bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of the Sweet Cherry Isolate of Plum Pox Potyvirus
Authors: Crescenzi A. , d'Aquino L. , Comes S. , Nuzzaci M. , Piazzolla P. , Boscia D. , Hadidi A.
Published: May 2007

An isolate of plum pox potyvirus from sweet cherry (PPV-SwC) in southern Italy was investigated. The isolate was mechanically or graft transmissible to different Prunus and Nicotiana spp. but not to Chenopodium spp. It was transmitted also by Aphis fabae and Myzus persicae in a nonpersistent manner. Restriction fragment length polymorphism analysis indicated and nucleotide sequencing confirmed that the isolate lacks AluI and RsaI sites in the C-terminal region of the coat protein (CP) gene. Western immunoblot results showed that the PPV-SwC CP has an electrophoretic mobility similar to that of strain PPV-D and faster than that of strain PPV-M. Double-antibody sandwich indirect enzyme-linked immunosorbent assay of the CP showed that PPV-SwC, although reacting with universal monoclonal antibodies to PPV, failed to react with antibodies specific to strains M and D. Results indicate that PPV-SwC is different from conventional strains of PPV but closely related to the sour cherry isolate of PPV from Moldova.
Conidial Germination and Appressorium Formation ofColletotrichum coccodeson Tomato Foliage
Authors: Byrne J. M. , Hausbeck M. K. , Hammerschmidt R.
Published: May 2007

Conidial germination and infection processes of Colletotrichum coccodes were quantified on foliage of processing tomatoes (Lycopersicon esculentum Mill.). The abaxial surface of two opposing terminal leaflets removed from a fully expanded leaf at the 4th to 5th node was inoculated with 10-μl droplets of C. coccodes conidial suspension. Leaflets were incubated for 2 to 24 h in 2-h intervals at 25°C under high relative humidity. Explants with the conidial droplet were fixed, cleared, and preserved for microscopic observation. The percentage of germinated conidia and those with unmelanized and melanized appressoria was determined for each leaf disk. Conidial germination increased linearly with time (R2= 0.73) (P = 0.001), maximizing (68.3%) 24 h after inoculation. The percentage of germinated conidia with unmelanized appres-soria peaked 6 h after inoculation (38.3%). Melanized appressoria formation followed a linear trend (R2= 0.74) (P = 0.001), maximizing (62.0%) 24 h after inoculation. Infection vesicles were produced in 2.7% of conidia by 22 h, indicating successful infection.
Genetics of Leaf Rust Resistance in Canadian Spring Wheats AC Domain and AC Taber
Authors: Liu J. Q. , Kolmer J. A.
Published: May 2007

The hard red spring wheat cultivar AC Domain and the Canada Prairie Spring wheat AC Taber have recently been licensed and released in western Canada and are resistant to leaf rust caused by Puccinia recondita f. sp. tritici. To determine the genetic basis of this resistance, the two cultivars were crossed with the leaf rust susceptible wheat Thatcher (Tc), and F1 plants were backcrossed to Thatcher. F2 families from Tc*2/AC Domain and AC Taber/Tc*2 were tested with isolates of P. recondita f. sp. tritici as seedlings in the greenhouse and as adults in the field rust nursery. Segregation of BC1F2 families indicated that AC Domain had seedling resistance genes Lr10 and Lr16, and the adult plant gene Lr34. AC Domain was also hypothesized to have the adult plant gene Lr12 based on infection types with P. recondita f. sp. tritici isolates that differed for virulence to Lr12. The effective field leaf rust resistance of AC Domain was conditioned by Lr16 and Lr34. Segregation of BC1F2 families and infection types of BC1F3-derived BC1F4 plants indicated that AC Taber had Lr14a for seedling resistance, the adult plant gene Lr13, plus an additional uncharacterized adult plant resistance gene currently designated as LrTb.
Effects of Herbicides on Sclerotinia Crown and Stem Rot of Alfalfa
Authors: Reichard S. L. , Sulc R. M. , Rhodes L. H. , Loux M. M.
Published: May 2007

This study was conducted to determine whether herbicides and adjuvants registered for poste-mergence use in alfalfa have an effect on Sclerotinia crown and stem rot (SCSR). In a controlled environment, disease severity index (DSI) of alfalfa seedlings was reduced by pronamide and 2,4-DB compared with the untreated control, whereas bromoxynil and 13% sethoxydim + petroleum-based adjuvant (PBA) increased DSI. In the field, disease severity in all herbicide treatments was similar to that in untreated alfalfa. In a second controlled-environment study, pronamide and 2,4-DB reduced DSI compared with the no herbicide control when seedlings were inoculated 1 day after herbicide application, but this protective effect was not observed when seedlings were inoculated 8 days or longer after herbicide application. The results demonstrate that several herbicides are capable of suppressing or enhancing SCSR severity in a controlled environment if seedling inoculation occurs soon after herbicide application; however, the residual effect of these herbicides on SCSR appeared to be much shorter than the 4- to 6-week infection period occurring in the field.
Epiphytic Populations of Xanthomonas campestris pv. vesicatoria on Pepper: Relationships to Host-Plant Resistance and Exposure to Copper Sprays
Authors: Pernezny Ken , Collins Janice
Published: May 2007

