bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance of the Biocontrol Fungus Piriformospora indica on Wheat Under Greenhouse and Field Conditions
Authors: Serfling Albrecht , Wirsel Stefan G. R. , Lind Volker , Deising Holger B.
Published: May 2007

The endophyte Piriformospora indica colonizes roots of a range of host plants and increases biomass production and resistance to fungal pathogens and, thus has been considered a biocontrol fungus. However, the field performance of this fungus has not yet been tested in temperate climates. Therefore, we evaluated the performance of this fungus in different substrata under greenhouse and practical field conditions. Roots of winter wheat were colonized efficiently, and biomass was particularly increased on poor substrata. In greenhouse experiments, symptom severity of a typical leaf (Blumeria graminis f. sp. tritici), stem base (Pseudocercosporella herpotrichoides), and root (Fusarium culmorum) pathogen was reduced significantly. However, in field experiments, symptoms caused by the leaf pathogen did not differ in Piriformospora indica-colonized compared with control plants. In the field, Pseudocercosporella herpotrichoides disease severity was significantly reduced in plants colonized by the endophyte. Increased numbers of sheath layers and hydrogen peroxide concentrations after B. graminis attack were detected in Piriformospora indica-colonized plants, suggesting that root colonization causes induction of systemic resistance or priming of the host plant. Although the endophyte is not well suited for growth at Central European temperature conditions, it remains to be shown whether P. indica is more suitable for tropical or subtropical farming.
Molecular Detection of Phytophthora ramorum by Real-Time Polymerase Chain Reaction Using TaqMan, SYBR Green, and Molecular Beacons
Authors: Bilodeau G. J. , Lévesque C. A. , de Cock A. W. A. M. , Duchaine C. , Brière S. , Uribe P. , Martin F. N. , Hamelin R. C.
Published: May 2007

Sudden oak death, caused by Phytophthora ramorum, is a severe disease that affects many species of trees and shrubs. This pathogen is spreading rapidly and quarantine measures are currently in place to prevent dissemination to areas that were previously free of the pathogen. Molecular assays that rapidly detect and identify P. ramorum frequently fail to reliably distinguish between P. ramorum and closely related species. To overcome this problem and to provide additional assays to increase confidence, internal transcribed spacer (ITS), β-tubulin, and elicitin gene regions were sequenced and searched for polymorphisms in a collection of Phytophthora spp. Three different reporter technologies were compared: molecular beacons, TaqMan, and SYBR Green. The assays differentiated P. ramorum from the 65 species of Phytophthora tested. The assays developed were also used with DNA extracts from 48 infected and uninfected plant samples. All environmental samples from which P. ramorum was isolated by PARP-V8 were detected using all three real-time PCR assays. However, 24% of the samples yielded positive real-time PCR assays but no P. ramorum cultures, but sequence analysis of the coxI and II spacer region confirmed the presence of the pathogen in most samples. The assays based on detection of the ITS and elicitin regions using TaqMan tended to have lower cycle threshold values than those using β-tubulin and seemed to be more sensitive.
Epidemiological Effect of Gene Deployment Strategies on Bacterial Blight of Rice
Authors: Ahmed Hafiz U. , Finckh Maria R. , Alfonso Rizal F. , Mundt Christopher C.
Published: May 2007

Experiments were conducted in farmers' fields at two locations of the irrigated lowlands of Laguna province in southern Luzon island, Philippines, during the wet seasons of 1993 and 1994. Nine rice populations were studied including pure stands, two-component mixtures, two-gene combinations of backcrossed lines containing varying combinations of the bacterial blight resistance genes Xa-4, xa-5, and Xa-10, and a non-isogenic cultivar containing Xa-4 and partial resistance to bacterial blight. The area under the disease progress curve (AUDPC) of both gene combinations studied was significantly less than the single most effective gene of each combination deployed singly. A mixture of a susceptible and a resistant line expressed an AUDPC significantly less than the mean of its component pure stands, but two other mixtures did not. The cultivar IR20, which contains both Xa-4 and partial resistance, reduced the AUDPC by about two-thirds as compared with IR-BB4, which contains Xa-4 and little or no partial resistance.
Polygalacturonase Isozymes Produced byPhomopsis cucurbitaein Relation to Postharvest Decay of Cantaloupe Fruit
Authors: Zhang Jiuxu , Bruton Benny D. , Biles Charles L.
Published: May 2007

Production of polygalacturonase (PG), a cell wall-degrading enzyme, by Phomopsis cucurbitae (latent infection fungus) was studied in relation to different carbon sources and various stages of cantaloupe fruit development. P. cucurbitae produced multiple PG isozymes both in vitro and in vivo. The fungus produced the highest PG activity and the greatest number of isozymes on pectin compared with those produced on glucose, galactose, and sucrose. Eight P. cucurbitae PG isozymes (pIs 3.7, 4.2, 6.6, 7.0, 7.3, 7.5, 7.8, and 8.6) were detected in extract from inoculated mature fruit (40 days after anthesis) by isoelectric focusing. Isozyme bands with pIs of 4.2, 7.3, and 7.8 were the most prominent. A similar set of PG isozymes was produced by P. cucurbitae in autoclaved mature fruit tissue (mesocarp). When tissue discs taken from 20-, 30-, 40-, and 50-day postanthesis fruit were inoculated with P. cucurbitae, PG activity and the number of PG isozymes extracted from the macerated fruit tissue discs increased with the degree of fruit maturity and ripening. Increases in PG activity and PG isozymes were also correlated with reactivation of latent infections and the beginning of tissue maceration. An anionic PG isozyme (pI 4.2) was only visualized on decayed 50-day-old fruit exocarp, as well as 40- and 50-day-old fruit mesocarp. The experimental results support the hypotheses that P. cucurbitae PG isozymes play an important role in fruit decay once latent infection becomes active following harvest.
Inheritance of Resistance to Aflatoxin Production in the Cross Between Corn Inbreds B73 and LB31
Authors: Campbell K. W. , Hamblin A. M. , White D. G.
Published: May 2007

