bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Evidence That Strain BV-15 of Peanut Stunt Cucumovirus Is a Reassortant Between Subgroup I and II Strains
Authors: Hu C.-C. , Ghabrial S. A.
Published: May 2007

In Northern hybridization assays, RNA1 of peanut stunt virus (PSV) strain BV-15 hybridized strongly with a cloned cDNA probe to RNA1 from strain PSV-W (subgroup II). Cloned probes to PSV-W RNA2 and RNA3, however, did not hybridize with the corresponding RNAs from strain BV-15. The complete nucleotide sequence of PSV-BV-15 RNA2 has been determined, and sequence comparison analysis showed that it is closely related to PSV subgroup I strains; the percent nucleotide sequence identity between PSV-BV-15 RNA2 and RNA2 sequences from PSV subgroup I and II strains were 90.5 and 75%, respectively. The possibility that PSV-BV-15 RNA2 may contain short regions derived from a subgroup II strain (i.e., represent a mosaic structure indicative of recombination) was investigated. Results indicated, however, that the entire PSV-BV-15 RNA2 sequence is derived from a subgroup I strain. PSV-BV-15 RNA3 has previously been shown to belong to subgroup I strains. These results thus establish that PSV strain BV-15 is a natural reassortant between PSV subgroups I and II strains. A reverse transcription-po-lymerase chain reaction assay is proposed for differentiating between this reassortant strain and PSV strains in subgroups I and II.
Comparison of Monoclonal Antibodies and Polymerase Chain Reaction Assays for the Typing of Isolates Belonging to the D and M Serotypes of Plum Pox Potyvirus
Authors: Candresse T. , Cambra M. , Dallot S. , Lanneau M. , Asensio M. , Gorris M. T. , Revers F. , Macquaire G. , Olmos A. , Boscia D. , Quiot J. B. , Dunez J.
Published: May 2007

Plum pox potyvirus (PPV) isolates may be divided into four groups separated by serological, molecular, and epidemiological differences. Monoclonal antibodies specific for the two major groups of isolates, represented by the D and M serotypes of the virus, have been obtained. Polymerase chain reaction (PCR)-based assays allowing the direct detection and differentiation of PPV isolates have also been developed. We now report on a large-scale comparison of these two typing approaches. The results obtained show an overall excellent correlation between the results obtained in indirect double-antibody sandwich enzyme-linked immunosorbent assay using PPV-D— and PPV-M—specific monoclonal antibodies and those derived from either specific PCR assays or restriction fragment length polymorphism analysis of PCR fragments. Without exception, all isolates reacting positively with the PPV-M—specific monoclonal antibody were found to belong to the M serotype using the PCR-based assays, while 51 out of 53 isolates recognized by the D-specific monoclonal antibodies belonged to the D serotype according to the PCR typing results. However, failure to react with a specific monoclonal antibody did not prove as effective a predictor of the serotype of the isolate analyzed. In a few cases, the results obtained with the various techniques diverged, indicating low level variability of the epitopes recognized by the serotype-specific monoclonal antibodies. Isolates belonging to the two minor groups of PPV (El Amar and Cherry) also gave divergent results, indicating that the current typing assays are not suited for the analysis of such isolates.
Effect of a Soil Amendment on the Survival of Ralstonia solanacearum in Different Soils
Authors: Michel Vincent V. , Mew T. W.
Published: May 2007

The effect of a soil amendment (SA) composed of urea (200 kg of N per ha) and CaO (5,000 kg/ha) on the survival of Ralstonia solanacearum in four Philippine soils was investigated in a series of laboratory experiments. Within 3 weeks after application, the SA either caused an initial decrease, a final decline, or no change in the pathogen population, depending on the particular soil type. An initial decrease occurred in a soil with a basic pH and resulted in a significantly (P < 0.001) lower pathogen population immediately and at 1 week after amending the soil. This decrease was probably due to the high pH in the soil during urea hydrolysis. A final decline in the R. solanacearum population after 3 weeks occurred in two soils in which nitrite accumulated after 1 week. In these soils, no decline in bacterial levels occurred when nitrite formation was inhibited by 2-chloro-6-trichloromethylpyridine. In the soil with low pH, no nitrite accumulated and the R. solanacearum population did not decline. The suppressive effects of pH and nitrite on R. solanacearum growth were confirmed by in vitro experiments. Ammonium reduced the growth of R. solanacearum, but was not suppressive. Interactions of pH with ammonium and nitrite also occurred, whereby ammonium reduced growth of R. solanacearum only at pH 9 and nitrite was suppressive only at pH 5. Nitrate had no effect on R. solanacearum growth in vitro.
Biological, Serological, and Molecular Differences Among Isolates of Potato A Potyvirus
Authors: Rajamäki M. , Merits A. , Rabenstein F. , Andrejeva J. , Paulin L. , Kekarainen T. , Kreuze J. F. , Forster R. L. S. , Valkonen J. P. T.
Published: May 2007

