bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Tillage Practices on Anthracnose Development and Distribution in Dry Bean Fields
Authors: Ntahimpera N. , Dillard H. R. , Cobb A. C. , Seem R. C.
Published: May 2007

Three tillage practices—chiseling, rototilling, and moldboard plowing—were evaluated in 1993 and 1994 to determine their impact on initial disease development, distribution, and progression over time in a field of the susceptible kidney bean cultivar Horizon. The tillage treatments were administered in the spring in a field infested in 1992 with the bean anthracnose pathogen, Colletotrichum lindemuthianum race β. Initial disease incidence was highest in the chiseled plots, where more bean debris was left on the surface than in the other treatments. Significantly higher final disease incidence and area under the disease progress curve (AUDPC) occurred in the chiseled plots than in the rototilled and moldboard plowed plots. There was a significant correlation (r = 0.75) between the percentage of debris left on the surface and subsequent disease incidence on pods in the field. Anthracnose incidence or severity in the field was highly correlated with disease incidence on harvested pods (r values ranged between 0.87 and 0.98). Results from the ordinary runs analysis showed that anthracnose occurred randomly within the field early in the season, indicating that initial inoculum was from bean debris within the field. Later in the season, plant-to-plant spread resulted in a more clustered distribution of diseased plants.
Effects of Temperature on Sporulation and Latent Period of Colletotrichum Spp. Infecting Strawberry Fruit
Authors: King W. T. , Madden L. V. , Ellis M. A. , Wilson L. L.
Published: May 2007

Effects of temperature on sporulation of Colletotrichum acutatum, C. gloeosporioides, and C. fragariae, causes of anthracnose of strawberry, were determined in controlled-environment studies. Detached immature fruit were inoculated with a conidial suspension and incubated up to 36 days at constant temperatures of 5, 10, 15, 20, 25, 30, and 35°C. Latent period (time to first sporulation) depended on temperature and ranged from 2 to 3 days at 25°C to 6 to 17 days at 5°C. C. acutatum had a shorter latent period than the other species at 5 and 10°C; at higher temperatures, latent periods of the species were very similar. During the first 4 days of sporulation, there was an optimum-type relationship between the logarithm of conidia per fruit [log(Y)] and temperature, with maximum observed sporulation (generally 106 to 107 conidia per fruit) from 15 to 30°C. Sporulation increased over time at temperatures of 15°C and above. The greatest difference among the species was at 5 and 10°C, where tested C. acutatum isolates produced from 10 to 100 more conidia per fruit than the other species. Polynomial regression equations were used successfully to represent log(Y) as a function of temperature and incubation time. The rate of increase in sporulation over time was a function of temperature, with a predicted optimum of 22 to 26°C. Equations were validated by predicting sporulation of the three species infecting fruit attached to plants growing in controlled-environment chambers. Although the predictions tended to be slightly larger than observed, mean error [100(observed - predicted)/ observed] was only -0.7% (95% confidence interval: -2.4 to 1.0%).
Genetic Variation Among Fusarium oxysporum Isolates from Sugar Beet as Determined by Vegetative Compatibility
Authors: Harveson R. M. , Rush C. M.
Published: May 2007

One hundred sixty Fusarium oxysporum isolates were collected over a 3-year period (1992 to 1994) from diseased sugar beet and pigweed plants from seven counties in Texas. Disease symptoms on sugar beet included root-tip-rot symptoms with wilting and vascular necrosis, and wilting and vascular necrosis only. Pathogenicity testing on sugar beets indicated that 132 isolates of the 160 recovered were pathogenic and were considered to be F. oxysporum f. sp. betae (FOB). Of the 132 isolates of FOB, 28 were initially chosen as testers and paired in all possible combinations to estimate the number of vegetative compatibility groups (VCGs) present. Once VCGs were determined from the 28 isolates, a nitrate nonutilizing mutant (nit) 1 or nit 3 from each of the remaining isolates was paired against a Nit M from each of the established VCGs. Thirty-three isolates obtained from other sugar-beet-growing states also were tested for vegetative compatibility. A total of 95 of the 132 isolates of FOB from Texas were assigned to one of seven VCGs identified. Sixty-three isolates were assigned to VCG 1, with VCGs 2 through 7 containing 6, 16, 2, 2, 2, and 4 isolates, respectively. VCGs 1, 3, and 6 were recovered from both sugar beet and pigweed. Two additional isolates collected from Texas in 1987 also belonged to VCG 1. A number of the isolates collected from Texas could not be assigned to any of the seven established VCGs. These included two single-member Nit Ms, 11 self-incompatible isolates, and 24 of unknown affiliation. None of the isolates from any one state were compatible with those from any other state. Results suggest that substantial variation exists among sugar beet isolates of FOB from the U.S., and that these populations of F. oxysporum are apparently distinct and endemic to their respective areas.
Improved Biocontrol Efficacy of Trichoderma harzianum 1295-22 for Foliar Phases of Turf Diseases by Use of Spray Applications
Authors: Lo C.-T. , Nelson E. B. , Harman G. E.
Published: May 2007

