bluuebunny/crossref_metadata_2025 huggingface dataset:
Pathogenicity of Macrophomina phaseolina to Mature Plant Tissues of Alfalfa and White Clover
Authors: Pratt R. G. , McLaughlin M. R. , Pederson G. A. , Rowe D. E.
Published: May 2007

Macrophomina phaseolina has been observed on alfalfa and white clover in North America, but its pathogenicity to mature plants of these species has not been adequately documented and Koch's postulates have not been fulfilled. Isolates of M. phaseolina from alfalfa and white clover were evaluated for pathogenicity by inoculating tissues of mature plants with infested toothpick pieces. Excised leaf tissues also were inoculated with mycelium. In stolons of white clover and stems of alfalfa, M. phaseolina caused a brown-black, basipetally progressive necrosis of vascular tissue with subsequent collapse of the surrounding pith and epidermis to produce radially constricted, expanding lesions. In taproots and crowns of alfalfa, M. phaseolina caused dark discoloration of vascular tissues in bands or streaks above and below inoculation points with subsequent invasion and death of cortical tissues, lateral roots, and stems. Sclerotia formed in all tissues of both species. Excised leaf tissues were rapidly parasitized, but significant differences in rates of parasitism between genotypes suggested that differences in host resistance to M. phaseolina may be present in both species. Pycnidia formed on leaves of bean, lima bean, and cotton. All isolates of M. phaseolina were reisolated from margins of necrosis in all types of inoculated tissues and regrown in pure culture. These results fulfill Koch's postulates for M. phaseolina as a pathogen of mature white clover and alfalfa in North America, and they demonstrate its capacity to parasitize a variety of tissues of both species in the absence of other pathogens. Results indicate that M. phaseolina should be considered a potential cause for lack of persistence of white clover and alfalfa during summer months in the southeastern United States.
Characterization of Fusarium Root Rot Isolates from Sugar Beet by Growth and Virulence at Different Temperatures and Irrigation Regimes
Authors: Harveson R. M. , Rush C. M.
Published: May 2007

Fusarium root rot, caused by Fusarium oxysporum f. sp. betae is one of several root diseases damaging to sugar beet production in Texas. As a primary symptom, most isolates produce a severe tip rot on the distal end of the taproot, in addition to discoloration of vascular elements and wilting. Tip rot distinguishes Fusarium root rot from another F. oxysporum f. sp. betae-incited disease, Fusarium yellows, which induces vascular discoloration and wilting but no root rot. This study was conducted to further characterize a selection of five Texas F. oxysporum f. sp. betae isolates representing different vegetative compatibility groupings, symptom types (tip rot, and non-tip rot), and hosts. Radial growth at six temperatures was measured for each isolate in culture on half-strength potato dextrose agar. Significant growth differences were detected, indicating a substantial amount of variation among the isolates. Virulence of isolates was evaluated by inoculating 6-week-old sugar beet plants with a microspore suspension and transplanting them into infested field soil. The plants were incubated at 20 and 30°C in controlled temperature boxes within the greenhouse and grown under two different irrigation schedules. After 6 weeks, plants were harvested and assigned a root disease rating, and root and foliar dry weights were determined. Disease ratings among isolates at 30°C resulted in three isolates (all tip rot isolates) being severe, one mild, and one intermediate. At 20°C, only one isolate caused appreciable root damage. Irrigation treatments had no effect on disease incidence or severity. Significant differences in colony diameter growth and virulence among isolates at the two temperatures provide further evidence of variation among Texas F. oxysporum f. sp. betae populations. Results also suggest that the tip rot phenotype may be induced by some genetic factor unique to tip rot isolates. Therefore, the form name F. oxysporum f. sp. radicis-betae is proposed for those isolates from Texas causing a tip rot.
Estimating the Economic Impact of Breeding Nonspecific Resistance to Leaf Rust in Modern Bread Wheats
Authors: Smale M. , Singh R. P. , Sayre K. , Pingali P. , Rajaram S. , Dubin H. J.
Published: May 2007

Breeding for resistance to rust diseases in wheat is an example of productivity maintenance research. Productivity maintenance research is necessary to avoid contractions in the wheat supply curve that result from changes in the biological or physical environment. In this study, the benefits of incorporating nonspecific resistance to leaf rust caused by Puccinia recondita into modern bread wheats (Triticum aestivum) have been estimated using data on resistance genes identified in cultivars, trial data, and area sown to cultivar in the Yaqui Valley, Sonora State, Mexico. In the most pessimistic scenario, the gross benefits generated in the Yaqui Valley from 1970 to 1990 were 17 million U.S. dollars (in 1994 real terms). Even when costs were overstated and benefits were understated, the internal rate of return on capital invested was 13%, well within the range recommended for use in project evaluations by the World Bank. Substantial economic benefits likely are associated with deployment of nonspecific resistance in many wheat-producing areas of developing countries where farmers change cultivars slowly because of delays in cultivar release, incomplete seed markets, and economic factors related to adoption or where disease pressure is heavy and the costs of treating disease outbreaks is high.
First Report of Leaf Rust of Blueberry Caused by Pucciniastrum vaccinii in Argentina
Authors: Dal Bello G. , Perelló A.
Published: May 2007

