bluuebunny/crossref_metadata_2025 huggingface dataset:
Biological Control of Bacterial Speck of Tomato Under Field Conditions at Several Locations in North America
Authors: Wilson M. , Campbell H. L. , Ji P. , Jones J. B. , Cuppels D. A.
Published: May 2007

Bacterial speck of tomato, caused by Pseudomonas syringae pv. tomato, continues to be a problem for tomato growers worldwide. A collection of nonpathogenic bacteria from tomato leaves plus P. syringae strains TLP2 and Cit7, P. fluorescens strain A506, and P. syringae pv. tomato DC3000 hrp mutants were examined in a greenhouse bioassay for the ability to reduce foliar bacterial speck disease severity. While several of these strains significantly reduced disease severity, P. syringae Cit7 was the most effective, providing a mean level of disease reduction of 78% under greenhouse conditions. The P. syringae pv. tomato DC3000 hrpA, hrpH, and hrpS mutants also significantly reduced speck severity under greenhouse conditions. The strains with the greatest efficacy under greenhouse conditions were tested for the ability to reduce bacterial speck under field conditions at locations in Alabama, Florida, and Ontario, Canada. P. syringae Cit7 was the most effective strain, providing a mean level of disease reduction of 28% over 10 different field experiments. P. fluorescens A506, which is commercially available as Blight-Ban A506, provided a mean level of disease reduction of 18% over nine different field experiments. While neither P. syringae Cit7 nor P. fluorescens A506 can be integrated with copper bactericides due to their copper sensitivity, there exist some potential for integrating these biological control agents with “plant activators”, including Actigard. Of the P. syringae pv. tomato DC3000 hrp mutants tested, only the hrpS mutant reduced speck severity significantly under field conditions.
Nonchemical Management of Soilborne Pests in Fresh Market Vegetable Production Systems
Authors: Chellemi D. O.
Published: May 2007

Nonchemical methods including host resistance, organic amendments, crop rotation, soil solarization, and cultural practices have been used to control soilborne pests in fresh market vegetable production systems. Their suitability as alternatives to methyl bromide will depend on the approach to pest management used by the grower. Traditionally, methyl bromide is used in production systems that rely on the single application of a broad-spectrum biocide to disinfest soils prior to planting. Non-chemical methods are not suitable for a single tactic approach to pest management because they do not provide the same broad spectrum of activity or consistency as fumigation with methyl bromide. Nonchemical methods are compatible with an integrated pest management (IPM) approach, where multiple tactics are used to maintain damage from pests below an economic threshold while minimizing the impact to beneficial organisms. However, adoption of IPM is hindered by the paucity of economically feasible sampling programs and thresholds for soilborne pests and by a reluctance of growers to commit additional resources to the collection and management of biological information. A novel approach to the management of soilborne pests is to design the crop production system to avoid pest outbreaks. Using this “proactive” approach, a tomato production system was developed using strip-tillage into existing bahia-grass pasture. By minimizing inputs and disruption to the pasture, growers were able to reap the rotational benefits of bahiagrass without cultivating the rotational crop. While minimizing the need for interventive procedures, a proactive approach is difficult to integrate into existing crop production systems and will require several years of testing and validation.
Evidence for Oxidative Stress Involved in Physiological Leaf Spot Formation in Winter and Spring Barley
Authors: Wu Yue-Xuan , von Tiedemann Andreas
Published: May 2007

A leaf spot disease with unknown etiology has become more pronounced in spring and winter barley in Germany in recent years. The symptoms are similar to net blotch and Ramularia leaf spots, but the causal agents of these diseases are not identified. The symptom expression varied much on cultivars. Cultivars most affected by the disease of both spring and winter barley showed a significantly higher level of superoxide (O2¯) production and lipid peroxidation (malondialdehyde), but a lower level of antioxidant potential expressed as superoxide dismutase (SOD) activity, catalase activity, and integral water-soluble antioxidant capacity (ACW) than insensitive cultivars. A high positive correlation between O2¯ production and leaf spot development between ear emergence and milk ripeness was established in the most sensitive winter barley cv. Anoa (r2 = 0.9622) and spring barley cv. Barke (r2 = 0.9434). Leaf H2O2 levels increased with the severity of leaf spots. The histochemical localization of O2¯ and H2O2 in the tissues adjacent to leaf spots indicated that these two active oxygen species (AOS) are involved in the formation of leaf spots. Reduction of symptom severity by applying strobilurin and azole fungicides was always associated with elevated SOD activity and ACW content and suppressed O2¯ production. However, peroxidase activities were significantly higher in sensitive cultivars and in more severely affected tissues and decreased by applying fungicides. Thus, it is assumed that a possible genetic mechanism based on the imbalanced AOS metabolism contributes to formation of physiological leaf spots.
Polymerase Chain Reaction Assays for the Detection and Discrimination of the Soybean Rust PathogensPhakopsora pachyrhiziandP. meibomiae
Authors: Frederick Reid D. , Snyder Christine L. , Peterson Gary L. , Bonde Morris R.
Published: May 2007

Soybean rust occurs in Australia and many countries throughout Africa, Asia, and South America. The causal agents of soybean rust are two closely related fungi, Phakopsora pachyrhizi and P. meibomiae, which are differentiated based upon morphological characteristics of the telia. Determination of the nucleotide sequence of the internal transcribed spacer (ITS) region revealed greater than 99% nucleotide sequence similarity among isolates of either P. pachyrhizi or P. meibomiae, but only 80% sequence similarity between the two species. Utilizing differences within the ITS region, four sets of polymerase chain reaction (PCR) primers were designed specifically for P. pachyrhizi and two sets for P. meibomiae. Classical and real-time fluorescent PCR assays were developed to identify and differentiate between P. pachyrhizi and P. meibomiae. Identification of P. pachyrhizi from infected soybean leaves using the real-time PCR assay will allow for more rapid diagnoses.
A Non-Hypersensitive Resistance in Pepper to the Bacterial Spot Pathogen Is Associated with Two Recessive Genes
Authors: Jones J. B. , Minsavage G. V. , Roberts P. D. , Johnson R. R. , Kousik C. S. , Subramanian S. , Stall R. E.
Published: May 2007