The inheritance of resistance to aflatoxin production in corn (Zea mays) caused by the fungus Aspergillus flavus was studied following inoculation in progeny derived from the cross between the susceptible inbred B73 and the resistant inbred LB31. In 1993, the susceptible parent B73 (P1), resistant parent LB31 (P2), F1, F3, and BCP1-selfed generations were evaluated. In 1994, the study was expanded to include the F2, BCP1, and BCP2generations. Aflatoxin concentrations were higher in 1993 than 1994. Generation mean analysis showed that additive and dominant gene action were important for resistance to aflatoxin production. Potence ratios indicated dominance for resistance in both years. In 1993, aflatoxin values of the F1generation were significantly lower than the calculated mid-parent values, indicating dominant gene action favoring resistance. In 1994, values of the F1generation were not significantly lower than the calculated midparent value. The frequency distributions of aflatoxin values for families of the F3and BCP1-selfed generations were skewed toward the resistant parent, also indicating dominance. Heritability based on a progeny mean basis of F3families representing the additive variance plus one-fourth of the dominance variance was estimated at 66% over both years combined. Based on these results, selection for resistance to aflatoxin production in progeny derived from the cross between B73 and LB31 should be effective.
Populations ofXylella fastidiosain Plants Required for Transmission by an Efficient Vector
Authors: Hill B. L. , Purcell A. H.
Published: May 2007

Xylella fastidiosa, a xylem-limited bacterium that causes Pierce's disease (PD) of grapevine and other diseases, is transmitted efficiently by xylem-feeding leafhoppers. Acquisition of a PD strain of X. fastidiosa by the blue-green sharpshooter (BGSS) from five plant host species—grapevine (Vitis vinifera), Himalayan blackberry (Rubus discolor), California mugwort (Artemisia douglasiana), watergrass (Echinochloa crus-galli), and Bermuda grass (Cynodon dactylon)—was tested at various time intervals after vector inoculation. The minimum incubation periods in plant hosts before BGSS acquired X. fastidiosa were 4, 22, 29, and 25 days for grapevine, blackberry, mugwort, and watergrass, respectively. There were no transmissions by vectors or recoveries of X. fastidiosa by culturing from Bermuda grass in 133 attempts, including 80 attempts with the green sharpshooter, Draeculacephala minerva. The first acquisitions and subsequent transmissions by BGSS occurred after X. fastidiosa multiplied to a population of about 104CFU/g of stem tissue. Higher populations of bacteria in plants resulted in higher rates of transmission. In grapevine, the rate of transmission increased over time (4.5% in the first 10 days to 55% after day 25) as the maximum number of viable CFU of X. fas-tidiosa recovered by culturing also increased (from 5 × 105CFU/g during the first 10 days to 5 × 108after day 25).
Resistance to Leaf Scald Disease Is Associated with Limited Colonization of Sugarcane and Wild Relatives by Xanthomonas albilineans
Authors: Rott P. , Mohamed I. S. , Klett P. , Soupa D. , de Saint-Albin A. , Feldmann P. , Letourmy P.
Published: May 2007

A streptomycin- and rifampicin-resistant mutant of Xanthomonas al-bilineans was used to study symptom expression of leaf scald disease (LSD) and colonization of sugarcane (Saccharum spp.) and its wild relatives by this bacterial pathogen. A total of 40 sugarcane cultivars and 15 clones from the Saccharum complex that differed in resistance to LSD were inoculated by a decapitation technique in both field and greenhouse experiments. In the plant crop, disease severity varied between 0 for the most resistant genotypes and 100 for the most susceptible ones. Resistance to LSD was characterized by limited colonization of the host plant by X. albilineans. Although almost all genotypes were colonized by the pathogen, the greatest bacterial population densities were found in the susceptible cultivars. There was a high correlation between disease severity and pathogen population in the apex. Several genotypes exhibited no or slight symptoms even though they were highly colonized in the upper and/or basal nodes of stalks. Two mechanisms, therefore, may play an important role in resistance to LSD: resistance to colonization of the apex, which is characterized by absence of symptoms, and resistance to colonization of the upper and lower parts of the stalk. In contrast, disease severity and pathogen population densities in the first ratoon crop in the field were nil or very low in the stalks, except for the highly susceptible cv. CP68-1026. Sugarcane ratoons, therefore, may recover from the disease after plant cane infection. Nevertheless, because low levels of the pathogen were still detected in some stalks, it is possible that LSD could develop from latent infections if favorable environmental conditions occur.
A Major Quantitative Trait Locus for Rice Yellow Mottle Virus Resistance Maps to a Cluster of Blast Resistance Genes on Chromosome 12
Authors: Ghesquière A. , Albar L. , Lorieux M. , Ahmadi N. , Fargette D. , Huang N. , McCouch S. R. , Notteghem J. L.
Published: May 2007

