bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification of Races of Colletotrichum lindemuthianum with the Aid of PCR-Based Molecular Markers
Authors: Mesquita A. G. G. , Paula T. J. , Moreira M. A. , de Barros E. G.
Published: May 2007

Inoculation of a common bean differential series is the usual method for identification of races of Colletotrichum lindemuthianum. This procedure is extremely useful for phytopathological as well as breeding purposes, but it requires strict control of the number of spores and incubation conditions. Furthermore, this method may result in misclassifications of isolates because of the subjectivity of symptom evaluation. We propose the use of DNA-based molecular markers as an auxiliary tool to aid the classification of races of C. lindemuthianum. Specific DNA bands were identified for races 73, 65, and 64 by polymerase chain reaction (PCR) amplification of bulked DNA samples from isolates of these three races with random primers. The presence of these bands was checked on four isolates previously classified by inoculation on a differential series as belonging to races 23, 72, 79, and 585. The molecular procedure showed that two of these isolates had been misclassified, confirming the high potential of the proposed procedure to aid the identification of races of C. lindemuthianum. Amplification products obtained with 44 different primers also allowed the determination of the genetic distances among isolates from races 73, 65, and 64. These data were used to cluster the isolates into three groups that coincide with the ones obtained by inoculation.
Epidemiology of Phytoplasma-Associated Papaya Diseases in Queensland, Australia
Authors: Guthrie J. N. , White D. T. , Walsh K. B. , Scott P. T.
Published: May 2007

Three phytoplasma-related diseases of papaya (Carica papaya), dieback, yellow crinkle, and mosaic, are recognized within Australia. Immature leaf material was sampled every week for 8 months from a cohort of 60 female plants, located within a commercial papaya plantation, to determine the minimum time between infection and symptom expression. Phytoplasma DNA was detected using the polymerase chain reaction (PCR) with primers specific for phytoplasmas in general, and for the stolbur group of phytoplasmas. The dieback-associated phytoplasma was detected 1 week prior to (four cases) or the same week (nine cases) as symptom expression, while phytoplasma DNA was detected between 3 and 11 weeks prior to expression of mosaic symptom (six cases). Lateral shoot regrowth on the lower stem of plants which had suffered dieback disease failed to generate stolbur-specific PCR products in 15 cases. A dual infection with dieback and yellow crinkle or mosaic was diagnosed in a further two cases, using restriction fragment length polymorphism digests, and both cases were interpreted as secondary infections by the dieback-associated phytoplasma. Regrowth in three of seven cases of yellow crinkle- and three of nine cases of mosaic-affected plants tested positive for phytoplasma-specific DNA. Ratooning of dieback-affected plants and removal of yellow crinkle- or mosaic-affected plants is suggested for the management of these diseases.
Differentiation of Biologically Distinct Peanut Stripe Potyvirus Strains by a Nucleotide Polymorphism-Based Assay
Authors: Pappu S. S. , Pappu H. R. , Chang C. A. , Culbreath A. K. , Todd J. W.
Published: May 2007

A necrotic strain of peanut stripe potyvirus (PStV-Ts) was used to design and test strain-differentiating oligonucleotides. The 3′ region of PStV-Ts, including a part of the NIb region, the complete coat protein (CP) gene, and the 3′-untranslated region, was cloned and sequenced. PStV-Ts had a high degree of sequence identity (92 to 95%) to the known non-necrotic (blotch) strains both at the nucleotide and amino acid sequence levels. Nucleotide sequence differences unique to the necrotic strain were identified when compared to the available non-necrotic isolates of PStV. Nucleotide polymorphism in the CP gene sequences was utilized in designing oligonucleotides that were specific to the necrotic strain, and were employed in an assay to differentiate the necrotic strain from non-necrotic. The 3′ end mismatch in the oligonucleotides contributed in particular to the differentiation of the strains. This approach facilitated rapid, sensitive, and reliable detection and differentiation of PStV strains.
Genotypic Diversity of Aspergillus parasiticus in an Illinois Corn Field
Authors: McAlpin C. E. , Wicklow D. T. , Platis C. E.
Published: May 2007

Aspergillus parasiticus was isolated from direct platings of soil from a corn field near Kilbourne, Illinois. Soil contained 0.2 to 4.0 CFU of Aspergillus flavus and/or A. parasiticus per g of soil. Sixty isolates of A. parasiticus, each from a separately collected soil sample, were examined for ability to produce sclerotia and aflatoxins, and were subjected to DNA fingerprinting. PstI digests of total genomic DNA from each isolate were probed using the pAF28 repetitive sequence. Among 60 isolates analyzed, 33 (55%) distinct DNA fingerprint groups were identified (each group sharing less than 80% pAF28 band similarity), including 50 distinct genotypes (83%) with less than 100% pAF28 band similarity. A single A. parasiticus fingerprint group represented 13% of the sample population. The 83% genotypic diversity of the A. parasiticus population was equivalent to the 81% genotypic diversity recorded earlier for a population of 31 A. flavus isolates from the same field soil. Sclerotia were produced by 82% of the 50 A. parasiticus genotypes during dark incubation at 25°C. All isolates of A. parasiticus producedaflatoxin B1B2 and G1G2, whereas only 36% of the 31 A. flavus isolates from these soils produced aflatoxins.
First Report of Cucumber Mosaic Cucumovirus Subgroup 1 in South Africa, from Banana with Infectious Chlorosis
Authors: Pietersen G. , Staples M. S. , Kasdorf G. G. F. , Thomas J. E.
Published: May 2007

Cucumber mosaic cucumovirus (CMV) is the etiological agent of infectious chlorosis disease in bananas (Musa spp.). In South Africa, diagnosis of CMV on banana has been based only on symptoms (1). A Grande Naine (Cavendish, AAA) plant with typical infectious chlorosis disease was obtained from Letsitele. Sap from this plant was inoculated to indicator plants. Virus was isolated by two serial local lesion transfers on Chenopodium quinoa and maintained on Nicotiana benthamiana. It was identified as a subgroup I CMV based on its reaction to CMV DTL-, but not CMV ToRS- monoclonal antibodies in double antibody sandwich (DAS)—enzyme-linked immunosorbent assay (ELISA). The identity was further confirmed by the polyhedral particle morphology under the electron microscope by negatively staining, and decoration in immunoelectron microscopy with antiserum to a local tomato isolate of CMV. Infectious chlorosis disease symptoms were induced by sap inoculation to healthy Grande Naine plants, and the virus detected by ELISA. This is the first confirmed diagnosis of CMV on bananas in South Africa. The isolate was deposited in the PPRI Virus Collection.

