Browsing Plant Science & Landscape Architecture Theses and Dissertations by Subject "Agriculture, Plant Pathology"
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- ItemAssessment of select isolates of Trichoderma virens as a potential biocontrol against Meloidogyne incognita(2004-05-03) Mallozzi, Tonya Suzanne; Kratochvil, Robert J.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Three isolates of the soil-dwelling fungal organism, Trichoderma virens (Miller, Giddens and Foster) von Arx., were studied as potential biocontrols for the management of root-knot nematode (RKN) on bell pepper (Capsicum annuum L.). The study was conducted within the Moisture Replacement System (MRS), which was concurrently evaluated for its ability to serve as a culture system for Meloidogyne incognita (Kofoid and White) Chitwood and as an environment supportive of the growth and maintenance of Trichoderma isolates for biocontrol studies of this nature. Trichoderma isolates selected for study did not suppress populations of RKN on bell pepper under the conditions of this study. A review of the literature provided a multitude of complexities potentially contributing to the final results obtained. Investigation into these various complexities with the incorporation of the MRS will help to fully ascertain Trichoderma's potential as a biocontrol and perhaps reveal viable alternatives in the management of RKN.
- ItemBiology of Ophiosphaerella agrostis, epidemiology of dead spot, and a molecular description of the pathogen(2004-10-21) Kaminski, John; Dernoeden, Peter H.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ophiosphaerella agrostis is a newly described pathogen that incites dead spot disease of creeping bentgrass (Agrostis stolonifera) putting greens throughout the eastern United States. The objectives of this research project were to: 1) monitor environmental conditions and develop a predictive model for disease progress and pathogen dispersal under field conditions; 2) determine the effect of various fertilizers on dead spot recovery in bentgrass; and 3) develop molecular methods to diagnoses the disease and determine genetic variation among O. agrostis isolates. Field studies showed that the appearance of dead spot infection centers was influenced predominantly by air (greater than or equal to 18 degrees Centigrade) and soil (greater than or equal to 20 degrees Centigrade) temperature, but other factors including low relative humidity (less than or equal to 80%), shortened periods of leaf wetness (less than or equal to 14 hours), and high levels of solar radiation (greater than or equal to 230 W m to the minus 2) were associated with the development of dead spot epidemics. Patch diameter of O. agrostis infection centers and pseudothecia production generally increased at a linear rate between mid-June and early to mid-August. In a growth chamber study, ascospores were released from pseudothecia following a sharp decrease in relative humidity. Field studies revealed that ascospore release occurred primarily at dawn and dusk or during precipitation events. During precipitation events, ascospores may be forcefully discharged during the entire event, but most ascospores are released within the first 10 hours after precipitation begins. O. agrostis successfully over-wintered in bentgrass leaf sheaths, crowns, roots, and stolons, but little or no reactivation of the disease occurred in the second year. Plots treated with ammonium sulfate and isobutylidene diurea were among the fastest and slowest to recover from dead spot, respectively. In the second year (2003), dead spot recurred in plots treated since 2002 with KNO3, Ca(NO3)2, urea, and a complete fertilizer (20-20-20), but disease symptoms did not recur in plots receiving ammonium sulfate. Species-specific primers capable of detecting O. agrostis at very low concentrations (5 pg DNA) were developed and can be used to assist in diagnosing dead spot. Amplified fragment length polymorphism (AFLP) DNA fingerprinting resulted in placement of isolates (n=77) into three distinct clades that were greater than or equal to 69% similar.
- ItemChemotherapeutic Treatment Options to Manage Xylella fastidiosa in Shade Trees(2005-12-13) DeStefano, Darren Albert; Sullivan, Joseph; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Xylella fastidiosa is a fastidious, xylem-limited, broad spectrum, bacterial plant pathogen native to the Americas, causing substantial economic losses to the viticulture, citrus, and shade tree industries. In shade trees the disease is manifested as a chronic late season leaf scorch largely confined to urban areas of southeastern North America. Proposed treatments include antibiotics and growth regulators. Recently paclobutrazol, a diastereomeric triazole with fungistatic and growth regulation properties has been associated with symptom remission. Investigation into direct interaction of paclobutrazol with X. fastidiosa show no significant reduction in growth at the manufacturers recommended dosage of 20 µg ml-1; however significant reductions in growth were observed at a dosage of 200 µg ml-1. Therefore high levels of paclobutrazol may have a direct effect on X. fastidiosa while other plant physiological effects induced by paclobutrazol merit investigation for association in symptom mitigation of X. fastidiosa.
