R. C. Clarke. J. Int. Hemp Assoc. 3:55, 1996. (2) I. M. Lee et al. Int. J. Syst. Evol. Microbiol. 54:337, 2004. (3) Q. Liu et al. Plant Dis. 88:770, 2004. (4) Q. Liu et al. Plant Dis. 89:529, 2005.
Resistance in Annual Medicago spp. to Phoma medicaginis and Leptosphaerulina trifolii and Its Relationship to Induced Production of a Phytoestrogen
Authors: Barbetti Martin J.
Published: May 2007

Foliar and stem diseases of annual Medicago spp. caused by Phoma medicaginis and Leptosphaerulina trifolii can not only reduce yield, but also affect herbage quality by inducing the production of the phytoestrogen coumestrol. To determine differences in host reaction to these pathogens, 33 cultivars and lines in 1993 and 10 cultivars in 1995 were evaluated in inoculated field tests. In the 1993 test, a number of genotypes with high levels of resistance to leaf and stem disease caused by P. medicaginis and to leaf disease caused by L. trifolii were identified. Genotypes with very high levels of resistance to stem disease caused by P. medicaginis were M. sphaerocarpos GRC5659.4.1 and SAD10069, M. murex GRC87.1, GRC707, and GRC708, M. truncatula Z771, and M. solerolii DZA3180.1, all of which had stem disease scores of ≤1.0 (scale 0 to 10) by the end of the growing season. The levels of coumestrol produced ranged from 114 to 1,230 ppm dry weight in stems across the genotypes, and the score for stem disease caused by P. medicaginis in the corresponding cultivars ranged from ≤0.8 to 8.9, respectively. The 1995 test confirmed the relative responses of nine cultivars (Caliph, Circle Valley, Cyprus, Harbinger AR, Zodiac, Paraggio, Santiago, Serena, and Orion) of annual Medicago spp. to leaf and stem disease caused by P. medicaginis and to stem disease caused by L. trifolii. Those with the lowest levels of coumestrol in the stems were M. solerolii DZA3180.1, M. truncatula Paraggio, and M. sphaerocarpos SAD10069, all with levels ≤130 ppm. The highest level was found in M. polymorpha SA4178 (1,230 ppm). M. littoralis Harbinger AR, Z286, Z298, and Z912, M. murex 89F16.1.1, M. orbicularis SA8460, and M. polymorpha SA4188, all had coumestrol levels of >600 ppm. For stem disease caused by P. medicaginis in particular, there was significant correlation of the level of disease with the level of coumestrol in stems at the end of the growing season. In contrast, for L. trifolii, there was significant negative correlation (leaf disease) or only a weak positive correlation (stem disease) with coumestrol in stems at the end of the growing season. Incorporation of these identified disease resistances into commercial cultivars offers a promising avenue not only as a long-term strategy for management of foliar diseases in annual Medicago spp., but also as a means of reducing phytoestrogen levels in commercial annual Medicago spp. pastures in order to minimize the adverse effects of phytoestrogens on fertility levels in sheep.
Detection and Identification of a Group 16SrIII-Related Phytoplasma Associated with Coffee Crispiness Disease in Colombia
Authors: Galvis Carlos A. , Leguizamón Jairo E. , Gaitán Álvaro L. , Mejía Juan F. , Álvarez Elizabeth , Arroyave José
Published: May 2007

