bluuebunny/crossref_metadata_2025 huggingface dataset:
Daily Inoculum Levels of Gibberella zeae on Wheat Spikes
Authors: Francl L. , Shaner G. , Bergstrom G. , Gilbert J. , Pedersen W. , Dill-Macky R. , Sweets L. , Corwin B. , Jin Y. , Gallenberg D. , Wiersma J.
Published: May 2007

The inoculum level of Gibberella zeae on wheat spikes was measured during 1995 and 1996 in nine locations of Canada and the United States prone to Fusarium head blight of wheat. Spikes were exposed after exsertion and until kernel milk or soft dough stage in fields with wheat or corn residue as a source of inoculum; other spikes were exposed in a location remote from any obvious inoculum source; and in 1995 only, control plants remained in a greenhouse. After 24 h, spikes were excised and vigorously shaken in water to remove inoculum. Propagules were enumerated on selective medium and identified as G. zeae from subcultures. Significantly more inoculum was detected from fields in epidemic areas than from remote sites in an epidemic and from fields in nonepidemic areas. The median inoculum level was 20 CFU of G. zeae per spike per day in fields experiencing an epidemic, 4 CFU in locations remote from epidemic fields, 2 CFU in nonepidemic fields, and 1 CFU in locations remote from a source of inoculum in non-epidemic areas. In an epidemic region, inoculum levels near corn stubble reached up to 587 CFU of G. zeae per spike per day, and the median inoculum level of 126 CFU was significantly higher than the median of 13 CFU found near wheat residue. Inoculum was not detected or occurred sporadically during extended dry periods. While inoculum increased during rainy periods, timing of increased levels was variable. Fusarium head blight epidemics were associated with multiple inoculation episodes and coincident wet periods.
Comparison of Stenocarpella maydis Isolates for Isozyme and Cultural Characteristics
Authors: Dorrance A. E. , Miller O. K. , Warren H. L.
Published: May 2007

Isolates of Stenocarpella maydis from seed companies and plant disease clinics in the United States and the Republic of South Africa were assayed for isozyme polymorphisms and cultural variability. A low level of isozyme polymorphisms was detected in this collection of isolates. Isozyme polymorphisms were detected for α-esterase, hexose kinase, and malate dehydroge-nase of the enzymes assayed. Fungi often have limited variability among isozyme profiles, and this is especially true for fungi that have host specialization such as biotrophs or fungi with formae speciales designations. Optimum growth temperature, colony color, and pycnidiospore production were also measured. All isolates had an optimum temperature of 28 to 31°C for colony growth on acidified potato dextrose agar. Colony color and pycnidiospore production were variable over the course of several experiments, indicating that these phenotypes are poor genetic markers.
Aggressiveness to Mature Maize Plants of Fusarium Strains Differing in Ability to Produce Fumonisin
Authors: Jardine Douglas J. , Leslie John F.
Published: May 2007

Four strains each of Fusarium moniliforme (syn. Fusarium verticillioides) and Fusarium thapsinum were tested for aggressiveness toward two maize inbred lines grown under greenhouse conditions. All strains induced significantly longer stalk lesions than those observed in the controls. Mean lesion length resulting from inoculation with strains of F. moniliforme was longer than the mean lesion length resulting from inoculation with strains of F. thapsinum. Within each species, however, there was a broad range of lesion lengths observed, and all tested strains of both species probably should be regarded as potential pathogens of maize. No isolate × inbred interaction was detected. Fumonisins may play a role in aggressiveness, but under our conditions, stalk rot and the ability to produce fumonisins in vitro were not correlated.
First Report of Pestalotiopsis guepini on Loquat in Argentina
Authors: Perelló A. E. , Larran S.
Published: May 2007

Loquat, Eriobotrya japonica (Thunb.) Lindl., is used as an ornamental plant in home gardens in the La Plata area of Buenos Aires, Argentina. During spring 1998, loquat branches with spotted leaves and fruits were submitted to the Plant Disease Diagnostic Laboratory. Symptoms on leaves consisted of small (2 to 5 mm in diameter), circular to oblong, greenish brown lesions that expanded to amphigenous, isolated, or confluent, dark brown spots. On fruits the disease appeared as circular to elongated, sunken spots. Advancing lesions spread over the surface resulting in the death of the fruit. Acervuli were observed within lesions. Isolations from symptomatic tissue onto acidified potato dextrose agar medium consistently yielded white fungal colonies of sparse aerial mycelium with acervuli containing black, slimy spore masses. The fungus was initially identified as Pestalotiopsis guepini (Desmaz.) Steyaert based on conidial and cultural characteristics (1), and the identification was confirmed by Institute Spegazzini, La Plata, Buenos Aires, Argen-tina. Loquat branches with fruit and 3- to 6-month-old loquat plants were mechanically injured and sprayed with a conidial suspension of one of the P. guepini isolates (4.5 × 105 per ml). Plants were incubated in a moist chamber for 48 h and then maintained in a greenhouse. After 6 days, lesions similar to the original symptoms were observed on the inoculated plant and P. guepini was reisolated, confirming Koch's postulates. Control plants sprayed with distilled water remained symptomless. This is the first report of P. guepini causing leaf and fruit spots on loquat in Argentina.

