bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence That Xylella fastidiosa Is Associated with Pecan Fungal Leaf Scorch
Authors: Sanderlin R. S.
Published: May 2007

Several different leaf scorch symptomatologies occur on the foliage of pecan (Carya illinoinensis). The causes of these different scorch symptoms have been associated with environmental stresses, nutritional imbalances, mites, and pathogens. One type of leaf scorch is characterized by necrosis beginning at the tips or margins of the leaflets and progressing toward the midrib and base of the leaflets. The most distinguishing feature of this type of leaf scorch is a dark brown, black, or purplish band of tissue at the interface of the necrotic and green leaflet tissue. This band does not occur on all affected leaflets, but is a consistent feature with this symptomatology. Leaflets with this leaf scorch usually abscise before the entire leaflet becomes necrotic. Affected leaflets will abscise from a compound leaf, while leaflets without symptoms remain on the rachis. When this scorch is severe, the entire leaf including the rachis may abscise. The symptoms are often confined to one area of the tree. Symptoms of this disease appear as early as June but often begin in July. Incidence and severity increase through the remainder of summer and into fall. Over the past 25 years, several different genera of fungi have been reported as being associated with this leaf scorch (2). The phenomenon was named fungal leaf scorch (FLS) because of the association with fungi and the observation that some fungicides reduced the severity of leaf scorch. Genera of fungi implicated in the development of FLS were Pestalotia, Epicoccum, Curvularia, and Fusarium. Recent work has indicated that the disease could be caused by a Phomopsis sp. or Glomerella cingulata or both (1). The symptoms and epidemiology of the FLS are similar to other leaf scorch diseases of hardwood caused by the fastidious xylem-limited bacterium Xylella fastidiosa. A commercial enzyme-linked immunosorbent assay (Agdia, Elkhart, IN) was used to screen for this organism in association with FLS. Assays were conducted by extracting from a composite sample of 9 to 12 sections (approximately 3 cm long) taken from 3 to 4 rachises of each tree tested. Positive reaction for the presence of X. fastidiosa in rachises was recorded from 10 of 10 trees with symptoms of FLS on the Cape Fear cultivar. One of two trees was positive from Cape Fear leaves without symptoms. Symptomless foliage from two less susceptible cultivars, Stuart (two trees) and Sumner (one tree), assayed negative for the bacterium. The association of X. fastidiosa with symptoms of FLS provides evidence that this organism is involved in the etiology of pecan leaf scorch; however, further work is needed to determine the exact etiology.

References: (1). A. J. Latham et al. Plant Dis. 79:182, 1995. (2) R. H. Littrell and R. E. Worley. Phytopathology 62:805, 1972.
Aspergillus flavus Infection and Aflatoxin Accumulation in Resistant and Susceptible Maize Hybrids
Authors: Windham G. L. , Williams W. P.
Published: May 2007

Field studies were conducted for 2 years in Mississippi to monitor maize kernel infection and aflatoxin accumulation caused by Aspergillus flavus at various times during the growing season. Hybrids resistant and susceptible to A. flavus were compared to determine temporal differences in infection and aflatoxin levels. The resistant hybrids tested were Mo18W × Mp313E, Mp420 × Tx601, and SC54 × SC76; and the susceptible hybrids tested were GA209 × Mp339, Mp307 × Mp428, and Mp68:616 × SC212M. The top ear of each plant was inoculated with a suspension containing A. flavus conidia at 7 days after midsilk (50% of the plants in a plot had silks emerged) using the side needle technique. Inoculated ears were harvested 35, 42, 49, 56, and 63 days after midsilk to determine kernel infection by A. flavus and aflatoxin contamination. Differences in aflatoxin levels between resistant and susceptible hybrids occurred in all harvest dates. However, significant differences between resistant and susceptible hybrids for kernel infection were not observed until 42 days after midsilk. Differences between resistant and susceptible hybrids occurred for kernel infection and aflatoxin concentrations 49, 56, and 63 days after midsilk. Incidence of kernel infection (8.1% for GA209 × Mp339) was the highest 49 days after midsilk, and aflatoxin concentrations (510 ng/g for Mp307 × Mp428) were the highest 63 days after midsilk. Maximum differences between resistant and susceptible hybrids for aflatoxin levels were observed 63 days after midsilk. Two of the resistant hybrids, Mo18W × Mp313E and Mp420 × Tx601, had significantly less aflatoxin than the three susceptible hybrids 63 days after midsilk.
Seed Treatment Using Pre-infiltration and Biocontrol Agents to Reduce Damping-off of Corn Caused by Species of Pythium and Fusarium
Authors: Mao W. , Lumsden R. D. , Lewis J. A. , Hebbar P. K.
Published: May 2007

