bluuebunny/crossref_metadata_2025 huggingface dataset:
Iris Yellow Spot Tospovirus Detected in Onion (Allium cepa) in Israel
Authors: Gera A. , Cohen J. , Salomon R. , Raccah B.
Published: May 2007

During March 1997, 20 to 30% of field-grown onion (Allium cepa), observed in Bet Shean Valley, Israel, had unusual viral symptoms of straw-colored ringspots on leaves and flower stalks. Leaf samples were analyzed by transmission electron microscopy (EM) of leaf dip preparations. Typical tospovirus-like particles were observed only with samples taken from symptomatic plants. Crude sap from symptomatic tissue was mechanically transmitted to Nicotiana benthamiana, Chenopodium quinoa, and Gomphrena globosa. On inoculated plants of N. benthamiana, chlorotic spots developed on inoculated leaves, followed by systemic necrosis, 4 and 7 days post inoculation (DPI), respectively. On inoculated plants of C. quinoa and G. globosa, necrotic local lesions developed by 4 to 5 DPI. EM studies with ultrathin sections of infected onion and N. benthamiana leaves revealed the presence of tospovirus-like particles. Virus was purified from mechanically infected N. benthamiana and identified as Iris yellow spot tospovirus (IYSV) by Western blots (immunoblots) and enzyme-linked immunosorbent assay (ELISA) (anti-IYSV antiserum was provided by D. Peters, Wageningen, the Netherlands). A high incidence of the disease observed in the surrounding fields and in other onion-growing areas in Israel was associated with large populations of the onion thrips (Thrips tabaci). Although characteristic symptoms have been noted on a frequent basis, effects on yield have yet to be determined. IYSV is known to occur in the Netherlands, where it has been occasionally detected in Iris (1) and leek (A. Porrum) (J. Verhoeven, personal communication). The detection of IYSV in Israel and the wide distribution of thrips in the natural vegetation may be an important constraint on onion and other bulb-crop production in Israel.

Reference: (1) A. F. L. M. Derks and M. E. C. Lemmers. Acta Hortic. 432:132, 1996.
Characterization of a Potyvirus Causing Mild Mosaic on Tuberose
Authors: Chen C. C. , Chang C. A.
Published: May 2007

A virus inducing mild mosaic symptoms on the leaves and peduncles of tuberose (Polianthes tuberosa) was isolated and partially characterized. The isolate, designated Tbr1, could be transmitted mechanically and by green peach aphids (Myzus persicae) in a non-persistent manner to tuberose seedlings but not to 16 common assay species. Flexuous rod-shaped particles with a mean length of 750 nm could be easily seen in infected leaf dips and in purified samples. Cytoplasmic cylindrical inclusions, pinwheel and laminated aggregates similar to those assigned to potyviral cylindrical inclusion type II, were observed in infected tuberose leaves. The purified capsid contained a single species of protein monomer with an estimated relative mass of 38 kDa. In reciprocal sodium dodecyl sulfate-immunodiffusion tests, antiserum against Tbr1 reacted only with its homologous antigen but not with 22 different known potyviruses. Using primer pairs designed for potyvirus sequence amplification, a 2-kb DNA product equivalent to the estimated size for potyviruses was consistently amplified from purified Tbr1 virions or from crude infected tissue by reverse transcription polymerase chain reaction. On the basis of these results, Tbr1 was recognized as a unique species in the genus Potyvirus and hence designated as tuberose mild mosaic potyvirus (TMMV).
Influence of Inoculum Density, Wetness Duration, Plant Age, Inoculation Method, and Cultivar Resistance on Infection of Pepper Plants by Colletotrichum coccodes
Authors: Hong Jeum Kyu , Hwang Byung Kook
Published: May 2007

Effects of inoculum density, wetness duration, plant age, inoculation method, and cultivar resistance on the development of pepper anthracnose caused by Colletotrichum coccodes were evaluated under controlled environmental conditions. As inoculum density of C. coccodes increased from 103 to 106 conidia/ml, symptoms of anthracnose developed. Disease severity also increased with increasing time of wetness duration from 0 to 60 h. Wetness duration above 48 h and a high inoculum density at 106 conidia/ml caused severe defoliation and blight symptoms in pepper seedlings. Inoculum at 104 conidia/ml and 24 to 36 h of continuous wetness duration was enough to form irregular or circular brown lesions on pepper leaves. Age-related resistance was expressed as pepper plants matured. To evaluate resistance, the foliar-inoculation method was more reliable than the soil-drench method, which did not induce symptoms on older plants. The responses of 35 pepper cultivars or accessions tested to C. coccodes were quantitative rather than qualitative. No hypersensitive symptoms were observed in any of the cultivars inoculated with any of the two isolates. No significant differences in susceptibility to anthracnose were found among cultivars from Korea, the United States, India, and Thailand or accessions tested, irrespective of genetic or country origin of cultivars. The Korean cultivar Kwangbok was relatively less susceptible to anthracnose, compared with the other cultivars tested
Seedborne Infection of Rice by Pyricularia oryzae and Its Transmission to Seedlings
Authors: Manandhar H. K. , Jorgensen H. J. Lyngs , Smedegaard-Petersen V. , Mathur S. B.
Published: May 2007

