Factors affecting susceptibility to - and management of - postharvest soft rot of sweetpotatoes caused by Rhizopus stolonifer.

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dc.contributor.advisor James W. Moyer, Committee Member en_US
dc.contributor.advisor D. Michael Benson, Committee Member en_US
dc.contributor.advisor Gerald J. Holmes, Committee Chair en_US
dc.contributor.advisor Lee-Ann Jaykus, Committee Member en_US
dc.contributor.author Edmunds, Brooke Aurora en_US
dc.date.accessioned 2010-04-02T19:00:22Z
dc.date.available 2010-04-02T19:00:22Z
dc.date.issued 2008-11-25 en_US
dc.identifier.other etd-08112008-152749 en_US
dc.identifier.uri http://www.lib.ncsu.edu/resolver/1840.16/4748
dc.description.abstract Studies were undertaken to explore the relationship of R. stolonifer susceptibility with preharvest growing conditions and postharvest handling of sweetpotatoes. Additional studies were also completed to identify effective decay control products. A three-year study investigated the effect of preharvest conditions on R. stolonifer and Erwinia chrysanthemi susceptibility. Roots were harvested from 75 sweetpotato fields and information collected including soil samples, weather during the growing season, weed density, and insect injury (153 predictors). Roots were inoculated after 100 days in storage. Mean R. stolonifer incidence was 34.9% (standard deviation=31.7%) and mean E. chrysanthemi incidence was 51.0% (standard deviation=30.5%). Predictive models were developed using forward stepwise regression to identify predictors of interest, followed by mixed model analysis (p-value<0.05) to produce a final model. R. stolonifer susceptibility is best predicted by soil calcium (% CEC), plant-available soil phosphorus, soil humic matter (%), mean air temperature, mean volumetric soil moisture at 40 cm, and mean soil temperature at 2 cm (all over the growing season). E. chrysanthemi susceptibility is best predicted by soil pH and days that soil temperature exceeds 32 ºC (14 days pre- harvest). Studies were also conducted to define the relationship between postharvest handling and susceptibility to R. stolonifer. Experiments designed to simulate packingline handling found root ends are more susceptible that mid-sections and that increasing the number of time a root is dropped as well as increasing the impact force resulted in increased decay susceptibility. ‘Hernandez’ roots were significantly more susceptible than ‘Beauregard’ in all experiments. To confirm the relationship of impacts and disease development, Beauregard roots were sampled from locations along commercial packinglines. High decay in inoculated as compared to non-inoculated roots indicates that wounding is occurring that could result in disease if the pathogen was present at higher levels. Evaluations of reduced-risk fungicides, bio-fungicides and generally recognized as safe products for efficacy against R. stolonifer found that reduced-risk chemistries boscalid+pyraclostrobin and fludioxonil significantly reduced R. stolonifer development and performed similarly to dicloran. Pseudomonas syringae based products were moderately effective although results were extremely variable among tests. Generally recognized as safe treatments were ineffective by testing methods used. en_US
dc.rights I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dis sertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. en_US
dc.subject disease en_US
dc.subject postharvest en_US
dc.subject sweetpotatoes en_US
dc.title Factors affecting susceptibility to - and management of - postharvest soft rot of sweetpotatoes caused by Rhizopus stolonifer. en_US
dc.degree.name PhD en_US
dc.degree.level dissertation en_US
dc.degree.discipline Plant Pathology en_US

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