- ItemEVALUATION OF SCAB RESISTANCE QUANTITATIVE TRAIT LOCI (QTL) EFFECTS ON WHEAT(2010) Kang, Jing; Costa, Jose; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Fusarium Head Blight (FHB) of wheat (Triticum aestivum), caused by Fusarium graminearum, is a disease that periodically strikes the mid-Atlantic region of the USA. Breeding for resistant wheat cultivar is an effective method of disease control. McCormick, a genotype adapted to the mid-Atlantic region, was used in a backcross program with the Chinese cultivar Ning7840. Eight Near-Isogenic Lines (NIL) were developed by marker-assisted backcrossing. Three FHB resistance QTL on chromosomes 3BS, 2DL, and 5A were introgressed from non-adapted Ning7840 into the elite soft red winter wheat McCormick. The objective of this study was to evaluate the effects of QTL singly and in combination on FHB resistance. The 3BS+2DL NIL showed higher resistance and lower deoxynivalenol content than other NIL in both field and greenhouse studies. This suggests that the 3BS+2DL NIL can be used in the mid-Atlantic region to breed for improved FHB resistance.
- ItemFactors Affecting Fungicide Performance when Targeting Dollar Spot Disease in Creeping Bentgrass(2009) Pigati, Ray L.; Dernoeden, Peter H; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Creeping bentgrass (Agrostis stolonifera) is commonly grown on golf course fairways and dollar spot (Sclerotinia homoeocarpa) is perhaps the most chronically severe disease of bentgrass. Field studies were conducted to: a) determine the influence of simulated rainfall and two mowing timings (AM and PM) on the performance of four fungicides, and b) to assess the effects of two fungicide spray volumes (468 and 935 L water ha-1) and application timings (AM and PM) on dollar spot control in creeping bentgrass. Fungicide effectiveness generally was reduced by simulated rain imposed about 30 minutes after application. Boscalid and chlorothalonil were most and least rain-safe; respectively, and propiconazole and iprodione were intermediate in rain-safeness. Fungicide performance was improved by mowing in the AM prior to fungicide application. A tank-mix of chlorothalonil + propiconazole was unaffected by spray volume or application timing, but the performance of chlorothalonil and propiconazole applied separately was inconclusive.
- ItemManagement of White Rust (Caused by Albugo Occidentalis) Of Spinach and Its Impact on the NonTarget Invertebrate Community(2003-12-16) Diagne, Mbisin; Everts, Kathryne L; Dively, Galen P; Grybauskas, Arvydas P; Plant Science and Landscape Architecture (PSLA)White rust, caused by the oomycete Albugo occidentalis, is a major foliar disease of spinach (Spinacia oleracea). Favorable environmental conditions are required for its initiation and development. A modified version of a weather-based spray advisory program was evaluated using chemicals with different modes of action. Entomopathogenic fungi may infect Myzus persicae, a major pest of spinach. The nontarget effects of chemicals used in the management of white rust on entomopathogenic fungi and on the invertebrate community were also investigated. Both acibenzolar-S-methyl initiated at the second true leaf stage and pyraclostrobin applied according to the advisory program and weekly, reduced disease incidence compared to untreated plots. Naiad sprayed weekly reduced the percentage of aphid infested leaves, however no entomopathogenic fungi were isolated. All three chemicals caused population increases in predatory mites and phytophageous thrips. Actigard and Naiad caused increases in oribatid mites and beetle larvae populations
- ItemPhysiological and Molecular Studies of Ethylene Effects on Soybean Root Infection by Soybean Cyst Nematodes(2007-12-10) Xue, Ping; Solomos, Theophanes; Tucker, Mark L.; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Soybean cyst nematode (SCN), Heterodera glycines, is one of the most devastating pests of soybean in the world. Several earlier reports demonstrated that ethylene is involved in nematode feeding cell formation in Arabidopsis and tomato. I investigated whether or not ethylene is involved in SCN feeding cell formation in soybean. My results show that SCN parasitism was increased by treatment of roots with ethylene and inhibited by suppressors of ethylene action or in an ethylene resistant soybean mutant. My results also indicate that excised soybean roots colonized by SCN produced ethylene at 1.5-3 times the rate of non-infected roots between 14 and 22 days post inoculation. To determine if ethylene was being synthesized in feeding cells, an ethylene-responsive promoter fused to a GUS reporter gene was constructed and transformed into soybean roots with Agrobacterium rhizogenes. Overall, the results suggest that ethylene plays an important role in SCN infection in soybean