Showing papers in "Phytopathology in 1990"
TL;DR: The distribution of Fusarium spp.
Abstract: (...) All species found in northern states also were found in southern states, although differences in tissue, debris, and soil populations were observed. All species were recovered from at least one Alfisol site, and all but F. avenaceum were recovered from at least one Ultisol site. (...) The distribution of Fusarium spp. observed in this study is consistent with the hypothesis that these fungi are widely distributed in host tissue under field conditions and that they respond to stress in the plant by taking advantage of preferential growth conditions to incite disease
252 citations
245 citations
TL;DR: Results of immunoelectron microscopy suggest that CTV-MCA13 may react to a cryptic epitope on the viral coat protein and monoclonal antibody is an IgG2a immunoglobin and did not react to extracts of healthy citrus or citrus infected with other viruses.
Abstract: (...) Discrimination of CTV isolates by CTV-MCA13 was similar in indirect ELISA with plate-trapped antigen and in double antibody sandwich indirect ELISA with antigen trapped on polyclonal antibody-coated plates. Results of immunoelectron microscopy suggest that CTV-MCA13 may react to a cryptic epitope on the viral coat protein. The monoclonal antibody is an IgG2a immunoglobin and did not react to extracts of healthy citrus or citrus infected with other viruses
226 citations
TL;DR: Ten winter wheat genotypes were inoculated with three Dutch strains of Fusarium culmorum and path anlysis suggested a relation between deoxynivalenol and kernel weight reduction.
Abstract: Ten winter wheat genotypes were inoculated with three Dutch strains of Fusarium culmorum (IPO 39-01, IPO 348-01 and IPO 436-01). Seed samples were anlyzed for several trichothecene mycotoxins and zearalenone. Deoxynivalenol was detected in concentrations ranging from 0 to 48 mg/kg. Interactions between strains and genotypes were observed for head blight and kernel deoxynivalenol content. Path anlysis suggested a relation between deoxynivalenol and kernel weight reduction
216 citations
TL;DR: Treatment of wounds with washed cells of C. laurentii at 10 4 -10 5 cells per wound effectively reduced or prevented development of decay by Botrytis cinerea at all temperatures compared with controls and was comparable in effectiveness to preinoculation application of benomyl at the postharvest label rate.
Abstract: Treatment of wounds with washed cells of C. laurentii at 10 4 -10 5 cells per wound effectively reduced or prevented development of decay by Botrytis cinerea at all temperatures compared with controls and was comparable in effectiveness to preinoculation application of benomyl at the postharvest label rate. Treatment of wounds with cell-free culture filtrates of C. laurentii were not effective in preventing decay and resulted in greater lesion diameters than in inoculated, buffer-treated wounds
216 citations
194 citations
189 citations
TL;DR: Single locus and multilocus analysis of RFLP data indicated that a high level of genetic variability was distributed on a fine scale within this population of fungal pathogen population.
Abstract: Restriction fragment length polymorphism (RFLP) markes were used to measure the amount and distribution of genetic variation in a fungal pathogen population on a microgeographical scale. Ninety-three isolates of Septoria tritici sampled from a single wheat field were assayed for RFLP variation using eight probes that hybridized to single RFLP loci and one probe that hybridized to two RFLP loci in nuclear DNA. Single locus and multilocus analysis of RFLP data indicated that a high level of genetic variability was distributed on a fine scale within this population (...)
179 citations
TL;DR: Twenty-two strains of Verticillium dahliae, originally assigned to 15 vegetative compatibility groups (VCGs) using microsclerotial color mutants, were tested for vegetative Compatibility using complementary, auxotrophic nitrate-nonutilizing (nit) mutants.
Abstract: Twenty-two strains of Verticillium dahliae, originally assigned to 15 vegetative compatibility groups (VCGs) using microsclerotial color mutants, were tested for vegetative compatibility using complementary, auxotrophic nitrate-nonutilizing (nit) mutants. Nit mutants were generated from wild-type strains of V. dahliae by selecting chlorate-resistant sectors on cornmeal agar with dextrose amended with potassium chlorate (15-25 g/l). Complementation tests between nit mutants derived from these strains led to the identification of only four distinct VCGs (...)
172 citations
TL;DR: A strain of Trichoderma isolated from a sample of peat collected in New Brunswick, displays the ability to produce chitinases and inhibits growth of the pathogenic fungus, Fusarium oxysporum f.
