Publications (7)10.67 Total impact
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Article: Differential responses of Arabidopsis ecotypes to cold, chilling and freezing temperatures
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ABSTRACT: Arabidopsis plants show an increase in freezing tolerance in response to exposure to low nonfreezing temperatures, a phenomenon known as cold acclimation. In the present study, we evaluated the physiological and morphological responses of various Arabidopsis ecotypes to continuous growth under chilling (14°C) and cold (6°C) temperatures and evaluated their basal freezing tolerance levels. Seedlings of Arabidopsis plants were extremely sensitive to low growth temperatures: the hypocotyls and petioles were much longer and the angles of the second pair of true leaves were much greater in plants grown at 14°C than in those grown at 22°C, whereas just intermediate responses were observed under the cold temperature of 6°C. Flowering time was also markedly delayed at low growth temperatures and, interestingly, lower growth temperatures were accompanied by longer inflorescences. Other marked responses to low temperatures were changes in pigmentation, which appeared to be both ecotype specific and temperature dependent and resulted in various visual phenotypes such as chlorosis, necrosis or enhanced accumulation of anthocyanins. The observed decreases in chlorophyll contents and accumulation of anthocyanins were much more prominent in plants grown at 6°C than in those grown at 14°C. Among the various ecotypes tested, Mt-0 plants markedly accumulated the highest levels of anthocyanins upon growth at 6°C. Freezing tolerance examination revealed that among 10 ecotypes tested, only C24 plants were significantly more sensitive to subzero temperatures. In conclusion, Arabidopsis ecotypes responded differentially to cold (6°C), chilling (14°C) and freezing temperatures, with specific ecotypes being more sensitive in particular traits to each low temperature.Annals of Applied Biology 03/2006; 148(2):113 - 120. · 2.18 Impact Factor -
Article: Induction of Resistance to Penicillium digitatum in Grapefruit by the Yeast Biocontrol Agent Candida oleophila.
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ABSTRACT: ABSTRACT 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 10(8) to 10(9) 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 beta-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.Phytopathology 05/2002; 92(4):393-9. · 2.80 Impact Factor -
Article: Induction of Chitinase and β-1,3-Endoglucanase Proteins by UV Irradiation and Wounding in Grapefruit Peel Tissue
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ABSTRACT: UV irradiation enhanced the resistance of grapefruit against the development of green mold décay caused byPenicillium digitatum, the main postharvest pathogen of citrus fruit, and significantly inhibited the fungus’ growth at the fruit wound sites. Immunoblotting analysis using specific citrus chitinase and β-1,3-endoglucanase antibodies, showed that UV irradiation, wounding of the fruit, or a combination of these two treatments, induced the accumulation of a 25 kD chitinase protein in the fruit’s peel tissue. On the other hand, UV irradiation or wounding of the fruit alone was unable to induce the accumulation of 39 and 43 kD β-1,3-endoglucanase proteins, but the combination of the two treatments increased these protein levels. It is suggested that both chitinase and β-1,3-endoglucanase may play a role in the UV-induced resistance of grapefruit againstP. digitatum.Phytoparasitica 04/1999; 27(3):233-238. · 0.89 Impact Factor -
Article: Influence of CaCl(2) on Penicillium digitatum, Grapefruit Peel Tissue, and Biocontrol Activity of Pichia guilliermondii.
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ABSTRACT: ABSTRACT Interactions between CaCl(2), grapefruit peel tissue, Penicillium digitatum, and the yeast antagonist Pichia guilliermondii strain US-7 were investigated. Application of 68 or 136 mM CaCl(2) to grapefruit surface wounds reduced the incidence of green mold caused by Penicillium digitatum by 43 to 52%. In laboratory tests, a cell suspension (10(7) cells/ml) of Pichia guilliermondii containing either 68 or 136 mM CaCl(2) reduced the incidence of green mold from 27 to 3%. In large scale tests, dip application of 136 mM CaCl(2) with US-7 (10(7) cells/ml) significantly decreased the number of wounds infected by Penicillium digitatum. CaCl(2), with or without yeast cells, stimulated ethylene production in grapefruit tissue. Increasing concentrations of CaCl(2) resulted in decreased spore germination and germ tube elongation of Penicillium digitatum. Pectinolytic activity of crude enzyme preparations of Penicillium digitatum was also inhibited by the presence of increasing concentrations of CaCl(2). US-7 exhibited a strong ability to maintain cytosolic Ca(2+) homeostasis at levels that did not exceed 1.4 muM when exposed to 150 mM CaCl(2). On the other hand, strain 114 of Debaryomyces hansenii, which failed to give any protection against infection by Penicillium digitatum, showed reduced capacity to maintain Ca(2+) homeostasis. The effect of calcium in reducing infection of grapefruit wounds by Penicillium digitatum could be due to direct effects on host tissue (making cell walls more resistant to enzymatic degradation) or the pathogen (interfering with spore germination, growth, and inhibition of fungal pectinolytic enzymes). Alternatively, the ability of US-7 to maintain calcium homeostasis may allow it to grow or assist in its competitive ability in a microenvironment that, because of high levels of calcium ions, is inhibitory to growth of the green mold pathogen.Phytopathology 04/1997; 87(3):310-5. · 2.80 Impact Factor -
Article: Characterization of extracellular lytic enzymes produced by the yeast biocontrol agent Candida oleophila.
