Sclerotinia blight, caused by <i>Sclerotinia minor</i>, is a severe disease of peanut in Virginia. Vinclozolin (V), iprodione (I), dicloran (D), and pentachloronitrobenzene (PCNB) were evaluated for their fungitoxicity to <i>S. minor</i>. The mean ED₅₈ values for five isolates were found to be 0.07, 0.11, 0.91, and 1.27 μg/ml, for V, I, D, and PCNB, respectively, on fungicide-amended glucose yeast-extract agar (GYEA). Fungicide-resistant growth sectors developed on media amended with I or V. Nine such strains occurred; they were capable of growth on GYEA amended with up to 1000 μg/ml of I or V, and were cross-resistant to D or PCNB. Resistance was maintained in all but two strains after repeated culture in the absence of fungicide for 3 yr. In field microplots, two resistant strains were pathogenic to peanut and survived as well as a fungicide-sensitive field isolate. D, I and V were applied to peanuts in the microplots for 3 yr at total annual rates of 8.41, 3.36, and 2.52 kg/ha, respectively. Disease severity caused by the resistant strains was suppressed 19, 33, and 87% by D, I, and V, respectively, as compared to 15, 24, and 76% for the sensitive isolate. Isolates recovered from tissue biopsies still grew on fungicide-amended GYEA indicating that <i>in vitro</i> and <i>in vivo</i> resistance are not equivalent in this case. Fungicide treatments reduced sclerotial populations of all strains, and reduced the viability of sclerotia from sensitive but not resistant strains. Fungicide-resistant strains were capable of surviving and competing pathogenically in microplots infested with equal numbers of sclerotia from a sensitive and a resistant strain; this trend was enhanced by fungicide applications. A survey of 763 isolates from fields treated with these fungicides failed to detect resistant strains. One fungicide-resistant isolate was recovered from an iprodione-treated microplot originally infested with a sensitive field isolate. A technique utilizing excised peanut stems was devised to evaluate isolate pathogenicity, cultivar resistance to the disease, susceptibility of different age peanut tissues, and fungicide persistence on peanut stems in the field. The method was also used to screen fungicides; results verified previous findings which indicated that <i>in vitro</i> resistance is not equivalent to <i>in vivo</i> resistance. Resistance to these fungicides may eventually become a field problem, but with correct management they should provide years of disease control. / Ph. D. / incomplete_metadata

An evaluation was made of soil solarization to control Macrophomina phaseolina and Sclerotium rolfsii under the climatic conditions of the Sonoran Desert region of Arizona. Tarping of moist soil with clear polyethylene in the summer was most effective in raising soil temperatures, while tarping during the fall and spring were less efficient. In one summer trial, the maximum temperatures achieved were 7-8 C higher than control plots at 1, 15, and 30 cm depths. In none of the tests was the application of tarp effective in reducing M. phaseolina populations to non-detectable levels. After a six-week summer solarization treatment, S. rolfsii was controlled at the 15-cm but not the 30-cm depth. During a fall treatment control of S. rolfsii was achieved only at the 1-cm depth. After solarization, seeds of Euphorbia lathyris were planted in solarized and control plots. The incidence of M. phaseolina-associated mortality among seedlings planted in solarized plots was always the same as the control plot with the highest disease incidence. The utility of this technique may be limited by the heat tolerance of the target organisms. Studies of bacterial antagonists were initiated to determine their utility in enhancing pathogen control after the solarization treatment. Screening 43 bacterial isolates showed that seven of Pseudomonas fluorescens and one of Serratia marcescens exhibited some form of antagonism toward M. phaseolina, S. rolfsii and Verticillium dahliae in vitro. Antagonism was manifested as a complete inhibition of fungal development or reduced hyphal development coupled with suppression of sclerotial development. The action of the antagonists was found to be fungitoxic or fungistatic rather than fungicidal. None of the four P. fluorescens isolates tested were effective in preventing M. phaseolina infection of E. lathyris seedlings. The ability of these bacteria to prevent sclerotial formation while still permitting hyphal growth may be a useful technique for studying the two phases of the fungal life cycle separately.

