bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of Tan Spot of Wheat Caused by Pyrenophora tritici-repentis in the Pacific Northwest
Authors: Peever T. L. , Murray T. D.
Published: May 2007

In late May 2001, lesions resembling tan spot were observed on lower leaves of winter wheat (Triticum aestivum L.) in early boot stage in Nez Perce County, ID. Abundant sporulation was observed from tan lesions with chlorotic haloes after 2 days incubation in a moist chamber at room temperature. Conidia were multicelled, straw colored, approximately 100 × 15 µm, rounded at the apex, and borne singly on dark brown conidiophores. The fungus fit the morphological description of Drechslera tritici-repentis (Died.) Shoemaker, the anamorphic state of Pyrenophora tritici-repentis (Died.) Drechs. (2). Three single-conidial isolates were sampled from infected plants in a 5 × 1 m area of the affected field and induced to sporulate. Two of the isolates were used to spray-inoculate 3-week-old susceptible wheat (cv. Madsen) in the greenhouse (one plant per isolate, 1 × 105 conidia/ml), and tan spot lesions were apparent 3 to 5 days after inoculation with both isolates. DNA was extracted from all three isolates, and the entire nuclear ribosomal internal transcribed spacer (ITS) was amplified with ITS1 and ITS4 primers (4). Similarly, 610 bp of the 5′ end of the glyceraldehyde-3-phosphate-dehydrogenase gene (gpd) was amplified with gpd-1 and gpd-2 primers (1). ITS and gpd amplicons were direct-sequenced on both strands, and alignment revealed that all three isolates were identical for both regions. A BLAST search of the NCBI database with the ITS sequence revealed P. tritici-repentis accessions AY004808 and AF071348 and D. tritici-repentis accession AF163060 as the closest matches with 100, 99.8, and 98.8% sequence similarity, respectively. A similar search with the gpd sequence revealed P. tritici-repentis accessions AY004838 and AF081370 and P. bromi accession AY004839 as the closest matches with 100, 100, and 99.0% sequence similarity, respectively. These results, coupled with the morphological identification and inoculation results, confirm the identity of the fungus as P. tritici-repentis. Although reported on other grass hosts in the region (3), to our knowledge, this is the first report of tan spot of wheat in the Pacific Northwest. This disease has been of little concern to wheat producers in the Pacific Northwest due to low rainfall and relative humidity during the growing season.

References: (1) M. L. Berbee et al. Mycologia 91:964, 1999. (2) M. B. Ellis, Dematiaceous Hyphomycetes. CMI, Kew, Surrey, UK. 1971. (3) R. Sprague. Diseases of Cereals and Grasses in North America (Fungi, Except Smuts and Rusts). Ronald Press Co. New York, 1950. (4) T. J. White et al. Pages 315–322 in: PCR Protocols: A Guide to Methods and Applications. Academic Press Inc., New York, 1990.
First Report of Papaya leaf curl virus Infecting Papaya Plants in Taiwan
Authors: Chang L.-S. , Lee Y.-S. , Su H.-J. , Hung T.-H.
Published: May 2007

Papaya leaf curl disease was first reported in India in 1939 (1). Caused by begomovirus, Papaya leaf curl virus (PaLCV) (2), this disease was discovered in the papaya orchards of southern Taiwan in 2002. Infected papaya developed symptoms such as downward curling of leaves, twisted petioles, vein enation, and stunting. Diseased plants produced small and distorted fruits that tend to fall prematurely. Typical twin virion was observed in the diseased papaya cells by electron microscopy. In addition, our whitefly-transmission test demonstrated that the sweet potato whitefly (Bemisia tabaci) could transmit this virus. For further molecular identification, two opposing primers were selected for the polymerase chain reaction (PCR) detection of PaLCV from the published nucleotide sequences of PaLCV (Genbank Accession No. NC004147) (3). The primer pair, composed of the forward primer 5′ -GCT AGA AAT TAT GTC GAA GCG-3′ and the reverse primer 5′-TCA ACT ACA ACC TGA GGA AAG C-3′, was designed to amplify a PaLCV-specific 1,031-bp fragment containing 774 bp of the coat protein gene open reading frame (CP-ORF) using PCR. Five diseased papaya samples with typical leaf-curl symptoms tested positive in the PCR-based assay with this specific primer pair, whereas five healthy papaya samples tested negative. However, the sequencing results of the PCR product from five PaLCV-infected papayas indicated the CP-ORF of PaLCV in Taiwan (PaLCV-Tw) was somewhat different from PaLCV in India (PaLCV-Id). The DNA sequences (Genbank Accession No. AY183472) of CP-ORF of PaLCV-Tw were 80% identical to those of PaLCV-Id, and their translated amino acid sequences were 77% identical. This indicates that PaLCV-Tw and PaLCV-Id are two different species or strains.

References: (1) K. M. Thomas and C. S. Krishnaswamy. Curr. Sci. 8:316,1939. (2) S. Saxena et al. Plant Dis. 82:126, 1998. (3) S. Saxena et al. Biochem. Mol. Biol. Int. 45:101, 1998.
Mungbean yellow mosaic virus-Vi Agroinfection by Codelivery of DNA A and DNA B From One Agrobacterium Strain
Authors: Jacob S. S. , Vanitharani R. , Karthikeyan A. S. , Chinchore Y. , Thillaichidambaram P. , Veluthambi K.
Published: May 2007