Reference: (1) J. B. H. J. Desmazières. Ann. Sci. Nat. Ser. 2. 13:181, 1840.
First Report of Alternaria alternata Causing Leaf Spot on English Walnut
Authors: Belisario A. , Forti E. , Corazza L. , van Kesteren H. A.
Published: May 2007

A foliar disease of English walnut (Juglans regia L.) was observed in 1998 in an orchard in northern Italy. Symptoms consisted of circular, necrotic spots bordered with concentric zones of darker tissue. Average lesion diameter was 20 mm, although lesions could extend to half of the leaflet lamina. A fungus identified as Alternaria alternata (Fr.:Fr.) Keissl. (1) was observed on the necrotic tissue and was consistently isolated from the margins of the necrosis. Conidia from leaves were brown, ellipsoid to ovoid (primary conidia 28 to 60 × 8 to 15 μm; secondary conidia 10 to 30 × 7 to 13 μm), with walls often ornamented, 1 to 6 transversely septate and 0 to 3 longitudinally septate. For pathogenicity tests, three isolates were grown on potato dextrose agar for 2 weeks. Inoculations were performed on detached, surface-sterilized, healthy J. regia leaflets. Four drops (5 μl each) of a sterile water suspension of 1 × 105 conidia per ml were placed on each leaflet; three leaves per isolate were used. Leaves were incubated in a moist chamber. After 10 days, leaf spots similar to the original symptoms developed on all the inoculated points for all three isolates, and the pathogen was reisolated. Control leaflets inoculated with sterile, distilled water remained symptomless. The experiment was performed three times and the results were similar. Alternaria alternata is a well-known pathogen on many crops but a few records report this fungus as a causal agent of leaf spot on deciduous trees. This is the first report of A. alternata on English walnut.

Reference: (1) E. G. Simmons. Mycotaxon 37:79, 1990.
First Report of a Septoria sp. on Common Ragweed (Ambrosia artemisiifolia) in Europe
Authors: Bohár Gy. , Schwarczinger I.
Published: May 2007

During a survey for potential biocontrol agents of common ragweed (Ambrosia artemisiifolia var. elatior (L.) Descourt) in 1997, plants exhibiting irregular, brown leaf spots were collected repeatedly from six roadside locations in Pest County, Hungary. Many pycnidia developed in the necrotic tissues on detached leaves after 2 days in moist chambers. Pycnidia were globose to slightly flattened, brown, thin walled, 58 to 100 μm in diameter, with a definite ostiole. Conidia were hyaline, filiform with 2 to 3 septa, and 22.0 to 38.0 × 0.7 to 1.3 μm in size. The fungus was isolated on potato dextrose agar and identified as a Septoria sp. To confirm pathogenicity, potted ragweed seedlings were sprayed with a suspension of 5 × 106 conidia per ml from pure cultures of the Septoria sp., placed in a dew chamber for 72 h, and then grown in a greenhouse at 16 to 24°C. After 2 weeks, inoculated plants developed small, brown lesions on leaves and leaf petioles. Three weeks after inoculation, necrotic lesions had enlarged to 1 to 3 mm in diameter with irregular, distinct margins and light brown centers. The lesions on the lower leaves were larger and more numerous than on leaves nearer the tops of the plants. Pycnidia developed on the senescent leaves after 1 month. Infected leaves became completely necrotic and occasionally entire plants died. The pathogen was reisolated from all inoculated plants, thus satisfying Koch's postulates. A voucher specimen was deposited at the Department of Botany of the Hungarian Natural History Museum in Buda-pest (No. BP 92081). Septoria ambrosiae Hemmi et Naito was described on ragweed in Japan (1), but our isolate is morphologically distinct from that species. This is the first report of a Septoria sp. on A. artemisiifolia in Europe.

Reference: (1) N. Naito. Mem. Coll. Agric. Kyoto 47:41, 1940.
Peracetic Acid and Chlorine Dioxide for Postharvest Control of Monilinia laxa in Stone Fruits
Authors: Mari M. , Cembali T. , Baraldi E. , Casalini L.
Published: May 2007

The effects of different concentrations of peracetic acid (PAA; 62.5, 125, 250, 500, and 1,000 μg/ml)and chlorine dioxide (ClO2; 12.5, 25, 50, 100, and 200 μg/ml) on germination of Monilinia laxa conidia were tested. Conidia germination was related to the concentration of chemical product used, as well as duration of treatment. Complete inhibition of germination was observed with PAA at 500 μg/ml after 5 min of contact with conidia and with ClO2 at 50 μg/ml after 1 min of contact with conidia. The results of in vitro tests were confirmed by inoculation of fruits with treated conidia. The PAA treatment also was effective 1 h after pathogen inoculation but only on plums, for which a 1,000 μg/ml treatment significantly reduced decay incidence by 50%. In a semi-commercial test, pathogen conidia dipped for 20 min in PAA at 250 μg/ml or ClO2 at 10 μg/ml or for 5 min in PAA at 250 μg/ml were completely inhibited, and no brown rot was observed in inoculated wounded nectarines and plums.
First Report of Onion Yellow Dwarf Virus in Ontario
Authors: Stobbs L. W. , Van Driel L.
Published: May 2007

Onion yellow dwarf virus (OYDV) (1) was identified in a commercial planting of garlic (Allium sativum L.) near Delhi, Ontario, in 1998. Infected plants exhibited mild mosaic symptoms that became less noticeable by mid-July. Many plants were co-infected with garlic latent virus (GLV) (4), which was mechanically transmitted to leek (A. porrum L.). Since leek is not susceptible to OYDV (3), it is an appropriate host for the differentiation of GLV and OYDV. OYDV was transmitted nonpersistently by Myzus persicae (Schultz) from garlic to garlic and onion (A. cepa L.). Infected onion exhibited yellow striping, leaf curling, and pronounced stunting. Necrotic lesions were not present on inoculated leaves of Chenopodium amaranticolor Coste & Reyn. and C. quinoa Willd., which are often associated with co-infection with leek yellow dwarf virus (2). The isolate reacted strongly in enzyme-linked immunosorbent assay with OYDV antisera (from M. Fukami, Chiba Prefectural Agric. Exp. Stn., Chiba 266, Japan; D. Z. Maat, DLO Research Instit., Plant Prot., Wageningen, The Netherlands). Electron microscopic observations of negatively stained preparations of infected leaf tissues revealed virus particles averaging 765 ± 45 nm with typical pinwheel inclusions.