Abstract: A strain of Trichoderma, isolated from a sample of peat collected in New Brunswick, displays the ability to produce chitinases and inhibits growth of the pathogenic fungus, Fusarium oxysporum f. sp. radicis-lycopersici, in dual culture tests. Scanning electron microscope investigations of hyphal interactions show that growth inhibition of the host mycelium does not result from hyphal penetration by Trichoderma (...)
168 citations
TL;DR: Inoculation of aseptically cultured minitubers with cell-free extracts from scab lesions of field-grown and cultured tubers infected with Streptomyces scabies reproduced symptoms typical of the common scab disease.
Abstract: Inoculation of aseptically cultured minitubers with cell-free extracts from scab lesions of field-grown and cultured tubers infected with Streptomyces scabies reproduced symptoms typical of the common scab disease. Isolation and fractionation of the active components in tissue extracts by a combination of normal and reversed phase thin-layer chromatography yielded two active compounds. These have been designated thaxtomin A and thaxtomin B and characterized as unique 4-nitroindol-3-yl containing 2,5-dioxopiperazines. These phytotoxic principles satisfy all of the basic criteria of vivotoxins
TL;DR: Lesion size and frequency of Botrytis rot were significantly less in fruit pretreated with aqueous suspensions of strains 87 and 101 and significant, but marginal, reduction of Penicillium rot was observed in treatments with these yeasts.
Abstract: (...) Lesion size and frequency of Botrytis rot were significantly less in fruit pretreated with aqueous suspensions of strains 87 and 101. Significant, but marginal, reduction of Penicillium rot was observed in treatments with these yeasts. Biological control of Botrytis rot was enhanced when wounds were treated with strain 87 in aqueous solutions of CaCl 2 , KCl and CaCO 3 . Salt solutions applied to wounds without yeast cells did not reduce rot. The ability of the salt solutions to enhance control with yeasts was not related to the osmotic potential of the solutions. Calcium chloride was the most effective salt (...)
TL;DR: Exposure of strain EP713 to high light intensity partially relieved the hypovirulence-associated suppression of pigmentation, conidiation, and oxalate accumulation observed at low or intermediate light intensity.
Abstract: Phenotypic expression by cultured isogenic virulent (EP155) and hypovirulent (EP713) strains of the chestnut blight fungus, Cryphonectria parasitica, was examined under different light regimens. Colony morphology and the levels of pigmentation, conidiation, oxalate accumulation, and phenol oxidase production were all influenced by light intensity, but to different degrees in the two strains. Significantly, exposure of strain EP713 to high light intensity partially relieved the hypovirulence-associated suppression of pigmentation, conidiation, and oxalate accumulation observed at low or intermediate light intensity (...)
TL;DR: It is proposed that the pattern of RFLP variation observed is most likely the result of genetic divergence within and among intraspecific groups.
Abstract: (...) Isolates from anastomosis groups 3, 4, 7, 8, and BI all possess a single, invariant RFLP unique to each intraspecific group. A relatively low level of RFLP variation also was characteristic of isolates within AG-1-IB, AG-1-IC, AG-2-2, and AG-9. In contrast, a relatively high level of RFLP diversity was observed among isolates within AG-1-IA, AG-2-1, AG-5, and AG-6. We did not observe any obvious relationship between levels of RFLP within intraspecific groups and variation of other biological factors (host range, morphological variation, etc). Instead, we propose that the pattern of RFLP variation observed is most likely the result of genetic divergence within and among intraspecific groups
TL;DR: Squash silverleaf, a newly recognized disorder of many squash varieties in Florida, is of unknown etiology and Extracts from SSL-affected tissue did not react with antisera to several cucurbit and whitefly-transmitted viruses.
Abstract: Squash silverleaf (SSL), a newly recognized disorder of many squash varieties in Florida, is of unknown etiology. Extracts from SSL-affected tissue did not react with antisera to several cucurbit and whitefly-transmitted viruses. Silverleaf was not graft or mechanically transmitted. Early SSL symptoms were induced in new foliar growth of squash (Cucurbita pepo Senator') after 3 days of feeding by nymphs of the sweetpotato whitefly (SPWF), Bemisia tabaci (average number = 25.4 nymphs per plant). The SPWF nymphs produced chlorotic spots on leaves at their feeding sites, which were clearly different from SSL symptoms (...)