Coffee crispiness (“crespera”), a disease of uncertain etiology, has been endemic in coffee (Coffea arabica L.) plantations in Colombia for at least 60 years. Symptoms typically consist of bud proliferation, abundant short and narrow leaves, phyllody, floral abortion, monospermic fruit, and dwarfing of plants. In severe cases, coffee crispiness disease (CCD) can affect production significantly. In this study, association of a phytoplasma with CCD was indicated by the accumulation of Diene's stain, or 4′, 6-diamidino-2-phenylindole fluorescence, only in phloem of affected plant tissues. The presence of polymorphic phytoplasma cells in phloem sieve tube elements was confirmed by transmission electron microscopy. The disease was transmitted successfully by grafting symptomatic shoots from CCD-affected C. arabica plants onto young, healthy rootstocks; however, symptoms failed to develop after mechanical inoculation of young plants with extracts derived from diseased plant tissues. A nested polymerase chain reaction (PCR) assay employing primer pairs P1/P7 followed by FU5/rU3 amplified a 16S ribosomal DNA product (941 bp) exclusively from DNA of diseased plants. Sequence and phylogenetic analysis of the nested PCR product identified the CCD phytoplasma as a new strain member of group 16SrIII (X-disease group). This is the first report of a phytoplasma infecting coffee plants.
Variation in Infection Capacity and in Virulence Exists Between Genotypes ofSugarcane yellow leaf virus
Authors: Ahmad Youssef Abu , Costet Laurent , Daugrois Jean-Heinrich , Nibouche Samuel , Letourmy Philippe , Girard Jean-Claude , Rott Philippe
Published: May 2007

Two experiments, one in Guadeloupe and one in Réunion Island, were performed to transmit different genotypes of Sugarcane yellow leaf virus (SCYLV) to eight sugarcane cultivars differing in resistance to infection by the virus and to yellow leaf. Transmission was attempted from SCYLV-infected sugarcane plants or leaves to healthy tissue-cultured plantlets grown in vitro and with the aphid vector Melanaphis sacchari. After inoculation and elimination of insects with an insecticide, plantlets were transferred to Montpellier, France and grown in a greenhouse. Plants were tested for presence of SCYLV by tissue-blot immunoassay and reverse-transcription polymerase chain reaction after 5 to 6 months of growth. SCYLV genotypes BRA-PER, CUB, and REU were detected in 47, 62, and 39% of plants inoculated with these genotypes in Guadeloupe, respectively. SCYLV genotypes BRA-PER and REU and a mixed infection of genotypes BRA-PER and REU were detected in 56, 33, and 42% of plants inoculated with these genotypes in Réunion Island, respectively. Genotypes BRA-PER and CUB could be transmitted to all eight sugarcane cultivars, but genotype REU could never be transmitted to resistant sugarcane cvs. H78-4153 and H78-3567. SCYLV genotype REU was transmitted successfully to sugarcane cv. R570 in Guadeloupe, but not in Réunion Island. Genotypes BRA-PER and CUB induced yellow leaf symptoms in susceptible or highly susceptible sugarcane cultivars, whereas genotype REU induced very few symptoms. SCYLV was not found in several symptomatic plants, suggesting an association of disease with undetectable populations of the virus or a nonviral cause. This is the first report of variation in infection capacity and in virulence of SCYLV.
Rapid Screening of Musa Species for Resistance to Black Leaf Streak Using In Vitro Plantlets in Tubes and Detached Leaves
Authors: Twizeyimana M. , Ojiambo P. S. , Tenkouano A. , Ikotun T. , Bandyopadhyay R.
Published: May 2007

