bluuebunny/crossref_metadata_2025 huggingface dataset:
First Report of the Reniform Nematode Rotylenchulus reniformis on Cotton in Virginia
Authors: Eisenback J. D. , Hopkins Nina , Phipps P. M.
Published: May 2007

In Virginia during September 2002, the reniform nematode, Rotylenchulus reniformis Linford and Oliveira (1), was found for the first time following a grower's concern about poor growth and yield of cotton (Gossypium hirsutum L.) cv. Fiber Max 989BR. The infested field was planted with cotton each year for the last eight growing seasons. The field was located on Hall Road in Southampton County, Virginia at coordinates 77°16′28.8926″W, 36°37′10.6428″N near the town of Branchville. The soil was loamy sand, which is typical of sandy textured soils in the region. Rainfall from May to September at a nearby weather station was nearly 50% below normal, which may have contributed to the suppression of plant growth. The vermiform nematodes were extracted with a North Carolina State University model semiautomatic elutriator and centrifugation/sugar flotation. Populations were 30 to 150 per 500 cm3 of soil in areas with noticeable stunting. Cultures were established on cotton cv. Delta Pine 64 and tomato (Lycopersicon esculentum Mill. cv. Rutgers) and were maintained in a greenhouse. Reproduction was moderate on cotton and high on tomato. Identifications were based on morphology and measurements of vermiform females and males: immature female length (L) = 407 ± 22 (376 to 418) μm, stylet L = 18.5+1.7 (17.0 to 21.3) μm; and male L = 351 ± 17 (339 to 367) μm. Voucher specimens were placed and are maintained in the Virginia Tech Nematode Collection.

Reference: (1) M. B. Linford and J. M. Oliveira. Proc. Helminthol. Soc. Wash. 7:35, 1940.
AFLP Analysis of Phytophthora cactorum Isolates from Strawberry and Other Hosts: Implications for Identifying the Primary Source of Inoculum
Authors: Huang H. , Jeffers S. N. , Layne D. R. , Schnabel G.
Published: May 2007

Forty-seven isolates of Phytophthora cactorum from North America and Germany were subjected to amplified fragment length polymorphism (AFLP) analysis to investigate genetic diversity among isolates and geographical populations; 42 isolates were recovered from cultivated strawberry plants (Fragaria × ananassa), and five isolates had been recovered from plants in four other genera (Syringa, Abies, Malus, and Panax). From all isolates evaluated, 226 out of 264 markers (85.6%) were polymorphic and provided 42 unique AFLP profiles. The genetic diversity among isolates of P. cactorum from strawberry was greater than that among isolates from the other hosts. Isolates collected during recent crown rot epidemics in strawberry fields in South Carolina were genetically diverse and scattered among isolates from other geographical areas in an unweighted pair-group mean analysis (UPGMA) dendrogram. Isolates collected during recent crown rot epidemics in North Carolina also were genetically diverse, but most isolates clustered with isolates collected in 1997 from Florida strawberry fields. These data suggest that recent outbreaks of Phytophthora crown rot in the southeastern United States resulted from use of transplants already infected or infested with P. cactorum rather than from endemic populations of this pathogen, which would affect recommendations for disease management.
Soybean Cultivar and Foliar Fungicide Effects on Phomopsis sp. Seed Infection
Authors: Wrather J. A. , Shannon J. G. , Stevens W. E. , Sleper D. A. , Arelli A. P.
Published: May 2007

Phomopsis seed decay (PSD) caused by Phomopsis spp. can be severe when soybean seed producers in the southern United States use the early soybean production system (ESPS) to avoid late-July through early-September drought damage to soybean. The usefulness of this production system would be greater if developing seed could be protected from PSD by foliar application of fungicides or by planting Phomopsis spp.-resistant soybean lines. The objective of this research was to determine the affects of the fungicides benomyl and azoxystrobin applied to soybean, at various times, on percent Phomopsis spp. infection of seed in Asgrow 3834, a PSD-susceptible cultivar, and SS93-6012, a PSD-resistant soybean line, planted in mid-April. The percent Phomopsis spp. infection of Asgrow 3834 seed averaged over years was significantly less for the benomyl (0.28 kg a.i. ha-1) applied at R3 + R5 treatment (48.6% seed infection) than the control (52.8% seed infection) and significantly greater for the azoxystrobin (0.17 kg a.i. ha-1) applied at R3 + R5 treatment (61.6% seed infection) than the control (52.8% seed infection). This method of managing PSD will not be acceptable to soybean growers. The percent of Phomopsis spp. infection of Asgrow 3834 seed averaged over years (52.8% seed infection) was significantly greater than for line SS93-6012 (2.8% seed infection). There were no differences in percent Phomopsis spp. infection of SS93-6012 seed between the control (2.8% seed infection) and benomyl treatment (4.0% seed infection). The most effective method for PSD management was to plant a resistant soybean line. Line SS93-6012 will be useful in breeding programs focused on developing high yielding PSD-resistant cultivars.
First Report of Southern Blight of Ruellia brittoniana Caused by Sclerotium rolfsii in Louisiana
Authors: Holcomb G. E.
Published: May 2007

