bluuebunny/crossref_metadata_2025 huggingface dataset:
Identification and Characterization of theSSB1Locus Involved in Symptom Development bySpring beauty latent virusInfection inArabidopsis thaliana
Authors: Fujisaki Koki , Hagihara Fumi , Azukawa Yoshihiro , Kaido Masanori , Okuno Tetsuro , Mise Kazuyuki
Published: May 2007

The natural variation of Arabidopsis thaliana in response to a bromovirus, Spring beauty latent virus (SBLV), was examined. Of 63 Arabidopsis accessions tested, all were susceptible when inoculated with SBLV, although there was a large degree of variation in symptom development. Most accessions, including Columbia (Col-0), were symptomless or developed only mild symptoms, but four accessions, including S96, showed severe symptoms of SBLV infection. Genetic analysis suggested that the difference in the responses of Col-0 and S96 to SBLV was controlled by a single semidominant locus. We have designated this locus SSB1 (symptom development by SBLV infection). By using genetic markers, SSB1 was mapped to chromosome IV. The patterns of distribution and accumulation of SBLV in sensitive accessions were similar to those in the insensitive accessions. In addition, symptom development in S96 by SBLV infection was critically interrupted by the presence of the NahG gene, which encodes salicylic acid (SA) hydroxylase. These data suggest that symptom development in A. thaliana controlled by SSB1 is independent of the efficiency of SBLV multiplication and is dependent on SA signaling.
Temporal Expression of PR-1 and Enhanced Mature Plant Resistance to Virus Infection Is Controlled by a Single Dominant Gene in a New Nicotiana Hybrid
Authors: Cole Anthony B. , Király Lóránt , Lane Leslie C. , Wiggins B. Elizabeth , Ross Kathleen , Schoelz James E.
Published: May 2007

A new variety of Nicotiana edwardsonii, designated N. edwardsonii cv. Columbia, expresses pathogenesis-related (PR) proteins in a temporal manner 45 to 49 days postplanting and also exhibits enhanced resistance to Tobacco mosaic virus, Tobacco necrosis virus, and Tomato bushy stunt virus. In contrast, PR proteins were not expressed in the original N. edwardsonii variety at comparable ages but were induced after onset of a hypersensitive response to viral infection. The temporal induction of PR proteins in ‘Columbia’ was correlated with increases in salicylic acid and glycosylated salicylic acid. Earlier studies noted that some Nicotiana hybrids derived from interspecific crosses constitutively express PR proteins, but the genetic basis of this phenomenon had not been investigated, likely because many interspecific Nicotiana crosses are sterile. However, the close genetic relationship between N. edwardsonii and ‘Columbia’ indicated that a hybrid between these two plants might be fertile, and this proved to be true. Genetic crosses between ‘Columbia’ and N. edwardsonii demonstrated that a single, dominant gene conditioned temporal expression of PR proteins and enhanced resistance. This gene was designated TPR1 (for temporal expression of PR proteins).
Genome-Wide Identification of Plant-Upregulated Genes of Erwinia chrysanthemi 3937 Using a GFP-Based IVET Leaf Array
Authors: Yang Shihui , Perna Nicole T. , Cooksey Donald A. , Okinaka Yasushi , Lindow Steven E. , Ibekwe A. Mark , Keen Noel T. , Yang Ching-Hong
Published: May 2007

A green fluorescent protein-based in vivo expression technology leaf array was used to identify genes in Erwinia chrysanthemi 3937 that were specifically upregulated in plants compared with growth in a laboratory culture medium. Of 10,000 E. chrysanthemi 3937 clones, 61 were confirmed as plant upregulated. On the basis of sequence similarity, these were recognized with probable functions in metabolism (20%), information transfer (15%), regulation (11%), transport (11%), cell processes (11%), and transposases (2%); the function for the remainder (30%) is unknown. Upregulated genes included transcriptional regulators, iron uptake systems, chemotaxis components, transporters, stress response genes, and several already known or new putative virulence factors. Ten independent mutants were constructed by insertions in these plant-upregulated genes and flanking genes. Two different virulence assays, local leaf maceration and systemic invasion in African violet, were used to evaluate these mutants. Among these, mutants of a purM homolog from Escherichia coli (purM∷Tn5), and hrpB, hrcJ, and a hrpD homologs from the Erwinia carotovorum hrpA operon (hrpB∷Tn5, hrcJ∷Tn5, and hrpD∷Tn5) exhibited reduced abilities to produce local and systemic maceration of the plant host. Mutants of rhiT from E. chrysanthemi (rhiT∷ Tn5), and an eutR homolog from Salmonella typhimurium (eutR∷Tn5) showed decreased ability to cause systemic inva sion on African violet. However, compared with the wild-type E. chrysanthemi 3937, these mutants exhibited no significant differences in local leaf maceration. The pheno type of hrpB∷Tn5, hrcC∷Tn5, and hrpD∷Tn5 mutants further confirmed our previous findings that hrp genes are crucial virulence determinants in E. chrysanthemi 3937.
Incidence ofSoybean dwarf virusand Identification of Potential Vectors in Illinois
Authors: Harrison Barbara , Steinlage Todd A. , Domier Leslie L. , D'Arcy Cleora J.
Published: May 2007

