bluuebunny/crossref_metadata_2025 huggingface dataset:
Early Symptom Development and Histological Changes Associated with Migration of Bursaphelenchus xylophilus in Seedling Tissues of Pinus thunbergii
Authors: Ichihara Y. , Fukuda K. , Suzuki K.
Published: May 2007

In order to clarify the mechanism of pine wilt caused by the pinewood nematode (PWN), Bursaphelenchus xylophilus, nematode migration in tissues and disease symptoms in Pinus thunbergii seedlings were investigated. One-year-old seedlings were inoculated with different pathogenic isolates of PWN under two different temperatures. At an early stage of symptom development, a virulent isolate of PWN multiplied in both bark and xylem and was distributed in cortical resin canals, cortical tissue, and xylem resin canals at 30°C. Cell death and disease symptoms developed in both bark and xylem. The virulent isolate of PWN at 25°C and the avirulent isolate of PWN at 30°C were distributed mainly in cortical resin canals, but rarely in xylem resin canals and cortical tissue. Disease symptoms and cell death occurred in cortical resin canals and rarely occurred in other tissues. These results demonstrated that the virulent isolate of PWN at low temperature and avirulent nematodes could not easily migrate to xylem resin canals and cortical tissue. It was shown that cell death and early symptom development coincided with PWN migration and, therefore, PWN invasion induces cell death and early symptom development.
First Report of Fusarium Wilt on Hebe sp. in Italy and Europe
Authors: Garibaldi A. , Minuto A. , Gilardi G. , Gullino M. L.
Published: May 2007

Hebe (showy speedwell), an increasingly important crop in the Riviera Ligure (northern Italy), is cultivated in greenhouses and open fields. During summer 1999, a serious wilt of hybrids (Hebe speciosa × H. franciscana cvs. Paula, Linda, and Heidi) grown in plastic pots (14 to 16 cm diameter) in a peat/pomix/clay (70:20:10, vol/vol) substrate was observed. Symptoms appeared on one side of the plant or on a single branch. Affected plants showed only slight yellowing before wilting. Wilting progressed acropetally. Eventually, affected plants were completely wilted, and stems showed dark blue-black necrosis, often covered by mycelia. An intense brown discoloration of the vascular system was evident shortly after the appearance of the first symptoms. In some cases, whole plants suddenly wilted. Infected plants generally were stunted and eventually died. Fusarium oxysporum was isolated consistently from diseased plants on Komada's (1) Fusarium-selective medium. One single-spore isolate of F. oxysporum, freshly isolated from wilted plants, was used for artificial inoculation of healthy plants to complete Koch's postulates. Rooted cuttings were transplanted in soil artificially infested with 1 × 103 CFU/ml of soil. Inoculation was performed on 20 plants belonging to two cultivars (Paula and Heidi). Noninoculated plants of each cultivar served as controls. Plants were maintained in a glasshouse at 25°C. The first symptoms developed 20 days after transplanting in infested soil. Symptoms resulting from artificial inoculation were similar to those observed on naturally infected plants. F. oxysporum was consistently reisolated from inoculated plants. Fusarium wilt of Hebe is favored by temperatures higher than 20°C. Symptoms did not develop on inoculated plants maintained in the open field during the month of October nor in the greenhouse at temperatures lower than 18°C. This is the first report of Fusarium wilt on Hebe sp. in Italy and Europe. A similar wilt on H. buxifolia and other Hebe spp. has been reported by Raabe in the United States (2,3).

References: (1) H. Komada. Rev. Plant Prot. Res 8:114, 1975. (2) R. D. Raabe. Phytopathology 47:532, 1957. (3) R. D. Raabe. Plant Dis. 69:450, 1985.
Yellow Leaf Disease of Muskmelon from Thailand Caused by Tomato leaf curl virus
Authors: Samretwanich K. , Chiemsombat P. , Kittipakorn K. , Ikegami M.
Published: May 2007

Muskmelon (Cucumis melo L. var. reliculatus) plants exhibiting a yellow leaf disease have been observed in central Thailand since 1993. The pathogen is transmitted to muskmelon by the whitefly, Bemisia tabaci Genn. Based on leaf yellowing symptoms and whitefly transmission, infection by a geminivirus was suspected. Five naturally infected musk-melon plants showing leaf yellowing were collected from a field at Kam-phaengsaen, Nakorn Pathom, Thailand, in 1996. Virus cultures were maintained in muskmelon plants in a screenhouse. Inoculations were done with B. tabaci, and leaf symptoms were the same as symptoms in the field. Geminivirus DNA associated with yellow leaf disease of musk-melon was amplified by polymerase chain reaction with geminivirus-specific degenerate primers (2) that anneal within the rep (replication-associated protein) and cp (coat protein) genes (2). Fragments of 1.2 kb were amplified and cloned from affected muskmelon plants. The insert of three independent clones was sequenced, and identical 32-base stem loop regions were found, including the conserved nonanucleotide sequence TAATATTAC present in all geminiviruses. The iterative sequence GGCGTC also was found in the intergenic region (IR; 434 bp) of the amplified fragments (1). The B component was not found from the total length of the restriction fragment sizes of dsDNA isolated from infected muskmelon. The nucleotide sequences of IR and V1 (precoat open reading frame) were compared with 28 well-studied whitefly-transmitted geminiviruses and revealed ≍97% sequence similarity with DNA A of Tomato leaf curl virus (genus Geminivirus) from India (ToLCV-In2; GenBank Accession no. u15016) (1). The iterative sequence GGCGTC in the IR also was identical to ToLCV-In2. These results establish the provisional identity of the virus causing melon yellow leaf disease as ToLCV or closely related strains.