A 24-hour fermentation of the optimized synbiotic composed of B. longum and EPR was performed to give a cell-free fermentation broth (S24). S24 was co-cultured with two colon cancer cell lines (Caco-2 and SW620) and normal colon cells (FHC). S24 significantly inhibited cell proliferation for both colon cancer cells but promoted FHC cell growth by 10-25% as shown by MTT and BrdU arrays. Primary DNA damage analysis by alkaline comet assay showed S24 caused DNA damage to a comparable extent as the positive control of 10 mM H2O2 (treated for 1 hour) for both cancer cells. Dynamic analysis on DNA damage-associated DNA repair showed the two colon cancer cells had different response pattern to S24. Flow cytometric analysis showed that both Caco-2 and SW620 when treated with S24 (IC 50=3.66 mM of acetate) were arrested initially at G2/M and subsequently at S phase accompanied with large sub-G1 peaks. Dual staining with PI/AnnexinV further proved the appearance of apoptosis. Live cell imaging analysis on Caco-2 cells treated with S24 showed the following events: mitochondria were rapidly destroyed within the first two-hour treatment, the cells bubbled and the nucleus condensed after the mitochondrial had shrunken, followed by apoptosis. / Despite active research on synbiotic on anti-carcinogenesis of colon cancer by synbiotics, the underlying mechanism still remains unclear. This study investigated a novel synbiotic composed of non-digestible carbohydrates (NDCs) extracted from mushroom sclerotia as prebiotics and Bifidobacteria as probiotics. Preliminary results on incubation of two probiotics ( Bifidobacterium longum and Lactobacillus brevis) and one pathogenic bacterium (Clostridium celatum) separately with 3 NDCs extracted from mushroom sclerotia [Poria cocos (PC), Polyporus rhinocerus (PR) and Pleurotus tuber-regium (PT)] indicated that the growth of B. longum and L. brevis was stimulated more preferentially than C. celatum after 72-hour fermentation. The short-chain fatty acid (SCFA) profile was dominated by acetate (> 98% of total SCFAs) with very little butyrate (&lt; 2.0% of total SCFAs) and the organic matter disappearance (OMD) during fermentation was consistent with the bacterial growth. Among the synbiotic combinations, NDC from PR and B. longum gave the largest amount of acetate (2.47+/-0.232 mmol/g of organic matter disappearance). / Results obtained from human pathway finder RT2 Profiler(TM) PCR Array indicated that S24 could modulate the proliferation of colon cancer cells mainly by various pathways such as cell cycle and DNA damage repair, apoptosis and cell senescence, etc. In SW620 cells, PCR Array of Human Cell Cycle further revealed that the modulated genes mainly belonged to the gene cluster of S phase and DNA replication as well as G2 and G2/M transition. While for Caco-2 cells, the cell-cycle modulated genes mainly belonged to the cluster of G2 and G2/M transition. Immuno-blotting on the pivotal upstream regulators showed that phosphorylation of ATM at Serine 1981 was significantly increased in both cancer cells. Site-specific phosphorylation of pRB was decreased and phosphorylation of Chk1 was increased in both cancer cells while Chk2 were increased in SW620 cells. Cdc25A was phosphorylated at serine17 in both cancer cells. It can be proposed that the blockage of DNA synthesis or DNA damage was due to the down-regulation of some pivotal DNA replication related proteins such as RPA3, PCNA and MCMs, detected by ATM-Chk1/Chk2-Cdc25A pathway. This would cause the prolonged staying of cells at the G1/S checkpoint which further moved on to S phase arrest for SW620 cells. Moreover the sharply up-regulated p21, an important inhibitor of Cdk2 would further hinder the cells passing the G1/S checkpoint in SW620 cells. / The tumor suppressor p53 was detected phosphorylated at various sites in SW620 but not in Caco-2 cells. In SW620 cells, G2/M arrest was caused by the inhibition of CDK1/CDC2 due to increased expression of GADD45A and p21 and phosphorylation of Cdc25A, while for Caco-2, the G2/M arrest was caused by degradation of Cdc25A due to the absence of p53-activated GADD45A and p21 expression as shown in the pathway finder results. Some apoptosis-related proteins of Bax, Apaf-1 and PARP were modulated as shown by immuno-blotting in both colon cancer cells. (Abstract shortened by UMI.) / Gao, Shane. / Adviser: Peter Chi-Keung Cheung. / Source: Dissertation Abstracts International, Volume: 72-11, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 55-94). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