References: (1) L. Bos. CMI/AAB Descrip. Plant Viruses no. 158, 1976. (2) K. Graichen. Nachrichtenbl. Pflanzenschutz DDR 32: 245, 1978. (3) K. Graichen and H. U. Leistner. Arch. Phytopathol. Pflanzenschutz 23:165, 1987. (4) L. W. Stobbs et al. Plant Dis. 80:343, 1996.
Evaluation of Methods to Detect Fruit Infected byMonilinia vaccinii-corymbosiin Mechanically Harvested Rabbiteye Blueberry
Authors: Scherm H. , Copes W. E.
Published: May 2007

Blueberry fruit infected by Monilinia vaccinii-corymbosi (causal agent of mummy berry disease) are unfit for processing because of the formation of hardened structures (pseudosclerotia) within them. In commercial packinghouses in Georgia, fruit loads exceeding the tolerance level for mummy berry are appraised at lower quality grades, resulting in severe economic penalties to producers. Two methods to detect and enumerate mummy berry in blueberry loads were evaluated in the laboratory using fruit samples with known numbers of infected fruit. The first method involved destructive processing of the samples in a blender. The resulting blueberry puree was passed through a series of screens and the number of pseudosclerotia of M. vaccinii-corymbosi retained on the screens assessed tactilely. The second method consisted of visual symptom assessment of intact fruit. Bias and coefficients of variation of the blender method in five experiments ranged from -63.0 to 152.4% and 6.9 to 44.1%, respectively, indicating that the method was inaccurate and imprecise. Several factors probably contributed to its poor performance, including the formation of multiple fragments from single pseudosclerotia during blending and subjectivity in the tactile assessment of pseudosclerotia. Bias and coefficients of variation of the visual assessment method in four experiments ranged from -3.41 to 1.97% and 1.16 to 5.17%, respectively. Thus, the visual method was considerably more accurate and more precise than the blender method. Visual assessment was further evaluated under commercial packinghouse conditions, with >70,000 fruit assessed individually for symptoms of mummy berry and other abnormalities. Bias ranged from -11.1 to 33.3%, indicating that visual assessment was less accurate under packinghouse conditions than under laboratory conditions. This was due to the low number of infected fruit encountered in most of the loads, which resulted in large relative errors if only a single fruit was misidentified. In a two-year packinghouse survey, a high incidence of partial infection, together with successional variations in discoloration of infected portions of the fruit as the harvest season progressed, resulted in a greater variation of mummy berry symptoms than previously described.
Relationship Between Soilborne and Seedborne Inoculum Density and the Incidence of Dwarf Bunt of Wheat
Authors: Goates Blair J. , Peterson Gary L.
Published: May 2007

The incidence of dwarf bunt of wheat as a function of inoculum density was studied in a susceptible and a partially resistant cultivar at three disease-conducive locations for three seasons. Prior to seeding, plots were fumigated with methyl bromide to eliminate residual inoculum. Each cultivar was seeded into two 1.2-m rows in four replicates. The soil surface was inoculated with 0, 16 × 102, 16 × 103, 16 × 104, 16 × 105, and 16 × 106 teliospores of Tilletia controversa per row, or seed was inoculated with 0, 2 × 102, 2 × 103, 2 × 104, 2 × 105, and 2 × 106 teliospores per gram. To determine maximum possible infection, two 3.1-m rows of each cultivar were soil-surface inoculated at 10× the highest treatment rate. In the soil-inoculated plots, a minimum of 16 × 103 teliospores/row was needed to cause trace amounts of disease (0.6% maximum), even when the positive indicator treatment had up to 88% incidence. Only trace amounts or no disease occurred below the 16 × 105 rate. In the seed-inoculated plots, infection was rare and occurred only at inoculation rates of 2 × 105 teliospores/g or higher; the highest incidence was 0.4%.
Fate of Pierce's Disease Strains ofXylella fastidiosain Common Riparian Plants in California
Authors: Purcell A. H. , Saunders S. R.
Published: May 2007

The fate of strains of the bacterium Xylella fastidiosa that cause Pierce's disease of grapevines was investigated in 33 species of mostly perennial plants common in riparian habitats in northern coastal California grape-growing regions. Plants were inoculated in the field with needle puncture using cultured cells of X. fastidiosa as inoculum or inoculated in the laboratory with infective insect vectors (Graphocephala atropunctata). Populations of X. fastidiosa were highest in most plant species within 3 to 6 weeks of inoculation, followed by declines in populations of viable bacteria over the next 3 to 4 months. Homogenates of petioles of California black walnut (Juglans hindsii) and coffeeberry (Rhamnus californica) inhibited in vitro growth of X. fas-tidiosa, precluding culture of the bacterium from these plants. Big leaf maple (Acer macrophyl-lum), California buckeye (Aesculus californica), California blackberry (Rubus ursinus), coast live oak (Quercus agrifolia), elderberry (Sambucus mexicana), French broom (Genista monspessulanus), periwinkle (Vinca major), valley oak (Quercus lobata), and the grape root-stock Vitis rupestris supported systemic populations of X. fastidiosa that survived throughout the year outdoors in Napa Valley, California.
Biological Suppression of SeedborneFusariumspp. During Cold Stratification of Douglas Fir Seeds
Authors: Hoefnagels M. H. , Linderman R. G.
Published: May 2007

