bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report on the Transmission of ‘Candidatus Liberibacter americanus’ from Citrus to Nicotiana tabacum cv. Xanthi
Authors: Francischini F. J. B. , Oliveira K. D. S. , Astúa-Monge G. , Novelli A. , Lorenzino R. , Matiolli C. , Kemper E. , Da Silva A. C. R. , Kitajima E. W.
Published: May 2007

Huanglongbing (HLB), also known as greening, is one of the most important diseases of citrus worldwide. The causal agent is a gram-negative bacterium known to inhabit the phloem of infected plants. Three different candidate species infect citrus: ‘Candidatus Liberibacter africanus’ found in the African continent; ‘Ca. L. asiaticus’ found in Asia, Brazil, and the United States; and ‘Ca. L. americanus’ found in Brazil. (1). Tobacco is an easily transformable plant species that can be used as an experimental host system to quickly screen for candidate genes useful to control plant pathogens. However, no evidence exists on the ability of this plant species to sustain populations of ‘Ca. L. americanus’. With the purpose of transmitting ‘Ca. L. americanus’ from citrus to tobacco, fragments of healthy stems of Cuscuta spp. (dodder) were used to connect an HLB-infected sweet orange plant to each of 10 healthy plants of Nicotiana tabacum L. cv. Xanthi and allowed to remain connected for 30, 45, and 50 days. Three different HLB-infected orange plants and 30 tobacco plants were used in three independent experiments. Most HLB-exposed Xanthi plants exhibited chlorotic leaves after 50 days of exposure probably because of the parasitic effect of dodder; however, an average of 6, 1, and 3 Xanthi plants exhibited a unique blotchy mottle symptom after 30, 45, and 50 days of exposure, respectively. Symptomatic and asymptomatic leaves were collected and analyzed by PCR. The results consistently confirmed the presence of ‘Ca. L. americanus’ only in symptomatic leaves. Sequencing of the PCR product and comparison to the NCBI database also confirmed the identity of the pathogen as ‘Ca. L. americanus’. Electron microscopy analysis of four symptomatic leaves indicated the presence of bacterium-like bodies with round to elongated bacilliform shapes and surrounded by two membranes. These bodies resembled those already described in HLB-infected citrus in Brazil (1). The evidence presented above confirms the successful transmission of ‘Ca. L. americanus’ from citrus to Xanthi using the parasitic plant Cuscuta spp.

Reference: (1) F. A. O. Tanaka et al. Fitopatol. Bras. 31:99, 2006.
Exserohilum pedicellatum Root Rot of Corn in Texas
Authors: Isakeit T. , Gao X. , Kolomiets M.
Published: May 2007

Extensive blighting associated with root rot was seen in a 0.5-ha field of flowering corn (Zea mays inbred line ‘Tx714B’) at the Texas Agricultural Experiment Station in Weslaco, TX (Hidalgo County) in October of 2006. All plants were affected and most of the leaves of each plant were dead. Plants subsequently failed to produce any seed. Primary and secondary roots of blighted plants had extensive, dark brown necrotic lesions. Symptomatic root samples from 11 plants were surface disinfested with 10% bleach for 1 min, followed by two rinses with sterile distilled water, and plated onto water agar plus streptomycin. Fungal growth was transferred to one-fifth-strength potato dextrose agar plus streptomycin (PDAS). A dematiaceous hyphomycete was isolated from 45% of plated root segments from eight plants. The isolates had characteristics consistent with Exserohilum pedicellatum (Henry) Leonard & Suggs: straight, elongated conidia 57 to 75 μm long × 23 to 25 μm wide, with 4 to 6 pseudosepta, a protuberant hilum, and a prominent pedicel-like extension at the base (2). Four isolates were evaluated for pathogenicity. Conidia were scraped from PDAS plates, suspended in 100 ml of water, and mixed with 2.9 kg of autoclaved 1:1 (v/v) sand/sandy loam soil to obtain a density of 150 to 475 conidia per g of soil. Soil was placed in 20- × 4-cm-diameter plastic Cone-Tainer cells (Stuewe & Sons, Corvallis, OR) and a corn seed (‘Tx714B’) was planted 1.5 cm deep in each. Seeds were previously disinfested 2 min with 10% commercial NaOCl. Plants were kept in a growth chamber at 26°C for 4 weeks. There were six replicates per isolate and the experiment was repeated once. All four isolates caused a dark brown root necrosis covering 16 to 29% of the nodal roots and 43 to 83% of the seminal roots. Necrosis did not occur on roots from noninfested control containers. The pathogen was consistently reisolated from symptomatic roots, fulfilling Koch's postulates. This fungus is also pathogenic to sorghum (1), which is grown in rotation with corn in this field, increasing the chances that the fungus will persist. To our knowledge, this is the first report of the disease on corn in Texas.

References: (1) R. J. Shepherd et al. Phytopathology 57:52, 1967. (2) A. Sivanesan. IMI Descriptions of Fungi and Bacteria 89(887):1, 1986.
First Report of Phakopsora pachyrhizi on Kudzu (Pueraria montana var. lobata) in North Carolina and Increased Incidence of Soybean Rust on Soybean in 2006
Authors: Koenning S. R. , Frye J. W. , Butler S. C. , Creswell T. C.
Published: May 2007