Agroinfection of bipartite geminiviruses is routinely done by mixing two Agrobacterium strains that independently harbor partial tandem repeats of DNA A and DNA B. We report here an improved agroinfection method for bipartite geminiviruses that utilizes one strain of Agrobacterium that harbors DNA A and DNA B partial tandem repeats on two compatible replicons. A cointegrate vector, pGV2260∷pGV1.3A, with the partial tandem repeat of Mungbean yellow mosaic virus-Vi (MYMV-Vi) DNA A and a binary vector, pGA1.9B, with the partial tandem repeat of MYMV-Vi DNA B gave an agroinfection efficiency of 24% when harbored in two Agrobacterium strains and an efficiency of 61% when harbored in one Agrobacterium strain. A combination of binary vectors, pGA1.9A with MYMV-Vi DNA A partial tandem repeat and pGA1.9B with DNA B partial tandem repeat, gave an agroinfection efficiency of 74% when harbored in two strains. But pGA1.9A and pPZP1.9B (a partial tandem repeat of DNA B), when present in the same Agrobacterium strain, gave 100% agroinfection. Accumulation of viral DNA was shown by Southern blotting. The single-strain method using two compatible replicons consistently gave 100% agroinfection efficiency.
Laboratory, Greenhouse, and Field Assessment of Fourteen Fungicides for Activity Against Claviceps africana, Causal Agent of Sorghum Ergot
Authors: Prom Louis K. , Isakeit T.
Published: May 2007

Commercial formulations of 14 fungicides representing seven chemical classes were assessed in vitro and in vivo for activity against Claviceps africana, causal agent of sorghum ergot. All fungicides markedly reduced spore germination in vitro on water agar, with effective concentration (EC)50 values (based on active ingredient) that ranged from 0.01 μg ml-1 for thiophanatemethyl and trifloxystrobin to 1.18 μg ml-1 for cyprodinil. In vivo assays included applications of fungicide on full bloom panicles of a male-sterile line, ATx623, and then inoculating panicles with a conidial suspension immediately after the fungicide had dried. In greenhouse trials and in the 2000 field evaluation, a single application of propiconazole, tebuconazole, triadimefon, myclobutanil, or azoxystrobin at a rate of 25 μg ml-1 markedly suppressed ergot severity on ATx623. In the 2001 field evaluation, tebuconazole applied at 25 μg ml-1 was most effective in reducing levels of ergot severity. Ergot control was greater when fungicides were applied at 25 μg ml-1 than at 5 μg ml-1. Generally, triazole and strobilurin classes of fungicide were more effective in controlling ergot than benzimidazole, anilinopyrimidine, ethylenebisdithiocar-bamate (EBDC), pyridinamine, and organometallic classes. At the two fungicide rates used in this study, ergot severity increased between 7 and 10 days after inoculation. Results showed that in vitro fungicide screening by measuring spore germination inhibition was not a good predictor of performance in the field. Results from the field trials suggest that control, particularly under ergot-favorable environments, may require higher rates than used in this study.
First Report of Blackleg Disease Caused by Leptosphaeria maculans on Canola in Brazil
Authors: Fernando W. G. D. , Parks P. S. , Tomm G. , Viau L. V. , Jurke C.
Published: May 2007

Canola (Brassica napus L.) is a relatively new crop in Brazil, having been grown there for approximately 8 years. In 2000, leaf lesions and stem cankers were observed in cvs. Hyola 420 and Hyola 401 in farmers' fields in the state of Rio Grande do Sul. Cankered stems were received at the University of Manitoba, Canada, from Rio Grande do Sul for disease identification. Small pieces of the stem were cut from the cankered area, and standard protocol was followed to surface sterilize the stem pieces. Stem pieces were plated on V8 agar medium and incubated under light for 12 days. Typical fungal colonies with concentric rings containing pycnidia formed on the V8 agar. The colony characteristics were typical of the blackleg pathogen, Leptosphaeria maculans (Desmaz.) Ces. & De Not. (anamorph = Phoma lingam) (Tode:Fr.) Desmaz.). Blackleg is an economically important and serious disease in many parts of the world including Australia, Canada, the United States, and Europe. L. maculans strains can be characterized in four pathogenicity groups (PG1 through PG4) based on differential testing procedures giving interaction phenotype (IP) reactions (2). Two weeks after plating on V8 media, plates were flooded with sterile distilled water, and pycnidiospores were harvested. Flats of multipots filled with Metro Mix were seeded with three cultivars (Westar, Glacier, and Quinta). One-week-old cotyledons from the three cultivars were inoculated with pycnidiospore suspensions (2 × 107 pycnidiospores per ml) of seven Brazilian isolates, numbered 7, 8, 9, 11, 15, 16, and 18, respectively. Each cotyledon leaf, punctured in the center with a needle, was inoculated with a 10-μl droplet of the inoculum. Disease evaluations were made 11 days after inoculation using a 0 to 9 rating scale (1). This screening was repeated three times from February 2001 to October 2001. After the second repeat, the isolates from Rio Grande do Sul were passed through the highly susceptible canola cv. Westar. Results from all four trials were consistent, and yielded one PG1 isolate (No. 7) and six PG3 isolates. PG1 is classified as a nonaggressive strain, whereas PG3 isolates are classified as aggressive. PG3 isolates would have an IP reaction of 7 to 9, 7 to 9, and 3 to 6 on cvs. Westar, Glacier, and Quinta, respectively. PG2 is the most commonly found aggressive strain in the Canadian prairies. PG3 is predominantly found in Australia, the United Kingdom, and the United States. To our knowledge, this is the first report of blackleg disease caused by L. maculans on canola in Brazil. Differential testing fulfilled Koch's postulates and determined the PG groups found in Brazil (PG1 and PG3).