Seedborne infection of rice by Pyricularia oryzae and its transmission to seedlings were studied quantitatively with naturally infected seeds of three rice cultivars collected from three locations in Nepal. A linear relationship on a logistic scale was found between panicle symptoms and seed infection, i.e., the more symptoms the higher seed infection. However, healthy-looking panicles and branches of panicles could also yield infected seeds. Postharvest measures such as winnowing and sun-drying significantly reduced seed infection by P. oryzae and filled grains had a lower degree of infection than unfilled grains. Sporulation of P. oryzae was most often confined to the embryonal end of germinating seeds. In contrast, most of the nongerminating seeds had sporulation all over the seed surface. Transmission of P. oryzae from seeds to seedlings, studied under various seeding conditions, showed that the transmission rate was always low. Thus, a seed sample with 21% seed infection resulted in less than 4% seedlings with blast lesions. Seed transmission was found for light covering of the seeds with soil or for moist seeding without covering. Transmission was rarely found when seeds were completely covered, and never in seedlings raised under water seeding conditions. Lower infection frequency was observed in seedlings raised in unsterilized soil than in seedlings raised in sterilized soil. Also, percent recovery of P. oryzae from infected seeds was higher in sterilized soil than in unsterilized soil and declined with time. Seedlings grown under low temperature (15 to 20°C) conditions did not develop blast lesions but when the same plants were transferred to high temperature (25 to 30°C) conditions, blast lesions were detected. This confirmed the latent infection in seedlings by P. oryzae grown under low temperature conditions.
Efficacy of Fungicides for Control of Entomosporium Leaf and Berry Spot of Saskatoon
Authors: Lange Ralph M. , Bains Piara S. , Howard Ronaldo J.
Published: May 2007

Studies were conducted to identify non-phytotoxic fungicides that would effectively control Entomosporium leaf and berry spot of saskatoon. Of 13 fungicides tested, benomyl, imazalil, myclobutanil, propiconazole, and thiophanate-methyl completely restricted in vitro radial growth of a monoconidial Entomosporium mespili isolate. Chlorothalonil, imazalil, propiconazole, and thiophanate-methyl completely inhibited conidiospore germination in vitro at 1 ppm a.i., the lowest concentration tested. In 1995, chlorothalonil and propiconazole provided the best control of Entomosporium leaf and berry spot at three orchard test sites in Alberta, Canada, while benomyl was also effective at two of these sites. Multiple applications of chlorothalonil (970 g ha–1) and propiconazole (125 g ha–1) effectively reduced disease severity at two of three test sites in 1996.
Progress of White Rot on Garlic Cultivars Planted at Different Times
Authors: Pinto Cleide M. F. , Maffia Luiz A. , Berger Richard D. , Mizubuti Eduardo S. G. , Casali Vicente W. D.
Published: May 2007

In the region of Amarantina, Minas Gerais state, Brazil, four annual experiments with garlic (Allium sativum) were established in fields infested with Sclerotium cepivorum, causal agent of garlic white rot, to investigate the effect of time of planting on the day when disease was first noticed (tonset), incidence at harvest (yf), duration of epidemics (tf — tonset), and the response of five cultivars to white rot. Most epidemiological parameters were similar among cultivars. In 1986 to 1988, no white rot was observed on garlic planted during the warm temperatures in January. The average onset of white rot occurred at different times dependent on the day of planting as average temperatures decreased from January to May. That is, for February plantings, onset occurred after 93 to 140 days (between 1 June and 5 July); for March plantings, about 90 days (15 to 28 June); for mid-April plantings, about 77 days (1 July); and mid-May plantings, about 66 days (20 July). Because of these different times of onset, the average duration of epidemics was shorter for crops planted in February (30 days) compared to crops planted in March (48 days) or April to May (54 to 69 days). In general, most disease (highest incidence and longest duration) occurred on crops planted in March to May. Therefore, severe losses to white rot would be expected when garlic is planted at the traditional times (March and April) in areas infested with sclerotia of S. cepivorum. The early planting of garlic is recommended as an important management strategy to avoid white rot in areas with these infested soils.
Evaluation of Simplified Leaf Inoculation Procedures for Identification of Quantitative Resistance to Sclerotinia trifoliorum in Alfalfa Seedlings
Authors: Pratt R. G. , Rowe D. E.
Published: May 2007

Previous studies established that excised leaf tissues of alfalfa can be inoculated with Sclerotinia trifoliorum to select for heritable resistance, but the original procedures were not practical for use in large-scale screening programs. In this study, simplified leaf inoculation procedures for more rapid screening for resistance, based on direct application of leaf tissues to colonies of the pathogen on agar media, were evaluated. Cotyledons, unifoliate leaves, and leaflets of trifoliolate leaves of plants 7 to 21 days old from three relatively susceptible cultivars and one resistant germ plasm were applied, with and without wounding, directly to colony margins of S. trifoliorum on cornmeal agar, V8 juice agar, and water agar. Leaves were scored according to the rate and extent of development of necrosis. Significant differences between alfalfa populations were expressed in unifoliate leaves and trifoliolate leaflets but not in cotyledons. Disease severity in the resistant germ plasm (Mississippi Sclerotinia-Resistant [MSR]) was less than in the three cultivars on all agar media. Wounding of leaf tissues increased disease severity and greatly reduced the incidence of symptomless leaves, which are indicated to be escapes, but wounding generally did not prevent expression of resistance in MSR. Results indicate that initial screening for resistance to S. trifoliorum in alfalfa seedlings may be accomplished by applying wounded unifoliate leaves and leaflets of trifoliolate leaves directly to colonies on cornmeal or V8 juice agars.
Effect of Temperature Regime and Growth Stage Interaction on Pattern of Virus Presence in TSWV-Resistant Accessions of Capsicum chinense
Authors: Soler Salvador , Díez M. José , Nuez Fernando
Published: May 2007

