bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlling Foliar Blights of Wheat in the Rice-Wheat Systems of Asia
Authors: Duveiller E.
Published: May 2007

Foliar blight caused by Cochliobolus sativus and Pyrenophora tritici-repentis is the main biotic stress of wheat in the rice-wheat systems of South Asia, where it causes, on average, up to 15% yield loss. Increases in food production have to come from higher and sustainable productivity. It requires a multidisciplinary approach combining novel resistance sources and adapted agronomic practices. Better host plant resistance has been achieved by crossing genetic resistance sources or wild relatives to high-yielding cultivars. Germ plasm improvement methods centered on regional partnerships are now more specifically addressing the needs of warmer areas. Observations in long-term trials underline the increasing role of soil fertility in reducing disease severity. Studies focusing on the effect of stress conditions on disease development increase knowledge about the stability of resistance. This makes breeding more efficient and helps recommend better-adapted crop management practices. The adoption of reduced tillage methods and soil conservation practices imply farmers' direct participation in the research process. Foliar fungicide treatments are not a viable alternative for small farmers, but seed treatment may prove useful as part of an integrated disease management approach based on improved genetic resistance and good agronomy.
First Report of Blueberry scorch virus on Highbush Blueberry in Connecticut and Massachusetts
Authors: DeMarsay A. , Hillman B. I. , Petersen F. P. , Oudemans P. V. , Schloemann S.
Published: May 2007

During June and July 2001, the Marucci Center received 33 foliage samples from healthy- and unhealthy-looking highbush blueberry (Vaccinium corymbosum L.) bushes from growers in Connecticut and Massachusetts, via local extension agents. Unhealthy bushes were reported to exhibit symptoms including leaf chlorosis and necrosis, blossom blight, tip dieback, or a general decline in vigor. Marginal leaf chlorosis, reddening, or necrosis characterized foliage samples from these bushes. Five-leaf samples from each bush were tested for Blueberry scorch virus (BlScV) (3) with Agri-Check detection kits (Hydros, Inc., Falmouth, MA). These kits use an indirect enzyme-linked immunosorbent assay (ELISA) protocol and antibodies developed at Rutgers University that are specific to the two eastern strains of BlScV (NJ1 and NJ2) (1). The ELISA extraction buffer was based on that used by Martin and Bristow (3) with 1% (wt/vol) nonfat dry milk powder added as a blocking agent. Fourteen samples from cvs. Blueray and Berkeley in both states and cvs. Elliott, Bluecrop, and Coville in Massachusetts tested positive for BlScV. These results were confirmed by a second test. Six of seven samples from symptomatic bushes and 8 of 26 samples from asymptomatic bushes harbored BlScV. Virus preparations extracted from five infected plants (two from Connecticut and three from Massachusetts) were examined using reverse transcription-polymerase chain reaction (RT-PCR) with oligonucleotide primers (5′-TGTGTCAAACAATATGGC-3′ and 5′-GCATTTCGATGA-TTGCGG-3′) designed to amplify a portion of the coat protein gene from any of the three known virus strains (1,2). Sequence analysis of fragments amplified from their coat protein genes revealed that two of the isolates from Massachusetts (GenBank Accession Nos. AY530957 and AY530958) and the two isolates from Connecticut (GenBank Accession Nos. AY530955 and AY530956) were similar but not identical to one another, and these four were most similar to strain NJ2. One isolate from Massachusetts (GenBank Accession No. AY530958) was most similar to strain NJ1. To our knowledge, this is the first report of BlScV on the east coast outside of New Jersey, where it was first reported in 1983 (4). These results indicate that the disease is now present in other blueberry-growing areas in the northeast and is likely to be spreading locally within those areas. Because blueberry scorch is symptomless in propagation material and may take several years to express symptoms in the field, the initial spread of the disease was probably due to the shipping of latently infected plants to BlScV-free areas before reliable testing was available.

References: (1) T. D. Cavileer et al. J. Gen. Virol. 75:711, 1994. (2) B. T. Halpern and B. I. Hillman. Plant Dis. 80:219, 1996. (3) R. R. Martin and P. R. Bristow. Phytopathology 78:1636, 1988. (4) A. W. Stretch. (Abstr.) Phytopathology 73:375, 1983.
Presence of Tomato yellow leaf curl virus Infecting Squash (Curcubita pepo) in Cuba
Authors: Zubiaur Y. Martinez , Fonseca D. , Quiñones M. , Palenzuela I.
Published: May 2007

In a survey conducted in Havana Province during January and February 2003, symptoms of curling and light yellowing of leaves were found in squash plants (Curcubita pepo). DNA from leaves of six symptomatic squash plants was extracted (1) and hybridized at high stringency with specific probes of the intergenic region of Tomato yellow leaf curl virus (TYLCV, genus begomovirus) isolated in Cuba by using a nonradioactive hybridization kit (AlkPhos Direct Labeling and Detection Systems; Amersham Pharmacia Biotech Inc., Piscataway, NJ). Three samples were positive in the nonradioactive analyses. The same samples were positive using polymerase chain reaction (PCR) when the DNA was analyzed with degenerate primers PAL1v1978/PAR1c715 for DNA-A (5), specific primers, ORITY1/ORITY2, for the intergenic region (2), and overlapping specific primers for TYLCV (3). Fragments of 1.4, 0.750, and 2.8 kb were cloned using pGem-T Easy (Promega, Madison, WI), and the six clones obtained were sequenced using the Terminator Cycle Sequencing Kit in a SEQ 4 × 4 machine (Amersham Pharmacia Biotech Inc.). Sequences of three fragments exhibited 95 to 97% homology with TYLCV (GenBank Accession Nos. AF414089 and AF260331). Additionally, we did not obtain a PCR product when DNA was amplified using degenerate primers PBV1c800/PBC1v2039 for DNA-B (4). These results suggest that TYLCV is present in squash in field plantations, and these plants may serve as a virus reservoir for other crops such a tomatoes.