References: (1) P. A. Delwiche. Genetic aspects of blackleg (Leptosphaeria maculans) resistance in rapeseed (Brassica napus) Ph.D. thesis. University of Wisconsin-Madison, 1980. (2) A. Mengistu et al. Plant Dis. 75:1279, 1991.
Evaluation of Postharvest Burning and Fungicides to Reduce the Polyetic Rate of Increase of Choke Disease in Orchardgrass Seed Production
Authors: Pfender W. F. , Alderman S. C.
Published: May 2007

Epichloë typhina, causal agent of choke disease, is detrimental to orchardgrass seed production. The fungus grows systemically, persists indefinitely as an endophyte within the perennial host, and produces a stroma bearing conidia and ascospores at the time of host flowering. The ascospores or conidia are thought to infect plants through the cut ends of tillers after swathing at harvest. The objective of this study was to evaluate the potential of systemic fungicides and postharvest treatments (burning and reclipping) to reduce the rate of increase of choke disease among plants. The fungicides propiconazole and azoxystrobin reduced germination of conidia of E. typhina in vitro, but had no effect on development of stroma or viability of conidia produced on infected plants. In field tests, fungicides applied to the cut ends of tillers after harvest were ineffective at reducing the rate of increase in disease. Likewise, reclipping of orchardgrass stubble after harvest, in an attempt to remove incipient infections in the tillers, did not reduce the rate of disease increase in the stand. However, propane-assisted burning of postharvest stubble did reduce the polyetic epidemic rate to 2.7% per year, compared with approximately 9.2% per year in plots receiving the fungicide, reclipping, or control treatments. The results suggest that postharvest burning may be useful in controlling choke disease and raise the possibility that there are infection courts other than the pith of cut reproductive tillers.
Molecular Analyses of Citrus tristeza virus Subisolates Separated by Aphid Transmission
Authors: Brlansky R. H. , Damsteegt V. D. , Howd D. S. , Roy A.
Published: May 2007

Citrus tristeza virus (CTV) exists in field isolates as a complex of virus isolates. This complex may contain both mild and severe CTV. Using single and multiple aphid transmissions, subiso-lates of the various field isolates were separated. Some CTV isolates that tested negative with the monoclonal antibody MCA13 consisted of MCA13-positive subisolates. Using primers to specific and variable regions of the CTV genome, molecular profiles of the isolates and subisolates were generated and compared. The profiles of the subisolates sometimes were very different from the parent field isolates from which they were transmitted.
Effects of Plant Essential Oils on Ralstonia solanacearum Population Density and Bacterial Wilt Incidence in Tomato
Authors: Pradhanang P. M. , Momol M. T. , Olson S. M. , Jones J. B.
Published: May 2007

Greenhouse experiments were conducted to determine the effectiveness of plant essential oils as soil fumigants to manage bacterial wilt (caused by Ralstonia solanacearum) in tomato. Potting mixture (“soil”) infested with R. solanacearum was treated with the essential oils at 400 mg or μl and 700 mg or μl per liter of soil in greenhouse experiments. R. solanacearum population densities were determined just before and 7 days after treatment. Populations declined to undetectable levels in thymol, palmarosa oil, and lemongrass oil treatments at both concentrations, whereas tea tree oil had no effect. Tomato seedlings transplanted in soil treated with 700 mg/liter of thymol, 700 ml/liter of palmarosa oil, and 700 ml/liter of lemongrass oil were free from bacterial wilt and 100% of plants in thymol treatments were free of R. solanacearum. Soil amendment with fresh leaves of essential oil-producing plants did not reduce bacterial wilt incidence compare to untreated inoculated control. Some thyme oil-producing plants such as thyme (Thymus vulgaris) cv. German winter, Creeping thyme (Thymus serpyllum), and Greek oregano (Origanum vulgare subsp. hirtum), while remaining symptomless, became systemically infected by R. solanacearum and were therefore identified as hosts of R. solanacearum.
First Report of Puccinia helianthi (Race 314) on Sunflower in Mozambique
Authors: Zazzerini A. , Tosi L.
Published: May 2007

Rust of sunflower (Helianthus annuus L.) caused by Puccinia helianthi Schwein. is a major sunflower disease in Mozambique where local ecotypes, from Peredovik and Record selections, and South African commercial varieties were all susceptible to race 4, which was prevalent among isolates collected from 1996 to 1997 (1). Disease surveys carried out in southern Mozambique (Maputo) from August until September 2002 revealed an increase in the incidence and severity of sunflower rust compared to previous investigations on the same varieties. Rust symptoms, observed in all fields, appeared on the last leaf pairs of plants at the 5.1 growth stage. Disease severity (percentage of leaf area infected) (2) ranged from 20 to 60%, but the disease did not cause noticeable yield loss because rust infection started near the end of the season. Argentine and African commercial varieties and some experimental Mozambican selections from sunflower accessions of different origin were the most severely affected. Two rust samples were collected from infected leaves, stored at 5°C, and increased on the universal suscept (S-37-388). Race identification of both isolates was determined on three sets of nine differential lines (three lines per each set): S-37-388, CM 90 RR, MC 29; P-386, HA-R1, HA-R2; and HA-R3, HA-R4, HA-R5 using the triplet coding system (3). The 2-week-old seedlings (four per 10-cm pot) of each differential line (four pots per line) were inoculated on the upper surface of the first pair of true leaves. Inoculated seedlings were covered with plastic bags, placed in a growth chamber without light for 18 to 22 h, and then transferred to a greenhouse under alternate day/night temperatures of 22/18 ± 2°C, 60 to 70% relative humidity, and 12 h of light (180 μE·m-2·s-1) per day. The inoculation test was repeated twice. Assessment of host differential reactions, 14 days after inoculation, was based on five categories of sunflower reaction to rust (4). Both isolates were identified as race 314 and to our knowledge, this is the first report of this race in Mozambique. Since P. helianthi completes its life cycle annually, the occurrence of new races is expected. The opportunity for new races to occur is particularly high and severe in Mozambique where all sunflower varieties grown as summer (January to June) and winter (August to December) crops are susceptible.