References: (1) M. Padidam et al. J. Gen. Virol. 76:249, 1995. (2) M. R. Rojas et al. Plant Dis. 77:340, 1993.
Responses of 11 Fraxinus Cultivars to Ash Yellows Phytoplasma Strains of Differing Aggressiveness
Authors: Sinclair W. A. , Gleason M. L. , Griffiths H. M. , Iles J. K. , Zriba N. , Charlson D. V. , Batzer J. C. , Whitlow T. H.
Published: May 2007

Five cultivars of Fraxinus americana (white ash) and five of F. pennsylvanica (green ash) were graft-inoculated with three strains of ash yellows phytoplasmas at Ames, IA, and with thrsee other strains at Ithaca, NY. A sixth green ash cultivar was tested only in New York. Trees were allowed to grow in field plots for 3 years. Infection was detected via the DAPI (4′, 6-diamidino-2-phenylindole 2HCl) fluorescence test. Incidence of witches'-brooms on infected trees was greater on white ash than green ash and varied significantly among phytoplasma strain treatments at both locations. Volume growth of infected ash, averaged across cultivars over 2 years in Iowa and 3 years in New York, was 49 and 59%, respectively, as great as that of noninfected trees. Foliar greenness was reduced significantly by infection at both locations, and this reduction was positively correlated with growth reduction. Cultivars at each location varied significantly in growth of noninfected trees and in growth of diseased trees relative to that of nonin-fected trees (a measure of phytoplasma tolerance), but cultivar means for these variables in Iowa were not significantly correlated with those in New York. Green ash cvs. Bergeson, Dakota Centennial, and Patmore and white ash cv. Autumn Applause were above average in tolerance at both locations. Phytoplasma strains at each location varied significantly in aggressiveness as indicated by host growth suppression.
Relationship Between Apple Fruit Epicuticular Wax and Growth ofPeltaster fructicolaandLeptodontidium elatius, Two Fungi that Cause Sooty Blotch Disease
Authors: Belding Robert D. , Sutton Turner B. , Blankenship Sylvia M. , Young Eric
Published: May 2007

Sooty blotch severity varied among apple cultivars or selections surveyed in 1989 and 1992. No mycelial growth was observed on russetted areas of the cuticle that are considered impermeable. Ursolic acid and n-alkanes were the most prominent components of the epicuticular waxes of the cultivars or selections evaluated. Although there were differences in the relative proportions of these compounds among the cultivars, the differences were not related to the severity of sooty blotch. Peltaster fructicola and Leptodontidium elatius were grown on compounds that comprise the epicuticular wax of the fruit to determine if one or more of these were needed for growth. The fungi did not grow on any of the five major components of the epicuticular wax unless dilute apple juice was included. Scanning electron microscopy studies showed that mycelia of P. fructicola grew on the surface of the wax and did not appear to degrade it. Our studies support the hypothesis that P. fructicola and L. elatius fungi are epiphytes and obtain their nutrients not from components of the cuticle, but more likely from fruit leachates.
Incidence and Impact of Swiss Needle Cast in Forest Plantations of Douglas-fir in Coastal Oregon
Authors: Hansen E. M. , Stone J. K. , Capitano B. R. , Rosso P. , Sutton W. , Winton L. , Kanaskie A. , McWilliams M. G.
Published: May 2007

An epidemic of Swiss needle cast, caused by the ascomycete Phaeocryptopus gaeumannii, is causing defoliation and growth reductions in Douglas-fir forest plantations along the Oregon Coast. The area of symptomatic plantations has been monitored annually since 1996 by aerial survey; in spring 1999, 119,500 ha were affected. Pathogen and symptom development have also been monitored on nine permanent plots in stands of differing disease severity. Infection levels and symptom severity are greatest in low elevation plantations close to the coast. In areas of severe disease, trees retain only current year needles. Defoliation is proportional to the number of stomata occluded by pseudothecia of the fungus, with needles being shed when about 50% of stomata are occupied, regardless of needle age. Fungus sporulation and premature needle abscission are greatest on the upper branches of trees. Annual application of fungicides increases needle retention significantly. Tree height and diameter growth and total tree volume are reduced by disease, and tree volume is significantly correlated with needle retention on our plot trees. The epidemic continues to be most severe in Douglas-fir plantations established on sites where Sitka spruce and western hemlock or red alder predominated in earlier times.
Cucurbit leaf curl virus, a New Whitefly Transmitted Geminivirus in Arizona, Texas, and Mexico
Authors: Brown J. K. , Idris A. M. , Olsen M. W. , Miller M. E. , Isakeit T. , Anciso J.
Published: May 2007