During March, 1997, a leaf rust was observed on Vaccinium corymbosum L. cv. Bluegold in Argentina. Leaf lesions began as chlorotic flecks that expanded and developed into necrotic spots with several uredinia. The typical orange pustules of the disease developed mostly on the abaxial sides of leaves. Urediniospores were elliptical to obovate (17 to 28 × 11 to 23 μm) and finely verrucose. Telia were round, covered by the epidermis, slightly elevated, and brown to black. Teliospores were sessile and oblong to columnar (7 to 11 × 14 to 17 μm) with two or more vertical cell walls, and were smooth and brown. Urediniospore and teliospore morphology and dimensions were consistent with the description of Pucciniastrum vaccinii (G. Wint.) Jørst (syn. P. myrtilli Arth.) (1). A pathogenicity test was conducted with 18-month-old cv. Bluegold plants. Fully expanded leaves were sprayed, using a hand-held sprayer, with freshly collected urediniospores (1 mg of spores per ml of 0.05% water solution of Tween 20), covered with plastic bags, and placed in a growth chamber at 20°C for 48 h with 12 h of light per day. The plastic bags were then removed and the plants mantained in a greenhouse. After 10 days, orange rust pustules similar to the original symptoms developed on all plants. As the rust was not reported on ornamental Ericaceae in Argentina, and hemlock, the alternate host, is not present in the area, it is suggested that P. vaccinii is cycling on blueberry. This is the first report of P. vaccinii on blueberry in Argentina.

Reference: (1) P. R. Bristow and A. W. Stretch. 1995. Pages 20–22 in: Compendium of Blueberry and Cranberry Diseases. F. L. Caruso and D. C. Ramsdell, eds. American Phytopathological Society, St. Paul, MN.
Split Applications of Copper Fungicides Improve Control of Melanose on Grapefruit in Florida
Authors: Timmer L. W. , Zitko S. E. , Albrigo L. G.
Published: May 2007

Citrus melanose, caused by Diaporthe citri, is a major disease of fresh market grapefruit which is controlled primarily by preventive applications of copper fungicides. The goal of this research was to improve melanose control without increasing the total amount of metallic copper utilized. Disease control was assessed in field experiments for 3 years using one, two, three, or four applications of copper fungicides in which the same total amount of metallic copper was applied per season in each program. Melanose was severe in 1995 and 1997, and the four-application schedule provided better control than the one-, two-, or three-application programs. In 1996, disease pressure was low and all programs and fungicides provided equally effective control. Analysis of copper residues on the fruit indicated that loss of protection was attributable more to increase in fruit surface area when fruit were growing rapidly than to removal of copper by weathering. On larger, slower-growing fruit, loss of copper residues was apparently due to both factors. Economic evaluation of improved packouts of fresh market fruit and additional application costs indicated that net returns would be increased by $650 to $1,250 per hectare during years in which melanose was severe when the four-spray program was compared to a single spray.
Effects of Seedborne Potato Virus Y Infection in Two Potato Cultivars Expressing Mild Disease Symptoms
Authors: Hane D. C. , Hamm P. B.
Published: May 2007

The effects of seedborne potato virus Y (PVY) in Shepody and Russet Norkotah, two new cultivars that express mild disease symptoms, were determined by comparing tuber yield and specific gravity of plants grown from PVY-infected seed with those of adjoining plants grown from virus-free seed. Seedborne PVY-infected Shepody plants produced 28.7% less total yield in 1994, and 41.1 and 47.3% less in two trials in 1995. Marketable yield was reduced 55.8 and 79.4% in 1995 trials. PVY infection did not affect specific gravity in Shepody. Seedborne PVY infections in Russet Norkotah reduced total yield by 45.5 and 48.8% in the 1994 and 1995 trials, respectively. During the 1995 trial, marketable yield from seedborne infected plants was reduced 65.1% compared with adjacent plants grown from noninfected seed. Additionally, specific gravity was lower for tubers from seedborne infected Russet Norkotah plants than from plants grown from noninfected seed in 1994. Seedborne infected plants of both varieties had fewer and smaller tubers than did plants grown from virus-free seed. No compensatory yield increase was measured for plants originating from PVY-free seed and growing adjacent to seedborne infected plants for either variety. Rather, yield reduction was observed in Russet Norkotah plants growing adjacent to seed infected plants in 1995. Enzyme-linked immunosorbent assay (ELISA) on Shepody in 1995 showed most plants grown from PVY-free seed became infected within 6 weeks of emergence.
Natural Infection of Muskmelon by Eggplant Mottled Dwarf Rhabdovirus in Italy
Authors: Ciuffo M. , Roggero P. , Masenga V. , Stravato V. M.
Published: May 2007

Eggplant mottled dwarf rhabdovirus (EMDV) is endemic in the Mediterranean area but within the family Cucurbitaceae has been reported only in cucumber (1). In the spring of 1998 unusual symptoms of stunting, short internodes, fruit deformation, and vein yellowing were observed in about 5% of muskmelon (Cucumis melo L. var. reticulatus Naudin) cv. Hombre F1 grown under plastic in Tuscany (Central Italy). Electron microscopy of negatively stained preparations of crude sap from such melon plants revealed the presence of large numbers of particles resembling rhabdovirus. The virus, sap transmitted to several test plant species, had a host range identical to that of typical EMDV isolates, including the isolate from cucumber. Based on both electron microscopy and test plant reactions, the presence of other viruses was excluded. As with other known isolates, symptoms did not appear until about 30 days after inoculation, except for necrotic local lesions in Gomphrena globosa, which appeared in 10 days. Systemic leaf symptoms of field melon were reproduced by mechanically inoculating glasshouse melon seedlings with sap from infected White Burley tobacco. The virus was identified as EMDV by serology with an antiserum (As-0136) against the type isolate (EMDV-PV-0031), both obtained from the Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH (DSMZ), Germany. No differences in protein pattern in Western blots (immunoblots) were observed by coelectrophoresis of the type isolate and our melon isolate. The virus was easily detected in several experimental hosts by antigen-coated plate enzyme-linked immunosorbent assay (ELISA). The vector of EMDV is unknown, but the virus generally infects in low percentage a wide range of plant species belonging to different families. This suggests that a polyphagous insect with low vector efficiency may be involved in transmission.

