Charcoal rot of soybean is an important disease affecting soybean. Charcoal rot is caused by the ubiquitous soilborne fungus Macrophomina phaseolina (Tassi) Goid. The fungus infects over 500 plant species. Although charcoal rot occurs primarily under drought-like conditions, it has also been reported in high-yield irrigated soybean environments. Symptoms of charcoal rot on soybean include wilting, stunting, and premature death. Management options to reduce charcoal rot-associated losses are limited. The objective of this research was to reduce M. phaseolina colonization of soybean by supplementing with secondary nutrients, specifically calcium and magnesium; therefore, reducing the concentration of the associated toxin, and determine if isolates of M. phaseolina from non-soybean hosts are pathogenic on soybean and rotational hosts. Between 2014 and 2016, non-irrigated, M. phaseolina-inoculated field and field replicate greenhouse experiments evaluated applications of 1,120 kg/ha of Ca and Mg alone and in combination at pre-plant, at-plant, and pre-plant followed by at-plant compared with an inoculated and non-inoculated. Disease ratings were visually assessed from roots collected at R3, R5, R7, and R8. Colony forming units (CFU) were used to quantify fungal colonization in root tissue. Gas chromatography mass spectrometry was used to quantify the concentration of botryodiplodin, a toxin previously associated with charcoal rot from root tissue. An application of calcium applied pre-plant provided the greatest numerical reduction, 39.7%, in toxin concentration and also reduced disease severity by 1.0% and CFUs by 15.4% when compared to the inoculated control in a moderately resistant cultivar. Although numerical benefits were observed, these data do not support applications of Ca and Mg as a charcoal rot management option. Numerical differences were observed between rotational hosts and isolates in pathogenicity studies. The greatest numerical reduction of 34% in soybean dry plant weight was observed with the corn isolate when compared to the non-inoculated control. Macrophomina isolates from corn had up to an 8% greater colonization in soybean than corn or cotton plants. Although no significance was observed between isolates with regard to dry plant weight and colonization, colonization occurred regardless of treatment; suggesting crop rotation should not be a stand-alone charcoal rot management option.

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Lettuce (Lactuca sativa L.) seedlings diseases caused by soilborne pathogens are characterised by root rot, stem rot and damping-off of the seedlings that can occur at any time during growth. Fusarium solani, Pythium ultimum and Rhizoctonia solani are known to be the important destructive pathogens of lettuce, causing severe yield losses in South Africa. The aim of this research was to evaluate the effects of three selected fungicides to control these pathogens on lettuce seedlings. In this study the fungicides metalaxyl (Apron®), fludioxonil (Celest®) and mefenoxam (Subdue®) were applied at two concentrations as single and double doses on lettuce seedlings to determine their efficacy to control the pathogens Fusarium solani, Pythium ultimum and Rhizoctonia solani after significant reduction of mycelia growth was observed in vitro. Cultures of P. ultimum (UPGH024), R. solani (UPGH122) and F. solani (UPGH122) were obtained from the culture collection of the Department of Microbiology and Plant Pathology, University of Pretoria and cultivated on PDA for 2 days at 25ºC. Pasteurised soil was artificially inoculated with these pathogens. For the first experiment lettuce seeds were planted in polystyrene seedling trays at a depth of 1.0 cm. There were four replications of 50 seeds per treatment. In Experiment 2 pots (12 cm x 7 cm) were filled with pasteurised growing medium and 3-week old seedlings were transplanted. There were three replications of six pots containing three plants each. Seedling trays and pots were drenched with fungicides and placed in a randomised block design in a controlled environment room at 20- 26°C with a 12h-light/dark regime. The seedling trays and pots were rotated daily in the room. Seedling trays and pots were watered daily to maintain field capacity. The seedlings were able to grow larger in the pots than in seedling trays. It was confirmed that the treatment with fludioxonil (Celest®) at double and single dose inhibited the growth of the three fungi F. solani, P. ultimum and R. solani on lettuce seedlings without causing phytotoxicity. All three fungicides significantly reduced the diseases caused by the three pathogens. These findings are consistent with previous reports that fludioxonil, metalaxyl and mefenoxam can control oomycete fungi. There are few registered fungicides for the control of Fusarium solani, Pythium ultimum and Rhizoctonia solani on lettuce, therefore further work will aim to confirm these results in the field. / Dissertation (MInstAgrar)--University of Pretoria, 2008. / Microbiology and Plant Pathology / unrestricted