Sequences of the coat protein (CP) and 3′-end nontranslated region (3′NTR) of 13 isolates and the helper component proteinase (HC) of nine isolates of potato A potyvirus (PVA) were determined and compared with the eight previously determined PVA CP and 3′NTR sequences and one HC sequence. CP amino acid (aa), 3′NTR nucleotide, and HC aa sequence identities were 92.9, 93.4, and 94.8%, respectively. Sequence data, serological tests, and the necrotic local lesions induced in the leaves of the potato hybrid ‘A6’ confirmed that tamarillo mosaic virus is a strain of PVA. The aa substitutions A6T and G7S in the CP N-terminus were correlated with loss of aphid transmissibility. Development of necrotic lesions or nonnecrotic symptoms in the systemically infected leaves or lack of systemic spread in potato cv. King Edward were used to place the PVA isolates into four strain groups, but this grouping was not correlated with any differences in CP, HC, or 3′NTR. Recognition of CP by three monoclonal antibodies was used to place the PVA isolates into three groups different from the four groups above. The epitopes of two mono-clonal antibodies were mapped by site-directed mutagenesis to the same lysine residue at the CP aa 34.
Comparison of Ambisense M RNA of Watermelon Silver Mottle Virus with Other Tospoviruses
Authors: Chu Fang-Hua , Yeh Shyi-Dong
Published: May 2007

Double-stranded genomic RNAs (dsRNAs) extracted from Chenopodium quinoa infected with watermelon silver mottle virus (WSMV) were similar to those of tomato spotted wilt virus (TSWV, serogroup I) and impatiens necrotic spot virus (INSV, serogroup III), except that the S dsRNA of WSMV is 0.75 and 0.6 kbp longer than those of TSWV and INSV, respectively. The complete nucleotide sequence of the genomic M RNA of WSMV was determined from cDNA clones generated from separated M dsRNA. The M RNA is 4,880 nucleotides in length with two open reading frames (ORFs) in an ambisense organization. The M RNA-encoded nonstructural (NSm) ORF located on the viral strand encodes a protein of 312 amino acids (35 kDa), and the G1/G2 ORF located on the viral complementary strand encodes a protein of 1,121 amino acids (127.6 kDa). The RNA probe corresponding to the NSm or G1/G2 ORF of WSMV failed to hybridize with the M dsRNAs of TSWV and INSV. Comparison of M and S RNAs of WSMV, TSWV, INSV, and peanut bud necrosis virus (PBNV, serogroup IV) revealed a consensus sequence of eight nucleotides of 5′-AGAGCAAU…-3′ at their 5′ ends and 5′-…AUUGCUCU-3′ at their 3′ ends. The low overall nucleotide identities (56.4 to 56.9%) of the M RNA and the low amino acid identities of the NSm and G1/G2 proteins (30.5 to 40.9%) with those of TSWV and INSV indicate that WSMV belongs to the Tospovirus genus but is phylogenetically distinct from viruses in serogroups I and III. The M RNA of WSMV shares a nucleotide identity of 79.6% with that of PBNV, and the two viruses share 83.4 and 88.7% amino acid identities for their NSm and G1/G2 proteins, respectively. It is concluded that they are two related but distinct species of serogroup IV. In addition to the viral or viral complementary full-length M RNA, two putative RNA messages for the NSm gene and the G1/G2 gene, 1.0 and 3.4 kb, respectively, were detected from the total RNA extracted from WSMV-infected tissue of Nicotiana benthamiana. The 1.0- and 3.4-kb RNAs were also detected in the viral RNAs extracted from purified nucleocapsids, suggesting that the putative messages of the M RNA of WSMV can also be encapsidated by the nucleocapsid protein.
Characterization of the Crater Disease Strain of Rhizoctonia solani
Authors: Meyer L. , Wehner F. C. , Nel L. H. , Carling D. E.
Published: May 2007

Crater disease (CD) of wheat is caused by a Rhizoctonia solani strain of ambiguous phylogeny. Anastomosis reactions confirmed placement of CD-causing R. solani in anastomosis group (AG) 6, with results indicating a closer affinity to AG-6 GV than to AG-6 HG. Cultures of CD isolates were initially white to cream, turning a yellowish light brown after 10 days. Concentric rings of dark and light mycelium were evident from an early stage. Mycelium generally was appressed to the agar surface, with sparse aerial growth. A few light-colored, irregularly shaped sclerotia could be discerned after 2 weeks. The mean hyphal diameter of CD-causing R. solani was 7.46 μm (ranging from 5.0 to 10.0 μm), and cells contained a mean number of four (ranging from two to eight) nuclei, compared to a mean hyphal diameter of 8.58 and 8.42 μm and a mean nuclear number of six and four for AG-6 HG and AG-6 GV, respectively. The CD isolates had a slower growth rate (15.3 mm/day) than AG-6 HG (29.1 mm/day) and AG-6 GV (22.6 mm/day) but, like AG-6, were thiamine prototrophic. Conspicuous nodulose swellings were produced by CD-causing R. solani on roots of wheat, and infection resulted in retarded shoot growth. Smaller nodules were evident on bean and soybean roots. Fingerprint patterns generated for the various isolates with four enzymes, HpaII, Sau3AI, TaqI, and CfoI, showed the presence of a unique 610-bp fragment in the pathogen. It is proposed that CD-causing R. solani isolates represent a distinct intersterility group within AG-6 that is more related to subgroup GV than to subgroup HG.
Tissue Culture Methods for the Screening and Analysis of Putative Virus-Resistant Transgenic Potato Plants
Authors: Russo P. , Slack S. A.
Published: May 2007