We studied the resistance to tomato spotted wilt virus in plant introduction accession (PI)-151225 and PI-159236 under Mediterranean climatic conditions. Two temperature regimes were utilized, corresponding to early and late cultivation cycles. Inoculations were made at 2- and 4-leaf stages to determine the effect of early infection. The existence of interaction between temperature regime and developmental stage was also studied. When plants of both PIs were maintained at 30/18°C (day/night), all plants at both growth stages when inoculated developed systemic infection. At 25/18°C, only those plants inoculated at 2-leaf stage became systematically infected; however, those inoculated at the 4-leaf stage behaved as resistant. Thus, there was an interaction between temperature regime and growth stage. There is potential for using this type of resistance in areas with mild climates, providing seedling infections are avoided.
Spatial Distribution of Armillaria mellea in Pear Orchards
Authors: Rizzo D. M. , Whiting E. C. , Elkins R. B.
Published: May 2007

Pears have traditionally been considered to be highly resistant to Armillaria root disease (causal agent: Armillaria mellea). In recent years, however, the incidence of Armillaria root disease in pears has increased in California. To determine the spatial distribution of Armillaria root disease in the field, a total of 156 isolates of Armillaria were collected from dead and dying pear trees located within two orchards in Lake County. All isolates from these two orchards, as well as from an additional 10 pear orchards, were identified as Armillaria mellea sensu stricto. Based on pairings among 102 Armillaria isolates, four somatic incompatibility groups (SIGs) were identified at orchard 1. Three of the four SIGs at this site were over 100 m in length; the largest SIG was at least 200 m in length. Pairings among 54 isolates identified five SIGs at orchard 2. The SIGs at orchard 2 were generally smaller than those detected at orchard 1 and ranged from 20 to 60 m in length. The size of the SIGs points toward long-term establishment of the fungus on the two sites, most likely predating the establishment of the pear orchards. Extensive root excavations of 19 trees indicated that the primary means of secondary spread of Armillaria was via rhizomorphs, as opposed to root-to-root contact.
Detection of a Geminivirus Infecting Sweet Potato in the United States
Authors: Lotrakul P. , Valverde R. A. , Clark C. A. , Sim J. , De La Torre R.
Published: May 2007

In 1994, a sweet potato sample showing leaf curl symptoms was collected from the field in Louisiana. When graft-inoculated, Ipomoea nil cv. Scarlett O'Hara reacted with severe leaf distortion and chlorosis symptoms. I. aquatica reacted with a bright yellow mottle. The virus isolated was designated the United States isolate of sweet potato leaf curl virus (SPLCV-US). It was transmitted to I. nil by the sweet potato whitefly, Bemisia tabaci biotype B. DNA probes prepared with component A of pepper Huasteco geminivirus, with an isolate of bean golden mosaic geminivirus from Guatemala, with an isolate of tomato mottle geminivirus from Florida, and with an isolate of tomato yellow leaf curl geminivirus from the Dominican Republic (TYLCV-DR) hybridized with a 2.6-kb DNA band present in DNA extracts from plants infected with SPLCV-US. Probes prepared with the B component of these geminiviruses did not hybridize with these DNA extracts. We were unable to amplify SPLCV-US DNA products by polymerase chain reaction (PCR) in quantities that could be visualized by ethidium bromide staining. However, Southern blots from amplifications with primers AV494/AC1048 revealed PCR products of approximately 600 bp and 550 bp when hybridized with the TYLCV-DR probe. These results were consistently obtained from infected I. cordatotriloba and less consistently from I. aquatica or I. setosa. Fibrillar inclusions were occasionally seen, and granular aggregates of viruslike particles were observed in the nucleus of infected I. cordatotriloba. These results suggest that the virus isolated from sweet potato with leaf curl symptoms belongs to the geminivirus group.
First Report of Butternut Canker Caused by Sirococcus clavigignenti-juglandacearum in New Brunswick, Canada
Authors: Harrison K. J. , Hurley J. E. , Ostry M. E.
Published: May 2007

In June 1997, butternut canker was found for the first time in New Brunswick, Canada, at Stickney, Carleton County. A fungal isolate recovered from a young branch canker on butternut (Juglans cinerea L.), cultured on potato dextrose agar, produced spores and cultural morphology as previously described (1). This strain was retained as FSC-758 in the Fredericton Stock Culture Collection at the Atlantic Forestry Centre. The disease was also detected at four other locations in Carleton County along the Saint John River watershed within 20 km of the State of Maine. One stem canker examined at Peel, Carleton County, suggests the disease has been present at this site in New Brunswick for at least 7 years. The butternut tree is at the northeastern edge of its natural range in New Brunswick and, prior to the pathogen's detection, was believed to be far enough from infected butternut in the northeastern United States, Ontario, and Quebec to escape infection. Because planted specimens of butternut exist outside the tree's natural range in New Brunswick and in the neighboring provinces of Nova Scotia and Prince Edward Island, efforts are underway to determine how far the fungus has spread in the Maritime Provinces.

Reference: (1) V. M. G. Nair et al. Mycologia 71:641, 1979.
Viral Satellite RNAs for the Prevention of Cucumber Mosaic Virus (CMV) Disease in Field-Grown Pepper and Melon Plants
Authors: Montasser M. S. , Tousignant M. E. , Kaper J. M.
Published: May 2007

A benign viral satellite RNA, in combination with a mild strain of cucumber mosaic virus (CMV-S), was used as a “vaccine” or “preinoculum” to demonstrate the feasibility of protecting pepper (Capsicum annuum cv. California Wonder) and melon (Cucurbita melo cv. Janus des Canaries) against two severe CMV strains, CMV-D and CMV-16, in the final 2 years of a 4-year pilot field and greenhouse experiment. In the field, healthy pepper and melon seedlings challenged with CMV-D and CMV-16 reduced yields by 33 to 60%; CMV-S caused only limited yield reduction in pepper and had no effect on the yield of melon. Different time intervals between preinoculation of pepper and melon seedlings with CMV-S and challenge inoculation with the severe CMV strains were tested. All plants challenged 3 weeks after vaccination showed nearly complete protection from subsequent infection by severe strains. The yield from preinoculated and challenged pepper plants was 80% that of untreated plants, while the yield from preinoculated and challenged melon plants was increased slightly over the untreated control plants. The use of this technology for biological control of plant viruses is discussed.
Comparative Efficacy of Preplant Fumigation and Postplant Chemical Treatment of Replant Citrus Trees in an Orchard Infested with Tylenchulus semipenetrans
Authors: le Roux H. F. , Ware A. B. , Pretorius M. C. , Wehner F. C.
Published: May 2007