Fusarium spp. are important soil- and seedborne pathogens of Douglas fir (Pseudotsuga menziesii) in conifer seedling nurseries. We investigated the effects of culture media and cold stratification on isolation of Fusarium spp. from three Douglas fir seedlots and tested whether the numbers and species mixtures found on stratified seeds could cause disease. Nearly all cold-stratified seeds plated on three semiselective culture media yielded Fusarium spp., including F. avenaceum, F. culmorum, F. lateritium, F. moniliforme, F. poae, F. proliferatum, F. sambucinum, F. solani, and F. tricinctum. Species composition did not differ significantly among the media. Isolation of Fusarium spp. from seeds plated on Komada's medium (pH 6.8) at various stages of imbibition and cold stratification progressively increased from 10 to 22% to 65 to 100%. When stratified seeds were planted in conditions conducive to disease development, however, little disease attributable to Fusarium spp. resulted. A subsequent study was conducted to determine whether a biological control agent applied during imbibition could reduce the proliferation of Fusarium spp. during stratification. Unstratified Douglas fir seeds were imbibed for 24 h in a suspension of Pseudomonas chlororaphis isolate RD31-3A, a rifampicin-resistant fluorescent pseudomonad with previously demonstrated biocontrol activity against F. oxysporum. This treatment reduced the proliferation of Fusarium spp. during cold stratification without significantly affecting subsequent seed germination. The greatest reduction in poststratification populations of seedborne Fusarium spp. was achieved when preimbibition treatment with hydrogen peroxide was followed by seed imbibition in live bacteria. Seed imbibition in bacterial suspensions may be an effective means to deliver biological control agents to Douglas fir seeds.
Infection of Potatoes by Oospores of Phytophthora infestans in Soil
Authors: Strömberg A. , Persson L. , Wikström M.
Published: May 2007

Phytophthora infestans (Mont.) de Bary, causing late blight on potatoes and considered to be a typical airborne disease, was found to be infective also by oospores in the soil. P. infestans is heterothallic, and is known to reproduce asexually in Sweden since only one mating type, A1, was present until 1986. Since the 1970s, the other mating type, A2, of P. infestans has migrated to most parts of the world from its original location in central Mexico (2). When A1 and A2 meet, they may form oospores, which are thick-walled, resting structures, giving the pathogen a possibility to recombine as well as survive without its host, for instance in the soil. The soil stages of the pathogen are now therefore under intense investigation. Oospores of P. infestans were produced from two Scandinavian A1 and A2 isolates in Rye A broth mixed with talcum powder and dried for 7 weeks. The inoculum was mixed with sterile, standardized soil in concentrations of 10, 150, 250, and 400 oospores per ml of soil. Cv. Bintje plants cultivated in vitro from nodal cuttings on Murashige and Skoog medium were transplanted to the soil after rooting. Brown discolorations were obtained on the underground stems and tubers on potato plants grown in the two highest concentrations of oospores for 1 month at 15°C and 16-h day length. After 3 days of incubation on P. infestans-selective medium (3), sporangia covered the tissue from plants grown in 250 and 400 oospores per ml of soil and the pathogen was reisolated. This shows that germinating oospores of P. infestans can infect underground stems and tubers of potatoes in soil and further explains the early attack of late blight as observed in a potato crop in Sweden 1996 and 1997 (1).

References: (1) B. Andersson et al. Potato Res. 41:305, 1998. (2) D. Andrivon. Phytopathology 85:1053, 1995. (3) G. W. Griffith et al. Mycologist 9:87, 1995.
An Immunity (QL3) Breaking Strain of Sorghum Mosaic Potyvirus in India
Authors: Mali V. R.
Published: May 2007

Sorghum (Sorghum bicolor) line Tx2786 is immune to strains or isolates of sorghum mosaic potyvirus (SrMV strains SCH and SCH) but susceptible to strains of maize dwarf mosaic (MDMV) and sugarcane mosaic (SCMV) potyviruses (1,2). When grown in proximity to sugarcane, Tx2786 was infected with a virus that caused mosaic and necrotic symptoms during the postrainy season of 1994 (14 to 30°C) at Parbhani (Maharashtra, India). Leaf-dip electron microscopy performed on virus-infected sorghum and sugarcane tissues revealed particles, 720 × 12 nm, typical of a potyvirus. A potyvirus isolate (designated IBS) was readily transmitted mechanically from field-infected sorghum (Tx2786) and sugarcane (Saccharum officinarum cv. Co.740) to 18 glasshouse-grown sorghum inbred lines. All sorghum lines (QL-3 from India and Tx2786), including those resistant to SrMV, SCMV, MDMV, and johnsongrass mosaic potyvirus (JGMV), were infected. IBS caused necrosis in Cargill-40, Hegari, PI-35038, RTx09, Tx2786, QL-3 from India, and Redlan lines and mosaic symptoms in RTx430, SA-394, Atlas, Martin, BTx3048, Caprock, NM-31, QL-11, SCO-175-14E, Rio, and BTx623 lines. Sorghum reactions to sorghum and sugarcane virus isolates were similar. IBS also infected maize (Zea mays cv. African Tall), johnsongrass (S. halepense cv. 81, symptomless infection), and sorghum (S. bicolor cv. CS-3541) but not prosomillet (Panicum miliaceum), fingermillet (Eleusine coracana cv. IE-2540), pearl millet (Pennisetum typhoides cv. NHB-3), or oat (Avena sativa cv. Kent) when sap transmitted. IBS also was transmitted by the corn leaf aphid (Rhopalosiphum maidis) in a nonpersistent manner from sorghum and sugarcane to all 18 sorghum lines in a glasshouse. Based on direct antigen-coating enzyme-linked immunosorbent assay (DAC-ELISA), serologically specific electron microscopy, and Western blot tests, IBS was serologically related to SrMV strains SCH and SCI (2–4) but not to MDMV strains A, D, and E; SCMV strains A, B, D, SC, and MDB; or JGMV type strain from Australia and strain O from Texas (2). IBS induced formation of cytoplasmic cylindrical inclusions consisting of pinwheels associated with long, straight, laminated aggregates (subdivision type II) in sorghum and sugarcane host cells. Purified IBS contained one major polypeptide of 40 kDa and a ribonucleic acid of 3.0 × 106 Da. Polyclonal antiserum to IBS was produced in rabbits and used in DAC-ELISA to confirm the identity of IBS in sugarcane, sorghum lines, and other test plant species. On the basis of biological and serological properties, IBS isolated from field-infected sorghum grain Tx2786 and sugarcane cv. Co.740 is identified as an immunity (QL3) breaking strain of SrMV (SrMV-IBS).