Ruellia brittoniana, Mexican petunia, is an herbaceous flowering perennial grown in hardiness zones 8 to 10 in the southern and western United States. Popular dwarf forms with flower colors of white, pink, and blue are used as ground covers and borders. In April of 2003, root and stem rot that caused plant death was observed on cv. Katie (dwarf form, pink flowers) at a wholesale nursery in southern Louisiana. Plants were growing in a vermiculite and sand mix. The grower had purchased the plants from an out-of-state source, and approximately one-half of 1,440 plants were dead or dying. Symptoms included wilt, basal stem rot, and root rot. Peripheral roots were covered with a white mycelial layer that contained white sclerotial initials and small, brown sclerotia. Fungal isolates from infected roots grown on potato dextrose agar (PDA) produced white mycelia and 1- to 2-mm-diameter dark brown sclerotia. Sclerotia were nearly round with smooth surfaces and distributed over the entire colony. Isolates were identified as Sclerotium rolfsii on the basis of mycelial characteristics and color, size, and distribution of sclerotia. Two-month-old seedlings (6 to 10 cm high) of R. brittoniana, from seed of cv. Katie, were used in pathogenicity tests. Inoculum was grown in 10-cm-diameter plastic, culture dishes on PDA medium. Blended inoculum was prepared from a single 1-week-old culture that was composed of mycelia and sclerotia and blended 4 to 6 s at high speed in 100 ml of distilled water. In test one, 5 ml of inoculum was placed at the base of each inoculated plant. In test two, a single 5-mm-diameter agar plug with mycelium plus four sclerotia was placed beside plant stems near soil line. In test three, 5 ml of blended inoculum was dripped on exposed roots after plants were removed from pots. In test four, exposed plant roots were dipped in the blended inoculum. Each test contained 10 inoculated plants, and 10 noninoculated plants served as controls. All plants were placed in a dew chamber maintained at 28°C for 2 days and then returned to a greenhouse to observe development of symptoms and signs of disease. In tests one and two, basal stem rot and wilt developed on inoculated plants after 2 days and after 5 to 8 days all were dead. Inoculated plants from tests three and four were alive 4 months after inoculation, but were showing symptoms including leaf yellowing and drop, moderate to severe root rot, and some plants had begun to show white mycelia and white sclerotial initials on peripheral roots by January 2004. All noninoculated plants remained healthy and S. rolfsii was reisolated from infected plants in each test. To my knowledge, this is the first report of S. rolfsii causing disease on R. brittoniana.
Field Isolates of Streptomyces Differ in Pathogenicity and Virulence on Radish
Authors: Wanner Leslie A.
Published: May 2007

Common scab is a significant disease of potato, and affects root and tuber crops worldwide. Streptomycetes, a diverse group of soil-inhabiting gram-positive bacteria, cause common scab. To better understand the basis for variability in disease symptoms seen in field situations, strep-tomycetes were isolated from scabby potato plants. Isolates differed in morphology and pigmentation. Isolates were evaluated for pathogenicity and virulence in radish. Scab lesions varied in appearance and severity. Disease symptoms also included plant stunting, wilting, necrosis, and death. Some pathogenic isolates were missing genes from the putative pathogenicity island (PAI); several lacked the nec1 gene, and one was missing the txtA gene encoding thaxtomin biosynthesis, the most reliable pathogenicity determinant. Studies of disease severity over 5 logs initial inoculum density showed that there is a threshold inoculum density for disease. Disease severity increased with inoculum density over three logs, then reached a maximum, which is characteristic of individual Streptomyces strains. Lesion severity was not correlated with presence of melanin, the nec1 gene, or whether an isolate reduced seedling emergence or plant survival. Differences in disease symptoms and severity combined with absence of known pathogenicity determinants (txtA) or factors (nec1) suggest that there may be pathogenicity factors in addition to thaxtomin.
Assessment of Resistance to Witches'-Broom Disease in Clonal and Segregating Populations of Theobroma cacao
Authors: Surujdeo-Maharaj S. , Umaharan P. , Butler D. R.
Published: May 2007

Fourteen clonal genotypes of cacao (Theobroma cacao) and their open-pollinated progenies were tested for their resistance to witches'-broom disease (Crinipellis perniciosa) using an agar-droplet inoculation method in separate, replicated greenhouse experiments. Nine measures of resistance were evaluated for precision, ability to discriminate between levels for resistance, and their correlation to field resistance. Correlations among the various measures of resistance were also ascertained. Data were re-examined to determine the accuracy and precision associated with individual plant measurement as well as the optimum sample size to assess segregating populations for resistance. The agar-droplet method was able to effectively discriminate various levels of resistance. Incubation period provided a precise, sensitive, valid, and heritable measure of resistance to C. perniciosa. Furthermore, incubation period was highly correlated with broom size and moderately correlated with broom frequency, two epidemiologically important components of resistance. The study also shows that 25 to 30 open-pollinated progeny are sufficient to provide a good estimate of a parent's resistance. The implications of the findings for identifying resistance among cacao germplasm collections as well as within segregating populations for resistance breeding are discussed.
A Comparison of Methods Used to Estimate the Maturity and Release of Ascospores of Venturia inaequalis
Authors: Gadoury David M. , Seem Robert C. , MacHardy William E. , Wilcox Wayne F. , Rosenberger David A. , Stensvand Arne
Published: May 2007