Soybean dwarf virus (SbDV), which causes an important disease of soybeans in Japan, is persistently transmitted by aphids and is endemic in forage legumes in the United States. To determine the incidence of SbDV in Illinois, we collected clovers and forage legumes in a total of 49 Illinois counties in 2001 and 2002 and tested them for the presence of SbDV by reversetranscription-polymerase chain reaction. SbDV was detected in 43% of red clover (Trifolium pratense), 10% of white clover (T. repens), and 3% of yellow sweet clover (Melilotus officinalis) plant samples. The dwarfing strain (SbDV-D) was the predominant strain detected in Illinois. In 2000, Aphis glycines, an aphid species that colonizes soybeans, was reported for the first time in North America. To determine whether A. glycines or aphid species found colonizing clover were vectors of SbDV, transmission studies were conducted. Aphids of the species Nearctaphis bakeri reproducibly vectored SbDV among red clovers, and from red clover to soybean. A. glycines did not transmit SbDV; neither did two other clover-infesting aphid species, Acyrthosiphon pisum and Therioaphis trifolii.
Comparison of Visual and Multispectral Radiometric Disease Evaluations of Cercospora Leaf Spot of Sugar Beet
Authors: Steddom K. , Bredehoeft M. W. , Khan M. , Rush C. M.
Published: May 2007

Visual assessments of disease severity are currently the industry standard for quantification of the necrosis caused by Cercospora beticola on sugar beet (Beta vulgaris) leaves. We compared the precision, reproducibility, and sensitivity of a multispectral radiometer to visual disease assessments. Individual wavebands from the radiometer, as well as vegetative indices calculated from the individual wavebands, were compared with visual disease estimates from two raters at each of two research sites. Visual assessments and radiometric measurements were partially repeated immediately after the first assessment at each site. Precision, as measured by reduced coefficients of variation, was improved for all vegetative indices and individual waveband radiometric measures compared with visual assessments. Visual assessments, near-infrared singlewaveband reflectance values, and four of the six vegetative indices had high treatment F values, suggesting greater sensitivity at discriminating disease severity levels. Reproducibility, as measured by a test-retest method, was high for visual assessments, single-waveband reflectance at 810 nm, and several of the vegetative indices. The use of radiometric methods has the potential to increase the precision of assessments of Cercospora leaf spot foliar symptoms of sugar beet while eliminating potential bias. We recommend this method be used in conjunction with visual disease assessments to improve precision of assessments and guard against potential bias in evaluations.
Pathogenicity of Fusarium Species on Different Plant Parts of Spring Wheat Under Controlled Conditions
Authors: Fernandez M. R. , Chen Y.
Published: May 2007

Most of the Fusarium species responsible for Fusarium head blight of wheat in Saskatchewan, Canada, have also been isolated from discolored subcrown internodes/crowns of wheat. It was therefore of interest to compare the susceptibility of heads and ground/underground tissue of wheat to isolates of Fusarium species from different sources. Controlled-environment pathogenicity tests were conducted on heads, seeds, and seedlings of spring wheat. Overall, F. culmorum and F. graminearum were the most pathogenic species, although the former was more pathogenic than the latter. F. equiseti and F. poae were the least pathogenic species, whereas F. avenaceum had intermediate pathogenicity in the head and seed tests, but low pathogenicity in the seedling test. There was a similar pathogenicity among isolates of each Fusarium species from different sources to heads and ground/underground plant parts, indicating a lack of adaptation of these isolates. Our observations suggest that Fusarium inoculum on or in infected seed or plant debris might infect plants at or below soil level, which could then become a source of inoculum for infection of heads in the following season(s). Survival of fungal inoculum in underground plant parts might be important during dry conditions.
First Report of Onion yellow dwarf virus, Leek yellow stripe virus, and Garlic common latent virus in Garlic in Washington State
Authors: Pappu H. R. , Hellier B. C. , Dugan F. M.
Published: May 2007

Washington State ranks fourth in the country in garlic (Allium sativum) production (2). The impact of viruses on garlic production may be significant in Washington State, but little is known about the occurrence or identity of specific viruses (2). The USDA-ARS Western Regional Plant Introduction Station (WRPIS) collects, maintains, and distributes garlic accessions. As part of the regeneration process, accessions are grown in field conditions at the WRPIS farm in Pullman, WA. In June 2004, several WRPIS accessions developed symptoms indicative of viral infection, primarily chlorotic spots and yellow stripes on leaves and scapes. Cultivars Georgia Fire and Georgia Crystal showed more than 90% incidence of symptomatic plants. Some chlorotic spots appeared similar to those caused by Iris yellow spot virus on other Allium spp. such as A. cepa. However, enzyme-linked immunosorbent assay (ELISA), as well as polymerase chain reaction (PCR) with IYSV-specific primers (1) did not reveal the presence of IYSV. Degenerate, group-specific primers to potyviruses (3) and carlaviruses (courtesy of S. D. Wyatt) were used on total nucleic acids extracted from each symptomatic plant with reverse transcription (RT)-PCR. The samples (n = 26) gave an RT-PCR product of the expected size with the group-specific potyvirus RT-PCR test. One sample was positive with the carlavirus group RT-PCR test. RT-PCR products from both tests were cloned and sequenced. Comparisons with sequences in GenBank showed that all but one had Onion yellow dwarf virus (OYDV), whereas one sample had a mixed infection of OYDV and Leek yellow stripe virus. Sequence analysis showed that the carlavirus was Garlic common latent virus. Sequence identities ranged from 95 to 99% for each of the viruses when compared with those available in GenBank. All samples were then tested for each of these viruses with commercially available antisera. Results of ELISA confirmed the findings of RT-PCR. To our knowledge, this is the first report for each of these garlic viruses from Washington State. This finding prompts the need for evaluating all garlic accessions for the potential impact of these viruses on garlic germ plasm conservation and distribution.