References: (1) P. M. Vicente and A. Zazzerini. Helia 20:25, 1997. (2) T. J. Gulya et al. NDSU Extension Serv. PP-998, 1990. (3) T. J. Gulya and S. Masirevic. FAO Eur. Res. Network on Sunflower. Bucarest, Romania, 31, 1995. (4) S. M. Yang. Ann. Phytopathol. Soc. Jpn. 52:248, 1986.
First Report of the Presence of Albugo tragopogonis on Cineraria maritima in Italy
Authors: Garibaldi A. , Minuto A. , Bertetti D. , Gullino M. L.
Published: May 2007

Cineraria maritima L. (synonym Senecio cineraria DC.), commonly known as dusty-miller, is grown in Italy for landscape use in parks and gardens. In the spring of 2001, severe outbreaks of a previously unknown disease were observed in commercial farms located in northern Italy. Leaves of infected plants showed several sori on the abaxial surface, progressing to the adaxial surface, and often in the interveinal areas. On the adaxial surface of leaves, chlorotic areas developed and eventually turned brown. Severely infected leaves wilted, but remained attached to the stem. Signs of the fungus were present as whitish and catenulate sporangia emerging from the sori. Sporangia, organized in chains, had an average diameter of 20.5 × 26.5 μm. On the basis of the microscopic observations, the causal agent of the disease was identified as Albugo tragopogonis. Pathogenicity was confirmed by inoculating leaves of healthy C. maritima plants with a sporangial suspension (5 × 102 sporangia per ml) obtained from infected plants. Noninoculated plants served as a control. Plants were kept covered with plastic bags for 72 h and maintained at 15°C. After 10 days, typical symptoms of white rust developed on inoculated plants starting from the basal leaves. Within 30 days, affected leaves were completely wilted. Microscopic examination of sporangia within sori verified the pathogen to be A. tragopogonis. No symptoms developed on the control plants. A. tragopogonis has been reported as the causal agent of white rust on several species belonging to the genus Senecio in the United States (1). In New Zealand, the presence of A. tragopogonis was reported on the genus Cineraria in 1959 (2). To our knowledge, this is the first report of the presence of white rust on Cineraria maritima in Italy.

References: (1) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St Paul, MN, 1989. (2) J. M. Dingley. N. Z. J. Agric. Res. 2:380, 1959.
Weeds as Alternative Hosts of the Citrus, Coffee, and Plum Strains of Xylella fastidiosa in Brazil
Authors: Lopes S. A. , Marcussi S. , Torres S. C. Z. , Souza V. , Fagan C. , França S. C. , Fernandes N. G. , Lopes J. R. S.
Published: May 2007

In Brazil, Xylella fastidiosa is present in citrus (Citrus sinensis), coffee (Coffea arabica), and plum (Prunus sp.) crops, causing the citrus variegated chlorosis (CVC), coffee leaf scorch (CLS), and plum leaf scald (PLS). Also present in these crops and infesting weeds, which ultimately could serve as sources of inoculum for the cultivated trees, are diverse populations of xylem-feeding leafhopper vectors. In order to assess host range of X. fastidiosa among weeds and to better understand their role in epidemics, field surveys, mechanical inoculations, and insect transmission tests were conducted. Polymerase chain reaction (PCR) and culture plating were used to detect the pathogen from plant tissues. X. fastidiosa was detected in 10 out of 23 species of the weed plants sampled in two citrus groves affected by CVC. None of the weed plants showed external symptoms. In the greenhouse, the average percentages of infection on plants mechanically inoculated with the CVC, CLS, and PLS strains of X. fastidiosa were, respectively, 25, 10, 0 in Medicago sativa; 70, 45, 20 in Echinochloa crus-galli; 45, 30, 0 in Brachiaria decumbens; 72, 70, 40 in Brachiaria plantaginea; 13, 10, 0 in Digitaria horizontalis; 31, 30, 0 in Solanum americanum; and 17, 0, 0 in Bidens pilosa. Symptoms were observed only in S. americanum and citrus and only when inoculated with the CVC strain. In insect transmission tests, the grass leafhopper Ferrariana trivittata was first caged on citrus plants showing CVC symptoms and then on healthy citrus and on the four most common weeds. No plants tested positive by PCR or culture, or showed symptoms for at least 4 months after inoculation. The amount of X. fastidiosa cells that may accumulate in weeds inoculated by leafhoppers is probably under insect acquisition thresholds, a factor that would limit their importance to the CVC epidemics, as studies on spatial distribution of diseased citrus trees over time indicate.
Effect of Commercial Adjuvants on Vegetable Crop Fungicide Coverage, Absorption, and Efficacy
Authors: Gent David H. , Schwartz Howard F. , Nissen Scott J.
Published: May 2007

The addition of an appropriate adjuvant with foliar fungicide can significantly improve coverage, absorption, and efficacy. Laboratory and field studies evaluated coverage, absorption, and efficacy of commercial adjuvants with diverse chemistries on multiple host-pathogen systems. Organosilicone-based adjuvants improved coverage by 26 to 38% compared with a latex spreader-sticker and water. Significant crop by coverage interaction effects were also detected. The organosilicone/methylated seed oil-based adjuvant, Aero Dyne-Amic, significantly improved total [14C]azoxystrobin absorption on onion and potato by 30 and 21%, respectively, compared with water. The spreader-sticker, Bond, improved [14C]azoxystrobin absorption on onion and dry bean by 41 and 39%, respectively, compared with water. In experimental field plots, dry bean rust incidence was reduced by 52% when Kinetic or Latron AG-98 was added to maneb compared with maneb alone. The area under the potato early blight disease progress curve was reduced 29, 24, or 21% when Kinetic, Bond, or Latron AG-98 was added to maneb, respectively, compared with maneb applications alone.
Sensitivity of Populations ofBotrytis cinereafrom Pear-Related Sources to Benzimidazole and Dicarboximide Fungicides
Authors: Lennox Cheryl L. , Spotts Robert A.
Published: May 2007