Maturation and release of ascospores of Venturia inaequalis were assessed at Geneva and Highland, NY, and at Durham, NH, by microscopic examination of crushed pseudothecia excised from infected apple leaves that were collected weekly from orchards (squash mounts) in 14 siteyear combinations. Airborne ascospore dose was monitored at each location in each year of the study by volumetric spore traps. Additional laboratory assessments were made at Geneva to quantify release from infected leaf segments upon wetting (discharge tests). Finally, ascospore maturity was estimated for each location using a degree-day model developed in an earlier study. Ascospore maturation and release determined by squash mounts and discharge tests lagged significantly behind cumulative ascospore release as measured by volumetric spore traps in the field. The mean date of 98% ascospore discharge as determined by squash mounts or discharge tests occurred from 23 to 28 days after the mean date on which 98% cumulative ascospore release had been detected by volumetric traps. In contrast, cumulative ascospore maturity estimated by the degree-day model was highly correlated (r2 = 0.82) with observed cumulative ascospore release as monitored by the volumetric traps. Although large differences between predicted maturity and observed discharge were common during the exponential phase of ascospore development, the date of 98% cumulative ascospore maturity predicted by the model was generally within 1 to 9 calendar days of the date of 98% cumulative ascospore recovery in the volumetric traps. Cumulative ascospore discharge as monitored by the volumetric traps always exceeded 98% at 600 degree days (base = 0°C) after green tip. Estimating the relative quantity of primary inoculum indirectly by means of a degree-day model was more closely aligned with observed ascospore release, as measured by volumetric traps, than actual assessments of ascospore maturity and discharge obtained through squash mounts and discharge tests. The degree-day model, therefore, may be a more accurate predictor of ascospore depletion than squash mounts or discharged tests, and has the added advantage that it can be widely applied to generate site-specific estimates of ascospore maturity for any location where daily temperature data are available.
Genetic Interactions Between Glycine max and Sclerotinia sclerotiorumUsing a Straw Inoculation Method
Authors: Auclair J. , Boland G. J. , Kohn L. M. , Rajcan I.
Published: May 2007

Genetic interactions for disease response between cultivars of Glycine max and isolates of Scle-rotinia sclerotiorum were evaluated in controlled-environment inoculations of five soybean cultivars with four genetically unique isolates of S. sclerotiorum. The objective of this study was to identify host-pathogen interactions using isolates of the pathogen which had different geographical and crop-wise distribution as well as a different DNA-based fingerprint. To do so, 4-week-old soybean plants were inoculated with individual isolates of S. sclerotiorum using a straw inoculation method. Inoculated plants were incubated for 48 h in continuous leaf wetness and rated for disease severity 1 and 2 weeks after inoculation. Significant differences in disease severity were detected among the soybean cultivars, and NK S08-80 consistently had the lowest disease severity among the five cultivars tested. No significant differences in disease severity were observed among pathogen isolates and no significant interactions were detected between soybean cultivars and pathogen isolates. These results suggest the following interpretations: (i) either the clonal genotype of the four pathogen isolates as determined by mycelial compatibility and DNA fingerprint was not associated with level of virulence on the five soybean cultivars or (ii) the soybean cultivars themselves were not capable of revealing any differences in virulence among isolates that would be related to their genetic fingerprint or regional distribution. The results of this study are consistent with the practice of considering different isolates of S. scle-rotiorum sampled from soybean in the same geographical region as equivalent for the evaluation of soybean cultivars for resistance to Sclerotinia stem rot.
Watermelon as a New Host of Pseudomonas viridiflava, Causal Agent of Leaf and Stem Necrosis, Discovered in Turkey
Authors: Mirik M. , Aysan Y. , Cetinkaya-Yildiz R. , Sahin F. , Saygili H.
Published: May 2007

Severe leaf and stem necrosis symptoms were observed on watermelon seedlings (Citrullus lanatus cv. Euroca) in Adana, Turkey during a warm and humid period in January 2004. Streak-plate isolations were made from leaf and stem lesions on King's medium B. A fluorescent, yellowish mucoid, gram-negative, and oxidase-, levan- and arginin dihydrolase-negative bacterium was consistently isolated from diseased plant samples. All seven representative strains isolated were pectolytic on potato slices and hypersensitive reaction positive on tobacco leaves. The result of LOPAT tests and morphology of the strains were different from Pseudomonas syringae pathovars. The strains produced acid from sorbitol, fructose, glucose, L (+) arabinose, D (+) xylose, D (-) mannitol, but not from D (+) sucrose, trehalose, maltose, melibiose, lactose, and D (-) arabinose. Utilization of D (-) tartrate was positive. Incubation was at 28°C, and the results of the tests were evaluated 7 days after inoculation. Fatty acid analysis (Ataturk University, Erzurum, Turkey) confirmed the bacterial strains as P. viridiflava with a similarity index of 83 to 86% (3). The strains were pathogenic on watermelon, melon, and tomato plants with needle inoculation of bacterial suspensions containing 108CFU ml-1 in a 0.85% saline. Water-soaking and stem necrosis symptoms were observed on the inoculated plants 5 to 7 days after inoculation. The bacterium was readily reisolated from inoculated plants and identified as strains of P. viridiflava, which has been previously reported as a pathogen of melon grown in Turkey (1) and Greece (2). To our knowledge, this is the first study demonstrating the occurrence and outbreak of leaf and stem necrosis disease caused by P. viridiflava on watermelon in the world.