In 1998 to 1999, geminivirus-like symptoms were observed in whitefly-infested pumpkin, honeydew melon, and muskmelon in Arizona and Texas and in Coahuilla, Mexico (MX), respectively. Plants exhibited leaf curl and/or mottling, reminiscent of symptoms caused by Squash leaf curl virus (SLCV-WAZ) described from Arizona in 1981 (2). The isolate from Arizona pumpkin fields was experimentally transmitted to pumpkin seedlings by the “B type” of Bemisia tabaci (Genn.), and symptoms were indistinguishable from those observed in infected fields. Samples from AZ, MX, and TX were assessed for begomovirus presence by polymerase chain reaction (PCR) using degenerate primers that amplify a contiguous fragment containing the viral coat protein (Cp) gene and common region (CR) of the A component (CR-A) (~2,100 bp) and a fragment containing the CR of the B component (CR-B) (~1,100 bp). One to four isolates from each location were examined by PCR using both primer pairs, and at least three amplicons per isolate were cloned and their sequences determined. Alignment of viral Cp nucleotide (nt) sequences revealed that AZ [AF256199], MX, and TX field isolates shared 98.7 to 100% sequence identity, but were only 84.5 to 85.6% identical to the Cp gene of SLCV-extended (SLCV-E) [M38183] and SLCV-restricted (SLCV-R) (S. G. Lazarowitz, unpublished), respectively, suggesting a new, previously undescribed begomoviral species (3). Further, the Cp nt sequence of the three field isolates was 6 nt shorter than SLCV-E, SLCV-WAZ [AF256203], and SLCV-R Cp sequences. The CR-A [AF256200] and CR-B [AF256201] sequences (179 nt, each) of field isolates, including the theoretical Rep binding element, GGTGT, were 100% identical. Although the Rep binding site is identical among field isolates, SLCV-E, SLCV-R, and SLCV-WAZ, the field isolate CR sequence shared only 64.2, 67.5, and 66.9% overall identity with CR-A SLCV-E, SLCV-R [M63155], and SLCV-WAZ [AF256202], respectively. Prior to 1998 to 1999, SLCV-WAZ was the only New World begomovirus of cucurbits known to infect both melon (Cucumis) and pumpkin (Cucurbita) (1). Therefore, SLCV was initially suspected as the causal agent. However, here we provide evidence for a new, previously undescribed bipartite begomovirus of cucurbits in AZ, MX, and TX that is herein provisionally designated Cucurbit leaf curl virus (CuLCV). Prediction of its closest begomovirus relatives by Cp nt sequence and Rep binding site comparisons suggest that CuLCV is a new member of the SLCV lineage, also containing Bean calico mosaic virus, Cabbage leaf curl virus, SLCV-E, and Texas pepper virus-TAM.

References: (1) J. K. Brown and M. R. Nelson. Phytopathology 74:1136, 1984. (2) J. K. Brown and M. R. Nelson. Ann. Appl. Biol. 115:243, 1986. (3) M. A. Mayo and C. R. Pringle. J. Gen. Virol. 97:649, 1998.
First Report of Root Rot Caused by Pythium aphanidermatum on Artichoke
Authors: Stanghellini M. E. , Vilchez M. , Kim D. H. , Aguiar J. L. , Armendariz J.
Published: May 2007

In the deserts of Southern California, globe artichokes (Cynara scolymus L.) are grown as annuals. Greenhouse-grown seedlings (5 to 6 weeks old) are commonly transplanted into minimum-tilled, drip-irrigated beds in late summer (August to September) and harvested in winter and spring (December to April). By mid-October of 1997 and 1999, up to 30% of the plants in some commercial fields were either stunted or dead. There was no further progression of the disease over the remainder of the production season. Primary and secondary roots of symptomatic plants submitted for diagnosis in October of 1997 and 1999 exhibited extensive root rot. The organism consistently isolated from rotted roots that were plated onto water agar grew optimally at 37°C, produced inflated sporangia, intercalary antheridia, and oospores characteristic of Pythium aphanidermatum Edson (Fitzp.). Soil temperatures at the 10 cm depth during late summer range from 25 to 34°C. These high soil temperatures are known to be favorable to the pathogenic activity of P. aphanidermatum. To confirm Koch's postulates, 6-week-old artichoke seedlings were transplanted into potting soil that was artificially infested with the pathogen (20 oospores per g of soil). Oospores were obtained from 2-week-old V8 agar cultures of the fungus. Inoculated and noninoculated control plants were incubated at 28°C and the experiment was repeated once. All inoculated plants died within 2 weeks and P. aphanidermatum was recovered only from the rotted roots of inoculated plants. This is the first report of P. aphanidermatum causing root rot on artichoke.
Geminiviruses Infecting Tomato Crops in Nicaragua
Authors: Rojas Aldo , Kvarnheden Anders , Valkonen Jari P. T.
Published: May 2007

Geminiviruses transmitted by whiteflies are believed to be responsible for the devastating epidemic in tomato crops in Nicaragua, as well as in other Central American countries. Polymerase chain reaction with degenerate primers was used to amplify partial sequences of the geminivirus coat protein gene from samples of diseased tomato plants collected from the major tomato-growing areas of Nicaragua. The data indicated the presence of geminiviruses in all tested regions of the country. DNA sequence analysis and phylogenetic analysis of the amplified sequences showed that they corresponded to four different geminiviruses related to the other begomoviruses native to the Americas. One of the viruses, which was detected in three regions of Nicaragua, is probably Sinaloa tomato leaf curl virus. The sequences of two of the other detected viruses showed close relationships with several geminiviruses, including Tomato mottle virus, Tomato leaf crumple virus, and Sida golden mosaic virus, all of which previously have been reported from Central America. The fourth virus is closely related at sequence level to a tomato-infecting geminivirus from Honduras, putatively designated Tomato mild mottle virus. This virus seems to be different from the other known American begomoviruses because it groups separately in the phylogenetic analysis.
Evaluation of Tactics for Management of Thrips-Vectored Tomato spotted wilt virus in Tomato
Authors: Riley D. G. , Pappu H. R.
Published: May 2007