Trichoderma harzianum strain 1295-22 is an effective biocontrol agent for several fungal diseases. The efficacy of granule and spray applications of strain 1295-22 for control of Pythium root rot, brown patch, and dollar spot of creeping bentgrass was investigated. Spray applications of conidial suspensions (SA) of strain 1295-22 significantly reduced all three diseases of creeping bentgrass turf in both greenhouse and field experiments. Control was greatest when Triton X-100 at 0.1% was added to aqueous spray suspensions. When SA were applied weekly, the biocontrol treatments were equivalent to standard fungicides. Broadcast granule applications (GA) also significantly reduced foliar symptoms of Pythium root rot, dollar spot, and brown patch; turf quality also was enhanced. The populations of Trichoderma spp. in the root zone of a bentgrass putting green treated with SA or GA of strain 1295-22 increased 10- to 100-fold after treatment compared with untreated plots. However, strain 1295-22 was present at high levels on bentgrass leaves only following SA. Collectively, the results suggest that strain 1295-22 possesses both rhizosphere and phylloplane competence. The combination of broadcast applications of granules followed by spray applications of conidia reduced damage from both root and foliar diseases.
Reaction of Four Musa Genotypes at Three Temperatures to Isolates of Mycosphaerella fijiensis from Different Geographical Regions
Authors: Romero Ronald A. , Sutton Turner B.
Published: May 2007

Two tetraploid banana hybrids, FHIA1 and FHIA2, with resistance to black Sigatoka, and two highly susceptible, naturally occurring triploids, Grand Naine and False Horn, were evaluated at three temperatures for their resistance to isolates of Mycosphaerella fijiensis from five geographical regions. The youngest open leaf of young plants was inoculated, and plants were incubated at 22, 26, and 30°C in growth chambers. Duration of the incubation period and disease severity were used to evaluate the reactions of the genotypes. The incubation period was the shortest at 26°C. Disease severity was greatest at 26°C on Grand Naine and False Horn, but there was no clear temperature effect for the FHIA genotypes. The incubation period was longer on both FHIA genotypes than on Grand Naine and False Horn. With few exceptions, isolates with the shortest incubation periods caused greater disease severity than those with longer incubation periods. The level of resistance between the two FHIA genotypes was similar, and both expressed high resistance across temperatures and isolates of M. fijiensis, indicating that no physiological races of the pathogen were detected. There were differences in durations of the incubation periods and disease severities associated with the geographical origin of the isolates. Isolates that originated in Honduras, Colombia, and Costa Rica produced more disease on Grand Naine and False Horn than did isolates from Cameroon and Asia. However, no differences associated with the geographical origin of the isolates were observed for both FHIA genotypes. Also, there were no differences in disease severities within isolates that originated from Honduras, Colombia, and Costa Rica.
Detection of Pythium ultimum Using Polymerase Chain Reaction with Species-Specific Primers
Authors: Kageyama K. , Ohyama A. , Hyakumachi M.
Published: May 2007

This study was conducted to sequence the rDNA internal transcribed spacer (ITS) region of Pythium ultimum and Pythium group HS, design species-specific primers for polymerase chain reaction (PCR), and detect P. ultimum from diseased seedlings using PCR. The sequence of the ITS region of P. ultimum was identical with that of Pythium group HS. The results support the reports that the HS group is an asexual strain of P. ultimum. Using PCR, the primer pair K1+K3, designed on portions of the sequence of the ITS region, amplified isolates of P. ultimum and the HS group but not isolates of 20 other Pythium species. DNA extracts from damped-off seedlings were not amplified, but a 10-fold dilution of the extracts with Tris-EDTA (TE) buffer diluted the inhibitors and allowed PCR amplification. The primer pair used detected P. ultimum from a single diseased seedling.
A Survey for Strains of Xylella fastidiosa in Citrus Affected by Citrus Variegated Chlorosis and Citrus Blight in Brazil
Authors: Beretta M. J. G. , Barthe G. A. , Ceccardi T. L. , Lee R. F. , Derrick K. S.
Published: May 2007

Polymerase chain reaction amplification of DNA from various strains of Xylella fastidiosa with tRNA consensus primers produced three different fingerprint groups. The citrus variegated chlorosis (CVC) and mulberry leaf scorch strains were unique and readily separated from each other and all other strains tested. Internal primers were designed based on the sequence of a DNA fragment unique to the CVC strain. An assay was developed with a mixture of these primers and those reported to detect 18 strains of X. fastidiosa. The assay was used to survey citrus in Brazil. The strain identified to be the cause of CVC was found in constant association with trees with CVC symptoms. On occasion, trees with no symptoms were found to have the CVC strain; this was presumably due to presymptomatic infections. No other strains were found in this survey, and X. fastidiosa was not associated with citrus blight.
Assessment of Greenhouse and Laboratory Screening Methods for Evaluating Potato Foliage for Resistance to Late Blight
Authors: Dorrance Anne E. , Inglis Debra Ann
Published: May 2007

Greenhouse and laboratory screening methods for assessing potato foliage for resistance to late blight were compared using 15 cultivars and advanced breeding selections with known field response to late blight. Screening methods included greenhouse inoculation of plants in several age classes, and laboratory assays of detached leaflets, leaf disks, and stem cuttings. Greenhouse inoculation of plants 7 to 11 weeks after planting, near the time of flowering, corresponded best to results obtained in field evaluations, but there were significant differences in disease severity between separate greenhouse tests. This is consistent with variation in late blight severity on a year-to-year basis when cultivars are compared in the field. The greenhouse inoculation method allowed for testing of several components of partial resistance, such as infection efficiency and lesion growth rate, which may exist for each cultivar. Laboratory assays proved less reliable than greenhouse assays for overall ratings of partial resistance, but could be useful for measuring specific components of resistance. Screening evaluations for late blight resistance should include standard cultivars with known reaction to Phytophthora infestans to reference the disease potential within the screening evaluation.
A Bipartite Geminivirus Infecting Tomatoes in Cuba
Authors: Martinez Y. , de Blas C. , Zabalgogeazcoa I. , Quiñones M. , Castellanos C. , Peralta E. L. , Romero J.
Published: May 2007