References: (1) A. Aysan et al. Plant Pathol. 52:800, 2003. (2) D. E. Goumans and A. K. Chatzaki. Eur. J. Plant Pathol. 104:181, 1998. (3) J. D. Janse et al. Syst. Appl. Microbiol. 15:538, 1992.
First Report of Phytoplasma Infection in Hop Plants
Authors: Solarska E. , Kamińska M. , Śliwa H.
Published: May 2007

Disease symptoms of severe shoot proliferation resembling phytoplasmal disease symptoms were observed in early spring of 2003 in hop (Humulus lupulus L.) plant cvs. Magnum and Marynka that were grown in a commercial farm in Poland. Proliferation of shoots has not been previously reported in hop plants. To detect the presence of phytoplasmas in hops, young shoots from four symptomatic (two cultivars) and two symptomless (‘Magnum’) plants were assayed for phytoplasma 16S rDNA using polymerase chain reaction (PCR). In addition, leaf samples from healthy Catharanthus roseus plants and plants experimentally infected with the reference strains of aster yellows phytoplasma (AY1, group 16SrI-B) or apple proliferation phytoplasma (AP, group 16SrX-A) were included for comparison. Amplifications were performed using the universal phytoplasma primer pair P1/P7 in an initial assay, and universal primer pairs fA/rA (1), Pc399/P1694, or R16F2n/R16R2 (2) and group specific primer pair R16(I)F1/R16(I)R1 (3) in a nested reaction. Specific products were obtained in direct PCR with the universal primer pairs P1/P7 only for the control samples of the reference strains AY and AP. No visible product was amplified by the direct PCR from samples obtained from hops and healthy periwinkle plants. However, in nested PCR with primer pairs P1/P7 followed by primer pairs fA/rA, R16F2n/R16R2, Pc399/P1694, or R16(I)F1/R16(I)R1, specific DNA bands were observed from naturally infected hop plants (both four symptomatic and two symptomless) tested. No amplification products were observed from healthy periwinkle plants. The specificity of PCR products (obtained with universal R16F2n/R16R2 primer pair) was confirmed by restriction fragment length polymorphism (RFLP) analysis using AluI, MseI, HhaI, and RsaI for enzymatic digestion. RFLP patterns of these rDNA fragments for samples of naturally infected hops and for AY1 reference strain were similar and were characteristic of phytoplasma 16SrI-B subgroup. To our knowledge, this is the first evidence that hop shoot proliferation disease is associated with natural infection by phytoplasmas. Furthermore, detection of phytoplasma in asymptomatic hops underscores the need to fully elucidate the etiological role of this pathogen in the disease.

References: (1) U. Ahrens and E. Seemüller. Phytopathology 82:828, 1992. (2) I.-M. Lee et al. Phytopathology 83:834, 1993. (3) I.-M. Lee et al. Phytopathology 84:559, 1994.
First Report of Alfalfa mosaic virus in Lavandula officinalis
Authors: Martínez-Priego Ll. , Córdoba M. C. , Jordá C.
Published: May 2007

For several years, in ornamental nurseries in the Mediterranean area of Spain, stunting and yellow leaf spotting have been observed in young plants of Lavandula officinalis. Symptoms eventually disappeared as the plants matured. During the summer of 2003, the number of plantlets affected and the intensity of symptoms increased significantly. Symptomatic plants tested positive using enzyme-linked immunosorbent assay (ELISA) (Phyto-Diagnostics, INRA, France) for the presence of Alfalfa mosaic virus (AMV). ELISA results were verified using reverse transcription-polymerase chain reaction (RT-PCR). Total RNA extracts from symptomatic plants were analyzed using primers designed specifically for the coat protein region of AMV utilizing sequence data from GenBank Accession No. AF215664: AMVcoat-F: GT GGT GGG AAA GCT GGT AAA and AMVcoat-R: CAC CCA GTG GAG GTC AGC ATT. The thermocycling schedule was as follows: reverse transcriptase step at 50°C for 30 min, first PCR cycle at 94°C for 2 min, 35 cycles each of 30 s at 94°C, 30 s at 54°C, 30 s at 72°C, followed by a final extension at 72°C for 10 min. A 700-pb PCR product of the expected size was obtained from plants that were positive for AMV using ELISA. The two systems provide for rapid detection of AMV in L. officinalis. A regular screening program will assist in providing virus-free plants to ornamental nurseries. These results demonstrate the presence of AMV in L. officinalis. Alfalfa (Medicago sativa L.) is a typical source of AMV. However, because the nurseries where L. officinalis is grown are not in the vicinity of alfalfa fields, we suggest the source of the infection originated in the propagation material. AMV has currently been reported in L. officinalis only in Italy and France (1). To our knowledge, this is the first report of AMV in L. officinalis in Spain.

Reference: (1): A. Garibaldi et al. Ed. Edagricole-Edisioni Agricole della Calderini s.r.l., Bologna, 2000.
Reduced Sensitivity in Monilinia fructicola to Propiconazole in Georgia and Implications for Disease Management
Authors: Schnabel Guido , Bryson P. Karen , Bridges William C. , Brannen Phillip M.
Published: May 2007

