Publications by authors named "Dennis Margosan"

8 Publications

  • Page 1 of 1

Identification of race-specific resistance in North American Vitis spp. limiting Erysiphe necator hyphal growth.

Phytopathology 2012 Jan;102(1):83-93

United State Department of Agriculture - Agricultural Research Service, Parlier, CA, USA.

Race-specific resistance against powdery mildews is well documented in small grains but, in other crops such as grapevine, controlled analysis of host-pathogen interactions on resistant plants is uncommon. In the current study, we attempted to confirm powdery mildew resistance phenotypes through vineyard, greenhouse, and in vitro inoculations for test cross-mapping populations for two resistance sources: (i) a complex hybrid breeding line, 'Bloodworth 81-107-11', of at least Vitis rotundifolia, V. vinifera, V. berlandieri, V. rupestris, V. labrusca, and V. aestivalis background; and (ii) Vitis hybrid 'Tamiami' of V. aestivalis and V. vinifera origin. Statistical analysis of vineyard resistance data suggested the segregation of two and three race-specific resistance genes from the two sources, respectively. However, in each population, some resistant progeny were susceptible in greenhouse or in vitro screens, which suggested the presence of Erysiphe necator isolates virulent on progeny segregating for one or more resistance genes. Controlled inoculation of resistant and susceptible progeny with a diverse set of E. necator isolates clearly demonstrated the presence of fungal races differentially interacting with race-specific resistance genes, providing proof of race specificity in the grape powdery mildew pathosystem. Consistent with known race-specific resistance mechanisms, both resistance sources were characterized by programmed cell death of host epidermal cells under appressoria, which arrested or slowed hyphal growth; this response was also accompanied by collapse of conidia, germ tubes, appressoria, and secondary hyphae. The observation of prevalent isolates virulent on progeny with multiple race-specific resistance genes before resistance gene deployment has implications for grape breeding strategies. We suggest that grape breeders should characterize the mechanisms of resistance and pyramid multiple resistance genes with different mechanisms for improved durability.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1094/PHYTO-03-11-0062DOI Listing
January 2012

Acute cigarette smoke exposure reduces clot lysis--association between altered fibrin architecture and the response to t-PA.

Thromb Res 2010 Nov 1;126(5):426-30. Epub 2010 Sep 1.

Division of Cardiovascular Medicine, University of California San Francisco, Fresno, CA 93721, USA.

Background: Enhanced thrombolysis is a proposed mechanism for reduced mortality in cigarette smokers with STEMI ("smoker's paradox"). The mechanisms remain unclear but studies suggest fibrin architecture (FA) may affect thrombolysis. Our group has previously shown that acute cigarette smoke exposure (CSE) alters FA. This study was done to evaluate the association between FA, thrombolysis and CSE.

Methods And Results: Otherwise healthy smokers (n=22) were studied before and after smoking two cigarettes. Non-smokers (n=22) served as controls. Two ex-vivo models were used to evaluate clot lysis of venous blood and these data were compared to FA as determined by SEM. In the first model, clot lysis in a glass tube at 60minutes after addition of t-PA was measured. The second model quantified lysis utilizing thromboelastography. With the latter, after a clot reached maximum strength, t-PA was added and clot lysis at 60min was noted. SEM studies were performed on platelet poor plasma mixed with thrombin and FA was examined at 20K. Clot lysis was similar in both groups except that post-smoking, TEG showed a significantly lower lysis compared to pre- and non-smoking clots. SEM analysis showed significantly thinner fibers and denser clots post-smoking.

Conclusions: Venous clots from smokers failed to show an enhanced lysis when exposed to t-PA. In fact, acute CSE was associated with changes in FA and increased resistance to thrombolysis. These findings in part may explain enhanced thrombogenicity but suggest that mechanisms other than enhanced fibrinolysis are likely to be responsible for "smoker's paradox."
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.thromres.2010.07.021DOI Listing
November 2010

Effects of cigarette smoke exposure on clot dynamics and fibrin structure: an ex vivo investigation.

Arterioscler Thromb Vasc Biol 2010 Jan 8;30(1):75-9. Epub 2009 Oct 8.

Division of Cardiovascular Medicine, University of California San Francisco, Fresno, 2823 N Fresno Street, Fresno, CA 93721, USA.

Objective: The purpose of this study was to examine the effect of cigarette smoke exposure (CSE) on clot dynamics and fibrin architecture and to isolate the relative contribution of platelets and fibrinogen to clot dynamics.