Bioassays were conducted in a greenhouse at 18°C to determine the effectiveness of a seed treatment used in combination with biocontrol agents for the reduction of corn damping-off caused by species of Pythium and Fusarium. Corn seeds were infiltrated with tap water, drained, air-dried, and then coated with biomass of an antagonistic fungus, Gliocladium virens isolate Gl-3, or an antagonistic bacterium, Burkholderia cepacia isolates Bc-B or Bc-1, or a combination of Gl-3 with each of the bacterial isolates. A nonsterile field soil was infested with a combination of pathogens: Pythium ultimum, P. arrhenomanes, and Fusarium graminearum at 2 inoculum rates (1× and 4×). Pre-infiltration enhanced (P ≤ 0.05) disease control with most treatments at both inoculum rates. Treatments with biocontrol agents alone or in combination, as well as the fungicide captan, effectively reduced the disease at a pathogen inoculum rate of 1×, resulting in greater (P ≤ 0.05) seedling stands, plant height, and fresh weight, and lower (P ≤ 0.05) root rot severity compared with untreated seeds in infested soil. At a pathogen inoculum rate of 4×, stands were lower (P ≤ 0.01) and root-rot severity was higher (P ≤ 0.01) compared to those at 1× for all treatments. Nevertheless, coating seeds with all biocontrol agents (alone or in combination), except with Bc-1 alone, reduced disease (P ≤ 0.05) compared to untreated seeds in infested soil. At both inoculum rates of 1× and 4×, coating seeds with Gl-3 + Bc-B was more effective (P ≤ 0.05) in disease control than any other treatment, resulting in stands, growth rate (plant height and fresh weight), and root rot severity similar to plants from untreated seeds in noninfested soil. In addition, when the exudate from a 2-h infiltration of corn seed was added to the seeds during seed coating, seedling stand was often lower and root rot severity was often higher than those from infiltrated seeds (P ≤ 0.05). These results indicated that the infiltration process removed certain exudates, including nutrients and/or stimulants (not detected in this study) that might be utilized by pathogens to initiate seed infection. A thin-layer chromatography (TLC) profile of the exudates showed the presence of eight amino acids and three major carbohydrates.
Evaluation of Resistance of Winter Wheat to Fusarium acuminatum by Inoculation of Seedling Roots with Single, Germinated Macroconidia
Authors: Mergoum M. , Hill J. P. , Quick J. S.
Published: May 2007

Fusarium acuminatum is one of the causal agents of dryland root rot of winter wheat in Colorado. The effect of F. acuminatum seedling root infection, recorded at heading, on winter wheat cultivars Sandy and CO84 was investigated in the greenhouse. Winter wheat seeds were surface disinfested, germinated, and vernalized. Vernalized seedling roots were inoculated by placing a single, germinated macroconidium of F. acuminatum on the largest root. Inoculated and non-inoculated vernalized seedlings were transplanted to pots and half the plants subjected to water stress. Inoculated plants had significantly lower survival rates and, at maturity, lower relative leaf water content, fewer tillers, shorter plant height, and higher cell ion leakage than non-inoculated plants. Wheat cultivars differed significantly for most traits studied. CO84 was susceptible whereas Sandy was more tolerant of the pathogen, particularly under water stress conditions. These results suggest that relative leaf water content, cell ion leakage, and to some extent seedling survival may be useful attributes for evaluation of resistance to the root rot pathogen.
Mixed Infection of Hard Red Winter Wheat with High Plains Virus and Wheat Streak Mosaic Virus from Wheat Curl Mites in Nebraska
Authors: Mahmood T. , Hein G. L. , Jensen S. G.
Published: May 2007

A new disease of wheat and corn caused by the High Plains virus (HPV) has been observed in the High Plains region of western United States. HPV is transmitted by the wheat curl mite, Aceria tosichella, which is also the vector of wheat streak mosaic virus (WSMV). In the field it is extremely difficult to visually differentiate plants infected with WSMV from those with HPV. An indirect protein-A sandwich enzyme-linked immunosorbent assay (PAS-ELISA) and Western blot analysis were used to identify WSMV and HPV. Samples of wheat curl mites were collected from arbitrarily chosen sites from commercial wheat plantings in 1995 and 1996 and used to infest caged wheat plants. After 3 weeks, leaf samples were harvested and assayed. Both Western blot analysis and PAS-ELISA were effective at identifying samples positive for WSMV and HPV, both alone and in mixed infections. Western blot results showed that over the 2 years, 65% of the samples were positive for WSMV, 46% were positive for HPV, and mixed infections were found in 40% of the samples. HPV presence was verified with similar results from field collected plant samples. These levels of virus indicate an unexpectedly high incidence of HPV in wheat curl mite populations in Nebraska.
Effects of Chitin and Chitosan on the Incidence and Severity of Fusarium Yellows of Celery
Authors: Bell Ashley A. , Hubbard Judith C. , Liu Li , Davis R. Michael , Subbarao Krishna V.
Published: May 2007

The effects of chitin and chitosan on disease incidence and severity of Fusarium yellows of celery and on populations of Fusarium oxysporum were investigated between 1994 and 1996. Field experiments were conducted at two locations with a history of severe Fusarium yellows. Disease incidence and severity were significantly reduced by pre-plant chitin amendments to soil. Chitosan applied as a root dip alone did not reduce disease incidence but significantly (P < 0.05) reduced disease severity when used with a tolerant celery cultivar. Standard soil dilution methods were used to enumerate populations of soil microflora. Chitin increased bacterial and actinomycete populations in soil in 2 of the 3 years of study. The effects of potential biocontrol agents recovered from chitin-treated plots in 1995 were studied in 1996; enriching the transplant medium with isolates of bacteria and actinomycetes 4 weeks and 1 week prior to transplanting did not alter the established equilibrium in the field, and no biocontrol effect was observed. Chitin amendments to soil or chitosan treatment of transplants did not reduce soil populations of F. oxysporum. Whether these treatments affected the F. oxysporum f. sp. apii subpopulation within the F. oxysporum population could not be determined.
Severe Outbreak of Stemphylium Leaf Blight, a New Disease of Cotton in Brazil
Authors: Mehta Y. R.
Published: May 2007