Single-spore isolates of Monilinia fructicola were collected from commercial orchards in South Carolina and Georgia with prolonged past exposure to demethylation inhibitor (DMI) fungicides and from an orchard with no DMI history (baseline population). Sensitivity to propiconazole was determined using the concentration in agar media required to suppress radial growth of mycelium by 50% (EC50. Mean EC50 values from six South Carolina populations were not different from the baseline population (P < 0.05). Two of five populations from Georgia revealed (significantly higher mean EC50 values compared with the baseline population (P < 0.05). Isolates with high (AP5 and AP6) and low (DL71 and DL72) EC50 values were selected to determine disease incidence on peach fruit after protective or curative applications of propiconazole at 0.15 or 0.3 liter/ha (half and full label rate, respectively). Disease incidence was significantly greater on peaches inoculated with AP5 and AP6 after curative treatment with propiconazole at 0.15 liter/ha (P < 0.05). Following protective or curative treatments at 0.3 liter/ha, disease incidence was significantly greater for AP6 but not for AP5. These results suggest that a shift toward reduced sensitivity has developed in some M. fructicola populations from Georgia, and that isolates with reduced sensitivity to propiconazole are more difficult to control in the field. Field testing of DMI fungicides, captan, QoI fungicides, and fenhexamid in experimental orchards) indicated that the DMI fungicides are still among the most efficacious products for brown rot (control, and that new products containing QoI fungicides may be viable disease control alternatives or rotation partners.
First Report of White Mold Caused by Sclerotinia sclerotiorum on Thymus × citriodorus in Italy
Authors: Garibaldi A. , Minuto A. , Gullino M. L.
Published: May 2007

Thymus × citriodorus is well known for the citrus aroma released by its leaves and is grown as a potted plant in northern Italy. This species is widely used in gardens and landscapes and for culinary purposes. In the Liguria Region alone, 1.5 million plants are grown. In the winter of 2002, extensive chlorosis was observed on potted plants of Thymus × citriodorus cv. Silver Queen grown outdoors on commercial farms near Albenga. Initial symptoms included stem necrosis at the soil level and darkening of leaves. As stem necrosis progressed, infected plants wilted and died. Wilt, characterized by the presence of soft and watery tissues, occurred within a few days on young plants. Necrotic tissues became covered with whitish mycelium that produced dark sclerotia. Sclerotinia sclerotiorum (Lib.) de Bary (1) was consistently recovered from infected stem pieces of Thymus × citriodorus. The diseased stem tissue was disinfested for 1 min in 1% NaOCl and plated on potato dextrose agar (PDA) amended with 100 ppm of streptomycin sulfate. Sclerotia produced on PDA were ellipsoid and measured 5.2 to 4.4 × 2.1 to 1.5 mm (average 3.5 × 3.0 mm). Pathogenicity of three isolates obtained from infected plants was confirmed by inoculating 30-day-old plants grown in 14-cm-diameter pots in a screenhouse. Inoculum that consisted of wheat kernels infested with mycelium and sclerotia of each isolate was placed on the soil surface around the base of each of 10 plants. Noninoculated plants served as controls. The inoculation trial was repeated once. All plants were kept at temperatures ranging between 5 and 26°C and watered as needed. Inoculated plants developed symptoms of leaf yellowing within 13 days, soon followed by the appearance of white mycelium, and eventually wilted. Control plants remained symptomless. White mycelium and sclerotia developed on infected tissues and S. sclerotiorum was reisolated from inoculated plants. To our knowledge, this is the first report of white mold of Thymus × citriodorus caused by S. sclerotiorum. The economic importance of this disease for the crop can be considered low.

Reference: (1) N. F. Buchwald. Den. Kgl. Veterin.er-og Landbohojskoles Aarsskrift, 1949.
Rubber Tree (Hevea brasiliensis) Bark Necrosis Syndrome III: A Physiological Disease Linked to Impaired Cyanide Metabolism
Authors: Chrestin H. , Sookmark U. , Trouslot P. , Pellegrin F. , Nandris D.
Published: May 2007

First attempts to discriminate between tapping panel dryness (TPD) and bark necrosis (BN), two Hevea sp. bark diseases leading to the cessation of latex production, showed differences in latex biochemical characteristics (1). Further, contrary to TPD, BN is characterized by inner phloem necrosis starting at the rootstock/scion junction (RS/S) and spreading upward to the tapping cut. Recent etiological (3) and epidemiological studies did not provide evidence of a causative pathogen for BN, but showed that BN is favored by a combination of various stresses (2). Searching for molecular markers of BN using sodium dodecyl sulfate-polyacrylamide gel electrophoresis analyses highlighted differential expression of some proteins in the latex and bark, especially a 67-kDa protein, which accumulates in the inner phloem of the BN trees. This protein was identified by peptide microsequencing as a linamarase (cyanogenic β-glucosidase). This led to the suspicion of the involvement of cyanogenesis in the spread of the syndrome inside the inner bark. The cDNAs of enzymes involved in cyanide (CN) metabolism (linamarase, hydroxynitrile lyase, and cyanoalanine synthase) were cloned from our Hevea sp. phloem specific cDNA library. In addition, the most BN-susceptible rubber clones were shown to exhibit higher cyanide potentions in the leaves and bark, together with low cyanoalanine synthase (CAS) gene expression and activity. Furthermore, linamarine (the cyanogene glucoside substrate of linamarase) was shown to accumulate in the phloem at the base of the trunk, especially above the rootstock/scion junction. The results of biochemical and gene expression studies associated with recent ecophysiological advances (2) strongly suggest a possible cell decompartmentalization near the RS/S junction, resulting in a local release of toxic concentration of highly diffusive CN. This, combined with a lethal imbalance between cyanogenic and CN-detoxifying activities (CAS) in the phloem of BN trees, could lead to poisoning of neighboring cells and to the spread of tissue necrosis toward the tapping cut. In conclusion, after providing evidence of exogenous factors favoring BN (2), this report highlights endogenous disorders that may be at the origin of this physiological disease leading to BN.