Reference: (1) P. Roggero et al. Plant Dis. 79:321, 1995.
Identification and Epidemic Distribution of Two Flavescence Dorée—Related Phytoplasmas in Veneto (Italy)
Authors: Martini Marta , Murari Ermanno , Mori Nicola , Bertaccini Assunta
Published: May 2007

Grapevine yellows associated with phytoplasmas of the elm yellows group (16SrV), better known as flavescence dorée (FD), is a serious quarantine problem in some important grapevine growing regions in the European Union. A survey was carried out in 1997 to 1998 in Veneto region (Italy) where a serious outbreak of FD was in progress. Phytoplasma identification by nested polymerase chain reaction (PCR)/restriction fragment length polymorphism (RFLP) analyses on 275 grapevine samples and on batches of Scaphoideus titanus was carried out. RFLP analyses of the 16S rDNA/spacer region with TaqI detected the presence of two distinct elm yellows phytoplasma subgroups designated 16SrV-C and 16SrV-D in 77 FD-infected grapevine samples. Only phytoplasmas of the 16SrV-D subgroup were detected in S. titanus. In 1997, the two phytoplasma subgroups appeared to be located in two diverse geographic areas; but in 1998, the 16SrV-D type also was detected in the provinces where in 1997 only 16SrV-C type was identified. The sequencing of a 400-bp fragment at the 3′ end of 16S rDNA plus spacer region allowed a specific primer construction that was successfully employed for detection of both FD types in grapevine by direct PCR.
The Genetic Basis of High Resistance to Rice Yellow Mottle Virus (RYMV) in Cultivars of Two Cultivated Rice Species
Authors: Ndjiondjop M. N. , Albar L. , Fargette D. , Fauquet C. , Ghesquière A.
Published: May 2007

Three cultivars of Oryza sativa (IR64, Azucena, and Gigante) and four cultivars of O. glaberrima (Tog5681, Tog5673, CG14, and SG329) were evaluated for their resistance to two isolates of rice yellow mottle virus (RYMV) by enzyme-linked immunosorbent assay (ELISA) and symptomatology. Cultivars Tog5681 and Gigante were highly resistant, and no symptoms were observed when either virus isolate was inoculated at 10 or 20 days postgermination and assayed by ELISA at 7, 14, 22, 35, 50, or 64 days postinoculation. Azucena showed a partial resistance, whereas the other cultivars were susceptible. Symptom appearance was associated with increase in ELISA absorbance in the systemically infected leaves. The best discrimination among the cultivars occurred when the plants were inoculated at 10 days postgermination. Crosses were made between the highly resistant (Gigante and Tog5681) and the susceptible (IR64) cultivars to determine the genetic basis of resistance to RYMV. Evaluation of F1 hybrids and interspecific progenies, as well as the segregation of resistance in F2 and F3 lines of the IR64 × Gigante cross, provided results consistent with the presence of a single recessive resistance gene common to Tog5681 and Gigante.
Increased Susceptibility to Bacterial Spot of Peach Trees Growing in Soil Infested withCriconemella xenoplax
Authors: Shepard D. Petra , Zehr Eldon I. , Bridges William C.
Published: May 2007

Young Suwanee peach trees were planted in soil infested or not infested with the nematode Criconemella xenoplax. Five months after soil infestation, the leaves were inoculated with Xanthomonas campestris pv. pruni to measure the influence of nematode infestation on bacterial spot development. Bacterial spot lesions in inoculated leaves were more numerous and covered a greater leaf surface area for trees growing in nematode-infested soil than for those in noninfested soil. When the trees were growing in nematode-infested soil, the leaf area diseased was slightly greater on trees in nonsteamed field soil than in soil treated with aerated steam (57 to 62°C for 75 min) prior to infestation with C. xenoplax. Results indicate that bacterial spot damage may become more severe on peach trees if the soil is infested with C. xenoplax than when nematodes have been suppressed.
Improved Diagnostic Techniques for Tomato Yellow Leaf Curl Virus in Tomato Breeding Programs
Authors: Pico Belén , Díez M. José , Nuez Fernando
Published: May 2007

Breeding for tomatoes resistant to tomato yellow leaf curl geminivirus (TYLCV) is difficult, mainly due to the lack of an accurate system for selecting resistant plants. The variable nature of the genotypes used (wild or wild-derived genotypes and advanced breeding lines) makes the development of a reproducible selection procedure necessary during the breeding program. Serological and nucleic acid-based diagnostic techniques for detecting TYLCV were evaluated for their sensitivity, reliability, and possibility of quantification in order to select the combination of techniques that provides the most rapid and accurate characterization of the resistance level of each item. Squash blot followed by the more sensitive polymerase chain reaction (PCR) detection of inconclusive samples is recommended for the screening of new resistant sources among asymptomatic Lycopersicon spp., as they accumulate extremely low viral concentrations that cannot be detected by serological methods. A triple antibody sandwich-enzyme-linked immunosorbent assay (TAS-ELISA), modified to reduce the background, can be used in large-scale field screening of advanced breeding lines if combined with the more sensitive squash blot, which is less affected by the age and state of the tissue. Hybridization methods were also more appropriate to assess viral distribution throughout the plant than TAS-ELISA or even PCR, which fails to reliably detect TYLCV in tissues like roots.
Repeatability and Relationship of Incidence and Severity Measures of Scab of Wheat Caused by Fusarium graminearum in Inoculated Nurseries
Authors: Groth J. V. , Ozmon E. A. , Busch R. H.
Published: May 2007