Following regeneration, putative virus-resistant transgenic plants are usually transferred from tissue culture to a greenhouse or growth chamber to screen for resistance to infection and disease development using mechanical, graft, or insect vector inoculation methods. To reduce initial screening costs and time, we developed mechanical and graft inoculation methods suitable for tissue culture use. The in vitro methods were validated by comparing them with similar greenhouse screens using putative potato virus Y strain o (PVY°) replicase-mediated resistant regenerants of the potato cultivar Atlantic. Five transgenic lines were tested, with similar results obtained from in vitro and greenhouse experiments. Two of the transgenic lines, A1 and A3, showed the greatest resistance to PVY°infection, as indicated by low enzyme-linked immunosorbent assay values and infection rates. In vitro mechanical inoculation methods were also used to infect wild-type tomato and tobacco plants with cucumber mosaic virus and potato virus Y. Potato plants were also infected with the phloem-restricted potato leafroll virus, a low-titer virus, using in vitro graft inoculation methods. These results suggest the potential usefulness of these simple, effective, and economical techniques for screening large numbers of putative virus-resistant plants.
Isolation, Characterization, and Distribution of a Biocontrol Fungus from Cysts of Heterodera glycines
Authors: Kim D. G. , Riggs R. D. , Correll J. C.
Published: May 2007

Seventy-six populations of Heterodera glycines were collected from 33 counties in 10 states of the United States along the Mississippi and Missouri Rivers in 1992 and 1993. A sterile hyphomycete fungus of an unnamed taxon, designated ARF18 and shown to be a parasite of eggs of H. glycines, was isolated from eggs and cysts of 10 of the populations from Kentucky, Louisiana, Mississippi, and Tennessee. Ten isolates of ARF18 obtained in this study and seven isolates obtained in earlier studies were characterized for cultural morphology on several growth media, the ability to produce sclerotium-like structures (SLS) on cornmeal agar, growth rates, pathogenicity to eggs of H. glycines in vitro, and mitochondrial (mt) DNA restriction fragment length polymorphisms (RFLPs). All 17 isolates of ARF18 readily grew on potato dextrose agar, cornmeal agar, and nutrient agar. Based on colony morphology and SLS appearance on cornmeal agar, the isolates could be grouped into two morphological phenotypes. Isolates that produced SLS that were composed of a compact mass of hyphae were designated ARF18-C, whereas isolates that produced SLS composed of a mass of loosely clumped hyphae were designated ARF18-L. Only minor differences in growth rates were detected among the ARF18-C and ARF18-L isolates. All 10 ARF18-C isolates, which were from Arkansas, Louisiana, Mississippi, and Tennessee, belonged to a single mtDNA RFLP haplotype. The seven ARF18-L isolates shared many comigrating mtDNA restriction fragments with one another, but belonged to three distinct mtDNA RFLP haplotypes. Ability to infect eggs of H. glycines in vitro varied considerably among the various isolates of ARF18. In particular, several of the ARF18-C isolates were consistently able to infect over 50% (mean = 70.0%, standard deviation = 16%) of the eggs of H. glycines, whereas ARF18-L infected eggs to a lesser degree (mean = 25%, standard deviation = 27%). ARF18-C was isolated only from H. glycines populations from below 37° N latitude. The presence of ARF18 was associated with soils with Mg levels <314 kg/ha, cyst numbers >4.5 per 100 cm3, and iron levels >203.5 kg/ha; or with Mg levels >314 kg/ha and Na levels <121 kg/ha. The widespread distribution of ARF18 and the ability of some isolates to aggressively colonize eggs of H. glycines are indications that it has potential as a biological control agent for H. glycines.
Satellite RNA of Cucumber Mosaic Cucumovirus Spreads Epidemically in Natural Populations of Its Helper Virus
Authors: Alonso-Prados José Luis , Aranda Miguel A. , Malpica José M. , García-Arenal Fernando , Fraile Aurora
Published: May 2007

Three hundred thirty-eight isolates of cucumber mosaic cucumovirus (CMV), sampled from natural populations in six areas of Spain between 1989 and 1996, were screened for the presence of satellite RNA (satRNA). The frequency of CMV isolates with satRNA approached 1.00 in Valencia (east Spain) between 1990 and 1994 where a tomato necrosis epidemic induced by CMV+satRNA had started in 1986 and was smaller north and west of this area in 1992 and 1993. After 1994, satRNA almost disappeared from all CMV populations. Genetic typing of satRNA variantswas done by ribonuclease protection assay, and from these data, genetic distances were estimated for any pair of satRNA variants. CMV-satRNA populations were highly diverse, containing 0.07865 nucleotide substitutions per site on average. Data also showed that the whole compared set of 100 satRNA variants form a single population that is not structured according to place, year, host plant, or strain of helper virus (HV). This is in sharp contrast with the metapopulation structure of the Spanish CMV population. Thus, the genetic structure and dynamics of populations of CMV and its satRNA are not coupled. This shows that CMV-satRNA spreads epidemically, as a hyperparasite, in the population of its HV. This conclusion is relevant to the use of CMV-satRNA as a biocontrol agent of CMV.
Effects of a Cover Crop on Splash Dispersal ofColletotrichum acutatumConidia
Authors: Ntahimpera N. , Ellis M. A. , Wilson L. L. , Madden L. V.
Published: May 2007

A rain simulator, with generated rains of 11 and 30 mm/h, was used to determine the effect of a cover crop or intercrop on the splash dispersal of Colletotrichum acutatum conidia. Dispersal through sudangrass, which can be used as a ‘living mulch’, was tested at two planting densities (140 or 280 kg/ha) and two heights (5 and 20 cm) and compared with a control consisting of a bare soil. Dispersal of C. acutatum conidia was assessed by counting colonies formed from spore-bearing splash droplets deposited in sheltered petri plates containing a selective medium. Both a cover crop and rain intensity significantly affected splash dispersal as measured by the interpolated total number of colonies (denoted by Σ) from 0 to 72 cm from the inoculum source and in a time span of 61 min of generated rain (P < 0.001). However, there was no significant interaction of cover crop and intensity (P > 0.90). Dispersal with a 30-mm/h rain was higher than dispersal with a 11-mm/h rain, and presence of a cover crop significantly reduced dispersal compared with bare soil (P < 0.001). Of the treatments with sudangrass, cover crop planting density did not affect dispersal overall, but there was greater spore dispersal with the taller sudangrass at the higher planting density, due in part to the higher rate of water splashing with the tall grass compared with the short grass. Spore deposition in the petri plates could be functionally related to distance and time using a diffusion-type model, and parameter estimates could be used to explain the effects of cover crop on Σ. Although the relationship between cover crop properties and splash dispersal is complex, results show the potential beneficial effects of the cover crop on disease management.
Sinaloa Tomato Leaf Curl Geminivirus: Biological and Molecular Evidence for a New Subgroup III Virus
Authors: Idris A. M. , Brown J. K.
Published: May 2007