Epiphytic populations of Xanthomonas campestris pv. vesicatoria were monitored on leaves and in buds of resistant and susceptible pepper cultivars over five seasons. Epiphytic populations were higher on the susceptible cultivar Jupiter than on the resistant cultivar Boynton Bell in four of the five seasons. In copper-sprayed plots, populations in buds of Jupiter plants were consistently higher than on leaves. In one test, copper sprays reduced X. campestris pv. vesicatoria populations by 99% on leaves, compared with only a 51% reduction in buds. In another test on a commercial pepper farm, no differences were found between populations on resistant and susceptible plants spaced as close as 1.2 m. However, combined data on buds for the three cultivars showed populations were higher than those on leaves on three of four sampling dates. These differences were attributed to the heavy use of copper on this farm.
Outbreak of Ergot (Claviceps purpurea) in Iowa Barley, 1996
Authors: Munkvold G. P. , Carson T. , Thoreson D.
Published: May 2007

An outbreak of ergot, caused by Claviceps purpurea, occurred in barley (Hordeum vulgare) grown in northeastern Iowa and southwestern Wisconsin in 1996. In a nine-county area of intensive dairy production in Iowa, approximately 40% of the barley hectarage (approximately 1,200 ha) was affected by the disease. Several cultivars were affected, including Robust, Excel, and Chilton, and no differences in ergot contamination levels were observed among cultivars. Barley samples examined by the Iowa State University Seed Science Center averaged 0.2% ergot by weight, with a maximum of 0.53%. Prolonged cool, wet weather during heading and greater barley planting than usual contributed to the high incidence of infection, but other influential factors have not been identified. Symptoms were not noticed in barley in the field and much of the infested grain was fed to cattle (primarily dairy cows), resulting in a considerable incidence of ergotism. An estimated 1,000 animals displayed symptoms of ergotism, manifested as loss of milk production and hyperthermia. Approximately 10 to 15 animals died or were destroyed. Ergot also was prevalent in forage grasses, including brome (Bromus spp.), Kentucky bluegrass (Poa pratensis), orchardgrass (Dactylis glomerata), quackgrass (Agropyron repens), and timothy (Phleum pratense). Minor symptoms of ergotism were associated with consumption of infested hay and pasture grasses. Negligible incidences of ergot occur annually in small grains and forage grasses in Iowa; ergotism of this extent has not been observed for several decades. Crop rotation and early harvest of grass hay have been recommended for 1997 to prevent a recurrence of the disease.
Colletotrichum dematium: Causal Agent of a New Cowpea Stem Disease in South Africa
Authors: Smith J. E. , Aveling T. A. S.
Published: May 2007

During surveys of cowpea (Vigna unguiculata (L.) Walp.) fields in the Gauteng province, a destructive stem disease was observed. Stem symptoms began as tan brown discolorations that later spread, becoming dark purplish-brown. Sunken, necrotic lesions and small, black acervuli also were visible on the stems. Colletotrichum dematium (Pers.) Grove was consistently isolated from diseased material. Pathogenicity of an isolate of C. dematium from cowpea stems (deposited with the National Collection of Fungi, South Africa, designated PPRI 6121) was confirmed by inoculating stems of 20 cowpea seedlings with a 105 conidia per ml suspension. Inoculated plants were maintained in humidity chambers for 48 h and then returned to the greenhouse. After 7 days, symptoms resembling those observed in the field were apparent. C. dematium was reisolated from these plants and produced cultures identical to those of the original isolate. This is the first report of C. dematium on cowpea in South Africa.
An Anatomical Study of Prune Brown Line Disease and Immuno-localization of Tomato Ringspot Virus in Plum Bark
Authors: Kommineni K. V. , Ramsdell D. C.
Published: May 2007

Bark from the graft union of tomato ringspot virus (ToRSV) infected plum, symptomatic for brown line disease, showed anatomical changes characteristic of the wound response process. The wound tissue consisted of necrotic cells demarcated by pinkish purple necrophylactic periderm, whose function is to protect living tissues from detrimental effects associated with necrosing cells. However, formation of gray exophylactic periderm led to the sloughing off of the wound tissue and the necrophylactic periderm, resulting in discontinuity of the exophylactic periderm and secondary virus invasion into the wound site. The changes seen in the bark suggest that the hypersensitive response in plum rootstock bark to ToRSV is slow, allowing a systemic movement of the virus and development of a brown line (BL) along the scion and rootstock union. Necrophylactic periderm was not seen in the bark from the graft union of a healthy plum tree. In the graft union of a plum tree without a BL, but testing ToRSV-positive in the roots, localized areas of wound tissue with pinkish purple necrophylactic periderm developed only in the rootstock portion of the tree. Silver-enhanced protein A-colloidal gold immunolabeling was seen on the cell wall and in the cytoplasm of bark tissue from the BL region of scion and rootstock and leaves from the rootstock suckers.
SalmonellaContamination Associated with Bacterial Soft Rot of Fresh Fruits and Vegetables in the Marketplace
Authors: Wells J. M. , Butterfield J. E.
Published: May 2007

Wash water from 66% of 401 samples of fresh fruits and vegetables collected in the marketplace and affected by bacterial soft rot were positive for suspected strains of Salmonella, i.e., black, hydrogen sulfide-positive colonies on Salmonella-Shigella agar incubated for 24 h at 37°C. By comparison, 30% of 402 healthy samples were positive. Incidence of suspected Salmonella in broth enrichment cultures was 59% in 533 soft rotted samples and 33% in 781 healthy samples. Thirty percent of 166 representative strains of suspected Salmonella, selected at random from 20 different commodities, were confirmed to be Salmonella by physiological and serological tests. Adjusting incidence values accordingly, Salmonella contamination was potentially present in at least 18 to 20% of soft rotted samples and in 9 to 10% of healthy samples. Wash water from 120 paired healthy and soft rotted fruits and vegetables contained an average of 1.0 × 105and 3.7 × 106CFU/ml, respectively, of suspected Salmonella-a ratio of 1:37. Average concentrations of suspected Salmonella in enrichment cultures of healthy and soft rotted samples were 7.5 × 107and 2.7 × 109CFU/ml, respectively, also in the ratio of 1:37. Fresh potato, carrot, and pepper disks coinoculated with the soft rot bacterium Erwinia carotovora and with Salmonella typhimurium, and incubated for up to 72 h at room temperature, contained approximately 10 times the concentration of S. typhimurium as did disks inoculated with Salmonella alone. Disks coinoculated with Pseudomonas viridiflava and S. typhimurium contained approximately three times the Salmonella populations as disks inoculated with Salmonella alone.
Bacterial Streak and Bulb Rot of Onion: I. A Diagnostic Medium for the Semiselective Isolation and Enumeration of Pseudomonas viridiflava
Authors: Gitaitis R. , Sumner D. , Gay D. , Smittle D. , McDonald G. , Maw B. , Johnson W. C. , Tollner B. , Hung Y.
Published: May 2007