References: (1) L. J. du Toit et al. Plant Dis. 88:222, 2004. (2) R. M. Hannan and E. J. Sorensen. Crop Profile for Garlic in Washington. Washington State University Coop Extension and the U.S. Department of Agriculture, 2002. (3) S. S. Pappu et al. J. Virol. Methods 41:9, 1993.
First Report of the Root-Knot Nematode Meloidogyne arenaria Race 2 from Several Vegetable Crops in Jordan
Authors: Karajeh M. , Abu-Gharbieh W. , Masoud S.
Published: May 2007

Meloidogyne arenaria (Neal) Chitwood (race 2) is reported for the first time in Jordan. The nematode populations were recovered from several vegetable crops, including tomato (Lycopersicon esulentum Mill), squash (Cucurbita pepo L.), cucumber (Cucumis sativus L.), and bean (Phaseolus vulgaris L.), at Dier Alla in the northern area of the Jordan Valley. Symptoms included root galling, leaf chlorosis, and stunting. Galled plant root samples were collected during a survey conducted from May 2002 to August 2003 covering most of the irrigated agricultural areas of Jordan. Eighty-three Meloidogyne spp. populations were collected from various vegetable crops and fruit trees. Identification to species and race levels of the nematode populations was based on combination of currently available methods including nematode morphology, host preference based on the North Carolina (NC) differential host test (1), and cytogenetics and DNA-fingerprinting. Seventy of the eighty-three collected populations were identified as M. javanica, five as M. incognita (race 1), three as M. incognita (race 2), and five as M. arenaria (race 2). The perineal patterns of M. arenaria were characterized by a low, round to indented dorsal arch near the lateral field with irregular forks in the lateral field, fine smooth striae, and a distinct whorl. Race 2 was identified with the NC differential host test. Cytogenetic studies indicated that M. arenaria populations were triploid with an average of 52.2 chromosomes, while the populations of M. incognita (race 1), M. incognita (race 2), and M. javanica were hypotriploid with an average of 45.2, 46.1, and 46.7 chromosomes, respectively. Two polymerase chain reaction (PCR)-based assays were used to confirm species identification and to study genetic variability of the Meloidogyne spp. populations including sequence characterized amplified regions (SCAR) and random amplified polymorphic DNA (RAPD). In the SCAR-PCR-based assay (2), typical DNA products of 420, 670, or 1,200 bp in size were amplified by using extracted DNA of M. arenaria (race 2), M. javanica, or M. incognita (race 1 or 2), respectively, as template DNA. The RAPD-PCR primer, OPA-01, produced DNA patterns with bands that clearly distinguished M. arenaria from the other two Meloidogyne spp. To our knowledge, this is the first report of the root-knot nematode, M. arenaria race 2, in Jordan.

References: (1) A. Taylor and J. Sasser, North Carolina State University Graphics, Raleigh, NC, 1978. (2) C. Zijlstra et al. Nematology 2:847, 2000.
Effect of the F129L Mutation in Alternaria solani on Fungicides Affecting Mitochondrial Respiration
Authors: Pasche J. S. , Piche L. M. , Gudmestad N. C.
Published: May 2007

Isolates of Alternaria solani previously collected from throughout the Midwestern United States and characterized as being azoxystrobin sensitive or reduced sensitive were tested for sensitivity to the Quinone outside inhibitor (QoI) fungicides famoxadone and fenamidone and the carboxamide fungicide boscalid. All three fungicides affect mitochondrial respiration: famoxadone and fenamidone at complex III, and boscalid at complex II. A. solani isolates possessing reducedsensitivity to azoxystrobin also were less sensitive in vitro to famoxadone and fenamidone compared with azoxystrobin-sensitive isolates, but the shift in sensitivity was of lower magnitude, approximately 2- to 3-fold versus approximately 12-fold for azoxystrobin. The in vitro EC50 values, the concentration that effectively reduces germination by 50% relative to the untreated control, for sensitive A. solani isolates were significantly lower for famoxadone and azoxystrobin than for fenamidone and boscalid; whereas, for reduced-sensitive isolates, famoxadone EC50 values were significantly lower than all other fungicides. Isolates of A. solani with reducedsensitivity to azoxystrobin were twofold more sensitive in vitro to boscalid than were azoxystrobin-sensitive wild-type isolates, displaying negative cross-sensitivity. All isolates determined to have reduced-sensitivity to azoxystrobin also were determined to possess the amino acid substitution of phenylalanine with leucine at position 129 (F129L mutation) using real-time polymerase chain reaction. In vivo studies were performed to determine the effects of in vitro sensitivity shifts on early blight disease control provided by each fungicide over a range of concentrations. Reduced-sensitivity to azoxystrobin did not significantly affect disease control provided by famoxadone, regardless of the wide range of in vitro famoxadone EC50 values. Efficacy of fenamidone was affected by some azoxystrobin reduced-sensitive A. solani isolates, but not others. Boscalid controlled azoxystrobin-sensitive and reduced-sensitive isolates with equal effectiveness. These results suggest that the F129L mutation present in A. solani does not convey cross-sensitivity in vivo among all QoI or related fungicides, and that two- to threefold shifts in in vitro sensitivity among A. solani isolates does not appreciably affect disease control.
Impatiens necrotic spot virus in Greenhouse-Grown Potatoes in New York State
Authors: Perry K. L. , Miller L. , Williams L.
Published: May 2007