References: (1) S. L. Dellaporta et al. Plant. Mol. Biol. Rep. 1(4):19, 1983. (2) Y. Martínez et al. Rev. Prot. Veg. 18(3):168, 2003. (3) M. K. Nakhla et al. Plant Dis. 78:926, 1994. (4) M. Rojas et al. Plant Dis. 77:340, 1993.
Occurrence of Soybean Stem Canker (Diaporthe phaseolorum var. meridionalis) in Wisconsin
Authors: Li S. , Kurtzweil N. C. , Grau C. R. , Hartman G. L.
Published: May 2007

Soybean (Glycine max) developed symptoms characteristic of stem canker during the 2000 to 2003 growing seasons in Wisconsin. Symptoms were widespread in 2003 and were associated with yield losses of ≈1% statewide and as much as 25% in individual fields. Affected plants expressed dieback of foliage beginning at growth stage R3 and progressed until the R6 growth stage. Dark brown lesions were frequently observed at a single node on the lower portion of stems of plants expressing foliage dieback. Fungi were isolated from symptomatic plants collected from seven growers' fields in Rock, Sauk, Veron, and Walworth counties and the Arlington and Marshfield Agricultural Research Stations. Stems with lesions were cut into ≈5-mm pieces, surface disinfested with a 0.5% NaOCl solution for 3 min, rinsed three times in sterile distilled water, and placed on water agar (WA) or potato dextrose agar (PDA) at pH 4.5. Hy-phal tips from colonies of interest were excised and placed on acidified PDA at 25°C under continuous light for 25 to 30 days. In addition to Diaporthe phaseolorum var. caulivora (the cause of northern stem canker), four isolates of D. phaseolorum var. meridionalis (the cause of southern stem canker) were isolated. Colonies of D. phaseolorum var. meridionalis isolates were white, lanose, and became tan with age as previously described for D. phaseolorum var. meridionalis (1). Pycnidia with alpha conidia (no beta conidia) and perithecia with 3.1 to 3.4 × 9.5 to 9.8 μm ascospores formed on oat flakes on acidified WA after 30 days. Stromata were brown to black and irregularly shaped. Four isolates of D. phaseolorum var. meridionalis were tested for pathogenicity in a controlled environment using a cut stem inoculation method (2). Stems of 3-week-old seedlings of cv. Sturdy were cut at the midpoint between the second and third node, and a PDA mycelial plug (4 mm in diameter) was placed on the surface of the cut stems. This method was used to inoculate 15 plants in three replicates for each isolate tested. Inoculated plants were placed in a mist chamber in the dark at 25°C for 4 days and later moved to a greenhouse with a 16-h photoperiod at 24 ± 3°C for 3 days. All plants challenged by this method exhibited stem lesions that were 2 to 3 cm long and of similar color to lesions observed in field-grown plants. For each isolate tested, D. phaseolorum var. meridionalis was reisolated from three randomly selected symptomatic plants. Negative controls with a PDA plug did not produce lesions. To our knowledge, this is the first report of D. phaseolorum var. meridionalis on soybean in Wisconsin. The significance of this report relates to the potential spread of D. phaseolorum var. meridionalis beyond its known southern range in the United States.

References: (1) F. A. Fernandez et al. Stem Canker. Pages 33–35 in: Compendium of Soybean Diseases, 4th ed. G. L. Hartman et al., eds. The American Phytopathological Society, St. Paul, MN, 1999. (2) S. Li et al. Plant Dis. 85:1031, 2001.
Factors Affecting Soybean Root Colonization by Calonectria ilicicola and Development of Red Crown Rot Following Delayed Planting
Authors: Kuruppu P. U. , Schneider R. W. , Russin J. S.
Published: May 2007

Field studies were conducted in 1994, 1995, and 1996 to determine the effects of planting date, cultivar susceptibility, and soil pathogen population on soybean root colonization by Calonectria ilicicola and subsequent development of red crown rot. Early season colonization of roots was important for red crown rot symptom development. Symptom development in the more susceptible cultivar, Sharkey, was reduced following delayed planting and remained low in the less susceptible cultivar, Cajun, regardless of planting date. Taproot colonization was positively correlated with inoculum density during all three growing seasons but was strongest in 1994. Also, lateral root colonization correlated positively with inoculum density in 1994, the only year in which foliar symptoms were detected. A substantial decrease in inoculum density in 1995, along with reduced soybean root colonization, were attributed to high soil temperatures and probably low rainfall recorded during that summer. The effect of soybean plant age on root colonization was examined by exposing plants to the pathogen at different ages. Soybean plants were most susceptible to C. ilicicola during the first week after seedling emergence. By the second week, susceptibility was reduced by nearly half, and it remained near that level for the next several weeks.
Effects of Soil Temperature on Microsclerotia of Calonectria ilicicola and Soybean Root Colonization by this Fungus
Authors: Kuruppu P. U. , Schneider R. W. , Russin J. S.
Published: May 2007

