Salmonella has been shown to survive in soils for extended periods. Anaerobic soil disinfestation (ASD) represents a promising alternative to fumigation used to manage soilborne diseases and pests; however, little is known about ASD's impact on Salmonella. The study aimed to compare Salmonella die-off following inoculation in ASD and non-ASD processed soil and compare Salmonella die-off in amended and non-amended soils following ASD. Two independent experiments were arranged in randomized complete block designs (four replications per treatment). Sandy-loam soil was inoculated with a Salmonella cocktail (5.5±0.2 log CFU/g) and amended with field-applicable rates of rye (R), rapeseed (RS), hairy vetch (HV), or pelletized poultry litter (PPL). Non-amended, anaerobic (ANC) and non-amended, aerobic controls (AC) were performed in parallel. Soils were irrigated to saturation and covered with plastic mulch. ASD was terminated by removal of plastic (3-weeks). Triplicate soil samples were collected pre-ASD and 0, 1, 2, 3, 7, 10, 14, 21, 28, 31, 35, 38 and 42d post-ASD. Post-ASD soil was irrigated weekly. Salmonella was quantified using standard methods and a modified MPN enrichment protocol. Concentrations between treatments and time-points were analyzed for significance (P≤0.05). Separate log-linear models were used to examine effect of amendment and irrigation on Salmonella die-off during ASD and post-ASD. Salmonella concentrations decreased in all treatments during ASD with the greatest decrease being observed in ASD and non-ASD controls. Among ASD-processed, amended soil, the rye and rapeseed amendments had the greatest decrease in Salmonella concentrations. Salmonella concentrations decreased by ~1 log between pre-ASD and post-soil saturation (95% Confidence Interval (CI) =-1.31, -0.99), and by approximately 2 logs between pre-ASD and termination of ASD (CI=-2.14, -1.83). Salmonella concentrations were ~1 log higher in ASD-processed, pelletized poultry litter-amended soil, compared to the ASD control (CI=0.81, 1.26). The average daily die-off rate of Salmonella post-ASD was -0.05 log per g (CI=-0.05, -0.04). Following irrigation, Salmonella concentrations were 0.14 log greater, compared to no irrigation within 7 d (CI=0.05, 0.23). Salmonella serovar distribution differed by treatment, with >70% survival of Newport in pelletized poultry litter. ASD does not eliminate Salmonella concentrations in soil; instead some amendments may enhance Salmonella survival. / Master of Science in Life Sciences / Anaerobic soil disinfestation (ASD) is the process of removing soilborne weeds, soilborne diseases and insect by creating an anaerobic environment in the soil by incorporating easily decomposable soil amendments, covering with plastic mulch, and irrigating to saturation. The anaerobic soil environment persists for two- to six-weeks. ASD represents a promising alternative to fumigation used to manage soil-borne diseases and pests. However, little is known about ASD's impact on Salmonella, which has been shown to survive in soils for extended periods of time and can contaminate the edible part of produce. This study aimed to determine if ASD is an effective strategy to reduce or eliminate Salmonella from soils that contain typical amendments added to promote soil health, determine the distribution of Salmonella serovars in ASD treated soils, and examine the impact of irrigation. Two independent experiments were conducted in growth chambers. A common soil type in produce growing regions of the Eastern Shore of VA, sandy-loam soil was inoculated with a five-serovar Salmonella cocktail (~5.5±0.2 log CFU/g) and mixed with field-applicable rates of rye, rapeseed, hairy vetch, or pelletized poultry litter. ASD processed soils were irrigated to field saturation, covered with plastic mulch, and left for 3 weeks. Post-ASD, soils were irrigated weekly. Salmonella was quantified at least once per week for up to 6 weeks in soil samples collected in triplicate pre-ASD, post-field saturation, and post-ASD. The three-week anaerobic soil environment, created during ASD, allowed for greater Salmonella survival, compared to the aerobic soil environment. Salmonella survival in ASD processed soil was dependent on amendment. Salmonella concentrations decreased in all treatments during ASD with the greatest decrease being observed in ASD and non-ASD controls. Among ASD-processed, amended soil, the rye and rapeseed amendments had the greatest decrease in Salmonella concentrations. Pelletized poultry litter amended soil, in combination with ASD, had the highest Salmonella concentration, while rye had the lowest at each time-point post-ASD. Salmonella serovar distribution differed by treatment with greater survival of S. Poona in rye, S. Braenderup in hairy vetch and S. Newport in pelletized poultry litter. , Salmonella concentrations were 0.14 log greater, compared to no irrigation within 7 d. Overall, ASD did not eliminate Salmonella in soils. Compared to non-ASD processed soil, ASD processed soil had greater survival of Salmonella and the soil amendment used influenced the survival ability. While more research is needed on ASD and different soil amendments, the findings of this research would suggest pelletized poultry litter not be used as an amendment (i.e., carbon source in ASD) for fields used to grow produce eaten raw, especially when soils are potentially contaminated with Salmonella.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/106636 |
| Date | 21 May 2020 |
| Creators | Marik, Claire Margaret |
| Contributors | Food Science and Technology, Strawn, Laura K., Eifert, Joseph D., Ponder, Monica A. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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