Asian soybean rust, caused by Phakopsora pachyrhizi H. Sydow & Sydow, was first detected in the continental United States in soybean (Glycine max (L.) Merr.) in Louisiana on 6 November 2004 (3) and in kudzu (Pueraria montana var. lobata) in Florida during February 2005 (1). Soybean rust was first confirmed in North Carolina in commercial soybean fields in Brunswick, Columbus, and Robeson counties on 25 October 2005 (2). Subsequently, the disease was detected in soybean in 18 counties, but not in kudzu, even when it was growing adjacent to infected soybean. During 2006, soybean rust was first detected in North Carolina in soybean on 14 September 2006 from a sample from Columbus County that was submitted to the North Carolina State University Plant Disease and Insect Clinic (NCSU-PDIC). Thus, the first detection of soybean rust in North Carolina occurred almost 6 weeks earlier in 2006 than in 2005. Subsequently, in 2006, soybean rust was found in soybean in 42 counties in North Carolina through survey, sentinel plot monitoring, and samples submitted to the NCSU-PDIC. In addition, what appeared to be soybean rust was observed in two samples of kudzu collected on 3 and 6 November 2006 from Moore (35.28313°N, 79.38020°W) and Johnston (35.42742°N, 78.18154°W) counties of North Carolina. The diagnosis of P. pachyrhizi in kudzu was confirmed visually and by ELISA protocol supplied with the EnviroLogix QualiPlate kit (Portland, ME). ELISA tests for each kudzu sample were run in triplicate. PCR was also conducted on infected kudzu samples with a protocol previously reported (1). The PCR master mix that was used came from a dilution scheme based on previous PCR work completed by G. Z. Abad. A total of 24 reactions were run, including four 1-kb molecular markers, four positive controls, four negative controls, and four infected kudzu leaf tissue samples. The results of all diagnostic techniques confirmed the presence of P. pachyrhizi in diseased kudzu. To our knowledge, this is the first report of P. pachyrhizi in kudzu in North Carolina.

References: (1) P. F. Harmon et al. Online publication. doi:10.1094/PHP-2005-0613-01-RS. Plant Health Progress, 2005. (2) S. R. Koenning et al. Plant Dis. 90:973, 2006. (3) R. W. Schneider et al. Plant Dis. 89:774, 2005.
Suppression of Fusarium moniliforme in Rice by Rice-Associated Antagonistic Bacteria
Authors: Rosales A. M. , Mew T. W.
Published: May 2007

The potential of antagonistic bacteria from paddy water, rhizosphere soils, sclerotia, and rice plants to control “bakanae” caused by Fusarium moniliforme was assessed. Experiments were conducted to determine the in vitro antibiosis and effect of bacteria on seed germination. Out of 441 isolates, 113 were inhibitory to mycelial growth of the pathogen. Bacterial strains were classified into three groups based on effect on seed germination: (i) those that promoted germination and enhanced seedling vigor; (ii) those that had no effect on germination; and (iii) those that were deleterious and inhibited germination. Bacterization of naturally infected seeds reduced bakanae incidence in seedbox and seedbed tests. In a seedbed experiment with IR 58 seeds soaked in suspensions of bacterial strains, bakanae incidence and disease control ranged from 0.9 to 6.8% and 71.7 to 96.3%, respectively. From the 3 years of field trials, 10 strains reduced bakanae. Five strains consistently reduced bakanae, but the other five exhibited variable effects among trials. Specificity of suppression by antagonistic bacteria against different pathogenic isolates of F. moniliforme from various locations in the Philippines was observed.
Transmission of Sorghum Stunt Mosaic Rhabdovirus by the Leafhopper Vector, Graminella sonora (Homoptera: Cicadellidae)
Authors: Creamer R. , He X. , Styer W. E.
Published: May 2007

The transmission parameters of sorghum stunt mosaic rhabdovirus (SSMV) by the leafhopper Graminella sonora were determined. The minimum acquisition and inoculation times were 6 and 1 h, respectively, while 100% transmission was obtained from a 48-h acquisition access or a 24-h inoculation access period. Transmission efficiency was highest at temperatures of 24 to 36°C. The minimum latent period prior to transmission was 9 days at 30°C, with an 11-day incubation period necessary for 100% transmission. After a 14-day incubation period at 16°C, no transmission was obtained; however, doubling the incubation period to 28 days gave high levels of transmission. Double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) of individual leafhoppers held at 16°C for a 14-day incubation period detected no virus in leafhoppers, whereas over 50% of the leafhoppers had detectable virus after a 28-day incubation period. Graminella nigrifrons and Peregrinus maidis were not able to transmit SSMV.
Summer Pruning as a Method for Reducing Flyspeck Disease on Apple Fruit
Authors: Cooley Daniel R. , Gamble James W. , Autio Wesley R.
Published: May 2007

Summer pruning of apples, as opposed to the conventional commercial practice of dormant pruning, consistently reduced the incidence of flyspeck on apple fruit by approximately 50% in each of 2 years in trees where no fungicides were applied. In commercial orchard blocks using fungicides, summer pruning also produced a slight but significant decrease in disease severity. There appear to be at least two mechanisms contributing to decreased flyspeck incidence and severity in summer-pruned apple trees. Summer pruning resulted in a small change in the apple canopy microclimate, decreasing the hours of relative humidity >95% in the canopy by 63% and increasing the evaporative potential. Summer pruning also resulted in improved spray deposition in the upper two-thirds of the tree canopy when applications were made with an airblast sprayer.
Cross Pathogenicity of Gaeumannomyces graminis var. graminis from Bermudagrass, St. Augustinegrass, and Rice in Florida and Texas
Authors: Datnoff L. E. , Elliott M. L. , Krausz J. P.
Published: May 2007