References: (1) D. Nandris et al. Eur. J. For. Pathol. 21:325, 1991. (2) D. Nandris et al. Plant Dis. 88:1047, 2004.
Iris yellow spot virus on Onion in New Mexico
Authors: Creamer R. , Sanogo S. , Moya A. , Romero J. , Molina-Bravo R. , Cramer C.
Published: May 2007

Onions are an important crop for New Mexico with 7,700 acres (3,116 ha) harvested in the state in 2003 (3). In 2002, onions of several cultivars were first noticed with diamond-shaped chlorotic or bleached lesions on seed stalks or leaves, typical of those reported for Iris yellow spot virus (IYSV). A more widespread survey of breeding stocks and commercial onion fields revealed similar symptoms on thrips-infested onions in Dona Ana and Rio Arriba counties. Incidence of disease symptoms ranged from <0.5 to nearly 30%. Symptomatic leaves were assayed for the presence of IYSV using enzyme-linked immunosorbent assay (ELISA; Agdia, Elkhart, IN) and antisera acquired from Agdia. Symptomatic leaves from breeding and commercial fields tested positive for IYSV. The virus was transmitted by Thrips tabaci from symptomatic onions to three onion cvs. New Mex Mesa, New Mex Vado, and New Mex Cryspy in growth chamber tests. All three cultivars showed symptoms of IYSV and tested positive for the disease using ELISA. However, New Mex Vado and New Mex Cryspy cultivars each showed 24% infection (4 infected plants of 17 tested) compared with 59% infection (10 infected plants of 17 tested) for New Mex Mesa, suggesting that not all cultivars are equally susceptible to the virus. To our knowledge, this is the first report of IYSV in onions in New Mexico, which has also been reported in the western United States in Idaho, Oregon, Colorado, and Washington (1,2,4).

References: (1) L. J. du Toit et al. Plant Dis. 88:222, 2004. (2) J. M. Hall et al. Plant Dis. 77:952, 1993. (3) National Agricultural Statistics Service, On-line publication. USDA, 2004. (4) H. F. Schwartz et al. Plant Dis. 86:560, 2002.
Distribution and Characterization of Citrus tristeza virus in South Florida Following Establishment of Toxoptera citricida
Authors: Halbert Susan E. , Genc Hanife , Cevik Bayram , Brown Lawrence G. , Rosales I. M. , Manjunath Keremane L. , Pomerinke Mark , Davison David A. , Lee Richard F. , Niblett C. L.
Published: May 2007

The incidence of Citrus tristeza virus (CTV) was found to increase significantly in southern Florida within 2 years after the establishment of its most efficient vector, Toxoptera citricida (Kirkaldy). Increased incidence of both mild and severe strains was documented, with the incidence of severe strains increasing more than mild strains. Molecular probes capable of differentiating mild, quick decline and various types of stem-pitting strains demonstrated that trees often were infected with more than one strain of CTV, with trees containing up to five different strains. Some CTV strains detected in the southeast urban corridor of Florida and in commercial groves in southwest Florida were found to react with probes specific for stem-pitting strains known from elsewhere in the world. The implications of the presence of these CTV strains in Florida and their possible presence in citrus budwood scion trees are discussed.
Pearl Millet for the Management of Pratylenchus penetrans in Flue-Cured Tobacco in Quebec
Authors: Bélair Guy , Dauphinais Nathalie , Fournier Yvon , Dangi Om P.
Published: May 2007

Two 1-year rotation experiments were conducted from 1998 to 2000 to assess the impact of forage and grain pearl millet (Pennisetum glaucum) on Pratylenchus penetrans populations in a tobacco field (Nicotiana tabacum cv. Delgold) in Quebec. Performance of these crops was compared with rye, the standard rotation crop. Rye plots were doubled to include a fumigated standard (application of metham sodium at 67.4 liters/ha on a band). Forage pearl millet increased tobacco yields by an average of 103% compared with nonfumigated rye. In 2000, leaf dry weights of tobacco following grain pearl millet CGPM H5 and CGPM H6 was increased by 70 and 73%, respectively, when compared with nonfumigated rye and were not significantly different from the fumigated plots following rye. Forage and grain pearl millet should be considered as a viable alternative to fumigation for controlling P. penetrans infestation in flue-cured tobacco production in Quebec.
Development and Pathogenicity of the Fungus Crinipellis perniciosa on Interaction with Cacao Leaves
Authors: Kilaru Aruna , Hasenstein Karl H.
Published: May 2007

We investigated developmental changes in the primary mycelium of Crinipellis perniciosa upon its interaction with immature and mature leaves of Theobroma cacao. On nutritive medium, the primary mycelium grew significantly slower in the presence of host tissue than without host tissue. In the absence of the cacao leaves, incomplete phase transition occurred after 5 days, wherein older hyphae progressed to the dikaryotic state and growing tips remained monokaryotic. Phase transition occurred between 3 and 5 days on mature leaves, 10 and 12 days on meristematic leaves, and required 2 weeks on T. cacao callus tissue. The biotrophic mycelia were able to invade immature and mature cacao leaves without open wounds or stomata. Club-shaped hyphal tips and the formation of adhesive structures were induced by cuticle extracts and suggest host recognition. The initial cuticular disintegration at the site of penetration was followed by blister formation and complete digestion of leaves by the primary mycelium. The data suggest specific interactions between host and pathogen that control the onset of the necrotrophic phase of the fungus. The data further indicate that primary mycelium rather than spores can be used to study C. perniciosa pathogenicity.
Survival Analysis of Time to Abscission of Blueberry Leaves Affected by Septoria Leaf Spot
Authors: Ojiambo P. S. , Scherm H.
Published: May 2007