Whitefly-transmitted geminiviruses have increased in their distribution and importance during the last decade, apparently due to a wider distribution of their vector Bemisia tabaci (Gennadius). In Cuba, symptoms of geminivirus disease have been observed since the early 1990s. A survey of geminivirus-caused diseases in tomato plants has been conducted since 1994 in the province of La Habana. The most severe symptoms were observed in the commercial varieties Campbell 28, Criollo Quivican, and HC 3880. In some plants the Israeli strain of tomato yellow leaf curl geminivirus (TYLCV) was detected (1). In other cases, a viral DNA with a genome size smaller than that of TYLCV that could not be amplified with primers specific for the Israeli strain was also detected by hybridization. In these samples a polymerase chain reaction amplification with broad-spectrum, degenerate primers designed for whitefly-transmitted bipartite geminivirus (2) was carried out. Two fragments of about 1.1 and 0.6 kb, corresponding to components A and B, respectively, were amplified, indicating that a bipartite geminivirus was present. The 1.1-kb fragment amplified from a sample showing strong leaf yellowing and slight curling was cloned and sequenced. A sequence of 1,174 nucleotides was obtained and compared with geminivirus sequences deposited in the GenBank, by multiple alignment (CLUSTAL W, European Bioinformatics Institute, Hinxton Hall, UK). Genetic distances were calculated by Kimura's two parameters method. Percentages of similarities obtained with the sequence were as follows: tomato mottle virus 78%, abutilon mosaic virus 73.8%, and tomato golden mosaic 61.8%. Partial sequences of the open reading frames AL1 and AR1 and the intergenic region were present. Percentages of similarities obtained with the intergenic region were as follows: tomato mottle virus 78.1%, sida golden mosaic virus 63%, bean dwarf mosaic virus 62.6%, abutilon mosaic virus 57.1%, and tomato golden mosaic virus 32%. These results suggest that we have detected in Cuban tomatoes a new bipartite geminivirus related to tomato mottle virus, and we propose that it be named Havana tomato virus. Frequency of distribution of viruses in commercial varieties and their relationship with the presence of whiteflies are currently being studied.

References: (1) Y. Martinez et al. J. Phytopathol. 144:277, 1996. (2) M. R. Rojas et al. Plant Dis. 77:340, 1993.
Effect of Stalk Desiccation on Sugarcane Red Rot
Authors: Yin Zhi , Hoy J. W.
Published: May 2007

The effect of drought conditions at planting time on sugarcane red rot, caused by Colletotrichum falcatum, was evaluated in experiments conducted under controlled conditions and in the field. For experiments under controlled conditions, detached and topped mature stalks of five cultivars were inoculated with conidia of C. falcatum, then exposed to a 3-week desiccation treatment, followed by 3 weeks without desiccation, or maintained for 6 weeks without desiccation. Disease severity, assessed as the number of nodes beyond which rot symptoms extended, number of nodes rotted, internode rot severity, and a rot severity index, was increased in five cultivars by exposure to desiccation. However, response of individual cultivars varied for some disease traits assessed. In field experiments, C. falcatum inoculation alone did not reduce spring shoot populations for seven cultivars. The lowest shoot populations occurred in plantings of inoculated stalks exposed to desiccation. Some cultivars were adversely affected by desiccation alone. These results demonstrate that red rot severity can be increased by the occurrence of drought conditions during the initial growth processes of vegetatively propagated sugarcane stalks.
Control of Dollar Spot of Creeping Bentgrass Caused by an Isolate of Sclerotinia homoeocarpa Resistant to Benzimidazole and Demethylation-Inhibitor Fungicides
Authors: Burpee L. L.
Published: May 2007

The effects of fungicides were studied on two isolates of Sclerotinia homoeocarpa that differed in fungicide sensitivity. Concentrations of benzimidazole (benomyl and thiophanate-methyl), demethylation inhibitor (fenarimol, propiconazole, and triadimefon), and nitrile (chlorothalonil) fungicides required to inhibit mycelial growth in vitro by 50 and 90% (effective concentration; EC50,90) were significantly greater for isolate S088 than for isolate S084. No differences were observed in the EC50,90 values of a pyridylaniline (fluazinam) or dicarboximide (iprodione) fungicide. In field tests conducted on creeping bentgrass, S088 had a significantly shorter incubation period than S084 in plots treated with propiconazole applied at 0.2 or 0.8 kg a.i. ha-1 in 1994 or 0.4 kg a.i. ha-1 in 1995, thiophanate-methyl applied at 1.5 or 3.0 kg a.i. ha-1 in 1994 and 1995, or a tank-mix of propiconazole and iprodione applied at 1.6 + 0.8 kg a.i. ha-1 in 1994. No differences in incubation periods occurred in plots treated with chlorothalonil or iprodione in either year, or with fluazinam in 1995 and 1996. Fewer days were required to reach 5% disease severity in turf inoculated with isolate S088, compared to isolate S084, in plots treated with propiconazole, thiophanate-methyl, or certain tank-mixes containing propiconazole, in 1994 and 1995. Several treatments, including propiconazole, thiophanate-methyl, and fluazinam, resulted in suppression of disease caused by isolate S084 to less than 5% severity for more than 21 days, while only fluazinam applied at 1.6 or 3.2 kg a.i. ha-1 provided more than 21 days of disease suppression in turf inoculated with either of the isolates tested. Slope coefficients from linear regressions between incubation period or days to 5% disease and concentrations of fungicide applied in 1996 were significantly different for isolate S084 compared to isolate S088 in plots treated with propiconazole, but not in plots treated with fluazinam.
Effect of Previous Crop, Seedborne Inoculum, and Fungicides on Development of Stagonospora Blotch
Authors: Milus E. A. , Chalkley D. B.
Published: May 2007