Isolates of Gaeumannomyces graminis var. graminis were obtained from St. Augustinegrass, bermudagrass, and rice in Florida, and rice and St. Augustinegrass in Texas. In Florida, all seven isolates evaluated were cross pathogenic on each of the three grass hosts. Rice isolate FL-173 caused significantly greater disease of the lower leaf sheath and root disease severity of rice compared with other isolates, whether from rice or both turfgrass species. The rice and both turfgrass isolates generally suppressed heights and shoot and root weights compared with the control. All isolates from either rice or both turfgrass species generally had root disease ratings significantly different from the control for either bermudagrass or St. Augustinegrass. However, rice isolate FL-173 and St. Augustinegrass isolate FL-104 were significantly more aggressive on St. Augustinegrass; whereas the maximum root disease rating of bermudagrass was only associated with bermudagrass isolate FL-19 and St. Augustinegrass isolate FL-104. In Texas, both the rice isolate TX-91-1 and the St. Augustinegrass isolate TX-10466-2 of G. graminis var. graminis were pathogenic on St. Augustinegrass, common bermudagrass, and rice. Both isolates caused similar disease severity on common bermudagrass and St. Augustinegrass, but isolate TX 10466-2 caused less severe disease symptoms on rice than did isolate TX-91-1. Overall, G. graminis var. graminis was most aggressive on the host from which it was originally isolated, such as rice or St. Augustine, but differences in host-plant reactions were not always statistically significant, especially with bermudagrass.
Use of a Tissue Blotting Immunoassay to Examine the Distribution of Pineapple Closterovirus in Hawaii
Authors: Hu J. S. , Sether D. M. , Liu X. P. , Wang M. , Zee F. , Ullman D. E.
Published: May 2007

Specific monoclonal antibodies made to a pineapple closterovirus (PCV) were used in a tissue blotting immunoassay (TBIA) for the detection of PCV in pineapple. More than 2,000 samples were tested in 5 days by one person using this rapid and reliable assay. A survey was conducted using this assay to test more than 20,000 Hawaiian pineapple samples for the presence of PCV. PCV was detected in symptomless pineapple plants in the field and in the USDA pineapple germ plasm collection. Studies of the association of PCV with mealybug wilt of pineapple (MWP) suggest that PCV may be involved in MWP.
Efficacy and Economics of Management Strategies to Control Anthracnose Fruit Rot in Processing Tomatoes in the Midwest
Authors: Byrne J. M. , Hausbeck M. K. , Latin R. X.
Published: May 2007

Anthracnose (Colletotrichum coccodes) is the major fungal disease affecting processing tomato fruit in the midwestern United States. Currently available disease management strategies evaluated for controlling anthracnose fruit rot (AFR) on processing tomatoes include genetic resistance and the fungicide chlorothalonil applied according to conventional schedules or a disease-forecasting system (Tom-Cast). Experimental field plots were established in West Lafayette, Indiana, and East Lansing, Michigan, in 1993 to 1995. Chlorothalonil was applied every 7, 10, or 14 days or according to Tom-Cast with a threshold of 20 disease severity values, and was not applied to the control. In Michigan, Phytophthora infestans (1993) and C. coccodes (1993 to 1994) caused 91.8% (1993) and 30.7% (1994) fruit rot in the unsprayed plot. In Indiana, C. coccodes caused 69.8% (1993) and 39.0% (1994) AFR in the unsprayed plot. In 1995, Ohio 8245 (Michigan and Indiana), considered to be less prone to anthracnose, and Ohio 7814 were integrated into the conventional and Tom-Cast—prompted spray programs. Cultivar did not affect the incidence of AFR or foliar blight caused by Septoria lycopersici and Alternaria solani in either location. In 1993 and 1994, chlorothalonil applied at 10-day intervals in Indiana resulted in the highest benefit per hectare (BPH) and return per fungicide dollar (RPFD). In 1995, the highest BPH and RPFD resulted from chlorothalonil applied every 14 days to Ohio 8245 (Michigan). Chlorothalonil applied according to the Tom-Cast program resulted in a level of AFR that was generally not statistically different from the 7-day treatment but was high enough to result in crop rejection and high economic loss in 2 of the 3 years the study was conducted. Based on data from this study, it is not commercially feasible to grow processing tomatoes in Michigan and Indiana without chlorothalonil to protect against AFR even when a resistant cultivar is used.
First Report of Phytophthora megasperma and Pythium irregulare As Olive Tree Root Pathogens
Authors: Sánchez-Hernández M. E. , Ruiz-Dávila A. , Trapero-Casas A.
Published: May 2007

Several species of the genus Phytophthora are associated with root rot and trunk cankers in olive trees (Olea europaea L.). Among them, Phytophthora megasperma has been cited as being associated with olive root rots in Greece (1). Unidentified species of Pythium and Phytophthora have also been associated with olive tree root rots in the United States. However, the status of P. megasperma and Pythium spp. as olive tree root pathogens has remained unclear. Following a 5-year period of severe drought in southern Spain, autumn-winter rainfall rates in 1996 to 1997 steadily increased in both quantity and frequency. Under these unusually wet conditions, olive trees remained waterlogged for several months. During this period, we observed foliar wilting, dieback, and death of young trees, and later found extensive root necrosis. In 46 of 49 affected plantations surveyed, P. megasperma was consistently isolated from the rotted rootlets, particularly in young (<1- to 10-year-old trees) plantations. This fungus was not detected on plant material affected by damping-off from several Spanish olive tree nurseries. The opposite situation occurred with P. irregulare. This species was not associated with rotted rootlets in the field. In contrast, it was consistently isolated from necrotic rootlets from young olive plants affected by damping-off. These plants were grown in a sand-lime-peat soil mixture under greenhouse conditions and showed foliar wilting and extensive necrosis of the root systems. Pathogenicity tests were conducted with several isolates of P. megasperma and P. irregulare on 6-month-old rooted cuttings of olive, under both weekly watering and waterlogged conditions. Under waterlogged conditions, both fungal species produced extensive root necrosis 2 weeks after inoculation that resulted in wilting of the aerial parts and rapid plant death. Waterlogged control plants remained without foliar symptoms but a low degree of root necrosis was recorded. In addition, under weekly watering conditions, plants inoculated with either species showed some degree of root rot but foliar symptoms were not evident. No differences in pathogenicity were observed within the Phytophthora or Pythium isolates.