Two doubled-haploid rice populations, IR64/Azucena and IRAT177/ Apura, were used to identify markers linked to rice yellow mottle virus (RYMV) resistance using core restriction fragment length polymorphism (RFLP) maps. Resistance was measured by mechanical inoculation of 19-day-old seedlings followed by assessment of virus content by enzyme-linked immunosorbent assay tests 15 days after inoculation. IR64/Azucena and IRAT177/Apura populations, 72 and 43 lines, respectively, were evaluated, and resistance was found to be polygenic. Resistance was expressed as a slower virus multiplication, low symptom expression, and limited yield loss when assessed at the field level. Bulked segregant analysis using the IR64/Azucena population identified a single random amplified polymorphic DNA marker that mapped on chromosome 12 and corresponded to a major quantitative trait locus (QTL) evidenced by interval mapping. When pooling RFLP data, integrated mapping of this chromosome revealed that the QTL was common to the two populations and corresponded to a small chromosomal segment known to contain a cluster of major blast resistance genes. This region of the genome also reflected the differentiation observed at the RFLP level between the subspecies indica and japonica of Oryza sativa. This is consistent with the observation that most sources of RYMV resistance used in rice breeding are found in upland rice varieties that typically belong to the japonica subspecies.
Host-Specific Toxin Production by Rhizoctonia solani, the Rice Sheath Blight Pathogen
Authors: Vidhyasekaran P. , Ponmalar T. Ruby , Samiyappan R. , Velazhahan R. , Vimala R. , Ramanathan A. , Paranidharan V. , Muthukrishnan S.
Published: May 2007

Rhizoctonia solani, the rice sheath blight pathogen, produces a toxin that reproduces all symptoms of the disease. The toxin has been partially purified and it was found to be a carbohydrate containing glucose, mannose, N-acetylgalactosamine, and N-acetylglucosamine. The toxin was also detected in infected leaves. Highly virulent isolates produced more toxin than less virulent isolates. Several R. solani isolates from rice and one each from cotton and tomato produced a similar toxin. All rice cultivars tested were susceptible to the pathogen and sensitive to the toxin. Host specificity of the toxin has been demonstrated using hosts and nonhosts of the pathogen.
Selection of Populations of Puccinia recondita f. sp. tritici for Shortened Latent Period on a Partially Resistant Wheat Cultivar
Authors: Lehman Jeffrey S. , Shaner Gregory
Published: May 2007

Wild-type fungal population 851-WT was selected for shortened latent period on cv. CI 13227 for five uredinial generations to study the adaptation of Puccinia recondita f. sp. tritici to partially resistant wheat cultivars. Differences among wild-type and selected populations for traits contributing to parasitic fitness (i.e., latent period, infection frequency, and uredinium area and growth rate) were assessed in monocyclic infection experiments on susceptible cv. Monon and partially resistant cvs. Suwon 85, Sw 72469-6, L-574-1, and CI 13227. Differences were greatest among fungal populations on cv. CI 13227. The mean latent period of selected population 851-C5 was 2 days shorter (~20%) than that of wild-type population 851-WT. In addition, uredinia of population 851-C5 expanded 40% faster and produced ~75% more urediniospores. On cv. L-574-1, the selected population was also more fit than the wild-type progenitor for initial uredinium area and growth rate and cumulative urediniospore production. In contrast to wild-type and selected populations on cvs. CI 13227 and L-574-1, selected population 851-C5 on cv. Monon produced slower expanding uredinia with fewer urediniospores than did population 851-WT on Monon. These results show that variation in the latent period of P. recondita f. sp. tritici populations is partially under genetic control and wild-type P. recondita f. sp. tritici populations contain members reproductively more fit on partially resistant wheat cultivars but not necessarily on susceptible cultivars. Such members are capable of partially overcoming quantitative host resistance.
Oospore Production of Phytophthora infestans in Potato and Tomato Leaves
Authors: Cohen Y. , Farkash S. , Reshit Z. , Baider A.
Published: May 2007

Fungal, host, and environmental factors affecting sexual reproduction of Phytophthora infestans in planta were studied. Intact and detached leaves were coinoculated with sporangia of various combinations of A1 and A2 mating-type isolates; leaves were incubated under various conditions, and oospore production was estimated microscopically within whole, clarified leaflets. Some A1 + A2 isolate combinations were more reproductive than others, whereas some potato genotypes better supported oospore formation than others. Tomato usually supported more oospore formation than potato. To induce oospore formation, A1 and A2 sporangia were usually mixed at a 1:1 ratio. Ratios of 1:19 to 19:1, however, also allowed abundant production of oospores. Optimal temperatures for sexual sporulation ranged from 8 to 15°C, but oospores also were produced at 23°C. Oogonia developed 5 to 6 days after sporangial coinoculation, and oospores developed after 8 to 10 days. Light had little effect on oospore formation in both tomato and potato leaves provided that initial lesions were established under photoperiodic conditions. Although A1 and A2 sporangia usually were mixed before inoculation on leaves to obtain oospores, we found that discrete A1 and A2 lesions produced on opposite sides of the midvein of tomato leaves also induced oospore formation in the midvein and adjacent tissues. Oospores also formed when the two halves of the leaves were cut and separated at 3 days after sporangial coinoculation, which corresponded with the appearance of late blight lesions. The continuous supply of moisture to infected leaves was essential to oospore production. No oospores or oogonia formed in severely diseased plants kept at 50 to 80% relative humidity. Such plants did allow some oospore formation when kept continuously wet for 2 weeks in plastic boxes or tents. Detached leaves floated on water supported the highest sexual sporulation. Under optimal conditions of wetness and temperature, as many as 100 oospores per mm2 of tissue were observed.
Characterization of the Suppressiveness of Hairy Vetch-Amended Soils toThielaviopsis basicola
Authors: Candole B. L. , Rothrock C. S.
Published: May 2007