References: (1) L. M. Giorda et al. Plant Dis. 70:624, 1986. (2) D. D. Shukla et al. Phytopathology 79: 223, 1989. (3) D. D. Shukla et al. 1998. AAB Description of Plant Viruses No. 359. AAB, Kew, Surrey, England. (4) Z. N. Yang and T. E. Mirkov. Phytopathology 87:932, 1997.
First Report of Powdery Mildew Caused by an Oidium sp. on Torenia fournieri
Authors: Holcomb G. E.
Published: May 2007

Torenia fournieri Lind. ex Fourn. (wishbone flower, bluewings) is a popular summer bedding plant in Louisiana. Clown Mixture cultivars are available in garden centers in March and April. Transplants of cultivar Clown Rose were purchased, transplanted to larger pots, and maintained in a greenhouse. A powdery mildew was observed on these plants in March and all plants (six) were severely diseased by May. Symptoms included leaf distortion and yellowing. Powdery mildew was not present on transplants and none was found in later checks of garden centers. An Oidium sp. was observed sporulating on both leaf surfaces of infected plants. Conidia were ellipsoid, produced in chains, lacked fibrosin bodies, and averaged 41 × 22 μm in dimensions. No sexual stage was observed. Healthy plants of Clown Mixture cultivars were obtained and inoculated by brushing conidia from infected plant leaves to leaves of healthy plants. Plants were maintained in a greenhouse where temperatures ranged from 16 to 26°C. Hyphal growth appeared on inoculated plants after 5 days and the reproductive structures formed later appeared the same as those on originally infected plants. Uninoculated plants remained healthy. No previous reports of powdery mildew diseases of T. fournieri in the United States were found. Other powdery mildew pathogens reported on T. fournieri are Sphaerotheca fuliginea (Schlechtend.:Fr.) Pollacci in Finland and Japan and an Erysiphe sp. in Japan (1).

Reference: (1) K. Amano. Host Range and Geographical Distribution of the Powdery Mildew Fungi. Japan Scientific Press, Tokyo, 1986.
First Report of Golden Dwarf Mistletoe on Pinus maximinoi
Authors: Mathiasen R. , Sesnie S. , Calderon J. , Soto A.
Published: May 2007

Golden dwarf mistletoe (Arceuthobium aureum subsp. aureum Hawksw. & Wiens) is endemic to east-central Guatemala (Departments Alta Verapaz, Baja Verapaz, and Quiche) (1,2). Its principal hosts are Pinus pseudostrobus Lindl., P. montezumae Lamb., and P. oaxacana Mirov (1). In May 1999, A. aureum subsp. aureum was observed infecting Pinus maximinoi H. E. Moore at four locations: 1.0 km south (altitude 1,580 m) and 5.4 km north (altitude >1,630 m) of La Cumbre, Baja Verapaz on Route CA-14, 8 km west (altitude 1,670 m) of Chilasco, Baja Verapaz, and 5 km west (altitude 1,490 m) of San Cristobal Verapaz, Alta Verapaz on Route 7-W. Although previous reports (1,2) indicated that golden dwarf mistletoe does not induce witches'-brooms on its hosts, older (>50 years), severely affected P. maximinoi were observed to have formed large witches'-brooms as a result of dwarf mistletoe infection. Although it has been suggested that Pinus oocarpa Schiede is susceptible to golden dwarf mistletoe (1), several large trees of this species were observed growing within 5 m of infected P. maximinoi at three of the four locations, but none were infected. This is the first report of golden dwarf mistletoe on P. maximinoi.

References: (1) F. G. Hawksworth and D. Wiens. 1996. Dwarf Mistletoes: Biology, Pathology, and Systematics. USDA Agric. Handb. 709. (2) D. Wiens and C. G. Shaw, J. Idaho Acad. Sci. 30:25, 1994.
First Report of Pepino Mosaic Virus on Tomato
Authors: van der Vlugt R. A. A. , Stijger C. C. M. M. , Verhoeven J. Th. J. , Lesemann D.-E.
Published: May 2007

Early in 1999 a new viral disease occurred in protected tomato (Lycopersicon esculentum) crops in the Netherlands. Infected plants showed yellow leaf spots and mosaic. Transmission electron microscopic analysis revealed particles typical of potexviruses. Only three potexviruses have been reported to infect solanaceous crops: Pepino mosaic virus (PepMV), Potato aucuba mosaic virus (PAMV), and Potato virus X (PVX). Inoculation of test plants and serological tests showed that the new virus clearly differed from PAMV and PVX. Immuno-electron microscopy with antiserum to PepMV (1), the original PepMV isolate, and the virus from tomato showed decoration titers of 1:800 (homologous) and 1:400, respectively. Neither virus reacted with antiserum to PVX, nor did PVX react with antiserum to PepMV. Results of host plant analysis with 17 plant species mostly resembled those expected for PepMV. Nucleotide sequence alignment of DNA fragments obtained by reverse-transcriptase polymerase chain reaction with a specific primer set for potexviruses, directed against the RNA polymerase region, showed 93% identity between PepMV and the virus from tomato, while homologies with PVX, PAMV, and other potexviruses were <60%. Results indicate that the potexvirus in tomato is PepMV. PepMV was first found in pepino (Solanum muricatum) in Peru in 1974 and described by Jones et al. in 1980 (1). This is the first report of a natural infection of tomato by PepMV.