Reference: (1) H. Kouyeas and A. Chitzanidis. Ann. Inst. Phytopathol. Benaki 8:175, 1968.
Long-Term Storage of Ustilago tritici
Authors: Menzies J. G. , Nielsen J. , Thomas P. L.
Published: May 2007

An extensive collection of isolates of Ustilago tritici from around the world is maintained at the Cereal Research Centre. As the collection size increases, however, the time and effort needed to maintain the collection becomes greater, as does the need for a good technique for long term storage of U. tritici. Race T2 of U. tritici was inoculated to spikelets of wheat in February 1976. The matured inoculated heads were thrashed and the seed stored in a desiccator with silica-gel at -15°C. Every 2 years, 60 seeds were removed and planted to determine viability and proportion of infected adult plants. Between 57 and 83% of the seed produced adult plants, and the percent of infected plants ranged between 56 and 98% during the 20 years. There was no significant change in seed germination over time, but there was a positive relationship (P < 0.0664, R2 = 0.452) between the time of storage and the arcsine of the proportion of smutted plants. Storage of U. tritici in infected seed at -15°C and low relative humidity is an efficient method for long-term storage of this fungus.
First Report of Gummy Stem Blight, Caused by Didymella bryoniae, on Watermelon Transplants in California
Authors: Koike S. T.
Published: May 2007

In 1997, greenhouse-produced transplants of watermelon (Citrullus lanatus) developed water-soaked lesions on leaf petioles and main stems. As disease progressed, petioles and stems became necrotic and shriveled, and exuded a sticky, translucent tan liquid. Symptoms spread to leaves, which wilted and collapsed. Affected transplants eventually died. Although fruiting bodies were not observed on diseased plants, a fungal agent was consistently isolated from symptomatic tissues. When incubated under lights (12 h light/12 h dark cycle), isolates on potato dextrose agar produced numerous pycnidia with hyaline, cylindrical, one-septate conidia with mean dimensions of 5.6 × 2.8 μm. Under the same incubation conditions, isolates on V8 juice agar produced sparse ostiolate pseudothecia with bitunicate asci and hyaline, oval, one-septate ascospores with mean dimensions of 12.0 × 4.0 μm. Based on these characters, the isolates were identified as Didymella bryoniae (anamorph Phoma cucurbitacearum) (1,2). Pathogenicity was tested by producing conidial inocula of representative isolates and inoculating wounded cotyledons, true leaves, and petioles of watermelon (cv. Sangria), and wounded true leaves and petioles of cucumber (Cucumis sativus cv. Premier Hybrid) (3). Sterile, distilled water was applied to corresponding wounded tissues of control plants. All plants were kept in a humid chamber for 4 days. After 6 (watermelon) to 10 (cucumber) days, inoculated plants exhibited water-soaked lesions followed by necrosis, petiole and leaf wilting, and shriveling of tissues. Pycnidia were observed on cucumber plants after 18 days. The pathogen was reisolated from all inoculated plants and identified as D. bryoniae. Control plants developed no disease symptoms. In addition, agar plugs colonized with the watermelon isolates were placed onto cucumber fruit that were wounded slightly with a sterile scalpel. Fruit were incubated at 22 to 24°C in humid chambers and after 2 days sunken, circular lesions developed. The same pathogen was reisolated from the margins of fruit lesions. Wounded control fruit received sterile agar plugs and did not develop any symptoms. This is the first documentation of gummy stem blight on watermelon transplants in California.

References: (1) W. F. Chiu and J. C. Walker. J. Agric. Res. 78:81, 1949. (2) A. P. Keinath et al. Phytopathology 85:364, 1995. (3) A. J. Wyszogrodzka et al. Euphytica 35:603, 1986.
First Report of Tomato Gray Leaf Spot Caused by Stemphylium solani in the Andes Region of Venezuela
Authors: Cedeño L. , Carrero C.
Published: May 2007

Since 1994, tomato (Lycopersicon esculentum Mill.) grown in Mérida State, located in the Venezuelan Andes, have been consistently affected by a gray leaf spot disease with symptoms on leaves, petioles, and stems. Yield is reduced, and in some cases entire crops have been destroyed over short time. Because of its prevalence, distribution, and severity, the disease has become the major factor limiting tomato production in this region. Disease symptoms were commonly observed on seedlings and plants. On leaves the disease first appeared as circular to elongated dark specks. As the spots enlarged, they became gray and bright. Old lesions dried and usually cracked. Severely infected leaves turned yellow and then died and dropped. Lesions on petioles and stems were elongate. Disease severity was generally higher following the beginning of fruiting. The fungus was isolated from leaves, petioles, and stems of tomato cv. Rio Grande on 2% water agar acidified with lactic acid. On potato-carrot agar, conidiophores and conidia were produced with the characteristics of Stemphylium. Two species of Stemphylium, S. solani G. F. Weber and S. lycopersici (Enjoji) W. Yamamoto, cause gray leaf spot symptoms on tomato. Based on morphology, size, and the length/width ratio of the conidia, the fungus was identified as S. solani (1). Inoculations done by spraying a conidial suspension on plants of tomato cv. Rio Grande produced symptoms similar to those observed in the field. S. solani was consistently isolated from experimentally infected tissues, thus confirming Koch's postulates. This is the first report of S. solani causing gray leaf spot on tomato grown in the Andes of Venezuela.