Reference: (1) B. Q. Manicom. 1993. Pages 102–103 in: Handbook of banana growing in South Africa. J. C. Robinson, ed. Agric. Res. Counc., Inst. Trop. Subtrop.Crops, Nelspruit, South Africa.
Effects of Wounding, Inoculum Density, and Biological Control Agents on Postharvest Brown Rot of Stone Fruits
Authors: Hong Chuanxue , Michailides Themis J. , Holtz Brent A.
Published: May 2007

The effects of wounding, inoculum density, and three isolates (New, Ta291, and 23-E-6) of Trichoderma spp. and one isolate (BI-54) of Rhodotorula sp. on postharvest brown rot of stone fruits were determined at 20°C and 95% relative humidity (RH). Brown rot was observed frequently on wounded nectarine, peach, and plum fruits inoculated with two spores of Monilinia fructicola per wound, and occasionally on unwounded nectarine and peach fruits inoculated with the same spore load. Brown rot was observed on wounded plums only. A substantial increase in lesion diameter of brown rot was also recorded on wounded nectarines and peaches inoculated with suspensions of ≤20 spores and ≤200 spores per wound, respectively, compared with unwounded fruit. At concentrations of 107 and 108 spores per ml, all Trichoderma isolates substantially reduced brown rot on peaches (63 to 98%) and plums (67 to 100%) when fruits were inoculated with M. fructicola following the application of a biological control agent. Similarly, at 108 spores per ml, the yeast BI-54 also suppressed brown rot on peaches completely and on plums by 54%. Significant brown rot reduction was also achieved with the isolate New at a concentration of 108 spores per ml, even when the biocontrol agent was applied 12 h after inoculation with M. fructicola and under continuous conditions of 95% RH. The isolates Ta291 and 23-E-6 also reduced brown rot significantly under drier (50% RH) incubation conditions. These isolates provided the best control of brown rot on plums when they were applied 12 h earlier than inoculation with M. fructicola. Satisfactory control of brown rot on plums inoculated with M. fructicola at 8 × 104 spores per ml was achieved with New at 106 spores per ml and with Ta291 at 107 spores per ml. Measures taken to avoid injuring fruit will greatly reduce brown rot of stone fruit at any spore load for plum, but only at ≤50 spores per mm2 for peach, and at ≤5 spores per mm2 for nectarine. This study identifies two isolates (Ta291 and New) of Trichoderma atroviride, one isolate (23-E-6) of T. viride, and one of Rhodotorula sp. that show potential for further development as biocontrol agents of postharvest brown rot of stone fruits.
Development of an Infection Assay for Sporisorium reilianum, the Head Smut Pathogen on Sorghum
Authors: Osorio Jairo A. , Frederiksen Richard A.
Published: May 2007

The practical value of dry teliospores of Sporisorium reilianum as inoculum in head smut infection assays was determined from a series of studies using three different isolates of the pathogen. Overall germinability of teliospores ranged from 8.0 to 28.0% on culture media after 48 h of incubation. Teliospores germinated at slower rates in the vicinity of sorghum seedlings growing on germination paper, reaching maximum values of 11.5 to 13.0% after 120 h. These results suggest adaptation in the germination strategy of S. reilianum, probably modulated by the variable soil environment. Fifteen percent (15%) of the seedlings of a head smut susceptible maize hybrid inoculated with teliospores of S. reilianum at root protrusion openings of the mesocotyl tissues became infected, while seedlings similarly inoculated with sporidial suspensions remained uninfected. Three sorghum lines susceptible to head smut were inoculated in three separate experiments with dry teliospores of isolates from Corpus Christi and Taylor, Texas. Seeds were imbibed for 18 h, and the seedlings were planted in soil at 40% moisture content (wt/wt) and covered with a 1:50 (vol/vol) mixture of teliospores and autoclaved soil. Infection levels obtained in these experiments were 2.5 to 2.8 times higher than field infection levels on susceptible lines RT×7078 and B1. In this study, average infection levels of 65 to 79.5% and 84 to 87% for RT×7078 and B1, respectively, were obtained with Corpus Christi isolates of S. reilianum; whereas Taylor isolates infected 91.9 and 82.3% of the plants in these two lines. It is postulated that the increased infection efficiency observed with this inoculation technique results from uniform and higher levels of inoculum, timely delivered under stable soil conditions that provide the pathogen with an environment more conducive for infection.
Soybean Cultivar Responses to Sclerotinia sclerotiorum in Field and Controlled Environment Studies
Authors: Wegulo S. N. , Yang X. B. , Martinson C. A.
Published: May 2007