Two studies were conducted in Georgia during the spring of 1997 and 1998 to evaluate various management practices for reducing thrips and thrips-vectored Tomato spotted wilt virus (TSWV) in tomato. Populations of the two species of thrips responsible for transmitting TSWV in tomato fields, Frankliniella occidentalis and F. fusca, were determined using blossom and sticky trap samples. Management practices evaluated were host plant resistance, insecticide treatments, planting date, and light-reflective mulch. In both years, intensive insecticide treatment had the largest effect in reducing thrips and spotted wilt and increasing marketable yield, compared with host plant resistance and reflective mulch. The effect of planting date was consistent in that the later planting date resulted in higher incidence of TSWV, lower thrips numbers, and lower tomato yields, both in fruit quality and dollar value. Host plant resistance and reflective mulch significantly reduced thrips and TSWV. In both years, early planting on black plastic with an intensive insecticide treatment resulted in the highest yield.
Incidence of Latent Infection of Immature Peach Fruit byMonilinia fructicolaand Relationship to Brown Rot in Georgia
Authors: Emery K. M. , Michailides T. J. , Scherm H.
Published: May 2007

Peach fruit are most susceptible to infection by Monilinia fructicola during the preharvest ripening stage. Although various sources of inoculum for preharvest infection have been characterized, the role of latent infection of immature fruit in the carryover of M. fructicola from the spring (blossom blight phase) to the preharvest period (fruit rot phase) is unknown for the southeastern United States. From 1997 to 1999, immature peach fruit were collected at 14-day intervals from orchards in middle and northern Georgia. Fruit were surface disinfested and treated with paraquat (1997) or frozen overnight (1998 and 1999) to induce tissue senescence and activate latent infections. Across sites and years, the incidence of latent infection remained low until the final sampling date 7 to 12 days before harvest. The incidence of latent infection on the final sampling date ranged from 0 to 22.0% and correlated significantly with both the incidence of blossom blight earlier in the season (r = 0.9077, P = 0.0332) and the incidence of fruit rot at harvest (r = 0.9966, P = 0.0034). There also was a significant association between the incidence of latent infection at the onset of pit hardening (between 7 and 10 weeks before harvest) and subsequent fruit rot incidence (r = 0.9763, P = 0.0237). Weather variables (cumulative rainfall or rainfall frequency) alone did not correlate with fruit rot incidence (P > 0.05), whereas combined latent infection-rainfall variables did. The results suggest that latent infections can serve as a source of inoculum for subsequent fruit rot in peach orchards in Georgia. Despite its significant association with fruit rot incidence, the potential for using latent infection incidence as a biological indicator of disease risk at harvest may be limited; the assessment of latent infection during the fruit ripening stage (similar to the timing of the final sampling date in this study) would not provide sufficient lead time for preharvest disease management decisions, whereas an earlier assessment (e.g., at the onset of pit hardening) would require large sample sizes due to the low incidence of latent infection present during that period.
Effect of Irrigation and Soil Water Stress on Densities of Macrophomina phaseolina in Soil and Roots of Two Soybean Cultivars
Authors: Kendig S. R. , Rupe J. C. , Scott H. D.
Published: May 2007

The effects of irrigation and soil water stress on Macrophomina phaseolina microsclerotial (MS) densities in the soil and roots of soybean were studied in 1988, 1989, and 1990. Soybean cvs. Davis and Lloyd received irrigation until flowering (TAR2), after flowering (IAR2), full season (FSI), or not at all (NI). Soil water matric potentials at 15- and 30-cm depths were recorded throughout the growing season and used to schedule irrigation. Soil MS densities were determined at the beginning of each season. Root MS densities were determined periodically throughout the growing season. Microsclerotia were present in the roots of irrigated as well as nonirrigated soybean within 6 weeks after planting. By vegetative growth stage V13, these densities reached relatively stable levels in the NI and FSI treatments (2.23 to 2.35 and 1.35 to 1.63 log [microsclerotia per gram of dry root], respectively) through reproductive growth stage R6. After R6, irrigation was discontinued and root densities of microsclerotia increased in all treatments. Initiation (IAR2) or termination (TAR2) of irrigation at R2 resulted in significant changes in root MS densities, with densities reaching levels intermediate between those of FSI and NI treatments. Year to year differences in root colonization reflected differences in soil moisture due to rainfall. The rate of root colonization in response to soil moisture stress decreased with plant age. Root colonization was significantly greater in Davis than Lloyd at R5 and R8. This was reflected in a trend toward higher soil densities of M. phaseolina at planting in plots planted with Davis than in plots planted with Lloyd. Although no charcoal rot symptoms in the plant were observed in this study, these results indicated that water management can limit, but not prevent, colonization of soybean by M. phaseolina, that cultivars differ in colonization, and that these differences may affect soil densities of the fungus.
Assessment of Virulence of Acremonium cucurbitacearum and Monosporascus cannonballus on Cucumis melo
Authors: Bruton B. D. , Garcia-Jimenez J. , Armengol J. , Popham T. W.
Published: May 2007

Assessment of plant response to inoculation with soilborne pathogens is essential for evaluation of fungal virulence. Combined plant responses (damage to hypocotyl, root-stem junction, primary root, secondary roots, and reduction in leaf area) used to derive a disease severity index (DSI) provided a functional assessment of both plant damage and pathogen virulence. Spanish isolates of Acremonium cucurbitacearum ranged from virulent to highly virulent on muskmelon cv. Magnum 45, whereas isolates from the Lower Rio Grande Valley (LRGV) of Texas ranged from weakly virulent to moderately virulent. Spanish isolates of Monosporascus cannonballus ranged from nonpathogenic to weakly virulent, whereas LRGV isolates ranged from weakly virulent to moderately virulent. Regression analysis of multiple inoculum densities established that CFU per gram of soil of 5, 10, 20, and 40 for M. cannonballus and 0.1 × 104, 1 × 104, 2 ×104, and 3 × 104 for A. cucurbitacearum, respectively, were adequate for virulence assessment of isolates of either fungus in greenhouse tests on seedlings. Seed planting depth had a significant effect on DSI. The 4-cm depth generally had smaller standard errors of the mean disease rating, indicating greater precision in determining isolate virulence.
First Report of Pre- and Postemergence Damping-off of Cowpea Caused by Pythium ultimum in South Africa
Authors: Aveling T. A. S. , Adandonon A.
Published: May 2007