The damping-off and stem rot disease syndrome is harmful to many cultivated crops. Damping-off and stem rot caused by Sclerotium rolfsii Sacc. on cowpea results in yield losses with serious socio-economic implications. The objectives of the present study were to investigate the occurrence of the diseases in Benin, study etiology and factors influencing the diseases, and develop strategies for the control of the diseases in the field. Results showed that the diseases are distributed countrywide. Sclerotium rolfsii was the main causal agent but minor pathogens, namely Pythium sp., Rhizoctonia solani Kühn and Phoma pomorum Thüm were also recorded. In the Ouémé valley, the diseases were favoured by soil moisture and S. rolfsii initial inoculum that were higher closer to the river. Sclerotium rolfsii isolates collected in the valley showed genetic diversity in terms of pathogenicity, mycelial compatibility groups and ITS rDNA sequences. A paper-based screening method was found to be a rapid laboratory method for screening for resistance in cowpea cultivars. Furtheremore, Moringa oleifera L. leaf extracts, Trichoderma Kd 63 and Trichoderma IITA 508 significantly reduced the disease incidence. The best disease control was recorded in the field when M. oleifera seed treatment was integrated with a soil sprinkle of Trichoderma. The present work provides information on damping-off and stem rot of cowpea in Benin and control strategies for ecologically sustainable cowpea production. / Thesis (DPhil (Microbiology and Plant Pathology))--University of Pretoria, 2006. / Microbiology and Plant Pathology / unrestricted

Stem rot of peanut (Arachis hypogaea L.), caused by a soilborne fungus Athelia rolfsii (Curzi) C. C. Tu and Kimbr. (anamorph: Sclerotium rolfsii Sacc.), is one of the most important diseases in peanut production worldwide. Though new varieties with increased partial resistance to this disease have been developed, there is still a need to utilize fungicides for disease control during the growing season. Fungicides with activity against A. rolfsii are available, and several new products have been recently registered for control of stem rot in peanut. However, fungicides are most effective when applied before or during the early stages of infection. Current scouting methods can detect disease once signs or symptoms are present, but to optimize the timing of fungicide applications and protect crop yield, a method for early detection of soilborne diseases is needed. Previous studies have utilized optical sensors combined with machine learning analysis for the early detection of plant diseases, but these studies mainly focused on foliar diseases. Few studies have applied these technologies for the early detection of soilborne diseases in field crops, including peanut. Thus, the overall goal of this research was to integrate sensor technologies, modern data analytic tools, and properties of standard and newly registered fungicides to develop improved management strategies for stem rot control in peanuts. The specific objectives of this work were to 1) characterize the spectral and thermal responses of peanut to infection with A. rolfsii under controlled conditions, 2) identify optimal wavelengths to detect stem rot of peanut using hyperspectral sensor and machine learning, and 3) evaluate the standard and newly registered peanut fungicides with different modes of action for stem rot control in peanuts using a laboratory bioassay. For Objective 1, spectral reflectance and leaf temperature of peanut plants were measured by spectral and thermal sensors in controlled greenhouse experiments. Differences in sensor-based responses between A. rolfsii-infected and non-infected plants were detected 0 to 1 day after observation of foliar disease symptoms. In addition, spectral responses of peanut to the infection of A. rolfsii were more pronounced and consistent than thermal changes as the disease progressed. Objective 2 aimed to identify specific signatures of stem rot from reflectance data collected in Objective 1 utilizing a machine learning approach. Wavelengths around 505, 690, and 884 nm were repeatedly selected by different methods. The top 10 wavelengths identified by the recursive feature selection methods performed as well as all bands for the classification of healthy peanut plants and plants at different stages of disease development. Whereas the first two objectives focused on disease detection, Objective 3 focused on disease control and compared the properties of different fungicides that are labeled for stem rot control in peanut using a laboratory