The responses of 12 soybean cultivars to Sclerotinia sclerotiorum were evaluated under field and controlled environment conditions. The 12 cultivars were planted in fields naturally or artificially infested with S. sclerotiorum and evaluated for disease incidence. In controlled environment studies, the cultivars were compared with respect to lesion size on detached leaves and stems inoculated with mycelial disks, incidence of stem rot following mycelial inoculation of foliage, lesion lengths on stems discolored by oxalic acid, and levels of soluble pigment(s) in stems. Significant differences (P ≤ 0.05) in disease incidence, lesion sizes, and levels of soluble pigment(s) were detected among the 12 cultivars in all evaluations, but ranking of cultivars varied among methods and experiments within methods. Corsoy 79 and S19-90 were consistently most resistant in all methods; whereas Kenwood, A2242, Bell, and Williams 82 were least resistant. Pearson correlation coefficients (R) for disease incidence between location years in field experiments (FE) ranged from 0.86 to 0.95. R values between FE and controlled environment experiments (CEE) ranged from 0.01 to 0.62 for detached leaf assays (DLA), -0.20 to 0.47 for lesion lengths on stems inoculated with mycelial disks (LLM), 0.38 to 0.45 for incidence of stem rot from mycelial inoculation of foliage (MIF), 0.08 to 0.66 for lesion lengths on stems discolored by oxalic acid (LLO), and -0.55 to -0.37 for levels of soluble stem pigment(s) (SSP). Absolute values of R between FE and CEE were 0.40 or greater in 40, 17, 33, 29, and 83% of all correlation analyses for DLA, LLM, MIF, LLO, and SSP, respectively. Spearman's coefficients of rank correlation (r s) between FE and CEE based on average performance were 0.55, -0.20, 0.40, 0.42, and -0.44 for DLA, LLM, MIF, LLO, and SSP, respectively. Disease development was slow when foliage was inoculated with a mycelial suspension. Based on experiment (E) by cultivar (C) interaction and rs values between replicate experiments within each method, determination of soluble stem pigment levels (0.86 ≤ rs ≤ 0.97; P < 0.001 for 100% of six analyses; P = 0.98 for E × C interaction) and measurement of lesion lengths on stems discolored by oxalic acid (0.27 ≤ rs ≤ 0.85; rs ≥ 0.58 and P ≤ 0.05 for 68% of 28 analyses; P = 0.07 for E × C interaction) were the most repeatable methods. The results from this study suggest that determination of levels of soluble pigments in stems, measurement of lesion lengths on stems discolored by oxalic acid, and the detached leaf assay may be better than mycelial inoculation of stems or foliage in evaluating soybean cultivars for field resistance to S. sclerotiorum.
Tomato Mosaic Tobamovirus, Causal Agent of a Severe Disease of Pepino (Solanum muricatum)
Authors: Prohens J. , Soler S. , Pérez-Benlloch L. , Nuez F.
Published: May 2007

Pepino (Solanum muricatum Aiton), a vegetatively propagated herbaceous crop from the Andes, is esteemed for its edible, juicy, and fragrant fruits. Its cultivation as a crop for diversification is increasing in many frost-free areas throughout the world (2). In 1994, a severe viruslike disease, previously undescribed, was observed on pepino plants in Valencia, Spain. The disease has continued to cause economic losses in pepino plantings in subsequent years. Symptoms, which are exacerbated at temperatures above 30°C, include dark and light green mosaic predominantly in young leaves, leaf puckering and distortion, short internodes, fruit deformation, delay in ripening, and yield reduction. Samples from affected plants were analyzed by enzyme-linked immunosorbent assay (ELISA). All samples displaying viruslike symptoms reacted positively with antiserum made against tomato mosaic tobamovirus (ToMV) but not with antisera made against alfalfa mosaic alfamovirus, cucumber mosaic cucumovirus, potato Y potyvirus, tobacco mosaic tobamovirus, tomato spotted wilt tospovirus, or tomato yellow leaf curl bigeminivirus. A leaf extract from diseased plants was heated at 72°C for 10 min. This treatment inactivates most plant viruses but does not eliminate infectivity of ToMV (1). Inoculation of a collection of pepino clones resulted in the development of symptoms in most clones. Symptomatic clones were also ELISA-positive for ToMV. A few clones showed a hypersensitive reaction, which consisted of the development of necrotic lesions in the inoculated area. New growth on these clones was asymptomatic and ELISA-negative for ToMV. These results clearly point to a causal relationship between ToMV infection and the observed disease. The initial source of the infection should be eliminated from commercial plantings, as ToMV is easily transmitted when the pepino plants are trellised and pruned. Special care must also be taken to ensure that mother plants from which cuttings are taken are free from this virus. In addition, ToMV is usually found in meristematic tissues, even after thermotherapy and chemotherapy treatments are applied, making the regeneration of virus-free plants from infected clones by meristem tip culture difficult. Therefore, it seems that the best strategy against this disease is the development of resistant cultivars.

References: (1) H. Laterrot. Ann. Amélior. Plant. 23:287, 1973; (2) J. Prohens et al. Econ. Bot. 50:355, 1996.
First Report on the Multiplication of Tomato Spotted Wilt Tospovirus in Tobacco Thrips, Frankliniella fusca
Authors: Pappu H. R. , Todd J. W. , Culbreath A. K. , Bandla M. D. , Sherwood J. L.
Published: May 2007

In Georgia, tomato spotted wilt tospovirus (TSWV) causes significant losses in peanut, tobacco, tomato, and pepper. Transmission of TSWV in Georgia primarily is by tobacco thrips (TT), Frankliniella fusca (Hinds), and western flower thrips, F. occidentalis (Pergande), with TT being the predominant vector species in peanut (2). TSWV must be acquired at the larval stage for the adult to transmit the virus. Detection of NSs (a non-structural TSWV protein present only following virus replication) in thrips by enzyme-linked immunosorbent assay (ELISA) is a reliable indicator that the virus had multiplied in the vector and thus the vector is competent to transmit TSWV. While this has been accomplished with F. occidentalis (1), information is lacking for F. fusca, the predominant vector in Georgia and other states in the Southeast. Thus, the nature of the TSWV-TT association was investigated and the proportion of transmitters in a field population determined in 1,436 individual adult TT collected from sticky cards positioned in selected peanut fields in south Georgia. Additionally, 650 larvae collected from volunteer peanut plants were reared to adults in the laboratory and the resulting 295 adult TT were individually evaluated by ELISA. Of those collected from the sticky cards, NSs was detected in 8% of the adult insects, indicating that the virus had multiplied in TT. NSs was not detected in control TT that had no access to the virus. Of the adult TT that emerged from larvae collected from volunteer peanuts, 6.1% were positive for NSs. Our study provides the first immunological evidence that TSWV multiplies in TT.