Factor(s) involved in soil suppressiveness to Thielaviopsis basicola when hairy vetch was used as a green manure were studied in a cotton production system. Soil suppressiveness was assessed in vitro at hairy vetch amendment levels of 0, 0.25, and 0.75% (wt/wt) by observing chlamydospores, using a nylon fabric technique. Chlamydospore germination in all soils was below 5%, and microscopic examination showed no germ tube lysis or visible propagule destruction. Viability (chlamydospore germination on T. basicola-carrot-etridiazol-nystatin [TB-CEN] medium) was reduced by 29% within 48 h after hairy vetch amendment. Viability also was reduced in atmospheres of amended soils, suggesting that the suppressiveness was due to a volatile factor. In a field study, chlamydospore viability in amended soils was reduced by 16%. T. basicola hyphal growth was more sensitive to ammonia than Rhizoctonia solani or Pythium ultimum, and chlamydospore mortality of T. basicola was 100% in petri dish atmospheres with 0.4 ppm of ammonia (50% lethal dose = 0.15 ppm). Soil atmospheric ammonia was 0.08 and 0.10 ppm for 0.25 and 0.75% amendment levels, respectively, both at 3 and 7 days after incorporation. In the field, 0.11 and 0.14 ppm of ammonia were detected in soil atmospheres 3 and 7 days after incorporation, respectively. The levels of ammonia detected were sufficient to account for the loss in T. basicola chlamydospore viability, indicating that ammonia is responsible for the suppressiveness observed.
Effect of Modified Atmosphere for Control of Black Spot, Caused byAlternaria alternata, on Stored Persimmon Fruits
Authors: Prusky D. , Perez A. , Zutkhi Y. , Ben-Arie R.
Published: May 2007

Modified atmosphere packaging (MAP) of persimmon fruit resulted in the accumulation of acetaldehyde to a level of 80 μg/ml; ethanol to a level of 900 μg/ml; and CO2up to 30%. When fruits were stored at -1°C for 4 months in such atmospheres, the incidence of black spot disease, caused by Alternaria alternata, was reduced. The effects of each of these gases were examined to determine their individual involvement in the inhibition of Alternaria development during storage. When A. alternata, grown at 20°C on potato dextrose agar or inoculated in persimmon fruit, was exposed for 24 h to different levels of each volatile, acetaldehyde was the most fungistatic but only at concentrations higher than those that accumulated under MAP; CO2was moderately inhibitory at concentrations from 10 to 60%, whereas ethanol had no effect. Similar inhibitory effects were obtained with acetaldehyde at 620 μg/ml or 30% CO2when in vitro cultures of A. alternata and infected fruits were exposed for up to 2 weeks at 20°C, but 1,000 μg of ethanol per ml had only a transitory inhibitory effect under these conditions. Based on analysis of the effect of concentration versus time for each gas accumulating in MAP, we suggest that the increasing concentration of CO2during storage is the principal factor in the inhibition of black spot disease development.
Incorporation of Weather Forecasting in Integrated, Biological-Chemical Management ofBotrytis cinerea
Authors: Shtienberg D. , Elad Y.
Published: May 2007

A strategy for integrated biological and chemical control of Botrytis cinerea in nonheated greenhouse vegetables was developed. The biocontrol agent used was a commercial preparation developed from an isolate of Trichoderma harzianum, T39 (Trichodex). Decisions concerning whether to spray the biocontrol agent or a fungicide were made based on a weather-based disease warning system. The integrated strategy (BOTMAN [short for Botrytis manager]) was implemented as follows: when slow or no disease progress was expected, no spraying was needed; when an outbreak of epidemics was expected, use of a chemical fungicide was recommended; in all other cases, application of T. harzianum T39 was recommended. Future weather information (a 4-day weather forecast provided by the Israel Weather Forecast Service) was more useful for disease warnings than immediate past weather. The integrated strategy was compared with weekly applications of fungicide in 11 experiments conducted over 3 years in greenhouse-grown tomato and cucumber. Disease reduction in the integrated strategy (63.9 ± 3.0%) did not differ significantly (P < 0.05) from the fungicide-only treatment (70.1 ± 3.6%). The number of fungicide sprays in the integrated strategy ranged from 2 to 7 (mean 4.2) compared to 7 to 13 (mean 10.5) in the fungicide treatment. The integrated strategy averaged 5.9 sprays of T. harzianum T39. For the integrated strategy, one treatment omitted use of T. harzianum T39 to estimate the contribution of this agent to disease control. Disease reduction in that treatment (49.1 ± 4.8%) was significantly (P < 0.05) inferior to the combined chemical and biological strategy, indicating that the T. harzianum T39 sprays had a measurable effect on disease control.
Population Genetic Structure of Phytophthora infestans in Ecuador
Authors: Forbes Gregory A. , Escobar Ximena C. , Ayala Catalina C. , Revelo Jorge , Ordoñez Maria E. , Fry Barbara A. , Doucett Katharine , Fry William E.
Published: May 2007

The population genetic structure of Phytophthora infestans in Ecuador was assessed from 101 isolates collected from 1990 to 1992 and 111 isolates collected in 1993. All isolates were analyzed for mating type and allozyme genotype. Both samples were dominated (>95%) by a clonal lineage (EC-1) defined from neutral markers: 90/100 genotype for glucose-6-phosphate isomerase, 96/100 genotype for peptidase, A1 mating type, and a previously unreported nuclear DNA fingerprint. The remaining isolates belonged to the US-1 clonal lineage, which has a worldwide distribution. Isolates in the 1993 sample were analyzed for virulence and metalaxyl sensitivity. All representatives of EC-1 had complex patho-types, with three pathotypes representing >60% of the collection. There was variation for metalaxyl sensitivity. There was no evidence for geographical substructuring on the basis of neutral markers, but there was evidence for limited substructuring based on metalaxyl sensitivity and specific virulence. We hypothesize that EC-1 has been recently introduced to Ecuador.
Effects of Water Stress on Colonization of Poplar Stems and Excised Leaf Disks by Septoria musiva
Authors: Maxwell D. L. , Kruger E. L. , Stanosz G. R.
Published: May 2007