Preplant soil fumigation with methyl bromide at 49 and 98 g/m2 was compared with various postplant nematicide and fungicide programs in a replant citrus orchard infested with the citrus nematode Tylenchulus semipenetrans and the fungal pathogens Phytophthora nicotianae, Fusarium solani, and F. oxysporum. Postplant treatments comprised multiple applications of fenamiphos at 4.0 g a.i./m2 soil, aldicarb at 4.5 g a.i./m2 soil, metalaxyl at 4 g a.i./m2 soil, fose-tyl-Al stem painting at 400 g a.i./liter, and combinations of fenamiphos + fosetyl-Al and aldi-carb + fosetyl-Al at the same rates as for single treatments. P. nicotianae could not be detected in the entire experimental site after replanting, but populations of F. solani and F. oxysporum showed only a temporary decline following site preparation. T. semipenetrans did not re-establish in any of the treatments within the first 2 years. Numbers of juveniles remained low in most treatments during the third year, but thereafter both juveniles and females increased significantly in all except the fumigated plots. Female populations on roots of citrus trees planted in fumigated soil remained suppressed for 8 years and the trees developed more vigorously and produced higher yields and larger fruit than those in non-fumigated soil. Compared with the control, net income for the period 4 to 8 years after planting increased by 101 and 46% in plots fumigated with 49 and 98 g/m2, respectively. With the exception of aldicarb, all other treatments showed net losses.
Transmission Frequency of Clavibacter michiganensis subsp. insidiosus to Alfalfa Seed and Identification of the Bacterium by PCR
Authors: Samac Deborah A. , Nix Ronda J. , Oleson Arland E.
Published: May 2007

A sensitive polymerase chain reaction (PCR)-based identification method was developed for Clavibacter michiganensis subsp. insidiosus, the causal agent of alfalfa bacterial wilt. The method, which targets a high-copy-number insertion element, is rapid and specific for this plant pathogen. The assay was used to determine the frequency of transmission of the pathogen to alfalfa seed. Seed was produced from infected plants grown and pollinated in the greenhouse, from infected plants grown in the field and transplanted to the greenhouse to produce seed, and from diseased 2-year-old field-grown plants. Seed from each infected plant were assayed to identify infected seed lots. Seed were ground to a fine powder and soaked in a liquid medium, after which a portion of the seed slurry was plated on a semi-selective agar medium. The PCR assay was used to identify C. michiganensis subsp. insidiosus colonies on plates. Approximately 6.3 to 7.7% of diseased plants transmitted C. michiganensis subsp. insidiosus to seed. In assays in which individual seed were analyzed from infected seed lots, approximately 2.5 to 8.7% of seed contained the bacterium.
Biology of the Transmission of Peach Mosaic Virus by Eriophyes insidiosus (Acari: Eriophyidae)
Authors: Gispert Carmen , Oldfield George N. , Perring Thomas M. , Creamer Rebecca
Published: May 2007

Experiments were undertaken to elucidate the characteristics of the transmission of peach mosaic virus (PMV) by Eriophyes insidiosus. Transmission efficiency by single E. insidiosus was as high as 17%. The minimum inoculation access period was between 3 and 6 h. E. insidiosus acquired the virus after a minimum acquisition access period of 3 days. No latent period was demonstrated. While most plant viruses which are transmitted by eriophyid mites are transmitted in a persistent mode, our data are more consistent with a semipersistent model.
First Report of Macrophomina phaseolina Causing Pre-harvest Cassava Root Rot in Benin and Nigeria
Authors: Msikita W. , James B. , Wilkinson H. T. , Juba J. H.
Published: May 2007

In diagnostic surveys conducted in parts of Benin and Nigeria to determine the incidence of pre-harvest cassava root and stem rot during the dry season, Macrophomina phaseolina (Tassi) Goidanich constituted 14.2 and 18.7% of the total fungi (n = 201) associated with cassava root and stem rot from Benin and Nigeria (1). Pathogenicity of M. phaseolina on cassava was tested with cv. Agric. Inocula for pathogenicity tests were prepared by incubating 5-mm-diameter mycelial plugs for each of five isolates (Mp 1 to Mp 5, all collected from Benin) with 500 ml of autoclaved, sterilized, dehusked rice seed for 14 days at 30°C. Five 30-cm-long stem portions per isolate were cut from healthy cassava, surface disinfested in hot water (52°C, 5 min), and planted into 1-liter pots containing autoclaved, sterilized sand mixed with 10 ml of air-dried inoculum. Five plants per isolate similarly treated but not inoculated served as controls. Plants were watered once a week, and maintained in a greenhouse under natural light at 28 to 30°C. Lower leaves of inoculated plants gradually wilted, usually preceded by chlorosis, and brown to black lesions formed on the lower stem portions of some roots. Control plants remained asymptomatic. Plant height and percentage of leaf wilt (determined by counting the number of leaves wilted per plant and dividing by the total number of leaves per plant) were measured on a weekly basis for 8 weeks for each of the control and inoculated plants. At the end of 8 weeks, lesion length on the lower stem was measured. There were significant differences (P < 0.05) in length of the lesions and percentage of leaf wilt induced by the different isolates of M. phaseolina. Isolate Mp 1 induced the longest lesion (7.2 cm), followed by Mp 4 (4.1 cm), Mp 3 and Mp 5 (3.8 cm each), and Mp 2 (1.2 cm). Mp 4 induced the highest percentage of wilted leaves (53%), followed by Mp 1, Mp 3, and Mp 5 (30%), and Mp 2 (10%). All five M. phaseolina isolates (except Mp 3) reduced plant height, compared with control treatments. M. phaseolina was isolated from all infected plants, and the identification was independently confirmed by the International Mycological Institute, Surrey, UK. This is the first report of M. phaseolina causing pre-harvest cassava root rot in Benin and Nigeria.