References: (1) M. D. Bandla et al. Phytopathology 84:1427, 1994. (2) J. R. Chamberlin et al. J. Econ. Entomol. 86:40, 1993.
First Report of Basil Leaf Spot Caused by Pseudomonas cichorii in Louisiana and Cultivar Screening Results
Authors: Holcomb G. E. , Cox P. J.
Published: May 2007

A leaf spot of basil, Ocimum basilicum L., was observed on container-grown and field plantings of cultivars Aussie Sweet and Sweet Basil. The disease was of minor importance under field conditions, but was of potential economic importance in seedling production. Gray to black, watersoaked, necrotic spots commonly developed at leaf margins. Large numbers of bacteria were released from cut lesions when viewed by light microscopy. Single colony bacterial isolates were established on nutrient dextrose agar (NDA) and yeast extract-dextrose-calcium carbonate agar (YDC). Pathogencity tests were performed by misting a water suspension containing 104 bacterial cells per ml on healthy basil plants. Plants were held for 24 h in a dew chamber at 26°C and then moved to a greenhouse for observation. Typical leaf spots developed on inoculated plants in 2 days, but not on healthy control plants, and the bacterium was reisolated. The bacterium was characterized as a gram-negative, motile rod, negative for potato rot test, positive in tobacco hypersensitivity test, and oxidase positive. Isolates were identified as Pseudomonas cichorii according to the Biolog Microplate system (similarities ranged from 0.937 to 0.995). Screening tests were conducted by inoculating 15 basil cultivars, six replicates each, and rating them for disease severity based on a scale of 1 to 5 in which 1 = no disease and 5 = dead plants. Cultivars most resistant to bacterial leaf spot (ratings in parentheses are averages of two tests and those followed by the same letter are not significantly different according to Tukey's Studentized Range Test, P = 0.05) were Green Bouquet (2.0 a), Piccolo (2.2 a), Mrs. Burn's Lemon (2.2 a), Genovese (2.4 a), and Dark Opal (2.5 ab). Moderately susceptible cultivars were Bush Green (2.8 abc), Sweet Basil (2.8 abc), Large Green (2.9 abcd), Lemon (3.1 abcd), and Mexican Spice (3.6 bcd). The most susceptible cultivars were Lettuce Leaved (3.8 cd), Thai (3.8 cd), Napoletano (4.0 de), Green Ruffles (5.0 e), and Purple Ruffles (5.0 e). Bacterial leaf spot of basil caused by P. cichorii was first reported in the U.S. from Florida (1). Other bacterial diseases reported on basil include leaf blight from Egypt caused by P. syringae (2) and leaf necrosis from California caused by P. viridiflava (3). This is the first report on the occurrence of basil bacterial leaf spot in Louisiana and the first reported information on cultivar susceptibility.

References: (1) S. M. Burgess et al. Proc. Fla. State Hortic. Soc. 99:249, 1986. (2) S. A. M. El-Sadek et al. Assiut J. Agric. Sci. 22:2, 1991. (3) E. L. Little et al. Plant Dis. 78:831, 1994.
Mapping the Root-Knot Nematode Resistance Gene (Rk) in Tobacco with RAPD Markers
Authors: Yi H.-Y. , Rufty R. C. , Wernsman E. A. , Conkling M. C.
Published: May 2007

Random amplified polymorphic DNA (RAPD) analysis was conducted to map the Rk gene in tobacco which conditions resistance to races 1 and 3 of the root-knot nematode, Meloidogyne incognita. Resistant burley tobacco genotype NC 528, containing the Rk gene, and the susceptible cultivar Ky 14 were screened with 1,500 random decamers. A low rate of genetic polymor-phism (<10%) was detected among these lines. Two populations (F1 and F3) of maternally de-rived doubled haploid (MDH) lines of burley tobacco, developed from the cross NC 528 × Ky 14, were used to map the Rk gene. NC 528, Ky 14, three Rk-resistant (Rk-R) DNA bulks, andthree Rk-susceptible (Rk-S) bulks generated from F1-derived MDH individuals were screenedwith the primers that amplified bands polymorphic between Rk-R and Rk-S lines. A total of 67 F1MDH lines and 59 F3MDH lines were screened with the primers that amplified bands polymorphic between Rk-R bulks and Rk-S bulks to confirm linkage between candidate markers and the Rk gene. Sixteen RAPD markers were positioned at six loci in a map 24.1 centimorgans long. Six RAPD markers, including one identified in the F3MDH population, were mapped at the Rk locus.
A Method for Extraction and Enumeration of Teliospores of Tilletia indica, T. controversa, and T. barclayana in Soil
Authors: Babadoost M. , Mathre D. E.
Published: May 2007