This project focuses on the conceptual design of the spin rotator for a proposed electron polarization upgrade of the SuperKEKB. The goal is to achieve the longitudinal electron polarization at the interaction point (IP). In this design, four existing dipoles will be replaced with four rotator magnets on both sides of the IP. The rotator magnet structure consists of dipole-solenoid combined function magnets with skew-quadrupoles installed on top to decouple the x-y plane. The advantage of this design is that the original machine geometry is maintained, and the original machine can be recovered by turning off the solenoid-quadrupole in the rotator magnet. With Bmad, a powerful lattice simulation tool applied to perform the optimizations for this design, the longitudinal spin alignment at the IP reaches a significantly high level, greater than 99.99%. Furthermore, the influence of the installation of the spin rotator on the original machine dynamics is minimized to an acceptable level. / Graduate

Two endemic late-season grape rot diseases, ripe rot and sour rot continue to pose a significant challenge to grape growers in Virginia and similar climates. Managing these diseases in the vineyard is challenging due to concerns over the increased risk of resistance against traditional single-site mode of action pesticides. This study evaluated the efficacy of different biopesticides and novel chemical options with a series of field trials across four vineyards in northern Virginia in 2021 and 2022. Among the tested products, a potassium-based nutrient formulation resulted in consistent ripe rot suppression in two of the three trials, showing around 46% and 83% less mean disease severity at the AHS AREC trial in 2022 and 2021, respectively, and 63% and 19% less mean disease incidence at the South Loudoun trial in 2021 and AHS AREC trial in 2022. For sour rot, zeta-cypermethrin with cyprodinil + fludioxonil or hydrogen peroxide + peroxyacetic acid resulted in effective control in two of the five trials, with a high of 71% and 73% less mean disease incidence compared to the untreated check in the Frederick trial in 2021 and 2022, respectively. In general, treatments with spinosad were less effective and resulted in lower disease control compared to those with zeta-cypermethrin and its fungicides/antimicrobials counterpart. The results suggest that integrating these biopesticides and novel chemicals into a spray program could offer a more sustainable solution for sour rot and ripe rot disease management without compromising the level of disease control. / Master of Science in Life Sciences / Ripe rot and sour rot are two diseases of concern for growers in Virginia and many other grape-growing regions due to significant losses in fresh cluster yield and the risk of contamination during the winemaking process. Traditional pesticides are often used; however, the breakdown of the effectiveness of these pesticides after continuous application, i.e., pesticide resistance, has become a critical issue. The other issues include, but are not limited to, adverse effects on human health, nature, and winemaking. On the other hand, biopesticides derived from microorganisms, their products, plant extracts, etc., are considered relatively safer and more sustainable options. This study evaluated the efficacy of biopesticides and novel chemicals against ripe rot and sour rot through field trials over two years at four locations in northern Virginia. Although no clear-cut winners were among the tested treatments, one of the tested chemicals (a potassium-based plant nutrient formulation) provided consistent disease suppression (up to 83%) against ripe rot. In the case of sour rot, several treatments, including a biologically derived insecticide, produced comparable disease suppression (up to 73%) compared to the current standard application. These safer options can be included in the spray schedule without compromising the level of disease control, meanwhile aiding the sustainability of the spray program in the long run.

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The effects of photoperiod, drought stress and cold storage treatments on the susceptibility of strawberry plants (Fragaria ananasa x Duch.) cvs. Tamella, Cambridge Favourite and Red Gauntlet to crown rot caused by Phytophthora cactorum (Leb. and Cohn.) Schroet. were studied. Infection and disease susceptibility were assessed by; a) the time from inoculation to first symptom appearance; b) measurement of crown necrosis; c) measurement of fungal colonisation by a comminution-colony count method developed during the study; d) detached leaf bioassay. The effect of photoperiod was assessed independently from photosynthetically active radiation and long day treatments consistently increased susceptibility; a result contradicting previous findings. Drought treatments applied prior to inoculation generally increased plants' resistance to colonisation and necrosis. Treatments applied after inoculation significantly reduced the level of colonisation capable of causing wilt symptoms. Cold storage treatments increased the susceptibility of plants to infection, colonisation and wilt symptom development. Susceptibility to infection by normally non-pathogenic isolates was also increased by cold treatments although no wilt symptoms resulted from these infections. Plants stored with latent infections developed immediate chronic symptoms when transplanted from cold storage. The mortality of these plants in the cold store also increased with storage time. Cold storage-enhanced susceptibility occurred irrespective of pathogen factors. Large-scale sudden collapse of cold-stored strawberry stands was caused by carriage of oospores through storage, either in soil or in scattered latent infections. P. cactorum produced the cell wall degrading enzymes (CWDEs) exo 1,4--galactanase and endo polygalacturonase in culture. Both enzymes were detected in infected plants. CWDE activities increased with colonisation and symptoms, and levels of PG and galactanase were significantly greater in cold-stored tissues than in controls but their importance in symptom expression and virulence was not conclusively demonstrated.

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