Reference: (1) W. Msikita et. al. Plant Dis. 81:1332, 1997.
First Report of Natural Occurrence of Zucchini Lethal Chlorosis Tospovirus on Cucumber and Chrysanthemum Stem Necrosis Tospovirus on Tomato in Brazil
Authors: Nagata Tatsuya , Resende Renato de O. , Kitajima Elliot W. , Costa Helcio , Inoue-Nagata Alice K. , de Ávila Antonio C.
Published: May 2007

During a field survey in 1994, five cucumber (Cucumis sativus) cv. Hokushin plants showing symptom of yellowing, mottling, and vein banding on the leaves were collected from a commercial field of the Federal District. By electron microscopy, quasi-spherical particles with double membrane, typical tospovirus-like particles were found in the infected leaf material. All samples strongly reacted with antibody of zucchini lethal chlorosis tospovirus (ZLCV), but not with antibodies of other to-spoviruses reported in Brazil (1): tomato spotted wilt virus (TSWV), tomato chlorotic spot virus (TCSV), groundnut ringspot virus (GRSV), chrysanthemum stem necrosis virus (CSNV), or iris yellow spot virusonion isolate (IYSV-BR). The virus was identified as ZLCV, which was first isolated in 1994 from zucchini (Cucurbita pepo) in São Paulo State, Brazil. Tomato (Lycopersicon esculentum) plants showing stem necrosis and necrotic spots and rings on the leaves were collected in Viçosa, Minas Gerais State. By electron microscopy, molecular studies, and enzyme-linked immunosorbent assay with antibodies of the six tospoviruses occurring in Brazil, the virus was identified as CSNV. This virus was first reported in 1995 on a Chrysanthemum sp. in São Paulo State and recently reported in the Netherlands from Dendranthema indicum. This is the first report of the natural occurrence of ZLCV and CSNV on cucumber and tomato, respectively.

Reference: (1) A. C. de Ávila et al. 1998. Pages 32–34 in: Int. Symp. on Tospoviruses and Thrips in Floral and Vegetable Crops, 4th.
Fusarium moniliforme and F. proliferatum Isolated from Crown and Root Rot of Asparagus and Their Association with Asparagus Decline in Argentina
Authors: Lori G. , Wolcan S. , Mónaco C.
Published: May 2007

During the summer of 1995-1996, an 80-ha field of 6-year-old asparagus plants (cv. UC 72) in Saladillo (Province of Buenos Aires) was affected by a decline syndrome (1). The plants showed a decline in vigor and approximately 60 to 70% of the plants died. The symptomatic plants were chlorotic, stunted, with stem lesions and crown and root rot. Fusarium moniliforme and F. proliferatum were isolated from vascular and epidermal tissues of roots, crowns, and stems. Identification of Fusarium to species was made by examining conidiogenous cells from colonies cultured on KCl medium (2). Microconidia were born in long and short chains and false heads. The isolates were identified based on the the presence of polyphialides in F. proliferatum and their absence in F. moniliforme, which produces monophialides only (2). In two separate trials, asparagus seeds (cv. UC 72) were surface sterilized and placed in steamed soil infested with a conidial suspension of each species. The viable propagules in the soil (CFU per g) were estimated by soil plate dilutions on Nash & Snyder-PCNB (pentachloronitrobenzene) medium. The F. moniliforme and F. proliferatum soil densities were 19.2 × 103 and 23 × 103 CFU per g of soil, respectively. The pots were placed in the greenhouse on different benches to avoid cross-contamination. After 4 months, inoculated plants showed root and crown discoloration. F. moniliforme and F. proliferatum were reisolated (64 and 75%, respectively) from discolored portions of internal and external root and crown tissues. Although the stems did not show symptoms, F. moniliforme and F. proliferatum were also recovered (27 and 38%, respectively) from asymptomatic tissues. Six months after inoculation the plants developed chlorotic symptoms with crown and root rot, and then wilted. F. moniliforme and F. proliferatum were reisolated from root systems, crowns, and stems of all inoculated plants. F. moniliforme and F. proliferatum are involved in corn stalk and ear rot in Argentina. Corn and asparagus are frequently grown in close proximity and often follow one another at a particular site. Airborne and soil debris carrying F. moniliforme and F proliferatum from corn may be an additional source of inoculum for asparagus in Argentina. The results indicate that the presence of F. moniliforme and F. proliferatum is a factor that contributes to asparagus decline in Argentina.