Stagonospora blotch of wheat has been difficult to control in the eastern United States. The objectives of this research were to evaluate the effects of field inoculum, seedborne inoculum, and seed treatment and foliar fungicides on Stagonospora blotch development and to develop more effective management strategies. In 1995 and 1996, similar experiments were established in “infested” and “clean” fields using two seed lots of Coker 9543 (“low” and “high” levels of seed infection) and six seed or foliar fungicide treatments. Planting in clean fields, planting seed with a low level of seedborne inoculum, treating seed with difenoconazole or triadimenol + thiram, and applying propiconazole or tebuconazole to the foliage all contributed toward reducing leaf infections by Stagonospora nodorum, severity of leaf and glume blotch, and incidence of S. nodorum in the harvested seed. Propiconazole alone was the least effective treatment. Planting in an infested field tended to negate the beneficial effects of low level of seed infection and fungicide seed treatments. Crop rotations and tillage that allow wheat debris to decompose before the next wheat crop along with difenoconazole or triadimenol seed treatment to reduce seedborne inoculum should be sufficient to avoid serious losses. In fields where wheat is grown every year, tillage and seed treatment would still be helpful, but a foliar fungicide at GS 8 may be necessary for adequate control. Applying an effective fungicide to seed appears to be a more efficient means of reducing seedborne inoculum than does producing seed with low levels of inoculum.
Role of Green Peach Aphid Flights in the Epidemiology of Potato Leaf Roll Disease in the Columbia Basin
Authors: Thomas Peter E. , Pike Keith S. , Reed Gary L.
Published: May 2007

Three distinct and highly predictable green peach aphid (GPA) (Myzus persicae) flights that occur seasonally in the spring, summer, and fall were detected at a southern, central, and northern location in the Columbia Basin of the Northwestern United States. Intensity and timing of the flights was approximately the same at the three locations. Timing and number of alatae captured in the spring and summer flights was associated with heat unit accumulation. The spring flight, which originates on the overwintering peach tree host, colonized but did not introduce potato leafroll virus (PLRV) into virus-free potato plots. The summer flight, which originates from volunteer potatoes and spring herbs originally colonized by the spring flight, did introduce PLRV into virus-free potatoes. The fall flight was too late to affect potato production. When plots contained a point source of PLRV, the virus spread rapidly in a plant-to-plant mode to all plants in plots after aphids arrived in the spring. Rate of spread from point sources of infection was not affected by timing or intensity of the spring flight, but timing of virus spread in the plots depended on time of arrival of the aphids. Once PLRV was introduced to virus-free plots by the summer flight, virus spread to other plants within the plots. GPA overwintered on peach trees. Although GPA apterae and alatae were present on winter annual weed and crop hosts in the fall, none survived winters on these species. In addition to the GPA, one other vector of PLRV, Macrosiphum euphorbiae, was rarely collected in aphid traps. These results suggest that chemical control of aphids could be delayed until mid-July if PLRV-free potato seed were available.
Streptomyces spp. Isolated from Potato Scab Lesions Under Nordic Conditions in Finland
Authors: Lindholm Päivi , Kortemaa Hanna , Kokkola Mirkka , Haahtela Kielo , Salkinoja-Salonen Mirja , Valkonen Jari P. T.
Published: May 2007

Actinomycetes isolated from scab lesions of potato tubers in Finland (60°–68°N, 21°–31°E) were characterized using physiological tests and production of necrosis on potato minitubers. Seven strains were additionally analyzed for their whole cell fatty acid profiles. The majority of the pathogenic strains were similar to the Streptomyces scabies type strain ATCC 49173 that is characterized by gray to brown colonies, gray spores, spiral sporophores, melanin production, and utilization of the International Streptomyces Project (ISP) sugars. However, two groups of strains (designated as Group 4, 38 strains; and Group 5, nine strains), each containing several pathogenic isolates, differed from S. scabies ATCC 49173 in at least two phenotypic traits. Additionally, a single, highly virulent strain (SSC 122) differed from all other strains for its phenotypic traits. The fatty acid compositions of the three pathogenic strains of Group 4 and the strain SSC 122 differed from S. scabies ATCC 49173 and S. acidiscabies ATCC 49003. In SSC 122, the ratio of saturated and unsaturated and the iso and anteiso forms of fatty acids were different from all other streptomycetes analyzed. Thus, the strains of Group 4 and 5 and SSC 122 may represent three novel Streptomyces spp. pathogenic on potato. SSC 122 and the pathogenic strains identified to S. scabies grew at pH 5.0 but not at pH 4.6, whereas the pathogenic strains of Group 4 and 5 grew at pH 4.6 or 4.4 but not at pH 4.2.
Aspergillus flavus Infection and Aflatoxin Contamination of Preharvest Maize in Benin
Authors: Sétamou M. , Cardwell K. F. , Schulthess F. , Hell K.
Published: May 2007