The pepper genotype, ECW-12346, was developed with bacterial spot resistance derived from Pep13, PI 271322, and ECW123 (Early Calwonder containing Bs1, Bs2, and Bs3 genes). For genetic analysis of this resistance, ECW12346, ECW123, F1, F2, and backcrosses were inoculated with a pepper race 6 (P6) strain. Two recessive genes were identified that determined resistance. The genes are designated bs5 and bs6 for the resistance derived from PI 271322 and Pep13, respectively. In greenhouse and field studies, ECW12346 was highly resistant, whereas ECW123 had significant defoliation. In growth-room studies, electrolyte leakage and population dynamics were determined. Following infiltration of both genotypes with 108CFU/ml of a P6 strain, there was no rapid increase in electrolyte leakage within 72 h, whereas a rapid increase in electrolyte leakage occurred within 24 h when a similar concentration of a P3 strain (containing the avrBs2 gene) was infiltrated into the intercellular spaces of the leaf. When 105CFU/ml of a P6 strain was infiltrated into leaves, complete tissue collapse was evident in ECW123 10 days later as determined by visual assessment and electrolyte leakage data, but no confluent necrosis was detected in ECW12346. Internal populations were at least two logarithmic units higher in ECW123 than in ECW12346. Therefore, ECW12346 inhibits population build-up without inducing the typical hypersensitive reaction characterized by an increase in electrolyte leakage.
Improved Control of Postharvest Decay of Pears by the Combination ofCandida sake(CPA-1) and Ammonium Molybdate
Authors: Nunes Carla , Usall Josep , Teixidó Neus , Abadias Maribel , Viñas Immaculada
Published: May 2007

The potential enhancement of Candida sake (CPA-1) by ammonium molybdate to control blue and gray mold caused by Penicillium expansum and Botrytis cinerea, respectively, on Blanquilla pears was investigated. In laboratory trials, improved control of blue and gray molds was obtained with the application of ammonium molybdate (1, 5, 10, and 15 mM) alone or in combination with C. sake at 2 × 106or 2 × 107CFU ml-1on Blanquilla pears stored at 20°C. In semicommercial trials at 1°C for 5 months, the efficacy of C. sake at 2 × 106CFU ml-1on reducing P. expansum and B. cinerea decay was enhanced more than 88% with the addition of ammonium molybdate 5 mM in the 1999-2000 season. In two seasons, the performance C. sake at 2 × 106CFU ml-1plus ammonium molybdate was similar to or greater than that of C. sake at 2 × 107CFU ml-1. Similar control of blue mold was obtained on pears stored under low oxygen conditions. The preharvest application of ammonium molybdate did not reduce postharvest blue mold decay. The population of C. sake on pear wounds significantly decreased in the presence of ammonium molybdate 1 and 5 mM at 20 and 1°C.
Survival of Xanthomonas axonopodis pv. citri in Leaf Lesions Under Tropical Environmental Conditions and Simulated Splash Dispersal of Inoculum
Authors: Pruvost O. , Boher B. , Brocherieux C. , Nicole M. , Chiroleu F.
Published: May 2007

Asiatic citrus canker (ACC) is a severe disease of several citrus species and hybrids in many tropical and subtropical areas. Populations of Xanthomonas axonopodis pv. citri in leaf and twig lesions are the most important inoculum source for secondary infections. In areas with a marked winter season (e.g., Argentina and Japan), low temperatures induce a decrease of 102 to 104 in population sizes in lesions, thus creating a discontinuity in the X. axonopodis pv. citri life cycle. The purpose of this study was to evaluate the dynamics of X. axonopodis pv. citri populations in leaf lesions exposed to the mild winter temperatures prevailing in a tropical environment. Internal X. axonopodis pv. citri population levels in Mexican lime leaf lesions reached 106 to 107 CFU lesion-1 whatever the lesion size. These densities, however, were not strongly negatively affected by winter temperatures prevailing under experimental conditions. The estimated decrease in internal X. axonopodis pv. citri population sizes was approximately 10-fold. When exposed to 35 mm h-1 of simulated rainfall, internal population sizes decreased over time by ≈1 log unit for lesions 1 and 2 months old, but did not for older lesions. A microscopic examination indicated that lignin-like compounds are present in lesions more than 6 months old. The slow decrease over time of X. axonopodis pv. citri population sizes in leaf lesions may be the balanced result of defense reactions by the host at late stages of disease development, and the concomitant multiplication of the pathogen at the margin of old lesions. We conclude that the epidemiological significance of overwintered leaf lesions in the tropics is higher than that reported in other areas.
Factors Affecting Germination of Puccinia jaceae var. solstitialis Teliospores from Yellow Starthistle
Authors: Bruckart William L. , Eskandari Farivar
Published: May 2007