Methods And Results: From young healthy males smokers (n=34) and nonsmokers (n=34) a baseline blood was drawn, and smokers had another blood draw after smoking 2 regular cigarettes. Using thromboelastography (TEG) the degree of platelet-fibrin interaction was measured. In additional experiments, abciximab (20 microg/mL) was added to the smokers samples (n=27) to reduce the effects of platelet function from the TEG parameters. The maximum clot strength (G) obtained with abciximab measured mainly the contribution of fibrinogen to clot strength (GF). By subtracting GF from G, the contribution of platelets to clot strength (GP) was presumed. A significant difference was found for all TEG parameters between nonsmokers versus postsmoking and pre- versus postsmoking samples. Postsmoking both GF and GP were significantly higher as compared to presmoking. On electron microscopy and turbidity analysis, postsmoking fibrin clots were significantly different compared to presmoking and nonsmoking samples.

Conclusions: Acute CSE changes clot dynamics and alters fibrin architecture. Both functional changes in fibrinogen and platelets appear to contribute to heightened thrombogenicity after acute CSE.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1161/ATVBAHA.109.195024DOI Listing
January 2010

Effect of chitosan dissolved in different acids on its ability to control postharvest gray mold of table grape.

Phytopathology 2009 Sep;99(9):1028-36

Department of Environmental and Crop Science, Marche Polytechnic University, via Brecce Bianche, 60131 Ancona, Italy.

Chitosan is a natural biopolymer that must be dissolved in an acid solution to activate its antimicrobial and eliciting properties. Among 15 acids tested, chitosan dissolved in 1% solutions of acetic, L-ascorbic, formic, L-glutamic, hydrochloric, lactic, maleic, malic, phosphorous, and succinic acid. To control gray mold, table grape berries were immersed for 10 s in these chitosan solutions that had been adjusted to pH 5.6. The reduction in decay among single berries of several cultivars (Thompson Seedless, Autumn Seedless, and grape selection B36-55) inoculated with Botrytis cinerea at 1 x 10(5) conidia/ml before or after immersion in chitosan acetate or formate, followed by storage at 15 degrees C for 10 days, was approximately 70%. The acids alone at pH 5.6 did not control gray mold. Decay among clusters of two cultivars (Thompson Seedless and Crimson Seedless) inoculated before treatment was reduced approximately 60% after immersion in chitosan lactate or chitosan acetate followed by storage for 60 days at 0.5 degrees C. The viscosity of solutions was 1.9 centipoises (cp) (ascorbate) to 306.4 cp (maleicate) and the thickness of chitosan coating on berries was 4.4 microm (acetate) to 15.4 microm (ascorbate), neither of which was correlated with solution effectiveness. Chitosan acetate was the most effective treatment which effectively reduced gray mold at cold and ambient storage temperatures, decreased CO2 and O2 exchange, and did not injure the grape berries.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1094/PHYTO-99-9-1028DOI Listing
September 2009

Mutation at β-Tubulin Codon 200 Indicated Thiabendazole Resistance in Penicillium digitatum Collected from California Citrus Packinghouses.

Plant Dis 2006 Jun;90(6):765-770

USDA-ARS, San Joaquin Valley Agricultural Sciences Center, 9611 South Riverbend Avenue, Parlier CA 93648.

Thiabendazole (TBZ) is commonly applied to harvested citrus fruit in packinghouses to control citrus green mold, caused by Penicillium digitatum. Although TBZ is not used before harvest, another benzimidazole, thiophanate methyl, is commonly used in Florida and may be introduced soon in California to control postharvest decay of citrus fruit. Isolates from infected lemons and oranges were collected from many geographically diverse locations in California. Thirty-five isolates collected from commercial groves and residential trees were sensitive to TBZ, while 19 of 74 isolates collected from 10 packinghouses were resistant to TBZ. Random amplified polymorphic DNA analysis indicated that the isolates were genetically distinct and differed from each other. Nineteen TBZ-resistant isolates and a known TBZ-resistant isolate displayed a point mutation in the β-tubulin gene sequence corresponding to amino acid codon position 200. Thymine was replaced by adenine (TTC → TAC), which changed the phenylalanine (F) to tyrosine (Y). In contrast, for 49 TBZ-sensitive isolates that were sequenced, no mutations at this or any other codon positions were found. All of the isolates of P. digitatum resistant to TBZ collected from a geographically diverse sample of California packinghouses appeared to have the same point mutation conferring thiabendazole resistance.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1094/PD-90-0765DOI Listing
June 2006

Control of Citrus Green Mold by Carbonate and Bicarbonate Salts and the Influence of Commercial Postharvest Practices on Their Efficacy.

Plant Dis 1999 Feb;83(2):139-145

Advanced Packinghouse Systems, LLC, Fresno, CA 93721.