This study investigated the utility of inoculation of in vitro plantlets in tubes and detached leaves as reliable and rapid assays for screening Musa genotypes against Mycosphaerella fijiensis, the causal agent of black leaf streak. In the first part of the study, three types of inocula were evaluated to determine suitability for in vitro inoculation. Inoculation of in vitro plantlets with mycelial fragments resulted in significantly (P < 0.05) higher levels of disease severity and faster rates of disease progress compared with inoculations using conidial suspensions. In the detached leaf assay, amending agar medium with plant hormones significantly (P < 0.0001) aided retention of green leaf color. Leaf pieces on medium containing gibberellic acid at 5 mg/liter had about 5% chlorosis at 52 days after plating. When in vitro plantlets in tubes and detached leaves of 10 Musa genotypes with different levels of disease resistance were inoculated with M. fijiensis, there were significant (P < 0.05) differences among genotypes in leaf area infected, incubation time, and symptom evolution time. For incubation time and leaf area infected, cultivars responded depending on their level of disease resistance, with resistant genotypes Calcutta-4 and PITA-17 having significantly (P = 0.001) longer incubation times and lower infected leaf areas compared with the susceptible cultivar Agbagba and moderately resistant cultivar FHIA-23. A similar pattern in cultivar response was observed for symptom evolution time. Leaf area infected was not significantly (P = 0.2817 for two-tailed t test) different when assessed using the two assays, and infected leaf areas in both assays were strongly correlated (r = 0.88, n = 48, P < 0.0001). Although incubation times were significantly (P = 0.0062 for two-tailed t test) different between the two assays, values from the two assays were strongly correlated (r = 0.69, n = 48, P < 0.0001). These results show that these two assays are rapid and space-effective, and can reliably be used for screening Musa genotypes for resistance to black leaf streak.
Potato Silver Scurf Affected by Tuber Seed Treatments and Locations, and Occurrence of Fungicide Resistant Isolates of Helminthosporium solani
Authors: Geary Brad , Johnson Dennis A. , Hamm Philip B. , James Steve , Rykbost Ken A.
Published: May 2007

The effectiveness of various seed-tuber treatments was evaluated for control of silver scurf on potato (Solanum tuberosum), caused by Helminthosporium solani, at four locations in Washing-ton and Oregon using seed-tubers from the same source. Disease incidence was determined at harvest and following storage, and differed significantly among locations. The highest incidence of disease was observed at Redmond, OR and the lowest was at Hermiston, OR. Significantly less silver scurf occurred on progeny-tubers, regardless of location, when seed was treated with the fungicide treatments fludioxonil, fludioxonil + quintozene, azoxystrobin, or thiophanate-methyl + mancozeb compared with the nontreated control. A sample of H. solani from seed planted in the Columbia Basin of Washington and Oregon was assessed for resistance to thia-bendazole (TBZ) and thiophanate-methyl (TPM). Sensitivity of 20 isolates of H. solani to TBZ was determined on V8 media amended with TBZ. Four isolates, selected as a subset from the 20 isolates tested for TBZ sensitivity, were tested for resistance to TPM, mancozeb, and TPM + mancozeb on amended V8 media. Isolates differed significantly in sensitivity to both chemicals. Thirteen isolates out of the 20 tested were resistant to TBZ. One out of the four subsets of isolates was resistant to both TBZ and TPM. TBZ sensitivity was not related to geographic origin of the isolates. Variation in resistance was evident on a small scale as seen with one resistant and one sensitive isolate collected from the same tuber. This is the first report that silver scurf incidence is affected by location despite the same tuber-seed source and also the first report of TBZ and TPM resistant isolates of H. solani from the Columbia Basin (Oregon and Washington) production area.
Natural Occurrence of Cucumber mosaic virus on Rauvolfia serpentina, A New Record
Authors: Raj S. K. , Kumar S. , Pratap D. , Vishnoi R. , Snehi S. K.
Published: May 2007

Rauvolfia serpentina, family Apocynaceae, is widely cultivated in India and adjoining countries for the production of roots used in several herbal formulations (1). Severe mosaic and stunting of the whole plant was observed on R. serpentina growing in experimental plots of NBRI, Lucknow, in 2006. The causal pathogen was transmitted by sap inoculation on Nicotiana tabacum cv. White Burley, N. rustica, and N. glutinosa, which produced necrotic local lesions and systemic mosaic. The virus reacted positively with antiserum of Cucumber mosaic virus (CMV; PVAS 242a, ATCC, Manassas, VA) in gel double diffusion tests, indicating the presence of CMV. Total RNA was isolated from infected and healthy leaf tissues of R. serpentina, and reverse transcription (RT)-PCR was performed using CMV specific primers AM180922/AM180923. RT-PCR resulted in an expected size (~650 bp) amplicon in infected but not healthy samples. The amplicon was cloned, sequenced, and the data was submitted to GenBank (Accession No. DQ914877). BLAST search analysis of the virus isolate showed highest (99%) sequence identity with CMV isolates (GenBank Accession Nos. DQ640743, AF350450, X89652, and AF281864). The virus isolate showed a close phylogenetic relationship with Indian isolates of CMV belonging to subgroup IB. A literature survey revealed that there is no report of occurrence of any virus on R. serpentina except some fungal infections (2). To our knowledge, this is the first record of natural occurrence of CMV on R. serpentina.