References: (1) W. H. Elmer et al. Plant Dis. 80:117, 1996. (2) P. E. Nelson et al. Fusarium Species: An Illustrated Manual for Identification. Pennsylvania State University, University Park, 1983.
Wheat: A New Natural Host for the Mal De Río Cuarto Virus in the Endemic Disease Area, Río Cuarto, Córdoba Province, Argentina
Authors: Pardina P. E. Rodriguez , Pecci M. P. Giménez , Laguna I. G. , Dagoberto E. , Truol G.
Published: May 2007

The fijivirus known as “Mal de Río Cuarto” that affects corn is endemic to the area of Río Cuarto, Cordoba Province, Argentina. One of the preferred species for the development of its vector, the insect Delphacodes kuscheli Fennah, is wheat. In this area, wheat plants with deformed leaves, spikes and spikelets, shortened internodes, leaves with serrated borders, and sterile spikelets were detected, suggesting the possibility that Mal de Río Cuarto Virus could also be infecting this crop. Samples originating in Río Cuarto, Sampacho, and La Carlota (Córdoba Province) that showed symptoms, were analyzed by double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA), polyacrylamide gel electrophoresis, and electron microscopy, confirming, for the first time, the occurrence of the disease in wheat. The frequency of the disease was assessed in random samples from 14 wheat plots located in the Department of Río Cuarto (Córdoba Province). The samples were analyzed using the DASELISA immunoenzymatic technique, and the disease was detected in the majority of the fields assessed, with levels of incidence that ranged between 2.5 and 24%. We must be aware of the presence of this virus in the wheat crop, where it appears to play a double role in the epidemiology of the disease, acting both as a virus reservoir and as a preferred host for the development of populations of the vector virus, D. kuscheli.
Identification of Erwinia amylovora by Growth Morphology on Agar Containing Copper Sulfate and by Capsule Staining with Lectin
Authors: Bereswill Stefan , Jock Susanne , Bellemann Peter , Geider Klaus
Published: May 2007

Erwinia amylovora strains formed yellow colonies on minimal agar medium MM2 containing asparagine and copper sulfate (MM2Cu), in contrast to a white morphology on minimal agar without copper salt. Additionally, the colonies were mucoid to various extents. The yellow color was characteristic for the fire blight pathogen, including strains from raspberry and from other unusual host plants, and was used to establish a novel plating technique for identification of E. amylovora. The new identification method was especially superior to semi-selective media with sucrose when natural levan-deficient strains were assayed. No growth of E. amylovora was observed for the similar medium MM1 containing 2 mM CuSO4, due to its low content of as paragine. Identification by colony morphology on MM2 agar with copper was confirmed by staining the bacterial capsules with FITC-labeled lectin from Abrus precatorious, a compound which has a high affinity for galactose residues, the main sugar in the capsular exopolysaccharide amylovoran of E. amylovora. Other plant-associated bacteria usually did not produce the typical colony morphology of E. amylovora on MM2 agar with copper. Furthermore, those cells were not stained with the Abrus lectin. Capsule staining was also observed for weakly mucoid strains of E. amylovora, but not for strains with mutations affecting amylovoran synthesis. The secretion of fluorescent compounds by Pseudomonas syringae pathovars and even growth of any other bacterial colonies adjacent to E. amylovora could interfere with the formation of typical yellow colonies on MM2Cu, which could be white in case of dense plating. After screening for white colonies on LB agar, E. amylovora was identified in extracts from Cotoneaster leaves and in bark from apple trees with fire blight symptoms by its yellow growth pattern on MM2Cu agar and by capsule staining. The proposed selective medium gives a clear signal, is easy to prepare, does not contain dyes or any compounds toxic to humans, and can also detect E. amylovora strains deficient in levan synthesis.
Response of Bell Pepper Cultivars to Bacterial Spot Pathogen Races that Individually Overcome Major Resistance Genes
Authors: Kousik C. S. , Ritchie D. F.
Published: May 2007

The effect of major resistance genes (Bs1, Bs2, and Bs3) or gene combinations for resistance to bacterial spot of bell peppers (Xanthomonas campestris pv. vesicatoria) in 15 commercial cultivars on disease reduction and yield were studied during 1995 and 1996. Reaction of cultivars to specific races (races 1, 2, or 3) of the pathogen corresponded with seed company claims for resistance against these races. Races 1 to 4 were used as initial inoculum in 1995, and races 1 to 6 in 1996 field experiments. Cultivars with no known resistance genes to bacterial spot (e.g., Camelot, Jupiter, and Valiant), a single resistance gene (X3R Camelot, King Arthur), or a combination of Bs1 and Bs3 genes (Guardian, Sentinel, and Admiral) were severely diseased. Yields were reduced in all inoculated cultivars compared to non-inoculated cultivars used as controls. Although races 4 and 6 caused significant disease in cultivars with only Bs1 (King Arthur) or Bs2 (X3R Camelot) genes, cultivars with a combination of Bs1 and Bs2 (Boynton Bell, PR9300-8) had much lower levels of bacterial spot. Roger 4178, a hybrid with a combination of Bs1, Bs2, and Bs3 genes, had the lowest disease ratings. Overall, race 3 was predominant during 1995, while races 3 and 6 were recovered most frequently in 1996.
Survival of Phytophthora colocasiae in Field Soil at Various Temperatures and Water Matric Potentials
Authors: Quitugua R. J. , Trujillo E. E.
Published: May 2007

A large number of the zoosporangia of Phytophthora colocasiae incorporated into moist soils germinated by zoospore discharge, and/or lysed in the soil during the first 5 days of incubation, decreasing the initial number of colony-forming units from 1 × 104 to 1 × 102 per g of soil in all treatments. Eighteen days after incorporation, the viable zoosporangia present in moist soils had thickened their cell walls and germinated only directly, often producing smaller zoosporangia. A few thick-walled chlamydospores were observed, and they germinated only directly. Zoosporangia in soils at -1,500 J/kg matric potential survived longer than 107 days, and the amount of viable Zoosporangia present at that time was approximately 0.1 × 102 CFU/g of soil. Apparently the great majority of the thin-walled zoosporangia produced on V8 agar, when incorporated into moist soil, germinated indirectly in the first 5 days of incubation. Zoosporangia that did not germinate became resting zoosporangia by increasing their wall thickness or by producing chlamydospores. These enabled the pathogen to survive in soil at -1,500 J/kg matric potential for more than 3 months. However, in the absence of the host, the pathogen is predicted to survive less than 1 year due to its lack of saprophytic ability to colonize nonhost tissues.
A Psorosis-Like Agent Prevalent in Florida's Grapefruit Groves and Budwood Sources
Authors: Powell C. A. , Pelosi R. R. , Sonoda R. M. , Lee R. F.
Published: May 2007