Botrytis cinerea is responsible for a major portion of postharvest decay in winter pears in the Pacific Northwest. The baseline sensitivity levels (mean EC50values) of a wild-type B. cinerea population to thiabendazole and iprodione were 6.66 and 0.56 mg/liter, respectively. B. cinerea from commercial orchards not treated with a benzimidazole had significantly lower incidence of resistance (0.59%) to a discriminatory concentration of thiabendazole at 10 mg/liter than did isolates from orchards in which benomyl had been applied for experimental purposes (16.0%), unsprayed control trees in benomyl-sprayed orchards (5.34%), and isolates from packinghouses where thiabendazole was applied as a prestorage drench or packingline spray (3.23%). The mean EC50value of isolates in the wild-type population was lower than those of resistant isolates from all other sources. High-level thiabendazole resistance (EC50> 100 mg/liter) was found in 0.20% of isolates from unsprayed commercial orchards, 9.33% of isolates from benomyl-sprayed orchards, and 2.67% of isolates from unsprayed control trees in these benomyl-sprayed orchards. In isolates from packinghouses where a thiabendazole line spray was applied, 1.52% had high-level thiabendazole resistance. All isolates from all pear-related sources tested were sensitive to iprodione at 10 mg/liter. This study provides evidence supporting current recommendations of a single postharvest application of a benzimidazole to control decay caused by B. cinerea, and no application of benzimidazole fungicides in the orchard.
First Report of Fusarium Wilt of Alfalfa in Greece
Authors: Antonopoulos D. F. , Elena K. , Tjamos E. C.
Published: May 2007

In August 2000, samples of alfalfa (Medicago sativa L.) plants cv. Iliki showing wilt symptoms consistent with those reported for Fusarium wilt (1) were collected from an alfalfa field of the Agricultural University of Athens. Symptoms of the disease were chlorosis, yellowing, premature defoliation, wilting, vascular discoloration (dark brown), stunting, and death of plants. Fusarium oxysporum was isolated from the stems of diseased plants. Fresh cultures of the isolated fungus on potato dextrose agar (PDA) media developed whitish purple mycelium, short phialides, microconidia, and later, macroconidia and chlamydospores matching the description of F. oxysporum Schlechtend.:Fr. f. sp. medicaginis (Weimer) W.C. Snyder & H.N. Hans. (2). The fungus was maintained on PDA cultures at 4°C. Pathogenicity tests were conducted in a greenhouse (12-h photoperiod at 25 to 32°C) on alfalfa Greek cv. Iliki. An aqueous suspension of 107 microconidia per ml was prepared, and roots of 7-week-old seedlings were dipped for 20 min and then returned to pots. Within 15 days, all inoculated plants exhibited typical Fusarium wilt symptoms similar to those observed in the field. Four weeks after inoculation, almost all plants were dead. Control seedlings (root-dipped for 20 min in sterile distilled water) remained healthy. The fungus was reisolated from the symptomatic seedlings, fulfilling Koch's postulates. Weimer (3) first described Fusarium wilt of alfalfa and identified the causal organism as Fusarium oxysporum f. sp. medicaginis. Cross-artificial inoculation to cotton plants cv. Myrto, Christina, and Acala CJ2 was also performed, but none of the cultivars developed any macroscopic symptoms of the disease. To our knowledge, this is the first report of alfalfa Fusarium wilt in Greece. Although the pathogen was located in a rather isolated spot of alfalfa cultivation in Attica County, the occurrence of the pathogen and its importance in other alfalfa growing regions of Greece will be investigated.

References: (1) D. C. Erwin. Fusarium wilt. Pages 33–34 in: Compendium of Alfalfa Diseases. 2nd ed. D. L. Stuteville and D. C. Erwin eds. The American Phytopathological Society, St. Paul, MN, 1990. (2) W. C. Snyder and H. N. Hansen. Am. J. Bot. 27:64, 1940. (3) J. L. Weimer. J. Agric. Res. 37:419, 1928.
Breakdown of a Brassica rapa subsp. sylvestris Single Dominant Blackleg Resistance Gene in B. napus Rapeseed by Leptosphaeria maculans Field Isolates in Australia
Authors: Li H. , Sivasithamparam K. , Barbetti M. J.
Published: May 2007

Blackleg, caused by Leptosphaeria maculans, is a major disease of oilseed rape (Brassica napus) grown in Canada, Europe, and Australia. Cv. Surpass 400 was released in Australia in 2000 as the most resistant cultivar to L. maculans. It carries a single dominant resistance gene from B. rapa subsp. sylvestris. This cultivar usually shows a hypersensitive response to L. maculans characterized by small, dark brown lesions that are necrotic, localized, and without pycnidia on cotyledons, leaves, and stems. However, in 2001 on a Western Australian experimental farm, a small proportion of the lesions on the lower stem and crown region of cv. Surpass 400 were typical of those observed in susceptible cultivars, which were brown, necrotic lesions with a darker margin, but they contained fewer pycnidia. Forty seedlings of cv. Surpass 400 and susceptible cv. Westar were inoculated with pycnidiospore suspensions (106/ml) of each of 18 isolates taken from lesions on cv. Surpass 400. All 18 isolates caused collapse of cotyledons of susceptible cv. Westar. Four of these isolates caused large cotyledon lesions with some pycnidia on cv. Surpass 400. Three of these four isolates were subsequently inoculated onto 60 seedlings per isolate, at each of the four cotyledon lobes of each seedling of the two cultivars. Inoculated plants were assessed for disease severity on cotyledons and transplanted to the field 14 days after inoculation. The cotyledons of inoculated cv. Surpass 400 showed characteristic large, necrotic lesions with pycnidia, while the cotyledons of cv. Westar had collapsed and contained a mass of pycnidia. Blackleg disease severity in the crown region of the stem was assessed at 2 weeks before harvest. Fifty-four percent of the cv. Surpass 400 transplanted inoculated plants subsequently developed susceptible symptoms of crown cankers on stems. These symptoms were deep, girdling, brown lesions on the plant crowns with some pycnidia. One hundred percent of cv. Westar plants were infected and dead at this stage. This confirmed the ability of these field isolates to overcome the single dominant resistance gene present in cv. Surpass 400. To our knowledge, this is the first report of breakdown of a single dominant B. rapa subsp. sylvestris gene based resistance to blackleg in oilseed rape in the field.
Genetic Variation Among Isolates of the Web Blight Pathogen of Common Bean Based on PCR-RFLP of the ITS-rDNA Region
Authors: Godoy-Lutz G. , Steadman J. R. , Higgins B. , Powers K.
Published: May 2007