A severe epidemic of a leaf blight of cotton occurred in the state of Paraná, Brazil, during 1994 and 1995, causing up to 100% yield losses in some commercial fields of cultivar Paraná 3. The severity of the disease among fields was variable and cultivar-dependent. Attempts were made to identify the organism causing the leaf blight symptoms, which were characterized as circular to irregular dark brown to black spots turning reddish brown with age and varying between 2 and 10 mm in diameter. The older lesions showed cracks and/or holes in the center. Severely diseased leaves dried rapidly and abscised. Fructifications of a fungus in the genus Stemphylium were observed on young, as well as on old, lesions. The Stemphylium sp. was consistently isolated on potato dextrose agar from disease samples collected from five cultivars in 14 locations. In inoculation tests, the Stemphylium isolates from cotton were highly aggressive to cotton, tomato, potato, and blue lupines; whereas an isolate of S. solani from tomato was highly aggressive on tomato and potato but less aggressive on cotton. On the basis of its morphological, cultural, and pathogenic characteristics, the principal pathogen causing leaf blight symptoms was identified as Stemphylium solani. Epidemics caused by S. solani on cotton have not been reported previously in commercial cotton cultivation.
First Report of Tomato Spotted Wilt Tospovirus Infection of Watermelon in Georgia
Authors: Pappu S. S. , Pappu H. R. , Gitaitis R. D. , Gay J. D.
Published: May 2007

In 1996, volunteer watermelon plants in a tobacco field in Coffee County, GA, exhibited foliar symptoms that included necrotic ring spots and veinal necrosis. Watermelon plants from experimental plots of the Coastal Plain Experiment Station in Tifton, GA, similarly showed necrotic lesions, often resulting in necrotic ring spots during the late summer of 1997. Out of 16 samples tested for the presence of tomato spotted wilt tospovirus (TSWV) with a commercially available enzyme-linked immunosorbent assay (ELISA) kit (Agdia, Elkhart, IN), six were positive for TSWV. Primers specific to the nucleocapsid gene of TSWV were used in a reverse transcription-polymerase chain reaction assay (RT-PCR) (1) to verify the presence of TSWV. RT-PCR gave an expected PCR product of approximately 350 bp. The amplicon was cloned in pGEM-T vector and the recombinant clone was sequenced. The sequence of the cloned PCR product confirmed the identity of TSWV, thus verifying TSWV infection of watermelon. The potential impact of TSWV on watermelon crop in Georgia will be investigated. This is the first report of natural infection of watermelon by TSWV in Georgia.

Reference: (1) H. R. Pappu et al. Tobacco Sci. 40:74, 1996.
Effects of an Apple Scab-Resistant Cultivar on Use Patterns of Inorganic and Organic Fungicides and Economics of Disease Control
Authors: Ellis M. A. , Ferree D. C. , Funt R. C. , Madden L. V.
Published: May 2007

An inorganic (sulfur) and a conventional organic fungicide spray program were evaluated on an apple scab-resistant (Liberty) and a scab-susceptible (McIntosh) cultivar for control of scab and for cost effectiveness. Trees of both cultivars were either nontreated, treated with inorganic fungicides only, or treated with a conventional fungicide program. McIntosh trees received full-season fungicide applications and Liberty trees received only the summer cover sprays (after petal fall) for control of summer diseases. In 1991, the number of fungicide applications ranged from 0 for nontreated Liberty to 12 for the full-schedule inorganic program on McIntosh, with both treatments providing excellent scab control. All nontreated McIntosh fruit were unmarketable due to scab infection. Due to a dry growing season and lack of summer disease development, nontreated Liberty fruit was of high quality. In 1992, the number of fungicide applications ranged from 0 for nontreated Liberty to 14 for the full-schedule inorganic treatment on McIntosh, with both treatments providing good to excellent disease control. Results were very similar in 1993. Scab incidence was low for all treatments except the nonsprayed McIntosh over all years. Over 3 years of testing, the conventional fungicide program resulted in an average of 9 and 5 applications per year for McIntosh and Liberty, respectively, compared to 12.6 and 7 applications, respectively, for the inorganic fungicide program. The large reduction in the number of sprays for both programs was due to the elimination of all pre-petal-fall applications on Liberty; post-petal-fall applications are needed to control summer diseases such as flyspeck and sooty blotch. An economic analysis for total cost of fungicide applications for each spray program and cultivar was conducted for hypothetical 4.0-, 8.1- and 16.2-ha farms. Regardless of farm size, the cost of fungicides per ha varied among treatments and cultivars. The inorganic and conventional spray program for McIntosh had similar total costs. On Liberty, the inorganic and conventional programs had 73 and 57% less total cost, respectively, than on McIntosh. Fungicides for the conventional program on Liberty were 1.45 times more costly per ha than fungicides in the inorganic program, but the inorganic program required more applications, resulting in a small difference in total treatment cost per ha.
Spread of Ergot of Sorghum (Claviceps africana) in Central Mexico
Authors: Velasquez-Valle R. , Narro-Sanchez J. , Mora-Nolasco R. , Odvody G. N.
Published: May 2007

By late August 1997, sorghum ergot (Claviceps africana Frederickson, Mantle & De Milliano) had not been detected in the Bajio area in central Mexico, the second-largest sorghum (Sorghum bicolor (L.) Moench) producing area in the country, despite earlier 1997 reports of the disease in the adjacent states of San Luis Potosi, Michoacan, and Jalisco. A mid-September survey was conducted in el Bajio, primarily in the state of Guanajuato, and adjacent areas in the states of Michoacan and Jalisco. Infected sorghum heads showing ergot symptoms of honeydew and white secondary sporulation were observed in commercial grain and hybrid seed fields in all three states. Environmental conditions, late summer rains and early low temperatures promoting abundant dew, as well as extended periods of sorghum blooming, contributed to a low and delayed incidence of ergot in Guanajuato. In Michoacan and Jalisco the higher relative humidity and rainfall (around 750 ml) probably contributed to the observed epidemic of ergot. Johnsongrass (Sorghum halepense (L.) Pers.) florets also showed ergot symptoms. Macroconidia in honeydew were hyaline, oblong to oval, slightly constricted at the center, with an average size of 15 × 7 μm, agreeing with the given description of Sphacelia sorghi McRae (2), the anamorph stage of C. africana. No sclerotia were found on any host. Ergot control in this region of Mexico is being attempted by chemical means and burning of heads, even in commercial fields with minimal incidence of ergot. This report of ergot spread complements an earlier note describing the initial detection of the disease in Tamaulipas, the largest sorghum-producing state in Mexico (1).