bioassay of detached peanut tissues. All of the foliar-applied fungicides evaluated provided inhibition of A. rolfsii for up to two weeks on plant tissues that received a direct application. Succinate dehydrogenase inhibitors provided less basipetal protection of stem tissues than quinone outside inhibitor or demethylation inhibitor fungicides. Overall, results of this research provide a foundation for developing sensor/drone-based methods that use disease-specific spectral indices for scouting in the field and for making fungicide application recommendations to manage stem rot of peanut and other soilborne diseases. / Doctor of Philosophy / Plant diseases are a major constraint to crop production worldwide. Developing effective and economical management strategies for these diseases, including selection of proper fungicide chemistries and making timely fungicide application, is dependent on the ability to accurately detect and diagnose their signs and/or symptoms prior to widespread development in a crop. Optical sensors combined with machine learning analysis are promising tools for automated crop disease detection, but research is still needed to optimize and validate methods for the detection of specific plant diseases. The overarching goal of this research was to use the peanut-stem rot plant disease system to identify and evaluate sensor-based technologies and different fungicide chemistries that can be utilized for the management of soilborne plant diseases. The specific objectives of this work were to 1) characterize the temporal progress of spectral and thermal responses of peanut to infection and colonization with Athelia rolfsii, the causal agent of peanut stem rot 2) identify optimal wavelengths to detect stem rot of peanut using hyperspectral sensor and machine learning, and 3) evaluate standard and newly registered peanut fungicides with different modes of action for stem rot control in peanuts using a laboratory bioassay. Results of this work demonstrate that spectral reflectance measurements are able to distinguish between diseased and healthy plants more consistently than thermal measurements. Several wavelengths were identified using machine learning approaches that can accurately differentiate between peanut plants with symptoms of stem rot and non-symptomatic plants. In addition, a new method was developed to select the top-ranked, non-redundant wavelengths with a custom distance. These selected wavelengths performed better than using all wavelengths, providing a basis for designing low-cost optical filters to specifically detect this disease. In the laboratory bioassay evaluation of fungicides, all of the foliar-applied fungicides provided inhibition of A. rolfsii for up to two weeks on leaf tissues that received a direct application. Percent inhibition of A. rolfsii decreased over time, and the activity of all fungicides decreased at a similar rate. Overall, the findings of this research provide a foundation for developing sensor-based methods for disease scouting and making fungicide application recommendations to manage stem rot of peanut and other soilborne diseases.

Incidence and severity of southern blight caused by Sclerotium rolfsii Sacc. is increasing in the mid-Atlantic region of the U.S. affecting both conventional and organic vegetable production systems. Traditional southern blight management relied on fumigants and fungicides with often inconsistent and uneconomical results. Moreover, with the phase-out of methyl bromide, and the high cost and toxicity of other available fumigants, it is necessary to identify effective and economical southern blight management alternatives. Therefore, the objectives of this research were to 1) evaluate the effect of planting date and potato (Solanum tuberosum L.) cultivar selection on southern blight incidence and tuber yield and quality; 2) compare potato cultivar tuber susceptibility to S. rolfsii in post-harvest settings; and 3) assess the suitability of six cool-season cover crop biomasses and three locally organic materials as carbon sources for anaerobic soil disinfestation (ASD) treatments and their impact on S. rolfsii viability and soil. In a three-year field study, ten commercial potato cultivars and four planting dates per year were evaluated on the Eastern Shore of Virginia. Later potato plantings generally produced greater disease incidence (85-94%) and lower tuber yield (1.8-9.4 Mg ha-1) and quality (47-78%), likely driven by humid, warm weather later in the season that was conducive to disease and detrimental to the potato crop. While no potato cultivar was completely immune to S. rolfsii incidence, cultivar 'Accumulator' consistently had one of the lowest disease incidences (12-71%) and greatest tuber yield among cultivars (6.2-37.3 Mg ha-1), and 'Adirondack Blue' and 'Red Norland' had the overall greatest disease incidence (33-100%). Following harvest of the field experiment, the susceptibility of tubers from the ten cultivars to post-harvest rot caused by S. rolfsii was compared in a laboratory experiment under controlled conditions. 