In the southeastern United States, Septoria leaf spot, caused by Septoria albopunctata, can result in premature defoliation of blueberry plants during summer and fall, thereby reducing yield potential for the following year. The effects of disease severity and leaf attributes (leaf age and leaf location in the canopy) on the dynamics (timing and extent) of defoliation were quantified in field plots of Premier rabbiteye blueberry (Vaccinium ashei) in 2002 and 2003. In each year, 50 shoots were selected for assessment in early spring, and all leaves on these shoots (n = 410 and 542 in 2002 and 2003, respectively) were monitored individually for disease progress and time of abscission at 3- to 10-day intervals throughout the season. In both years, disease progress was characterized by an exponential increase in disease severity up to late September, followed by a decline toward the end of the assessment period in late November. Defoliation was sporadic up to late August, followed by more rapid and sustained levels of leaf loss. Abscission of severely infected leaves could explain the decline in disease severity toward the end of the season. Final disease severity (i.e., disease severity on the last assessment date before leaf drop) was highest for leaves that abscised early and lowest for leaves that had not abscised by the end of the assessment period. Survival analysis revealed that older leaves (located on the lower halves of shoots) and leaves with high levels of disease (≥5 spots/leaf at the time of fruit harvest in mid-June) abscised significantly (P < 0.0001) earlier than younger leaves and leaves with lower disease severity. Relative to their respective reference groups, mean times to abscission were ≈2 weeks shorter for the older leaf group and ≈3 weeks shorter in the leaf group afflicted by high disease severity. When an accelerated failure time model was fitted to the data, the resulting parameter estimates indicated that each additional leaf spot present at harvest accelerated time to leaf abscission (expressed using late August as a starting point) by 1.9 and 4.5% in 2002 and 2003, respectively. Leaf location in upper or lower portions of the canopy had no significant effect on time to abscission (P > 0.05).
Virulence Genes in Heterodera glycines: Allele Frequencies and Ror Gene Groups Among Field Isolates and Inbred Lines
Authors: Dong K. , Barker K. R. , Opperman C. H.
Published: May 2007

Genetic variation in field populations of Heterodera glycines is a key issue for both resistance gene deployment and basic understanding of virulence-gene flow in populations. In this study, we examined phenotypically defined genes for virulence under selection from host resistance. We separated the most common H. glycines genotypes in the United States into two virulence groups, based on their reproductive abilities on the resistant soybean plant introduction (PI) 88788. These groups correspond to previously identified virulence genes in the nematode, as follows: the dominant gene in H. glycines to PI88788, and the recessive genes to PI90763 and Pickett/Peking. Virulence allele frequencies and virulence genotype frequencies of selected field isolates were investigated by testing the host range of single-female-derived lines, which were developed through single-female inoculation on the standard susceptible soybean ‘Lee 68’. By comparing virulence genotype frequencies between the original field isolates and their single-female-derived lines, we were able to determine allele frequencies in the field populations. The results suggest that tremendous variation in H. glycines virulence genes exists among field populations. Potential mechanisms of selection which could cause virulence genotype frequency increases are discussed as related to population genetics equilibrium theory.
Gentian mosaic virus: A New Species in the Genus Fabavirus
Authors: Kobayashi Y. O. , Kobayashi A. , Hagiwara K. , Uga H. , Mikoshiba Y. , Naito T. , Honda Y. , Omura T.
Published: May 2007

A viral isolate, designated N-1 and obtained from a gentian (Gentiana scabra) plant that exhibited mosaic symptoms, was transmitted mechanically to nine plant species in six families. These plants are known as hosts of fabaviruses. The N-1 isolate was composed of isometric particles 30 nm in diameter and included two RNA molecules of approximately 6.0 and 3.6 kb in length, as estimated by agarose gel electrophoresis. The RNAs were encapsidated separately in two of the three types of particle. Each particle contained two distinct proteins with Mr values of 39.3 × 103 and 26.6 × 103, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Analysis of complete nucleotide sequences of the RNAs suggested that each encoded a single large polyprotein, in which putative functional proteins were arranged in a manner similar to those in Broad bean wilt virus 1 (BBWV-1) and Broad bean wilt virus 2 (BBWV-2), which are members of the genus Fabavirus (family Comoviridae). Analysis of the deduced amino acid sequences of the proteins indicated that those of isolate N-1 shared 38 to 66% identity with those of BBWV-1 and BBWV-2 but only 16 to 42% identity with those of a comovirus, Cowpea mosaic virus. Phylogenetic analysis, based on the amino acid sequences of RNA polymerase, placed isolate N-1 in a separate lineage from BBWV-1 and BBWV-2. In indirect-enzyme-linked immunosorbent assay, isolate N-1 exhibited distant serological relationship to BBWV-1, BBWV-2, and Lamium mild mosaic virus, another fabavirus. Our results suggest that N-1 represents a new species of Fabavirus. We propose the name Gentian mosaic virus for this new species.
Inducible Expression of a Phytolacca heterotepala Ribosome-Inactivating Protein Leads to Enhanced Resistance Against Major Fungal Pathogens in Tobacco
Authors: Corrado Giandomenico , Bovi Pasquale Delli , Ciliento Rosalia , Gaudio Luciano , Di Maro Antimo , Aceto Serena , Lorito Matteo , Rao Rosa
Published: May 2007