A semiselective, diagnostic agar medium (T-5) and low temperature incubation technique were developed for recovering Pseudomonas viridiflava from the environment or plant material. Medium T-5 contains the following per liter: NaCl, 5.0 g; NH4H2PO4, 1.0 g; K2HPO4, 1.0 g; MgSO4·H2O, 0.2 g; D-tartaric acid, 3.0 g; phenol red, 0.01 g; agar, 20.0 g; bacitracin, 10 mg; vancomycin, 6 mg; cycloheximide, 75 mg; novobiocin, 45 mg; penicillin G, 5 mg. The pH is adjusted to 7.4. Antibiotics are added aseptically after autoclaving. P. viridiflava recovery from artificially infested, field-soil (Tifton loamy-sand), with a cropping history of no onion production, was high, with a corresponding reduction of 99.99% of nontarget bacteria. However, soils from fields with a long history of onion production, near Vidalia, Georgia, contained significantly larger populations of background microflora that grew on medium T-5. Incubation at 5°C reduced contaminating microflora 1,000- to 10,000-fold with no reduction in recovery of the target organism. However, this low temperature incubation required an increased incubation period of 3 weeks and reduced the level of fluorescence of P. viridiflava.
Correlation of Haplotypes of a Fungal Plant Pathogen with their Respective Host Species of Origin
Authors: Garr Stephanie S. , Hughes Carolyn , Welch Jacqueline , Brown Scott A. , Perlin Michael H.
Published: May 2007

The anther smut fungus, Microbotryum violaceum, infects over 200 species of Caryophyllaceae (Pinks). However, limited published studies, as well as anecdotal evidence, suggest that each isolate of the fungus is restricted to one or a few species that it can productively infect. In the absence of physical differences, it would be useful to have molecular markers to identify individuals with specific host ranges prior to genetic analyses of host preference. With this purpose in mind, 17 isolates from eight different host species were characterized for differences in their respective γ-tubulin genes. The region of the gene including the sixth and seventh introns and some surrounding coding regions was amplified and sequenced and the results were analyzed phylogenetically. Despite the small sample size and the geographical distribution of their respective host plants, isolates from the same host species showed no differences in the DNA regions examined; isolates of closely related pathovars also grouped together. In contrast, relative to the corresponding regions from other pathovars, isolates from host species that were genetically or taxonomically more distant showed a marked number of differences in both introns and in the third (wobble) position of codons in the seventh exon. Thus, DNA sequence differences in this highly conserved gene may be used to distinguish isolates from different host species. Such information may prove useful as markers for the different formae speciales in future analyses of host preference.
Outbreak of Sugarcane Mosaic in Commercial Sugarcane Cultivar CP 72-2086, in Florida
Authors: Comstock J. C. , Mirkov T. E.
Published: May 2007

In May 1996, an outbreak of sugarcane mosaic virus (SCMV) was detected in Florida affecting a major commercial sugarcane (Saccharum spp. hybrid) cultivar, CP 72-2086. Identification of SCMV was confirmed by enzyme-linked immunosorbent assay (ELISA) with SCMV antiserum (ATCC no. PVAS 115), and by reverse transcription(RT)-PCR (1,2). The strain of SCMV was identified as E with an RT-PCR-based restriction fragment length polymorphism analysis (1). Although SCMV strain E has been detected in Florida for many decades, it had been confined primarily to S. officinarum clones, to occasional susceptible sugarcane clones in breeding programs, and to various grasses throughout the sugarcane production area. CP 72-2086 plus seven other sugarcane cultivars and 10 sorghum cultivars reacted similarly to inoculation with the isolate of SCMV found recently on CP 72-2086 and an isolate of SCMV collected in 1986. CP 72-2086 was released in 1982 and currently is the second most widely grown cultivar, constituting 18.0% of the commercial sugarcane area in Florida. At the epicenter of infection, located 11 km southeast of Canal Point, over 50% of CP 72-2086 plants had SCMV symptoms. The incidence of mosaic decreased rapidly away from the epicenter. No SCMV was observed in the western area of the sugarcane production area, west of South Bay, FL.