References: (1) Anonymous. Wealth of India 8:376, 1969. (2) R. S. Shukla et al. EPPO Bull. 36:11, 2006.
Salt MarshClaviceps purpureain Native and InvadedSpartinaMarshes in Northern California
Authors: Fisher A. J. , DiTomaso J. M. , Gordon T. R. , Aegerter B. J. , Ayres D. R.
Published: May 2007

The fungal pathogen Claviceps purpurea (subgroup G3) has a worldwide distribution on salt marsh Spartina spp. In Northern California (United States), native Spartina foliosa sustains high rates of infection by G3 C. purpurea in marshes north of the San Francisco Estuary. Invasive populations of S. alterniflora and S. alterniflora × foliosa hybrids are virtually disease free in the same estuary, although S. alterniflora is host to G3 C. purpurea in its native range (Atlantic Coast of the United States). Greenhouse inoculation experiments showed no differences in susceptibility among S. foliosa, S. alterniflora, and Spartina hybrids. Under field conditions, S. foliosa sustained a higher incidence of disease in coastal marshes than in marshes within the bay. This geographic effect may be attributable to environmental differences between the coast and the bay proper, with the former being more conducive to infection by C. purpurea. Seed set of S. foliosa spikelets was 40 to 70% lower on infected than on uninfected inflorescences, but seed germination was not affected. The C. purpurea epidemic on S. foliosa on the coast north of the San Francisco Estuary further reduces the meager competitive ability of this declining native plant species.
First Report of Helminthosporium solani Causing Silver Scurf of Potato in Hebei Province, North China
Authors: Tian S. M. , Chen Y. C. , Zou M. Q. , Xue Q.
Published: May 2007

Silver scurf disease of potato (Solanum tuberosum) caused by Helminthosporium solani Durieu & Mont. occurs worldwide. Severe occurrence of the disease, the resulting weight loss of stored potatoes, and lower market classes of potato caused by the fungus have been documented in Europe and North America (1). Tubers infected with the pathogen develop tan-to-gray lesions that have a characteristic silvery appearance when moist. In 2005, gray spots with a defined margin and silvery appearance when seen against light were observed on potato tubers of cv. Weishu No. 1. The silver symptoms were distinguished from those of black rot disease of potato caused by Colletotrichum coccodes. The potato tubers were obtained from Weichang County of Hebei Province, North China. Conidia were scraped from the spots with a sterile scalpel and identified primarily as the fungus H. solani on the basis of morphological characters of the spores. The fungus was isolated, purified, and cultured on potato dextrose agar (PDA) amended with penicillin and streptomycin. To produce conidia, the fungus was incubated on V8 juice medium at 20 ± 2°C for 15 days under near-UV light (360 to 400 nm, 12-h light/dark cycles). The culture colony developed slowly and is gray to brown. Conidia form in whorls on conidiophores that are black, unbranched, irregular, and multiseptate. Conidia are appreciably tapered, straight or slightly curved, brown, thick walled, and have two to eight pseudosepta. The size of the conidia ranged from 14 to 70 μm long and 4 to 9 μm wide. The spore suspension was adjusted to 1.5 × 105 spores per ml by using sterile distilled water containing 0.2% Tween 20. Twenty healthy tubers were washed with distilled water and then inoculated by spraying the spore suspension onto the surface with a hand atomizer, while 10 washed tubers were sprayed with distilled water as controls. Inoculated tubers were kept in containers covered with plastic and placed in an incubation chamber at 20°C for 3 weeks. Gray-to-brown blemishes with a silvery appearance as described above were observed on tubers inoculated with the fungus and the tuber surface areas infected were from 1 to 10%, whereas no infection was visible on tubers inoculated with water. The causal agent was reisolated, cultured, and identified microscopically as H. solani. H. solani has been identified from potato tubers in Yunnan Province, Southwest China (2), but to our knowledge, this is the first report of H. solani causing silver scurf of potato in Hebei Province, North China.