Field soil artificially infested with laboratory-produced microsclerotia of Calonectria ilicicola was incubated for 1, 2, 3, or 6 weeks at 20, 25, 30, 35, and 40°C. These temperatures approximate soil temperatures that were measured in soybean fields during the growing season in south Louisiana. Germinable microsclerotia were enumerated after incubation at different temperatures, and soybean seeds were planted in these soils. After 8 weeks, percent root colonization was determined as a measure of infectivity of microsclerotia. Results showed that soil temperature is a critical factor in survival of microsclerotia. The optimal soil temperature range for survival of microsclerotia was 20 to 30°C, and the maximum soil temperature limit was 35°C, above which microsclerotia did not survive. Effects of temperature on soybean root colonization were examined in growth chambers by growing soybean plants in soil infested with laboratory-grown microsclerotia for 4 weeks after seed germination. Maximum infection of young soybean roots by C. ilicicola occurred between 25 and 30°C but decreased with increasing temperatures and was negligible at 40°C. According to these results, soil temperature is a critical environmental factor controlling the development of red crown rot in soybeans in Louisiana. These findings suggest that, if red crown rot is a threat, soybean planting time should be based on soil temperature rather than calendar dates.
Detection and Isolate Differentiation of Citrus tristeza virus in Infected Field Trees Based on Reverse Transcription-Polymerase Chain Reaction
Authors: Huang Zhipeng , Rundell Phyllis A. , Guan Xiong , Powell Charles A.
Published: May 2007

Reverse transcription-polymerase chain reaction (RT-PCR) was compared with enzyme-linked immunosorbent assay (ELISA) and direct tissue blot immunoassay (DTBIA) for detection of non-decline-inducing and decline-inducing isolates of Citrus tristeza virus (CTV) in 21 field sweet orange and grapefruit plants on sour orange rootstock in Fort Pierce, FL. Among these samples, seven, six, and eight were infected with decline-inducing, non-decline-inducing, and both decline-inducing and non-decline-inducing isolates of CTV, respectively. However, there was not a good correlation between field symptoms and detection of the decline-inducing isolate. The results confirmed that RT-PCR is not only able to detect and differentiate decline-inducing and non-decline-inducing isolates of CTV in Florida, but also can detect both isolate types in a single field sweet orange or grapefruit tree. For most samples, results from RT-PCR, ELISA, and DTBIA were the same. However, the 320-bp fragments produced only from decline-inducing isolates were amplified from two sweet orange and two grapefruit samples that did not react with decline-inducing CTV-specific monoclonal antibody MCA13 in ELISA or DTBIA, indicating that RT-PCR has a higher sensitivity than these immunological tests for field sweet orange or grapefruit samples. Thus, RT-PCR is a simple, rapid, and specific procedure for CTV identification applicable to both research and diagnostic needs.
Ability of an ELISA-Based Seed Health Test to Detect Erwinia stewartii in Maize Seed Treated with Fungicides and Insecticides
Authors: Pataky J. K. , Block C. C. , Michener P. M. , Shepherd L. M. , McGee D. C. , White D. G.
Published: May 2007

Two sets of experiments were done to examine whether seed-treatment chemicals affected the ability of an enzyme-linked immunosorbent assay (ELISA)-based seed health test to detect Erwinia stewartii. The chemicals evaluated included Actellic, Apron, Captan, Cruiser, Gaucho, Maxim, Poncho, Thiram, and Vitavax in 11 seed-treatment combinations. In one experiment, seed-treatment chemicals were evaluated quantitatively in a critical region of ELISA absorbance values near 0.5 using maize seed that were spiked with uniform quantities of a liquid suspension of E. stewartii. The number of bacteria in each sample was estimated from ELISA absorbance values using standard curves. Log CFU of E. stewartii per sample were not significantly different among the untreated control and the 11 seed treatments compared with Tukey's Studentized Range Test (P = 0.05). Means of log CFU/ml for all treatments were tightly clustered around 5.70 which corresponded to an absorbance value of 0.440 and a bacterial population of about 500,000 CFU/ml. In a second set of experiments, seed treatment chemicals were evaluated based on qualitative decisions that resulted from the ELISA-based seed health test of seed lots of Jubilee and A632 infected with E. stewartii. The number of negative samples was not substantially greater than expected based on binomial probabilities except for samples of Captan/Vitavax-treated A632, which we considered to be a type I error. The mean absorbance values of positive samples ranged from 1.42 to 1.72 for A632 and from 1.51 to 1.91 for Jubilee and did not differ significantly among the seed treatments. There was no consistent evidence from these experiments that fungicide or insecticide seed treatments interfered with the sensitivity of the ELISA or altered low (e.g., 0.5) or high (e.g. 1.4 to 1.9) absorbance values. The ability of the ELISA-based seed health test to detect E. stewartii in maize seed was not affected by these seed treatments.
Identification of Soybean mosaic virus Strains by RT-PCR/RFLP Analysis of Cylindrical Inclusion Coding Region
Authors: Kim Yul-Ho , Kim Ok-Sun , Roh Jae-Hwan , Moon Jung-Kyung , Sohn Soo-In , Lee Sang-Chul , Lee Jang-Young
Published: May 2007

A reverse-transcriptase polymerase chain reaction/restriction fragment length polymorphism (RT-PCR/RFLP) was employed successfully for detection and identification of Soybean mosaic virus (SMV) strains. A primer pair amplifying a 1,385-bp fragment of the cylindrical inclusion (CI) coding region was used for RT-PCR and the RFLP profiles of the RT-PCR products were compared after restriction digestion with RsaI, EcoRI, or AccI restriction endonucleases. These enzymes were chosen based on the nucleotide sequences of SMV strains G2, G5, G5H, G7, and G7H in the CI coding region. These five strains, as well as seedborne SMV isolates from local soybean cultivars, could be differentiated by RT-PCR/RFLP analysis. The results correlated well with strain identification by symptom phenotypes produced on differential cultivars inoculated with strains and isolates. The sensitivity of RT-PCR enabled detection of SMV from plants with necrotic symptoms in which the number of virus particles was too low to be detected by enzyme-linked immunosorbent assay.
Bacterial Canker (Clavibacter michiganensis subsp. michiganensis) of Tomato in Commercial Seed Produced in Indonesia
Authors: Anwar A. , van der Zouwen P. S. , Ilyas S. , van der Wolf J. M.
Published: May 2007