The rust fungus Puccinia jaceae var. solstitialis is a candidate for biological control of yellow starthistle (YST). Part of the risk assessment includes determining if safflower seedlings are susceptible to infection by teliospores of P. jaceae. A protocol for germination of P. jaceae teliospores is needed to verify that teliospores used in comparative studies are viable. The protocol developed from this research has two steps: first, priming teliospores on water agar at 4°C in the dark, and second, incubating them at warmer temperatures for 1 week in the presence of an exogenous stimulator. Priming longer than 4 weeks resulted in significantly greater germination than priming for shorter periods. Sources of effective stimulator included seeds and seedlings of YST or safflower. The greatest germination occurred during incubation at 18°C in the dark. Teliospore germination was reduced after incubation with a 12- or 14-h photoperiod. A low percentage (<20%) of teliospores of two isolates germinated after 44 and 96 weeks of dry storage at room temperature; samples of each isolate tested after that did not germinate. Data indicate teliospores of several isolates of P. jaceae are viable, and the protocol will be used to prepare teliospores of P. jaceae for comparative studies with P. carthami on safflower seedlings.
Induction of Resistance to Penicillium digitatum in Grapefruit by the Yeast Biocontrol Agent Candida oleophila
Authors: Droby S. , Vinokur V. , Weiss B. , Cohen L. , Daus A. , Goldschmidt E. E. , Porat R.
Published: May 2007

The yeast Candida oleophila, the base of the commercial product Aspire, is recommended for the control of postharvest decay in citrus and pome fruit. Its modes of action include nutrient competition, site exclusion, and direct mycoparasitism. In the present study, we showed that application of Candida oleophila to surface wounds or to intact ‘Marsh Seedless’ grapefruit elicited systemic resistance against Penicillium digitatum, the main postharvest pathogen of citrus fruit. The induction of pathogen resistance in fruit was already pronounced 24 h after elicitation; it was distance, concentration, and time dependent and restricted to the peel tissue closely surrounding the yeast application site. The induction of pathogen resistance required viable yeast cells at concentrations of 108 to 109 cells ml-1. Nonviable autoclaved or boiled yeast cells or lower yeast concentrations were ineffective in enhancing fruit disease resistance. Application of Candida oleophila cell suspensions to grapefruit peel tissue increased ethylene biosynthesis, phenylalanine ammonia lyase activity, and phytoalexin accumulation, and increased chitinase and β-1,3-endoglucanase protein levels, indicated by western immunoblotting analysis. Scanning electron microscope observations revealed that spore germination and germ tube growth of Penicillium digitatum were markedly inhibited in wounds made near the yeast-treated sites. Overall, this study provides evidence that induced resistance against postharvest decay of citrus fruit should be considered an important component of the multiple modes of action of the yeast Candida oleophila.
Tomato yellow leaf curl virus in the Dominican Republic: Characterization of an Infectious Clone, Virus Monitoring in Whiteflies, and Identification of Reservoir Hosts
Authors: Salati Raquel , Nahkla Medhat K. , Rojas Maria R. , Guzman Pablo , Jaquez Jose , Maxwell Douglas P. , Gilbertson Robert L.
Published: May 2007

Epidemics of tomato yellow leaf curl disease (TYLCD) in the Dominican Republic in the early to mid-1990s resulted in catastrophic losses to processing tomato production. As part of an integrated management approach to TYLCD, the complete nucleotide sequence of a full-length infectious clone of an isolate of Tomato yellow leaf curl virus (TYLCV) from the Dominican Republic (TYLCV-[DO]) was determined. The TYLCV-[DO] genome was nearly identical in sequence (>97%) and genome organization to TYLCV isolates from Israel and Cuba. This established that TYLCV-[DO] is a bonafide TYLCV isolate (rather than a recombinant virus, such as isolates from Israel [Mild], Portugal, Japan, and Iran), and provided further evidence for the introduction of the virus from the eastern Mediterranean. A reduction in the incidence of TYLCV in the northern and southern processing tomato production areas of the Dominican Republic has been associated with the implementation of a mandatory 3-month whitefly host-free period (including tomato, common bean, cucurbits, eggplant, and pepper). Monitoring TYLCV levels in whiteflies, by polymerase chain reaction with TYLCV-specific primers, established that the incidence of TYLCV decreased markedly during the host-free period, and then gradually increased during the tomato-growing season. In contrast, TYLCV persisted in whiteflies and tomato plants in an area in which the host-free period was not implemented. Surveys for TYLCV reservoir hosts, conducted to identify where TYLCV persists during the host-free period, revealed symptomless infections in a number of weed species. The implications of these findings for TYLCV management in the Dominican Republic are discussed.
A Mathematical Simulation of Growth of Fusarium in Maize Ears After Artificial Inoculation
Authors: Stewart D. W. , Reid L. M. , Nicol R. W. , Schaafsma A. W.
Published: May 2007

Fusarium spp. in maize can contaminate the grain with mycotoxins if environmental conditions are favorable for fungal growth. To quantify the relationship between growth of Fusarium spp. and environmental conditions, a mathematical model was developed to simulate growth of F. graminearum and F. verticillioides on maize ears following silk inoculation in field experiments from 1992 to 1995. Each species was inoculated separately and as a mixture of the two for 3 of the 4 years on one maize hybrid. Disease progress in ears was measured by a visual rating scale that was converted to percent visual infection. Measurements were made at regular time intervals after silks were inoculated 5 days after silk emergence. Differential equations were used to relate growth rates of Fusarium spp. in maize ears to hourly air temperature and relative humidity and to daily precipitation. Integration of these equations over time produced quantitative estimates of fungal growth. Model calculations compared well with measurements (R2 = 0.931, standard error of estimate [SEE] = 2.11%) of percent visual disease infection of maize ears over 3 years. The model was tested against a second set of data (R2 = 0.89, SEE = 5.9%) in which silks were inoculated at nine different times after first silk emergence for each of 2 years (1994 and 1995) with the two species of fungi on the same maize hybrid. At this time, a silk function was developed to account for changes in the susceptibility of silks to disease. F. graminearum responded to wet conditions more than F. verticillioides, and for the conditions of this experiment, grew much faster than F. verticillioides when inoculated separately. When they were inoculated together, F. graminearum growth rates were much lower, indicating some interference by F. verticillioides. During 1993, weather conditions before inoculation reduced the growth of both species in silks.
Multiple Citrus Viroids in Citrus from Japan and Their Ability to Produce Exocortis-Like Symptoms in Citron
Authors: Ito Takao , Ieki Hiroyuki , Ozaki Katsumi , Iwanami Toru , Nakahara Kenji , Hataya Tatsuji , Ito Tsutae , Isaka Masahiro , Kano Takeshi
Published: May 2007