References: (1) D. Errampalli et al. Plant Pathol. 50:141, 2001. (2) K. Y. Ryu et al. China Potato. 15:195, 2001.
First Report of Tan Spot of Wheat Caused by Pyrenophora triticirepentis in the Northern Hills and Northwestern Plains Zones of India
Authors: Singh D. P.
Published: May 2007

Tan spot of wheat, caused by Pyrenophora tritici-repentis (Died.) Drechs. (anamorph Drechslera tritici-repentis), is an important disease of wheat especially in cooler countries of the world. The fungal pathogen produces necrotic and chlorotic symptoms on different wheat genotypes. A survey was done to detect this disease in India during seven crop seasons (1999-2006). Blighted leaf samples (1,600) from 257 genotypes were collected from 46 locations in six agroclimatic zones of India. The tan spot pathogen was identified from scrapings of necrotic spots placed on glass slides and examined and from fungal growth on 2-cm pieces of infected leaves incubated on water-soaked Whatman No. 1 filter paper in presterilized transparent plastic petri dishes that were incubated for 3 days with a regimen of 21°C and 24 h of light and 16°C and 24 h of dark. On incubated leaf pieces, the pathogen produced erect, single, dark yellow-brown conidiophores with single, light yellow-brown conidia, 5 to 9 distoseptae, 75 to 200 μm, and a basal cell with a snake-like head typical of D. tritici-repentis(2). Disease incidence data revealed that the tan spot was most common in the northern hills zone (comprising the states of Uttaranchal, Himachal Pradesh, Jammu, and Kashmir) as well as in the Kalimpong locality in West Bengal. The pathogen was isolated from 26 to 83% of 374 leaf samples from the northern hills zone and 5 to 11% of 560 leaf samples from the northwestern plains zone (comprising the states of Punjab, Haryana, Western Uttar Pradesh, and Rajasthan). Suspensions of single-spored cultures grown on V8 potato dextrose agar with 3,000 conidia/ml until runoff were inoculated with a fine atomizer on 2-week-old seedlings of A-9-30-1 and Katepwa wheat genotypes in a polyhouse at the Directorate of Wheat Research, Karnal, India. Tween 20 (one drop per 100 ml of suspension) was used before inoculation. Necrotic and chlorotic symptoms that developed on the plants confirmed pathogenicity of the cultures. The pathogen has previously been reported from the northern plains and central zones of India during 1934 and 1972, respectively, (3,4) and from Pakistan during 2000 (1). The currently used practices of zero tillage and incorporation of crop residue back into fields may promote tan spot in the future. With the possibility that tan spot may become a major problem, particularly in the cooler parts of India, we recommend that the future wheat varieties to be planted in the northern hills and plains zones be screened for susceptibility to tan spot and that resistant varieties be developed to minimize possible loss.

References: (1) S. Ali et al. Plant Dis. 85:1031, 2001. (2) C. Drechsler. J. Agric. Res. 24:641, 1923. (3) A. P. Misra and R. A. Singh. Indian Phytopathol. 25:350, 1972. (4) M. Mitra. Indian J. Agric. Sci. 4:692, 1934.
First Report of Bacterial Speck of Tomato Caused by Pseudomonas syringae pv. tomato in Tanzania
Authors: Shenge K. C. , Mabagala R. B. , Mortensen C. N. , Stephan D. , Wydra K.
Published: May 2007