Breeders of hard red spring wheat (Triticum aestivum) are attempting to incorporate resistance to scab, caused by Fusarium graminearum. In artificially inoculated, replicated field plots, 37 wheat entries (inbred lines or cultivars) were evaluated for 3 years and an additional 60 entries for 2 of the 3 years for incidence (percent spikes infected), severity (percent infected spikelets within infected spikes), and disease index (percent infected spikelets in 50-spike sample). From year to year, entries had similar index values, with coefficients of determination (r 2) ranging from 0.59 to 0.78, with a mean of 0.73. Entries appeared slightly more similar from year to year for incidence than for severity, although both measures of disease had highly significant r 2 values. Incidence and severity were highly correlated in the wheat germ plasm examined; r 2 values in single years ranged from 0.51 to 0.67, with a mean of 0.64. A representative subset of 22 entries was included for a fourth year. None of the measures of disease in year 4 correlated with their counterparts in any of the first 3 years. This loss of repeatability may have been caused by severe lodging or by high temperatures during the evaluation period that accelerated disease progress and wheat maturity during year 4. Incidence and severity remained correlated in year 4 (r 2 = 0.60).
Freezing Temperature Effect on Survival ofPuccinia graminissubsp.graminicolainFestuca arundinaceaandLolium perenne
Authors: Pfender W. F. , Vollmer S. S.
Published: May 2007

The Willamette Valley in Oregon is a major seed production area for cool-season grasses. Puccinia graminis subsp. graminicola survives over winter on its hosts as uredinial infections and causes epidemics of stem rust, the area's major disease on perennial ryegrass and tall fescue. To determine the possible importance of freezing temperature on rust survival, infected plants taken from the field were subjected to controlled freezing across a range of temperatures representative of those that can occur in the region. After treatment, plants were placed in a warm greenhouse, and the number of actively sporulating pustules was recorded at 3-day intervals for 21 days. The pathogen responded similarly to freezing treatments whether in perennial ryegrass or tall fescue. Compared with the nontreated standard, there was no significant reduction in pustule number after exposure to -3 or -6°C. Exposure of infected plants to -10°C caused a 75 to 90% reduction in rust survival, and exposure to -13°C killed all rust infections in tall fescue and over 99% in perennial ryegrass. The decline in rust survival with temperature was slightly steeper for perennial ryegrass than for tall fescue. A higher absolute number of infections in perennial ryegrass than in tall fescue resulted in higher numbers of surviving infections on perennial ryegrass. Survival of rust infections appeared to be primarily a function of host tissue survival. Between 1960 and 1997, years with winter temperatures as low as -10 or -13°C have occurred in the Willamette Valley with frequencies of approximately 39 and 8%, respectively. We conclude that year-to-year variation in winter temperature could have a significant effect on the survival of the grass stem rust pathogen.
First Report of Hop Powdery Mildew in the Pacific Northwest
Authors: Ocamb C. M. , Klein R. , Barbour J. , Griesbach J. , Mahaffee W.
Published: May 2007

Hop powdery mildew (HPM) was first observed in commercial hop (Humulus lupulus L.) fields in Washington State on 10 June 1997 near Toppenish in the Yakima Valley. The disease appeared throughout the valley in 1997; by mid-July, scattered fields throughout the Yakima growing area reported HPM. Approximately 2,000 of 30,000 acres in production were not harvested in 1997 due to HPM. The pathogen apparently perennated in buds, and flagshoots originating from infected buds were observed during March and April 1998 at various locations throughout the Yakima Valley. During the 1999 growing season, the majority of hop acreage in Washington State was affected, and most fields planted to susceptible cultivars contained at least one infected plant. HPM was initially discovered in southern Idaho during early July 1998, in two adjacent fields of hops in Canyon County. HPM was found ≈644 km (400 miles) north in another hop-growing region of Idaho, Boundary County, during mid-July 1998. HPM eventually was observed in more than 20 Idaho hop fields. The initial discovery of HPM in Oregon's Willamette Valley was made during late-July 1998, in two neighboring hop fields. By the end of the growing season, HPM was observed in nine commercial fields representing 3.7% of the hop production acreage in Oregon. Affected cultivars include Brewer's Gold, Chinook, Cluster, Columbus/Tomahawk, Eroica, Fuggle, Galena, Golding, Liberty, Olympic, Perle, Symphony, Tettnanger, Willamette, and Zeus. Infected basal leaves of bines had small whitish circular spots on adaxial surfaces. In some cases, blisters preceded direct observation of the fungus. Cones also were infected, appearing stunted and malformed. The pathogen usually was visible on infected cones but sometimes was found only under overlapping bracts. Cleistothecia have not been observed in the field to date. Conidia were transferred to leaf disks (12 mm diameter) excised from greenhouse-grown cv. Galena hop plants. Inoculated leaf disks were incubated on moistened filter paper in glass petri dishes at 20°C with illumination provided for a 12 h day by two cool-white fluorescent bulbs. HPM lesions with chains of unicellular, barrel-shaped conidia (30 to 36 × 15 to 18 μm) were visible within 7 days. The causal agent was identified as Sphaerotheca macularis (Wallr.:Fr.) Lind (synonym S. humuli (DC.) Burrill) on the basis of conidial shape and size as well as host range (1).