Sequential polyacrylamide gel electrophoresis analyses showed many viroid-like RNAs in samples collected from citrus trees in Japan. Reverse transcription polymerase chain reaction and sequencing analyses of the amplified fragments verified that they were derived from variants of six citrus viroids, Citrus exocortis viroid (CEVd), Citrus bent leaf viroid (CBLVd) including CVd-I-LSS (a distinct variant of CBLVd), Hop stunt viroid, Citrus viroid III, Citrus viroid IV, and Citrus viroid OS. The samples induced symptoms with variable severity in Arizona 861-S1 ‘Etrog’ citrons (Citrus medica L.) likely due to the varying accumulation patterns produced by the different viroids. Some of the symptoms caused by the samples harboring the citrus viroids other than CEVd were as severe as those caused by CEVd. Some source citrus trees showing the severe bark scaling characteristic of exocortis disease in trifoliate orange (Poncirus trifoliata (L.) Raf.) rootstocks contained only citrus viroids other than CEVd in complex. This indicates that certain exocortis-like diseases in Japan were caused by some combination of citrus viroids not including CEVd.
Volatile Fatty Acids in Liquid Swine Manure Can Kill Microsclerotia of Verticillium dahliae
Authors: Tenuta Mario , Conn Kenneth L. , Lazarovits George
Published: May 2007

Liquid swine manure added to acidic soils killed microsclerotia of the wilt fungus Verticillium dahliae. We investigated whether volatile fatty acids (VFAs) in the manure were responsible for this toxicity. The survival of microsclerotia was determined after exposure to various dilutions of manure or its VFA components. Acetic, propionic, and isobutyric acids constituted the major VFAs in the manure, while n-butyric, n-valeric, iso-valeric, and n-caproic acids were present in lesser amounts. Formic acid was not detected. The individual VFAs were more toxic to microsclerotia as the solution pH was decreased, indicating that the protonated forms of the VFAs were toxic (e.g., acetic acid and not acetate). The effective concentration reducing germination of microsclerotia by 95% (EC95) for formic and n-caproic acids was approximately 4 mM, the most toxic of the acids tested; for n-valeric, the EC95 was 9.2 mM, isovaleric was 16.1 mM acids, and acetic, propionic, n-butyric, and isobutyric acids were approximately 30 mM. The toxicity of acetic acid, and likely all the others, was directly related to the duration of exposure. Inhibition of microsclerotia germination followed identical trends in solutions of the manure or in a mixture of VFAs with equivalent concentrations of the individual acids found in the manure. Similarly, germination declined to the same extent in the atmosphere above the manure or the VFA mixture, confirming the toxicity of VFAs to microsclerotia. Thus, under acid conditions, VFAs in liquid swine manure can kill microsclerotia of V. dahliae.
Molecular and Biological Characterization ofLettuce mosaic virus(LMV) Isolates Reveals a Distinct and Widespread Type of Resistance-Breaking Isolate: LMV-Most
Authors: Krause-Sakate Renate , Le Gall Olivier , Fakhfakh Hatem , Peypelut Martine , Marrakchi Mohammed , Varveri Christina , Pavan Marcelo A. , Souche Sylvie , Lot Hervé , Zerbini F. Murilo , Candresse Thierry
Published: May 2007

Lettuce mosaic virus (LMV) causes an economically important seedborne and aphid-transmitted disease of lettuce and ornamental crops worldwide. The genetic diversity among 73 LMV isolates was examined based on a 216-nucleotide sequence at the variable region encoding the NIb-coat protein junction. Three clusters of LMV isolates were distinguished: LMV-Yar, LMV-Greek, and LMV-RoW. In the latter cluster, two subgroups of isolates, LMV-Common and LMV-Most, accounted for a large proportion of the LMV isolates analyzed. These two subgroups included the seedborne isolates, consistent with this property contributing a selective advantage and resulting in widespread distribution. In addition to being seedborne, LMV-Most isolates overcome the two resistance genes commonly used in lettuce, mo11and mo12, and thus represent a potential threat to lettuce cultivation. The complete sequence of an LMV-Most isolate (LMV-AF199) was determined, allowing a better definition of the genetic relationships among LMV-Most, LMV-Common, and an additional isolate of the LMV-RoW cluster.
Transgenically Enhanced Expression of Indole-3-Acetic Acid Confers Hypervirulence to Plant Pathogens
Authors: Cohen Barry A. , Amsellem Ziva , Maor Rudy , Sharon Amir , Gressel Jonathan
Published: May 2007