A sucrose-centrifugation method was developed to extract teliospores of Tilletia indica, T. con-troversa, and T. barclayana from soil. Six soil types were artificially infested with teliospores of each of the three fungi separately to produce 102, 103, 104, or 105 teliospores per 10 g. Each 10 g of infested soil was suspended in 200 ml of water with one drop of Tween 20 and shaken for 30 s. The soil suspension was first passed through a 117-μm sieve and then through a 53-μm mesh filter, and the filtrate was collected. The filtrate was then passed through a 20-μm mesh filter, and materials caught on the mesh were washed into two 50-ml centrifuge tubes and spun for 3 min (1,200 × g). The pellet was suspended in 1.6 M sucrose solution and centrifuged for 40 s (200 × g). The supernatant was passed through a 20-μm mesh filter. The materials caught on the 20-μm mesh were collected, and the number of teliospores was determined. This procedure was initially used to extract teliospores of T. indica in soil. For extraction of teliospores of T. contro-versa and T. barclayana, 1.0 M and 1.3 M sucrose solutions, respectively, were used, and the 20-μm mesh was replaced with a 13-μm mesh filter. Teliospores of T. indica, T. controversa, T. barclayana, and T. indica-like fungus on rye grass were successfully extracted from naturally infested soils. The relationships between number of teliospores recovered from the soil and number of teliospores incorporated into the soil were Ŷ= -0.60 + 1.28(X) - 0.04(X2),Ŷ = -1.25 + 1.56(X) - 0.07(X 2), and Ŷ = -0.71 + 1.33( X) - 0.04(X2) for T. indica, T. controversa, and T. barclayana, respectively, where Ŷ = log10 of the number of teliospores recovered from soil and X = log10 of the actual number of teliospores in soil.
Development of Apothecia from Stone Fruit Infected and Stromatized by Monilinia fructicola in California
Authors: Holtz Brent A. , Michailides Themis J. , Hong Chuanxue
Published: May 2007

Apothecia were produced in the orchard, lath house, and laboratory from peach and nectarine fruit infected and stromatized by Monilinia fructicola. Fully stromatized “mummies” and nonstromatized infected fruit were placed in the orchard either on the soil surface or buried to a depth of 2 to 3 cm. Mummies were placed in the orchard at monthly intervals from August to February in 1993-94 and 1994-95. Nonstromatized infected fruit, which were fleshy and decomposed rapidly, were soon unavailable and were only placed in the orchard in August and September. Apothecia developed in February and early March only from mummies that were placed in the orchard in either October, November, or December. Mummies placed in the field in August, September, January, and February did not produce apothecia. Leaving mummies on the soil surface versus burying them 2 to 3 cm did not affect the development of apothecia. Apothecia were never produced from nonstromatized or recently-infected (fleshy) fruit. In the laboratory, apothecia were only produced from mummies that were partially buried in moist sand and stored without light at 2°C and >97% relative humidity (RH) for more than 8 weeks prior to incubation for 2 weeks (12, 15, or 20°C) with a 12-h photoperiod. Mummies that were incubated at >97% RH for less than 8 weeks or incubated at <90% RH never produced apothe-cia when stored at 2°C and then transferred to warmer temperatures with light. In orchard experiments, apothecia were only observed in plots with nondisturbed orchard floor vegetation; whereas no apothecia were found in either herbicide-treated or rototilled plots. Apothecia in the San Joaquin Valley were only produced from mummies that were subject to an 8-week or greater cold-temperature incubation while in contact with soil.
Virulence and Diversity of Wheat Leaf Rust in the United States in 1993 to 1995
Authors: Long D. L. , Leonard K. J. , Roberts J. J.
Published: May 2007

Isolates of Puccinia triticina were obtained from wheat leaf collections made by cooperators throughout the United States and from cereal rust field surveys of the Great Plains, Ohio Valley, and Gulf Coast states in 1993, 1994, and 1995. Sixty-two virulence/avirulence phenotypes on 14 host lines that are near-isogenic for leaf rust resistance were found among 681 single uredinial isolates in 1993, 42 phenotypes were found among 683 isolates in 1994, and 51 among 701 isolates in 1995. As in previous surveys, regional race distribution patterns showed that the central United States is a single epidemiological unit distinct from the eastern United States. The distinctive racial composition of collections from the Southeast, Northeast, and Ohio Valley indicates that populations of P. triticina in those areas are discrete, suggesting epidemics originate from localized overwintering sources.
First Report of Fusarium Wilt on Paris Daisy (Argyranthemum[Dendranthema] frutescens)
Authors: Garibaldi A. , Minuto A. , Gullino M. L.
Published: May 2007

Paris daisy (Argyranthemum frutescens) is an economically important crop on the Riviera Ligure (Northern Italy), where approximately 10 million plants per year are produced for export. In September 1997, a serious wilt of plants (cv. Camilla) grown in plastic pots (14 to 18 cm in diameter) was observed. The leaves of the affected plants turned yellow unilaterally and eventually wilted. Both yellowing and wilting progressed acropetally. Eventually, affected plants were completely wilted and the stems showed dark blue-black necrosis. An intense brown discoloration of the vascular system was evident, particularly after yellowing of the foliage was visible. Fusarium oxysporum was consistantly isolated from diseased plants on Komada's medium (1). Two monoconidial isolates of F. oxysporum freshly isolated from A. frutescens wilted plants were used for artificial inoculation of healthy cv. Camilla plants in order to complete Koch's postulates. Rooted cuttings were inoculated by a root dip (for 30 s, with 5 × 107 CFU per ml) and by infesting soil (1 × 103 CFU per ml of soil). Inoculation was carried out on 20 plants belonging to five cultivars. Noninoculated plants of each cultivar served as control. Plants were maintained in a glasshouse at 22 to 23°C. Symptoms developed 13 to 14 days after and were similar to those observed on naturally infected plants. F. oxysporum was consistantly reisolated from artificially inoculated plants. Fusarium wilt of A. frutescens is favored by temperatures higher than 20°C. To our knowledge, this is the first report of Fusarium wilt on A. frutescens.

