Author ORCID Identifier

Year of Publication


Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation


Agriculture, Food and Environment


Plant Pathology

First Advisor

Dr. Paul Vincelli


Organic farming is an ever-increasing segment of tomato production. Currently, limited information is available which directly compares conventional to organic treatment programs for disease control in tomato production. Furthermore, many methods available rely on the use of copper products which may be contribute to high Cu levels in agricultural soils. In this study, the efficacies of current conventional and organic methods were compared. In addition, newer disease-control programs, with and without copper were examined, which potentially could reduce over-reliance on copper products.

Standard organic and conventional spray programs were conducted over a four year period targeting two pathogens, Alternaria tomatophila (tomato early blight) and Xanthomonas euvesicatoria (tomato bacterial spot). Both programs contained a copper product (Nordox). Field trials with these programs were found to reduce the disease severity of both pathogens. Additionally, these two programs were not distinguishable statistically (p> 0.05) throughout the four years.

Subsequently, in a tomato high tunnel study, alternative bioproducts to copper were used to control powdery mildew (Oidium neolycopersici). These alternatives included a Bacillus sp. product and a novel microbial fermentation product (MFP). Although the Bacillus sp. treated tomatoes had statistically (p< 0.05) similar to the copper product, making it a viable candidate for further study.

The MFP was further investigated in an open field setting against X. euvesicatoria. The MFP and copper product were used in single product spray programs as well as tank-mixed with each other. In these field trials, as opposed to the high tunnel studies, although MFP treatment resulted in statistically (p< 0.05) better than either isolated product alone, indicating possible antagonistic behavior.

To understand these differences in efficacy of the MFP against O. neolycopersici and X. euvesicatoria, possible modes of action (MOA) were examined. A lack of detectable fast-growing organisms within the MFP indicated the MOA was likely not associated with either competition or hyperparasitism. Alternatively, MFP inhibited spore germination in Botrytis cinerea, Magnaporthe oryzae, and Colletotrichum higginsianum and reduced mycelial expansion in B. cinerea, Sclerotinia sclerotiorum, and C. higginsianum in-vitro assays indicating antibiosis/antimicrobial properties. MFP also reduced bacterial growth of X. euvesicatoria and Pseudomonas syringae at 8% concentration or higher in liquid culture. Northern blot and RNA-seq results indicate possible plant defense induction from the application of MFP at 8% v/v.

Results of these studies indicate that the MFP may be a potential alternative to copper in tomato cropping systems. However, the MFP’s efficacy appears limited based on either the environment or the target pathogen. Further investigation revealed the possibility of multiple MOAs. The primary mode of action appears to be an antibiosis/antimicrobial effect which may differ based on the resistance of the target pathogen. The secondary MOA may be induction of plant defense genes.

Digital Object Identifier (DOI)

Available for download on Friday, May 05, 2023