The biological and molecular properties of Sinaloa tomato leaf curl virus (STLCV) were investigated in line with the hypothesis that STLCV is a previously uncharacterized, whitefly-transmitted geminivirus from North America. STLCV causes yellow leaf curl symptoms in tomato and yellow-green foliar mottle in pepper. Five species belonging to two plant families were STLCV experimental hosts. STLCV had a persistent relationship with its whitefly vector, Bemisia tabaci. Polymerase chain reaction fragments of STLCV common region (CR) sequences of the A or B genomic components and the viral coat protein gene (AV1) were molecularly cloned and sequenced. The STLCV A- and B-component CR sequences (174 nucleotides each) shared 97.9% identity and contained identical cis elements putatively involved in transcriptional regulation and an origin of replication (the AC cleavage site within the loop of the hairpin structure and two direct repeat sequences thought to constitute the Rep binding motif), which collectively are diagnostic for subgroup III geminiviruses. The STLCV CR sequence shared 23.1 to 77.6% identity with CR sequences of representative geminiviridae, indicating the STLCV CR sequence is unique. Molecular phylogenetic analysis of CR or AV1 sequences of STLCV and the respective sequences of 31 familial members supported the placement of STLCV as a unique bipartite, subgroup III virus most closely related to other viruses from the Western Hemisphere. STLCV is provisionally described as a new species within the genus Begomovirus, family Geminiviridae.
Defective Movement of Viruses in the Family Bromoviridae Is Differentially Complemented in Nicotiana benthamiana Expressing Tobamovirus or Dianthovirus Movement Proteins
Authors: Rao A. L. N. , Cooper Bret , Deom Carl M.
Published: May 2007

Taxonomically distinct tobacco mosaic tobamovirus (TMV), red clover necrotic mosaic dianthovirus (RCNMV), cucumber mosaic cucumovirus (CMV), brome mosaic bromovirus (BMV), and cowpea chlorotic mottle bromovirus (CCMV) exhibit differences in their host range. Each of these viruses encodes a functionally similar nonstructural movement protein (MP) that is essential for cell-to-cell movement of a progeny virus. Despite the lack of significant amino acid identity among the MPs of CMV, TMV, and RCNMV, movement-defective CMV (CMVFnyΔMP-ΔKPN) was able to move locally and systemically in transgenic Nicotiana benthamiana expressing either TMV MP (NB-TMV-MP(+)) or RCNMV MP (NB-RCNMV-MP(+)). These observations contrast with those of previous studies in which transgenic N. tabacum cv. Xanthi plants expressing TMV MP supported only the cell-to-cell movement of CMVFnyΔMP-ΔKPN. To verify whether similar complementation could be observed for movement-defective bromoviruses, NB-TMV-MP(+) and NB-RCNMV-MP(+) plants were inoculated independently with movement-defective variants of BMV (B3ΔMP) and CCMV (CC3ΔMP). Neither NB-TMV-MP(+) nor NB-RCNMV-MP(+) was able to rescue the defective cell-to-cell and long-distance movement of B3ΔMP. In contrast, NB-RCNMV-MP(+) complemented the cell-to-cell, but not the long-distance, movement of CC3ΔMP. Taken together, these studies suggest that virus movement is a complex process and that, in some cases, the host species plays a major role in determining the long-distance movement function of a virus.
Transformants of Trichoderma longibrachiatum Overexpressing the β-1,4-Endoglucanase Gene egl1 Show Enhanced Biocontrol of Pythium ultimum on Cucumber
Authors: Migheli Quirico , González-Candelas Luis , Dealessi Laura , Camponogara Andrea , Ramón-Vidal Daniel
Published: May 2007

Nine transformants of Trichoderma longibrachiatum with extra copies of the egl1 gene were studied for mitotic stability, endoglucanase production, and biocontrol activity against Pythium ultimum on cucumber seedlings. The transformants showed a significantly higher level of expression of the egl1 gene in comparison to the wild type under both inducing and noninducing growth conditions. Transformants with the egl1 gene under the control of a constitutive promoter had the highest enzymatic activity. Both the endoglucanase activity and the transforming sequences were stable under nonselective conditions. When applied to cucumber seeds sown in P. ultimum-infested soil, T. longibrachiatum transformants with increased inducible or constitutive egl1 expression generally were more suppressive than the wild-type strain.
Glucosylation of Salicylic Acid in Nicotiana tabacum Cv. Xanthi-nc
Authors: Lee Hyung-il , Raskin Ilya
Published: May 2007