Impatiens necrotic spot virus (INSV; genus Tospovirus) was detected in experimental greenhouse-grown potatoes (Solanum tuberosum) and Nicotiana benthamiana in New York State in July and August of 2003 and 2004. Potato leaves exhibiting necrotic lesions with a concentric pattern similar to those induced by Tomato spotted wilt virus (1) were observed on cvs. Atlantic, Huckleberry, NY115, and Pentland Ivory. The presence of INSV was confirmed using double-antibody sandwich enzyme-linked immunosorbent assay and a rapid ‘ImmunoStrip’ assay (Agdia, Inc., Elkhart, IN). INSV-specific sequences were amplified from total RNA extracts using reverse transcription-polymerase chain reaction with ‘Tospovirus Group’ primers (Agdia, Inc.) and two independently amplified DNAs were sequenced. A common sequence of 355 nucleotides (GenBank Accession No. AY775324) showed 98% identity to coding sequences in an INSV L RNA. The virus was mechanically transmitted to potato and N. benthamiana and could be detected in asymptomatic, systemically infected potato leaves. Stems nodes and leaves were removed from infected potato plants, and sterile in vitro plantlets were established (2). None of the regenerated in vitro plantlets of cvs. Pentland Ivory (6 plantlets) or NY115 (5 plantlets) were infected with INSV. Two of ten regenerated cv. Atlantic plantlets initially tested positive, but INSV could not be detected after 6 months in tissue culture. In vitro tissue culture plantlets could not be established from infected cv. Huckleberry plants, even though they were consistently obtained from uninfected plants. Infected greenhouse plants were grown to maturity and the tubers harvested, stored for 6 months at 4°C, and replanted in the greenhouse. INSV could not be detected in plants from 26 cv. Huckleberry, 4 cv. NY115, or 4 cv. Atlantic tubers. Although this isolate of INSV was able to systemically infect potato, it was not efficiently maintained or transmitted to progeny tubers. This might explain why INSV has not been reported as a problem in potato production. Lastly, in both years, dying N. benthamiana provided the first sign of a widespread greenhouse infestation of INSV in a university facility housing ornamental and crop plants. INSV induced a systemic necrosis in N. benthamiana, and this host may be useful as a sensitive ‘trap’ plant indicator for natural infections in greenhouse production.

References: (1) T. L. German. Tomato spotted wilt virus. Pages 72–73 in: Compendium of Potato Diseases. W. R. Stevenson et al., eds. The American Phytopathological Society, St. Paul, 2001. (2) S. A. Slack and L. A. Tufford. Meristem culture for virus elimination. Pages 117–128 in: Fundamental Methods of Plant Cell, Tissue and Organ Culture and Laboratory Operations. O. L. Gamborg and G. C. Philips, eds. Springer-Velag, Berlin, 1995.
Genetics of Chickpea Resistance to Five Races of Fusarium Wilt and a Concise Set of Race Differentials for Fusarium oxysporum f. sp. ciceris
Authors: Sharma Kamal Dev , Chen Weidong , Muehlbauer Fred J.
Published: May 2007

Genetics of resistance in chickpea accession WR-315 to Fusarium wilt was investigated, and a concise set of differentials was developed to identify races of Fusarium oxysporum f. sp. ciceris. A population of 100 F7 recombinant inbred lines (RILs) from a cross of WR-315 (resistant) and C-104 (susceptible) was used to study genetics of resistance to races 1A, 2, 3, 4, and 5 of F. oxysporum f. sp. ciceris, and a population of 26 F2 plants from a cross between the same two parents was used to study inheritance of resistance to race 2. Segregations of the RILs for resistance to each of the five races suggest that single genes in WR-315 govern resistance to each of the five races. A 1:3 resistant to susceptible ratio in the F2 population indicated that resistance in WR-315 to race 2 was governed by a single recessive gene. A race-specific slow disease progress reaction was observed in chickpea line FLIP84-92C(3) to infection by race 2, a phenomenon termed as slow wilting, that is different from previously reported late wilting with respect to latent period, disease progress rate, and final disease rating. Twenty-nine germ plasm lines (27 Cicer arietinum and two C. reticulatum) including previously used differentials were evaluated for their reactions to infection by the five races. Only eight of the 29 germ plasm lines differentiated at least one of the five races based on either resistant or susceptible reactions, whereas the remaining germ plasm lines were either susceptible or resistant to all five races or differentiated them by intermediate reactions. A concise set of eight chickpea lines comprised of four genotypes and four F7 RILs with vertical resistance was developed as differentials for race identification in F. oxysporum f. sp. ciceris. These differential lines were characterized by early appearance of wilt symptoms, and clear and consistent disease phenotypes based on no wilt or 100% wilt incidence, which offers important improvements over previously available differential sets and provides more precise and unambiguous identification of the races.
Crown Rot of Abies balsamea var. phanerolepis Caused by Phytophthora cactorum in Virginia
Authors: Hong C. X. , Marston C. D.
Published: May 2007