In 2002, Clavibacter michiganensis subsp. michiganensis (Smith) Davis, the causal organism of bacterial canker of tomato (Lycopersicon esculentum), was isolated from two of six commercial asymptomatic tomato seed lots produced on Java in Indonesia. C. michiganensis subsp. michiganensis has not been reported in Indonesia previously. Methods based on the protocol of the International Seed Health Initiative were used to extract and identify the presence of C. michiganensis subsp. michiganensis in tomato seed. C. michiganensis subsp. michiganensis was isolated with dilution plating on the semiselective media D2ANX and mSCM. The identity of the colonies was confirmed by immunofluorescence microscopy, polymerase chain reaction (2), fatty methyl ester analysis, enzyme-linked immunosorbent assay based on monoclonal antibody 103 (1), and a pathogenicity test in which three replicate tomato plants were stem inoculated with 108 cells ml-1. Within 2 weeks, stripes on stems developed that split and exposed reddish brown cavities (stem cankers). The presence of C. michiganensis subsp. michiganensis poses a direct threat on tomato production, which is one of five economically most important vegetable crops in Indonesia.

References: (1) A. Alvarez et al. Phytopathology 83:1405, 1993. (2) M. S. Santos et al. Seed Sci. Technol. 25:581, 1997.
First Report of Powdery Mildew Caused by Oidium Subgenus Pseudoidium on Mandevilla splendens in Italy
Authors: Garibaldi A. , Minuto A. , Gullino M. L.
Published: May 2007

Mandevilla splendens (Hook.) Woodson is a tropical plant belonging to the Apocynaceae family and grown in Italy as an ornamental. It is generally potted and used to create small barriers on terraces and gardens. During February 2003, severe outbreaks of a previously unknown powdery mildew were observed in a commercial glasshouse located at Albenga (northern Italy) where 30% of the plants were affected by the disease. Infected young leaves were covered on both sides with white mycelia. Mycelia were more evident on the lower surface of older leaves. As the disease progressed, infected leaves turned reddish and eventually became yellow and died. Powdery mildew infections sometimes cause leaves to distort and have reduced growth. Conidia were hyaline, ellipsoid or cylindrical, sometimes appeared to adhere in chains, measured 9 to 15 × 14 to 28 μm (average 12 × 21 μm), and did not show fibrosin bodies. Foot cell was cylindric and appressorium lobed. Cleistothecia were not observed. The pathogen was identified as Oidium sp. subgenus Pseudoidium (1,2,3). Pathogenicity was confirmed by gently pressing diseased leaves onto young leaves of healthy, 1-year-old M. splendens plants grown in 3.5 liter pots. Three plants were inoculated, while three noninoculated plants served as controls. After inoculation, plants were maintained in a growth chamber at 18°C (12-h light, relative humidity >75%). After 60 days, powdery mildew symptoms were observed on inoculated plants. Noninoculated plants remained healthy. The pathogenicity test was carried out twice. To our knowledge, this is the first report of powdery mildew on M. splendens in Italy, as well as in the world. Specimens of this disease are available at the DIVAPRA Collection at the University of Torino.

References: (1) R. Belanger et al., eds. The powdery mildew A comprehensive treatise. The American Phytopathological Society, St Paul, MN, 2002. (2) U. Braun. Nova Hedwigia, 89:700, 1987. (3) R. T. A. Cook et al. Mycol. Res. 101:975, 1997.
Survival and Inoculum Production of Gibberella zeae in Wheat Residue
Authors: Pereyra S. A. , Dill-Macky R. , Sims A. L.
Published: May 2007

Survival and inoculum production of Gibberella zeae (Schwein.) Petch (anamorph Fusarium graminearum (Schwabe)), the causal agent of Fusarium head blight of wheat and barley, was related to the rate of wheat (Triticum aestivum L.) residue decomposition. Infested wheat residue, comprising intact nodes, internodes, and leaf sheaths, was placed in fiberglass mesh bags on the soil surface and at 7.5- to 10-cm and 15- to 20-cm depths in chisel-plowed plots and 15 to 20 cm deep in moldboard-plowed plots in October 1997. Residue was sampled monthly from April through November during 1998 and every 2 months through April to October 1999. Buried residue decomposed faster than residue placed on the soil surface. Less than 2% of the dry-matter residue remained in buried treatments after 24 months in the field, while 25% of the residue remained in the soil-surface treatment. Survival of G. zeae on node tissues was inversely related to the residue decomposition rate. Surface residue provided a substrate for G. zeae for a longer period of time than buried residue. Twenty-four months after the initiation of the trial, the level of colonization of nodes in buried residue was half the level of colonization of residue on the soil surface. Colonization of node tissues by G. zeae decreased over time, but increased for other Fusarium spp. Ascospores of G. zeae were still produced on residue pieces after 23 months, and these spores were capable of inducing disease. Data from this research may assist in developing effective management strategies for residues infested with G. zeae.
Evaluation of Systems for Timing of Fungicide Sprays for Control of Postbloom Fruit Drop of Citrus in Brazil
Authors: Peres N. A. R. , Souza N. L. , Furtado E. L. , Timmer L. W.
Published: May 2007