Reference: (1) R. Jones et al. Ann. Appl. Biol. 94:61, 1980.
Collar Rot and Wilt of Yellow Passion Fruit in Venezuela
Authors: Gonzalez M. S. , Suarez Z. , Rosales C. , Parra D.
Published: May 2007

Surveys were conducted to determine the occurrence of diseases of yellow passion fruit (Passiflora edulis f. flavicarpa) in plantations located in the central states of Aragua, Carabobo, Guarico, Miranda, and Yaracuy, Venezuela, from 1991 to 1998. Plants in both commercial plantations and passion fruit nurseries were symptomatic for wilt and reddish-brown collar rot. Symptomatic tissues were surface-disinfected and plated on PARPH medium (1). Phytophthora parasitica was frequently isolated from diseased tissues, and pathogenicity tests were conducted with the fungus under greenhouse conditions. Passion fruit seedlings were grown in pots containing a 1:1 (vol/vol) steamed soil/sand mixture, one plant per pot. Five-millimeter-diameter plugs of P. parasitica isolates were grown on clarified V8 agar. Three-month-old seedlings were wounded with a sterile scalpel in the collar region. Wounded and unwounded plants were inoculated with 10 ml of zoospore suspension (105 spores per ml) or sterile water (control). Fifty plants were evaluated per treatment, and the experiment was repeated. Wounded and unwounded seedlings inoculated with zoospores developed chlorosis and collar necrosis after 15 days. Seedling mortality reached 50% 1 month after inoculation, and the fungus was reisolated from symptomatic tissues. This is the first report of P. parasitica causing collar rot and wilt of yellow passion fruit in Venezuela.

Reference: (1) S. N. Jeffers and S. B. Martin. Plant Dis 70:1038, 1986.
Comparison of 16S rDNA and 16S/23S Intergenic Region Sequences Among Citrus Greening Organisms in Asia
Authors: Subandiyah Siti , Iwanami Toru , Tsuyumu Shinji , Ieki Hiroyuki
Published: May 2007

Polymerase chain reaction was used to amplify and sequence the 16S ribosomal RNA gene (rDNA) and 16S/23S intergenic region of several isolates of citrus greening organism (GO) from Japan, the Philippines, Indonesia, and Thailand. The sequences of 16S rDNA were identical among all the isolates studied, very similar to the published sequences of Thai (99.4 to 100% identity), Nepalese (100% identity), and Indian (98.8% identity) strains, and less similar to an African strain (97.5% identity). The sequences of the intergenic region between 16S and 23S rDNA were also identical among the isolates examined as well as the reported Nepalese and Thai isolates. They were close to the sequences of reported strains of India and China (99.2%) and apart from those of the African strain (85.5%). These results suggested that some isolates of GO from Japan, the Philippines, Indonesia, Thailand, and Nepal constitute one strain, which is similar to Indian and Chinese strains and distinct from the African strain.
Etiology of Sweet Potato Chlorotic Dwarf Disease in Argentina
Authors: Di Feo L. , Nome S. F. , Biderbost E. , Fuentes S. , Salazar L. F.
Published: May 2007

Chlorotic dwarf (CD), the most important disease in the sweet potato-producing regions of Argentina, is caused by the synergistic combination of two aphid-transmitted potyviruses with a whitefly-transmitted crinivirus. Sweet potato feathery mottle virus, sweet potato mild speckling virus, and a crinivirus (serologically related to sweet potato chlorotic stunt virus) were associated with CD. The synergistic combination of these three viruses reproduced the disease.
Chemiluminescent and Colorimetric Detection of Erwinia amylovora by Immunoenzymatic Determination of PCR Amplicons from Plasmid pEA29
Authors: Merighi M. , Sandrini A. , Landini S. , Ghini S. , Girotti S. , Malaguti S. , Bazzi C.
Published: May 2007

A molecular diagnostic technique (polymerase chain reaction enzyme-linked immunosorbent assay [PCR-ELISA]) for detection of Erwinia amylovora was developed. The protocol is based on the immunoenzymatic determination of PCR products. For in vitro amplification, we used previously published primers able to detect the cryptic plasmid pEA29, which is ubiquitous in E. amylovora. Amplicons were labeled with 11-digoxigenin (DIG)-dUTP during the amplification reaction, captured by hybridization to a biotinylated oligonucleotide in streptavidin-coated ELISA microplates, and then detected with anti-DIG-Fab′-peroxidase conjugated antibodies. The specificity of the assay was verified using E. amylovora strains from different host plants and geographical origins in addition to other plant-associated bacteria (either phytopathogenic or saprophytic) belonging to the genera Erwinia, Pseudomonas, and Agrobacterium. In detection threshold experiments with pure cultures, as few as 30 and 3 CFU/reaction tube were detected when the ABTS (colorimetric) and ECL (chemiluminescent) detection assays, respectively, were used. PCR-ELISA coupled with chemiluminescent detection was able to detect as few as 4 × 102 CFU/g of artificially infested pear twigs. The assay was further shown to be suitable for detection of E. amylovora in naturally infected plant organs, and the results were compared to those obtained using standard PCR assays with electrophoretic separation of amplicons.
Use of Colletotrichum graminicola KA001 to Control Barnyard Grass
Authors: Yang Young-Kook , Kim Soon-Ok , Chung Hoo-Sup , Lee Yong-Hwan
Published: May 2007

Isolates of Colletotrichum graminicola were obtained from barnyard grass showing anthracnose symptoms and the fungus was evaluated as a potential biocontrol agent. C. graminicola KA001 was highly pathogenic to two varieties of barnyard grass in a wide range of growth stages, with the most damage at the three- to four-leaf stages. Disease severity of barnyard grass increased with the increase of the inoculum density from 1 × 104 to 1 × 105 conidia/ml, but inoculum density above 1 × 106 conidia/ml did not increase disease severity. A total of 13 rice cultivars tested showed no disease symptoms when inoculated with this fungus. Appressoria were formed on both barnyard grass and rice leaves, but infection hyphae were only found in the cells of barnyard grass. The fungus grew and sporulated in a wide range of temperature regimes, with optimal temperature at 27 to 30°C. These data suggest that C. graminicola KA001 has potential as a mycoherbicide to control barnyard grass with a safe selectivity in rice fields.
Population Dynamics of the Sting Nematode in California Turfgrass
Authors: Bekal Sadia , Becker J. Ole
Published: May 2007