Salicylic acid (SA) is a key regulatory component of disease resistance in plants. In tobacco mosaic virus (TMV)-inoculated tobacco (Nicotiana tabacum cv. Xanthi-nc NN genotype), newly synthesized SA is converted primarily to SA 2-O-β-D-glucoside (SAG) and glucosyl salicylate (GS), a relatively minor metabolite. Similar patterns in the formation of GS and SAG were observed in tobacco inoculated with Pseudomonas syringae pv. phaseolicola, suggesting the accumulation of two glucosylated metabolites is a general phenomenon in tobacco plants. After SA infiltration, GS was synthesized rapidly, reached a maximal level at 6 h, declined, and remained relatively constant for at least 24 h. In contrast, SAG content increased gradually after SA treatment. Our in vitro and in vivo data suggest that a high concentration of free SA triggers transient formation of GS and continuous accumulation of SAG, which is a more stable metabolite of SA. The two distinct SA glucosyltransferases catalyzed the formation of GS and SAG, respectively. The activities of these enzymes were enhanced by TMV or P. syringae pv. phaseolicola inoculation or SA treatment and were found in different fractions of gel filtration chromatography.
Wheat Leaf Rust Severity as Affected by Plant Density and Species Proportion in Simple Communities of Wheat and Wild Oats
Authors: Pfleeger Thomas G. , Mundt Christopher C.
Published: May 2007

While it is generally accepted that dense stands of plants exacerbate epidemics caused by foliar pathogens, there is little experimental evidence to support this view. We grew model plant communities consisting of wheat and wild oats at different densities and proportions and exposed these communities to Puccinia recondita to induce wheat leaf rust. Wild oats was included because it is a common competitor of wheat and may act as a barrier to the dispersal of P. recondita spores among wheat plants. Disease severity was estimated as percentage of wheat flag leaves covered by rust lesions. Seeding density rarely had a significant influence on rust severity, probably because of compensation due to increased tillering at low seeding densities. In contrast, increasing the proportion of wheat in mixtures with wild oats consistently increased wheat leaf rust severity. Regression parameters describing wheat leaf rust severity as a function of wheat seeding density did not differ significantly between pure wheat stands and wheat-wild oat mixtures and, thus, failed to support an effect of wild oats on wheat leaf rust other than through its competitive impact on wheat tiller density.
Survey Methods for Assessment of Citrus Tristeza Virus Incidence
Authors: Hughes G. , Gottwald T. R.
Published: May 2007

The assessment of citrus tristeza virus incidence by sampling involves laboratory testing by enzyme-linked immunosorbent assay of leaf material collected in the field. Using field data and computer simulation, methods of field data collection were compared. One method was similar to that used by the Central California Tristeza Eradication Agency, in which 4 to 6% of the trees in a planting block are sampled and material from each tree sampled is assayed separately. This method was compared with an alternative method in which about 25% of the trees in a block are sampled, and material from groups of four trees is bulked and assayed together. Our comparative study indicated that the latter method results in increased accuracy and precision of estimates of citrus tristeza virus incidence without increasing unduly the number of laboratory assays required.
Characterization of Phytophthora spp. Causing Outbreaks of Citrus Brown Rot in Florida
Authors: Graham J. H. , Timmer L. W. , Drouillard D. L. , Peever T. L.
Published: May 2007

Epidemics of citrus brown rot from 1994 to 1997 in the south-central and east-coast citrus areas of Florida were characterized and the causal Phytophthora spp. identified. Two species of Phytophthora, P. palmivora and P. nicotianae, were consistently associated with brown rot. Epidemics caused by P. palmivora appeared to be initiated on immature fruit dropped on the orchard floor. The soilborne fungus infected and sporulated on these fruit and was then disseminated to fruit above 1 m in the canopy. In contrast, infection by P. nicotianae, the common cause of root rot, was confined to the lowest 1 m of the canopy. Fruit infected by P. palmivora produced large amounts of ellipsoidal sporangia available for splash dispersal, whereas those infected by P. nicotianae produced far fewer spherical sporangia. Isolates from brown rot epidemics were compared with P. nicotianae from citrus in Florida and Texas, P. citrophthora in California, P. palmivora, and selected Phytophthora spp. from other hosts. Brown rot symptoms produced by the different pathogenic citrus isolates on inoculated fruit were indistinguishable. Morphology, mating behavior, and isozyme patterns of brown rot isolates from 1988 to 1997 matched P. palmivora from citrus roots, other host plants, and other locations, but were different from characterized isolates of P. citrophthora in California and P. nicotianae in Florida and Texas. Cellulose acetate electrophoresis of the isozyme glucose-6-phosphate isomerase rapidly identified the causal citrus pathogen from infected fruit and soil isolation plates. Although P. palmivora is an aggressive pathogen of citrus roots, bark, and fruit, populations in orchard soils were low compared with P. nicotianae.
Suppression of Rice Blast by Preinoculation with Avirulent Pyricularia oryzae and the Nonrice Pathogen Bipolaris sorokiniana
Authors: Manandhar H. K. , Lyngs Jørgensen H. J. , Mathur S. B. , Smedegaard-Petersen V.
Published: May 2007

Avirulent isolates of Pyricularia oryzae and isolates of Bipolaris sorokiniana, a nonrice pathogen, were used to suppress rice blast caused by P. oryzae. In greenhouse experiments, both fungi substantially reduced leaf blast when applied 24 h or more before the pathogen. B. sorokiniana, but not avirulent isolates of P. oryzae, systemically reduced disease in leaf 5 when applied to whole plants at the four-leaf stage. In field experiments, both fungi were able to reduce neck blast significantly. No increase in grain yield was obtained by using avirulent isolates of P. oryzae, whereas five sprays with B. sorokiniana from seedling to heading stages increased the grain yield in two of three experiments conducted at two locations in Nepal. The significant increase in yield was observed under high inoculum pressure of P. oryzae. Induced resistance is suggested to be involved in the suppression of disease.
Specific Identification of Coconut Tinangaja Viroid for Differential Field Diagnosis of Viroids in Coconut Palm
Authors: Hodgson R. A. J. , Wall G. C. , Randles J. W.
Published: May 2007