Fusarium oxysporum and F. arthrosporioides, pathogenic on Orobanche aegyptiaca, were transformed with two genes of the indole-3-acetamide (IAM) pathway leading to indole-3-acetic acid (IAA) to attempt to enhance virulence. Transgenic F. oxysporum lines containing both the tryptophan-2-monooxyngenase (iaaM) and indole-3-acetamide hydrolase (iaaH) genes produced significantly more IAA than the wild type. IAM accumulated in culture extracts of F. oxysporum containing iaaM alone. F. arthrosporioides containing only iaaM accumulated IAM and an unidentified indole. Some transformants of F. oxysporum expressing only the iaaM gene also produced more IAA than the wild type. Sub-threshold levels (that barely infect Orobanche) of transgenic F. oxysporum expressing both genes and of F. arthrosporioides expressing iaaM were more effective in suppressing the number and size of Orobanche shoots than the wild type on tomato plants grown in soil mixed with Orobanche seed. Stimulating an auxin imbalance enhanced pathogen virulence by affecting the host in a manner similar to low doses of auxin herbicides such as 2,4-dichlorophenoxy acetic acid.
Dwarf Mistletoe-Host Interactions in Mixed-Conifer Forests in the Sierra Nevada
Authors: Maloney Patricia E. , Rizzo David M.
Published: May 2007

We determined the spatial pattern of dwarf mistletoe (Arceuthobium spp.) associated with two different conifer hosts, white fir (Abies concolor) and Jeffrey pine (Pinus jeffreyi), in forests around the Lake Tahoe Basin and at the Teakettle Experimental Forest, both located in the Sierra Nevada. We also examined a number of host variables and bark beetle incidence to determine how these factors might be involved in the Arceuthobium—conifer interaction. There was no significant relationship between dwarf mistletoe-infected trees and associated bark beetles. We found the highest incidence of dwarf mistletoe on Jeffrey pine in Lake Tahoe (87%), followed by dwarf mistletoe on white fir in Lake Tahoe (30%), with the lowest incidence on white fir at Teakettle (27%). Dwarf mistletoe incidence on white fir in our Lake Tahoe grid was not correlated to density but the dwarf mistletoe rating (DMR) was positively correlated to host size. At the Teakettle Forest, dwarf mistletoe incidence on white fir was not correlated with host density but the DMR was correlated with host size. Dwarf mistletoe incidence and DMR on Jeffrey pine were correlated with host density. Individuals, of both conifer species, in all diameter size classes were susceptible to dwarf mistletoe, with the lowest infection rate in the seedling-10-cm-diameter class. Arceuthobium on white fir in Lake Tahoe showed spatial dependence to a range of 20 m. However, Arceuthobium on Jeffrey pine in Lake Tahoe and on white fir at Teakettle showed no clear pattern of spatial structuring. The degree of infection and stand history appear to be important in the spatial dynamics of Arceuthobium spp.
Tomato leaf curl Karnataka virus from Bangalore, India, Appears to be a Recombinant Begomovirus
Authors: Chatchawankanphanich Orawan , Maxwell Douglas P.
Published: May 2007

The genome of Tomato leaf curl virus (ToLCV) from Bangalore, India, a whitefly-transmitted geminivirus, was cloned (pIND9) and sequenced. The circular DNA of 2,759 nucleotides (U38239) is organized similarly to that of other begomoviruses with monopartite genomes. Comparison of the nucleotide sequence of pIND9 with other tomato-associated begomoviruses from India (Tomato leaf curl Bangalore virus [ToLCBV, Z48182]) and Tomato leaf curl New Delhi virus-Severe (ToLCNdV-Svr, U15015) showed moderate DNA sequence identities (82 to 87%) between capsid protein (CP) genes but low identities (66 to 67%) for the intergenic regions and the replication-associated protein (Rep) genes (75 to 81% identity). Phylogenetic trees generated with nucleotide sequences of the Rep and CP genes of 26 begomoviruses indicated that this ToLCV is distinct from other begomoviruses and that it may be a recombinant virus derived from at least three different viral lineages. Tomatoes (Lycopersicon esculentum) inoculated with the cloned DNA monomer of ToLCV (pIND9) via particle bombardment developed leaf curling and yellowing symptoms. The virus was transmitted by Bemisia tabaci biotype B from tomatoes infected via particle bombardment to healthy tomatoes and by sap inoculation from infected tomatoes to tomato, Nicotiana benthamiana and N. tabacum. This ToLCV is a distinct member of the genus Begomovirus from India that differs from the previously characterized Tomato leaf curl Sadasivanagar virus isolate Bangalore 1 (L12739), ToLCBV (Z48182), ToLCBV isolate Bangalore 4 (AF165098), and the bipartite ToLCNdV (U15015, U15016). Thus, this ToLCV is named Tomato leaf curl Karnataka virus (ToLCKV).
Species and Mating-Type Distribution of Tapesia yallundae and T. acuformis and Occurrence of Apothecia in the U.S. Pacific Northwest
Authors: Douhan G. W. , Murray T. D. , Dyer P. S.
Published: May 2007

Eyespot of wheat is caused by the discomycete fungi Tapesia yallundae and T. acuformis. T. yallundae is considered the most important causal agent of the disease in this region but no apothecia of either species have been found in the U.S. Pacific Northwest (PNW). Two compatible isolates of T. yallundae from the PNW were used to inoculate a field plot in the fall of 1998 and apothecia developed in the spring and fall of 2000 on standing wheat stubble. In the spring of 2000, wheat stubble from eight naturally infected fields was examined for the presence of apothecia of T. yallundae and T. acuformis. Apothecia of T. acuformis were found in two fields but no apothecia of T. yallundae were found. This is the first report of apothecia of the eyespot pathogens occurring in the PNW. Species and mating-type distribution of T. yallundae and T. acuformis in the PNW were determined from 817 isolates collected from diseased wheat over 3 years at spatial scales ranging from within fields to across states. In all, 460 isolates were identified as T. yallundae and 357 isolates were identified as T. acuformis with MAT1-1/MAT1-2 ratios not significantly different from 1:1 based on χ2 tests at most scales tested. The apparent increase in frequency of T. acuformis from previous surveys may indicate a shift in the predominant species causing eyespot. The occurrence of apothecia under field conditions, along with the widespread distribution of mating types of both species, suggests that sexual reproduction may be occurring in both species.
Resistance to Scald (Rhynchosporium secalis) in Barley (Hordeum vulgare) Studied by Near-Isogenic Lines: I. Markers and Differential Isolates
Authors: Bjørnstad Å. , Patil V. , Tekauz A. , Marøy A. G. , Skinnes H. , Jensen A. , Magnus H. , MacKey J.
Published: May 2007