Postbloom fruit drop (PFD) of citrus, caused by Colletotrichum acutatum, infects petals of citrus flowers and produces orange-brown lesions that induce the abscission of young fruitlets and the retention of calyces. Proper timing of fungicide applications is essential for good disease control. Different systems for timing of fungicide applications for control of PFD in a major citrus-growing region in southern São Paulo state in Brazil were evaluated from 1999 to 2002. The following programs were compared to an unsprayed control using counts of diseased flowers, persistent calyces, or fruit: (i) a phenology-based program currently recommended in Brazil with one application at early and another at peak bloom; (ii) the Florida PFD model; (iii) the post-bloom fruit drop-fungicide application decision system (PFD-FAD), a new computer-assisted decision method; and (iv) grower's choice. In 1999, no disease developed, sprays applied with the phenology-based program had no effect, and the Florida PFD model saved two sprays compared with the phenology-based program. In 2000, PFD was moderate and the phenology-based and grower's choice treatments had a significantly lower number of persistent calyces and higher fruit numbers than the control, but no differences were found between those treatments and the PFD model. In 2001, PFD was severe with considerable yield loss. The PFD model, the phenology-based program, and the grower's choice reduced flower blight and the number of persistent calyces, and improved fruit yields with two to three applications, but the PFD-FAD achieved comparable yields with only one spray. In 2002, the disease was mild, with no yield loss, and the Florida PFD model and the PFD-FAD saved one spray compared with the other systems. The PFD model and the PFD-FAD were equally effective for timing fungicide applications to control PFD in Brazil. Scouting of trees is simpler with PFD-FAD; therefore, this system is recommended and should eliminate unnecessary sprays and reduce costs for growers.
Lack of Control of Citrus Canker by Induced Systemic Resistance Compounds
Authors: Graham J. H. , Leite R. P.
Published: May 2007

Induced systemic resistance compounds (ISRs), acibenzolar-S-methyl (Actigard), and harpin protein (Messenger) were assayed in the greenhouse against Xanthomonas axonopodis pv. citrumelo, the cause of citrus bacterial spot (CBS), and X. axonopodis pv. citri, the cause of Asiatic citrus canker. Actigard and Messenger applied as foliar sprays 3 to 7 days before inoculation reduced numbers of lesions when either bacterium at 103 or 104 CFU/ml was injection-infiltrated into Swingle citrumelo leaves. Based on this activity, the ISRs were evaluated in southern Brazil in orchards of sweet oranges with low to moderate canker disease incidence in spray programs with and without copper oxychloride (COC) and copper hydroxide (CuOH). Actigard and Messenger were applied full season or in the first two or three sprays of a six-spray program in an attempt to reduce early canker disease on foliage and thereby reduce subsequent fruit infection and premature drop. Sprays of COC and CuOH were moderately to highly effective in reducing canker disease incidence and preventing premature fruit drop. Actigard or Messenger in combination with COC and CuOH, respectively, did not significantly reduce citrus canker incidence on foliage or fruit drop compared with Cu alone. The lack of additional control with ISRs means they cannot be recommended at this time to augment Cu programs for management of citrus canker.
Overwintering of Conidia of Venturia inaequalis and the Contribution to Early Epidemics of Apple Scab
Authors: Holb I. J. , Heijne B. , Jeger M. J.
Published: May 2007

Overwintering of conidia of Venturia inaequalis associated with shoots and buds was determined, and the contribution to early spring epidemics of apple scab was evaluated during three consecutive seasons (1999 to 2001) in the Netherlands. Examinations of shoot samples collected before bud break showed that the percentage of shoots with superficial black fungal mycelia or conidia was above 65%, and the mean number of conidia on a 1-cm piece of shoot length ranged from 581 to 1,033. However, germination tests showed that the viability of conidia on shoots was less than 1.5%. No macroscopic scab lesions were detected on the scales of dormant buds. However, microscopic examinations of individual bud tissues demonstrated that the number of conidia was >3,000 per 100 buds in each year. The mean viability of conidia associated with buds ranged from 0.7 to 1.9% and from 3.7 to 10.5% for the outer and inner bud tissues, respectively. Results of field assessments at tight-cluster phenological stage showed that the percentage of infection caused by the viable overwintered conidia ranged from 0.3 to 3.8% in the various treatments. Our results indicated that conidia were unlikely to overwinter on the surface of shoots or outer bud tissues, where they were exposed to fluctuating environmental conditions, and, consequently, were unlikely to play a role in initiating an early epidemic of apple scab in the spring. However, our results indicated a risk from overwintered conidia in the inner bud tissues arising from a high level of scab the previous autumn. Therefore, orchards with high levels of apple scab, where ascosporic inoculum is much reduced, e.g., by sanitation, should be protected in early spring by means of fungicide treatment at green tip.
Resistance to Brown Stem Rot in Soybean Germ Plasm with Resistance to the Soybean Cyst Nematode
Authors: Hughes T. J. , Kurtzweil N. C. , Diers B. W. , Grau C. R.
Published: May 2007