References: (1) J. Aguirre R. et al. Plant Dis. 81:831, 1997. (2) D. E. Frederickson et al. Mycol. Res. 95:1101, 1991.
Leaf Spot of Radicchio Caused by Alternaria cichorii in California
Authors: Koike S. T. , Butler E. E.
Published: May 2007

A foliar disease of commercially grown radicchio (Cichorium intybus) was observed in 1996 and 1997 in the Salinas Valley (Monterey County), California. Symptoms consisted of circular to oblong, necrotic spots ranging in diameter from 3 to 20 mm and having concentric zones of darker tissue. A fungus identified as Alternaria cichorii Nattrass (1) was observed fruiting on the spots and was consistently isolated from the margins of the spots. Conidia from leaves were obclavate in shape with slender, unbranched beaks extending from the narrow end of the spore body. Spore body dimensions measured 56 to 78 × 14 to 20 μm, and beaks measured 36 to 81 × 1 to 2 μm. Spore bodies had 7 to 9 transverse septa. Often there were no longitudinal septa, but occasionally there were 1 or 2 such septa. For pathogenicity tests, five isolates were grown for 4 weeks on potato dextrose agar under a combination of cool white and Vita-Lite fluorescent tubes on a 12 h light/dark cycle. Conidial suspensions (4.0 × 104 conidia per ml) were sprayed onto 8-week-old radicchio (cv. Rossana Rogers). Plants were incubated in a moist chamber for 48 h and then maintained in a greenhouse. After 12 days, leaf spots similar to the original symptoms developed on all plants inoculated with the five isolates, and the pathogen was reisolated. Control plants sprayed with distilled water remained symptomless. The experiment was repeated and the results were similar. When inoculated onto endive (Cichorium endivia cv. Tres Fine Maraicchere) and two lettuce (Lactuca sativa) cultivars, the isolates caused small (1 to 2 mm in diameter), necrotic, circular leaf spots on endive and Romaine lettuce cv. Green Towers, but did not cause symptoms on the iceberg lettuce cv. Alpha. This is the first report of A. cichorii on commercially grown radicchio in California. In addition, the same disease was confirmed on commercially produced greenhouse transplants of radicchio, indicating that primary inoculum can possibly be seed-borne.

Reference: (1) J. C. David. Mycopathologia 129:41, 1995.
Resistance to Benomyl and Thiophanate-methyl inDidymella bryoniaefrom South Carolina and New York
Authors: Keinath Anthony P. , Zitter Thomas A.
Published: May 2007

An initial collection of 7 isolates of Didymella bryoniae were grown on media amended with 0, 1, 3.2, 10, 31.2, or 100 mg benomyl per liter. Four isolates grew at all five concentrations of benomyl, but the other 3 isolates did not grow at concentrations > 1 mg/liter. Colony diameter of the four resistant isolates was reduced by 50% at 33.1 mg benomyl per liter, relative to growth on nonamended medium. Of 394 isolates tested, 182 isolates were resistant to benomyl; 178 of these resistant isolates were from South Carolina, 1 was from New York, and 3 were from Florida. Of 196 isolates grown on medium amended with 100 mg/liter thiophanate-methyl, 95 were sensitive and 101 were resistant. Essentially all isolates that were resistant to benomyl were resistant to thiophanate-methyl. In greenhouse tests, watermelon plants were sprayed with 0, 1.5, 15, 150, or 1,500 mg benomyl per liter and inoculated 1 day later with either a sensitive or a resistant isolate of D. bryoniae. Relative percent leaf area diseased was greater (P≤0.02) for the resistant isolate than for the sensitive isolate at ≥1.5 mg benomyl per liter. The occurrence of pathogenic, benzimidazole-resistant D. bryoniae in the eastern United States may reduce the effectiveness of benzimidazole fungicides for gummy stem blight management.
Herbaceous Weeds Are Not Ecologically Important Reservoirs ofErwinia tracheiphila
Authors: de Mackiewicz D. , Gildow F. E. , Blua M. , Fleischer S. J. , Lukezic F. L.
Published: May 2007