Reference: (1) G. F. Weber. Phytopathology 20:513, 1930.
First Report of Papaya Leaf Curl Disease in Pakistan
Authors: Nadeem A. , Mehmood T. , Tahir M. , Khalid S. , Xiong Z.
Published: May 2007

Papaya plants with virus-disease-like symptoms were observed in back yards and commercial groves in Multan, Pakistan. Leaves of the diseased plants displayed downward curling and thickened, dark green veins. Leaf-like enations grew from the base of the diseased leaves. These symptoms are similar to those of cotton leaf curl disease. In addition, diseased papayas were stunted and distorted. Leaf extracts from 3 diseased and 2 healthy papayas were tested in enzyme-linked immunosorbent assay against antibodies to geminiviruses. SCRI-52 and SCRI-60, two monoclonal antibodies to Indian cassava mosaic virus (2), reacted positively (more than 7× healthy background) with the diseased samples but not with the healthy ones. Total nucleic acids from the papaya samples were used as templates in polymerase chain reaction with primers F500 and R1800 (1), which are capable of amplifying a region of DNA A component of the whitefly-transmitted geminiviruses. A DNA fragment of approximately 1.4 kb was amplified from the nucleic acids of the diseased but not the healthy papayas. Under high stringency conditions (1), cloned DNA A fragments of both cotton leaf curl virus and cotton leaf crumple virus cross-hybridized with the amplified DNA fragment, but the hybridization signals were much weaker than those of the homologous hybridization. This is the first report of the papaya leaf curl disease in Pakistan. These data demonstrated that a geminivirus may be the causative agent of this papaya disease. We are currently determining the relationship between the geminivirus infecting papaya and cotton leaf curl virus.

References: (1) A. Nadeem et al. Mol. Plant Pathol. (On-line: /1997/0612nadeem). (2) M. M. Swanson et al. Ann. Appl. Biol. 211:285, 1992.
Combination of Hot Water and Ethanol to Control Postharvest Decay of Peaches and Nectarines
Authors: Margosan Dennis A. , Smilanick Joseph L. , Simmons Gilbert F. , Henson Delmer J.
Published: May 2007

Spores of Monilinia fructicola or Rhizopus stolonifer were immersed in water or 10% ethanol (EtOH) for 1, 2, 4, or 8 min at temperatures of 46 or 50°C to determine exposure times that would produce 95% lethality (LT95). EtOH reduced the LT95 by about 90%. Peaches and nectarines infected with M. fructicola were immersed in hot water alone or with EtOH to control decay. EtOH significantly increased the control of brown rot compared to water alone. Immersion of fruit in water at 46 or 50°C for 2.5 min reduced the incidence of decayed fruit from 82.8% to 59.3 and 38.8%, respectively. Immersion of fruit in 10% ethanol at 46 or 50°C for 2.5 min further reduced decay to 33.8 and 24.5%, respectively. Decay after triforine (1,000 μg ml-1) treatment was 32.8%. Two treatments, 10% EtOH at 50°C for 2.5 min and 20% EtOH at 46°C for 1.25 min, were selected for extensive evaluation. The flesh of EtOH-treated fruit was significantly firmer, approximately 4.4 N force, than that of control fruit among seven of nine cultivars evaluated. No other factor evaluated was significantly influenced by heated EtOH treatments. The EtOH content of fruit treated with 10 or 20% EtOH was approximately 520 and 100 μg g-11 day and 14 days after treatment, respectively.
Influence of Fruit-to-Fruit Contact on the Susceptibility of French Prune to Infection byMonilinia fructicola
Authors: Michailides Themis J. , Morgan David P.
Published: May 2007

In eight commercial prune (Prunus domestica cv. French) orchards, 43 to 69% of brown rot (caused by Monilinia fructicola or M. laxa) infections occurred in clustered fruit as opposed to solitary fruit. Fruit-to-fruit contact surfaces had cracked and thin cuticles and larger microcracks (up to 2,255 μm in length) surrounding the lenticels than those of non-contact surfaces (cracks up to 351 μm in length). Furthermore, fruit-to-fruit contact surfaces retained greater proportions of methylene blue, indicating absence of epicuticular wax, than the non-contact surfaces. Carbohydrate content of exudates in water placed on fruit-to-fruit contact surfaces was 15 and 22 mg/ml, while those of non-contact surfaces were 13 and 19 mg/ml after 15 and 28 h, respectively. Conidia of M. fructicola germinated faster and at higher rates, and the incidence of infection was significantly higher on fruit-to-fruit contact than on non-contact surfaces. Densities of fungal CFU were greater (27 to 98 CFU/cm2) on fruit-to-fruit contact compared to those of non-contact surfaces (7 to 29 CFU/cm2). In four experiments, after spraying to runoff with distilled water, surfaces of solitary fruit dried after 7 to 8 h at 23 ± 1°C compared to 12 to 14 h for groups of 5 to 6 fruit. After spraying the same mature fruit with 1.2 × 105conidia/ml of M. fructicola and incubating at 24°C and >97% relative humidity, 26 to 70% and 38 to 100% of fruit placed in groups of 5 to 6 were infected after 3 days and 5 days, respectively, whereas only 2 to 13% and 21 to 65% of solitary fruit became infected. These results suggest that fruit-to-fruit contact surfaces predispose prune fruit to infection by M. fructicola, and that it might be possible to reduce fruit losses from brown rot in prune orchards by thinning fruit to reduce fruit clustering, applying early summer fungicide sprays before fruit contact occurs, and ultimately, by selection for non-clustering cultivars in prune breeding programs.
Sirococcus clavigignenti-juglandacearum on Heartnut (Juglans ailantifolia var. cordiformis)
Authors: Ostry M. E.
Published: May 2007