Reference: (1) D. J. Royle. 1978. Powdery mildew of the hop. Pages 381–409 in: The Powdery Mildews. D. M. Spencer, ed. Academic Press, New York.
Phytoplasmas Associated with Elm Yellows: Molecular Variability and Differentiation from Related Organisms
Authors: Griffiths H. M. , Sinclair W. A. , Boudon-Padieu E. , Daire X. , Lee I.-M. , Sfalanga A. , Bertaccini A.
Published: May 2007

Restriction fragment length polymorphism (RFLP) analyses were performed on polymerase chain reaction (PCR) amplimers of phytoplasmal DNA from eight samples obtained from Ulmus spp. (elms) affected by elm yellows (EY) in Italy and the United States, from Catharanthus roseus infected with strain EY1, and from five other plant species infected with phytoplasmas of the EY group sensu lato (group 16SrV). RFLP profiles obtained with restriction enzyme TaqI from ribosomal DNA amplified with primer pair P1/P7 differentiated elm-associated phytoplasmas from strains originally detected in Apocynum cannabinum, Prunus spp., Rubus fruticosus, Vitis vinifera, and Ziziphus jujuba. RFLP profiles obtained similarly with BfaI differentiated strains from A. cannabinum and V. vinifera from other phytoplasmas of group 16SrV. Elm-associated strains from within the United States had two RFLP patterns in ribosomal DNA based on presence or absence of an RsaI site in the 16S–23S spacer. Elm-associated phytoplasma strains from Italy were distinguished from those of American origin by RFLPs obtained with MseI in the same fragment of non-ribosomal DNA. Strain HD1, which was discovered in A. cannabinum associated with EY-diseased elms in New York State, was unique among the strains studied.
Antiviral and Antiviroid Activity of MAP-Containing Extracts fromMirabilis jalapaRoots
Authors: Vivanco Jorge M. , Querci Maddalena , Salazar Luis F.
Published: May 2007

Extracts of Mirabilis jalapa (Nyctaginaceae), containing a ribosome inactivating protein (RIP) called Mirabilis antiviral protein (MAP), were tested against infection by potato virus X, potato virus Y, potato leaf roll virus, and potato spindle tuber viroid. Root extracts of M. jalapa sprayed on test plants 24 h before virus or viroid inoculation inhibited infection by almost 100%, as corroborated by infectivity assays and the nucleic acid spot hybridization test. Antiviral activity of MAP extracts was observed against mechanically transmitted viruses but not against aphid-transmitted viruses. Purified MAP showed the same antiviral effect as the crude extracts.
The Effects of Planting Date and Insecticide Treatments on the Incidence of High Plains Disease in Corn
Authors: Fritts D. A. , Michels G. J. , Rush C. M.
Published: May 2007

Incidence of High Plains Disease (HPD) in a susceptible corn cultivar was examined in relation to planting dates, insecticide treatments, and wheat heading dates during 1994 to 1996. In the High Plains of Texas, this disease of susceptible corn was related to corn planting dates and winter wheat maturity. The incidence of HPD varied greatly from year to year; however, corn planted between 16 and 20 May had the highest disease incidence. Corn planted 10 to 30 days after wheat heading had the highest incidence of the disease. Chemical control of the vector, Aceria tosichella, was ineffective, except by the use of granular insecticides applied at planting, which had some beneficial effects. Results of this study suggest that producers can reduce the incidence of HPD by planting corn before or after the peak migration of wheat curl mite from wheat.
Efficacy of Fluazinam in Suppression of Monosporascus cannonballus, the Causal Agent of Sudden Wilt of Melons
Authors: Cohen R. , Pivonia S. , Shtienberg D. , Edelstein M. , Raz D. , Gerstl Z. , Katan J.
Published: May 2007

Sudden wilt (vine decline) of melon, caused by Monosporascus cannonballus, is a worldwide problem in arid and semi-arid regions. Soil disinfestation by fumigation with methyl bromide before planting is a common treatment for disease management but, because methyl bromide is expected to be banned from use within the next 10 years, alternative measures for disease suppression are needed. The efficacy of 29 fungicides against M. cannonballus was evaluated in vitro. Among the fungicides tested, fluazinam and kresoxim methyl were the most effective and both totally inhibited the growth of M. cannonballus in culture at concentrations of 10 μg a.i /ml. Because fluazinam also was effective in inhibition of Pythium aphnidermatum, which also may be involved in sudden wilt syndrome, and kresoxim methyl was not, fluazinam was chosen for further tests. The effective dose of fluazinam for M. cannonballus that reduced mycelial growth by 50% was 0.09 μg a.i./ml. Fluazinam efficacy was evaluated in three field experiments conducted in the spring and in the late summer cropping seasons. In two of the experiments, applications of fluazinam resulted in approximately 87% wilt reduction, whereas in the third experiment it was only 32%. The mobility of fluazinam in soil was determined in samples taken from the field. Fungicide mobility in soil was relatively limited; most of the compound was adsorbed to soil particles, resulting in a zone of high concentration that decreased with depth and distance from the application site. Nevertheless, rates measured even at a depth of 25 cm were sufficient to control M. cannonballus. This study shows that fluazinam may be used as one component in an integrated approach for suppression of sudden wilt of melons.
First Report of Transmission of Verticillium dahliae by Infested Manure in Olive Orchards in Andalucia (Southern Spain)
Authors: Lopez-Escudero F. J. , Blanco-Lopez M. A.
Published: May 2007