Tinangaja is a widespread lethal disease of putative viroid etiology affecting coconut palm on the island of Guam. Determination of its distribution and mode of spread requires a simple and reliable diagnostic procedure that is specific for the associated coconut tinangaja viroid (CTiVd). A method of extracting tissue followed by analytical agarose gel electrophoresis for CTiVd detection has been developed and used to identify the viroid in leaf samples of suspect symptomatic palms growing in the field. Two-dimensional polyacrylamide gel electrophoresis showed that the viroid band contained circular molecules that are typical for viroids. Confirmation of the identity of CTiVd and detection of low levels of viroid below the threshold of detection by agarose gel electrophoresis was achieved either by diagnostic oligonucleotide-probe (DOP) hybridization assay or by reverse-transcription polymerase chain reaction (RT-PCR) with the oligonucleotide probe as one of the two PCR primers. RT-PCR was not substantially more sensitive than DOP-hybridization assay. This procedure also was applicable to coconut cadang-cadang viroid (CCCVd), and oligonucleotide probes designed to be specific for either CTiVd or CCCVd distinguished between these two viroids in coconut leaf extracts. This strategy provides a rapid and specific indexing procedure for the two characterized viroids of coconut palm and will be applicable to further studies on the viroid-like sequences previously reported in tropical monocotyledons.
Tomato Breeding Lines Resistant and Tolerant to Tomato Yellow Leaf Curl Virus Issued fromLycopersicon hirsutum
Authors: Vidavsky Favi , Czosnek Henryk
Published: May 2007

Two tomato yellow leaf curl virus (TYLCV)-resistant plants from accessions LA1777 and LA386 of the wild tomato species Lycopersicon hirsutum have been crossed. The resulting resistant F1 plants were crossed with the domesticated tomato L. esculentum, and a series of selfing was performed. At each generation, individuals were selected for resistance (no symptoms and undetectable viral DNA) and tolerance (no symptoms but with detectable viral DNA) following controlled massive and repeated inoculations with viruliferous whiteflies. A stable BC1F4 line (denominated 902) that does not segregate for resistance was obtained. This line does not support virus accumulation, even upon extensive whitefly-mediated inoculation of young seedlings, and does not need protection with nets or insecticides. Another stable BC1F4 line (denominated 908) was tolerant to the virus. Both lines have good horticultural characteristics and bear 80- to 120-g red fruits. Analysis of segregation of susceptibility, tolerance, and resistance during the BC1F1 to BC1F4 crosses indicated that tolerance is controlled by a dominant major gene and resistance by two to three additive recessive genes. The resistant and tolerant lines do not need to be protected by insecticides or nets.
Genotypic and Pathogenic Diversity Among Pea-Infecting Strains of Aphanomyces euteiches from the Central and Western United States
Authors: Malvick D. K. , Percich J. A.
Published: May 2007

Pathogenic and genotypic variability among four populations of Aphanomyces euteiches from individual fields in Minnesota, Wisconsin, and Oregon were investigated using pathogenicity and randomly amplified polymorphic DNA (RAPD) analyses. About 50 strains were isolated from each of two pea fields in Minnesota, and 11 and 6 strains from pea fields in Wisconsin and Oregon, respectively, using pea (Pisum sativum) as a baiting host. Pathogenic variability and host range were evaluated in greenhouse studies with five pea lines or cultivars having different levels of resistance to Aphanomyces root rot and one cultivar each of alfalfa and snap bean. All strains were pathogenic on one or more pea cultivars, and 18 and 14% were pathogenic on alfalfa and bean, respectively. Disease severity incited by different strains varied significantly on individual pea cultivars and on all hosts combined. The percentage of strains pathogenic on different hosts varied among locations. Genotypic variation among all 114 strains was evaluated with RAPD analysis. Ten decanucleotide primers detected 92 polymorphic bands. Cluster and principal coordinates analysis revealed one large group containing 102 of the 114 strains from all locations. Two closely related minor groups of strains (12 strains) were genotypically distinct, with about 55% similarity to the main group of 102 strains. The strains in the minor groups were all isolated from the Minnesota locations and were pathogenic on two disease-resistant pea breeding lines (MN313 and MN314). Estimates of genetic diversity based on RAPD analysis ranged from 0.24 to 0.33 within populations to 0.35 among all strains from all populations. A. euteiches populations were genotypically and phenotypically variable, but no distinct genotypic differences were identified among populations from the four isolated locations.
Quantification of Mycelium of Botrytis spp. and the Antagonist Ulocladium atrum in Necrotic Leaf Tissue of Cyclamen and Lily by Fluorescence Microscopy and Image Analysis
Authors: Kessel G. J. T. , de Haas B. H. , Lombaers-van der Plas C. H. , Meijer E. M. J. , Dewey F. M. , Goudriaan J. , van der Werf W. , Köhl J.
Published: May 2007