In early July 2004, a severe crown rot of Canaan fir (Abies balsamea var. phanerolepis Fern.) was reported to the Virginia Cooperative Extension, Frederick County Office, and subsequently to the Virginia Tech Disease Clinic in Virginia Beach. One thousand five-year-old Canaan fir transplants (approximately 11 mm in caliper and 31 cm high) had been purchased from a tree nursery in Oregon and planted in the field in Frederick County, VA, in April of 2004. The field site had not been cultivated for 4 years after an apple orchard had been removed in 2000. By mid-May, needle browning had become serious, affecting the lower crown first. By August, transplants had suffered 40% mortality. Basal stems of affected plants were obviously discolored. Root and basal stem samples from several infected plants were then cultured on PARP-V8 agar on three different dates. Phytophthora sp. isolates were recovered from all stem samples but none from the roots. These isolates produced a large number of papillate sporangia that were caducous with short pedicels. Abundant oogonia with paragynous antheridia formed oospores directly on isolation plates within 7 days. The isolates were keyed as P. cactorum (2). This identification was confirmed using a single-strand-conformation polymorphism analysis of ribosomal DNA internal transcribed spacer (ITS)-1 (4). It appears that the source of inoculum was P. cactorum associated with the previous apple crop, since Canaan fir from the same transplant lot planted in a nearby field without a history of apples remained healthy. P. cactorum has been reported to cause root rot of noble fir (A. procera Rhedo), Pacific silver fir (A. amabilis (Dougl.) Forbes), and Shasta red fir (A. magnifica var. shastensis Lemm.) in the Pacific Northwest (3). It has also caused crown rot of Fraser fir (A. fraseri (Pursh) Poir.), noble fir, white fir (A. concolor (Gord. & Glend.) Lindl.), and balsam fir (A. balsamea (L.) Mill.) in Michigan (1). To our knowledge, this is the first report of P. cactorum attacking Canaan fir. Canaan fir currently is a recommended Christmas tree species for areas where Fraser fir does not do well due to root rot caused by Phytophthora cinnamomi. This study suggests that such a recommendation must be used with caution. Growing Canaan fir trees in P. cactorum-infested soil could result in devastating crop losses as reported in this note.

References: (1) G. C. Adams, Jr. and A. Bielenin. Plant Dis. 72:79, 1988. (2) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996. (3) P. B. Hamm and E. M. Hansen. Eur. J. For. Pathol. 12:167, 1982. (4) P. Kong et al. Fungal Genet. Biol. 39:238, 2003.
Pathogenicity of Xanthomonas translucens from Annual Bluegrass on Golf Course Putting Greens
Authors: Mitkowski N. A. , Browning M. , Basu C. , Jordan K. , Jackson N.
Published: May 2007

Bacterial wilt of Poa annua has been seen increasingly in the Northeast and mid-Atlantic United States in the past few years. The disease causes severe injury to putting greens and can kill large stands of turfgrass. For some time, however, both the bacterial origin of the disease and the causal agent were in doubt. In order to investigate the identity of the causal agent, isolation of the pathogen was undertaken and pathogenicity was confirmed using Koch's postulates on P. annua. Additional pathogenicity trials then were undertaken to determine the host range of the causal bacterium. Ability of the bacterium to cause disease was restricted to P. annua var. annua and P. attenuata. However, the bacterium was able to survive asymptomatically in vascular systems of P. annua var. reptans and P. trivialis. Experiments to determine the optimal growth temperature of the organism demonstrated that the bacterial growth peaked between 30 and 35°C. Fatty acid analysis suggested that the bacterium might be a species of Xanthomonas but was inconclusive. Ribosomal RNA analysis demonstrated significant similarity to the American Type Culture Collection isolate of Xanthomonas translucens pv. poae at 99.8%. Comparison of the host range to previously reported data agrees with our molecular findings and indicates that the likely casual organism of bacterial wilt of annual bluegrass is X. translucens pv. poae.
Effect ofCowpea severe mosaic viruson Crop Growth Characteristics and Yield of Cowpea
Authors: Booker H. M. , Umaharan P. , McDavid C. R.
Published: May 2007

Field experiments were carried out in St. Augustine, Trinidad & Tobago, West Indies to determine the effects of time of inoculation of Cowpea severe mosaic virus (CPSMV) and cultivar on crop growth and yield in cowpea (Vigna unguiculata). Crop growth and yield loss were investigated through growth analysis and yield component analysis on three cultivars in two seasons (wet and dry). Time of inoculation had the most profound impact on yield. Inoculations during the early log phase (seedling stage), 12 days after seeding (DAS), consistently had the greatest impact (50 to 85% yield loss) compared with those inoculated during the exponential growth phase (24 DAS; 22 to 66% yield loss) or linear growth phase (35 DAS; 2 to 36% yield loss). The effects were particularly pronounced in the dry season and in the more determinate cultivar, H8-8-27. Reduction in maximum leaf area index, leaf area duration, or maximum vegetative dry matter explained reductions in yield. Yield reductions resulted primarily from reduced pod number per plant and, to a lesser extent, from reduced average pod dry weight. The results show that CPSMV control measures should be aimed at delaying infection by CPSMV to minimize the impact on cowpea yield.
Evaluation of Avena spp. Accessions for Resistance to Oat Stem Rust
Authors: Steinberg J. Gold , Fetch J. Mitchell , Fetch T. G.
Published: May 2007