Olive (Olea europaea L.) is a traditional tree crop in Andalucia, southern Spain. Over the past several years, new plantations have been established in areas where other crops susceptible to Verticillium dahliae, such as cotton, sunflower, and vegetables, usually have been grown. Surveys performed from 1989 to 1996 showed that Verticillium wilt, caused by V. dahliae, has become the most important soilborne fungal disease affecting young olive trees in this area (3). Manure is sometime used as a soil amendment before and after tree planting to increase organic matter content of soil. In 1996, manure was used to establish an olive plantation in Sevilla Province. The dung came from sheep fed on harvested fields of cotton, sunflower, and sugar beet. The remaining manure was left in a pile in the field. In 1998, 2 years after planting, many olive plants in the field showed Verticillium wilt symptoms. Samples were collected from the soil and the surfaces and core of the manure pile for isolation and quantitative assessment of the pathogen. Wet-sieving and sodium pectate agar selective medium were used (1). V. dahliae was isolated from both the manure and soil. Mean inoculum density in the samples taken from the pile and soil were 8.4 and 7.2 microsclerotia per gram, respectively. Although it has been demonstrated that V. albo-atrum survives the digestive process in animals (2), this is the first report on dispersion of V. dahliae by manure from sheep fed on infested stubble. The use of manure infested with V. dahliae may contribute to pathogen dispersion and to the increase in Verticillium wilt incidence in olive orchards in Andalucia. Because animal manure is a potential means for V. dahliae transmission, it is recommended that before manure is applied tests be performed, when feasible, to make sure it is pathogen-free.

References: (1) E. J. Butterfield and J. E DeVay Phytopathology 67:1073, 1977. (2) H. C. Huang et al. Plant Dis. 70:218, 1986. (3) M. E. Sanchez Hernandez et al. Eur. J. Plant Pathol. 104: 347, 1998.
Isolates of Uromyces appendiculatus with Specific Virulence to Landraces of Phaseolus vulgaris of Andean Origin
Authors: Sandlin Craig M. , Steadman James R. , Araya Carlos M. , Coyne Dermot P.
Published: May 2007

Five isolates of the bean rust fungus Uromyces appendiculatus were shown to be specifically virulent on bean genotypes of Andean origin. This specificity was demonstrated by the virulence of five pairs of isolates on a differential set of 30 Phaseolus vulgaris landraces. Each isolate pair was from a different country in the Americas and consisted of one Andean-specific isolate and one nonspecific isolate. Of the differential P. vulgaris landraces, 15 were of Middle American origin and 15 were of Andean origin. The Andean-specific rust isolates were highly virulent on Andean landraces but not on landraces of Middle American origin. Rust isolates with virulence to Middle American landraces were also generally virulent on Andean material; no truly Middle American-specific isolates were found. Random amplified polymorphic DNA (RAPD) analysis of the rust isolates also distinguished the two groups. Four of the Andean-specific rust isolates formed a distinct group compared to four of the nonspecific isolates. Two of the isolates, one from each of the two virulence groups, had intermediate RAPD banding patterns, suggesting that plasmagomy but not karyogamy occurred between isolates of the two groups.
Physiologic Specialization ofPuccinia triticinain Canada in 1997
Authors: Kolmer J. A.
Published: May 2007

In 1997, leaf rust of wheat (Triticum aestivum), caused by Puccinia triticina, was widespread throughout the prairies of western Canada. Warm summer temperatures with frequent dew periods favored spread of the disease in wheat fields in Manitoba, Saskatchewan, and Alberta. The leaf rust epidemic of 1997 was the most widespread and severe in western Canada since 1991. The Canada Prairie Spring wheat cultivars (AC Vista, AC Foremost, AC Crystal) were susceptible to leaf rust, while the bread wheats (AC Domain, AC Barrie, AC Cora, AC Majestic) were more resistant. Forty-seven virulence phenotypes of leaf rust were described in 1997 using 16 near-isogenic differential lines of Thatcher wheat. Phenotypes with virulence to Lr16 comprised 16% of the isolates in Manitoba and Saskatchewan in 1997. Many recently released Canadian spring wheats have Lr16 in addition to adult plant resistance genes. Thirty-three isolates also were tested for virulence to plants with adult plant resistance genes Lr12, Lr13, Lr34, and Lr13,34. Most isolates were virulent to genes Lr12 and Lr13. All isolates had lower infection types on lines with Lr34 compared with the susceptible line Thatcher.
First Report of a Fruit Rot of Pumpkin Caused by Acidivorax avenae subsp. citrulli in Georgia
Authors: Langston D. B. , Walcott R. D. , Gitaitis R. D. , Sanders F. H.
Published: May 2007

In September 1998, a fruit rot was reported affecting pumpkin (Cucurbita pepo) in a commercial field in Terrell Co., Georgia. Symptoms on the surface of fruit occurred as round, necrotic spots or cracks a few millimeters in diameter. With age, the tissue surrounding these lesions became soft and wrinkled. A soft rot expanded into the flesh of the pumpkin, originating from the lesions observed on the surface. In time, infected pumpkins totally collapsed. V-shaped, necrotic lesions occurred at the margin of the leaf and extended inward toward the mid-rib. Samples were collected from the field and bacteria were isolated from fruit and leaf lesions onto King's medium B (1). The bacterium isolated was rod shaped, gram negative, nonflourescent, oxidase positive, Tween 80 positive, carboxymethyl cellulose positive, β-OH butyrate positive, and malonate negative. The bacterium reacted positively with polyclonal antibodies specific for the watermelon fruit blotch pathogen Acidivorax avenae subsp. citrulli and was identified as A. avenae subsp. citrulli by MIDI (Microbial Identification System, Newark, DE) according to statistical analysis of fatty acid data. Results from polymerase chain reaction (PCR) amplification of the bacterium isolated from pumpkin yielded 360-bp fragments that, when digested with the restriction enzyme HaeIII, had DNA banding patterns identical to those of stock A. avenae subsp. citrulli DNA. Koch's postulates were completed successfully with 2-week-old watermelon seedlings. This is the first report of A. avenae subsp. citrulli causing fruit rot of pumpkin in Georgia.