The potential of herbaceous weeds commonly growing in or adjacent to cucurbit crops to serve as alternate hosts and overwintering reservoirs of Erwinia tracheiphila, a causal agent of cucurbit wilt, was investigated. Methods for isolation, maintenance, long-term storage, and detection of E. tracheiphila from infected plants were developed. E. tracheiphila was consistently detected by enzyme-linked immunosorbent assay (ELISA) and reisolated from infected, susceptible, cucurbit species. When six common herbaceous weed species were inoculated, E. tracheiphila was detected in 49% (combined species) of the plants by ELISA 3 weeks after inoculation. However, we were unable to reisolate E. tracheiphila from these plants by standard techniques. Immunoaffinity isolation with a sensitivity of 2 CFU per sample also failed to recover E. tracheiphila from weed species. Comparisons of cucumber and goldenrod inoculated with live or formaldehyde-killed E. tracheiphila indicated that immunoassays could detect nonviable E. tracheiphila systemically spread in plants 3 weeks post-inoculation. In these tests, the pathogen was reisolated only from cucumber plants inoculated with live E. tracheiphila. Although we could reproduce serological evidence of E. tracheiphila antigen in the weeds investigated, our results do not support the hypothesis that E. tracheiphila can infect, survive in, or overwinter in the weed species tested.
Relationships Among Wilt-Inducing Isolates ofFusarium oxysporumfrom Sweetpotato and Tobacco
Authors: Clark C. A. , Hyun J-W. , Hoy M. W.
Published: May 2007

Thirty-five isolates of Fusarium oxysporum obtained from diseased sweetpotato or tobacco were compared for pathogenicity on two cultivars each of sweetpotato and tobacco, by random amplified polymorphic DNA (RAPD) profiles, and by vegetative compatibility group (VCG) analysis. Analysis of RAPD profiles revealed five clusters of isolates that corresponded to patterns of pathogenicity. One cluster of isolates, designated as F. oxysporum f. sp. nicotianae, induced severe wilting on both tobacco cultivars but varied from weakly to highly aggressive on the sweetpotato cultivars. Four of the 16 isolates from this group were originally isolated from sweetpotato, and 1 isolate caused severe disease on both crops. Three clusters included isolates from sweetpotato that were virulent on Porto Rico, caused little or no disease on Beauregard and burley tobacco (cv. Kentucky 5), and did not cause wilt on flue-cured tobacco (cv. Gold Dollar). These isolates were designated as race 0 of F. oxysporum f. sp. batatas. Isolates obtained from sweetpotato from California clustered separately from other sweetpotato isolates and the tobacco isolates. They differed from other sweetpotato isolates in being virulent on Beauregard and are proposed as a new race 1 of F. oxysporum f. sp. batatas. VCG analysis was of limited value with the isolates in this study because many isolates were self-incompatible. In each case, all members of a VCG fell within the same cluster defined by RAPDs. This study demonstrated that F. oxysporum from at least three genetically distinct lineages can cause Fusarium wilt on sweetpotato, and that the host ranges of F. oxysporum f. sp. batatas and F. oxysporum f. sp. nicotianae overlap and include plants from two different families.
Occurrence of Sclerotinia sclerotiorum in Soybean Fields in East-Central Illinois and Enumeration of Inocula in Soybean Seed Lots
Authors: Hartman G. L. , Kull L. , Huang Y. H.
Published: May 2007

Sclerotinia stem rot (SSR) of soybean is an important disease in the northern soybean-production areas of the United States. In Illinois, the occurrence of SSR has been limited to the northern-most soybean-production areas. In this study, soybean fields in east-central Illinois were surveyed for incidence of SSR. Of 68 fields surveyed, 31 contained SSR. Of the fields with SSR, 25 had between 1 and 5% SSR incidence, while 6 fields had more than 5% SSR incidence. The pattern of the disease in one field was mapped, and the spatial distribution of SSR was aggregated with a Lloyd's index of 1.4. In addition to field incidence of SSR, seed lots suspected of being contaminated with Sclerotinia sclerotiorum sclerotia were obtained from the Illinois Crop Improvement Association. Sclerotia and seeds were separated, and seeds were germinated to determine the level of seedborne infection by S. sclerotiorum. Sclerotia were recovered from 71 of 81 seed lots. Most of the seed lots were from the north-central area of Illinois, but one seed lot was from Madison County in the southwestern area of the state, and three and six seed lots contaminated with sclerotia were from Iowa and Wisconsin, respectively. Sclerotia counts ranged from 0 to 363 per seed lot. Normal-appearing seeds from the 81 seed lots (100 to 200 seeds per lot) were tested for germination and incidence of seedborne infection by S. sclerotiorum. Eight seed lots had at least one infected seed, and the incidence of seed infection ranged from 0.07 to 0.1%. From 10 randomly selected seed lots of the 81, discolored, shriveled seeds were selected and germinated to determine the incidence of seedborne infection. Seed infection rates ranged from 0 to 70%. The occurrence of SSR throughout Illinois and the importance of seedborne infection as a source of inoculum dispersal need further documentation.
Seasonal Development of Phomopsis Shoot Blight of Peach and Effects of Selective Pruning and Shoot Debris Management on Disease Incidence
Authors: Uddin W. , Stevenson K. L.
Published: May 2007

Seasonal development of shoot blight of peach caused by a Phomopsis sp. was evaluated in Oconee, Hall, and Peach counties in Georgia from April 1994 through May 1996. The frequency of infected buds in all three locations was highest during spring (mid-March to mid-May) and fall (early September to mid-October). The frequency of infected buds was highest in Hall County, which is the northernmost sampling location, followed by Oconee and Peach counties, which are located further south. During the same period of time, the effects of selective pruning and shoot debris management on disease incidence were evaluated in orchards in Oconee and Hall counties from May 1994 through May 1996. Selective pruning of infected shoots in May and October each year, following the major periods of infection, significantly reduced disease incidence during the following seasons in both locations. Disease incidence was similar regardless of whether shoot debris were left under the tree or removed from the orchard and destroyed. Our study indicates that major periods of infection of peach shoots by the Phomopsis sp. occur in the spring during the period of bud break, and in the fall when dormant buds and leaf scars are present. Additionally, our study indicates that reduction of inoculum by selectively removing infected shoots from the trees following the major periods of infection may significantly reduce disease incidence, although it may not eliminate the disease. Removal of infected shoot debris from the orchard does not appear to be necessary following pruning.
Sensitivity of Isolates of Sclerotium rolfsii from Peanut in Georgia to Selected Fungicides
Authors: Franke M. D. , Brenneman T. B. , Stevenson K. L. , Padgett G. B.
Published: May 2007