References: (1) T. E. Mirkov and J. E. Irvine. Sugar y Azucar 9:23, 1996. (2) G. R. Smith et al. Plant Dis. 78:557, 1994.
Isolation of Acremonium Species Causing Postharvest Decay of Peaches in Spain
Authors: Fernández-Trujillo J. P. , Martínez J. A. , Salmerón M. C. , Artés F.
Published: May 2007

Two Acremonium spp., A. tubakii and A. rutilum, were isolated from rotted peaches (Prunus persica (L.) Batsch ‘Miraflores’) after ripening at 15 and 20°C, respectively, for 10 days. Fruit harvested in September 1994 in Mula (Murcia) at a firm-ripe stage of maturity were either nontreated or washed with water at 18°C and sorted in a packing line. Sorted fruit were treated with an aqueous dilution of iprodione (Rovral 50% WP Rhône-Poulenc Agrochimie, Paris, France) at 2 g·liter-1, pH = 7, and 18°C for 5 min. Half of the iprodione-treated fruit were forced-air pre-cooled to reach 0°C at the endosperm in about 12 h. Isolations of fungi were made from subepidermic tissue of decay margins of fruit with potato dextrose agar (PDA). Fungal species were identified after axenic cultures were grown on PDA for 10 days at 30°C. Acremonium spp. were identified based on microscopic morphology of asexual reproduction structures, using taxonomic keys. No other fungi were isolated from fruit decayed by Acremonium spp. A. tubakii decayed 1.7% of the iprodionetreated and pre-cooled fruit ripened at 15 or 20°C and the fruit treated by iprodione without pre-cooling but ripened at 20°C. These fruit were completely decomposed and oozed liquid. Colonies of this species were light colored, with nonramified, nonseptate, and hyaline conidiophores. The one-cell, ovate, and hyaline conidia of the fungus were enclosed in slimy heads. A. tubakii did not cause any brown discoloration of the PDA media. A. rutilum affected 3.2% of the iprodione-treated fruit ripened at 20°C. In contrast to A. tubakii infection, A. rutilum affected only the surface of fruit, which remained dry. Cultures of A. rutilum were white to pink and the conidia were one-celled, ovate, and hyaline, forming a head on the tip of the nonramified conidiophores. Conidia were long, nonseptate, and distinct from the somatic hyphae. Acremonium spp. probably developed on injuries caused by handling and/or treatments, because these rots did not occur on untreated fruit. Rhizopus nigricans, and to a lesser extent other fungi such as Alternaria, Cladosporium, and Penicillium spp., also commonly caused decay of sampled fruit. A. tubakii is a ubiquitous soil fungus reported from various European countries. A. rutilum isolated from diseased apples were pathogenic upon reinoculation (1). Both fungi were not found in the Spanish type culture collection of 1990. Other Acremonium spp. have been identified in melon roots in Spain (2). To the best of our knowledge, this is the first report of Acremonium spp. causing decay of peach in Spain.

References: (1) C. Brooks et al. Phytopathology 4:403, 1914. (2) J. García-Jiménez et al. Plant Dis. 78:416, 1994.
Phytophthora Root and Crown Rot of Sage Caused by Phytophthora cryptogea in California
Authors: Koike S. T. , Henderson D. M. , MacDonald J. D. , Ali-Shtayeh M. S.
Published: May 2007

In 1996, commercial plantings of sage (Salvia officinalis) in the Salinas Valley in Monterey County, CA, were affected by a root and crown disease. Roots were necrotic, and crowns and lower stems turned black. Affected plants withered and died. A Phytophthora sp. was consistently isolated from roots and stems of the symptomatic plants. The species was identified as Phytophthora cryptogea based upon the formation of hyphal swellings, morphology of sporangia and oospores, and growth at cardinal temperatures (1). Pathogenicity of representative isolates was confirmed by applying 2 ml of a zoospore suspension (2.0 × 105 zoospores per ml) to roots and crowns of 3-month-old potted sage plants. After treatment, plants were placed for 24 h in shallow trays of water to saturate the root zone, then were removed from trays and incubated in a greenhouse. After 4 days, foliage of all inoculated plants began to wilt. After 7 days, plant crowns and stems turned black and the plants collapsed. P. cryptogea was reisolated and recharacterized from all plants. Control plants, which were treated with water and then handled in the same way as inoculated plants, did not develop any symptoms. The tests were repeated and the results were similar. This is the first report of P. cryptogea attacking commercial plantings of sage. The authors also detected this disease in experimental plantings of sage in Stanislaus County in 1990.

Reference: (1) D. C. Erwin and O. K. Ribeiro. 1996. Phytophthora Diseases Worldwide. American Phytopathological Society, St. Paul, MN.
Identification of a Gene Conferring High Levels of Resistance to Verticillium Wilt in Solanum chacoense
Authors: Lynch D. R. , Kawchuk L. M. , Hachey J. , Bains P. S. , Howard R. J.
Published: May 2007

Verticillium wilt (Verticillium albo-atrum) is an important disease affecting potato tuber yield and quality. In North America the major commercial cultivars are susceptible and management strategies for control of the pathogen rely mainly on soil fumigation and crop rotation. In this study 398 genotypes from accessions of Solanum berthaultii, S. chacoense, and S. tarijense were screened for resistance to Verticillium albo-atrum. Resistant genotypes were identified in all but two accessions; however, results indicate that tolerance is more common than resistance. We identified two genotypes in S. chacoense (PI 472819) that had low stem-colonization levels and also did not develop wilt symptoms when inoculated with V. albo-atrum. These genotypes and a susceptible genotype from PI 472810 (S. chacoense) were studied to determine genetic inheritance. Segregation ratios in F1, F2, and backcross populations indicated that resistance in one of the resistant genotypes (18-21R) was controlled by a single dominant gene. Transfer of the Vc gene to tetraploid germ plasm could provide effective and economical control of Verticillium wilt.
Epidemiology and Control of Citrus Greasy Spot on Valencia Orange in the Humid Tropics of Costa Rica
Authors: Hidalgo Herman , Sutton Turner B. , Arauz Felipe
Published: May 2007