Plant genetic engineering has long been considered a valuable tool to fight fungal pathogens because it would limit the economically costly and environmentally undesirable chemical methods of disease control. Ribosome-inactivating proteins (RIPs) are potentially useful for plant defense considering their antiviral and antimicrobial activities but their use is limited by their cytotoxic activity. A new gene coding for an RIP isolated from leaves of Phytolacca heterotepala was expressed in tobacco under the control of the wound-inducible promoter of the bean polygalacturonase-inhibiting protein I gene to increase resistance against different fungal pathogens, because an individual RIP isolated from P. heterotepala showed direct antifungal toxicity. Phenotypically normal transgenic lines infected with Alternaria alternata and Botrytis cinerea showed a significant reduction of leaf damage while reverse transcription-polymerase chain reaction and western analysis indicated the expression of the RIP transgene upon wounding and pathogen attack. This work demonstrates that use of a wound-inducible promoter is useful to limit the accumulation of antimicrobial phytotoxic proteins only in infected areas and that the controlled expression of the PhRIP I gene can be very effective to control fungal pathogens with different phytopathogenic actions.
Population Structure of Seedborne Phaeosphaeria nodorum on New York Wheat
Authors: Bennett Rebecca S. , Milgroom Michael G. , Bergstrom Gary C.
Published: May 2007

Population genetic and epidemiological studies have resulted in different hypotheses about the predominant source of primary inoculum in the Phaeosphaeria nodorum-wheat pathosystem (i.e., sexually derived, windborne ascospores versus asexual or seedborne inoculum). We examined the genetic structure of seedborne populations of P. nodorum as a further step toward evaluating the hypothesis that seedborne inoculum is an important contributor to foliar epidemics in New York's rotational wheat fields. In all, 330 seedborne isolates from seven field populations were genotyped at 155 amplified fragment length polymorphism loci. Seedborne populations possessed high levels of genotypic diversity, with virtually every isolate (326/330) having a unique haplotype. As in previous population genetic studies of P. nodorum, we found low levels of gametic disequilibrium, although we could reject the null hypothesis of random mating with the index of association test for two populations. Thus, genotypically diverse and seemingly panmictic populations of P. nodorum that have been observed in wheat foliage could be derived from seedborne primary inoculum. Although sexual reproduction and recombination may contribute to the diversity of foliar populations of P. nodorum, population genetic data do not rule out seed as a source of primary inoculum. Further experimentation will be needed to determine definitively the relative importance of windborne ascospores and seed-borne asexual inoculum in epidemics of Stagonospora nodorum blotch in New York.
Effect of Wound Position, Auxin, andAgrobacterium vitisStrain F2/5 on Wound Healing and Crown Gall in Grapevine
Authors: Creasap J. E. , Reid C. L. , Goffinet M. C. , Aloni R. , Ullrich C. , Burr T. J.
Published: May 2007

Agrobacterium vitis is the causal agent of crown gall disease in grapevine, which can be severe in many regions worldwide. Vitis vinifera cultivars are highly susceptible to freeze injury, providing the wounds necessary for infection by A. vitis. Wound position in relation to the uppermost bud of cuttings was determined to be important in tumor development. Inoculated wounds below buds developed tumors, whereas wounds opposite the bud did not, implying that indole-3-aectic acid flow contributes to tumor formation. If auxin was applied to wounds prior to inoculation with a tumorigenic A. vitis strain, all sites of inoculation developed tumors, accompanied by an increased amount of callus in the cambium. Wounds inoculated with an A. vitis biological control strain F2/5 prior to application of the pathogen did not develop galls. A closer examination of these wounds determined that callus cells formed in the cambium during wound healing are susceptible to transformation by the pathogen. Although the mechanism by which F2/5 prevents transformation is unknown, our observations suggest that F2/5 inhibits normal wound healing by inducing necrosis in the cambium.
Genetic Interaction of the Fusiform Rust Fungus with Resistance Gene Fr1 in Loblolly Pine
Authors: Kubisiak Thomas L. , Amerson Henry V. , Nelson C. Dana
Published: May 2007

We propose a method for defining DNA markers linked to Cronartium quercuum f. sp. fusiforme avirulence (Avr) genes. However, before this method can be successfully employed, a spore competition study was needed to determine the genetic composition of single pycnial drops and multiple drops on single galls when using the standard inoculation procedure, whether virulent (avr1) basidiospores ever predispose some resistant (Fr1/fr1) trees to infection by avirulent (Avr1) basidiospores, and whether avr1 and Avr1 basidiospores equally infect susceptible (fr1/fr1) trees. Results of this study suggest that multiple infections within a single gall are common using the concentrated basidiospore system, resulting on average in >4 infection events per tree. Due to multiple infections within a single gall, an individual pycnial drop cannot be assumed to consist of spores from only a single haploid pycnium. Roughly 57% of the drops harvested were found to consist of more than one haploid genotype, most likely due to the physical mixing of spores from genetically different pycnia. Most importantly, although multiple infections do occur in the formation of a single gall, there is no evidence to suggest that the genetics of the proposed gene-for-gene interaction are compromised. Only avr1 basidiospores were observed to cause infection on Fr1/fr1 trees, whereas both avr1 and Avr1 basidiospores were observed to cause infection on fr1/fr1 trees, albeit not at equal frequencies.