The fungicide sensitivity of more than 450 isolates of Sclerotium rolfsii from 11 different peanut fields in Georgia was determined based on percent inhibition of mycelial growth on agar amended with tebuconazole, flutolanil, or PCNB. The 11 locations represented a wide geographic distribution and variety of exposure histories to tebuconazole, flutolanil, and PCNB. Most of the populations sampled were significantly more sensitive than the populations that had the longest exposure to the fungicides. Of the three fungicides tested, tebuconazole and flutolanil demonstrated the strongest positive correlation in 1994 and 1995. The differences in sensitivity among locations suggest that fungicide sensitivity among S. rolfsii populations varies across Georgia. The location with the longest exposure history had the lowest sensitivity to all three fungicides.
Detection of Asymptomatic Fungal Infections of Soybean Seeds by Ultrasound Analysis
Authors: Walcott R. R. , McGee D. C. , Misra M. K.
Published: May 2007

Different levels of asymptomatic, seed-borne infection by storage fungi (Aspergillus and Penicillium spp.) or Phomopsis seed decay (PSD) (Phomopsis longicolla, Diaporthe phaseolorum var. sojae, and D. phaseolorum var. caulivora) were induced in sub-lots of separate soybean seed lots by incubation of seeds or pods, respectively, for different times at 25°C and at a relative humidity >95%. Seeds were then air-dried to a constant moisture content in the laboratory atmosphere, and each sub-lot was tested for incidence of infection, germination, and moisture content. Individual seeds in each sub-lot also were dropped 10 cm onto a transducer in an ultrasound analyzer. The average peak value of the ultrasound signals for each sub-lot, which indicates the weight of seeds, decreased linearly as the incidence of seed infection by storage fungi (r2 = 0.85) or PSD (r2 =0.82) increased. The slope and width of the signal, which indicates seed softness, increased as seed infection increased for both groups of fungi, although coefficients of determination were lower (r2 ranged from 0.42 to 0.59). Germination values, which decreased as seed infection for both pathogens increased, showed similar but inverse relationships to ultrasound parameters. Peak values of ultrasound signals decreased, and slope and width increased, as seed moisture content increased for sub-lots of soybeans at three levels of infection by Phomopsis seed decay. The potential for ultrasound technology to identify soybean seeds with asymptomatic infections of seed-borne pathogens was thus established.
First Report of Cucumber Mosaic Cucumovirus on Wasabi in Australia
Authors: Wilson C. R.
Published: May 2007

Wasabi (Wasabia japonica (Miquel) Matsum.), a native perennial of Japan and Shakhalin Island used to produce a condiment for Japanese dishes, is under commercial development in Tasmania, Australia. Plants propagated within shade houses showed systemic necrotic flecks and veinal necrosis in leaves and sunken necrotic stem lesions similar to those, reported in Japan (1), caused by cucumber mosaic cucumovirus (CMV). Necrosis progressed rapidly, resulting in death of plants transferred to or mechanically inoculated in a glasshouse (15 to 30°C) under full light. Disease progression in plants maintained in shade houses (5 to 20°C) was slower and symptoms less severe. Presence of CMV in symptomatic plants was confirmed by enzyme-linked immunosorbent assay (ELISA), using antiserum from Agdia (Elkhart, IN), and by sap transmission tests to healthy wasabi and Chenopodium quinoa plants. Incidence of CMV among plants in the shade houses was estimated at 10%. A survey of a commercial planting of 400 to 500 plants in November 1997, using ELISA, showed an incidence of 2.6% CMV-infected plants. They were concentrated at the field margins, suggesting that the inoculum originated from external sources rather than from transplants. This pathogen could have significant impact on the longevity and production of this crop in Australia.

Reference: (1) S. Adachi. 1987. Wasabi cultivation. Shizuoka Pref. Agric. Exp. Sta. Pub., Shizuoka, Japan.
First Report of Sorghum Ergot Caused by Claviceps africana in the United States
Authors: Isakeit T. , Odvody G. N. , Shelby R. A.
Published: May 2007

In March 1997, ergot was found on sorghum (Sorghum bicolor (L.) Moench) regrowth in several abandoned commercial grain sorghum fields in Cameron and Hidalgo counties in the Lower Rio Grande Valley (LRGV) of Texas. White sphacelia in florets produced honeydew containing macrospores (hyaline, oblong to oval, 10 to 25 μm × 5 to 7 μm) and microspores (hyaline, spherical, 3 μm in diameter). Macrospores germinated iteratively to form secondary conidia when placed on water agar and in situ following rain. Secondary conidia were hyaline, pyriform, with a protruding hilum, and measured 10 to 17 μm × 5 to 7 μm. High-pressure liquid chromatography analysis detected the alkaloid di-hydroergosine in sphacelia, which is unique to C. africana (1). The pathogen was also confirmed on adjacent johnsongrass (S. halepense). The spread of ergot across Texas was associated with the progressive maturation of the commercial sorghum crop as follows: LRGV (mid-May), Coastal Bend near Corpus Christi (June), Winter Garden area southwest of San Antonio (July), and the seed production region of the Texas Panhandle (mid-August). Ergot incidence ranged from a trace to 10% of the heads in (self-fertile) grain sorghum fields of the LRGV. Most heads had only a few infected florets, but a few heads had 35 to 50% of the florets infected. Only trace amounts were found in grain sorghum fields in other areas of the state. Incidence and severity of ergot were greatest in fields of male-sterile sorghums grown for forage. Ergot was generally low in primary heads of male-sterile sorghums in hybrid seed production fields but, in the absence of pollen, axillary tillers sometimes developed high levels of ergot. The major impact of sorghum ergot is expected to be in hybrid seed production fields in the High Plains of Texas.