A technique was developed to localize and quantify the internal mycelial colonization of necrotic leaf tissue of cyclamen (Cyclamen persicum) or lily (Lilium) by pathogenic Botrytis spp. and the antagonist Ulocladium atrum. This technique allows investigation of competitive substrate colonization by both fungi, which is a key process for biological control of Botrytis spp. by U. atrum. A combination of differential fluorescent labeling and image analysis was applied on cryostat sections of necrotic leaf tissue. Botrytis mycelium was labeled specifically by indirect immunofluorescence using a monoclonal antibody specific for Botrytis spp. And an antimouse fluorescein conjugate. Wheat germ agglutinin conjugated to the fluorochrome TRITC was used to label mycelium of both fungi. Image analysis was used to measure the relative surface area of the cryostat section covered by fluorescing hyphae of Botrytis spp. and by fluorescing hyphae of both fungi. A mathematical conversion was derived and used to calculate the relative mycelial volume of each fungal species in the necrotic tissue based on the measured relative surface areas. Temporal aspects of substrate colonization were studied in a short time series. An analysis of components of variance provided insight into spatial colonization patterns for the fungal species involved and allowed the design of efficient sampling strategies for future experiments.
Purification and Biological Characterization of Host-Specific SV-Toxins fromStemphylium vesicariumCausing Brown Spot of European Pear
Authors: Singh P. , Bugiani R. , Cavanni P. , Nakajima H. , Kodama M. , Otani H. , Kohmoto K.
Published: May 2007

Culture filtrates of a pathogenic isolate (IT37) of Stemphylium vesicarium, causing brown spot of European pear, induced veinal necrosis only on pear leaves susceptible to the pathogen. Two host-specific toxins, SV-toxins I and II, were purified from culture filtrates of IT37 by successively using Amberlite XAD-2 resin adsorption, cellulose thin-layer chromatography, and high-performance liquid chromatography under three different sets of conditions. Susceptible cultivars showed veinal necrosis at a SV-toxin I concentration of 0.01 to 0.1 μg/ml, whereas resistant cultivars were insensitive to the toxin at 1,000 μg/ml. SV-toxins I and II caused a dose-dependent increase in electrolyte loss from susceptible leaf tissues. No increase in electrolyte loss was detected in leaf tissues from resistant cultivars. The results of physiological studies indicated that SV-toxins appear to have an early effect on plasma membranes of susceptible leaves. Spores of a nonpathogenic isolate induced necrotic lesions on susceptible leaves in the presence of a small amount of toxin. SV-toxins were detected in intercellular fluids obtained from diseased leaves after inoculation with the pathogen. The results indicate that SV-toxins I and II produced by S. vesicarium can be characterized as host-specific toxins.
Influence of Stem Diameter, Water Content, and Freezing-Thawing on Bacterial Canker Development in Excised Stems of Dormant Stone Fruit
Authors: Cao T. , Sayler R. J. , DeJong T. M. , Kirkpatrick B. C. , Bostock R. M. , Shackel K. A.
Published: May 2007

In excised dormant stems of peach (Prunus persica), prune (Prunus domestica), and almond (Prunus dulcis), stem diameter, stem hydration, and freezing-thawing influenced the extent of infection caused by Pseudomonas syringae pv. syringae. Bacterial lesion length increased with increasing stem diameter, demonstrating the need to account for the effects of stem diameter when lesion length data are analyzed. Lesion length increased or decreased with stem hydration or dehydration, respectively. However, tissue water content was not a good indicator of tissue susceptibility to infection by P. syringae pv. syringae, as larger diameter stems had larger lesions and lower water content than did smaller diameter stems. After freezing at -5°C for 12 to 24 h, inoculations made during the thawing process produced significantly larger lesions than did inoculations performed before freezing or after thawing. These results support the hypothesis that the increased susceptibility to bacterial canker that is associated with noninjurious freezing is a result of the increased passive spread of bacteria through water redistribution when inoculation is performed during the thawing process. Plant tissue water relationship characteristics that can influence water movement during freezing and thawing may be an important component of bacterial canker development in stone fruit trees.
Effect of Temperature on the Incubation Period and Leaf Colonization in Bacterial Blight of Anthurium
Authors: Fukui R. , Fukui H. , Alvarez A. M.
Published: May 2007

Effect of temperature on leaf colonization in anthurium blight was studied using a bioluminescent strain of Xanthomonas campestris pv. dieffenbachiae. In a susceptible cultivar, colonization of leaf tissues (monitored by detection of bioluminescence) and symptom development (assessed visually) advanced rapidly at higher temperatures. For a susceptible cultivar, there was a linear relationship between degree-days and percent leaf area colonized by the pathogen, indicating that leaf colonization in a susceptible cultivar was a direct function of the cumulative effect of temperature. The degree-day intercept of the regression line represented the time from inoculation to detection of bioluminescence, and the slope indicated the increase of leaf colonization per degree-day. There also was a linear relationship between the logarithm of degree-days and the logarithm of percent leaf area showing visible symptoms in a susceptible cultivar. The degree-day intercept of this relationship represented the incubation period (about 500 degree-days). The degree-days required to detect bioluminescence was not considerably different between susceptible and resistant cultivars. However, the subsequent rates of leaf colonization were significantly lower for a resistant cultivar than for a susceptible cultivar in all temperature regimes. The results suggest that multiplication of the pathogen in the leaf tissues is optimized in the susceptible cultivar. In contrast, in the resistant cultivar, the defense mechanisms overshadow the temperature effect. The differential response to temperatures may be an additional indicator of cultivar susceptibility.
Displacement of Tomato Yellow Leaf Curl Virus (TYLCV)-Sr by TYLCV-Is in Tomato Epidemics in Spain
Authors: Sánchez-Campos S. , Navas-Castillo J. , Camero R. , Soria C. , Díaz J. A. , Moriones E.
Published: May 2007

