Os fungicidas são normalmente utilizados para o controle de doenças causadas por fungos fitopatogênicos em diversas culturas, incluindo frutas. Estes compostos, especialmente os descritos com atividade em múltiplos alvos, podem afetar organismos não alvos como leveduras, levando elas à morte por diferentes vias. O objetivo deste trabalho foi determinar o mecanismo de ação e de morte de três diferentes fungicidas utilizados na viticultura (mancozeb, captan e dithianon) sobre Saccharomyces cerevisiae. Os resultados mostraram que leveduras expostas ao mancozeb (100 µM, 6 h) levam a uma drástica redução da viabilidade, mas sem modificações na integridade da membrana celular. As células tratadas com mancozeb apresentaram marcadores apoptóticos como aumento na concentração intracelular de espécies reativas de oxigênio (ROS), hiperpolarização da membrana mitocondrial e externalização de fosfatidilserina, indicando que a morte celular de S. cerevisiae ocasionada por mancozeb é apoptótica e conforme observado pelo comportamento de linhagens mutantes, segue a via metacaspase dependente. Aproximadamente 80% das leveduras tratadas com captan (20 µM, 6 h) apresentaram disfunções na membrana citoplasmática, e a drástica redução na concentração de grupos tiólicos proteicos e não proteicos. Além disso, as células que mantiveram sua integridade de membrana após a exposição ao captan, exibiram externalização de fosfatidilserina e acumulação de ROS. Mutantes com deleção em YCA1 apresentaram resistência parcial ao captan, indicando a ativação da cascata apoptótica metacaspase dependente. Em fermentações vínicas o captan (2,5 µM) atrasa o início da fermentação de maneira dose dependente, devido à drástica redução na viabilidade celular. Porém, em dosagens subletais, as células remanescentes se adaptam ao fungicida e completam a fermentação sem alterações evidentes nas características físico-químicas do produto final. Da mesma forma, leveduras tratadas com dithianon (2 µM; 3 h) mostraram aumento no número de células com permeabilização da membrana citoplasmática, aumento de ROS e redução na quantidade de tióis, mas sem sinais de apoptose. De forma geral, os resultados indicam que o mancozeb induz apoptose em S. cerevisiae via metacaspase dependente, enquanto o captan leva a morte por necrose e apoptose e o dithianon mata as células por necrose. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, CAPES. / Fungicides are currently used to control fungal phytopathogenic diseases in many crops, including fruits. These compounds, especially those described as multisite activity fungicides, can affect non-target organisms like yeasts leading to their cell death by different pathways. The objective of this work was determining the mechanism of action and death of three fungicides used in viticulture (captan, dithianon and mancozeb) on Saccharomyces cerevisiae. The results showed that yeast exposition to the mancozeb (100 µM, 6 h) lead to a drastic reduction of cell viability, but no modification of cell membrane integrity. Mancozeb treated cells shown apoptotic markers as increase of intracellular reactive oxygen species (ROS), mitochondrial membrane hyperpolarization, and phosphatidylserine externalization, indicating that mancozeb induced cell death in S. cerevisiae is apoptotic and as shown by mutants strains, follow metacaspase-dependent pathway. Almost 80% of captan treated yeasts (20 µM, 6 h) showed citoplasmatic membrane dysfunction, and a drastic reduction on both non-proteic and proteic thiol concentrations. Moreover, the cells that retain their membrane integrity after exposure to the captan exhibited phosphatidylserine externalization and ROS accumulation, indicating apoptosis. YCA1 deletion mutant exhibited partial resistance to captan, suggesting a metacaspase dependent apoptotic cascade. In wine fermentations captan (2,5 µM) delays the beginning of alcoholic fermentations in a dose dependent manner, associated with a drastic reduction on yeast viability. However, in sub-lethal dosages, the reminiscent viable cells adapted to the fungicide, grow and complete fermentation with non-evident modifications on the physicochemical characteristics of the final product. Similarly, yeast cells treated with dithianon (2 µM; 3 h) showed cell membrane permeabilization, ROS increase, and decrease of cellular thiol compounds, but no signs of apoptosis. In general, the results indicated that mancozeb induces metacaspase dependent apoptotic cell death in S. cerevisiae, where captan leads to a dual necrotic and apoptotic cell death, and dithianon kills cells by necrosis.