Oat stem rust, caused by Puccinia graminis f. sp. avenae, can cause significant yield losses in the eastern prairie region of western Canada. Currently, the predominant race of P. graminis f. sp. avenae in this region is NA67. Few genes confer resistance to NA67, and none are present in any oat cultivars registered for production in Canada. To detect lines exhibiting resistance to race NA67, we evaluated 9,978 accessions from 22 Avena spp. in field nurseries from 2001 to 2004. In all, 35 accessions were highly resistant and 12 were moderately resistant, comprised mostly of the species A. strigosa. Seventy-one accessions had an intermediate response, comprised mostly of A. abyssinica, A. barbata, A. sterilis, and A. vaviloviana. All other accessions (9,860 = 98.8%) were susceptible to race NA67. Some highly resistant accessions were found to have been incorrectly classified previously as hexaploid species A. sativa or A. sterilis, and were confirmed by chromosome counts to be diploid or tetraploid. The most promising source of novel stem rust resistance is from the diploid species A. strigosa. Transfer of resistance from diploid and tetraploid species to A. sativa is very difficult, but the lines identified in this study should prove useful as new sources of resistance to oat stem rust.
The Root-Knot Nematode Meloidogyne fallax on Strawberry in the Netherlands
Authors: van der Sommen A. T. C. , den Nijs L. J. M. F. , Karssen G.
Published: May 2007

The root-knot nematode Meloidogyne fallax Karssen is closely related to M. chitwoodi Golden, O'Bannon, Santo & Finley. Both species have a wide host range and have been designated as quarantine nematodes by several countries. Strawberry (Fragaria ananassa L.) is considered a poor host for M. chitwoodi (2,3), but the host status for M. fallax in unknown. During 2003, a host suitability study was performed with four common strawberry cultivars (Ciflorette, Elsanta, Kimberly, and Mara des bois) on a field naturally infested with M. fallax near Wintelre, the Netherlands. The identity of the nematode was confirmed, prior to and after the test, by using morphological characteristics, isozymes, and polymerase chain reaction (PCR). The field was not infested with M. hapla Chitwood. The host test included 15 replicates per cultivar and started in April with a mean initial M. fallax density of approximately 4,500 second-stage juveniles per 100 ml of soil. The plants used in the field trial were multiplied by cuttings and grown on artificial substrate free from any Meloidogyne species. Upon plant harvesting in October, the number of root galls were counted and cvs. Mara des bois and Ciflorette did not show any typical root-knot symptoms, while cvs. Elsanta and Kimberly expressed only a few small galls. Additionally, high numbers of nematodes were found in the roots using the centrifugal floating method (1). The mean numbers of isolated nematodes for all cultivars (females, 116; males, 80; second-stage juveniles, 6,636; third- and fourth-stage juveniles, 49; and eggs, 920 per 10 g of roots) suggests that the tested strawberry cultivars are good hosts for M. fallax despite the lack of clear root galling or visible plant grow reduction as has been observed in the past for M. javanica on strawberry (4). To our knowledge, this is the first report of strawberry as a host for M. fallax, and it suggests that M. fallax could be spread by strawberry transplant grown in M. fallax infested soil. The Dutch Plant Protection Service is currently discussing appropriate action, such as an additional root-knot nematode test in addition to visual root inspection, before strawberry plants are shipped and cultivated.

References: (1) W. A. Coolen and J. D'Herde. A method for the quantitative extraction of nematodes from plant tissue. Ghent State Agriculture Research Centre, 1972. (2) A. M. Golden et al. J. Nematol. 12:319, 1980. (3) J. H. O'Bannon et al. Plant Dis. 66:1045, 1982. (4) D. P. Taylor and C. Netscher. Cah. O.R.S.T.O.M, Ser. Biol. 10:247, 1975.
Allamanda Mosaic Caused by Cucumber mosaic virus in Taiwan
Authors: Chen Y. K. , Yang C. C. , Hsu H. T.
Published: May 2007

Allamanda (Allamanda cathartica L., family Apocynaceae) is native to Brazil and is a popular perennial shrub or vine ornamental in Taiwan. Plants showing severe mosaic, rugosity, and leaf distortion symptoms on leaves are common in commercial nurseries and private gardens. Examination of crude sap prepared from symptomatic leaves using an electron microscope revealed the presence of spherical virus particles with a diameter of approximately 28 nm. The virus was mechanically transmitted to indicator plants and induced symptoms similar to those incited by Cucumber mosaic virus (CMV). The virus caused local lesions on inoculated leaves of Chenopodium quinoa and C. amaranticolor and systemic mosaic in Cucumis sativus, Lycopersicon esculentum, Nicotiana benthamiana, N. glutinosa, N. rustica, and N. tabacum. On N. tabacum, necrotic ringspots developed on inoculated leaves followed by systemic mosaic. Tests of leaf sap extracted from naturally infected allamanda and inoculated indicator plants using enzyme-linked immunosorbent assay were positive to rabbit antiserum prepared to CMV. Viral coat protein on transblots of sodium dodecyl sulfate-polyacrylamide gel electrophoresis reacted with CMV subgroup I specific monoclonal antibodies (2). With primers specific to the 3′-half of RNA 3 (1), amplicons of an expected size (1,115 bp) were obtained in reverse transcription-polymerase chain reaction (RT-PCR) using total RNA extracted from infected allamanda and N. benthamiana. The amplified fragment (EMBL Accession No. AJ871492) was cloned and sequenced. It encompasses the 3′ part of the intergenic region of RNA 3 (158 nt), CP ORF (657 nt), and 3′ NTR (300 nt) showing 91.8–98.9% and 71.4–72.8% identities to those of CMV in subgroups I and II, respectively. Results of MspI-digested restriction fragment length polymorphism patterns of the RT-PCR fragment and the nucleotide sequence analysis indicate that the CMV isolate from allamanda belongs to subgroup IB, which is predominant on the island. To our knowledge, CMV is the only reported virus that infects allamanda and was first detected in Brazil (3), and this is the first report of CMV infection in allamanda plants occurring in Taiwan.