Septoria musiva causes leaf spot and canker diseases of trees in the genus Populus, and is one of the most damaging fungal pathogens of hybrid poplar in eastern North America. The effect of host water stress on Septoria canker development was studied in two separate greenhouse experiments. Hybrid poplar clones NM6, NC11396, and NE308 were stressed by withholding water until predawn water potential fell below −1.0 MPa. Stems were treated by removing a leaf and applying agar plugs that were either colonized by S. musiva (inoculated) or sterile (control) to the wound. Cankers on inoculated water-stressed trees were significantly larger than those on nonstressed trees. A leaf disk assay also was conducted three times with the NM6 and NE308 trees. We cut two disks from each of 120 stressed and 120 well-watered trees, placing them on water agar in 24-well tissue culture plates. A conidial suspension was applied to one disk in each pair and sterile water to the other. Inoculated disks from water-stressed trees developed less necrosis than those from well-watered trees. These results demonstrate that environmental influences on host condition must be considered in evaluating resistance of clones proposed for widespread culture of hybrid poplar.
Biological and Molecular Variability of Lettuce Mosaic Virus Isolates
Authors: Revers F. , Lot H. , Souche S. , Le Gall O. , Candresse T. , Dunez J.
Published: May 2007

Lettuce mosaic potyvirus (LMV) causes severe disease of commercial lettuce crops. LMV isolates show wide biological variability, particularly in their ability to overcome the resistance genes described in Lactuca sativa. For a better understanding of the molecular interaction between lettuce and LMV, biological and molecular characterization of a collection of 10 LMV isolates known to differ in virulence or aggressiveness was performed. The ability of these isolates to overcome the resistance genes was reevaluated under standardized conditions. To study the molecular variability of LMV, an immunocapture-reverse transcription-poly-merase chain reaction technique, coupled with direct sequencing, was used to obtain nucleotide sequence data from three short regions of the LMV genome. Clustering analysis was performed and compared to the biological properties of the 10 isolates. Three groups of LMV isolates were discriminated based on the molecular data. These groups appear to correlate with the geographic origin of the isolates rather than with their pathogenicity. Sequence comparison with California isolates clearly showed that the California isolates are related to the western European isolates, raising the possibility of past exchanges of LMV between western Europe and California.
Effect of Carbon, Nitrogen, and C:N Ratio on Growth, Sporulation, and Biocontrol Efficacy of Talaromyces flavus
Authors: Engelkes C. A. , Nuclo R. L. , Fravel D. R.
Published: May 2007

Engelkes, C. A., Nuclo, R. L., and Fravel, D. R. 1997. Effect of carbon, nitrogen, and C:N ratio on growth, sporulation, and biocontrol efficacy of Talaromyces flavus. Phytopathology 87:500-505.Five-day biomass production by the biocontrol fungus Talaromyces flavus was measured in a liquid basal medium, pH 5.5, containing each of 37 carbon (C) sources with a single nitrogen (N) source, and each of 42 N sources with a single C source. In general, production of biomass was greatest on complex sugars such as polysaccharides (32 g/liter of medium) and β-glucosides (2.4 g/liter of medium), and was least on monosaccharides (1.3 g/liter of medium). Ascospore production at 6 weeks on solid basal medium with the same amount of these same 37°C sources was greatest on oligosaccharides (2.9 × 108 spores per 5.5-cm-diameter petri dish), and least on polysaccharides and monosaccharides (1.6 and 1.4 × 108 spores per 5.5-cm-diameter petri dish, respectively). For C sources, there was no correlation between production of ascospores and hyphal dry weight. The various N sources yielded 0 to 109 ascospores per 5.5-cm-diameter petri dish and 10-4 to 10-5 g of hyphal dry weight per milliliter. In general, N sources that resulted in the greatest number of ascospores also yielded the greatest hyphal dry weights. For the two C and two N sources tested, the number of ascospores increased as the ratio of C to N increased from 5:1 to 30:1. This effect was most obvious as the C:N ratio increased from 5:1 to 15:1. At low C:N ratios (<15:1), treatments with hypoxanthine as a N source resulted in significantly greater production of biomass than treatments with ammonium tartrate; no difference was observed at C:N ratios ≥15:1. Incidence of Verticillium wilt was 50% lower for eggplants drenched with ascospores grown on potato dextrose agar (PDA) compared with eggplants either nondrenched or drenched with ascospores grown on media with hypoxanthine plus lactose or maltose. Thus, C and N sources that slightly increased ascospore production of T. flavus reduced efficacy of biocontrol of Verticillium wilt compared with ascospores produced on PDA.
Relationships Between Disease Incidence at Two Levels in a Spatial Hierarchy
Authors: Hughes G. , McRoberts N. , Madden L. V. , Gottwald T. R.
Published: May 2007