In April 2004, there was a serious outbreak of a tomato (Lypersicon esculentum Mill.) leaf spot disease in Mgeta, Mvomero District of Tanzania. The disease was characterized by lesions on green tomato fruits that were small, sunken, and black and were surrounded by darker green haloes. Lesions on ripe tomato fruits were dark brown to black, superficial, and measured approximately 1 to 2 mm in diameter. On the leaves, lesions were small, black, and surrounded by chlorotic (yellow) haloes. In some cases, the specks coalesced to form large lesions on older leaves. Black lesions were also observed on stems and petioles. A disease survey of selected tomato-producing areas in Arusha, Dodoma, Iringa, and Morogoro regions of Tanzania during 2004 and 2005 revealed that the disease was widespread in farmers' fields in all areas surveyed. Disease incidence was approximately 80%, while severity, rated on the scale of Chambers and Merriman (1), ranged from moderate (11 to 40 lesions per plant) to severe (>40 lesions per plant). A bacterium that produced a greenish, diffusible pigment on King's medium B was consistently isolated from lesions on tomato fruits collected from the fields in all the surveyed areas. All 56 isolates obtained were gram negative, oxidase negative, and fluoresced on King's medium B under UV light. None utilized phenylethylamine as the sole carbon source, while three isolates utilized i-erythritol and lactulose. Biolog analysis of the isolates, along with two reference strains of P. syringae pv. tomato (Pst CEP-3 from Sokoine University of Agriculture, Tanzania and Pst BB6 [Race 1] from Göttinger Sammlung Phytopathogener Bakterien, Göttingen, Germany) identified them as P. syringae pv. tomato, with similarity indices of 0.518 to 0.933. They also were positively identified as P. syringae pv. tomato by repetitive sequence-based-PCR (2,3) and fragment length polymorphism analysis. Pathogenicity of the strains was confirmed by spraying 35-day-old tomato seedlings (cv. Tanya) with suspensions of the isolates at a concentration of 108 CFU ml-1 of sterile water. After approximately 72 h, small, water-soaked, dark brown lesions similar to those observed on the field plants were observed on leaves of all the inoculated tomato seedlings. There were no symptoms on control plants. The bacterium was reisolated from the infected plants and identified as P. syringae pv. tomato, in accordance with Koch's postulates. To our knowledge, this is the first report of the occurrence of tomato bacterial speck in Tanzania.

References: (1). S. C. Chambers and P. R. Merriman. Aust. J. Agric. Res. 26:657, 1975. (2). F. J. Louws et al. Appl. Environ. Microbiol. 60:2286, 1994. (3). M. Zaccardelli et al. Eur. J. Plant Pathol. 111:85, 2005.
First Report of Leaf Spot Caused by Cladosporium herbarum on Centaurea solstitialis in Greece
Authors: Berner D. K. , Smallwood E. L. , McMahon M. B. , Luster D. G. , Kashefi J.
Published: May 2007