Reference: (1) E. O. King et al. J. Lab. Clin. Med. 44:301, 1954.
Rating Scales for Assessing Infection Responses of Barley Infected with Cochliobolus sativus
Authors: Fetch Thomas G. , Steffenson Brian J.
Published: May 2007

Spot blotch, caused by Cochliobolus sativus, is a common foliar disease of barley that is controlled primarily through the deployment of resistant cultivars. Resistance is often assessed at the seedling and adult plant stages, but currently no comprehensive visual scale exists that describes the full spectrum of infection responses (IRs) occurring on barley. From the evaluation of a diverse collection of barley germ plasm and C. sativus isolates, a 1 to 9 IR scale was developed based on the type (presence of necrosis and chlorosis) and relative size of spot blotch lesions observed on the second leaves of barley seedlings. The nine IRs were classified into three general categories of low (IRs 1 to 3), intermediate (IRs 4 and 5), and high (IRs 6 to 9) host-parasite compatibility. Low IRs consisted of minute to small necrotic lesions with no or very slight diffuse marginal chlorosis. Intermediate IRs consisted of medium-sized necrotic lesions with a distinct but restricted chlorotic margin, while high IRs consisted of large necrotic lesions with distinct chlorotic margins and varying degrees of expanding diffuse chlorosis. In addition to the seedling IR scale, a four-class adult plant IR scale (R = resistant, MR = moderately resistant, MS = moderately susceptible, and S = susceptible) was developed based again on the type and relative size of lesions present on the leaves. These rating scales should be useful for many types of studies on spot blotch of barley.
Persistence and Latency of Clavibacter michiganensis subsp. sepedonicus in Field-Grown Seed Potatoes
Authors: Franc Gary D.
Published: May 2007

Whole seed tubers were inoculated with different inoculum doses of Clavibacter michiganensis subsp. sepedonicus and planted in the field. Ring rot symptom development and the persistence of C. michiganensis subsp. sepedonicus, in the absence of symptoms, was determined for four generations following introduction of inoculum. Seed tubers were not cut during propagation to preclude redistribution of inoculum. Detection of C. michiganensis subsp. sepedonicus was positively related to inoculum dose (r = 0.97) and rapidly declined with increasing generations. Although the frequency of detection was much less following inoculation with ≤102 cells versus inoculation with ≥104 cells, all inoculum doses established latent infections that were undetected for at least one, and up to three, generations. Latency for three generations, characterized by C. michiganensis subsp. sepedonicus detection or ring rot symptom development during the fourth generation, was the longest time interval tested. The occurrence of latent C. michiganensis subsp. sepedonicus infections and the persistence of inadvertent inoculum sources may, at least partially, explain our inability to eradicate ring rot based on visible symptom expression.
Relationship Between Shell Discoloration of Pistachio Nuts and Incidence of Fungal Decay and Insect Infestation
Authors: Doster Mark A. , Michailides Themis J.
Published: May 2007

Shell discoloration of pistachio (Pistacia vera) nuts collected from commercial orchards and processing plants was related to fungal decay and insect infestation of the kernel. Nuts with ruptured hulls (early split nuts and nuts with cracked hulls) varied considerably in the amount of shell discoloration, ranging from none to extensive. For both types of hull rupture, as shell discoloration increased, kernel decay also increased. Nuts with no discoloration had little or no fungal decay and navel orangeworm (Amyelois transitella) infestation. Processed nuts with an oily-shell appearance had the highest incidences of fungal decay and navel orangeworm infestation; nuts with a crinkled shell, nuts with extensive dark brown discoloration, and nuts with moderate dark brown discoloration along the suture had relatively high levels of decayed and infested kernels; while nuts with yellow discoloration, nuts with moderate dark brown discoloration not along the suture, and nuts with no discoloration had little or no decay and infestation. Also, as shell discoloration of processed nuts increased, kernel decay increased. Our results suggest that shell characteristics may be used by processors to identify poor quality nuts and to improve the quality of pistachio nuts sold to consumers.
First Report of Ralstonia (Pseudomonas) solanacearum Infecting Pot Anthurium Production in Florida
Authors: Norman D. J. , Yuen J. M. F.
Published: May 2007