Reference: (1) D. E. Frederickson et al. Mycol. Res. 95:1101, 1991.
Variability of Vomitoxin in Truckloads of Wheat in a Wheat Scab Epidemic Year
Authors: Hart L. P. , Schabenberger O.
Published: May 2007

Wheat scab, caused by Gibberella zeae, has been a serious disease in parts of the Midwest. One factor contributing to the importance of wheat scab is the contamination of grain by the mycotoxin vomitoxin (deoxynivalenol, DON), a toxic secondary metabolite. The U.S. Food and Drug Administration advisory levels for vomitoxin in wheat and wheat products require an accurate and precise assessment of vomitoxin concentration. In this study, randomly collecting probes of wheat from individual trucks and analyzing the ground wheat from each probe produced significantly less variability than subsampling and analyzing 50 g of whole kernels from the probes. The variability introduced by subsampling the probes and analyzing 50 g of whole kernels affects the precision and confidence of vomitoxin estimates. Tables of confidence intervals were developed for different sampling and subsampling patterns. To be 95% certain that the true vomitoxin concentration does not exceed the sample estimate by 1 μg/g, analyzing either four individual probes or 5–12% subsamples of these probes would be sufficient. To increase the accuracy to about 0.5 μg/g, either an analysis of seven probes or a 5–12% subsample of 10 probes would be necessary, based on a one-sided confidence interval.
Secondary Colonization of Pear Blossoms by Two Bacterial Antagonists of the Fire Blight Pathogen
Authors: Nuclo R. L. , Johnson K. B. , Stockwell V. O. , Sugar D.
Published: May 2007

Dispersal of the bacteria Pseudomonas fluorescens strain A506 and Erwinia herbicola strain C9-1S from treated to nontreated pear blossoms, and the effect of their spread on fire blight, were investigated in an orchard block of 10 rows containing 4 trees per row. Center rows of trees were sprayed with a mixture of P. fluorescens A506 and E. herbicola C9-1S at 30, 15, and 50% bloom in 1994, 1995, and 1996, respectively. Immediately after spraying, antagonists were detected only on treated blossoms. In 1994 and 1996, as bloom progressed, both P. fluorescens A506 and E. herbicola C9-1S were detected on nontreated blossoms located up to 4 rows (10 m) from the treated rows. In 1995, establishment of the antagonists on treated blossoms was poor and spread to nontreated trees was limited, apparently because of cold temperatures. Each year, honey bees were used to inoculate all trees with E. amylovora at 80% bloom. After full bloom in 1994 and 1996, the proportion of blossoms with E. amylovora populations >105 CFU per flower were highest in the outermost rows, and decreased linearly (P < 0.05) with proximity to treated rows. In 1994, diseased blossom clusters decreased significantly (P < 0.05) from the outermost rows to the treated rows, but there was no significant effect of distance on disease incidence in 1995 or 1996. Secondary colonization of blossoms by P. fluorescens A506 and E. herbicola C9-1S can play a role in disease suppression, but, among seasons, rates of secondary colonization by P. fluorescens A506 and E. herbicola C9-1S were variable, indicating that multiple applications of antagonists may be necessary to optimize biological control.
Composted Municipal Waste Reduces Infection of Citrus Seedlings byPhytophthora nicotianae
Authors: Widmer T. L. , Graham J. H. , Mitchell D. J.
Published: May 2007

Most citrus nurseries and orchards in Florida are infested with Phytophthora nicotianae, the causal agent of Phytophthora root rot. Although fungicides control the disease and increase seedling growth and tree yields, they are not always economically or environmentally sustainable. Amendment of citrus soils with composted municipal waste (CMW) may provide an alternative to fungicides for disease management. Citrus seedling growth decreased with increasing proportions of one CMW source, indicating the potential for phytotoxicity from soluble salts and acetic acid when the proportion of CMW in soil exceeded 20% (vol/vol). When a citrus soil was amended (20% vol/vol) with certain sources of CMW, the incidence of infection of 5-week-old susceptible citrus seedlings by P. nicotianae was reduced from 95% to as low as 5%. Addition of fresh CMW to two different citrus soils reduced colony growth of P. nicotianae after the fungus was incubated in the amended soil for 6 days and then recovered on PARPH selective medium. If CMW was stored for more than 3 months before amendment, the soil mixtures did not suppress colony development. In general, extracts of fresh CMW reduced mycelial growth in vitro; whereas suppressiveness of CMW from the same batch was lost after storage. Acetic acid was detected at higher concentration in fresh CMW that suppressed colony growth than in CMW that lacked activity. A species of Acremonium was isolated from another source of CMW that was suppressive to P. nicotianae. This fungus parasitized hyphae of P. nicotianae in vitro. Thus, CMWs have the potential to at least temporarily suppress P. nicotianae through chemical and microbial agents depending on source and age of the CMW.
First Report of Celery Mosaic Potyvirus on Dill (Anethum graveolens)
Authors: Bellardi M. G. , Rubies-Autonell C.
Published: May 2007

