Degree Type

Thesis

Date of Award

2020

Degree Name

Master of Science

Department

Plant Pathology and Microbiology

Major

Plant Pathology

First Advisor

Gary P Munkvold

Abstract

Fusarium graminearum is a soilborne and seedborne pathogen widely distributed in agricultural areas all over the planet. It can cause serious damage on several economic crops, such as maize, wheat, and soybean. The main tactics to manage diseases caused by this fungus are to plant resistant varieties, apply fungicides, and to plant fungicide-treated seeds.The importance of seed treatments has increased rapidly in the past decade, mainly due to their high efficacy controlling early-season pests and diseases, and due to their reduced environmental impact. If chemicals are applied as seed treatments, less pesticide is used and applied in the environment, and the selection pressure for the development of resistance in the pest population is much lower as well, compared to foliar or soil applications. However, the rapid dissipation of active ingredients after planting is associated with unpredictability about the effective duration of control, limiting the performance of this technology. Polyanhydrides are carbon polymers that can be used to deliver active ingredients or pharmaceuticals in pathology systems. They can promote a steady release of active compounds, enhancing the treatment of diseases and pathogens. Therefore, this research addresses one of the main limitations of seed treatment technology by using polyanhydride polymers to encapsulate two fungicides commonly used against F. graminearum: fludioxonil and thiabendazole.

In order to study these two encapsulated fungicides, we performed two types of assays on maize and soybean: a rolled-towel assay (simulating a seedborne infection) and a delayed emergence assay (simulating a soilborne infection). The rolled-towel assay is similar to a germination test, with additional inoculation and fungicide treatment steps. Fifteen seeds per replicate are placed on towels and incubated for seven days at 24°C. For the delayed emergence assay, ten seeds per treatment were planted in infested field soil and incubated in four different environments for four weeks. Each environment had a specific number of weeks at a non-emergence condition (10°C), to simulate a delayed emergence scenario. Our results suggest no evidence of enhanced efficacy for the full rate nanoparticle-encapsulated treatments against this pathogen for the rolled-towel assay. However, the half rate nanoparticle-encapsulated treatments performed similarly to the full rate nanoparticle and full rate conventional fungicide. In the delayed emergence assay, the nanoparticle formulations performed better than conventional active ingredient formulations in the treatment with a 1-week delay in emergence only. For longer emergence delay treatments, nanoparticle and conventional fungicide treatments showed similar levels of control. Additionally, a storage assay was performed to assess the stability of nanoparticle formulation efficacy. Our results suggest a similar level of storability compared to the conventional fungicides, measured over a 5-month storage period. Release kinetics assays were conducted to assess the pattern of release of the nanoparticle-encapsulated treatments used in this research. Results showed a high burst in the first few hours, reaching above 40% of the total amount of active ingredient independently of the temperature. In conclusion, polyanhydride nanoparticle encapsulation of fungicide seed treatments showed potential to provide enhanced efficacy and prolonged release of active ingredients when emergence is delayed due to cold temperatures. However, more research is needed on the dynamics of active ingredient release in soil under different environmental settings. Hence, more bioassays can be designed to evaluate employment of other chemicals and different types of pesticides, such as insecticides. The combination of different polyanhydride formulations carrying different pesticides could revolutionize how integrated pest management is implemented through seed treatments.

DOI

https://doi.org/10.31274/etd-20200624-62

Copyright Owner

Fernando Mauri Marcos

Language

en

File Format

application/pdf

File Size

74 pages

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