The soybean cyst nematode (SCN) and Phialophora gregata f. sp. sojae, the causal agent of brown stem rot (BSR), are two pathogens of soybean commonly found in the same field throughout the north-central United States. Field experiments designed to study the role of SCN-resistant germ plasm in soybean production have led to data suggesting that some sources of SCN resistance also may provide resistance to BSR. Soybean germ plasm with resistance to SCN was evaluated in greenhouse and field environments for resistance to BSR development based on the percentage of host tissue symptomatic of BSR. Comparison of SCN-resistant cultivars and plant introductions (PI) to standard BSR-resistant and -susceptible checks were conducted in two greenhouse experiments using a root-dip inoculation with a single isolate of P. gregata. For both greenhouse experiments, PI 209332 was the only source of SCN resistance with resistance to BSR similar to standard BSR-resistant checks. Nine other sources of SCN resistance, including PI 88788 and Peking, expressed BSR symptom severity similar to BSR-susceptible checks. Cultivars derived from most SCN-resistant sources, including PI 209332, also were susceptible to BSR development, while four of the five cultivars derived from PI 88788 were highly resistant to BSR development. SCN-resistant cultivars derived from PI 88788, Peking, and PI 209332 were planted along with standard BSR-resistant and -susceptible checks at two field locations naturally infested with P. gregata and SCN or P. gregata alone. As in greenhouse experiments, four of the five cultivars derived from PI 88788 expressed resistance to BSR development equal to or better than standard BSR-resistant checks at both locations. In contrast, cultivars derived from PI 209332 and Peking expressed varying levels of disease development depending on field environment. Yields observed for PI 88788-derived cultivars were higher than BSR-resistant checks regardless of the presence of SCN. Data from both greenhouse and field experiments suggest that cvs. Williams and Williams 82 may contain a gene or genes for BSR resistance that require one or more modifier genes, possibly located in the genome of PI 88788, for complete expression.
Development of a Robust Screening Method for Pathogenicity of Colletotrichum spp. on Strawberry Seedlings Enabling Forward Genetic Studies
Authors: Horowitz Sigal , Yarden Oded , Zveibil Aida , Freeman Stanley
Published: May 2007

Generation and screening for nonpathogenic mutants is a popular tool for identifying pathogenicity-related genes. Successful application of this technique for plant fungal pathosystems requires reliable and rapid screening procedures. This study reports on the development of a rapid in vitro bioassay enabling large-scale screening and isolation of nonpathogenic mutants of Colletotrichum gloeosporioides and C. acutatum on strawberry seedlings. Inoculation was carried out on strawberry seedlings at two different developmental stages: 12-week-old (young) and 15-week-old (older) seedlings. A comparison was made between two inoculation techniques, (i) foliar dip and (ii) root soak, at two incubation temperatures (19 and 25°C). Mortality of young seedlings was observed 4 days after inoculation with both species, reaching 50% within 10 days, using both techniques at 25°C. However, mortality of older seedlings was delayed by 4 days compared with that in the young seedlings when using the root-soak method. Disease development decreased in young and older seedlings at the lower temperature. This method also was reliable in determining pathogenicity of the cucurbit-specific C. magna that did not cause disease symptoms on strawberry by either inoculation method. The proposed method enabled screening of more than 980 restriction enzyme-mediated integration mutants resulting in a selection of five reduced-virulence isolates. Initial characterization of some of these mutants revealed large differences in germination and appressorial formation compared with pathogenic isolates.
Tolerance to Citrus mosaic virus in Transgenic Trifoliate Orange Lines Harboring Capsid Polyprotein Gene
Authors: Iwanami Toru , Shimizu Tokurou , Ito Takao , Hirabayashi Toshio
Published: May 2007

Trifoliate orange plants (Poncirus trifoliata) were transformed with a binary vector containing the capsid polyprotein (pCP) gene of Citrus mosaic virus (CiMV) via Agrobacterium tumefaciens LBA4404. Transformation was performed on the epicotyl segments obtained from a young seedling that was grown in the dark. Southern blot hybridization analysis showed that the transgene was stable in the transgenic lines after regeneration and propagation by grafting. Transgenic lines were screened for tolerance to CiMV by mechanical inoculation. Infection was monitored 30, 60, 90, and 120 days after inoculation by reverse transcription-polymerase chain reaction. The transgenic line 24 had the lowest infection rate (7.1%) at 60 days after inoculation, in contrast to that of nontransgenic plants (65.1%).The response of other lines to inoculation ranged from susceptibility to moderate tolerance.
Distribution of Phytophthora vignae f. sp. adzukicola Races in Adzuki Bean Fields in Hokkaido, Japan
Authors: Kondo N. , Notsu A. , Naito S. , Fujita S. , Shimada H.
Published: May 2007

Information on the distribution of races of Phytophthora vignae f. sp. adzukicola in Hokkaido, Japan, is important for the management of Phytophthora stem rot of adzuki bean. In all, 107 isolates of P. vignae collected between 1999 and 2001 from 63 fields were evaluated for patho-type using four differentials. In this study, 26, 52, and 28 isolates were identified as races 1, 3, and 4, respectively. One isolate was nonpathogenic on the differentials. Race 4 isolates had the broadest host range and were widely distributed in the adzuki bean-producing regions, especially in central and western Hokkaido. Additional management measures for P. vignae are required if the cultivation area of an agronomically promising cultivar like cv. Syumari (susceptible to race 4) is to be increased.
Integrated Management of Tomato Spotted Wilt on Field-Grown Tomatoes
Authors: Momol M. T. , Olson S. M. , Funderburk J. E. , Stavisky J. , Marois J. J.
Published: May 2007

Epidemics of spotted wilt caused by Tomato spotted wilt virus (TSWV) vectored by Frankliniella occidentalis and possibly other thrips species occur regularly in tomato in the southeastern United States. Field experiments were conducted to determine the effects of UV-reflective mulch, acibenzolar-S-methyl (plant activator), and insecticides on progress of tomato spotted wilt incidence and population dynamics of flower thrips (including F. occidentalis, F. tritici, and F. bispinosa). Whole plots of tomatoes grown on UV-reflective and black polyethylene mulch were divided into subplots of acibenzolar-S-methyl and no acibenzolar-S-methyl, and sub-subplots of insecticide and no insecticide for thrips control. The UV-reflective mulch was more effective than black polyethylene mulch each year in reducing colonization of thrips in May and the consequent primary infections of tomato spotted wilt. Application of acibenzolar-S-methyl further reduced tomato spotted wilt incidence in 2000 and 2002, when disease pressure was great. Reproduction of thrips on tomato was poor in these experiments, but their control in the insecticide-treated sub-subplots prevented secondary spread in both years. The combination of UV-reflective mulch, acibenzolar-S-methyl, and insecticides was very effective in reducing tomato spotted wilt incidence in tomato.
Powdery Mildew of Dill (Anethum graveolens): A New Disease Caused by Erysiphe heraclei Detected in Spain
Authors: Torés J. A. , de Vicente A. , López-Montoya O. , Gómez V.
Published: May 2007