Eighty and sixty maize fields were sampled in 1994 and 1995, respectively, to monitor Aspergillus infection and aflatoxin contamination of preharvest maize in Benin. Three Aspergillus species were isolated from different agroecological zones, with A. flavus being the most prevalent. The countrywide mean percentage of kernel infection was about 20% in both years. Aflatoxin was extracted from maize in at least 30% of the fields sampled. Toxin concentrations exhibited a distinct zonal variation, with relatively high levels in the Guinea Savanna. There was a trend toward higher rate of aflatoxin accumulation per percentage A. flavus infection from the south to the north. Damage by the ear borer, Mussidia nigrivenella, increased aflatoxin accumulation in maize. Hence, the geographic pattern observed in the occurrence of A. flavus and aflatoxin may be related to the incidence of M. nigrivenella.
First Report of Pratylenchus fallax on Turfgrass in Ontario
Authors: Yu Q. , Potter J. W. , Gilby G. A.
Published: May 2007

During 1995 and 1997 surveys of golf courses throughout southern Ontario for plant parasitic nematodes, one Pratylenchus sp. with a heavily sclerotized cephalic area, lip region with three annules, females with spermatheca full of sperms, and crenate tail was found in 13 of 14 soil samples taken from fairways. Males were also found in the samples. Monoxenic cultures of the nematode were established on excised corn roots, each culture started from a single mature female. In cultures, males were common, averaging about one male per five females. Following a comparative microscope study of about 50 specimens (20 measured), the species was identified as Pratylenchus fallax Seinhorst, 1968. Bluegrass (Poa pratensis L.) was the main type of grass in the fairways surveyed. P. fallax may cause significant damage to turfgrass by directly destroying the roots, and the wounded roots become vulnerable to secondary infection by soilborne pathogens (1). The nematode has been found once in Quebec, Canada, in 1976 (2). This is the first report of Pratylenchus fallax in Ontario.

References: (1) S. G. Fushtey and F. D. McElroy. Can. Plant Dis. Surv. 57:54, 1977. (2) P. W. Willis et al. Plant Dis. Rep. 60:207, 1976.
First Report of Banana Streak Badnavirus in Plantain Landraces in Southern Cameroon, Central Africa
Authors: Gauhl F. , Pasberg-Gauhl C. , Hughes J. d'A.
Published: May 2007

Banana streak badnavirus (BSV) has been reported from Musa spp. in many parts of West Africa, including Benin, Côte d'Ivoire, Ghana, and Nigeria (1). Symptoms of BSV infection in Musa spp. are sometimes similar to and confused with those caused by cucumber mosaic virus (CMV). BSV is prevalent in areas of southern Nigeria bordering Cameroon, and the disease may also be present in other Central African countries. In June 1996, six leaf samples with viruslike yellow/chlorotic streak symptoms were collected from plantain in the four villages, Awae, M'Balmayo, Nkolfep, and Nkolfoulou, within a 60-km radius of Yaoundé, Cameroon's capital. The samples were indexed for BSV and CMV by both triple antibody sandwich indirect enzyme-linked immunosorbent assay (TAS-ELISA) and immunosorbent electron microscopy (ISEM) to ascertain the presence of these two viruses. The TAS-ELISA was performed with rabbit polyclonal antiserum (obtained from B. E. L. Lockhart, University of Minnesota) for trapping and mouse polyclonal antiserum (obtained from G. Thottappilly, IITA) for detection. Out of the six samples, one tested strongly positive (>×2 A405 of the healthy control) and four were weakly positive (<×2 but >×1.5 A405 of the healthy control) for BSV by TAS-ELISA. However, all six samples contained BSV particles when examined by ISEM with rabbit polyclonal antiserum (from B. E. L. Lockhart) for trapping. None of the samples tested positive for CMV. These results confirm that BSV is present in Cameroon and that BSV is likely to be the causal agent of the symptoms.

Reference: (1) C. Pasberg-Gauhl et al. Plant Dis. 80:224, 1996.
Susceptibility of Pacific Yew to Phytophthora lateralis
Authors: Murray Marion S. , Hansen Everett M.
Published: May 2007

In 1991, Pacific yew was reported as a new host for Phytophthora lateralis, an aggressive root pathogen thought previously to be specific to Port Orford cedar. This study was designed to compare the pathogenicity of P. lateralis on the two hosts through seedling, stem, branch, and rootlet inoculations, and field survey. Mortality of inoculated plants averaged 72% for cedar and 4% for Pacific yew, and root colonization by P. lateralis was significantly greater in cedar seedlings than in Pacific yew seedlings. Lesion length on the cedar seedling stems was twice the lesion length on Pacific yew stems, and cedar branches had lesions four times longer than Pacific yew branches. Abundant zoospore aggregation occurred on cedar rootlets along the zone of elongation and the region of maturation. In comparison, far fewer zoospores encysted on Pacific yew rootlets, and they were concentrated on the root hairs. A field survey along 0.8-km stretches of three infested streams in southwest Oregon and northwest California revealed a total of 1,199 dead Port Orford cedar (46% mortality), and 86 dead Pacific yew (10% mortality). We conclude that Pacific yew is less susceptible to P. lateralis than Port Orford cedar.
Disease Progress of Black Dot on Tomato Roots and Reduction in Incidence with Foliar Applied Fungicides
Authors: Dillard H. R. , Cobb A. C.
Published: May 2007