Relationships between disease incidence measured at two levels in a spatial hierarchy are derived. These relationships are based on the properties of the binomial distribution, the beta-binomial distribution, and an empirical power-law relationship that relates observed variance to theoretical binomial variance of disease incidence. Data sets for demonstrating and testing these relationships are based on observations of the incidence of grape downy mildew, citrus tristeza, and citrus scab. Disease incidence at the higher of the two scales is shown to be an asymptotic function of incidence at the lower scale, the degree of aggregation at that scale, and the size of the sampling unit. For a random pattern, the relationship between incidence measured at two spatial scales does not depend on any unknown parameters. In that case, an equation for estimating an approximate variance of disease incidence at the lower of the two scales from incidence measurements made at the higher scale is derived for use in the context of sampling. It is further shown that the effect of aggregation of incidence at the lower of the two scales is to reduce the rate of increase of disease incidence at the higher scale.
Corn Seed Proteins Inhibitory to Aspergillus flavus and Aflatoxin Biosynthesis
Authors: Huang Zhengyu , White Donald G. , Payne Gary A.
Published: May 2007

This study reports the presence of two fractions from corn seeds inhibitory to aflatoxin formation. Using a sensitive laboratory assay that can measure both inhibition of fungal growth and inhibition of aflatoxin biosynthesis, we examined aqueous extracts from seeds of Tex6, a corn inbred shown to be highly resistant to aflatoxin accumulation in field and laboratory evaluations. In these extracts, we identified two biologically active fractions. One inhibited growth of Aspergillus flavus and, thus, aflatoxin accumulation, and the other inhibited aflatoxin formation with little effect on fungal growth. The compounds responsible for these activities appear to be proteaceous, as they are water soluble, heat labile, and sensitive to proteinase K treatment. The compounds were partially purified by ultrafiltration and chromatography. The estimated molecular mass of the growth inhibitor is approximately 28 kDa, and that of the aflatoxin biosynthesis inhibitor appears to be greater than 100 kDa. Partially purified preparations of the growth inhibitor and aflatoxin biosynthesis inhibitor cause 50% inhibition at 26 and 75 μg of protein/ml, respectively. The presence of these compounds in Tex6 may explain its resistance to aflatoxin accumulation.
Characterization of the Phytophthora infestans Population in the Columbia Basin of Oregon and Washington from 1992 to 1995
Authors: Miller Jeffrey S. , Hamm Philip B. , Johnson Dennis A.
Published: May 2007

Isolates of Phytophthora infestans collected from 1992 to 1995 from potato fields in the Columbia Basin of Oregon and Washington were analyzed for compatibility type, metalaxyl sensitivity, and glucose-6-phosphate isomerase (Gpi) genotype. In 1992, 30 of 31 isolates were of the US-1 multilocus genotype. A single metalaxyl-resistant isolate of the US-6 (A1 Gpi 86/100) genotype was found near the end of the growing season. In 1993, only 2 of the 59 isolates collected were A1 isolates with Gpi 86/100. Ten isolates were of the A2 compatibility type, seven with Gpi 100/111, two with Gpi 100/100, and one was undetermined. The remaining isolates were metalaxyl-resistant A1 compatibility types with either Gpi 100/100 or 100/111. The first A2 isolates in the Columbia Basin were found in 1993. In 1994, 10 of 18 isolates were of the US-1 genotype. The remaining isolates were US-6 and US-8 genotypes. In 1995, 97% of 268 isolates tested were of the US-8 genotype. Five isolates were A2 compatibility type with Gpi 100/122. One A2, metalaxyl-resistant isolate was Gpi 100/100/111, and two A1 isolates were Gpi 100/111/122. The population of P. infestans quickly changed between 1992 and 1995, from a population comprised almost exclusively of the US-1 genotype to a population represented by new or recombinant genotypes.
Biological Control of Grape Crown Gall by Strain F2/5 Is Not Associated with Agrocin Production or Competition for Attachment Sites on Grape Cells
Authors: Burr T. J. , Reid C. L. , Tagliati E. , Bazzi C. , Süle S.
Published: May 2007

Agrocin-minus mutants of nontumorigenic Agrobacterium vitis strain F2/5 controlled grape crown gall as well as the wild-type strain, indicating that agrocin is not a major factor in the mechanism of biological control. Relative levels of attachment to grape cells by tumorigenic and biocontrol strains were also measured. Attachment of tumorigenic strains (CG49 and K306) and biological control strains (F2/5 and agrocin-minus mutant 1077) was often reduced when mixtures of the strains were applied. However, high populations (103to 105CFU/ml) of all strains attached following mixed inoculations, suggesting that competition for attachment sites is also not a factor in the mechanism of biological control. Transfer of T-DNA to grape by CG49 was prevented or greatly inhibited in the presence of F2/5 or 1077 as measured by expression of the GUS reporter gene. The Ti plasmid virulence genes, however, were induced by exudates from grape shoots that had been inoculated with F2/5. Sonicated and autoclaved preparations of F2/5 and 1077 did not control crown gall or inhibit T-DNA transfer. Control by F2/5 is specific to grape, since gall formation on tomato, sunflower, and Kalanchoe daigremontiana were not inhibited.
Potato Root Diffusate-Induced Secretion of Soluble, Basic Proteins Originating from the Subventral Esophageal Glands of Potato Cyst Nematodes
Authors: Smant Geert , Goverse Aska , Stokkermans Jack P. W. G. , De Boer Jan M. , Pomp H. (Rikus) , Zilverentant Jacoline F. , Overmars Hein A. , Helder Johannes , Schots Arjen , Bakker Jaap
Published: May 2007