Cowpea is a worldwide-distributed crop, and is important to the livelihood of poor people in developing countries. Cowpea is also susceptible to a wide range of pests and pathogens, which can cause damage to the crop at all stages. Seedling diseases caused by pathogens such as Rhizoctonia solani Fusarium solani and Pythium spp. affect cowpea and result in low yields especially in rural areas where there are few or no control measures against these pathogens. This research aimed at evaluating the efficacy of a biological control agent and fungicides against fungal seedling diseases of cowpea. The bacterium, Bacillus cereus1, and the fungicides, Apron®, Subdue® and Celest® were screened for the control of cowpea seedling diseases, after obtaining promising in vitro results on their effectivity against Rhizoctonia solani, Pythium ultimum and Fusarium solani. The experiment was conducted in a greenhouse using seedling trays with 128 cells, each filled with pasteurised growing medium (Braaks lawn dressing). Seedling trays were placed randomly on greenhouse tables with four replication per treatment, each replication consisting of 56 plants. Cowpea seeds (Cultivar-Pietersburg blue) were obtained from the Dry Bean Seeds Producers Organisation. The pasteurised growing medium was artificially inoculated with the three fungi. Two plugs of actively growing fungal mycelium of the three pathogens were inoculated in each cell of the polystyrene seedling trays. Trays were drenched with Bacillus cereus1 at 106 cells/ml (3 ml per tray cell) at planting and fungicides were applied on the 14th and 28th days at the recommended rate. The experiment was conducted at temperatures ranging from 22-25 oC. Plants were harvested on the 35th day after planting and percentage germination, diseased height of the plants and dry mass of roots and shoots were determined. Results indicated that the biological control agent (B. cereus1) was able to significantly reduce the damage done by the pathogens Rhizoctonia solani, Pythium ultimum and Fusarium solani in all trials. It was also confirmed that the application of the biological control agent during planting could reduce disease incidence. The biological control agent increased seed emergence rate and shoot length. All three fungicides significantly reduced the disease incidence caused by all pathogens. All fungicides treatments applied increased emergence rate and shoot length. Seedling diseases should be given too much attention, as they cause severe losses to many crops. There is a need for future research on the effectivity of B. cereus1 as relatively little work has been published on its antagonistic behaviour against seedling diseases. There are also few registered fungicides available for the control of these seedling diseases on cowpea, therefore research on these and other potential products is required as seedling diseases play a major role in reducing yield of many crops. / Dissertation (MInstAgrar)--University of Pretoria, 2008. / Microbiology and Plant Pathology / unrestricted

Field studies were conducted in 2003, 2004, and 2005 in the Mississippi delta at 12 locations across common production practices to evaluate the impact of 12 single applications of fungicides at the R3 and R5 growth stage on soybean yield, seed quality, and net returns. Averaged across locations, azoxystrobin alone and mixed with other fungicides increased yields 161 to 343 kg/ha compared to the nontreated control. Fungicide applications made at R3-R4 were more efficacious and resulted in larger yield increases than applications made at R5-R6. Plots treated at the R3-R4 growth stage with 0.11kg ai/ha azoxystrobin alone or in combination with other fungicides yielded 135 kg/ha more than plots treated with the same treatments at the R5-R6 growth stage. Azoxystrobin at 0.11 kg ai/ha and azoxystrobin at 0.11 kg ai/ha + 0.035 kg ai/ha diflubenzuron were the most profitable treatments and increased net returns $23/ha and $31/ha, respectively compared to the nontreated control.

Photocopy of typescript. / Digitized by Kansas State University Libraries

Call number: LD2668 .T4 1961 B79

No description available.

published_or_final_version / Ecology and Biodiversity / Doctoral / Doctor of Philosophy

No description available.

Powdery mildew of cucurbits, which include cantaloupe, honeydew, watermelon, cucumber and squash, occurs every year in Arizona. Moderate temperatures and relative humidity, succulent plant growth and reduced light intensity brought about by a dense plant canopy are factors that promote development of powdery mildew, which is caused by the pathogenic fungus Sphaerotheca fuliginea. Potential new fungicides were evaluated and compared to existing chemicals for control of powdery mildew of cantaloupe in a field trial conducted during the spring of 1998 at the Yuma Agricultural Center. A high level of disease had developed by crop maturity (June 23). On the upper leaf surface where spray coverage was good and disease severity on nontreated leaves was moderate (24% of upper leaf surface infected), all treatments significantly reduced the severity of powdery mildew. These treatments included Sovran, Flint, Procure, Topsin M, Quadris, Benlate, quinoxyfen, Rally, Trilogy, Actigard, Bravo, JMS stylet oil, Kaligreen and Bayleton. In contrast, on the lower leaf surface where spray coverage was not as good and disease severity on nontreated leaves was very high (94% of lower leaf surface infected), the best disease control was achieved with chemistries that have systemic properties. Treatments that held the infected lower leaf surface to 20% or less included Sovran, Flint, Procure, Topsin + Microthiol, and Quadris. The potential availability of new chemistries for management of powdery mildew of cantaloupe and other cucurbits could help improve overall control of powdery mildew as well as the implementation of fungicide resistance management strategies, which strive to minimize the risk of resistance development by the pathogen to these compounds.

Erysiphe cichoracearum is the fungus that causes powdery mildew of lettuce, a disease favored by warm and dry weather conditions. Several potential new fungicides were evaluated for control of this disease in 1999. Untreated lettuce plants were heavily infected with powdery mildew, whereas the disease was very light to virtually nonexistent in plots treated with Sovran, BAS 500, Rally and DPX-MU752. Higher levels of powdery mildew, still significantly less than that observed on untreated plants, were recorded in plots treated with the standard materials Microthiol Special and Trilogy in addition to several other compounds. The possible availability of one or more of these chemistries under development could help in efforts to control powdery mildew of lettuce and to establish and maintain a fungicide resistance management program for plant disease control products of importance for this crop.