Variability of 45 isolates of Rhizoctonia solani (teleomorph Thanatephorus cucumeris) causing web blight (WB) of common bean, Phaseolus vulgaris, was examined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis of the internal transcribed spacer regions (ITS1 and ITS2) and the 5.8S subunit (5.8S) of the nuclear ribosomal DNA repeat (ITS-5.8S-rDNA). Isolates were collected from diseased bean leaves from Argentina, Costa Rica, Cuba, Dominican Republic, Honduras, Panama, and Puerto Rico. These WB isolates belong to AG-1 and AG-2 based on anastomosis reaction. Isolates of AG-1 that cause WB were separated into three distinct groups of RFLP patterns from enzymatic digestion of a 740-bp PCR fragment. Microsclerotia-producing isolates (<1 mm) were differentiated from macrosclerotia-producing isolates (5 to 20 mm) based on PCR-RFLP patterns even though they are placed in the same AG1-1B subgroup by anastomosis reaction. WB isolates of AG-2 were separated into two distinct PCR-RFLP groups as previously reported. AG-1 macrosclerotial-producing isolates were the most virulent, whereas isolates of AG-2 were the least virulent. Genetic variability of the WB pathogen may have influenced the failure or success of management practices implemented in the past in Latin America.
Characterization of Verticillium dahliae Isolates and Wilt Epidemics of Pepper
Authors: Bhat R. G. , Smith R. F. , Koike S. T. , Wu B. M. , Subbarao K. V.
Published: May 2007

Epidemics of Verticillium wilt in pepper fields of the central coast of California and isolates of Verticillium dahliae associated with these epidemics were characterized. The mean incidence of wilted plants per field ranged from 6.3 to 97.8% in fields with Anaheim, jalapeno, paprika, or bell peppers. In general, incidence of wilt in jalapeno and bell pepper crops was lower than in crops of other types of pepper. Inoculum density of V. dahliae in the surveyed pepper fields ranged from 2.7 to 66.6 microsclerotia g-1 dry soil, and the correlation between disease incidence and density of microsclerotia was high (r = 0.81, P < 0.01). Distribution of Verticillium wilt was aggregated in a majority of the pepper fields surveyed, but the degree of aggregation varied. Vegetative compatibility group (VCG) characterization of 67 isolates of V. dahliae indicated that 67% belonged to VCG 2, 22% to VCG 4, and 11% to a new group, designated VCG 6. The pathogenicity of isolates of V. dahliae from bell pepper and tomato plants was tested by inoculating 1-month-old bell pepper (cv. Cal Wonder) and tomato (cv. EP 7) seedlings and incubating the inoculated plants in the greenhouse. Seedlings of bell pepper were susceptible only to the isolates of V. dahliae from pepper, whereas seedlings of tomato were susceptible to both pepper and tomato isolates. Pepper isolates belonging to VCG 2, VCG 4, and VCG 6 were highly pathogenic to bell pepper and chili pepper. Temperatures between 15 and 25°C were optimal for mycelial growth of a majority of isolates of V. dahliae. Molecular characterization of pepper isolates of V. dahliae using a polymerase chain reaction (PCR)-based random amplified polymorphic DNA (RAPD) technique revealed minor variation among these isolates, but unique polymorphic banding patterns were observed for isolates belonging to VCG 6. Verticillium wilt of pepper is a major production constraint in the central coast of California. More aggressive isolates of V. dahliae may have been selected in this region as a result of intensive cropping practices.
Physiologic Specialization of Puccinia triticina on Wheat in the United States in 2001
Authors: Kolmer J. A. , Long D. L. , Kosman E. , Hughes M. E.
Published: May 2007

Collections of Puccinia triticina were obtained from rust-infected wheat leaves by cooperators throughout the United States and from surveys of wheat fields and nurseries in the Great Plains, Ohio Valley, Gulf Coast, California, Pacific Northwest, and Atlantic Coast States in order to determine the virulence of the wheat leaf rust fungus in 2001. Single uredinial isolates (477 in total) were derived from the wheat leaf rust collections and tested for virulence phenotype on lines of Thatcher wheat that are near-isogenic for leaf rust resistance genes Lr1, Lr2a, Lr2c, Lr3, Lr9, Lr16, Lr24, Lr26, Lr3ka, Lr11, Lr17, Lr30, LrB, Lr10, Lr14a, and Lr18. The isolates also were tested for virulence on adult plants with leaf rust resistance genes Lr12, Lr13, Lr22a, Lr22b, Lr34, Lr35, and Lr37. In the United States in 2001, 44 virulence phenotypes of P. triticina were found. Virulence phenotype MBDS, which is virulent to resistance gene Lr17, was the most common phenotype in the United States. MBDS was found in the Southeast, Great Plains, and Ohio Valley regions. Virulence phenotype THBJ, which is virulent to Lr16 and Lr26, was the second most common phenotype, and occurred almost exclusively in the north-central Great Plains region. Phenotype MCDS, which is virulent to Lr17 and Lr26, was the third most common phenotype and was found primarily in the Southeast, Ohio Valley, and Great Plains regions. The Southeast and Ohio Valley regions differed from the Great Plains region for predominant virulence phenotypes, which indicate that populations of P. triticina in those areas are not closely connected. The northern and southern areas of the Great Plains region differed for phenotypes with virulence to Lr16; however, the two areas had other phenotypes in common. Virulence to the adult plant resistance genes Lr35 and Lr37 was detected for the first time in North America in the MBDS, MCJS, and MCDS phenotypes.
Incidence and Survival of Cylindrocladium parasiticum in Peanut Seed
Authors: Glenn D. L. , Phipps P. M. , Stipes R. J.
Published: May 2007