Progression of black dot caused by Colletotrichum coccodes was determined at regular intervals on roots of processing tomatoes growing in a naturally infested field. In 1993 and 1994, C. coccodes was first isolated from tomato roots 30 and 37 days after transplanting, respectively, which corresponded to the opening of flowers in the first flower clusters. Black dot incidence increased rapidly from the time when large green fruit were present to production of mature red fruit. In both years, C. coccodes was isolated from the roots of 97% of the plants at the postharvest sampling date (162 days after transplanting). Areas under the incidence disease progress curves were not significantly different in the 2 years of study (1993 = 83.5, 1994 = 86.9). Root decay was severe at the postharvest sampling, and sclerotia of C. coccodes were abundant on the roots. C. coccodes was isolated from 38 and 44% of the root segments in 1993 and 1994, respectively. Areas under the disease progress curves for infected root segments were not significantly different in the 2 years of study (1993 = 25.8, 1994 = 33.9). In a separate study, chlorothalonil (2.5 kg/ha) or mancozeb (1.68 kg/ha) was applied at 7-, 10-, or 14-day intervals to tomato plants. Recovery of C. coccodes from root segments at harvest (113 to 118 days after transplanting) was significantly reduced in the chlorothalonil 7- or 10-day and mancozeb 10-day interval treatments in both years. However, the percentage of plants with black dot was not consistently reduced by fungicide applications.
Identification of the Bacterial Leaf Spot Pathogen of Lettuce, Xanthomonas campestris pv. vitians, in Ohio, and Assessment of Cultivar Resistance and Seed Treatment
Authors: Sahin F. , Miller S. A.
Published: May 2007

In 1995, a bacterial leaf spot disease was observed on lettuce plants grown on muck soils in north central Ohio. Characteristic symptoms were water-soaked circular, dark brown- or olivecolored spots, approximately 1 to 2 mm in diameter, along the margin of leaves; V-shaped lesions beginning at the leaf margins and advancing along the veins; and individual black spots scattered on the leaf surface. Five bacterial strains were isolated from infected leaves of two lettuce cultivars, Darkland and Go Go Green. These strains were identified as Xanthomonas campestris pv. vitians based on morphological, physiological, biochemical, and pathogenicity tests, as well as fatty acid methyl ester (FAME) analyses. One of the five strains tested was resistant to streptomycin sulfate (100 μg/ml), and none were resistant to copper sulfate. Eight commercial lettuce cultivars were evaluated for resistance to X. campestris pv. vitians. Of these cultivars, Redine was highly resistant; Focus and Crisp and Green were partially resistant; Slobolt, Tiara, and Carmona were susceptible; and Darkland and Go Go Green were highly susceptible to the pathogen. Surface disinfection with 0.52% sodium hypochlorite for 5 min nearly eliminated the bacterium from lettuce seed without affecting seed viability.
Abscission and Kernel Quality of Almond Fruit Inoculated with the Shot Hole Pathogen Wilsonomyces carpophilus
Authors: Teviotdale Beth L. , Goodell Nancy , Harper Dennis
Published: May 2007

Fruit of almond cultivar Mission were aerosol-spray inoculated with aqueous suspensions containing 103, 104, or 105 conidia/ml of Wilsonomyces carpophilus beginning when fruit emerged from the hypanthium and continuing at approximately weekly intervals until they reached full size and embryo development had begun. There was a linear increase in percent fruit abscission (P = 0.001) and average number lesions per fruit (P = 0.007) with increasing inoculum concentration. Percent fruit abscission decreased with increasing fruit length (maturity) at inoculation (P = 0.001). Lesions were most abundant when mid-size fruit were inoculated. The kernel quality of infected and healthy fruit of cultivar Carmel were compared in 1994 and 1995. Mid- to full-size fruit were inoculated one or three times with 105 conidia/ml of W. carpophilus. Kernels from inoculated fruit were shorter than those from uninoculated fruit (P = 0.007), but kernel weight did not differ. Fewer than 2.5% of kernels in 1994 and none in 1995 were covered with gum deposits or incompletely filled.
Effect of Fertilizers and Rates of Application on Incidence of Soybean Diseases in Northern Alabama
Authors: Pacumbaba R. P. , Brown G. F. , Pacumbaba R. O.
Published: May 2007

Field incidence of soybean stem canker (SSC), Phytophthora root rot (PRR), bacterial blight of soybean (BBS), soybean mosaic virus (SMV), and soybean cyst nematode (SCN) females on soybean cultivar Bragg were compared under complete (20-20-20), ammonium nitrate (34-0-0), superphosphate (0-46-0), and muriate of potash (0-0-60) fertilizers, and rate regimes with unfertilized controls on Decatur silty clay loam (Rhodic paleudult) in northern Alabama. Plants fertilized with muriate of potash had higher incidence of PRR and SMV. Plants fertilized with complete fertilizer had the lowest incidence of PRR and SMV, and the highest yield. Both complete and superphosphate fertilizers lowered the incidence of SMV at application rates from 0 to 100 kg/ha, then increased up to 200 kg/ha. Ammonium nitrate fertilizer had no effect on incidence of SMV. The incidence of BBS and the number of SCN females were not affected by either type of fertilizers or rate of application. Application rates of any of the four fertilizers reduced incidence of SSC. It is recommended to use only complete fertilizer to increase yield and reduce field incidence of PRR, SMV, and SSC.
Distribution, Severity, and Spread of Armillaria Root Disease in Kenya Tea Plantations
Authors: Onsando J. M. , Wargo P. M. , Waudo S. W.
Published: May 2007