Rio Grande Gummosis (RGG) is one of the most serious diseases of grapefruit in the Indian River region of Florida. Experiments were conducted to determine if a graft-transmissible agent was associated with this disease in commercial grapefruit, and if any such agent was present in scion sources used for grapefruit propagation. Indexing data from indicators revealed that 79% and 31% of the commercial grapefruit and scion trees, respectively, contained a psorosis-like agent (PLA). The PLA was present in both RGG-affected and symptomless trees. We conclude that Florida's grapefruit propagation sources are contaminated with a PLA that is now widespread in commercial plantings.
Analysis of Proteins of Disease-Free and Didymascella thujina-Infected Leaves of Western Red-Cedar (Thuja plicata)
Authors: Kope Harry H. , Ekramoddoullah Abul K. M. , Sutherland Jack R.
Published: May 2007

Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of crude extracts of disease-free and Didymascella thujina-infected foliage of western red-cedar revealed differences in several protein bands and suggests that distinct proteins of D. thujina origin can be identified by SDS-PAGE.
Postharvest Application of Organic and Inorganic Salts for Suppression of Silver Scurf on Potato Tubers
Authors: Olivier Claudia , Halseth Donald E. , Mizubuti Eduardo S. G. , Loria Rosemary
Published: May 2007

Seven organic and inorganic salts were tested for suppression of silver scurf, a postharvest disease of potato tubers caused by Helminthosporium solani. Potassium sorbate, calcium propionate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and ammonium bicarbonate were added to V8 agar at concentrations of 0.06–0.2 M. Radial growth of H. solani was significantly reduced (P < 0.05) by all salts at all concentrations. All salts except sodium bicarbonate and potassium bicarbonate were fungicidal at 0.2 M. Effects of postharvest salt treatments on disease severity and sporulation of H. solani on inoculated and naturally infected potato tubers were evaluated in separate experiments. Greenhouse-grown tubers were inoculated with H. solani spore suspensions (2 × 105 spores/ml), incubated for 5 days, dipped into 0.2 M solutions of each of the salts, and incubated in a moist chamber at 22–24°C for 6 weeks. All salt treatments prevented lesion development and sporulation of H. solani and differed significantly (P < 0.05) from the control. Postharvest applications of test compounds (0.2M) also significantly (P < 0.05) reduced disease severity and H. solani sporulation on naturally infected, field-grown tubers after 15 weeks of storage at 10°C. Salt treatments did not differ in disease or pathogen suppression. These relatively nontoxic organic and inorganic salts have potential as postharvest applications for control of silver scurf.
Acquisition of Ophiostoma quercus and Ceratocystis fagacearum by Nitidulids from O. quercus-Colonized Oak Wilt Mats
Authors: Juzwik Jennifer , Cease Kory R. , Meyer Jason M.
Published: May 2007

Field experiments were conducted to determine whether the frequency of Ceratocystis fagacearum and Ophiostoma quercus propagule acquisition by nitidulids visiting oak wilt fungal mats is affected by the presence of O. quercus on the mats. Augmentation sprays with O. quercus were used to achieve different levels of mat colonization by that fungus. The extent of colonization by O. quercus 7 to 14 days after spraying was greatest for postmature mats with open cracks (>0.5 cm) observed on the spray date (P< 0.02). Specifically, all six subsamples assayed per mat for 16 of 18 open, O. quercus-sprayed, postmature mats yielded O. quercus. The frequency of nitidulids with O. quercus was also highest (83%) for those collected from O. quercus-treated, postmature mats that were open on the spray date. The frequency of nitidulids with viable C. fagacearum (88%), however, was also greatest for beetles from the postmature mats. Thus, O. quercus colonization did not affect vector acquisition of C. fagacearum from the mats. In addition, O. quercus vectored by nitidulids probably does not result in natural biological control of overland transmission of C. fagacearum at fresh wound surfaces on healthy oaks, as previously suggested.
Interception of Xanthomonas campestris pv. dieffenbachiae on Anthurium Plants from the Netherlands
Authors: Sathyanarayana N. , Reddy O. R. , Latha S. , Rajak R. L.
Published: May 2007

Xanthomonas campestris pv. dieffenbachiae, the causal agent of anthurium bacterial blight, is a major concern of the anthurium industry worldwide. This pathogen has many hosts in the family Araceae (e.g., Anthurium, Dieffenbachia, Syngonium, Aglaonema, Philodendron, Xanthosoma, Caladium, and Colocasia). Most anthurium cultivars are susceptible to bacterial blight, making it very difficult to manage the disease once introduced to a production area. Therefore, sanitation and exclusion of the pathogen through pathogen-free propagative stock are vital aspects of anthurium cultivation. The anthurium industry is expanding in India, and as many new cultivars are being imported, the plant material is subject to thorough quarantine inspection at the port of arrival. During routine inspections on three separate occasions, Anthurium andreanum plants imported from The Netherlands had watersoaked spots at leaf margins bordered by chlorotic or necrotic zones. Xanthomonas-like colonies were isolated from four different cultivars with semiselective media (2). Bacteriological tests confirmed that the cultures were X. campestris. Pathogenicity tests, performed by rubbing leaves with a cotton swab dipped into a suspension of the bacteria (approx. 107 CFU/ml), resulted in production of leafspots in 6 days and early blight symptoms in 10 to 12 days. The bacterium was further identified as X. campestris by carbon source utilization (similarity coefficient = 0.582; Biolog, Hayward, CA). Enzyme-linked immunosorbent assay reaction patterns with a panel of monoclonal antibodies for X. campestris pv. dieffenbachiae designated as Xcd1 (clone 72E-E3-B9-C5, isotype IgG2a), Xcd2 (clone 97-2-1-01, isotype IgM), Xcd3 (clone 72B-F9-B6-E9, isotype IgM), Xcd7 (clone72D-E10-C2-D9, isotype IgM), T1 (clone 92-16, isotype IgM), and T2 (clone 92-59-1-1, isotype IgG) showed that the intercepted strain belong to the serogroup 5 of X. campestris pv. dieffenbachiae (1). This pathogen is not known to occur in India, and there is high probability of risk of introduction through large-scale import of anthurium plants with either visible or latent infections.