Reference: (1) H. Komada. Rev. Plant Prot. Res. 8:114, 1975.
First Report of Flag Smut of Wheat Caused by Urocystis agropyri in the United Kingdom
Authors: Sansford C. E. , Beales P. A. , Clarkson J. D. S.
Published: May 2007

An isolated occurrence of flag smut of wheat, caused by Urocystis agropyri (G. Preuss) J. Schröt., was confirmed in the county of Essex, UK, in autumn-sown winter wheat (Triticum aestivum L.) cv. Riband grown from certified seed. The origin of the infection is unknown. Symptoms were first observed on 22 May 1998. The presence of U. agropyri was confirmed on the basis of the macroscopic symptoms on the host and the morphology of the pathogen (2). Long gray-black streaks parallel with the veins were observed on leaf blades, especially the flag leaf, and on leaf sheaths. The streaks consisted of lines of fungal sori developing between the leaf veins, giving a striped appearance. Eruption of the sori through the epidermis of the leaves had caused them to fray, exposing dark brown to black powdery spore masses. Microscopic examination revealed spore balls measuring 20 to 28 μm in diameter containing 1 to 3 spores per ball. Spores were dark brown measuring 12 to 17.5 μm in diameter and were surrounded by light brown sterile cells measuring 7 to 7.5 μm. Affected plants were stunted to about half the height of healthy plants. Some affected plants tillered excessively and in some cases the ear failed to emerge from the boot. Some diseased leaves were twisted and, where the host epidermis had ruptured to expose the spore masses, the affected parts had the appearance of being covered in black soot. All of the symptoms are typical of flag smut on wheat. Flag smut has been observed on grasses in every continent except Antartica. However, the distribution of the pathogen on wheat is more limited. Flag smut of wheat is known to occur in at least some of the countries of the European Union as well as (e.g.) the USA and Australia. This finding is significant because it had been considered that U. agropyri on wheat had reached the limits of its ecoclimatic zone, since it requires specific environmental conditions for infection and disease development, particularly a mild winter and an arid summer (1). The climatic conditions in Essex between September 1997 when the affected crop was planted and May 1998 when symptoms were first observed were considerably drier and warmer than normal, thus favoring the pathogen. This is the first report of U. agropyri on wheat in the UK.

References: (1) R. F. Line. 1998. Pages 49–60 in: Bunts and Smuts of Wheat: An International Symposium. No. Am. Plant Prot. Org., Ottawa. (2) J. E. M. Mordue and J. M. Waller. 1981. Urocystis agropyri. CMI Descriptions of Pathogenic Fungi and Bacteria, No. 716. Kew, England.
Lilac Witches'-Broom in North Dakota
Authors: Walla J. A. , Guo Y. H.
Published: May 2007

Lilac witches'-broom (LWB), caused by the ash yellows (AshY) phytoplasma, was identified in common lilac (Syringa vulgaris L.) in Cass and Ransom counties in southeast North Dakota in 1997 and 1998. The infected plants were immature, naturally regenerating lilac in the understory of three 57- and 58-year-old Prairie States Forestry Project windbreaks that have lilac as a planted component. In late summer and early fall of 1997, the terminal ends of hardened-off, current-season shoots on more than 100 immature plants were dead, and two to three succulent, late-season shoots were present just below the dead tips. Succulent shoots collected from one such plant in each of two of the windbreaks (both in Ransom Co.) were positive for the AshY phytoplasma, using immunofluorescence (IF) with an AshY phytoplasma-specific monoclonal antibody (1). One of those shoots was also positive with a universal phytoplasma-specific primer pair (R16F2/R2) (2) in a polymerase chain reaction (PCR). Succulent shoots from a plant in the third windbreak (in Cass Co.) were IF negative. In late spring of 1998, more than 100 young plants in two of the same windbreaks (one each in Cass and Ransom counties) had abnormal shoot growth, including combinations of yellow, distorted leaves, multiple shoots, and twig dieback. A shoot from one of two plants sampled in the Ransom Co. windbreak was IF positive. Roots from two of four plants sampled in the Cass Co. windbreak were IF positive, while the other root samples and shoot samples from the same four plants were IF negative. A shoot from one of the IF positive plants was positive for phytoplasmas in a PCR. Witches'-brooms were not observed in the planted lilacs. This is the first report of LWB in North Dakota and in the Great Plains region of North America. While the AshY phytoplasma is known in green ash (Fraxinus pennsylvanica Marsh.) in the Great Plains, this report documents substantial extension of the known range of LWB westward from Wisconsin (3). Lilac is a very important shrub in both rural and urban plantings in the northern Great Plains and is the most commonly planted shrub in North Dakota. With this report, LWB should be considered among the possible damaging agents in lilac in this region.

References: (1) Y. H. Guo and T. A. Chen. Phytopathology 83:243, 1993. (2) I.-M. Lee et al. Phytopathology 83:834, 1993. (3) W. A. Sinclair et al. Plant Dis. 80:468, 1996.
Verticillium dahliae Resistance in Horseradish Germ Plasm from the University of Illinois Collection
Authors: Atibalentja N. , Eastburn D. M.
Published: May 2007

A total of 113 horseradish cultivars from the University of Illinois germ plasm collection at Urbana were evaluated for their reaction to Verticillium dahliae in the greenhouse following a root-dip inoculation. Root discoloration was rated 2 months after inoculation on a scale of 0 to 3 as follows: 0 = no symptoms; 1 = trace to less than 10% of the root cross-section with vascular discoloration; 2 = 10 to 50% of the root cross-section with vascular discoloration; and 3 = more than 50% of the root cross-section with vascular discoloration. The cultivars exhibited a large amount of variation in response to V. dahliae infection, with mean root discoloration ratings ranging from 0.2 to 2.6. The frequency distribution of responses of the 113 cultivars was normal, with a mean and a standard deviation of 1.2 and 0.4, respectively. Six cultivars, 635A, 1236A, 769A, 125A, 761A, and 28A, were identified as resistant to V. dahliae. The existence of resistance to V. dahliae in horseradish germ plasm from the University of Illinois collection is a great resource for the breeding of improved horseradish cultivars that will combine resistance to V. dahliae with other desirable characters.
Differentiation Among Potyviruses Infecting Sweet Potato Based on Genus-and Virus-Specific Reverse Transcription Polymerase Chain Reaction
Authors: Colinet D. , Nguyen M. , Kummert J. , Lepoivre P. , Xia Feng Zu
Published: May 2007