In preparasitic second-stage juveniles (J2) of potato cyst nematode Globodera rostochiensis, six proteins with molecular masses of 30, 31a/b, 32, 39, and 49 kDa were recognized on Western blots by a monoclonal antibody (MGR48) specific for the subventral esophageal glands. All of these subventral gland proteins (svp's) focused in the basic range (pI 6.8 to 8.6) of an immobilized pH gradient. Western blotting showed that the svp's were present in preparasitic and parasitic J2 and not in later juvenile stages and adult females. Minor svp quantities also were observed in adult males. Immunogold labeling of preparasitic J2 showed that the svp's were localized in the rough endoplasmic reticulum and secretory granules of the subventral esophageal glands. Potato root diffusate triggered the secretion of svp's through the stylet, and 5-methoxy-N,N-dimethyltryptamine-hydrogen-oxalate had only a quantitative, additional effect. The forward flow of svp's through the metacorporal pump chamber was confirmed by the presence of svp's in the circular lumen of the esophagus (procorpus), as established by immunoelectron microscopy. Our data provide conclusive evidence that secretory proteins of the subventral glands of G. rostochiensis can be secreted through the stylet and support the hypothesis that the subventral esophageal glands play an important role in the early events of this nematode-plant interaction.
Fusarium oxysporum f. sp. cubense Consists of a Small Number of Divergent and Globally Distributed Clonal Lineages
Authors: Koenig R. L. , Ploetz R. C. , Kistler H. C.
Published: May 2007

A worldwide collection of Fusarium oxysporum f. sp. cubense was analyzed using anonymous, single-copy, restriction fragment length polymorphism (RFLP) loci. Several lines of evidence indicated that this pathogen has a clonal population structure. Of the 165 isolates examined, only 72 RFLP haplotypes were identified, and nearly half the isolates were represented by the five most common haplotypes. Individuals with identical haplotypes were geographically dispersed, and clone-corrected tests of gametic disequilibrium indicated significant nonrandom association among pairs of alleles for 34 of 36 loci tested. Parsimony analysis divided haplotypes into two major branches (bootstrap value = 99%) that together contained eight clades supported by significant bootstrap values. With the exception of two isolates, all isolates within a vegetative compatibility group were in the same clade and clonal lineage. Clonal lineages were defined by isolates having coefficients of similarity between 0.94 and 1.00. Ten clonal lineages were identified, and the two largest lineages had pantropical distribution. Minor lineages were found only in limited geographical regions. Isolates composing one lineage (FOC VII) may represent either an ancient genetic exchange between individuals in the two largest lineages or an ancestral group. The two largest lineages (FOC I and FOC II) and a lineage from East Africa (FOC V) are genetically distinct; each may have acquired the ability to be pathogenic on banana independently.
Sensitivity to Protectant Fungicides and Pathogenic Fitness of Clonal Lineages of Phytophthora infestans in the United States
Authors: Kato Masayasu , Mizubuti Eduardo S. , Goodwin Stephen B. , Fry William E.
Published: May 2007

Since 1991, dramatic changes have occurred in the genetic composition of populations of Phytophthora infestans in the United States. Clonal lineages recently introduced into the United States (US-7 and US-8) are more common now than the previously dominant lineage (US-1). To help determine why these changes occurred, four clonal lineages of P. in-festans common during the early 1990s in the United States and Canada were evaluated for sensitivity to the protectant fungicides mancozeb and chlorothalonil using amended agar assays for isolates collected from 1990 to 1994. No isolate or lineage was resistant to either mancozeb or chlorothalonil. There were significant differences among isolates for degree of sensitivity to one fungicide individually, but there were no significant (P = 0.05) differences among the US-1, US-6, US-7, and US-8 clonal lineages for degree of sensitivity to both fungicides. Therefore, resistance to protectant fungicides cannot explain the rapid increase in frequency of the US-7 and US-8 clonal lineages. Three components of pathogenic fitness (latent period, lesion area, and sporulation after 96 h) were tested for the three clonal lineages that were detected most commonly during 1994 (US-1, US-7, and US-8). All but one of the isolates in this analysis were collected during 1994 and evaluated within 10 months of collection by inoculating detached leaflets of the susceptible potato cultivar Norchip. There were significant differences between the US-1 and US-8 clonal lineages for lesion area and sporulation, and between US-1 and US-7 for latent period. The US-6 clonal lineage was excluded from the pathogenic fitness experiments, because no isolates of this lineage were collected during 1994. Compared with US-7 and US-8, US-1 had the longest latent period and the smallest lesions with the least sporulation. Incorporation of the differences between US-1 and US-8 in computer simulation experiments revealed that significantly more protectant fungicide (e.g., 25%) would be required to suppress epidemics caused by the US-8 clonal lineage compared with US-1. These differences in pathogenic fitness components probably contribute to the general predominance of the “new” clonal lineages (especially US-8) relative to the “old” US-1 lineage.
Characterization of Colletotrichum acutatum Isolates Causing Anthracnose of Almond and Peach in California
Authors: Adaskaveg J. E. , Hartin R. J.
Published: May 2007