Near-isogenic lines (NILs) with resistance for scald in seventh generation backcross with ‘Ingrid’ as recurrent parent (RP) were tested with seven differential isolates of Rhynchosporium secalis in Norway and Canada. NILs of ‘Turk’, ‘Brier’, ‘CI 8162’, ‘La Mesita’, ‘Hispont’, ‘Atlas 46’, ‘Modoc’, ‘Hudson’, ‘Abyssinian’, ‘Steudelli’, and ‘CI 2222’ also were evaluated for field reactions. The genetic characterization of the NILs (degree of isogeneity with Ingrid) and with each other was carried out. The molecular marker pattern shows that the backcrossing program has resulted in from 86.3 to 100% RP genome in the NILs, depending on the marker system. On an average, 96% RP genome was found in the NILs. There were certain consistent (pairwise) differences between the NILs and RP on chromosomes 3H and 7H. Both chromosomes are known to contain loci conferring resistance to R. secalis, indicating successful introgression from the donors into the NILs. Approximately two-thirds of the observed RP-NIL polymorphisms were linked to the assumed resistance in the NIL. Based on the marker and phenotypic analyses of the NILs, suggestions for a more appropriate and updated terminology of genes for resistance to R. secalis in barley are made. The proposed changes in nomenclature also indicate the differentials that are available as NILs and those lacking.
Phylogeography and Genotype-Symptom Associations in Early and Late Season Infections of Canola by Sclerotinia sclerotiorum
Authors: Phillips D. V. , Carbone I. , Gold S. E. , Kohn L. M.
Published: May 2007

Both typical late season stem infections and atypical early season rosette infections of canola, a relatively new crop in the southeastern United States, were caused by Sclerotinia sclerotiorum. The 51 DNA fingerprints (from 71 isolates) did not match any fingerprints from previous studies of canola or other crops. Single locus haplotypes from nuclear DNA sequences included 18 in the intergenic spacer (IGS) of the rRNA repeat, four in 44.11, six in translation elongation factor 1α, three in calmodulin (CAL), and two in chitin synthase 1. Contingency permutation testing for associations of infection type with DNA fingerprint, single- or multilocus haplotype, or hierarchically nested clades based on single locus haplotypes found significant association of haplotype with mycelial compatibility group and DNA fingerprint for all loci except CAL. Significant association of IGS haplotypes with symptom type was detected in one pathogen population. Southeastern U.S. canola was infected by both recently evolved, geographically dispersed pathogen genotypes and older, indigenous genotypes (Carbone and Kohn, 2001. Mol. Ecol. 10:947–964). Indigenous haplotypes are infection-type generalists, and the most frequently isolated from rosette infections. In contrast, haplotypes from the most recently evolved, dispersed population were associated one-to-one with infection type, with only the most recently evolved haplotypes infecting rosettes.
Worldwide Phylogeography of the Citrus Brown Spot Pathogen, Alternaria alternata
Authors: Peever T. L. , Ibañez A. , Akimitsu K. , Timmer L. W.
Published: May 2007

Sixty-five isolates of Alternaria alternata were sampled from brown spot lesions on tangerines and mandarins (Citrus reticulata) and tangerine × grapefruit (C. reticulata × C. paradisi) hybrids in the United States, Colombia, Australia, Turkey, South Africa, and Israel to investigate the worldwide phylogeography of the fungus. Genetic variation was scored at 15 putative random amplified polymorphic DNA (RAPD) loci and 465 bp of an endo-polygalacturonase (endo-PG) gene was sequenced for each isolate. Cluster analysis of RAPD genotypes revealed significant differentiation between United State and Colombia isolates and Turkey, South Africa, Israel, and Australia isolates. Sequencing of endo-PG revealed 21 variable sites when the outgroup A. gaisen (AK-toxin-producing pathogen of Japanese pear) was included and 13 variable sites among the sampled isolates. Nucleotide substitutions at 10 of 13 variable sites represented silent mutations when endo-PG was translated in frame. Eight distinct endo-PG haplotypes were found among the sampled isolates and estimation of a phylogeny with endo-PG sequence data revealed three clades, each with strong bootstrap support. The most basal clade (clade 1) was inferred based on its similarity to the outgroup A. gaisen and consisted exclusively of pathogenic isolates from the United States and Colombia. Clade 2 consisted of pathogenic and nonpathogenic isolates from the United States, Australia, South Africa, and Israel and clade 3 contained pathogenic and nonpathogenic isolates from Australia, South Africa, Israel, and Turkey. Quantitative estimates of virulence (disease incidence) were obtained for isolates from the United States, Colombia, South Africa, Israel, and Turkey by spray inoculating detached citrus leaves and counting the number of lesions 24 h after inoculation. Large differences in virulence were detected among isolates within each location and isolates from the United States were significantly more virulent than isolates from other locations. Several isolates from Colombia, South Africa, Israel, and Turkey had low virulence and 8% of all isolates were nonpathogenic. All but one of the nonpathogenic isolates were found in clade 2 of the endo-PG phylogeny, which also included the most highly virulent isolates sampled.
Involvement ofBeet western yellows virus,Cauliflower mosaic virus, andTurnip mosaic virusin Internal Disorders of Stored White Cabbage
Authors: Hunter P. J. , Jones J. E. , Walsh J. A.
Published: May 2007