An epidemiological study of Mycosphaerella citri, the cause of greasy spot of citrus, was conducted for 2 years at Finca 6 and El Parque, Costa Rica. Ascospores were the primary source of inoculum; only a few conidia were trapped during the study. Ascospores were trapped first during late April or early May. The spore discharge pattern was associated closely with seasonal rainfall distribution; in both years, the number of ascospores trapped increased rapidly through May, peaked during early June, declined rapidly through July, and were negligible during the rest of the year. Most ascospores were trapped during a 6- to 8-week period. Three principal discharge patterns were observed. One pattern, associated with rainfall, was characterized by the release of large numbers of ascospores within 1 h of the beginning of rainfall. Ascospore release often continued for several hours after the rainfall ended. A second discharge pattern was associated with dew. Large numbers of spores were trapped during periods when dew was heaviest (0200 to 0700 h). A third pattern consisted of a combination of the first two patterns (i.e., discharge during evening rain followed by a second discharge associated with dew). No relationship was found between different combinations of rainfall data and either the first or peak ascospore catch. Similarly, there was no consistent relationship between weekly percentages of leaves at different stages of decomposition and ascospore catch that could be used to predict the period of peak ascospore discharge. Weekly total number of leaves on the orchard floor was a better predictor of total ascospore catch. Two sprays of a copper fungicide reduced greasy spot incidence, severity, and defoliation compared to an unsprayed control. Oil, sprayed twice as a standard grower treatment, did not reduce disease incidence or severity compared to the unsprayed control.
Stability of Stagonospora nodorum Isolates from Perennial Grass Hosts after Passage Through Wheat
Authors: Krupinsky J. M.
Published: May 2007

Eleven isolates of Stagonospora nodorum from smooth brome, western wheatgrass, intermediate wheatgrass, Altai wildrye, basin wildrye, and an Agropyron cross were passed through wheat five times using detached leaf inoculations. Lesion length, which was used as a measure of adaptation and aggressiveness, did not increase after passage through wheat. When the wheat-isolate check was removed from the analyses, the cultivar × isolate interactions were nonsignificant, indicating a lack of specificity among the original isolates and isolates passed through wheat. Inoculation of wheat seedlings in a glasshouse confirmed the results obtained with the detached leaf inoculations. These isolates showed no progressive adaptation to wheat and no significant change in their aggressiveness. This indicates that since most isolates from perennial grass hosts produce small lesions on wheat and do not easily adapt to wheat, they apparently would not cause severe symptoms on wheat.
Effects of Temperature and Light on Germination of Urediniospores of the Pearl Millet Rust Pathogen, Puccinia substriata var. indica
Authors: Tapsoba H. , Wilson J. P.
Published: May 2007

Germination of urediniospores of Puccinia substriata var. indica was evaluated after 2, 4, 6, and 8 h of incubation in petri dishes containing 2% water agar under 10, 16, 20, 25, 30, and 35°C in light (1650 lux, cool white fluorescent), dark, alternate light-dark, and alternate dark-light. Less than 1% germination occurred at 35°C. At 30°C, percent germination did not significantly change after 4 h. At 10°C, percent germination increased with longer incubation. Under all illumination conditions, percent maximum germination after 4 to 8 h occurred at 20–25°C. Response surface analysis indicated that under all four illumination regimes, urediniospore germination greater than 90% occurs between 19 and 22°C after 6–7 h of incubation. Two hours of continuous light appeared to significantly delay germination, but exposure to light during the first hour of incubation was stimulatory when followed by 1 h dark.
A Flow Visualization Study of Spore Release Using a Wind Tunnel-Mounted Laser Light Sheet
Authors: Davis J. M. , Eisner A. D. , Wiener R. W. , Main C. E.
Published: May 2007

A phase Doppler anemometry system in combination with a laser light sheet was used in a low-speed recirculating wind tunnel to examine the flow field around an individual leaf. Turbulence similar to that encountered near the surface of the earth in a neutral stability boundary layer was generated using a grid at the upwind end of the wind tunnel test section. Individual healthy and diseased plant leaves were introduced into the tunnel with the leaf tip pointing downwind. The Mie-scattered radiation from the spores departing the diseased leaf was captured on videotape. Image processing software was used to enhance the visual quality of the individual frames from the videotape and to make spore velocity calculations. Three main vortex regions around the leaf were identified. The importance of these regions to the separation of the spores from the leaf surface and their subsequent downwind movement was analyzed.
Reverse-Transcription Polymerase Chain Reaction Detection of Citrus Tristeza Virus in Aphids
Authors: Mehta Prem , Brlansky R. H. , Gowda S. , Yokomi R. K.
Published: May 2007

A rapid and simple reverse-transcription polymerase chain reaction (RT-PCR) method was developed for the detection of citrus tristeza virus (CTV) in three aphid species. Seven CTV isolates from a worldwide isolate collection were used for aphid acquisition feeding by three aphid species. These included the most efficient CTV vector, the brown citrus aphid, Toxoptera citricida; the melon aphid, Aphis gossypii; and the green peach aphid, Myzus persicae, a non-vector for CTV. A short procedure for nucleic acid extraction from single or groups of aphids was developed. Nucleic acid extracts from 1, 3, 5, and 10 aphids with acquisition-access periods of 24 and 48 h were reverse transcribed and amplified using primers for the coat protein gene of the Florida B3 (T-36) isolate of CTV. PCR-amplified fragments of approximately 670 bp were obtained from all the isolates tested and the amplified product from the aphids fed on citrus infected with isolate B3 was confirmed as the CTV coat protein gene by digesting with various restriction enzymes. This technique will be useful in investigations of CTV-vector-plant interactions and CTV epidemiology.
Effects of Verticillium dahliae Infection of Cotton Plants (Gossypium hirsutum) on Potassium Levels in Leaf Petioles
Authors: DeVay J. E. , Weir B. L. , Wakeman R. J. , Stapleton J. J.
Published: May 2007