Branch dieback was observed throughout the crown of a 25-year-old heartnut, a variety of Japanese walnut, growing in a mixed plantation with black walnut (J. nigra) in central Iowa in the spring of 1997. No cankers were evident. However, hyphal pegs and hyaline, two-celled, fusiform conidia were present on the affected 1996 branch wood. These are characteristic of S. clavigignenti-juglandacearum, the cause of branch and stem cankers on butternut, also called white walnut, (J. cinerea) (1). The fungus was isolated in pure culture from symptomatic twigs. The ability of this isolate to cause canker on butternut was compared with an isolate from butternut in Minnesota by inoculating the stems of potted, 2-year-old butternut seedlings in a greenhouse. Lignified stem portions of the seedlings were wounded by removing a 5-mm2 area of bark with a scalpel, exposing the cambium, and placing a plug cut from the margin of an actively growing culture on potato dextrose agar (PDA) fungus-side-down on the wound. Each of 30 seedlings received both isolates, 15 with the heartnut isolate on top (10 cm from shoot apex), and 15 with it on the bottom (30 cm from shoot apex) position of the stems. Noncolonized PDA control plugs were similarly placed on wounds in the middle position of each stem. Parafilm was used to hold the agar plugs in place and was removed 2 weeks later. After 10 weeks, canker lengths were recorded. Stem segments were surface sterilized, and wood chips from canker margins were placed onto PDA at 20°C. Cankers characteristic of S. clavigignenti-juglandacearum developed on all seedlings at each inoculation site. The means of lengths of cankers for the heartnut and butternut isolates (37.1 and 37.2 mm, respectively) did not differ significantly (P > 0.9). Hyphal pegs and conidia of S. clavigignenti-juglandacearum developed at inoculation sites of stems with both isolates. The fungus was recovered in pure culture from the canker margins. No cankers developed at the control wound sites and all wounds were callused over. This is the first report of S. clavigignenti-juglandacearum on Japanese walnut. This report and an earlier report of this fungus causing dieback on black walnut (2) indicate this fungus may occur on other Juglans spp. than previously reported and could be considered a potential pathogen in walnut plantings.

References: (1) V. M. G. Nair et al. Mycologia 71:641, 1979. (2) M. E. Ostry et al. Plant Dis. 81:830, 1997.
Occurrence of Peach Latent Mosaic Viroid in Stone Fruits and Its Transmission with Contaminated Blades
Authors: Hadidi A. , Giunchedi L. , Shamloul A. M. , Poggi-Pollini C. , Amer M. A.
Published: May 2007

Peach latent mosaic viroid (PLMVd) is widely distributed (approximately 55%) in peach germplasm from Europe, Asia, North America, and South America. PLMVd, or a closely related viroid, was occasionally detected in cherry, plum, and apricot germplasm from countries in Europe or Asia. The cherry isolate of PLMVd is 337 nucleotides in length and is 91 to 92% homologous to PLMVd isolates from peach. Molecular hybridization experiments demonstrated that PLMVd is not related to the agent of peach mosaic disease. PLMVd was readily transmitted (50 to 70%) by contaminated blades to green shoots and lignified stems of peach GF-305 plants. These results indicate that the viroid may be transmitted in orchards with contaminated pruning equipment.
Population Dynamics of Phialophora gregata in Soybean Residue
Authors: Adee E. A. , Grau C. R. , Oplinger E. S.
Published: May 2007

Brown stem rot frequently is more severe in no-till cropping systems. Population density of Phialophora gregata was monitored in soybean residue positioned below and on the soil surface. Current season residue was confined in nylon mesh bags that were placed in the field in the fall. Population density of the pathogen was measured monthly through the winter, or seasonally for 30 months, and expressed as CFU per gram of soybean residue. Population dynamics of P. gregata differed in surface residue, compared with buried residue. Population density of P. gregata was not significantly different in buried and surface residue from November/December to April. Beginning in late April or May, population density of P. gregata was significantly greater in surface residue than in buried residue. The population density of P. gregata in surface residue remained above 105 CFU per gram of residue after 30 months in the field. In contrast, the fungus was not detected in buried residue after 11 to 17 months. From November to May, the population destiny of P. gregata in surface residue increased more than 14 times the initial density. In contrast, the density of P. gregata in buried residue increased sixfold by April, then decreased to densities not significantly different from the initial population by May and June. Mass of buried residue decreased more rapidly than that of surface residue during April, May, and June. There was a positive correlation between residue weight and the population density of P. gregata in residue. P. gregata survived longer and at higher population densities in residue positioned on the soil surface (simulated no-till) than in buried residue (simulated conventional tillage). Although inoculum density of P. gregata remained high in surface residue, total inoculum declined because of loss of residue biomass.
Occurrence of Cowpea Stunt Disease Causing Viruses on Wild Bean in Arkansas
Authors: Kline A. S. , Anderson E. J. , Smith E. B.
Published: May 2007

Cucumber mosaic cucumovirus (CMV) and blackeye cowpea mosaic potyvirus (BlCMV) interact synergistically in dually infected plants to cause cowpea stunt disease (1,2). During a July 1996 survey of cowpea stunt-affected fields in the Arkansas River valley, several wild bean (Strophostyles helvola L. Elliott) plants expressing mosaic symptoms were observed and collected. Sap was extracted from symptomatic leaves and used as inoculum to conduct a host range study. Virus symptoms diagnostic for BlCMV, CMV, or cowpea stunt were observed 6 to 8 days post-inoculation on Vigna unguiculata (L.) Walp. subsp. unguiculata cv. Coronet, while chlorotic lesions and mild systemic mosaic symptoms developed on Nicotiana benthamiana. Enzyme-linked immunosorbent assays (ELISAs) conducted on extracts from symptomatic cowpea and N. benthamiana 14 days after inoculation verified the presence of CMV and BlCMV in single and mixed infections. Additional symptomatic wild bean plants were collected from the same site in October 1996. ELISAs and Ouchterlony gel diffusion assays confirmed the presence of CMV and BlCMV, as well as soybean mosaic potyvirus (SMV), cowpea chlorotic mottle bromovirus, and alfalfa mosaic virus (AlMV) in symptomatic wild bean plants. While some of the collected plants were infected with only one virus, others had combined infections of CMV and BlCMV or these two viruses with AlMV. Interestingly, AlMV isolated from wild bean caused symptoms on greenhouse-grown cowpeas that were as severe or more severe than those caused by the cowpea stunt synergy, often resulting in plant death within 8 to 10 days after inoculation. The SMV from wild bean did not induce symptoms on cowpea and was not detected in extracts from inoculated cowpea plants by Ouchterlony gel diffusion assays, but was able to systemically infect soybean (Glycine max L.) cvs. Bragg and Lee. Another virus known to infect cowpea, southern bean mosaic sobemovirus, was not detected in any of the samples tested. To our knowledge, this is the first report that wild bean can serve as an alternate host for cowpea stunt-causing viruses in single and mixed infections. In addition, these data suggest that AlMV may pose a threat to Arkansas-grown cowpeas.