Xanthomonas campestris pv. dieffenbachiae is a common pathogen of pot anthurium production in Florida. While X. campestris pv. dieffenbachiae was isolated from systematically infected plants with chlorotic, necrotic, and wilted leaves, a fluidal, beige bacteria was occasionally isolated on nutrient agar (Difco, Detroit, MI), as opposed to the common, yellow pigmented Xanthomonas sp. Distinction in the symptomology of plants systematically infected with a Xanthomonas sp. or this new bacterium could not be made. Three isolates were obtained of this unidentified bacterium from leaves and stems of three separate plants. With FAME (fatty acid methyl esters) analysis, using MIDI (Microbial Identification System, software version TSBA 3.90 [Newark, DE]), these isolates were classified as Ralstonia (Pseudomonas) solanacearum (syn. Burkholderia solanacearum) with a mean similarity indice of 0.895. Isolates were found to be gram negative, oxidase negative, catalase positive, motile, strictly aerobic, and metabolically classified as biovar 1; they accumulated poly-β-hydroxybutyrate and produced a hypersensitive response on tobacco within 24 h. A characteristic fluidal, white growth with a distinctive, red, swirling, egg-shaped, pigmentation pattern was observed on triphenyltetrazolium chloride medium. Further confirmation of identity as R. solanacearum was obtained by polymerase chain reaction amplification and electrophoretic analysis with species-specific primers (2), which in all cases produced a 148-bp product along with control strains. The three isolates were inoculated onto three plants of anthurium, tomato, triploid banana, and pothos. Inoculations were done at least twice; plants were inoculated either by stabbing the plant stems with a needle dipped in a suspension of bacteria or by applying 10 ml of a 1 × 108 CFU/ml suspension to the soil of the test plants. Chlorosis, necrosis, and wilt symptoms appeared within 2 weeks on all plant species tested. Recently, pothos (Epipremnum aureum) cuttings imported to Florida from Costa Rica have been implicated as a source of R. solanacearum (1). Imported cuttings of pothos were being grown in hanging baskets over the infected anthuriums. Although no R. solanacearum infections were detected in the pothos, these imported plants are the probable source of the initial inoculum for this disease outbreak on anthuriums.

References: (1) D. J. Norman and J. M. F. Yuen. Phytopathology 87:S70, 1997. (2) S. E. Seal et al. Appl. Environ. Microbiol. 58:3751, 1992.
First Report of Aerial Blight Caused by Pythium myriotylum on Tomato in Florida
Authors: Roberts P. D. , Urs R. , McGovern R. J.
Published: May 2007

In September 1996 and 1997, diseased tomato seedlings were observed with symptoms of an aerial watery rot on leaves, petioles, and stems. Tomato cvs. Sanibel and 10097 from commercial fields in southwest Florida (Collier and Lee counties) and west central Florida (Manatee County) exhibited similar symptoms that occurred at an incidence of 15 to 18% about 4 weeks after transplanting and resulted in plant death. Microscopic examination of symptomatic tissue revealed the presence of mycelium and oogonia typical of Pythium spp. A fungus was consistently isolated from four plants sampled from each site onto a medium selective for Pythium spp. and maintained in pure culture on V8 juice agar at 28°C. The isolates were identified as Pythium myriotylum Drechs. based on the following morphological data: lobate sporangium, 12 to 13 μm wide; vesicle 15.4 to 19.4 μm in diameter; exit tube 54 to 90 μm long, oogonium 23 to 30 μm in diameter; and oospore 21 to 26 μm in diameter (1,2). Pathogenicity tests were conducted with two isolates from diverse regions within Florida by spray inoculating the leaves and shoots of 6- to 8-week-old tomato seedlings with a sporangial suspension of 1 × 104 sporangia per ml. Noninoculated plants served as controls. Plants had 24 h of pre- and post-dark period, day/night temperatures of 28/21°C, a 14-h photoperiod, and near 100% relative humidity in a growth chamber. The foliage of inoculated tomato plants exhibited symptoms identical to those observed in field samples 24 h after inoculation and 100% mortality within 72 h. The reisolated fungus was morphologically identical to the original isolate. Noninoculated plants remained asymptomatic. The unusual rainfall recorded at some sites, such as in Manatee County in September 1997, was 36% higher than the 40-year average and may have contributed to the incidence of this previously undescribed foliar blight.

References: (1) Anonymous. C.M.I. Descriptions of Pathogenic Fungi and Bacteria No. 118. (2) T. Watanabe. Pictorial Atlas of Soil Fungi. Lewis Pub., London. p. 71.
First Report of Grapevine Downy Mildew (Plasmopara viticola) in Commercial Viticulture in Western Australia
Authors: McKirdy S. J. , Riley I. T. , Cameron I. J. , Magarey P. A.
Published: May 2007

Despite the suitability of climate, Western Australia was one of the few grape (Vitis vinifera L.) growing areas free of grapevine downy mildew (Plasmopara viticola (Berk. & M. A. Curtis) Berl. & De Toni in Sacc.). Area freedom had been maintained by restricting the movement of host material and machinery from outside the state and fungicide use in Western Australia vineyards had been considerably less. P. viticola was detected in 1997 in 14 of 15 vines growing at Kalumburu, a remote community in the semi-arid tropics of Western Australia, and was eradicated. In October 1998, grape leaves with oilspots typical of downy mildew were received from a grower in the Swan Valley near Perth, one of the main production areas of Western Australia. Sporangia were hyaline and ellipsoid (14 × 11 μm), were borne on treelike sporangiophores, and were consistent with those described for P. viticola (1). This is the first record of P. viticola in commercial viticulture in Western Australia. A response plan for exotic diseases was activated and after 2 weeks of surveillance the disease was found in 45 of 70 vineyards surveyed of the 280 vineyards in the Swan Valley. Given the extent of spread, eradication of downy mildew was not considered possible. Weather data for August to October 1998 indicated the likelihood of several infection periods from budburst to flowering when the disease was first detected. Crop loss will be considerable in many vineyards. P. viticola was also found in bench-grafted cuttings in pots in leaf consigned from the Swan Valley to several other areas in August 1998. Downy mildew was found in other areas only in association with these consigned vines. An industry code of practice, including hygiene, is being developed to slow the rate of spread of P. viticola in Western Australia.

Reference: (1) Anon. C.M.I. Descriptions of Pathogenic Fungi and Bacteria No. 980, 1989.