During a disease survey of cowpea (Vigna unguiculata (L.) Walp.) in Southern Africa in 1999, a major problem recorded by small-holder rural farmers in areas with wet soil types was reduced seedling emergence. Nongerminated, diseased seeds in these fields were either a brown blotchy color or had a soft rot and disintegrated upon touch. Germinated seedlings failing to emerge above the soil line were characterized by water-soaked lesions girdling the hypocotyl. Emerged seedlings had necrotic taproots and few lateral roots. Infected hypocotyls above the soil line had light brown lesions, and seedlings showed symptoms of wilting. Diseased seeds and seedlings were collected, surface-sterilized, plated on 2% water agar, and Pythium ultimum was isolated. Identification was based on characteristics given in van der Plaats-Niterink (1). Sterile soilbased compost, infested by mixing with P. ultimum mycelia (10 CFU/g of compost), was used to fill 104-cell plastic seedling trays (40 × 28 × 3.5 cm). A single cowpea seed was planted at a depth of 2 cm in each cell, and trays were maintained in a greenhouse at approximately 20°C. Seeds and seedlings showed symptoms identical to those in the field 10 days after planting, and the pathogen was successfully reisolated. Seedlings in noninoculated compost remained symptomless. This is the first report of P. ultimum on cowpea in South Africa.

Reference: (1) A. J. van der Plaats-Niterink. Monograph of the Genus Pythium. Centraalbureau voor Schimmelcultures, Baarn, 1981.
First Report of Bean common mosaic necrotic virus Infecting Bean Plants in Aguascalientes and Veracruz, Mexico
Authors: Flores-Estévez N. , Silva-Rosales L. , Acosta-Gallegos J. A.
Published: May 2007

Bean common mosaic necrosis virus (BCMNV) is a pathogen of Phaseolus vulgaris L. BCMNV was previously classified in serogroup A (for necrotic strains) of the Bean common mosaic virus (BCMV) subgroup; serogroup B included non-necrotic strains of BCMV. Both serogroups are currently classified as two different species in the BCMV subgroup of the Poytvirus genus; strains of either species will produce mosaic symptoms and, in the presence of hypersensitive I gene, necrosis in bean plants (1). Prior to this classification, BCMV was reported in Mexico by the presence of mosaic and necrotic symptoms (2). To investigate the presence of BCMNV in Mexico, samples were collected in two of the main bean producing states. The total extracted RNA was used for reverse transcription polymerase chain reaction using primers complementary to the middle portion of the NIa gene (5') and the 3' UTR of the NL3 Michigan isolate (accession number U19287). Two cDNA segments of 2 and 3 kb were obtained from infected plants from the state of Aguascalientes, in the highlands of central Mexico, and from the state of Veracruz, in the lowlands of the Gulf of Mexico, respectively. The cDNAs were cloned and sequenced. Alignment analysis of these sequences with the NL3 strain of BCMNV showed a similarity of 96.4 and 96.7%, respectively. The similarity between the Aguascalientes (accession number AJ01265) and Veracruz isolates was 99.6%, indicating that both are variants of the same species. On the other hand, alignment analysis of these isolates with some published BCMV strain sequences (i.e., accession numbers L15332 and U55315) displayed low similarities of 52.9 and 64.4%, respectively. These comparisons indicate that the Aguascalientes and Veracruz viral isolates belong to the BCMNV species and is the causal agent of mosaic and necrosis observed on the bean plants in those states.

References: (1) C. W. Collmer et al. Mol. Plant-Microbe Interact. 9:758, 1996. (2) E. Jimenez-García. SARH. Mexico. D. F. pp: 3–4, 1994.
Occurrence of Puccinia xanthii on Sunflower in South Africa
Authors: Pretorius Z. A. , van Wyk P. S. , Kriel W. M.
Published: May 2007

A severe outbreak of a foliar disease occurred on ornamental sunflower (Helianthus annuus L. cv. Tyao) cultivated under plastic protection near Potchefstroom in the North West Province during February 2000. According to previous descriptions of host range, symptoms, and spore morphology, the pathogen was identified as the microcyclic rust fungus, Puccinia xanthii Schwein. (2–4). Telia, reaching 9 mm in diameter and often coalescing to form larger lesions associated with chlorosis, occurred on the lower surface of leaves. Symptoms were first observed at the V-12 growth stage when approximately 40% of leaves displayed lesions. The disease subsequently spread to younger plants (V-2 stage) where an incidence of 100% was recorded. Severity estimates regularly reached 50% leaf area affected. The primary source of inoculum was thought to be nearby rust-infected Xanthium strumarium sensu lato (burweed or cocklebur) plants, a known host for P. xanthii (2,4). Infection studies were carried out on 3-week-old sunflower plants using a mini settling tower supporting an inverted water agar plate containing leaf disks with P. xanthii telia (2) obtained from either sunflower or burweed. Plants covered with a settling tower were kept in the dark in a dew chamber for 48 h. Microscopic examination of inoculum from both sources confirmed germination of teliospores and formation of basidiospores. Test entries had similar disease reactions regardless of whether inocula were collected from H. annuus or X. strumarium. Fleck symptoms were visible on the hybrids SNK 77 and Orit 5 days after placing plants in the dew chamber. On these entries, telia gradually increased in size, indicating susceptibility to P. xanthii. Furthermore, those leaves receiving high inoculum dosages were desiccated 11 days after inoculation. Hybrids Hysun 333 and CRN 1470 and the male sterility maintainer lines DC 4 and RK 74 produced resistant reactions. Hyperplasia of stem and petiole tissue was observed on certain Orit, DC 4, and CRN 1470 plants. Susceptibility of burweed, a common and widespread annual weed in southern Africa (1), to a sunflower isolate of P. xanthii, was also confirmed. Depending on the formation of teliospores, the identity of the causal organism was verified in all inoculation studies. P. xanthii damage on sunflower has not been reported from South Africa. However, the disease has now become economically important as severe foliar lesions rendered plants unacceptable for the ornamental sunflower market.

