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991.
992.
Vicente Rozas José Miguel Olano Lucía DeSoto David Bartolomé 《Annals of Forest Science》2008,65(8):809-809
993.
Numerical modelling was used to follow the evolution of the moisture content gradient and the stress field resulting from
the restrained differential dimensional response across a wooden cylinder, simulating sculptures, in response to variations
in temperature (T) and relative humidity (RH). Material properties of lime wood (Tilia sp.) were used in the modelling as this wood species was historically widely used. The allowable RH variations, below which mechanical
damage will not occur, were derived as functions of the amplitude, time period and starting RH level of the variation. Lime
wood can endure step RH variations of up to 15% in the moderate RH region, but the allowable domain narrows when RH levels
shift from the middle range. The allowable amplitude of the variations increases when time allowed for the change increases.
The stress field does not vanish even for slow, quasi-static changes in RH due to structural internal restraint resulting
from the anisotropy in the moisture-related dimensional change. 相似文献
994.
Three diagrammatic grading keys were designed for the assessment of the severity of late blight (caused by Phytophthora infestans ) in tomato leaves. Simplified and broad keys considered, respectively, six (3, 12, 22, 40, 60 and 77%) and eight (3, 6, 12, 22, 40, 60, 77 and 90%) levels of disease severity, whilst a modified key based on a previous proposal for potato late blight considered six levels (1, 5, 10, 16, 32 and 50%). The keys were validated by 24 evaluators who assessed digital images of tomato leaves exhibiting different areas with lesions. Evaluator errors were compared using a mixed model in which evaluators were considered as random effects and the keys and evaluations as fixed effects. The accuracy and precision of the evaluators were compared by simple linear regression between the estimated and actual values of disease severity. The repeatability of evaluators was assessed using Pearson's correlation coefficient. There was significant ( P ≤ 0·001) variability amongst the errors made by evaluators, although the precision of each of the three keys was high with a coefficient of determination (R2 ) of 0·96, 0·93 and 0·83 for the simplified, broad and modified key, respectively. Repeatability of estimations amongst the evaluators was adequate (correlation coefficients of 0·91, 0·91 and 0·90 for the three keys, respectively). The simplified and broad keys resulted in higher precision and accuracy for the estimation of severity than did the modified key. Since the simplified key considers a smaller number of disease severity levels, its use is recommended in the assessment of late blight in tomato leaves. 相似文献
995.
Joaquin A. Qui Lizbeth A. Castro-Concha Karlina García-Sosa Luis Manuel Peña-Rodríguez María L. Miranda-Ham 《Journal of General Plant Pathology》2009,75(5):331-339
Alternaria tagetica, a fungus that causes early blight in marigold (Tagetes erecta), produces two groups of phytotoxic metabolites: one hydrophilic and the other lipophilic that show phytotoxic activity when
tested by the leaf-spot assay in T. erecta. We evaluated the cellular effects of the phytotoxic culture filtrate of A. tagetica and the hydrophilic and lipophilic fractions, then determined whether the filtrate or the fractions differentially induced
pathogenesis-related mechanisms in the plant. The culture filtrate and the phytotoxic fractions had adverse effects on cell
viability, fresh mass, and the number of cells, and induced ROS accumulation, lipid peroxidation and DNA damage on T. erecta cell suspension cultures, and these effects are related to pathogenic mechanisms attributed to phytotoxins. However, although
exposure of marigold cells to the phytotoxic culture filtrate of A. tagetica triggered programmed cell death, the hydrophilic and the lipophilic phytotoxic fractions induced death that was more related
to a toxic effect leading to necrosis. This study presents a complementary perspective in the search for the roles of metabolites,
including phytotoxins, produced by phytopathogenic fungi during plant infection. 相似文献
996.
BACKGROUND: The development of controlled‐release formulations of alachlor to extend the period of weed control was studied. This extended duration reduces the need for high herbicide application rates that could lead to environmental contamination. For this purpose, the influence of formulation, as well as the influence of soil characteristics, on alachlor efficacy and persistence in soil of a commercial formulation (CF) and different ethylcellulose microencapsulated formulations (MEFs) was evaluated. RESULTS: Higher alachlor rates yielded an enhanced initial herbicidal activity. The prolonged release of alachlor provided by the MEFs resulted in a higher herbicidal efficacy and a longer period of weed control compared with the effects of CF in the two soils tested (at 40 days after treatment, oat growth inhibition for CF and MEFs was 1.96% and 93.5% respectively). Soil characteristics strongly influenced alachlor efficacy and weed control by MEFs. The highest alachlor efficacy and persistence were observed in the soil with lowest microbial activity and clay and organic matter content. CONCLUSIONS: The use of MEFs can be advantageous because they permit the maintenance of the desired concentration of the herbicide in the soil for longer periods of weed control. Copyright © 2009 Society of Chemical Industry 相似文献
997.