Surveys for Armillaria root disease severity were conducted over a 5-year period in small tea farms (0.5 to 1.0 ha) in the 12 tea-growing districts of Kenya. The disease occurred in all tea districts, but severity was greater in the districts east of the Rift Valley. Disease severity was associated with relative amounts of residual woody debris, especially roots, from trees and shrubs present when the land was converted to tea plantations. Excavation of tea bushes in disease centers showed that infection of tea bushes occurred primarily by mycelial growth from residual tree roots and from infected tea roots rather than from rhizomorphs. Rhizomorphs were scarce, and rarely involved in infection. They were confined mostly to the surface of the residual tree roots and were found growing freely in the soil in only one tea district. Rhizomorphs were more abundant in higher elevation plantations than in lower elevation plantations, where they occurred only on residual tree roots in the deeper, cooler, moister levels of the soil. Inoculum from residual tree debris in the soil was the most important source of infection in plantations of seed origin. Secondary spread from infected tea plants to healthy ones was limited and disease centers were small. In tea plantations derived from clonal cuttings, secondary disease spread from infected to healthy tea plants was more important resulting in large disease centers or gaps due to plant death and removal. Currently, soil sanitation by thorough removal of roots of forest trees and prompt removal of infected tea bushes is the best available management practice.
Sphaeropsis sapinea Morphotypes Differ in Aggressiveness, but Both Infect Nonwounded Red or Jack Pines
Authors: Blodgett J. T. , Stanosz G. R.
Published: May 2007

Two morphotypes of Sphaeropsis sapinea, designated A and B, are recognized in the north central United States. Nonwounded seedlings of red (Pinus resinosa) and jack pine (P. banksiana) were inoculated with conidial suspensions of isolates of each morphotype obtained from hosts in Michigan, Minnesota, and Wisconsin. Wounded seedlings were inoculated with water agar plugs colonized by these isolates. Both morphotypes penetrated both hosts without wounding. On nonwounded seedlings the frequency of symptoms was 97% for A isolates and 18% for B isolates on red pine and 42% for A isolates and 6% for B isolates on jack pine. On average, isolates of the A morphotype also were more aggressive than B isolates on wounded seedlings of both pine species (A isolates causing needle necrosis 7.0 cm from the inoculation sites and B isolates 1.4 cm). Based on symptom severity (distance from the inoculation site at which necrotic needles were observed), A isolates could be distinguished from all B isolates on red pine, but not on jack pine. These observations indicate the potential importance of distinguishing between S. sapinea morphotypes encountered in nurseries, plantations, and natural stands.
Development and Significance of Dicarboximide Resistance in Sclerotinia minor Isolates from Commercial Lettuce Fields in California
Authors: Hubbard J. C. , Subbarao K. V. , Koike S. T.
Published: May 2007

Three growth stages of each of 20 Sclerotinia minor isolates were tested for resistance to iprodione. Sclerotia and both vegetative and mature mycelium of each isolate were plated on potato-dextrose agar (PDA) amended with 0, 1, 5, 10, 25, and 100 µg of the fungicide per ml, and radial growth was measured. All wild-type field isolates were initially sensitive and did not grow in the presence of iprodione. However, fungicide resistance arose readily in vitro. All 20 isolates produced measurable growth (≥2 mm) on iprodione at 5 µg/ml after 2 weeks when started from mature mycelium, and 18 of 20 isolates produced measurable growth after 4 weeks when started from vegetative mycelium. In general, fungicide-resistant growth arose more frequently and mean colony diameters were significantly greater (P ≤ 0.05) with mature mycelium than with vegetative mycelium at all times and concentrations. In sclerotial germination tests, at least 1% of sclerotia germinated in 18 of 20 isolates after 2 weeks on iprodione at 5 µg/ml, and in 19 of 20 isolates after 5 weeks on 100 µg/ml. Of growth produced on 79 plates containing iprodione, 73 remained viable on PDA after 5 months, and 71 retained resistance to 5 µg/ml. Seventy of these also exhibited cross-resistance to vinclozolin, another dicarboximide fungicide. Pathogenicity of five fungicide-resistant strains was tested in greenhouse, microplot, and field experiments, with and without iprodione. Two months after in vitro production, one of the five resistant strains was avirulent, but disease incidence for the other four ranged from 40 to 75%, compared with 40% for the wild-type isolates. However, the virulence of the fungicide-resistant strains declined over time. Ten months after their production, two of the isolates were avirulent and disease incidence for the others ranged from 3 to 17%, compared with 40 to 90% for the wild-type isolates. The strains that remained virulent 5 and 7 months after in vitro production were not significantly controlled by iprodione sprayed according to labeled rates, although disease was significantly controlled by the fungicide in treatments inoculated with wild-type field isolates (P > 0.05). In experiments in commercial fields to determine the efficacy of fungicide sprays on the wild-type S. minor population, there was no evidence that fungicide resistance was the cause of lack of lettuce drop control observed in many coastal California fields. Application of fungicides at a less than optimal time may account for some incidents of control failure.
A Polymerase Chain Reaction Protocol for the Detection of Xanthomonas albilineans, the Causal Agent of Sugarcane Leaf Scald Disease
Authors: Pan Y.-B. , Grisham M. P. , Burner D. M.
Published: May 2007

A polymerase chain reaction (PCR) protocol was developed that amplified a 360-bp DNA product unique to Xanthomonas albilineans (Xa), the causal agent of sugarcane leaf scald disease. The assay utilizes previously described PCR primers that target the intergenic transcribed spacer (ITS) region between the 16S and 23S rRNA genes. Primer pair Ala4/L1 allowed amplification of a 360-bp DNA fragment from 71 Xa strains including representatives of serovars I, II, and III. Fragments of different sizes were also amplified from three unidentified saprophytic bacteria from sugarcane. Xa could be detected at a lower bacterial concentration with the PCR protocol than with a serological dot blot assay. With PCR, as little as 1.25 pg of Xa genomic DNA (125 fg if followed by Southern blot hybridization), or as few as 0 to 5 CFU of Xa per reaction were detected from infected sugarcane sap and leaf diffusate. Five CFU of Xa per reaction were detected from suspension culture. The PCR protocol provides a rapid, reliable, and economical tool for routine detection and identification of Xa.
First Report of Fusarium oxysporum on Purple Coneflower
Authors: Peichowski K. , Rizvi S. , Reese R. N.
Published: May 2007