Powdery mildew was observed for the first time on dill (Anethum graveolens L.) in several commercial greenhouses in Almería (southern Spain) during the spring and summer of 2002. Fungal growth appeared as typical white, dense, persistent powdery mildew colonies on leaves, inflorescences, and stems. Hyphae were 6 to 10 μm wide (mean = 6.88, standard deviation [SD] = 1.22, and n = 50). Conidia were produced singly on unbranched three-celled conidiophores, were cylindrical to ovate, and ranged in length from 26 to 42 μm (mean = 33.7, SD = 4.33, n = 55) and width from 12 to 18 μm (mean = 14.4, SD = 1.46). No fibrosin bodies were observed. Germ tubes were formed from the ends of conidia. Appressoria from mycelia were lobed. Conidiophores were 64 to 154 μm long (mean = 110, SD = 19.86, n = 30) with straight foot cells 24 to 42 μm long (mean = 33.8, SD = 6.17) and 6 to 10 μm wide (mean = 8.4, SD = 1). No cleistothecia were found so an accurate identification of the species was not possible. However, on the basis of morphological characteristics of the imperfect state, this powdery mildew corresponds with Erysiphe heraclei, the powdery mildew of umbelliferous crops (1) that was previously reported on dill from France and Portugal (2) and recently from Turkey (3). In Spain, the disease has been previously reported in other umbelliferous plants, such as carrot and celery (2), which are common crops in southern Spain. When infected with E. heraclei, these plants can serve as potential sources of inoculum.

References: (1) U. Braun. Page 216 in: A Monograph of Erysiphales (Powdery Mildew). Nova Hedwigia. J. Cramer Berlin-Stuttgart, 1987. (2) U. Braun. Pages 116–117 in: The Powdery Mildew (Erysiphales) of Europe. Gustav Fischer-Verlag, Jena, Germany, 1995. (3) E. M. Soylu and S. Soylu. Plant Pathol. 52:423, 2003.
First Report of Phytophthora nicotianae on Skimmia japonica in Italy
Authors: Garibaldi A. , Bertetti D. , Gullino M. L.
Published: May 2007

Skimmia japonica, an evergreen flowering shrub, is becoming increasingly popular as a potted ornamental plant in northern Italy and represents 5% of acidophilous plant production; cv. Rubella accounts for 99% of production. During the spring of 2003, in many commercial nurseries located in northwestern Italy, plants of S. japonica cv. Rubella showed extensive chlorosis and root rot, and diseased plants eventually wilted and died without dropping leaves. The disease was widespread and severe, and in some nurseries, 40% of plants were affected. A Phytophthora-like organism was isolated consistently from infected lower stem and root pieces of S. japonica that had been disinfested for 1 min in 1% NaOCl and plated on a medium selective for oomycetes (2). The pathogen was identified based on morphological and physiological features as Phytophthora nicotianae (= P. parasitica [1]). The sporangia produced on V8 medium were ± spherical to obpyriform, obturbinate, papillate, and measured 33 to 94 × 25 to 48 μm (average 56.4 × 36.8 μm). Papillae measured 3.5 to 19 μm (average 7.8 μm). Chlamydospores were spherical with a diameter ranging from 26 to 32 μm (average 29.2 μm). Pathogenicity of four isolates obtained from infected plants was confirmed by inoculating 9-month-old plants of S. japonica cv. Rubella grown in 1-liter pots containing a substrate based on sphagnum peatmoss, pine bark, and clay (70-20-10% vol/vol/vol). Inocula, which consisted of 90-mm-diameter V8 agar disks per pot containing mycelium of each isolate, were introduced and mixed into the substrate in all pots before transplanting. One plant was transplanted into each pot and served as a replicate, and noninoculated plants served as controls. Eight replicates were used for each isolate and the control treatment, and the trial was repeated. All plants were kept outside at temperatures ranging from 16 to 38°C (average temperature 27°C). Inoculated plants developed symptoms of chlorosis, root rot, and wilt within 20 days, while control plants remained symptomless. P. nicotianae consistently was isolated from inoculated plants. Previously, P. nicotianae has been reported on S. japonica in Poland (3). To our knowledge, this is the first report of P. nicotianae on S. japonica in Italy.

References: (1) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St Paul, MN, 1996. (2) H. Masago et al. Phytopathology, 67:425, 1977 (3) G. Szkuta and L. B. Orlikowski. Prog. Plant Prot. 42:808, 2002.
Occurrence of Radish mosaic virus on Cauliflower and Turnip Crops in Iran
Authors: Farzadfar S. , Pourrahim R. , Golnaraghi A. R. , Jalali S. , Ahoonmanesh A.
Published: May 2007

During the spring and summer of 2003, symptoms of mosaic, mottle, and crinkle were observed in cauliflower (Brassica oleracea) and turnip (Brassica rapa) fields in the Qazvin and Esfahan provinces of Iran, respectively. Leaf extracts of these plants, made infective by mechanical inoculation, caused necrotic local lesions on Chenopodium amaranticolor, chlorotic ring spot on Nicotiana tabacum cv. Samsun, and chlorotic local lesions followed by systemic mosaic on Brassica rapa (1). Using double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) and specific polyclonal antibodies (As-0120 and PV-0355) that were kindly prepared by S. Winter (DSMZ, Braunschweig, Germany), the samples were tested for the presence of Radish mosaic virus (RaMV) (family Comoviridae, genus Comovirus). ELISA results showed that the original leaf samples and inoculated indicator plants reacted positively to RaMV antibodies. RaMV has been reported in the United States, Japan, and Europe on turnip and other crucifers (1,2). To our knowledge, this is the first report of RaMV occurring in Iran.