Bioactive plants from Argentina and Bolivia 总被引:4,自引:0,他引:4
Antibacterial and molluscicidal activities of methanol and chloroform extracts of 16 plant species belonging to the families Compositae and Melastomataceae were evaluated. The chloroform extract of Vernonanthura tweediana and the methanol extract of Senecio santelisis resulted to be very toxic to brine shrimp nauplii (LC(50)=1 microg/ml). Chloroform extracts of S. santelisis and Senecio leucostachys as well as the methanol extract of Wedelia subvaginata displayed molluscicidal effects on Biomphalaria peregrina showing LC(100)<100 microg/ml. Moderate antibacterial action was produced by the chloroform extracts of Flaveria bidentis, Grindelia scorzonerifolia and Vernonia incana against two strains of Staphylococcus aureus. 相似文献
998.
Bastianel M de Oliveira AC Cristofani M Filho OG Freitas-Astúa J Rodrigues V Astúa-Monge G Machado MA 《Phytopathology》2006,96(10):1092-1096
ABSTRACT The genetic inheritance of resistance to leprosis, the most important viral disease of citrus in Brazil, was characterized through the phenotypic assessment of 143 hybrids resulting from crosses between tangor 'Murcott' (Citrus sinensis x C. reticulata) and sweet orange 'Pêra' (C. sinensis), considered to be resistant and susceptible to the disease, respectively. All plants were grafted onto Rangpur lime (C. limonia) and inoculated with Citrus leprosis virus, cytoplasmic type through the infestation with viruliferous mites, Brevipalpus phoenicis. The experiments were arranged in a completely randomized block design with 10 replicates. Incidence and severity of the disease in leaves and stems as well as plant growth parameters (plant height and stem diameter) were recorded for 3 years after the infestation with the viruliferous mites. The average values of all variables were analyzed using principal component analysis, discriminant factorial analysis, estimation of the clonal repeatability coefficients, and frequency of the distributions of the average values for each measured variable. The principal component analysis resulted in the identification of at least two groups with resistance and susceptibility to leprosis, respectively. About 99% of all hybrids were correctly classified according to the discriminant factorial analysis. The broad-sense heritability coefficients for characteristics associated with incidence and severity of leprosis ranged from 0.88 to 0.96. The data suggest that the inheritance of resistance to leprosis may be controlled by only a few genes. 相似文献
999.
The mechanism involved in systemic acquired resistance (SAR) can be non-specifically induced in susceptible plants. In response to pathogens, plants' natural defence mechanisms include the production of lignin and phytoalexins and the induction of plant enzymes. The aim of this research was to study the induction of SAR mediated by the chemical activator DL-3-aminobutyric acid (BABA) and the fungicide fosetyl-aluminium in potato cultivars with different levels of resistance against Phytophthora infestans (Mont) de Bary. To study the chemical induction of the resistance, the foliage of several potato cultivars was sprayed with BABA, fosetyl-aluminium or water (as a control treatment). After 3 days the foliage was inoculated with P. infestans. Seven days after inoculation, development of disease symptoms in the foliage was assessed. In postharvest tuber samples, evidence for enhancement of the defence response was evaluated by measuring the protein content of several hydrolytic enzymes as well as the phenol and phytoalexin content. The highest level of protection against late blight was observed when the chemicals were applied at early stages of crop development. An increase in resistance to late blight was also detected in tubers after harvest. There was also an increase in the protein level of beta-1,3-glucanase and aspartic protease as well as in the phenol and phytoalexin content of potato tuber discs obtained from postharvest tubers of treated plants. Thus the protective effect seemed to persist throughout the whole crop cycle. This treatment may offer the possibility of controlling both foliage and tuber blight and could have a major impact in reducing over-winter survival of P. infestans in tubers. 相似文献
1000.
Llop P Donat V Rodríguez M Cabrefiga J Ruz L Palomo JL Montesinos E López MM 《Phytopathology》2006,96(8):900-907
ABSTRACT An atypical strain of Erwinia amylovora was isolated near an outbreak of fire blight at a nursery in Spain in 1996. It was obtained from a Crataegus plant showing typical symptoms and was identified as E. amy-lovora by biochemical tests and enrichment-enzyme-linked immuno-sorbent assay, but not by polymerase chain reaction using primers based on the pEA29 sequence. Nevertheless, with primers from chromosomal regions, the isolate gave the expected amplification band. This strain carries one plasmid of approximately 70 kb, with no homology with the 29-kb plasmid common to all pathogenic strains, or with a large plasmid present in some E. amylovora strains. Growth of the strain in minimal medium without thiamine was slower compared with cultures in the same medium with thiamine, a characteristic typical of strains cured of the 29-kb plasmid. Nevertheless, aggressiveness assays on pear, apple, and Pyracantha plants and in immature pear fruit showed that this strain exhibited a virulence level similar to other strains containing pEA29. To the best of our knowledge, this is the first report of the isolation from naturally infected plant material of a pathogenic strain of E. amylovora without pEA29, but with a plasmid of approximately 70 kb not previously described. 相似文献