Sixty-three commercial seed lots of peanut produced in Virginia were examined for the presence of seed with speckled testae. Speckled seed were present in seed lots from the 1998, 1999, and 2000 growing seasons at average rates of 3, 1.2, and 0.6%, respectively. Speckled and normal seed from 19 seed lots were assayed on a medium selective for C. parasiticum. The fungus was isolated from speckled seed at rates ranging from 40 to 96%. C. parasiticum was isolated only from a single normal seed from one seed lot. The pathogen was recovered at high rates from speckled seed immediately after pods had been dried in commercial drying trailers at temperatures up to 35°C. Ambient temperatures during winter seed storage that fluctuated from -10 to 28°C in 1999 and -8 to 33°C in 2000 greatly reduced pathogen recovery in speckled seed stored for 16 or 24 weeks. In field plots with naturally infested soil, the number of speckled seed harvested was directly correlated to the number of symptomatic plants in plots on 29 September. Based on this finding, the harvest of seed peanuts in areas of a field with high incidence of Cylindrocladium black rot (CBR) should be avoided. Adoption of this policy is expected to lower the number of speckled seed entering commercial seed lots and reduce the risk for spread of CBR.
First Report of Tomato infectious chlorosis virus in Tomato in Indonesia
Authors: Verhoeven J. Th. J. , Willemen T. M. , Roenhorst J. W. , van der Vlugt R. A. A.
Published: May 2007

In 2002, a breeding company submitted several samples of tomato (Lycopersicon esculentum) for diagnosis. Samples originated in Indonesia and were taken from protected and nonprotected crops. Plants exhibited severe chlorosis on fully expanded leaves, while young leaves were symptomless. Symptoms resembled those of the criniviruses Tomato chlorosis virus (ToCV) and Tomato infectious chlorosis virus (TICV). Moreover, large numbers of whiteflies, potential vectors of these viruses, had been observed at the plots with symptomatic plants. A reverse transcription-polymerase chain reaction (RT-PCR) with specific primers for TICV (1) yielded amplicons of the expected size of approximately 500 bp for all samples. One of the amplicons was sequenced (Genbank Accession No. AY221097) and revealed more than 98.9% identity to six isolates of TICV in NCBI Genbank. cDNA synthesis using the universal crinivirus primer HSP_M2-DW (5′ -TCRAARGTWCCKCCNCCRAA-3′) followed by PCR with a ToCV specific primerset (ToCV-UP 5′-TCATTAAAACTCAATGGGACCGAG-3′ and ToCV-DW 5′-GCGACGT AAATTGAAACCC-3′) was negative in all cases. Grafting of symptomatic shoots onto healthy tomato seedlings of cv. Money-maker showed transmission of the virus, as chlorosis appeared on fully expanded leaves of lateral shoots after 6 weeks. The presence of TICV in the graft-inoculated plants was confirmed by RT-PCR. Furthermore, mechanical inoculation to a range of herbaceous test plants did not evoke any virus symptoms, indicating the absence of mechanically transmissible viruses. Although other nonmechanically transmissible viruses cannot be fully excluded, the results together with the symptoms observed, indicate that TICV is the cause of the disease. TICV has been reported from Greece, Italy, Japan, Spain, and the United States, but to our knowledge, this is the first report of TICV in Indonesia.

Reference: (1) A. M. Vaira et al. Phytoparasitica 30:290, 2002.
First Report of a Blight Caused by Rhizoctonia solani on Anubias heterophylla in Italy
Authors: Garibaldi A. , Minuto G. , Nicoletti R. , Gullino M. L.
Published: May 2007

Anubias heterophylla Engler, which is used in aquariums, is a species in the Araceae family native to western tropical Africa. A few nurseries in Italy produce plants for this market. During the spring of 2002, symptoms of blight were observed on Anubias plants grown in an ebb and flow soilless media system in a nursery in Sardinia, Italy. Approximately 10% of the plants were infected. Symptoms initially developed as water-soaked, zonate lesions on the base of stems. Symptoms progressed rapidly and affected the entire plant. Eventually the plant collapsed. The growing conditions (soilless cultivation, high plant density, temperatures at 22–24°C, and 95 to 98% humidity) were conducive to disease development. Isolations from infected leaf and stem tissue on potato dextrose agar (PDA) with streptomycin sulphate at 100 mg/l consistently yielded a fungus with mycelial and cultural characteristics of Rhizoctonia solani Kühn (2). The fungus was characterized as R. solani AG-IV based on hyphal anastomosis with several AG-IV tester isolates (1). Pathogenicity tests were conducted by placing 5-day-old mycelial plugs grown on PDA at the base of healthy A. heterophylla stems and maintaining the plants in a dew chamber at 18 to 22°C. After 7 days, symptoms of basal rot were observed on stems of inoculated plants, and the entire plants were wilted. Plants not inoculated remained healthy. Rhizoctonia solani AG-IV was reisolated from all inoculated plants. The pathogenicity test was repeated. To our knowledge, this is the first report of R. solani on A. heterophylla. Since there are only a few nurseries that grow Anubias, the economic impact of the disease in Italy is minimal.