Two isolates of Verticillium dahliae, a black microsclerotial isolate and an isolate from potassium deficient cotton plants that forms white colonies on agar media, were examined for their effects on the potassium content of cotton plants. The potassium content of petioles from fully expanded leaves collected at random from branches 6 to 7 nodes below the terminal node were monitored during July and August in 1993 to 1995. Potassium contents of petioles from plants inoculated with V. dahliae did not differ significantly from plants injected with sterile water until the plants were nearing peak boll load. Both isolates caused a gradual development of potassium deficiency symptoms in leaves of inoculated plants and a decrease in petiole potassium, often accompanied by chlorosis and necrosis typical of Verticillium wilt. These results suggest that infection of cotton plants by V. dahliae causes an impairment in the uptake and translocation of potassium that is often associated with the development of potassium deficiency symptoms in leaves of plants with large boll loads.
First Report of Grapevine Kober Stem Grooving in the United States
Authors: Golino D. A. , Rowhani A. , Sim S. , Cunningham M. , Smith R.
Published: May 2007

The last decade has brought extensive new plantings of grapevines (Vitis vinifera L.) to California vineyards. In some vineyards, severe viruslike problems have been observed (2). To ascertain possible causal agent(s), extensive testing for grapevine viruses was initiated. Testing included a 2-year woody index on indicators V. rupestris cv. Saint George, LN 33, V. vinifera cv. Cabernet Franc, and Kober 5BB. To our knowledge, this is the first field survey for grape virus diseases in the United States that includes woody indexing on Kober 5BB, a relatively new indicator for the grapevine rugose wood diseases (1). A Sonoma County field selection of Sauvignon Blanc grafted to the rootstock Freedom was included in these tests; the 2-year-old vines exhibited stunting, leaf rolling, leaf yellowing, wood necrosis, and pitting symptoms at the graft union. When indexed on the four indicators, the following disease symptoms were observed: stem pitting on V. rupestris; corky bark on LN 33; leafroll on Cabernet Franc; and stem grooving on Kober 5BB. An enzyme-linked immunosorbent assay confirmed the presence of grapevine leafroll-associated viruses 2, and 3, as well as Grapevine Virus A, which is associated with Kober stem grooving. The Sauvignon Blanc selection appears to be infected with several grapevine viruses, as is often the case when virus symptoms in vineyards are severe. Among these disease agents, only Kober stem grooving is reported to cause the severe pitting and grooving symptoms observed on the indicator Kober 5BB (1). This is the first report of Kober stem grooving in the United States.

References: (1) R. Garau et al. Vitis 33:161, 1994. (2) D. A. Golino. Am. J. Enol. Vitic. 44:148, 1993.
First Report of the A2 Mating Type of Phytophthora infestans on Potato in Hungary
Authors: Bakonyi J. , Érsek T.
Published: May 2007

Severe symptoms of potato late blight were observed in July 1996 on potato (Solanum tuberosum L.) cv. Desirée grown on a farm in western Hungary. Isolation was made directly from diseased leaf tissues onto selective pea-agar medium. A recovered isolate, H2a, was identified as Phytophthora infestans (Mont.) de Bary on the basis of Koch's postulates and morphological characteristics of the fungus. Pairing of H2a with isolates of known mating types, A1 and A2 from Germany, revealed that it represents the A2 mating type. After a 2-week incubation on pea-agar medium at 20°C, oospores formed in abundance in the region of contact between the colonies of H2a and the A1 mating type isolate. After extended incubation scattered formation of gametangia was observed when isolate H2a had been paired with itself or with the A2 mating type isolate. The same phenomenon of presumed self fertilization also took place when single, zoospore-derived colonies of H2a were combined with one another or with the known A2 isolate. Of an incomplete set of potato differentials, leaves of potato genotypes r, R2, R3, R4, R1.2.3.4, R7, R8, and R11 were all susceptible to infection with a zoospore suspension of the isolate H2a. The complex virulence phenotype of H2a, its tolerance to metalaxyl in agar cultures and on leaf disks (EC50 >100 mg liter-1), and its A2 mating type behavior collectively suggest that H2a represents a genotype that recently has been introduced into Hungary.
Onion Leaf Blight Caused by Xanthomonas campestris: Alternative Hosts and Resistant Onion Genotypes
Authors: O'Garro Leonard W. , Paulraj Litta P.
Published: May 2007

Tomato (Lycopersicon esculentum), pepper (Capsicum annuum), corn (Zea mays), French bean (Phaseolus vulgaris), soybean (Glycine max), winged bean (Psophocarpus tetragonolobus), lima bean (Phaseolus lunatus), field pea (Pisum sativum), moth bean (Phaseolus aconitifolins), and heliconia (Heliconia bihai) were evaluated as alternative hosts of Xanthomonas campestris, the causal agent of a leaf blight of onion (Allium cepa). On legumes, bacterial growth occurred in planta, and visible disease symptoms developed. From 19 commercial onion genotypes screened for leaf blight resistance, two cultivars, H-942 and H-508, were generally free of symptoms and had restricted bacterial growth in planta. These are the first known reports on alternative hosts of the bacterium and on resistance in onion to leaf blight.
Effect of Cluster Tightness on Botrytis Bunch Rot in Six Chardonnay Clones
Authors: Vail M. E. , Wolpert J. A. , Gubler W. D. , Rademacher M. R.
Published: May 2007