References: (1) C. Bromilow. 1995. Problem Plants of South Africa. Briza Publications, Pretoria, South Africa. (2) L. Morin et al. Can. J. Bot. 71:959, 1993. (3) L. Morin et al. Mycol. Res. 96:661, 1992. (4) J. Parmelee. Can. J. Bot. 47:1391, 1969.
Virulence of Botryosphaeria dothidea and Botryosphaeria obtusa on Apple and Management of Stem Cankers with Fungicides
Authors: Brown-Rytlewski Diane E. , McManus Patricia S.
Published: May 2007

The virulence of isolates of Botryosphaeria dothidea and B. obtusa was compared on apple fruit, trunks of 2-year-old apple trees, and twigs of mature apple trees. In general, B. dothideaisolates were more virulent than B. obtusa isolates. There was no correlation between virulence on fruit and virulence on 2-year-old trees. Several compounds were tested as topical wound treatments to control stem cankers caused by B. dothidea and B. obtusa. Benomyl, kresoxim-methyl, and trifloxystrobin, when applied at rates recommended for foliar application, consistently reduced the incidence and size of cankers compared with the water control. Clove oil, garlic extract, and neem oil did not reduce the incidence and size of cankers compared with the water control. Kresoxim-methyl was also effective when applied with an air-blast sprayer, despite incomplete spray coverage. Although fungicides reduced external canker symptoms, B. dothidea and B. obtusa were frequently isolated from xylem tissue, suggesting that fungicides might not provide long-term control of these pathogens.
First Report of Powdery Mildew on Heath Aster Caused by Erysiphe cichoracearum in Argentina
Authors: Wolcan S. , Ronco L.
Published: May 2007

In 1995, powdery mildew was observed on commercial greenhousegrown Aster ericoides L. from La Plata, Buenos Aires Province. The disease affected about 95% of the growers. Mildew first appeared as white circular patches on the adaxial surface of leaves. As disease progressed, the abaxial surface of leaves, petioles, stems, and calyces were covered by cottony masses of mycelium and conidia, and basal leaves later wilted and died. Young plants (4 to 5 leaves) through flowering plants were affected. Conidia were ovoid-cylindrical, often slightly constricted at the ends, and were produced in chains on unbranched conidiophores. Conidia lacked fibrosin bodies and ranged from 30 to 41 μm × 10 to 19 μm. Long unbranched germ tubes were formed from the ends of conidia. The morphological characteristics of the fungus fit those described for Erysiphe cichoracearum DC (1). In addition, the perfect stage was found on older tissues. Subglobose, dark brown cleistothecia (105 to 210 μm in diameter) with a basal ring of myceloid appendages were observed. Cleistothecia contained multiple ellipsoid asci (48 to 69 μm × 30 to 37 μm) with two hyaline, one-celled, ellipsoid ascospores (22 to 26 μm × 11 to 15 μm). Pathogenicity was tested by pressing diseased leaves onto healthy leaves of aster cv. Sunset and incubating plants in humidity chambers for 48 h. The powdery mildew that developed was morphologically identical to the original isolate. This is the first report of E. cichoracearum on heath aster in Argentina.

Reference: (1) H. J. Boesewinkel. Bot. Rev. 46:167, 1980.
Occurrence of Maize rayado fino virus in Maize in Argentina
Authors: Giménez-Pecci M. P. , Oliveira E. , Resende R. , Borgogno C. , Nome C. F. , Laguna I. G.
Published: May 2007

Symptoms of fine chlorotic stipple-striping of the veins, chlorosis, numerous dots and stripes, formation of holes in the leaf blade, and ears reduced in size, bearing few grains, were observed in maize crops in Tafí del Valle (Tucumán Province), Orán, El Galpón (Salta Province), Tilcara and Yaví (Jujuy Province), the subtropical area of northwest Argentina where the leafhopper vector Dalbulus maidis (DeLong & Wolcott) is present. Maize rayado fino virus (MRFV) was detected in these samples by a positive reaction in double antibody sandwich-enzyme-linked immunosorbent assay (DAS-ELISA) using an AGDIA kit. Electron microscopy revealed abundant isometric particles about 30 nm in diameter in the cytoplasm and vacuoles of phloem cells and xylem parenchyma cells. The virus was also detected by reverse transcription polymerase chain reaction (RT-PCR) using a primer pair MRFV-09/MRFV-10. Primers and PCR conditions were as previously described (1). Virus amplification was observed only in samples from symptomatic plants. In 1981 (2), the presence of MRFV in Argentina was revealed by serological assay in plants from temperate central areas. No further reports were released since then. This is the first evidence of MRFV in subtropical areas of Argentina and identification of the virus by combining DAS-ELISA, particle size, relation with plant tissues, and RTPCR.