Centaurea solstitialis L. (yellow starthistle), family Asteraceae, an invasive weed in California and the western United States, is targeted for biological control. In the summer of 2003, an epidemic of unknown etiology on dying C. solstitialis plants was observed near Kozani, Greece (40°22′07″N, 21°52′35″E, elevation, 634 m). Plants had necrotic light brown leaf spots on the lower leaves and the decurrent leaf bases along the stems. Often, necrotic lesions extended along the stems to the capitula. Virtually all plants in a solid stand of C. solstitialis (approximately 0.5 ha) showed disease symptoms. Diseased plants were collected, air dried, and sent to the quarantine facility of the Foreign Disease-Weed Science Research Unit (FDWSRU), USDA/ARS, Fort Detrick, MD. On the basis of culture growth (45-cm diameter after 2 weeks at 25°C on malt extract agar), fungal morphology (1), and comparison with 21 internal transcribed spacer sequences in GenBank, the putative causal organism was identified as Cladosporium herbarum (Pers.:Fr.) Link. (teleomorph = Davidiella tassiana (De Not.) Crous & U. Braun). Sixteen C. solstitialis plants in the rosette stage and 16 plants in the bolted stage were inoculated with an aqueous suspension of spores (106 conidia ml-1) and placed in an environmentally controlled chamber at 25°C with 8 h of dew and 12 h of light daily. Plants in the rosette stage were resistant, but the fungus was very aggressive on bolted plants. Within 4 to 6 days of inoculation, necrosis developed on leaves and stems and then spread up the stems to the capitula, often resulting in plant death. The fungus also infected developing flowers. Cladosporium herbarum was reisolated from each of the 16 bolted C. solstitialis plants in two separate tests at the FDWSRU and from all bolted inoculated plants at the European Biological Control Laboratory (EBCL) in Greece. In the greenhouse at the EBCL, the pathogen readily spread to (and was isolated from) another 10 noninoculated C. solstitialis plants in close vicinity to the inoculated C. solstitialis plants. Results of host range tests will establish if this isolate of Cladosporium herbarum has the potential as a biological control agent of C. solstitialis in the United States and does not pose a threat to other Centaurea spp. used in horticulture. A voucher specimen has been deposited with the U.S. National Fungus Collections (BPI 863446). Live cultures are being maintained at the FDWSRU and EBCL, Greece. To our knowledge, this is the first report of a disease caused by Cladosporium herbarum on C. solstitialis.

Reference: (1) M. H. M. Ho et al. Mycotaxon 72:115, 1999.
First Report of Blackberry chlorotic ringspot virus in Rubus sp. in the United States
Authors: Tzanetakis I. E. , Postman J. D. , Martin R. R.
Published: May 2007

Blackberry chlorotic ringspot virus (BCRV), genus Ilarvirus, has been found in Rubus sp. in Scotland (2) and rose in the United States (4). The possibility that BCRV infects other hosts in the United States was explored. We tested 18 accessions of Fragaria sp. and 30 of Rubus sp. maintained at the National Clonal Germplasm Repository in Corvallis, OR. Ilarviruses had been detected in these plants by reverse transcription (RT)-PCR, ELISA, or had caused symptoms typical of ilarviruses on indicator plants. The accessions were tested by RT-PCR with primers F (5′-GTTTCCTGTGCTCCTCA-3′) and R (5′-GTCACACCGAGGTACT-3′) (4) that amplify a 519 to 522 nt (depending on the isolate) region of the RNA 3 of BCRV. The virus was detected in two accessions of black raspberry (Rubus occidentalis L.): RUB433, cv. Lowden and RUB 9012, cv. New Logan. The sequences of the fragments amplified from these accessions (GenBank Accession Nos. EF041817 and EF041818, respectively) had 97% nt sequence identity to each other and 95 and 88% nt identity to the rose and Scottish isolates (GenBank Accession Nos. DQ329378 and DQ091195, respectively). Chenopodium quinoa indicator plants inoculated with isolate RUB 433 developed mild chlorotic spots on the inoculated leaves 4 days after inoculation. RT-PCR and sequencing of the amplicons verified BCRV infection of C. quinoa. RUB 9012 was used for the characterization of Black raspberry latent virus (BRLV), later thought to be an isolate of Tobacco streak virus (TSV). This accession was recently found to be infected with Strawberry necrotic shock virus (SNSV) but not TSV (3). It is possible that BRLV may be a mixture of SNSV and BCRV. SNSV is one of the most abundant viruses of Rubus sp. in the Pacific Northwest (1), and the finding of another ilarvirus, BCRV, may account in part for the rapid decline of Rubus sp. observed in several fields in Oregon and Washington. To our knowledge, this is the first report of BCRV infecting Rubus sp. outside the United Kingdom.

References: (1) A. B. Halgren. Ph.D. Diss. Oregon State University, Corvallis, OR, 2006. (2) A. T. Jones et al. Ann. Appl. Biol. 149:125, 2006. (3) I. E. Tzanetakis et al. Arch. Virol. 149:2001, 2004. (4) I. E. Tzanetakis et al. Plant Pathol. 55:568, 2006.