References: (1) R. L. Lipp et al. Phytopathology 82:677, 1992. (2) D. J. Norman and A. Alvarez. Plant Dis. 73:654, 1989.
Occurrence of Petunia Vein-Clearing Virus in the U.S.A.
Authors: Lockhart B. E. L. , Lesemann D.-E.
Published: May 2007

Petunia vein-clearing virus (PVCV), a tentative member of the caulimovirus group of plant pararetroviruses, was first identified in petunia (Petunia hybrida Vilm.) in Germany in the hybrid cv. Himmelröschen (1). A similar virus was recently identified in Minnesota in the petunia cv. Fantasy Pink grown from seed in commercial greenhouses. This virus has spherical particles 46 to 47 nm in diameter in preparations negatively stained with 1% uranyl acetate or sodium phosphotungstate, pH 7.0, and which contain a double-stranded DNA genome approximately 7.3 kb in size. The virus was shown by immunoelectron microscopy (IEM) to be closely related serologically to PVCV. No serological relationship to any other caulimoviruses was detected. Like PVCV, which is transmitted only by seed and grafting, the Minnesota virus isolate was not transmitted by mechanical inoculation to petunia or any other indicator plant. Symptoms associated with infection by PVCV in cv. Fantasy Pink consisted of mild vein clearing to severe vein yellowing, and reduction in leaf size and internode length. Symptoms were most frequently expressed when plants were under water and nutrient stress. Vigorously growing plants usually showed no symptoms, and no virions were detected by IEM in partially purified extracts from such plants. This suggests that infection of petunia hybrids by seed-borne PVCV may possibly be more widespread, but may go unnoticed because virus-induced symptoms may not be elicited in plants growing under favorable conditions.

References: (1) D. Lesemann and R. Casper. Phytopathology 63:1118, 1973.
First Report of Sclerotium Production by Sclerotinia sclerotiorum in Soil on Infected Soybean Seeds
Authors: Yang X. B. , Workneh F. , Lundeen P.
Published: May 2007

Stem rot of soybean caused by Sclerotinia sclerotiorum (Lib.) de Bary was not recognized as an important problem in the North Central Region of the United States until severe outbreaks occurred in 1992, 1994, and 1996 (2). Although sclerotia mixed with seeds are known to be important to the spread of this disease, the role of internally infested soybean seed in dissemination of the disease is unknown. Tu (1) demonstrated in dry bean, which differs from soybean in seed size and plant architecture, that internally infected seeds are important to the spread of the disease, by producing sclerotia in the soil after the seeds are planted. Experiments were conducted to determine if sclerotia are formed in soils from internally infected soybean seeds. Soybean seed from a field with 70% disease severity were collected and sorted into three classes: (i) normal quality seed, which included moderate or good seed; (ii) poor quality seed (shriveled and/or whitish); and (iii) seed of regular size with visible mycelial mats (S. sclerotiorum or Peronospora manshurica (Naumov) Syd. in Gäum) on the seed coat. Transfer of surface-disinfested seeds to potato dextrose agar and subsequent production of sclerotia showed that 2, 44, and 6% of the seed from each respective class were infested with S. sclerotiorum. One hundred seeds from each of these classes were planted into sterilized and nonsterilized soil at a rate of 5 seeds per pot. Toothpicks were placed to identify the location of each seed, and seeds were covered with 2 cm of soil. Pots were placed in growth chambers with a 14-h photoperiod under two temperature regimes: (i) at 20°C; and (ii) at 10°C for 10 days and then raised to 20°C. Soil was kept saturated by periodically top watering the pots for the first 10 days and bottom watering after that. Two weeks after planting, seeds were examined for formation of sclerotia and the percentages of seeds from which sclerotia were formed were calculated. The experiments were conducted four times. One to two (occasionally three) sclerotia were found in place of each seed that did not germinate. Sclerotia were mainly found from seeds of poor quality, with an average of 12% seeds that produced sclerotia. The frequency of sclerotia found in normal quality seeds was 0.4%, and no sclerotia were found from seeds with mycelial mats. The sclerotia were 2.36 ± 1.07 mm in width, 3.33 ± 1.11 mm in length, and 6.8 ± 3.7 mg in weight, with an averaged germination rate of 88% 8 months after production. Sclerotia production frequencies were 11.4 and 15.4% for temperature regimes (i) and (ii), respectively. Higher percentages of sclerotium production were found in sterilized soil (15.6%) than nonsterilized soil (7.5%). Our results indicate the possibility of internally infected soybean seeds as a means for field-to-field dissemination of S. sclerotiorum.

References: (1) J. C. Tu. J. Phytopathol. 121:40, 1988. (2) X. B. Yang. ICM Newsl. 18, 1997.