References: (1) R. W. Hammond et al. J. Gen. Virol. 78:3153, 1997. (2) S. F. Nome et al. RIA XIX:257, 1984.
A Severe Outbreak of Tobacco mosaic virus in Georgia's Flue-Cured Tobacco
Authors: Pappu H. R. , Bertrand P. F. , Moore J. M.
Published: May 2007

During the 2000 growing season, tobacco plants showing blotching of the leaves with light and dark green areas suggestive of Tobacco mosaic virus (TMV) infection were observed in several counties in Georgia. Symptomatic plants appeared in the field within 4 weeks after transplanting. The incidence in individual fields was as high as 100%. A survey was conducted in several tobacco-growing counties, and the presence of TMV was verified by enzyme-linked immunosorbent assay (ELISA). Symptomatic plants were collected from the following 20 counties: Appling, Bacon, Berrien, Coffee, Colquitt, Cook, Echols, Evans, Grady, Irwin, Jeff Davis, Lanier, Lowndes, Montgomery, Pierce, Tattnall, Tift, Toombs, Ware, and Wayne. Of the 79 samples tested by ELISA, TMV was found to be present in 76 samples. This high degree of incidence of TMV in Georgia's tobacco has not been observed in the past. Although the specific reasons are not clear, all severe cases of TMV were observed in two varieties, NC71 and NC72, or plants of other varieties out of beds or plant houses that held these two varieties and were clipped with the same mower. While TMV and Potato virus Y (PVY) were found most prevalent in Georgia's flue-cured tobacco in 1999 (2), none of the plants tested were positive for PVY in 2000. Cucumber mosaic virus was reported to be more common in Florida during the last 3 years (1). The severe outbreak of TMV highlights the importance of preventive measures such as observing sound sanitation practices.

References: (1) T. A. Kucharek et al. Plant Dis. 82:1172, 1998; (2) H. R. Pappu et al. Plant Dis. 84:201, 2000.
First Report of Sclerotium rolfsii on Jerusalem Cherry (Solanum pseudocapsicum) in Europe
Authors: Garibaldi A. , Minuto A. , Gullino M. L.
Published: May 2007

Jerusalem cherry (Solanum pseudocapsicum) has recently become popular as a potted ornamental plant in Italy. During the summer of 1999, a sudden wilt of 60-day-old plants was observed in the Albenga region (Northern Italy), an area of intensive floriculture. Initial symptoms included stem necrosis at the soil line and yellowing and tan discoloration of leaves. As stem necrosis progressed, infected plants wilted and died. Necrotic tissues were covered with whitish mycelium that differentiated into reddish brown, spherical (1 to 2 mm diameter) sclerotia. Sclerotium rolfsii was consistently recovered from the surface of symptomatic stem sections that were disinfected for 1 min in 1% NaOCl and then plated on potato-dextrose agar (PDA) amended with 100 ppm streptomycin sulfate. Pathogenicity of three S. rolfsii isolates was confirmed by inoculating 90-day-old S. pseudocapsicum plants grown in pots. Inoculum consisted of mycelium and sclerotia of the pathogen placed on the soil surface around the base of each plant. Noninoculated plants served as controls. All plants were kept in a growth chamber at 18 to 28°C and RH > 85%. Inoculated plants developed symptoms within 7 days, while control plants remained symptomless. Sclerotia developed on infected tissues and S. rolfsii was reisolated from symptomatic tissues. The disease has been observed in the United States (1), but this is the first report of stem blight of S. pseudocapsicum caused by S. rolfsii in Europe.

Reference: (1) S. A. Alfieri, Jr., K. R. Langdon, C. Wehlburg, and J. W. Kimbrough, J. W. Index Plant Dis. Florida Bull. 11:215, 1984.
Estimating Yield and Economic Loss from Constriction Canker of Peach
Authors: Lalancette Norman , Polk Dean F.
Published: May 2007

Constriction cankers, caused by Phomopsis amygdali, girdle and kill fruiting twigs which results in a direct crop loss. To quantitatively determine this loss from 1996 to 1998, the number of fruit lost per infected shoot was estimated as a function of disease incidence in 21 severely infected orchards in New Jersey. For each cultivar in 1997 and 1998, the distribution of fruit sizes at harvest and prices at shipping were used to calculate total crop value for typical expected yields. Economic loss was then calculated from yield loss and crop value estimates. The overall percent yield loss mean across all sites and cultivars, unadjusted for fruit remaining on infected shoots, was 22.2, 30.7, and 23.7% for 1996, 1997, and 1998, respectively. The frequency of these losses were not normally distributed, and the nonparametric Friedman test indicated that yield loss was significantly different among years. Assuming the remaining fruit on infected shoots were harvested, yield losses for 1997 and 1998 were 28.5 and 21.0%, which translated into average economic losses of $4,009 and 2,803/ha, respectively, for an expected yield level of 14,010 kg/ha. These loss values justify control measures for management of constriction canker in severely infected orchards.
A PCR-based Assay for Detection of Alternaria radicina on Carrot Seed
Authors: Pryor B. M. , Gilbertson R. L.
Published: May 2007

A pair of polymerase chain reaction (PCR) primers was developed based upon the sequence of a cloned random amplified polymorphic DNA (RAPD) fragment of Alternaria radicina, and a PCR-based seed assay was developed for the detection of A. radicina from infested carrot seed. The seed assay involved a 5-day incubation step, in which seed was maintained under high humidity conditions in order to increase fungal biomass. Seed was then incubated with lysis buffer, extracted with phenol-chloroform, and DNA was recovered using a silica matrix. PCR amplification of the target A. radicina DNA sequence was enhanced by the addition of skim milk to the PCR reaction mixture. With this PCR-based seed assay, A. radicina was detected from carrot seed lots with natural infestation rates as low as 0.3%. In seed lots prepared by mixing known amounts of A. radicina-infested seed with noninfested seed, this assay allowed for the detection of the pathogen from lots with infestation rates as low as 0.1%.
Incidence of Stenocarpella maydis Ear Rot of Corn Under Crop Rotation Systems
Authors: Flett B. C. , McLaren N. W. , Wehner F. C.
Published: May 2007