References: (1) E. J. Anderson et al. Ark. Farm Res. 43:14, 1994. (2) G. Pio-Ribeiro et al. Phytopathology 68:1260, 1978.
Bacterial Leaf Spot of Cilantro in Florida
Authors: Pernezny K. , Raid R. N. , Jones J. B.
Published: May 2007

In the 1995 to 1996 winter vegetable season, a leaf spot disease of cilantro (fresh coriander) (Coriandrum sativum L.) was widespread throughout commercial plantings in the Everglades Agricultural Area south and east of Lake Okeechobee. Symptoms first appeared as water-soaked spots ≤1 mm in diameter. These spots became dark brown to black and enlarged up to 2 mm in diameter. No chlorotic haloes developed around the lesions. The disorder was observed in numerous plantings of the cultivar Longstanding at four separate locations. Symptoms were apparent throughout each planting, with disease severity ranging from a few individual spots to numerous lesions covering nearly entire leaflets. Severe outbreaks were correlated with heavy precipitation events. In several instances, disease levels were great enough to render entire plantings totally unmarketable. A non-fluorescent bacterium was consistently isolated on King's medium B when a cooled inoculation needle was pushed through lesions. Six representative strains were chosen for further characterization. All strains were aerobic, gram-negative rods, and were oxidase and arginine dihydrolase negative. Levan was produced, but potato slices were not rotted. Tests for utilization of l-tartrate, l-lactate, and erythritol were negative. Biolog analysis identified all strains of the bacterium as Pseudomonas syringae. Highest similarity indices (0.52 to 0.81) were with P. syringae pv. pisi for four of the six strains. Suspensions of each strain were swab inoculated onto leaves of 4-week-old Longstanding cilantro seedlings in the greenhouse. Control plants were swabbed with sterile water only. Plants were covered with clear polyethylene bags for 72 h. Watersoaked spots were evident on test plants when bags were removed. Typical brown, greasy-looking leaf spots were seen by 6 days after inoculation. Control plants were symp-tomless. In a host-range study, cilantro and the following plants were mist-inoculated with a 107 CFU/ml suspension of each of the six test strains: carrot (Daucus carota L. ‘Fancy Pack’), celery (Apium graveolens L. var. dulce (Mill.) Pers., ‘June Belle’), garden pea (Pisum sativum L. ‘Melting Sugar’), snap bean (Phaseolus vulgaris L. ‘Pod Squad’), and onion (Allium cepa L. ‘Evergreen Bunching’). Six days after inoculation, characteristic symptoms were evident on the cilantro. Four of the six strains produced a few (less than 10 per plant) bacterial leaf spot symptoms in carrot from which P. syringae was readily recovered. Some necrosis was observed on young, emerging leaves of snap bean. No symptoms were recorded for the other host species or the controls. This disease is similar to one reported on cilantro in California (1) and Germany (2).

References: (1) D. A. Cooksey et al. Plant Dis. 75:101, 1991. (2) H. M. Toben and K. Rudolph. J. Phytopathol. 144:169, 1996.
Interaction of Ht and Partial Resistance to Exserohilum turcicum in Maize
Authors: Lipps P. E. , Pratt R. C. , Hakiza J. J.
Published: May 2007

Components of northern leaf blight resistance in maize due to race-specific resistance controlled by the Ht gene, partial resistance derived from inbred H99, and a combination of the two kinds of resistance, were studied subsequent to inoculation with Exserohilum turcicum race O. Lesion types, number of lesions (lesion number), percent leaf area affected (severity), and area under the disease progress curve (AUDPC) based on lesion number and severity were assessed in field studies conducted at two locations in Uganda and one location in Ohio in 1993. Lesion types observed were consistent for genotypes across locations. In general, significant differences among genotypes for data based on lesion number and severity were consistent for AUDPC based on lesion number and severity, respectively, at all locations. In Ohio, both Ht and partial resistance were effective in limiting disease development. In Uganda, susceptible inbreds (A619, A635, and B73) generally had higher severity than genotypes with partial resistance (H99, Mo17, and Babungo 3). However, there was a difference in response among genotypes depending on disease intensity at each location. Ht resistance and moderate partial resistance did not greatly affect lesion number at the higher disease intensity location, compared with the susceptible inbreds, but at the lower disease intensity location genotypes with partial resistance had fewer lesions than susceptible inbreds or the Ht conversions of the susceptible inbreds. At both plot locations, genotypes with partial resistance had lower severity than the susceptible inbreds or Ht conversions of the susceptible inbreds. Hybrids derived from crossing H99 with genotypes with moderate levels of partial resistance (Mo17 and Babungo 3) did not have significantly lower lesion numbers than hybrids of susceptible inbreds crossed with H99, but severity was significantly lower on these hybrids at the high disease intensity location. Results indicate that the level of partial resistance in H99 would be as effective in controlling northern leaf blight as using Ht resistance, or a combination of Ht resistance and moderate levels of partial resistance as found in Mo17.
Field Transmission of Grapevine Leafroll Associated Virus 3 (GLRaV-3) by the MealybugPlanococcus citri
Authors: Cabaleiro C. , Segura A.
Published: May 2007