References: (1) Y. K. Chen et al. Arch. Virol. 146:1631, 2001. (2) H. T. Hsu et al. Phytopathology 90:615, 2000. (3) E. W. Kitajima. Acta. Hortic. 234:451, 1988.
Reverse Transcription Loop-Mediated Isothermal Amplification of DNA for Detection of Potato virus Y
Authors: Nie Xianzhou
Published: May 2007

A reverse transcription loop-mediated isothermal amplification of DNA (RT-LAMP) for detection of Potato virus Y (PVY) was developed. In this procedure, a set of four primers matching a total of six sequences of the coat protein (CP) gene of PVY were designed in such a way that a loop could be formed and elongated during DNA amplification. Using PVY CP complementary DNA clones as templates, the LAMP reaction was optimized by adjusting the concentrations of MgSO4, dNTPs, and Bst DNA polymerase. The effects of fragment length of target DNA on LAMP also were investigated. Two-step and one-step RT-LAMPs were performed using RNA extracts of various PVY cultures, and the results were correlated with two-step reverse transcription polymerase chain reaction (RT-PCR) for detection of PVY. Further, the turbidity caused by precipitation of magnesium pyrophosphate formed in positive RT-LAMP reactions was used to measure the amplification by utilizing a time-saving spectrophotometric method. The one-step RT-LAMP-turbidity method gave results comparable with the two-step RT-PCR method for detection of PVY from potato leaf and tuber samples. Of the total 240 samples, 234 were diagnosed similarly by both methods.
Effect of Pruning on Apple Scab in Organic Apple Production
Authors: Holb I. J.
Published: May 2007

In a 3-year Hungarian study, the effectiveness of apple tree pruning as a management tactic for control of apple scab (Venturia inaequalis) was investigated on two susceptible (cvs. Jonagold and Mutsu), two moderately susceptible (cvs. Elstar and Idared), and two Vfresistant apple cultivars (cvs. Liberty and Prima) in three high-density organic apple orchards treated with copperand sulfur-based fungicide programs. The area under the disease progress curve (AUDPC) for leaf and fruit incidences was calculated to evaluate three winter pruning treatments (unpruned, weakly pruned, and strongly pruned). Strong pruning significantly decreased leaf scab on the susceptible and the moderately susceptible cultivars at all sites compared with unpruned ones. Moreover, for the cultivar Jonagold in all years and for the cultivar Mutsu in 2001, AUDPC values of strongly pruned trees were significantly lower at P = 0.05 compared with the weaklypruned trees. The effect of pruning on development of fruit scab was weaker than on leaf scab in all years and at all sites. For fruit scab incidence on susceptible cultivars, only strong pruning treatments decreased AUDPC significantly compared with unpruned treatments. The effects of pruning treatments on moderately susceptible cultivars were significant only in 2001 at all sites. Resistant cultivars showed no significant effect of pruning treatments on development of either fruit or leaf scab except for cultivar Liberty in 2001 at one site. Pruning resulted in no consistent difference in the apple tree canopy microclimate. However, strong pruning resulted in improved spray deposition in the tree canopy when applications were made with an airblast sprayer at midsummer. Results are compared with similar studies, and their biological interpretation is discussed.
Influence of Temperature and Relative Humidity on Sporulation of Cercospora zeae-maydis and Expansion of Gray Leaf Spot Lesions on Maize Leaves
Authors: Paul P. A. , Munkvold G. P.
Published: May 2007

Controlled environment studies were conducted to determine the effects of temperature on the expansion of lesions of gray leaf spot, and the effects of temperature and relative humidity on the sporulation of Cercospora zeae-maydis on maize (Zea mays). For the lesion expansion experiment, potted maize plants were spray inoculated at growth stage V6, bagged, and incubated at 25 to 28°C and 100% relative humidity for 36 to 40 h. Symptomatic plants were transferred to growth chambers and exposed to constant temperatures of 25, 30, and 35°C. Lesion area (length by width) was measured at 4-day intervals for 17 days. For sporulation studies, lesions were excised from naturally infected maize leaves, measured, and incubated at constant temperature (20, 25, 30, or 35°C) and relative humidity (70, 80, 90, or 100%) for 72 h. Sporulation was estimated as the number of conidia per square centimeter of diseased leaf tissue. A quadratic function was used to model the relationship between log-transformed conidia per square centimeter at 100% relative humidity and temperature. Temperature had a significant effect on lesion expansion (P ≤ 0.05). At 25 and 30°C, the rate of lesion expansion was significantly higher than at 35°C (P ≤ 0.05). The largest lesions and the highest mean rate of lesion expansion were observed at 30°C; however, the mean lesion expansion rate at this temperature was not significantly different from that at 25°C. The interaction effect of temperature and relative humidity on the log of conidia per square centimeter of diseased tissue was significant (P ≤ 0.05). At 100% relative humidity, the effect of temperature on sporulation was significant (P ≤ 0.05), with maximum spore production occurring at 25 and 30°C. The quadratic model explained between 49 and 80% of the variation in the log of conidia per square centimeter at 100% with variation in temperature. These results suggest that the rapid increase in gray leaf spot severity generally observed during mid- and late summer may be due to favorable conditions for lesion expansion during this period. When relative humidity is >95%, expanding lesions may serve as a source of inoculum for secondary infections.
Comparative Analyses of Lettuce Drop Epidemics Caused by Sclerotinia minor and S. sclerotiorum
Authors: Hao J. J. , Subbarao K. V.
Published: May 2007