Knowledge of virus diseases affecting sweet potato has been complicated due to the frequent occurrence of mixed infections and difficulties in isolating and purifying sweet potato viruses. A combined assay of reverse transcription and polymerase chain reaction (PCR) utilizing degenerate genus-specific primers POT1 and POT2 was applied to 18 sweet potato clones from China. The primers were designed to amplify the variable 5′ terminal region of the potyvirus coat protein gene. Molecular analysis of the amplified fragments identified the Chinese strains of sweet potato feathery mottle virus (SPFMV-CH), sweet potato latent virus (SPLV-CH), and sweet potato virus G (SPVG-CH). Among the detected potyviruses, a distantly related strain of SPFMV-CH, tentatively named SPFMV-CH2, was identified in sweet potatoes from China. On the basis of sequence identity, SPFMV-CH2 was closely related to the common (-C) strain of that virus. Identification of a closely related strain of SPVG-CH in one sweet potato clone from China further illustrated the usefulness of broad-spectrum PCR for detecting uncharacterized viruses. The acquisition of sequence information permitted the design of virus-specific primers for detecting and differentiating SPFMV, SPLV, and SPVG.
Survival of Colletotrichum coccodes in Infected Tomato Tissue and in Soil
Authors: Dillard H. R. , Cobb A. C.
Published: May 2007

Studies were initiated in 1988 and 1991 to assess long-term survival ability of Colletotrichum coccodes. Sclerotia and infected tomato fruit skin tissue were enclosed in nylon pouches and placed on the soil surface (0 cm) or buried 10 and 20 cm deep in fields located in Geneva, New York. Over time, the greatest decline in recovery of C. coccodes from tomato skin and decrease in viability of sclerotia were from samples placed on the soil surface. In the 1988 study, after 8 years in the field, 0, 90, and 88% of the sclerotia were viable, and C. coccodes was isolated from 0, 54, and 86% of the tomato skin tissues at the 0-, 10-, and 20-cm soil depths, respectively. In the 1991 study, after 5 years in the field, C. coccodes was isolated from 22, 35, and 37% of the tomato skin tissues, and 55, 91, and 92% of the sclerotia were viable at the 0-, 10-, and 20-cm soil depths, respectively. It is apparent that lengthy crop rotations are required to significantly decrease viable inoculum of C. coccodes. In a separate study, C. coccodes overwintered in naturally infected tomato roots in commercial fields and was consistently isolated from roots in the fall and the following spring. Fields sampled in the fall yielded similar numbers of plants with infected roots the following spring.
Vegetative Compatibility Groups and Pathogenicity Among Isolates of Fusarium oxysporum f. sp. cucumerinum
Authors: Ahn Pyung , Chung Hoo-Sup , Lee Yong-Hwan
Published: May 2007

Seventy-eight isolates of Fusarium oxysporum f. sp. cucumerinum, the causal agent of cucumber wilt, were isolated from symptomatic tissues of cucumber from four provinces in Korea. These isolates were grouped into vegetative compatibility groups (VCGs) by demonstrating heterokaryosis by complementation tests using nitrate nonutilizing (nit) mutants. All isolates were grouped into six VCGs—1-A, 1-B, 1-C, 1-D, 1-E, and 1-F. No self-incompatibility was observed in any of the isolates tested. VCG 1-A was the most common group within growing regions in Korea and proved to be the most virulent of the VCGs identified. These data indicate that the level of virulence in F. oxysporum f. sp. cucumerinum is related to VCG.
A Search for Resistance in Peas to Mycosphaerella pinodes
Authors: Kraft John M. , Dunne Brendan , Goulden David , Armstrong Stewart
Published: May 2007

In 1991, 1992, and 1994, 2,936 accessions of Pisum sativum from the USDA Plant Introduction collection were screened under field conditions for resistance to Mycosphaerella pinodes without replication due to seed supply. These trials were conducted at the Oak Park Research Station at Carlow, Ireland, where conditions are highly favorable for disease expression. In 1995, the 157 most resistant accessions were again screened at Carlow and at the Food and Crops Research Station at Gore, New Zealand, in replicated trials. At both locations, disease was severe and ranged from 20 to 100% foliar blight. Five accessions were as resistant as the commercial cultivar Radley at both locations: PI 142441, PI 142442, PI 381132, PI 404221, and PI 413691. No accessions were more resistant than the cultivar Radley.
First Report of a Closterovirus-Like Particle Associated with Pineapple Plants (Ananas comosus cv. Smooth Cayenne) Affected with Pineapple Mealybug Wilt in Cuba
Authors: Borroto Eduviges G. , Cintra Mayra , González Justo , Borroto Carlos , Oramas Pedro
Published: May 2007

Pineapple mealybug wilt (PMW) was first described in Hawaii in 1910 and has since spread wherever pineapple is cultivated. PMW is currently one of the most important field diseases of pineapple in Cuba, causing up to 40% crop loss. Leaves of plants affected with PMW turn bronze-red and lose turgidity, and the tips curve down. Root system size is decreased and fruits are unmarketable because the flesh is fibrous and sour. Leaves from wilt-affected pineapple plants were selected from the Experimental Station “Tomás Roig” at Ciego de Avila, Cuba. Asymptomatic plants derived from meristem tissue and cultivated under greenhouse conditions were also collected. Both samples were analyzed by several virus purification procedures and finally purified with a protocol modified from Gunashinge and German (1). Partially purified samples from symptomatic and asymptomatic plants were negatively stained and examined by a JEOL (JEM-2000 EX) transmission electron microscope at a magnification of ×30,000. Sixteen, long, flexuous, rod-shaped, viruslike particles (estimated length 1,200 to 1,450 nm; width about 12 nm) were observed in symptomatic leaves, using electron microscope micrographs. These particles were similar to those of the pineapple clostero-like virus found in Hawaii (1) and Australia (2). Particles were observed from symptomatic plants but not from plants propagated by primary meristem culture. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of viral proteins indicated that the coat protein has a molecular mass of approximately 23 kDa. This is the first report of closterovirus-like particles associated with pineapple plants (Ananas comosus cv. Smooth Cayenne) affected with PMW in Cuba.