Experiments over two growing seasons clearly showed that Turnip mosaic virus (TuMV) infection was associated with internal necrosis (sunken necrotic spots 5 to 10 mm in diameter) and Beet western yellows virus (BWYV) infection was associated with collapse of leaf tissue at the margins (tipburn) in heads of stored white cabbage (Brassica oleracea var. capitata). Virtually no tipburn was seen in cv. Polinius, whereas cv. Impala was affected severely. Internal necrotic spots were seen in both cultivars. BWYV appeared to interact with TuMV. Plants infected with both viruses showed a lower incidence of external symptoms and had less internal necrosis than plants infected with TuMV alone. Cauliflower mosaic virus (CaMV) did not induce significant amounts of internal necrosis or tipburn, but did, in most cases, exacerbate symptoms caused by TuMV and BWYV. BWYV-induced tipburn worsened significantly during storage. Post-transplanting inoculation with TuMV induced more internal necrosis than pre-transplant inoculation. There was a significant association between detection of TuMV just prior to harvest and subsequent development of internal necrotic spots. Individually, all three viruses significantly reduced the yield of cv. Polinius, whereas only BWYV and CaMV treatments reduced the yield of cv. Impala.
Vegetative Compatibility Groups in Colletotrichum coccodes, the Causal Agent of Black Dot on Potato
Authors: Nitzan N. , Hazanovsky M. , Tal M. , Tsror(Lahkim) L.
Published: May 2007

Black dot of potato, caused by Colletotrichum coccodes, is a disease of growing economic importance, but the degree of genetic diversity and pathogenic differentiation among isolates is unknown. Using nitrate auxotrophic (Nit) mutants, we characterized vegetative compatibility groups (VCG) diversity for C. coccodes for 110 isolates originating from Israel, The Netherlands, and France. We recovered frequencies of nit1 and NitM mutant classes at 38.5 and 7.2%, respectively, and selected 12 isolates as tester isolates. Using these testers, we defined four multimember VCGs at 7.3, 35.5, 20.0, and 10.0% frequency in this sample. Thirty isolates (27.3% of all tested isolates) could not be assigned to any of the major groups, and showed only self-compatibility. The frequency of recovery of Nit mutant sectors was highest in isolates from VCG4, with 50.9 and 13.6% recovery for nit1 and NitM, respectively. However, we did not detect differences in the frequency of mutant classes among the three countries of origin. In pathogenicity tests, isolates from VCG3 were the most aggressive to potato, as expressed by high stem colonization levels and sclerotia density on root and crown. These results suggest that there is significant VCG diversity in this species and that this VCG diversity may be correlated with pathogenic characteristics or specialization.
Expression of NEP1 by Fusarium oxysporum f. sp. erythroxyli After Gene Replacement and Overexpression Using Polyethylene Glycol-Mediated Transformation
Authors: Bailey B. A. , Apel-Birkhold Patricia C. , Luster Douglas G.
Published: May 2007

The necrosis inducing extracellular protein Nep1 is produced by Fusarium oxysporum f. sp. erythroxyli in liquid culture. NEP1, the Nep1 protein structural gene, was disrupted in F. oxysporum f. sp. erythroxyli isolate EN-4 by gene replacement using polyethylene glycol (PEG)-mediated transformation. NEP1 disruption was verified by polymerase chain reaction (PCR), Southern blot, and northern blot analysis. NEP1-disrupted transformants failed to produce Nep1 in liquid culture. NEP1 disruption did not affect the pathogenicity of isolate EN-4 toward Erythroxylum coca. Transformation of isolate EN-4 with construct pPB-FO11-45 carrying NEP1 between the trpC promoter and terminator resulted in increased production of Nep1 in potato dextrose broth plus 1% casamino acids or Czapek-Dox broth plus 1% casamino acids but not in potato dextrose broth alone. Transformation of EN-4 with construct pPB-FO11-45 was verified by PCR and Southern blot analysis. Overexpression of NEP1 was confirmed by northern blot and Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. NEP1-overexpressing transformant 15 produced 64 to 128 times as much Nep1 as EN-4 wild type when grown in shake cultures. Transformants overexpressing Nep1 in liquid culture were no more or less pathogenic toward E. coca than wild-type isolates. Nep1 was not detected in E. coca seedlings infected with NEP1-overexpressing transformants or with EN-4 wild type. In large-scale fermentations of NEP1-overexpressing transformant 15, the amount of secreted protein including Nep1 was 15.1 times that of the wild-type EN-4, providing a ready source of Nep1 for future study.
Repetitive Applications of the Biocontrol AgentPseudomonas putida06909-rif/nal and Effects on Populations ofPhytophthora parasiticain Citrus Orchards
Authors: Steddom K. , Becker O. , Menge J. A.
Published: May 2007