Cluster tightness was measured and Botrytis bunch rot was evaluated for six Chardonnay clones in each of two trials, one cane-pruned and the other spur-pruned. In both locations, University of California (UC) Foundation Plant Materials Service (FPMS) clone 4 was most compact and FPMS 15 was the least compact (P < 0.01). Cluster tightness among the six clones, measured by the UC Firmness Tester Method, ranged from 0.0028 newtons (N) for clone 15 to 0.0112 N for clone 4. Cluster tightness was positively correlated with cluster weight. Botrytis bunch rot development was greater in the cane-pruned trial than in the spur-pruned trial. In the cane-pruned trial, disease incidence was greatest in FPMS 16 (81.5%) and least in clone 15 (44.5%; P< 0.025), while disease severity did not differ significantly. Neither incidence nor severity were significant in the spur-pruned trial. Clone 15, the clone with the least compact clusters, had the lowest disease severity levels.
The Impact of Herbicides on the Incidence and Development of Rhizoctonia solani-Induced Cotton Seedling Damping-off
Authors: Heydari A. , Misaghi I. J.
Published: May 2007

The impact of three pre-plant herbicides, trifluralin, pendimethalin and prometryn, on the incidence and the development of Rhizoctonia solani-induced cotton seedling damping-off was investigated in the controlled environmental chamber and in the field. In the controlled environmental chamber experiments, trifluralin, pendimethalin and prometryn were applied to the soil at 1.8, 2.4, and 3.6 μg a.i. g-1 soil, respectively (equivalent to the respective recommended field concentrations of 0.7, 0.9, and 1.3 kg a.i. ha-1). In the controlled environmental chamber experiments, where soil was infested at planting, application of prometryn, but not pendimethalin or trifluralin, to the soil caused a significant (P < 0.05) increase in damping-off incidence. In controlled environmental chamber experiments where soil was infested after emergence, damping-off increased significantly (P < 0.05) in the presence of pendimethalin and prometryn, but not trifluralin. In a field experiment conducted in Safford, Arizona, pre-plant application of pendimethalin or prometryn, but not trifluralin, caused significant (P < 0.05) increases in disease incidence. In another field experiment in Tucson, Arizona, a significant (P < 0.05) increase in disease incidence was observed in plots treated with prometryn, but not in plots treated with pendimethalin or trifluralin. In both controlled environmental chamber and field experiments, application of selected herbicides had significant effects on disease development as judged by the slope of disease progress curves.
A Multivirus Epidemic of Tomatoes in Alabama
Authors: Sikora Edward J. , Gudauskas Robert T. , Murphy John F. , Porch Daniel W. , Andrianifahanana Mahefa , Zehnder Geoffrey W. , Bauske Ellen M. , Kemble Joseph M. , Lester Donald F.
Published: May 2007

During 1992, a multivirus epidemic reduced tomato production by as much as 25% in the major tomato-growing region of Alabama. Estimated yield losses of 100% resulted from the epidemic in over 250 ha in two counties of North Alabama. Cucumber mosaic cucumovirus (CMV), alone or in combination with potato potyvirus Y (PVY) and/or tobacco etch potyvirus (TEV), was responsible for the crop failure. CMV was detected alone or in combination with PVY and/or TEV in over 70% of the samples tested and was present in 90% of the fields surveyed. In 1993, 21 tomato fields were monitored weekly from transplanting through harvest for CMV, PVY, TEV, tobacco mosaic tobamovirus, and tomato spotted wilt tospovirus. All 5 viruses were detected, with CMV occurring most frequently. Incidence of CMV at the 61% level or higher was found in 16 of the 21 fields surveyed. Tomatoes transplanted in April and May were least effected and had relatively low virus incidence until late in their development. Tomatoes transplanted in June and July were infected at an earlier age, had the highest virus incidence, were the most severely affected, and suffered the greatest loss in yield. In 1994,Aphis gossypii, the cotton aphid, was the most common virus vector found during an aphid monitoring/virus spread study. Populations of A. gossypii peaked in late June, immediately preceding a period of rapid CMV incidence and spread.
First Report of Mycoleptodiscus terrestris Infecting Forage Legumes and Soybeans in Wisconsin
Authors: Smith R. R. , Grau C. R. , Gray L. E.
Published: May 2007

Soilborne plant pathogens are regarded as important causes of failures of newly established and mature stands of forage legumes and reduced yield of soybean (Glycine max (L.) Merr.) in the North Central Region of the U.S. Birdsfoot trefoil (Lotus corniculatus L.) plants exhibited decaying roots and stems in yield trials in 1994 and 1995 at the Arlington Agricultural Research Station, Arlington, WI. After first harvest, over 40% of the plants failed to produce regrowth or regrowth was extremely slow. Dark brown lesions were evident on root and crown tissue and occasionally spread to newly initiated stem tissue. A fungus resembling Mycoleptodiscus terrestris was isolated from birdsfoot trefoil by placing surface-disinfested plant tissue on potato dextrose agar (PDA) amended with 10 ppm chlorotetracycline or tetracycline and 100 μl liter-1 of tergitol. Isolates of M. terrestris produced dark green mycelium and black scerotia on PDA. These same isolates also produced conidia with characteristics similar to those described by Ostazeski (1) for M. terrestris when cultures were grown on gamma ray-sterilized chrysanthemum leaf pieces positioned on the surface of 2% water agar on petri dishes. The setaed conidia were generally two-celled and oval, and measured 24 to 30 × 4.5 to 7.4 μm. Isolates were also obtained from soybean plants that expressed a premature decline symptom at the R6 to R7 growth stage. Soybean plants in two commercial fields initially expressed curled leaves followed by defoliation. Lower stems expressed a gray-tan discoloration of the cortical tissue. Alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), birdsfoot trefoil, and soybean were inoculated with isolates of M. terrestris. All crop species expressed symptoms and M. terrestris was recovered from symptomatic tissue. M. terrestris isolates have also been baited from other soils from southern Wisconsin with red clover, birdsfoot trefoil, and soybean. Although recognized in states south of Wisconsin, M. terrestris has not been implicated previously in poor health of forage legumes and soybeans in Wisconsin. This report provides evidence that M. terrestris inhabits agricultural soils farther north than previously recognized.