References: (1) J. R. Parmeter et al. Phytopathology, 59:1270, 1969. (2) B. Sneh et al. Rhizoctonia Species: Taxonomy, Molecular Biology, Ecology, Pathology and Disease Control. Kluwer Academic Publishers, Dordrecht, the Netherlands 1996.
Cucumber mosaic virus Diagnosed in Desert Rose in Florida
Authors: Baker C. A. , Achor D. , Adkins S.
Published: May 2007

Desert rose (Adenium obesum (Forssk) Roem. & Schult.) is a member of the family Apocynaceae and characterized by fleshy leaves and stems and colorful flowers. This popular, exotic ornamental, originally from southeastern Africa, is propagated vegetatively and is a perennial in warm climates. Virus-like foliar symptoms, including a mosaic with dark green islands surrounding the veins and chlorosis on the leaf margins, were observed on desert rose samples from two southwest Florida nurseries in November 2002. Cucumber mosaic virus (CMV) was identified in symptomatic plants by serological testing for the presence of CMV coat protein with a commercially available ImmunoStrip test (Agdia, Elkhart, IN). A third sample expressing similar symptoms was observed in southeastern Florida in February 2003. The presence of CMV was confirmed by serological detection with a commercially available double-antibody sandwich enzyme-linked immunosorbent assay (Agdia). An agent was mechanically transmitted from the third sample to Chenopodium quinoa, resulting in the formation of chlorotic local lesions. Examination of inoculated C. quinoa leaves by double-stranded (ds) RNA analysis and electron microscopy (leaf dips) revealed the presence of a typical cucumovirus dsRNA profile and spherical virions ~28 nm in diameter, respectively, providing additional confirmation of a CMV infection. A possible satellite RNA of ~350 nucleotides was also observed by dsRNA analysis. To our knowledge, this represents the first report of CMV infection of desert rose.
Toxoflavin Produced by Burkholderia glumae Causing Rice Grain Rot Is Responsible for Inducing Bacterial Wilt in Many Field Crops
Authors: Jeong Yeonhwa , Kim Jinwoo , Kim Suhyun , Kang Yongsung , Nagamatsu Tomohisa , Hwang Ingyu
Published: May 2007

Severe wilt symptoms similar to bacterial wilt caused by Ralstonia solanacearum were observed in tomato, hot pepper, eggplant, potato, perilla, sesame, and sunflower in 2000 and 2001 in Korea. From diseased crops at 65 different locations, we obtained 106 isolates that produced green pigment on CPG medium; 36 were isolated from discolored rice panicles. The causal pathogen was identified as Burkholderia glumae based on its biochemical characteristics, fatty acid methyl ester analysis, and 16S rRNA gene sequence. Nine representative isolates produced toxoflavin, as determined by electrospray ionization mass spectrometry using a direct inlet system and TLC analyses, and caused bacterial wilt on tomato, sesame, perilla, eggplant, and hot pepper. However, BGR12, a wild-type isolate lacking toxoflavin production and toxoflavin-deficient mutants generated by Tn5lacZ failed to cause bacterial wilt on those five field crops. Cells of B. glumae and synthetic toxoflavin caused wilt symptoms on field crops, demonstrating a lack of host specificity. Synthetic toxoflavin caused wilt symptoms on tomato, sesame, perilla, eggplant, and hot pepper at 10 μg/ml concentration 1 day after treatment. This is the first report of bacterial wilt on various crops caused by B. glumae, and our results clearly demonstrate that toxoflavin is a key factor in wilt symptom development.
Uniformity of Strawberry Yield and Incidence of Botrytis Fruit Rot in an Annual Production System
Authors: MacKenzie S. J. , Xiao C. L. , Mertely J. C. , Chandler C. K. , Martin F. G. , Legard D. E.
Published: May 2007

A plant yield and disease incidence uniformity trial was conducted to provide information concerning the efficiency and precision of field trials used to evaluate Botrytis fruit rot control methods on strawberry. Fruit yield and Botrytis fruit rot incidence were recorded for individual strawberry plants of cultivars Sweet Charlie and Camarosa grown in an annual production system over two growing seasons. A nested analysis of variance model was used to measure plot edge effects and to obtain variance components to describe the relationship between plot size and plot variance. Mean seasonal yield for Sweet Charlie was 599 g/plant and for Camarosa 972 g/plant. Mean seasonal fruit rot incidence was 10.3% for Sweet Charlie and 3.0% for Camarosa. Plants growing on the edge of plots next to aisles had higher yields (637 versus 577 g/plant for Sweet Charlie and 1047 versus 923 g/plant for Camarosa), but there was no edge effect for disease incidence. Smith's equation was used to determine the relationship between plot size and plot variance within mulched beds. Smith's index was relatively high for yield (0.92 and 0.95) and Botrytis fruit rot incidence (0.91 and 0.69) for Sweet Charlie and Camarosa, respectively. This suggests a relatively uniform distribution of seasonal yield and disease incidence among plants within beds. Using plot variances estimated from Smith's equation, the power of hypothesis tests to discriminate hypothetical treatment effects of different magnitudes was examined for each cultivar. Power analysis suggests that treatment effects ranging from 11.3 to 21.3% of the mean seasonal yield observed for Sweet Charlie and 8.6 to 16.5% of the mean seasonal yield observed for Camarosa can be detected with a power of 0.80 using four replicates of each treatment group and plot sizes ranging from 32 to eight plants/plot. For Botrytis fruit rot incidence, a power of 0.80 is achieved with treatment differences ranging from 24.9 to 44.1% of mean seasonal Botrytis fruit rot incidence for Sweet Charlie and from 44.1 to 64.9% of the mean observed for Camarosa using plot sizes ranging from 32 to 8 plants/plot. Before planting, the crown diameter and leaf number of transplants were recorded. There was no consistent significant correlation between any of these growth traits and seasonal yields or Botrytis fruit rot incidence. However, there was a consistent positive correlation for both cultivars between yield and crown diameter and also yield and leaf number during the months of December and January in the early part of the season (0.1513 ≤ r ≤ 0.314 for crown diameter and 0.106 ≤ r ≤ 0.264 for leaf number).