Population densities of Belonolaimus longicaudatus were monitored at monthly intervals at the Tamarisk country club golf course (1993 to 1994) and at the Annenburg Estates and Desert Island golf courses (1998). All three courses are located at Rancho Mirage, Coachella Valley, CA. The bermuda grass in the sampling area typically exhibited chlorosis at the beginning of April when the sting nematode populations began to increase. At the Tamarisk golf course, population density peaked in October, with 1,000 nematodes per 100 cm3 of soil, but declined rapidly, with the lowest population density occurring in December with approximately 50 nematodes per 100 cm3 of soil. At the Annenburg Estates and Desert Island golf courses, the nematode population densities peaked in June and July but declined rapidly to less than half of that density, presumably because of B. longicaudatus-caused host decline. Soil temperature and fluctuation of nematode densities were significantly correlated at all locations. Nematode distribution was greatest in the top 15 cm of soil except during the hottest summer months, when the population was higher at depths of 15 to 30 cm.
Detection and Quantification ofBotrytis cinereaby ELISA in Pear Stems During Cold Storage
Authors: Meyer U. M. , Spotts R. A. , Dewey F. M.
Published: May 2007

Botrytis cinerea was detected and quantified in pear stems from six orchards in the Pacific Northwest, and changes in fungal biomass in the stems after 6 and 8 months of cold storage in regular (air) atmosphere were studied. The fungus was detected by plating stem halves on selective medium and by enzyme-linked immunosorbent assay (ELISA) using the Botrytis-specific monoclonal antibody BC-12.CA4. Both methods demonstrated that the incidence of B. cinerea increased from 6 to 8 months, but ELISA was more sensitive than standard isolation. Quantitative ELISAs on stems indicated that over 200 μg of B. cinerea biomass per gram of stem tissue was present in the stems of visibly rotted fruits, but usually less than 35 μg/g was present in stems from fruits without visible gray mold. Aureobasidium pullulans, Penicillium spp., Alternaria spp., and Cladosporium spp. were commonly isolated from stem tissue. A. pullulans was present in 86% of the stems from which B. cinerea was detected. Use of the monoclonal antibody BC-12.CA4 could help in determining the infection path of B. cinerea in pear stems and detection of latent infections, enabling the timing and method of control of stem end rot to be optimized.
Assessment of an Alternative IPM Program for the Production of Apples for Processing
Authors: Biggs Alan R. , Hogmire Henry W. , Collins Alan R.
Published: May 2007

Conventional and alternative integrated pest management (IPM) programs for managing arthropods and diseases affecting processing apple production were compared over 4 years. The effects of the two programs on populations of pest and beneficial insects, and on disease incidence and severity, were evaluated in the field and laboratory and at a commercial fruit processing plant by federal inspectors. The economic implications of the alternative management program were assessed by examining its relative costs and benefits compared with conventional management. In the alternative program, arthropods were managed with oil and Bacillus thuringiensis (Bt), and early-season diseases were managed with fungicides. Calcium chloride was used to suppress rot diseases. The alternative plots showed lower levels of indirect pests (aphids, leaf-hoppers, and mites) and increased numbers of arthropod natural enemies. On harvested fruit, there was significantly more injury in the alternative plots from codling moth or oriental fruit moth, plum curculio, and apple maggot. Levels of foliar diseases were similar between treatments; however, fruit from the alternative program exhibited significantly more sooty blotch, flyspeck, and rots. At the commercial processor, levels of cull fruit were higher for the alternative program in 2 of the 3 years with harvestable yield. Loads of fruit that were not acceptable for processing were due mostly to internal worms and worm damage. Incidence of decay was within the quality limits set by the processor, except for one conventional sample, in which decay exceeded 5%. Of the 36 loads of fruit that were examined from each program, 4 and 13 loads were rejected from the conventional and alternative programs, respectively. Net present value comparisons were dependent upon how rejected loads were valued. At cider prices for rejected loads, net returns were similar between programs. When rejected loads were valued at a complete loss, conventional net present value was over 140% higher than the alternative program. Among cultivars, Golden Delicious was most profitable and York was least profitable.
First Report of Puccinia sorghi Virulent on Sweet Corn with the Rp1-D Gene in Florida and Texas
Authors: Pate M. C. , Pataky J. K. , Houghton W. C. , Teyker R. H.
Published: May 2007