The spatial distributions of grape plants with symptoms of grapevine leafroll in nine vineyards in the Galician wine-growing region Rías Baixas (northwestern Spain) were analyzed. In five, significant aggregations of diseased plants and/or disease gradients toward one of the borders of the plots constituted indirect evidence of vector transmission by a nonflying vector. From 1991 to 1995, vines from two vineyards were tested for grapevine leafroll associated virus 3 (GLRaV-3) by enzyme-linked immunosorbent assay. In one of these vineyards, which had been virus-free when planted, GLRaV-3 was detected 3 years after planting. In the second, the incidence of GLRaV-3 increased from 33 to 83% between 1991 and 1995. The mealybug Planococcus citri was associated with the infected plants in this vineyard. GLRaV-3 was present in P. citri, and under controlled conditions this mealybug transmitted GLRaV-3 to five of five previously healthy grape plants.
Sensitivity of Uncinula necator to Benomyl, Triadimefon, Myclobutanil, and Fenarimol in California
Authors: Ypema H. L. , Ypema M. , Gubler W. D.
Published: May 2007

Sensitivity of Uncinula necator subcultures to benomyl and the demethylation-inhibiting (DMI) fungicides triadimefon, myclobutanil, and fenarimol was assessed in 1993, 1994, and 1995 with leaf disk bioassays. In 1993, 1994, and 1995, 81.8, 96, and 96.7% of the subcultures, respectively, did not grow on leaf disks treated with 30 mg of benomyl per liter, whereas growth of the remaining subcultures was inhibited by more than 90%. Median EC50 values of triadimefon, myclobutanil, and fenarimol decreased from 1993 to 1994, and those of triadimefon decreased again from 1994 to 1995. In the same period, median EC50 values of all three DMI fungicides increased in a vineyard never exposed to DMI fungicides. The highest means and ranges of EC50 values found were those of triadimefon. Means and ranges were lower for myclobutanil and lowest for fenarimol, reflecting differences in inherent activities of the fungicides and po-tential for development of resistance. Pairwise correlations between EC50 values of each DMI fungicide were positive and confirmed earlier indications of cross resistance.
Two Groups of Phytoplasmas from Japan Distinguished on the Basis of Amplification and Restriction Analysis of 16S rDNA
Authors: Okuda Seiichi , Prince James P. , Davis Robert E. , Dally Ellen L. , Lee Ing-Ming , Mogen Bradley , Kato Shosuke
Published: May 2007

Phytoplasmas (mycoplasmalike organisms, MLOs) associated with mitsuba (Japanese hone-wort) witches'-broom (JHW), garland chrysanthemum witches'-broom (GCW), eggplant dwarf (ED), tomato yellows (TY), marguerite yellows (MY), gentian witches'-broom (GW), and tsu-wabuki witches'-broom (TW) in Japan were investigated by polymerase chain reaction (PCR) amplification of DNA and restriction enzyme analysis of PCR products. The phytoplasmas could be separated into two groups, one containing strains JHW, GCW, ED, TY, and MY, and the other containing strains GW and TW, corresponding to two groups previously recognized on the basis of transmission by Macrosteles striifrons and Scleroracus flavopictus, respectively. The strains transmitted by M. striifrons were classified in 16S rRNA gene group 16SrI, which contains aster yellows and related phytoplasma strains. Strains GW and TW were classified in group 16SrIII, which contains phytoplasmas associated with peach X-disease, clover yellow edge, and related phytoplasmas. Digestion of amplified 16S rDNA with HpaII indicated that strains GW and TW were affiliated with subgroup 16SrIII-B, which contains clover yellow edge phytoplasma. All seven strains were distinguished from other phytoplasmas, including those associated with clover proliferation, ash yellows, elm yellows, and beet leafhopper-transmitted virescence in North America, and Malaysian periwinkle yellows and sweet potato witches'-broom in Asia.
Field Screening of Commercial and Experimental Soybean Cultivars for Their Reaction to Macrophomina phaseolina
Authors: Smith G. S. , Carvil O. N.
Published: May 2007

From 1992 to 1994, 24 soybean cultivars, ranging in maturity from early group III to late group IV, were assessed in the field for resistance and susceptibility to Macrophomina phaseolina. Cultivars were placed into four relative maturity classes-3.2 to 3.4; 3.5 to 3.8; 3.9 to 4.0; and 4.3 to 4.9—with six cultivars per class. Twelve cultivars were resistant and 12 were susceptible to Heterodera glycines, the soybean cyst nematode. Cultivars were planted on two dates (early May and early June) to assess the effect of environment on yield and lower stem and taproot colonization by the fungus at growth stage R7. Based on seed yields and the levels of lower stem and taproot colonization by M. phaseolina, four cultivars—Asgrow 4715, DeltaPineland 3478, Hamilton, and Jackson II—were rated moderately resistant to M. phaseolina. Seed yields and M. phaseolina levels in host tissues were affected by planting date, relative maturity class, H. glycines response, and the environmental conditions that prevailed over the 3 years of the study. However, in general, the environmental, agronomic, and host genetic factors present in these experiments did not affect the individual cultivar/pathogen interaction. Quantification of microsclerotial propagules in lower stem and taproot tissues at growth stage R7 was a reliable, but time-consuming, method to measure the degree of host compatibility between soybean cultivars and M. phaseolina.