The efficacy of crop rotation in reducing corn ear rot caused by Stenocarpella maydis in reduced and conventional tillage systems was determined over five and four seasons, respectively, at two sites in South Africa. Stenocarpella ear rot and S. maydis was isolated from kernels more frequently in monoculture corn and crop rotation where corn was planted for two consecutive seasons than where monoculture corn was interrupted by a rotation crop. Surface stubble mass, and consequently inoculum pressure, were affected similarly by crop rotation. Positive linear relationships were recorded between Stenocarpella ear rot incidence, surface stubble mass, and pycnidial counts. Wheat, soybean, and peanut were the most effective, and sunflower the least effective, rotation crops for reducing S. maydis ear rot.
Leaf Spot Disease of Broad Bean Caused by Alternaria tenuissima in Japan
Authors: Honda Y. , Rahman M. Z. , Islam S. Z. , Muroguchi N.
Published: May 2007

In April 1999, a leaf spot of broad bean (Vicia faba L.) was observed in commercial fields in Shimane prefecture of Western Japan. Lesions were concentric and brown in color. Older leaves were particularly affected. In later stages of the disease, plants defoliated as leaves blighted from margin to the center. Isolation was made from infected leaf tissue. The isolated fungus produced conidia on V8 medium (2) either in dark or under continuous irradiation of near ultraviolet radiation (NUV) from BLB fluorescent lamps. Conidial chains were unbranched or rarely formed a few lateral branches with a few conidia. The conidia of the fungus grown under continuous NUV were dark and smoothly tapered into the apical beak, and each conidium had a conspicuously thickened primary septum with a constriction of the conidial wall and often a darker median transverse septum. The conidia measured 21.2 to 45.5 μm (mean = 32.9 μm) × 7.3 to 17.7 μm (mean = 11.4 μm ) on V8 medium. Conidia produced on leaves and stem collected from field were similar in size and appearance. The fungus was identified as Alternaria tenuissima based on its cultural and morphological characteristics (2). An isolate was also sent to CABI Bioscience Identification Services (Egham, UK), which also identified the fungus as A. tenuissima. A conidial suspension (107 spores/ml) was prepared and used to inoculate detached leaves and intact plants of broad bean. Intact plants were inoculated by spaying with spore suspension and covered with polyethylene bags for maintaining high humidity. Detached leaves in moist petri dishes were inoculated with drops of spore suspension. Symptom developed on both detached and intact leaves 3 to 4 days after inoculation. Reisolating the pathogen from infected leaves completed Koch's postulates. In June 2000, the leaf spot was observed in all 15 fields surveyed in other areas of Shimane prefecture. In some fields, plants were defoliated and stems and pods were also infected. Isolates of A. tenuissima also were obtained from those fields. This pathogen has been isolated from other hosts in Japan (1). This is the first report of A. tenuissima on broad bean in Japan.

References: (1) Anonymous. 2000. Common Names of Plant Diseases in Japan. The Phytopathological Society of Japan, Tokyo. (2) E. G. Simmon. Mycotaxon 37:79–119, 1990.
First Report of Soybean Rust (Phakopsora pachyrhizi) in Nigeria
Authors: Akinsanmi O. A. , Ladipo J. L. , Oyekan P. O.
Published: May 2007

Rust caused by Phakopsora pachyrhizi H. & P. Sydow was observed for the first time on soybean (Glycine max [L.] Merr.) in Nigeria during the 1999 main soybean growing season. The disease was first noticed on soybean farms in Oniyo and neighboring villages located about 20 km west of Ogbomoso (Long. 4° 02′ E and Lat. 8° 06′ N), Oyo State, Nigeria. The area falls under the moist savanna vegetation with a bimodal rainfall pattern (from April to July, September to November) and an annual mean rainfall of 1,370 mm. Commercial cultivation of soybean by farmers in the area started in 1986. A similar disease outbreak in 1999 on soybean in Benue state, the major area of soybean production in Nigeria, could not be confirmed to be rust. In the Oniyo area, soybean is commonly grown as an early season crop usually planted between March and April in small plots to produce seeds for the main crop, normally planted in July. Rust was not observed on the early season soybean crop grown in the area in 1999. Symptoms were first observed on leaves close to the ground in September 1999 as chlorotic spots, which progressed to reddish brown lesions, then uredia. The symptoms appeared further up the plant until all the leaves were infected. Pimple-like uredia observed in the lesions were more pronounced and numerous on the lower surface of the leaves than on the upper leaf surface. Uredia were noted to cluster together in clumps (1). The urediospores released from a central ostiole in the uredia were hyaline and oblong, 17 μm wide (15 to 18 μm) and 22 μm long (19 to 25 μm). Premature defoliation occurred on infected plants. Seed weight of TGX 1485-1D, TGX 1448-2E, and TGX 1440-1E was reduced by 28, 52, and 49%, respectively. Disease severity was higher on the medium maturing cultivars and all those that were planted late.

Reference: (1) J. B. Sinclair. 1983. Compendium of Soybean Diseases, 2nd ed. The American Phytopathological Society, St. Paul, MN.