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.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/112654 |
| Date | 25 May 2021 |
| Creators | Garcia Gonzalez, Jose Francisco |
| Contributors | Plant Pathology, Physiology and Weed Science, Rideout, Steven L., Langston, David B., Mehl, Hillary L., Strawn, Laura K., Baudoin, Antonius B., Reiter, Mark S. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Coverage | United States |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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