A progressive displacement of tomato yellow leaf curl virus (TYLCV)-Sr by TYLCV-Is was observed in tomato epidemics in southern Spain based on incidence data of both virus species obtained during surveys conducted between 1996 and 1998. Ecological factors that might be involved in such a displacement, such as competition of TYLCV-Sr and TYLCV-Is in tomato, transmission by local biotypes (B and Q) of Bemisia tabaci, and presence in weeds and alternate crops, have been analyzed. No selective advantage is observed for TYLCV-Sr or TYLCV-Is in tomato plants either infected via Agrobacterium tumefaciens or via B. tabaci. However, TYLCV-Is is more efficiently vectored by local biotypes of B. tabaci; and common bean, a bridge crop between tomato crops, is a host for TYLCV-Is but not TYLCV-Sr. Therefore, common bean acts as a reservoir for TYLCV-Is. These two factors are probably responsible for the displacement of TYLCV-Sr by TYLCV-Is as the causative agent of epidemics in tomato in southern Spain.
Local and Systemic Induced Resistance to the Root-Knot Nematode in Tomato by DL-β-Amino-n-Butyric Acid
Authors: Oka Yuji , Cohen Yigal , Spiegel Yitzhak
Published: May 2007

Chemical inducers of pathogenesis-related proteins and plant resistance were applied to tomato plants, with the aim of inducing resistance to the root-knot nematode Meloidogyne javanica. Relative to control plants, foliar spray and soil-drenching with dl-β-amino-n-butyric acid (BABA) reduced root-galling 7 days after inoculation, as well as the number of eggs 30 days after inoculation. Other chemicals (α- and γ-amino-n-butyric acid, jasmonic acid, methyl jasmonate, and salicylic acid) were either phytotoxic to tomato plants or did not improve control of root-knot nematodes. Fewer second-stage juveniles invaded BABA-treated tomato roots, and root-galling indices were lower than in control tomato plants. Resistance phenomena in seedlings lasted at least 5 days after spraying with BABA. Nematodes invading the roots of BABA-treated seedlings induced small, vacuolate giant cells. Postinfection treatment of tomato plants with BABA inhibited nematode development. It is speculated that after BABA application tomato roots become less attractive to root-knot nematodes, physically harder to invade, or some substance(s) inhibiting nematode or nematode feeding-site development is produced in roots.
Detection of Fusarium oxysporum f. sp. dianthi in Carnation Tissue by PCR Amplification of Transposon Insertions
Authors: Chiocchetti Annalisa , Bernardo Ilaria , Daboussi Marie-Josée , Garibaldi Angelo , Gullino M. Lodovica , Langin Thierry , Migheli Quirico
Published: May 2007

Strains of the carnation wilt pathogen, Fusarium oxysporum f. sp. dianthi, can be distinguished by DNA fingerprint patterns, using the fungal transposable elements Fot1 and impala as probes for Southern hybridization. The DNA fingerprints correspond to three groups of F. oxysporum f. sp. dianthi strains: the first group includes isolates of races 1 and 8; the second group includes isolates of races 2, 5 and 6; and the third group includes isolates of race 4. Genomic DNAs flanking race-associated insertion sites of Fot1 (from races 1, 2, and 8) or impala (from race 4) were amplified by the inverse polymerase chain reaction (PCR) technique. These regions were cloned and sequenced, and three sets of primers overlapping the 3′ or 5′ end of the transposon and its genomic insertion were designed. Using fungal genomic DNA as template in PCR experiments, primer pairs generated amplification products of 295, 564 and 1,315 bp, corresponding to races 1 and 8; races 2, 5, and 6; and race 4, respectively. When multiplex PCR was performed with genomic DNA belonging to races 1 and 8, 2, or 4, single amplimers were generated, allowing clear race determination of the isolate tested. PCR was successfully performed on DNA extracted from susceptible carnation cv. Indios infected with isolates representative of races 1, 2, 4, and 8.
Spatial-Temporal and Quantitative Analysis of Growth and EPS I Production by Ralstonia solanacearum in Resistant and Susceptible Tomato Cultivars
Authors: McGarvey J. A. , Denny T. P. , Schell M. A.
Published: May 2007

One susceptible and two resistant cultivars of tomato were tested for differences in infection by Ralstonia solanacearum and for the subsequent multiplication, colonization, and production of the wilt-inducing virulence factor, exopolysaccharide I (EPS I). Bacterial ingress into the taproot was fastest in the susceptible cv. Marion, followed by the resistant cvs. L285 (fivefold slower) and Hawaii 7996 (15-fold slower). Once inside the taproot, R. solanacearum colonized, to some extent, almost all regions of the resistant and susceptible plants. However, colonization occurred sooner in the susceptible than in the resistant cultivars, as measured by viablecell counts of bacteria in the midstems. Rates of multiplication and maximum bacterial cell densities were also greater in the susceptible than in the resistant cultivars. Growth experiments utilizing xylem fluid from infected and uninfected plants indicated that neither antimicrobial activities nor reduced levels of growth-supporting nutrients in the xylem fluids were responsible for the reduced bacterial multiplication in the resistant cultivars. Quantification of EPS I in the infected plants, using an enzyme-linked immunosorbent assay, revealed that the bacterial populations in the susceptible cultivar produced greater amounts of EPS I per plant than those in the resistant cultivars. Immunofluorescence microscopy using antibodies against either EPS I or R. solanacearum cells revealed that bacteria and EPS I were distributed throughout the vascular bundles and intercellular spaces of the pith in the susceptible cultivar, whereas in the resistant cultivars, bacteria and EPS I were restricted to the vascular tissues.