The causal organism responsible for the recent outbreak of almond and peach anthracnose in California was identified and characterized as Colletotrichum acutatum. Isolates of C. acutatum from almond were found to be similar to California strawberry isolates and South Carolina peach and apple isolates of C. acutatum based on conidial morphology, temperature relationships, fungicide sensitivity, and polymerase chain reaction (PCR) methods using DNA species-specific primers. On almond, blossoms and immature or mature fruit were affected by the disease, causing direct losses of crop. On peach, the disease was observed only on mature fruit. Pathogenicity of almond and peach isolates of C. acutatum was demonstrated on wound- and nonwound-inoculated almond or peach fruit by fulfilling Koch's postulates. Conidial morphology of isolates was variable, depending on the medium or substrate used to culture the isolates. Isolates of C. acutatum from strawberry, almond, and peach were grouped together based on a similar response to temperature, with an optimal growth rate at 25°C (generally less than 10 mm/day), whereas isolates of C. gloeosporioides from citrus and papaya had an optimal growth rate at 30°C (generally greater than 10 mm/day). In fungicide disk assays, isolates of C. acutatum from strawberry, peach, and apple, as well as almond and peach isolates from California, were less sensitive to benomyl at 300, 600, or 1,200 μg/ml. In contrast, C. gloeosporioides isolates from citrus and papaya were very sensitive to benomyl at all concentrations evaluated. All isolates of both species were sensitive to captan (300, 600, or 1,200 μg/ml). Oligonucleotide primers were synthesized for C. acutatum, C. fragariae, or C. gloeosporioides using published DNA sequences from the internal transcribed spacer 1 region of ribosomal DNA. Thirty-two Colletotrichum isolates from almond fruit produced DNA products with a C. acutatum primer (CaInt-2) that matched products and approximate molecular weight of known C. acutatum isolates. No PCR products were produced with primers for C. gloeosporioides or C. fragariae. Isolates from citrus and papaya produced DNA products only with primers from C. gloeosporioides or C. fragariae. Thus, worldwide, anthracnose of almonds may be caused by either C. gloeosporioides, as previously reported, or by C. acutatum, as indicated in this study.
In Situ Localization of Barley Yellow Dwarf Virus-PAV 17-kDa Protein and Nucleic Acids in Oats
Authors: Nass Petra H. , Domier Leslie L. , Jakstys Birute P. , D'Arcy Cleora J.
Published: May 2007

Barley yellow dwarf virus strain PAV (BYDV-PAV) RNA and the 17-kDa protein were localized in BYDV-PAV-infected oat cells using in situ hybridization and in situ immunolocalization assays, respectively. The in situ hybridization assay showed labeling of filamentous material in the nucleus, cytoplasm, and virus-induced vesicles with both sense and antisense nucleic acid probes, suggesting that the filamentous material found in BYDV-PAV-infected cells contains viral RNA. BYDV-PAV negative-strand RNA was detected before virus particles were observed, which indicates that RNA replication is initiated before synthesis of viral coat protein in the cytoplasm. The 17-kDa protein was associated with filamentous material in the cytoplasm, nucleus, and virus-induced vesicles. The labeling densities observed using antibodies against the 17-kDa protein were similar in the nucleus and cytoplasm. No labeling of the 17-kDa protein was observed in plasmodesmata, but filaments in the nuclear pores occasionally were labeled. Since BYDV-PAV RNA and 17-kDa protein colocalized within infected cells, it is possible that single-stranded viral RNA is always associated with the 17-kDa protein in vivo. The 17-kDa protein may be required for viral nucleic acid filaments to traverse the nuclear membrane or other membrane systems.
Genetic Structure and Temporal Dynamics of a Colletotrichum graminicola Population in a Sorghum Disease Nursery
Authors: Rosewich U. L. , Pettway R. E. , McDonald B. A. , Duncan R. R. , Frederiksen R. A.
Published: May 2007

Restriction fragment length polymorphisms (RFLPs) were used to study the population genetics of Colletotrichum graminicola (= C. sublineolum), the causal agent of sorghum anthracnose. Screening of 80 anonymous probes from a genomic library detected polymorphisms in 81% of 299 probe-enzyme combinations among nine international isolates. Seven single- or low-copy probes were used to study a collection of 411 isolates sampled during 1991 to 1993 from a sorghum disease nursery in Georgia. Nei's gene diversity was moderately high, with = 0.215 on average, while genotypic diversity was extremely low with an average genotypic diversity value of Ĝ = 1.513. Only nine multilocus haplotypes were identified, with one haplotype being present at a frequency of approximately 80% each year. Two other haplotypes were found at significant frequencies (4 to 10%). Allele and haplotype frequencies did not differ over the 3 years, indicating that this population was stable. Our findings suggest that genetic drift and gene flow were not major contributors to genetic structure, while asexual reproduction had a significant effect.
Mixtures of Plant Growth-Promoting Rhizobacteria Enhance Biological Control of Multiple Cucumber Pathogens
Authors: Raupach Georg S. , Kloepper Joseph W.
Published: May 2007

Plant growth-promoting rhizobacteria (PGPR) strains INR7 (Bacillus pumilus), GB03 (Bacillus subtilis), and ME1 (Curtobacterium flaccumfaciens) were tested singly and in combinations for biological control against multiple cucumber pathogens. Investigations under greenhouse conditions were conducted with three cucumber pathogens—Colletotrichum orbiculare (causing anthracnose), Pseudomonas syringae pv. lachrymans (causing angular leaf spot), and Erwinia tracheiphila(causing cucurbit wilt disease)—inoculated singly and in all possible combinations. There was a general trend across all experiments toward greater suppression and enhanced consistency against multiple cucumber pathogens using strain mixtures. The same three PGPR strains were evaluated as seed treatments in two field trials over two seasons, and two strains, IN26 (Burkholderia gladioli) and INR7 also were tested as foliar sprays in one of the trials. In the field trials, the efficacy of induced systemic resistance activity was determined against introduced cucumber pathogens naturally spread within plots through placement of infected plants into the field to provide the pathogen inoculum. PGPR-mediated disease suppression was observed against angular leaf spot in 1996 and against a mixed infection of angular leaf spot and anthracnose in 1997. The three-way mixture of PGPR strains (INR7 plus ME1 plus GB03) as a seed treatment showed intensive plant growth promotion and disease reduction to a level statistically equivalent to the synthetic elicitor Actigard applied as a spray.