The toxicity to Penicillium digitatum and practical use of carbonate and bicarbonate salts to control green mold were determined. The effective dose (ED) concentrations to inhibit the germination of P. digitatum spores of sodium carbonate (SC), potassium carbonate, sodium bicarbonate (SBC), ammonium bicarbonate, and potassium bicarbonate were 5.0, 6.2, 14.1, 16.4, and 33.4 mM, respectively. All were fungistatic because spores removed from the solutions germinated in potato dextrose broth. SC and SBC were equal and superior to the other salts for control of green mold on lemons and oranges inoculated 24 h before treatment. When sodium content and high pH must be minimized, SBC could replace SC. Furthermore, because a higher proportion of NaOCl would be present in the active hypochlorous acid at the lower pH of SBC compared to SC, sanitation of the SBC solution should be easier to maintain. NaOCl (200 μg/ml) added to SBC at pH 7.5 improved green mold control. Rinse water as high as 50 ml per fruit applied after SC did not reduce its effectiveness; however, high-pressure water cleaning after SC did. Conversely, high-pressure water cleaning of fruit before SC improved control of green mold. The risk of injury to fruit posed by SC treatment was determined by immersing oranges for 1 min in 3% (wt/vol) SC at 28, 33, 44, 50, 56, or 61°C (±1°C) and followed by storage for 3 weeks at 10°C. Rind injuries occurred only after treatment at 56 and 61°C. The risk of injury is low because these temperatures exceed that needed for control of green mold. SC was compatible with subsequent imazalil and biological control treatments.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1094/PDIS.1999.83.2.139DOI Listing
February 1999

Combination of Hot Water and Ethanol to Control Postharvest Decay of Peaches and Nectarines.

Plant Dis 1997 Dec;81(12):1405-1409

Biological Aide, Horticultural Crops Research Laboratory, Agricultural Research Service, U. S. Department of Agriculture, 2021 S. Peach Avenue, Fresno, CA 93727.

Spores of Monilinia fructicola or Rhizopus stolonifer were immersed in water or 10% ethanol (EtOH) for 1, 2, 4, or 8 min at temperatures of 46 or 50°C to determine exposure times that would produce 95% lethality (LT95). EtOH reduced the LT95 by about 90%. Peaches and nectarines infected with M. fructicola were immersed in hot water alone or with EtOH to control decay. EtOH significantly increased the control of brown rot compared to water alone. Immersion of fruit in water at 46 or 50°C for 2.5 min reduced the incidence of decayed fruit from 82.8% to 59.3 and 38.8%, respectively. Immersion of fruit in 10% ethanol at 46 or 50°C for 2.5 min further reduced decay to 33.8 and 24.5%, respectively. Decay after triforine (1,000 μg ml) treatment was 32.8%. Two treatments, 10% EtOH at 50°C for 2.5 min and 20% EtOH at 46°C for 1.25 min, were selected for extensive evaluation. The flesh of EtOH-treated fruit was significantly firmer, approximately 4.4 N force, than that of control fruit among seven of nine cultivars evaluated. No other factor evaluated was significantly influenced by heated EtOH treatments. The EtOH content of fruit treated with 10 or 20% EtOH was approximately 520 and 100 μg g 1 day and 14 days after treatment, respectively.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1094/PDIS.1997.81.12.1405DOI Listing
December 1997

Reduction of Microbial Populations on Prunes by Vapor-Phase Hydrogen Peroxide .

J Food Prot 1997 Feb;60(2):188-191

United States Department of Agriculture, Agricultural Research Service, Horticultural Crops Research Laboratory, 2021 South Peach Avenue, Fresno, California 93727, USA.

Vapor-phase hydrogen peroxide (VPHP) was used to disinfect prunes. Concentrated hydrogen peroxide solution (35%, wt/wt) was volatilized into a stream of dried air to approximately 3.1 mg/l (wt/vol) of hydrogen peroxide. Dried prunes obtained from commercial dehydrators were treated with VPHP and compared to untreated prunes. Microbial populations were determined for treatment comparisons. Untreated dried prune microbial populations were 155, 107, and 111 CFU/g of prunes on aerobic plate count agar, potato dextrose agar, and dichloran rose bengal agar, respectively. In contrast, VPHP-treated prune microbial populations were reduced to near zero on all media after 10 minutes of VPHP exposure. The color of prunes exposed for 20 min or longer, however, showed oxidation damage. No hydrogen peroxide residues were detected 90 days after treatment.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.4315/0362-028X-60.2.188DOI Listing
February 1997
-->