References: (1) S. A. Ostazeski. 1967. Mycologia 59:970-975.
Occurrence of Wilt Disease Caused by Verticillium dahliae on Ailanthus glandulosa in Greece
Authors: Skarmoutsos G. , Skarmoutsou H.
Published: May 2007

Ailanthus glandulosa is an introduced tree species in Greece used as ornamental and is considered resistant to both fungal and insect attacks. However, since 1992, a great number of A. glandulosa plants of different ages and in different parts of northern Greece have been dying. The phenomenon appeared either in single trees or in groups, and the number of affected plants increased from year to year. The symptoms were characteristic of a wilt disease. Dieback started on one or more branches and gradually spread, or whole trees were affected from the beginning. Death may occur during spring when trees do not resume their activity or later in the summer. Leaves wilt, turn yellow and fall in a short time. Trees may die in 1 to 3 years depending on their age. In cross sections of branches a continuous discoloured ring or arc was present in the outermost sapwood. Isolations made from dying trees from 25 different locations have yielded V. dahliae, a pathogen known to cause vascular wilt on many plant hosts, including Ailanthus (1). Isolations made from healthy trees did not yield the fungus. Abundant mycelium developed in the host vessels of infected trees; the hyphae were cylindrical, hyaline, and septate. On malt agar fungal cultures developed quickly and were initially a whitish to cream color that later turned black due to the formation of microsclerotia. In culture, microsclerotia started to form centrally and were dark brown to black, consisting of swollen globular cells that formed irregular masses variable in shape. The fungus also produced abundant verticillate conidiophores with phialides and conidia. This is a first report of Verticillium wilt on A. glandulosa in Greece.

Reference: (1) G. Arnaud et al. Rev. Pathol. Veg. Entomol. Agric. Fr. 17:227, 1930.
Mating Type Distribution and Fertility Status of Magnaporthe grisea Populations from Various Hosts in India
Authors: Viji G. , Gnanamanickam S. S.
Published: May 2007

Production of perithecia, asci, and ascospores by Indian isolates of Magnaporthe grisea is rare and has not been found among the Southern Indian isolates of the blast pathogen. From among 138 monoconidial isolates that infect rice and other hosts, we now report the distribution of mating types (MAT1-1 and MAT1-2) of M. grisea in finger millet and paragrass (Brachiaria mutica)-infecting isolates. Twenty-eight of the 96 finger millet isolates, 5 of the 16 paragrass isolates, and none of the 26 rice isolates produced fertile perithecia in laboratory matings with fertile testers. Backcrosses of ascospore progenies to the parental M. grisea isolate but not to the tester strain resulted in fertile perithecial formation, and a further backcrossing scheme indicated definite fertility patterns of Mendelian inheritance in M. grisea.
Effect of a Leaf Spot Disease Caused by Alternaria alternata on Yield of Sunflower in Greece
Authors: Lagopodi Anastasia L. , Thanassoulopoulos Costas C.
Published: May 2007

Field experiments were conducted during the 1989 to 1993 growing seasons in order to determine the effect of natural infections of Alternaria alternata on yield of sunflower (Helianthus annuus). Number of seeds produced per head and seed weight were reduced by 16 to 65% and 15 to 79%, respectively. Number and weight of seeds produced per head were correlated negatively with disease intensity before anthesis. The fungus overwinters in sunflower leaf residues and may present a yearly problem for sunflower production in some areas.
Diallel Analysis of Bacterial Wilt Resistance in Tomato Derived from Different Sources
Authors: Hanson Peter M. , Licardo Olivia , Hanudin  , Wang Jaw-Fen , Chen Jen-tzu
Published: May 2007

Bacterial wilt, caused by Ralstonia solanacearum, is a major constraint to tomato production in the tropics and subtropics. Most bacterial wilt-resistant tomato cultivars have not shown consistently high resistance levels over locations. The objective of this study was to determine whether combining resistance derived from different sources would result in F1progenies with resistance greater than that of the parents. Five bacterial wilt-resistant tomato lines or accessions (CL5915, L285, CRA84, H7997, and GA219), each derived from different resistance sources, and a susceptible processing tomato line (UC204A) were crossed in all combinations without reciprocals. Parents, F1progenies, and F2progenies were evaluated in greenhouses at three locations (Taiwan, Philippines, and Indonesia) for percent survival 6 weeks after drench inoculation with virulent local strains of R. solanacearum. Percent survival means over locations were 17.4 to 83.0 for parents and F1progeny and 16.2 to 75.0 for parents and F2progeny. The percent survival means over locations of L285 × H7997 were highest among crosses in the F1(83.0) and F2(75.0) generations but were not significantly greater than that of H7997. Highly significant mean squares were found in the F1and F2progenies for general combining ability (GCA) and GCA × locations. Positive GCA effects over locations were detected for H7997, CRA84, and L285, indicating that progeny with those lines as parents showed bacterial wilt resistance that was greater than the average of all crosses. Only H7997, however, had positive GCA effects estimates at each location for each generation, and its GCA effects estimates over locations were significantly greater than those of the other parents in the F1and F2progenies. Among this set of parents, H7997 is the best source to develop bacterial wilt-resistant progeny. We did not observe statistically significant increases in resistance by combining different resistance sources. However, the presence of large GCA variances suggests that hybridization of parents that have high GCA for bacterial wilt resistance, such as H7997, CRA84, or L285, followed by selection in segregating populations might yield inbred progeny with resistance greater than that of the parents.