The narrow-leaf purple coneflower Echinacea angustifolia DC. is a perennial composite native to the central Great Plains. Because of its potential ornamental and pharmacological value, Echinacea is currently being brought into commercial production in South Dakota. A blight or wilt was observed in a field research plot on 1- to 3-year-old plants in the summers of 1993 and 1994. Affected plants showed necrosis along leaf margins, followed by wilting and eventual death. Examination of roots and stems revealed darkening of the vascular and ground tissues. Up to 5% of plants growing in the wetter portion of the field developed symptoms. No infected plants were found in the well-drained portions of the field. Plants displaying disease symptoms were also observed in cuttings and seedlings grown in the greenhouse. The pathogen was consistently isolated by plating 0.5-cm sterile stem segments on lactic acid potato dextrose agar. To complete Koch's postulates, a single hyphal tip of the pathogen was transferred to carnation leaf agar. Micro and macro conidia formed abundantly within 10 days and matched the description of Fusarium oxysporum Schlechtend.:Fr. Two- to 3-month-old coneflower seedlings, representing the full range of genetic diversity from our Echinacea collections, were inoculated with the isolated pathogen by placing six 2-mm-diameter mycelial plugs directly on the roots of each plant, just below the soil surface. Inoculated seedlings were placed in the greenhouse to allow development of the infectious agent. Infected seedlings showed typical diagnostic symptoms (30% of inoculated seedlings) within 3 weeks. Noninoculated plants remained symptomless. F. oxysporum was reisolated from the seedlings as above. This is the first report of F. oxysporum as a pathogen on E. angustifolia.
First Report of Colletotrichum gloeosporioides on Cyclamen persicum in Florida
Authors: Norman D. J.
Published: May 2007

Between March and April of 1996, an estimated 20% of the Cyclamen persicum Mill. grown in Florida were infected with Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. in Penz. Symptoms included extensive lesions on flowers, stems, and leaves. Acervuli containing masses of spores and dark setae were observed within lesions. The most severe damage was observed on the cultivar Red Delight. Infected tissues were dipped into 0.26% sodium hypochlorite for 5 s, blotted dry, embedded in water agar, and incubated at 27 ± 1°C. Hyphal tips that grew from lesions were transferred to potato dextrose agar (PDA) and incubated under cool-white fluorescent lights. Developing colonies were gray and contained masses of orange conidia. Conidia were straight with rounded or bulbous ends and averaged 16.8 (SD 5.2) × 2.25 (SD 0.54) μm. Three isolates were selected to complete Koch's postulates. Conidia of each isolate were obtained from 3-day-old PDA cultures, and suspended in sterile, distilled water (SDW) to 104 conidia/ml. These suspensions were sprayed till runoff with hand sprayers onto C. persicum plants. Plants were incubated in plastic bags for 24 h at 27°C, then placed in a glasshouse. Within 3 days, lesions had developed on flowers; within 7 days, they were visible on stems and leaves. Lesion diameter varied from 2 to 5 mm; however, lesions soon coalesced, causing leaf, stem, and flower death. The fungus was reisolated from acervuli that developed on the flowers, stems, and leaves, following previously outlined procedures. Inoculation tests were repeated once. Symptoms did not appear on controls sprayed with SDW nor was the teleomorph stage of the pathogen observed.
First Report of Pythium myriotylum in a Tobacco Seedling Float System in South Carolina
Authors: Anderson M. G. , Fortnum B. A. , Martin S. B.
Published: May 2007

Float bay production of seedlings accounts for approximately 62% of tobacco (Nicotiana tabacum L.) transplant production in South Carolina. Float systems utilize styrofoam trays containing soilless media that float in plastic-lined bays filled with nutrient solution. Oomycete fungi with motile zoospores, such as Pythium spp., can devastate plants grown hydroponically (3). This poses a serious concern for growers because no fungicides are labeled for control of Pythium spp. in nutrient solutions for tobacco greenhouse float systems. In May 1996, Pythium myriotylum Drechs. was recovered from diseased seedlings produced in float bays in Walterboro, SC. The pathogen was isolated on PAR selective medium (2). Koch's postulates were fulfilled by inoculating plants in an experimental float bay and then reisolating the pathogen on PAR from symptomatic plants. Diseased plants appeared chlorotic and stunted, with water-soaked lesions on the stem. Root systems were severely necrotic and infected plants could not be used as transplants. Disease development was confined to plants sharing a common nutrient solution in individual bays. Within affected bays nearly 100% of plants were diseased, suggesting pathogen spread through the nutrient solution. At the time of disease onset, the grower was attempting a second crop of transplants. The high late-season temperatures were favorable for P. myriotylum, which has a growth optimum of 37°C. Primary inoculum could potentially arise from contaminated media or water and/or improper sanitation procedures in greenhouse maintenance. Pathogenic isolates of several Pythium spp. were found in commercial potting media in North Carolina in 1995 (1).

References: (1) D. K. Cartwright et al. Plant Dis. 79:538, 1995. (2) S. N. Jeffers and S. B. Martin. Plant Dis. 70:1038, 1986. (3) M. E. Stanghellini and S. L. Rasmussen. Plant Dis. 78:1129, 1994.