References: (1) R. N. Campbell. Radish mosaic virus. No. 121 in: Descriptions of Plant Viruses. CMI/AAB, Surrey, England, 1973. (2) D. D. Sutic et al. Handb. Plant Virus Diseases. CRC Press, Boca Raton, FL, 1999.
Effect of Autumn Planting Date and Stand Age on Severity of Stem Rust in Seed Crops of Perennial Ryegrass
Authors: Pfender W. F.
Published: May 2007

Perennial ryegrass (Lolium perenne) grown for seed is planted in autumn for July harvest (first-year seed crop), then kept in production for subsequent yearly harvests. Plots of first-year perennial ryegrass planted in early November had only 3% as much stem rust in June as plots planted in mid-September. In other plots where fungicides were used to prevent rust development, seed yield from the November-planted plots was reduced by 23% compared with September-planted plots. In the second-year seed crop, stem rust severity in June was intermediate between severities in early- and late-planted first-year plots. The association of reduced stem rust severity with late planting for first-year crops was observed for five of six perennial ryegrass cultivars tested. Degree of reduction in disease severity due to planting date was greatest for the cultivars that had the highest disease severity in early-planted stands. Delay of autumn planting date may provide a useful cultural control method for first-year stands of perennial ryegrass seed crops.
Protecting Agriculture: The Legal Basis of Regulatory Action in Florida
Authors: Fegan Regina M. , Olexa Michael T. , McGovern Robert J.
Published: May 2007

The Division of Plant Industry of the Department of Agriculture and Consumer Services of Florida is empowered to protect the state's agriculture from both introduction and intrastate movement of pests. This responsibility is shared by similar regulatory agencies of the federal government and other states. The legal basis of such regulatory action, police power and eminent domain, is reviewed. The regulatory processes by the State of Florida of two important citrus pests, the burrowing nematode and Asiatic citrus canker, are presented. It was concluded that Florida's regulatory power to take property is of great importance to the agricultural industry and to Florida's economy. This power must be exercised within the constitutional limitation that “no person shall be deprived of life, liberty, or property without due processes of law.” However, the imminence of an emergency may justify state action without a prior hearing or just compensation of valueless items.
Identification and Characterization of Resistance to Phytophthora infestans in Leaves, Stems, Flowers, and Tubers of Potato Clones in the Pacific Northwest
Authors: Porter L. D. , Inglis D. A. , Johnson D. A.
Published: May 2007

Resistance to Phytophthora infestans in leaves, stems, flowers, and tubers of eight cultivars grown commercially in the Columbia Basin and 29 advanced clones from the Tri-State Potato Variety Development Program was quantified. Foliage of all eight cultivars was susceptible in field and greenhouse tests. Six advanced clones had high levels of resistance in stems and leaves in the field at Mount Vernon, WA, but only two of these six clones had high levels of resistance in leaves and stems in greenhouse tests. Flowers of most plants with high to moderate levels of foliar resistance were susceptible to infection in both the field and greenhouse. Tubers of Umatilla Russet, Russet Legend, Gem Russet, and nine advanced clones, including A90586-11, had high levels of resistance in most laboratory tests. Level of foliar resistance against US-8 and US-11 clonal lineages of P. infestans was variable among clones, but tuber resistance by pathogen clonal lineage varied little among clones. Clones with high resistance expressed quantitative differences compared with susceptible cultivars and likely possess a high level of partial resistance.
Virulence Associations in Oat Crown Rust
Authors: Leonard K. J. , Anikster Y. , Manisterski J.
Published: May 2007

Isolates of Puccinia coronata obtained from natural populations of Avena sterilis in Israel, winter oat (A. sativa) cultivars in Texas, and spring oat cultivars in the Northern Plains states of Minnesota, North Dakota, and South Dakota were analyzed for significance of pairwise virulence associations. Isolates from all three regions were tested on 25 oat lines with single P. coronata (Pc) genes for crown rust resistance from A. sterilis and one line with a Pc gene from A. sativa. Isolates from Israel were tested also on 11 Iowa backcross lines with undesignated crown rust resistance genes from A. sterilis. Four associated virulence groups were identified from significant positive virulence associations that were consistent across all three regions. Group 38 included virulence to Pc-38, Pc-39, Pc-55, Pc-63, and Pc-71; group 45 included virulence to Pc-45, Pc-46, Pc-48, Pc-52, Pc-54, and Pc-57; group 58 included virulence to Pc-35, Pc-40, Pc-58, and Pc-59; and group 61 included virulence to Pc- 36, Pc-51, Pc-56, Pc-60, and Pc-61. Virulence to Pc-70 showed the strongest association to virulences in group 38 but also showed significant association with virulence to Pc-45, Pc-35, and Pc-58. Virulences in group 61 were consistently negatively associated with virulences in group 38 in each region. In Israel, virulences to five of the Iowa lines showed positive associations to virulences in group 61 and negative associations to virulences in groups 38 and 45. Close similarity of reactions of nearly all isolates to Pc-39, Pc-55, and Pc-71 suggest that these genes may be identical or nearly identical alleles.