For the past 15 years, the Rp1-D gene has controlled common rust on sweet corn in North America. In August and September 1999, isolates of Puccinia sorghi were collected from Rp1-D sweet corn hybrids in Illinois, Wisconsin, Minnesota, Michigan, and New York. This was the first widespread occurrence in the continental United States of P. sorghi virulent on the Rp1-D gene (1). Isolates of P. sorghi collected from Los Mochis, Mexico, in March 2000 had a pattern of virulence similar to the pattern for the isolates collected in the Midwest in 1999 (2). In April and May 2000, small uredinia were observed on Rp1-D sweet corn in Florida and Texas. In Florida, isolates were collected from six different locations within a 13-km radius near Belle Glade. Three isolates were collected each from Rp1-D and non-Rp sweet corn hybrids. Isolates also were collected from two Rp1-D sweet corn hybrids and a non-Rp sweet corn hybrid near Hondo, TX. Inocula of isolates were increased through one uredinial generation in the greenhouse. Several 1-cm2 pieces of leaf tissue with sporulating uredinia were placed in 15 ml of a solution of water and Tween 20. This inoculum was placed in whorls of five two-leaved seedlings of a susceptible hybrid, ‘Primetime.’ Urediniospores from newly formed uredinia were collected 10 days later and used as inocula to assay each isolate. Two isolates from Florida (one each from an Rp1-D and a non-Rp hybrid) were assayed on a non-Rp susceptible check, 20 different single Rp genes, and nine compound Rp genes. Other isolates were assayed on two replicates of a non-Rp susceptible check, a source of Rp1-D, and five single Rp genes that were effective against the isolates collected from the Midwest in 1999 and from Mexico in 2000. Each experimental unit consisted of five plants grown in 10-cm-diameter pots. Plants at the two-leaf stage were inoculated three times within 5 days by filling whorls with a urediniospore suspension. Rust reactions were rated 10 days after the final inoculation. Isolates collected in Florida from non-Rp hybrids were avirulent on Rp1-D but those collected in Texas from non-Rp hybrids were virulent on Rp1-D. Isolates collected in Florida and Texas from Rp1-D hybrids had a similar pattern of virulence as isolates collected from the Midwest in 1999 and from Mexico in March 2000; that is, effective single Rp genes included Rp1-E, Rp-G, Rp1-I, and Rp1-K. A source that we previously believed was Rp1-L now appears to be Rp-G. These are the first reports from Florida and Texas of P. sorghi virulent on Rp1-D, and they are the first occurrences of virulence against Rp1-D in the continental U.S. in 2000. Apparently, P. sorghi with virulence against Rp1-D has become established in an area where common rust inocula for North America overwinters.

References: (1) J. K. Pataky and W. F. Tracy. Plant Dis. 83:1177, 1999. (2) J. K. Pataky et al. Plant Dis. 84:810, 2000.
First Report of Downy Mildew Caused by Peronospora lamii on Salvia splendens and Salvia coccinea
Authors: Holcomb G. E.
Published: May 2007

Angular chlorotic spots were observed on adaxial leaf surfaces of Salvia splendens (scarlet sage cvs. Empire Purple, Empire White, Red Pillar, and Red Hot Sally) and S. coccinea (scarlet or Texas sage cv. Lady in Red) in early May in Baton Rouge area nurseries. Leaf spots sometimes became necrotic and resulted in leaf drop. Abaxial leaf surfaces contained scattered patches of white mycelia with brown spores. Microscopic examination of mycelia revealed irregular dichotomously branched conidiophores with pointed tips and brown oval conidia. Conidiophores averaged 485 × 9 µm and conidia averaged 21 × 18 µm (16 to 26 × 15 to 23 µm) in dimensions. The fungus was identified as Peronospora lamii A. Braun (= P. swinglei Ellis & Everh.) based on these characters and its known occurrence on Salvia spp. and five other genera in the family Lamiaceae (2). Pathogenicity tests were performed by washing conidia from infected leaves into distilled water and mistinoculating S. coccinea cv. Lady in Red and S. splendens cv. Empire Purple with 50,000 spores/ml. Plants were held in a dew chamber at 20°C for 3 days, then moved to a greenhouse where temperatures ranged from 18 to 32°C. Typical angular chlorotic leaf spots developed on inoculated plants within 6 to 8 days and noninoculated plants remained healthy. The fungus did not sporulate under these greenhouse temperatures, but infected leaves that were removed and placed in a moist chamber at 25°C produced conidiophores and brown conidia typical of P. lamii within 2 to 3 days. P. lamii has been reported previously on S. officinalis (3) and S. reflexa (1) in the United States. This is the first report of downy mildew on S. coccinea and S. splendens. Appearance of the disease in retail nurseries that obtained plants from out of state (Arkansas) suggests a widespread occurrence of the disease on these host plants.

References: (1) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN. (2) S. M. Francis. 1981. Peronospora lamii. Descriptions of Pathogenic Fungi and Bacteria No. 688. Commonwealth Mycological Institute, Kew, England. (3) R. T. McMillan and W. R. Graves. Plant Dis. 78:317, 1994.
Evidence for Association of a Viroid with Tapping Panel Dryness Syndrome of Rubber (Hevea brasiliensis)
Authors: Ramachandran P. , Mathur S. , Francis L. , Varma A. , Mathew J. , Mathew N. M. , Sethuraj M. R.
Published: May 2007

Tapping panel dryness (TPD) is one of the most destructive maladies affecting rubber plantations and is becoming a matter of serious concern. Reduced latex yield leading to total drying of the tapping panel is the obvious symptom. The cause of TPD syndrome is unknown but has been mostly attributed to abiotic causes. In India, the high yielding commercial clone RRII 105 is affected by TPD, leading to enormous losses. We have observed that TPD-affected trees show symptoms of bark scaling, cracking, drying, necrotic streaking, and browning of internal bark leading to the decay of internal tissues. Often prominent abnormal bulges on the lower part of tree trunks occur where the first panel begins to dry. Investigations on TPD-affected rubber samples did not reveal the association of fungus, bacterium, virus, or a protozoan. Total nucleic acid extracts purified from leaf and bark tissues of affected samples and analyzed by polyacrylamide gel electrophoresis under denaturing conditions of low salt and high temperature showed the presence of nucleic acids similar in electrophoretic mobility to low molecular weight (LMW) RNA, of ~359 nucleotides such as potato spindle tuber viroid (PSTVd). The LMW nucleic acid detected from TPD-affected samples was found to be RNA based on its sensitivity to RNase and insensitivity to DNase, phenol, and heat treatments. The LMW RNA was purified and cloned in a pUC 19-derived vector by using primers specific to PSTVd (1). The cloned DNA, when random labeled and used as probe reacted specifically to nucleic acid extracts from TPD-affected rubber trees but not from healthy tissue in dot-blot hybridization assays. Based on the above findings, a viroid etiology for TPD syndrome is proposed.

Reference: (1) R. A. Owens, A. T. Candresse, and T. O. Diener. Virology 175:238, 1990.