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ABSTRACT: The yeast Candida oleophila, the base of the commercial product Aspire, is recommended for the control of postharvest decay of citrus and pome fruit. Competition for nutrients and space is believed to be the major mode of action. Involvement of fungal cell wall-degrading enzymes is also suggested to play a role in the mechanism of action of yeast antagonists. The present study showed that the yeast C. oleophila is capable of producing and secreting various cell wall-degrading enzymes, including exo-β-1,3-glucanase, chitinase and protease. Exo-β-1,3-glucanase and chitinase were produced and maximized in the early stages of growth, whereas protease reached a maximum level only after 6–8 days. Production of exo-β-1,3-glucanase, chitinase and protease was stimulated by the presence of cell wall fragments of Penicillium digitatum in the growth medium, in addition to glucose. This study also provided evidence that C. oleophila is capable of secreting exo-β-1,3-glucanase into the wounded surface of grapefruit. The role of exo-β-1,3-glucanase (CoEXG1) in the biocontrol activity of C. oleophila was tested using CoEXG1-knockouts and double-CoEXG1 over-producing transformants. In vitro bioassays showed that wild-type C. oleophila and exo-β-1,3-glucanase over-expressing transformants had similar inhibitory effects on spore germination and germ-tube elongation; and both were more inhibitory to the fungus than the knockout transformant. In experiments conducted on fruit to test the biocontrol activity against infection by P. digitatum, no significant difference in inhibition was observed between transformants and untransformed C. oleophila cells at the high concentrations of cells used, whereas at a lower concentration of yeast cells the knockout transformants appeared to be less effective. -
Article: Pilot Testing of Pichia guilliermondii: A Biocontrol Agent of Postharvest Diseases of Citrus Fruit
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ABSTRACT: The efficacy of the yeast Pichia guillierrnondii (US-7) in controlling postharvest decay of citrus fruit was evaluated in small-scale and pilot tests in commercial packinghouses. In scale-up fermentation on cheap industrial waste materials, P. guillierrnondii grew efficiently and maintained its antagonistic activity, as tested in in vitro assay against spore germination of Penicilliurn digitatum. In small-scale experiments with injured and non-injured fruits dipped in the yeast cell suspension, the development of decay in several citrus cultivars was effectively inhibited. The yeast was compatible with a mixture of commonly used waxes containing a low concentration of a chemical fungicide. In packinghouse tests, combining the yeast with 200 ppm thiabendazole (TBZ) resulted in a reduction in the incidence of decay to a level equal to that of the commercial treatment of 2000 ppm TBZ. The efficacy of US-7 could also be maintained under packinghouse conditions at a cell concentration of the yeast antagonist as low as 107 cells/ml. No significant difference in the efficacy of P. guilliermondii was found in either the drench or the spray application systems tested in citrus packing-houses.Biological Control 3(1):47-52. · 2.00 Impact Factor -
Article: Characterization of an Epiphytic Yeast Population of Grapefruit Capable of Suppression of Green Mold Decay Caused by Penicillium digitatum
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ABSTRACT: An epiphytic yeast population of grapefruit able to grow under high osmotic conditions and a wide range of temperatures was isolated and characterized for its biocontrol activity against green mold decay caused by Penicillium digitatum. Techniques based on random amplified polymorphic DNA (RAPD) and arbitrary primed polymerase chain reaction (ap-PCR), as well as homologies between sequences of the rDNA internal transcribed spacers (ITS) and 5.8S gene, were used to characterize the composition of the yeast population and to determine the genetic relationships among predominant yeast species. Epiphytic yeasts exhibiting the highest biocontrol activity against P. digitatum on grapefruit were identified as Candida guilliermondii, C. oleophila, C. sake, and Debaryomyces hansenii, while C. guilliermondii was the most predominant species. RAPD and ap-PCR analyses of the osmotolerant yeast population showed two different, major groups. The sequences of the ITS regions and the 5.8S gene of the yeast isolates, previously identified as belonging to different species, were found to be identical.Biological Control.
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