'Atlantic' followed by 'Accumulator' were the least susceptible (3.7-12.6 g of diseased tissue) whereas 'Adirondack Blue', followed by red-skinned potato cultivars had the greatest severity of post-harvest tuber rot (12-17.5 g of diseased tissue). Following three weeks of ASD treatments in growth chamber pot experiments utilizing nine carbon sources incubated at 15/25°C 12/12-h cycle, most carbon sources induced soil anaerobicity (33-90 % iron oxide paint removal), but they did not reduce sclerotial viability compared to nonamended aerobic controls. However, most amended soils undergoing ASD induced greater soil microbial activity (0.7-2.0 % CO2 in vol.) compared to nonamended controls (0.1-0.7 CO2 in vol.), increased soil pH, and some amendments increased soil nitrate accumulation. Overall, results of these studies indicate that southern blight can be effectively managed in potato by coupling early planting dates with cultivar selection, but though promising, additional studies are needed to determine the parameters to effectively decrease S. rolfsii viability with ASD treatments. / Doctor of Philosophy / The fungal disease southern blight, caused by the soilborne plant pathogen Sclerotium rolfsii Sacc., is increasing in the mid-Atlantic U.S. The increase of southern blight is likely due to a multitude of issues such as climate fluctuations, reduction in the use of fumigants, increased soil organic matter through conservation practices, and cropping systems that favor soilborne pathogens. Traditional management of S. rolfsii relied on pesticides and fumigants, but control was often inconsistent and expensive. Moreover, the use of some soil fumigants has been restricted due to environmental concerns, which has limited the options for the management of plant pathogens present in the soil, and management alternatives are needed. Through a series of field, laboratory, and greenhouse experiments, this study 1) evaluated the effect of planting date and potato (Solanum tuberosum L.) cultivar selection on southern blight incidence and tuber yield and quality; 2) compared potato cultivar tuber susceptibility to S. rolfsii in post-harvest settings; and 3) assessed the suitability of six cool-season cover crop biomasses and three locally-sourced organic materials as carbon sources in anaerobic soil disinfestation (ASD) treatments and their impact on S. rolfsii viability and soil. Results of a three-year field study demonstrated that an integrated approach to the management of southern blight that utilizes moderately resistant potato cultivars such as 'Accumulator' and early (March to early April) planting dates will minimize risk of disease and maximize tuber yield. Following harvest, inoculation of potato tubers under controlled conditions revealed that the cultivar 'Atlantic' followed by 'Accumulator' can avoid greater losses due to less tuber rot, while 'Adirondack Blue' followed by red-skinned potatoes have a greater risk of suffering post-harvest tuber decay from southern blight. The anaerobic soil disinfestation (ASD) treatments examined in this study indicated that cover crops biomass and poultry litter are suitable carbon sources to induce soil anaerobic conditions, but they may not reduce the survival of S. rolfsii propagules if treatment temperatures are below 25°C. However, ASD showed benefits such as increased activity of soil microbial communities compared to nonamended soil, increased soil acidity, and some amendments such as mushroom compost, poultry litter, and Austrian winter pea (Pisum sativum subsp. arvense) can contribute soil nutrients such as nitrate. Overall, this research demonstrates that choosing less susceptible cultivars coupled with early planting dates can minimize the negative impact of southern blight on potato yields and quality, and consequently minimize the use of pesticides as the main option to control southern blight on potato across the mid-Atlantic region. Though promising, additional studies are needed to determine the parameters that optimize ASD as an alternative to manage S. rolfsii with ASD treatments.