TL;DR: Isozyme variation of 219 isolates of Acremonium or Epichloe fungal endophytes from 17 host grass species was examined using starch gel electrophoresis, finding double or triple bands were observed for several enzymes in certain isolates, particularly those from tall fescue.
Abstract: Isozyme variation of 219 isolates of Acremonium or Epichloe fungal endophytes from 17 host grass species was examined using starch gel electrophoresis. Ten enzyme systems selected for use out of 17 examined were variable, with three to nine distinct electromorphs per enzyme. Most isolates produced a single band per enzyme, consistent with a haploid fungus and a single isozyme locus. Double or triple bands were observed for several enzymes in certain isolates, particularly those from tall fescue. Isozyme variation was observed among isolates from 10 out of 12 different hosts where multiple isolates were sampled (...)
TL;DR: A strong net downward flux of bacteria was measured in a soybean field during two different rain events, and the ice nucleation-activity and phytopathogenic host range of strains of Pseudomonas syringae isolated from rainwater and aerosols present during rain differed from those of the bacteria present on the soybeans.
Abstract: A strong net downward flux of bacteria was measured in a soybean field during two different rain events. The ice nucleation-activity and phytopathogenic host range of strains of Pseudomonas syringae isolated from rainwater and aerosols present during rain differed from those of the bacteria present on the soybeans. Bacteria that produce fluorescent pigments on an iron-deficient medium were 3-8%, 5-9%, and 81% of those isolated from aerosols during rain, from rain, and from the soybean leaves, respectively (...)
TL;DR: DNA extracted from CoYMV virions consists of linear and circular forms, which migrate separately in agarose gels, and appears to have two single-stranded discontinuities and was not shown to be infectious.
Abstract: (...) DNA extracted from CoYMV virions consists of linear and circular forms, which migrate separately in agarose gels. CoYMV genomic DNA appears to have two single-stranded discontinuities and was not shown to be infectious. Preliminary data on three other viruses similar to CoYMV in size and morphology-banana streak virus (BSV), canna yellow mottle virus (CaYMV), and Kalanchoe top-spotting virus (KaTSV)-indicate that they also contain double-stranded DNA of similar size. These plant viruses are of potential interest for use as vectors for gene transfer in higher plants
TL;DR: The DNA of the apple proliferation agent was cloned in Escherichia coli and the specificity of the cloned MLO DNA was confirmed by dot and Southern blot hybridization.
Abstract: (...) MLO DNA was obtained as a well-resolved band showing a lower buoyant density than the host plant DNA due to its low G+C content. This band was highly enriched in MLO DNA and comprised 0.1-3.0 % of the total DNA extracted from diseased plants. The DNA of the apple proliferation agent was cloned in Escherichia coli and the specificity of the cloned MLO DNA was confirmed by dot and Southern blot hybridization
TL;DR: It is proposed that some thermophilic fungi naturally present in 40-50 C compost temporarily interfered with the biocontrol activity of T. hamatum in the medium.
Abstract: (...) Humicola spp. were the predominant fungal taxa isolated from compost in this temperature zone, but they were unable to grow on potato-dextrose agar (PDA) at 25 C. Some isolates of Humicola significantly reduced efficacy but not population densities of T. hamatum in the medium. Bacteria isolated from the 40-50 C zone did not reduce efficacy of the biocontrol agent. Damping-off was suppressed by T. hamatum if the medium containing 40-50 C compost or compost fortified with Humicola spp. was incubated for three or more weeks at 25 C before bioassays were performed. We propose that some thermophilic fungi naturally present in 40-50 C compost temporarily interfered with the biocontrol activity of T. hamatum after compost-amended medium was first prepared
TL;DR: Generally, fruit disease incidence increased with increased wetness durations, but on mature fruit at 35 C, disease incidence decreased over time, and a regression model accurately described infection level as a function of wetness duration and temperature.
Abstract: (...) Generally, fruit disease incidence increased with increased wetness durations, but on mature fruit at 35 C, disease incidence decreased over time from a maximum of 39%. Optimum temperature for infection on both immature and mature fruit was between 25 and 30 C, with greater than 80% disease incidence after 13 hr of wetness. A regression model using the logit of disease incidence as the dependent variable accurately described infection level as a function of wetness duration (W) and temperature (T). Terms in the model were W, WT, WT 2 , and WT 3 , and all estimated parameters were significant. Coefficients of determination for combined data from three repetitions of the experiment were 0.71 and 0.83 for immature and mature fruit, respectively
TL;DR: Phytophthora capsici was isolated from seven pepper and seven cucurbit fields in North Carolina and the relative virulence of the isolates was tested on pepper, morphological characteristics of sporangia and oospores were evaluated, and mating type and growth response to temperature were determined.