In the spring and summer of 1997, nearly 90% of dill plants (Anethum graveolens L.) cultivated in a crop of Emilia-Romagna region (northern Italy), exhibited viruslike symptoms. Approximately 30% of the plants showed narrowing of the leaf lamina and stunting that evolved to yellow or bronze color. The plants appeared bushy and had low seed production. Electron microscopy of leaf-dip preparations revealed the association of flexuous, potyvirus-like particles of 750 nm in length with diseased dill plants. The identity of this virus was established by differential host reactions and serological assays. It was mechanically transmitted only to Chenopodium amaranticolor Coste et Reyn. and C. quinoa Willd. plants (which showed local chloro-necrotic lesions after about a week), and Petunia × hybrida Hort. Vilm.-Andr. plants (latently infected). No infections were obtained in several inoculated Umbelliferae plants, including dill and celery (Apium graveolens L.). Therefore, our isolate is similar to that described by others (1,2) and unlike the type strain that infects only members of the Umbelliferae. Virus particles reacted in protein A sandwich-enzyme-linked immunosorbent assay with antiserum to celery mosaic potyvirus (CeMV) (supplied from the Istituto di Fitovirologia Applicata, CNR, Turin, Italy). This result was further confirmed by immunosorbent electron microscopy decoration tests. CeMV in the field was likely transmitted to dill by abundant aphid populations from weeds and/or other Umbelliferae species cultivated in the same location. In particular, the weed host Daucus carota L. and the cultivated Petroselinum sativum Hoffm. plants both exhibited bronze foliage and stunting, and were found to be infected by CeMV. This note represents the first report of CeMV in A. graveolens.

References: (1) E. Luisoni et al. Ann. Phytopathol. 1:375, 1969. (2) C. Rubies-Autonell et al. Phytopathol Mediterr. 35:58, 1996.
A PCR-Based Technique for Detection of Neotyphodium Endophytes in Diverse Accessions of Tall Fescue
Authors: Doss Robert P. , Clement Stephen L. , Kuy Srey-Reath , Welty Ronald E.
Published: May 2007

A previously described polymerase chain reaction (PCR)-based method used for detection of Neotyphodium coenophialum in tall fescue detected Neotyphodium endophytes in some, but not all, infected plants from a geographically diverse sample. In the study reported here, a different set of primers, based on intervening sequences of the tubulin 2 gene, were prepared and used for PCR. PCR with these primers yielded the expected 444 base pair amplification product with DNA from 104 of the 106 infected accessions tested. In addition, one accession originally scored as endophyte-free on the basis of a tissue culture test was correctly rated as endophyte-infected using the PCR procedure. Results suggest that primers based on intervening sequences of the tubulin 2 gene can be used for PCR-based detection of Neotyphodium endophytes in tall fescue accessions of diverse origin.
Meteorological Factors Affecting Airborne Conidia Concentrations and the Latent Period of Podosphaera clandestina on Sweet Cherry
Authors: Grove Gary G.
Published: May 2007

Conidia of Podosphaera clandestina were trapped beginning about 1 month after bud burst and continuing through the majority of the fruit development period and beyond. The presence of airborne conidia generally followed a diurnal pattern, with peak concentrations occurring in late morning to early afternoon. The three general spore dispersal patterns described by Sutton and Jones for P. leucotricha were observed: diurnal dispersal with concentrations peaking about midday (type I dispersal); random dispersal in which the spore concentrations were not correlated with any measured meteorological parameter (type II dispersal); and dispersal associated with the onset of rain (type III dispersal). Positive correlations with wind speed and temperature, and negative correlations with relative humidity, were characteristic of days when spore dispersal was diurnal. Consistent correlations with meteorological parameters were not detected on days with random or rain-onset dispersal. The latent period of P. clandestina on cherry foliage was found to be shortest at 20 to 25°C and was influenced by temperature and incubation time.
Virulence Characterization of Single-Zoospore Isolates of Sclerospora graminicola from Pearl Millet
Authors: Thakur R. P. , Pushpavathi B. , Rao V. P.
Published: May 2007

Sclerospora graminicola, the causal agent of downy mildew in pearl millet, is well-known for variation in its virulence pattern. Nine single-zoospore isolates (Sg 026-Z-1 to Sg 026-Z-9) derived from an oosporic isolate Sg 026 from a pearl millet F1 hybrid cultivar Nath 4209 grown in a farmer's field in a village, Veelad, in Maharashtra state, India, and three controls (Sg 026, Field-1, and Field-2) were evaluated for their virulence in two experimental runs in a greenhouse. The isolates were maintained on pot-grown seedlings of a highly susceptible pearl millet line, 7042S, in a greenhouse through asexual (sporangial) generations. Pot-grown seedlings of six pearl millet potential differential lines/cultivars (7042S, NHB 3, MBH 110, ICMH 451, 843B, and 852B) were spray-inoculated with a sporangial suspension (5 × 105 sporangia ml-1) and maintained in a greenhouse at 25 ± 2°C. Data were recorded for latent period (days) and disease incidence (%), from which a virulence index (incidence × latent period-1) was calculated to quantify disease-causing potential of isolates. Results indicated significant variation in latent period, incidence, and virulence index among isolates. The isolates were classified into four distinct pathotype groups based on their virulence indices on six pearl millet lines. Because of the significant variation for virulence in the S. graminicola population infecting Nath 4209, it is recommended that the hybrid be regularly monitored for downy mildew infection in farmers' fields, and be replaced by a resistant cultivar that is genetically unrelated to the parental lines of Nath 4209. This will help delay or avoid development of downy mildew epidemics and the resulting heavy loss to pearl millet farmers in the region.