Pseudomonas putida 06909-rif/nal was applied repetitively during the irrigation season in two citrus orchards over 3 years. In a mature (50-yearold) commercial citrus orchard covering 2.02 ha, weekly applications of Pseudomonas putida 06909-rif/nal with an in-field fermentor resulted in soil populations that fluctuated between 2.83 log CFU + 1 per g of soil and 4.35 log CFU + 1 per g of soil. Resulting rhizosphere populations of Phytophthora parasitica were significantly reduced in 1999 but not 1997 or 1998. In a newly planted citrus orchard, yearly applications of Pseudomonas putida 06909-rif/nal at the beginning of the irrigation season resulted in high soil populations of Pseudomonas putida 06909-rif/nal that declined rapidly and never reduced the rhizosphere populations of Phytophthora parasitica. When Pseudomonas putida 06909-rif/nal was applied weekly, soil populations increased throughout the 1997 and 1998 irrigation seasons, reaching a maximum in 1998 and remained high throughout the 1999 irrigation season. Rhizosphere populations of Phytophthora parasitica were significantly reduced in 1998. Yearly applications of the fungicide metalaxyl and the nematicide phenamiphos reduced rhizosphere populations of Phytophthora parasitica in 1997 but not in 1998 or 1999. Pseudomonas putida 06909-rif/nal was uniformly distributed throughout the soil profile to a depth of 75 cm in both yearly and weekly applications. When applied through low-volume minisprinklers, Pseudomonas putida 06909-rif/nal was found in aerosols up to 3 m away.
Production, Survival, and Evaluation of Solid-Substrate Inocula of Penicillium oxalicum, a Biocontrol Agent Against Fusarium Wilt of Tomato
Authors: Larena I. , Melgarejo P. , De Cal A.
Published: May 2007

Production of conidia of Penicillium oxalicum (ATCC number pending), a biocontrol agent of Fusarium oxysporum f. sp. lycopersici, was tested in liquid and solid fermentation. P. oxalicum produced 250-fold more conidia in solid than in liquid fermentation at 30 days after inoculation of substrate. Solid fermentation was carried out in plastic bags (600 cm3) especially designed for solid fermentation (VALMIC) containing 50 g of peat/vermiculite (PV) (1:1, wt/wt) with 40% moisture, sealed, sterilized, and then inoculated with 1 ml of a conidial suspension of P. oxalicum (105 conidia g-1 dry substrate), sealed again, and incubated in darkness at 20 to 25°C for 30 days. Addition of amendments to PV in a proportion of 0.5 (wt/wt) significantly increased conidial production of P. oxalicum. The best production was obtained on PV plus meal of cereal grains (barley) or leguminous seeds (lentil) (100-fold higher). Conidial production obtained after 5 days of inoculation was similar to that obtained at 30 days. However, viability of conidia produced in PV plus lentil meal was 35% higher than that of conidia produced in PV plus barley meal. Changes in proportions (1:1:0.5, wt/wt/wt; 1:1:1, wt/wt/wt; 1:0.5:0.5, wt/wt/wt; 1:1:0.5, vol/vol/vol) of components of the substrate (peat/vermiculite/lentil meal) did not enhance production or viability of conidia. Optimal initial moisture in the substrate was 30 to 40%. At lower moistures, significant reductions of production of conidia were observed, particularly at 10%. There was a general decline in the number of conidia in bags with time of storage at -80, -20, 4, and 25°C, or at room temperature (range from 30 to 15°C), with the highest decline occurring from 60 to 180 days. Conidial viability also was reduced with time, except for conidia stored at -20°C. Fresh conidia produced in solid fermentation system or those conidia stored at -20°C for 180 days reduced Fusarium wilt of tomato by 49 and 61%, respectively.
Ribosomal Intergenic Spacer: A Polymerase Chain Reaction Diagnostic for Meloidogyne chitwoodi, M. fallax, and M. hapla
Authors: Wishart J. , Phillips M. S. , Blok V. C.
Published: May 2007

Polymerase chain reaction amplification of the intergenic spacer region between the 5S and 18S genes from Meloidogyne chitwoodi, M. fallax, and M. hapla enabled these three important temperate species to be differentiated. Length polymorphism was found between M. chitwoodi and M. fallax as a result of differing numbers of short repeats located between the 5S and 18S genes. The presence of the 5S gene within the rDNA cistrons was confirmed in the Meloidogyne spp. included in this study. The region between the 28S and 5S genes for M. chitwoodi and M. fallax was short and lacked variability in repeated sequences compared with the main tropical Meloidogyne spp. and M. hapla. Differences in the number of these repeats resulted in intraspecific length polymorphism for M.hapla
Copper Resistance in Pseudomonas syringae Strains Isolated from Mango Is Encoded Mainly by Plasmids
Authors: Cazorla Francisco M. , Arrebola Eva , Sesma Ane , Pérez-García Alejandro , Codina Juan C. , Murillo Jesús , de Vicente Antonio
Published: May 2007

Bacterial apical necrosis of mango, elicited by Pseudomonas syringae pv. syringae, limits fruit production in southern Spain and Portugal. Examination of a collection of P. syringae pv. syringae isolates for copper resistance showed that 59% were resistant to cupric sulfate. The survey of a mango orchard revealed an increase in frequencies of copper-resistant bacteria after repeated treatments with Bordeaux mixture. These data suggest that selection of copper-resistant strains could be a major reason for control failures following management with copper bactericides. Most copper-resistant isolates harbored plasmids, although the majority of them contained a 62-kb plasmid that also was present in copper-sensitive strains. The 62-kb plasmids were differentiated by restriction enzyme analysis and hybridization to copABCD DNA. The most frequently found copper-resistant plasmid type (62.1) was transferable by conjugation. Southern blot hybridizations showed that genetic determinants partially homologous to copABCD were present in all the copper-resistant strains examined, and usually were associated with plasmids; these determinants were not detected in copper-sensitive strains. The selective pressure exerted by copper bactericide sprays on the diversity of copper resistance determinants in bacterial populations of mango is discussed.