Abstract: Phytophthora capsici was isolated from seven pepper and seven cucurbit fields in North Carolina. The relative virulence of the isolates was tested on pepper (Capsicum annuum), morphological characteristics of sporangia and oospores were evaluated, and mating type and growth response to temperature were determined. All pepper and some cucurbit isolates of P. capsici were highly virulent on pepper, whereas other cucurbit isolates were less virulent on pepper. Sporangia of cucurbit isolates were greater than 55 μm in length and were less variable in length than sporangia of pepper isolates (...)
TL;DR: Stem injection of tobacco cultivar Ky 14 with Peronospora tabacina or lead inoculation with tobacco mosaic virus induced systemic resistance to both pathogens and elicited a systemic increase in peroxidase activity which was positively correlated with induced resistance.
Abstract: Stem injection of tobacco cultivar Ky 14 with Peronospora tabacina or lead inoculation with tobacco mosaic virus induced systemic resistance to both pathogens. The treatment also elicited a systemic increase in peroxidase activity which was positively correlated with induced resistance. Increases were evident in cytosol, intercellular fluid, and cell wall fractions. Upon challenge with P. tabacina, peroxidase activity further increased in the induced plants and remained higher after challenge as compared to the control plants (...)
TL;DR: Pseudomonas cepacia strain AMMD applied to pead seeds reduced preemergence damping-off caused by Pythium ultimum and P. sylvaticum by 47% in growth chamber experiments.
Abstract: Pseudomonas cepacia strain AMMD applied to pead seeds reduced preemergence damping-off caused by Pythium ultimum and P. sylvaticum by 47% in growth chamber experiments. Protection by the biocontrol agent was as effective as seed treatment with metalaxyl at all temperatures tested (16, 20, 24, and 28 C) Under controlled soil matric potential conditions (−6 kPA) at 24 C, Pythium began to infect nontreated seeds within 12 hr, and 100% of the seeds were infected 30 hr after planting. Incidence of seed infection during the first 48 hr was reduced 44-60% by seed treatment with metalaxyl or P. Cepacia strain AMMDR1, resistant to rifampicin (...)
TL;DR: Several strains showed host-induced variation of the dsRNA profile and, in some cases, seasonal variation, while greatest yields were obtained in spring and autumn from sweet orange and Dweet tangor.
Abstract: (...) Both seasonal and host variation was observed on the recovery of the dsRNA. Greatest yields were obtained in spring and autumn from sweet orange and Dweet tangor. DsRNA recovery was not always correlated with virus titer estimated by enzyme-linked immunosorbent assay. Several strains showed host-induced variation of the dsRNA profile and, in some cases, seasonal variation. Virus titer and the amount of dsRNA recovered were not necessarily correlated with symptom severity on Mexican lime, nor could the dsRNA pattern observed be correlated with any specific biological characteristics (...)
TL;DR: The purposes of this letter are to demonstrate that empirical data are not supportive of the probabilities hypothesis and to cite evidence countering the assumption of the probability hypothesis that mutations to virulence at different loci are necessarily independent.
Abstract: The purposes of this letter are to demonstrate that empirical data are not supportive of the probabilities hypothesis and to cite evidence countering the assumption of the probabilities hypothesis that mutations to virulence at different loci are necessarily independent. In doing so, rust disease will be used as examples because of the vast literature available on them and because resistance gene pyramids have been associated with an increase in the durability of race-specific resistance to wheat stem rust (...)
TL;DR: The fungus spread from the wound sometime after 14 days postinoculation, and at 28 days post inoculation it could be found in small amounts throughout all rachis tissues except the pith and lignified fibers.
Abstract: We describe the histology of fungal development in maize ears wound inoculated with Aspergillus flavus. Plants were inoculated 21 days after style emergence; wounded grains and adjacent spikelets (with their rachis segments) were harvested at intervals up to 28 days later. Tissues were processed for plastic embedding and 1.5-μm thick sections were examined by bright field microscopy. The fungus spread from the wound sometime after 14 days postinoculation, and at 28 days postinoculation it could be found in small amounts throughout all rachis tissues except the pith and lignified fibers (...)