Author ORCID Identifier

Year of Publication


Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation


Agriculture, Food and Environment


Plant and Soil Sciences

First Advisor

Dr. Seth DeBolt


Biologicals are increasingly becoming an important part of sustainable integrated pest management in agricultural crop production and encompass a wide variety of products with varying degrees of efficacy and available research data. As biologicals become more integrated into commercial production systems, it is critical to rigorously evaluate biological product efficacy and mode(s) of action in crops. The better that biologicals are understood in terms of effective application, integration into commercial programs, and their specific mechanisms in crop growth and protection, then the greater the opportunity for increasing yields and food security.

ACS811 is a microbial fermentation-based biological product from Alltech Crop Science. The active ingredients include fermentation media from a proprietary strain of Lactobacillus acidophilus and yeast cell wall extract from a proprietary strain of Saccharomyces cerevisiae and also contains a small percentage of yucca extract. Preliminary data suggest that application of ACS811 to crops induces plant defense responses. The treated plants display reduced disease severity in subsequent disease pressured environments. The objectives of this research were to evaluate the efficacy of ACS811 in reducing disease severity and improving yields of field grown tomatoes, and to investigate the molecular defense responses in the treated plants.

Field trials conducted over three years at the University of Kentucky Horticulture Research farm evaluated efficacy, optimal rates, and application frequency of ACS811 in field-grown tomatoes. Importantly, the 2018 trials showed no phytotoxic effects of ACS811 application to tomatoes at any rate. In 2019 trials switched to focus investigation on the efficacy of ACS811 in tomato disease reduction. Here, a 56% reduction in powdery mildew in treated plots (p-value < 0.001) was observed. Septoria leaf spot severity in treated plots was also significantly reduced by 22% (p-value = 0.023). Data from the 2020 trials evaluated the optimum application frequency of ACS811 both within and outside of the context of a commercial pesticide program. There was a 1.85% reduction in plant disease severity (consisting primarily of Septoria Leaf Spot) in a mid-season scoring in the commercially treated field in plots treated with ACS811 every 7-10 days (p-value = 0.0237).

To gain a mechanistic understanding, leaf samples from the 2019 field trial were collected following the initial treatment and transcriptionally profiled with RNA-sequencing. Results showed that at one hour treated plants responded with robust stress-related signaling, including up-regulation of ethylene, calcium ion, and reactive oxygen species signal pathways. Interestingly, the response is moderated via ROS remediation and regulation of programmed cell death initiators. At approximately 24 hours, treated plants shift to more systemic, long term stress tolerance and defense priming. This includes key biochemical and transcriptional players in Systemic Acquired Resistance (SAR) and Pattern Triggered Immunity (PTI) defense responses. Together, ACS811 effectively induces plant defenses, but in such a way that does not overly stress the plant or result in programmed cell death at this rate in tomatoes. Thus, no yield drag has been documented as a result of ACS811 application in three years of field collection. The resulting disease resistance state of the treated plant provides a broad-spectrum biotic stress resistance, reducing disease-related yield losses.

Digital Object Identifier (DOI)

Funding Information

This research was supported by Alltech (Nicholasville, KY, USA) from 2017-2021.

Available for download on Friday, December 08, 2023