References: (1) U. B. Gunasinge and T. L. German. Phytopathology 79:1337, 1989. (2) W. Wakman et al. Aust. J. Agric. Res. 46:947, 1995.
Control of Cotton Seedling Damping-off in the Field by Burkholderia (Pseudomonas) cepacia
Authors: Zaki K. , Misaghi I. J. , Heydari A. , Shatla M. N.
Published: May 2007

Four field trials were conducted in April 1995 and 1996 in Arizona to compare the effectiveness of: 1, a soil drench of isolate D1 of Burkholderia (Pseudomonas) cepacia; 2, isolate D1 barley meal formulation; 3, Deny seed treatment (a peat moss-based formulation of B. cepacia); 4, Deny soil drench; 5, Kodiak seed treatment (a formulation of Bacillus subtilis); 6, a mixture of three fungicides (metalaxyl, triadimenol, and thiram) seed treatment; and 7, a mixture of metalaxyl, triadimenol, thiram, and Kodiak seed treatment to increase cotton stand in the field. Except for D1, the other products are being marketed for the control of cotton seedling damping-off. Only D1 soil drench and a mixture of the three fungicides seed treatment increased cotton stand significantly (P ≤ 0.05) in three of four field trials.
Occurrence of Potato Tuber Necrotic Ringspot Disease (PTNRD) in Italy
Authors: Tomassoli L. , Lumia V. , Cerato C. , Ghedini R.
Published: May 2007

Potato tuber necrotic ringspot disease, caused by a tuber necrotic isolate of potato virus YN named PVYNTN, was originally described in Hungary in 1980; later on, the disease spread throughout northern and eastern Europe (1). Recently, the virus was reported in Portugal (2) on fresh-market potatoes. During the summer of 1997, the disease appeared in the north of Italy, causing serious damage in processing and fresh-market potatoes. After harvesting, we observed in most of the potato cultivars tubers showing the typical superficial necrotic rings and areas. These viral lesions were predisposed to secondary infection by fungi and bacteria. Moreover, PVYNTN causes degradation of tuber starch into simple carbohydrates. This metabolic activity resulted in undesirable browning in chips. In different areas of northern Italy, samples were collected from 48 stocks of cv. Hermes, the most important processing cultivar in Italy, and from 12 stocks of other potato cultivars (Ernterstolz, Liseta, Monalisa, Primura, Kennebec). The original seed of the stocks came from five different European countries: Austria, Italy, Scotland, Switzerland, and The Netherlands. Samples were serologically tested by indirect enzyme-linked immunosorbent assay with specific monoclonal antibodies to tobacco venial necrosis strain group of PVY. The results showed that 37 out of 60 analyzed stocks were infected by an isolate belonging to PVYN group, 7 stocks were infected by a common isolate of PVY, and 16 were PVY free. To distinguish the tuber-necrosis isolate (PVYNTN) from the PVYN isolates, reverse transcription-polymerase chain reaction (RT-PCR) and immunocapture-RT-PCR were carried out with specific primers for PVYNTN (3). Both tuber and leaf sap were tested. RT-PCR was performed on tuber sap and immunocapture-RT-PCR on leaf sap. Leaf and tuber sap of healthy, PVY-infected, and PVYNTN-infected tobacco was used in each experiment. At least two tubers from each of 32 PVYN-infected stocks were included in the molecular assay. All samples showed an amplified product of the characteristic size for PVYNTN (835 bp), whereas neither the healthy control nor the PVY sample gave a product. All tested cultivars were infected and all countries from which tuber seed came revealed infected stocks. The high proportion of samples in which PVYNTN was detected suggests that the virus is now endemic to potato-growing regions of northern Italy. The weather in these regions during 1997 was mild and drought in winter-spring and very warm in late summer; these conditions were ideal for disease diffusion by vectors and for symptom development. This is the first report of the occurrence of PVYNTN in Italy.

References: (1) C. Kerlan. Le Pomme de Terre Française 498:40, 1997. (2) M. C. Serra and H. L. Weidemann. Plant Dis. 81:694, 1997. (3) H. L. Weidemann and E. Maiss. Z. Pflanzenkrank. Pflanzenschutz 103:337, 1996.
Reduction of Green Mold on Grapefruit after Hot Forced-Air Quarantine Treatment
Authors: Shellie Krista C. , Skaria Mani
Published: May 2007

Lesions on grapefruit developing from wounds inoculated with a spore suspension of Penicillium digitatum just prior to heating for 300 min in 46°C moist, forced air developed less rapidly during 4 days of storage at 21°C than lesions formed from inoculations made after the fruit were heated, or lesions on non-heated fruit. Since the lesion size on fruit inoculated after heating was similar to that on fruit that were not heated, induced host resistance via lignification or accumulation of phytoalexins probably did not occur. Results from this research demonstrate that development of green mold on grapefruit caused by P. digitatum is inhibited by time and temperature regimes of moist, forced air that are known to provide quarantine security against Mexican fruit fly.