Temporal and spatial patterns of lettuce (Lactuca sativa) drop caused by Sclerotinia minor and S. sclerotiorum were determined in lettuce fields in the Salinas, Santa Maria, and San Joaquin Valleys in California during 1995 to 1998. Of the 25 commercial fields assessed, 14 had predominantly S. minor, 9 had predominantly S. sclerotiorum, and 2 had varying levels of both species. Sclerotinia infections were classified based on symptoms: those caused directly by eruptive germination of sclerotia (type I) and those caused by the airborne ascospores (type II). The precise location of diseased and healthy plants was mapped and lettuce drop progress was determined at different crop growth stages. Spatial patterns of disease incidence were analyzed using 1-by-1-, 2-by-2-, 3-by-3-, and 4-by-4-m quadrat sizes. Regardless of the analytical method employed, disease incidence with type I infection showed an aggregated pattern in a majority of the fields evaluated and random patterns in fields where incidence was low. In all fields with type I infection, disease progress followed the monomolecular model, typical of soilborne diseases. For fields with aggregated distribution, spatial dependence was observed up to 10 m and was either isotropic or random in direction, suggesting the potential influence of tillage operations on inoculum distribution and disease incidence. Lettuce drop incidence in fields with type II infection was erratic in time and peaked within a very short time. However, disease incidence showed an aggregated pattern in all fields evaluated. Spatial dependence of quadrats generally was detected in two adjacent directions, suggesting a directional gradient perhaps caused by wind direction during ascospore dissemination. Increasing quadrat sizes usually increased the degree of aggregation of lettuce drop, but not the distribution pattern itself. These results demonstrate that the source of inoculum and the type of infections they cause are most likely to determine spatial patterns of lettuce drop in the field.
Ascospore Deposition and Epiphytic Growth in Relation to Fungicide Timing for Control of Greasy Spot Rind Blotch Caused by Mycosphaerella citri
Authors: Mondal S. N. , Timmer L. W.
Published: May 2007

Greasy spot rind blotch is a serious problem in Florida for the production of grapefruit (Citrus paradisi) for the fresh market. In the 1970s to the early 1980s, the disease was described in detail and the cause was determined to be Mycosphaerella citri, the same species responsible for greasy spot of foliage. The most appropriate timing for fungicide sprays was determined at that time, but peak ascospore release has changed in recent years. In the present study, the relationship of ascospore deposition and fungal growth on fruit was determined in order to more accurately time fungicide applications. Infection of fruit appears to occur similarly to that of leaves: by deposition of ascospores and germination to produce epiphytic growth followed by penetration of the fungus through stomata. Ascospore deposition occurred mostly in May and June, but epiphytic growth began only after the onset of the summer rainy season in June in 2002 and 2003. Ascospore deposition was lower in 2002 than in 2003, but development of epiphytic growth was similar in both years. Timing of fenbuconazole sprays was evaluated in the 2001, 2002, and 2003 seasons. Of the single-spray applications, those in July were the most effective, sprays in June and August were moderately effective, and those made in May or September were ineffective. Two- and three-spray programs from June through August were usually more effective than single sprays, and four monthly sprays from May to August were needed for a high level of control. Fungicide applications are needed about every 3 to 4 weeks after the beginning of the rainy season in June through August for a high level of control of rind blotch.
Survey for Viruses of Grapevine in Oregon and Washington
Authors: Martin R. R. , Eastwell K. C. , Wagner A. , Lamprecht S. , Tzanetakis I. E.
Published: May 2007

Grapevines (Vitis spp.) in Washington and Oregon were surveyed for the prevalence of key grapevine viruses. Samples collected from 1,522 vines in Washington were tested for Rupestris stem pitting associated virus (RSPaV), Grapevine fanleaf virus (GFLV), Arabis mosaic virus (ArMV), Tomato ringspot virus (ToRSV), and Grapevine leafroll associated virus-3 (GLRaV-3). Tests were also conducted for GLRaV-1 and -2 on 420 samples from Washington. Two hundred forty samples collected from wine grape vineyards in Oregon were tested for GLRaV-1, -2, and -3, and an additional 2,880 samples were collected from 40 vineyards known to have high populations of Xiphinema americanum nematodes. The latter were tested for ArMV, ToRSV, and GFLV. GLRaV-1, -2, and -3 were detected in 2.6, 0.2, and 6.5% of the Washington samples and in 3.0, 0.4, and 4.4% of the Oregon samples. RSPaV was detected in 4.6% of the samples from Washington. No ToRSV, ArMV, or GFLV was detected in any of the samples from Oregon or Washington. Transmission of field isolates of GLRaV-3 from Washington by the grape mealybug also was demonstrated.