Sudden death syndrome (SDS) of soybean is responsible for important yield losses in Iowa and the Midwest. Annual yield losses due to SDS have reached 1.9 million metric tons in the US, with cumulative economic losses over 2.5 billion dollars for 1996-2016 in Iowa alone (Bandara et al. 2020). The disease is caused by Fusarium virguliforme, a soil-borne fungus that causes root rot and premature defoliation.
SDS management strategies rely primarily on the use of resistant soybean varieties and fungicide seed treatments. Neither approach is completely effective at suppressing SDS. Two fungicide seed treatments are currently available to manage SDS: ILeVO (fluopyram) and Saltro (pydiflumetofen). However, these treatments are expensive and may not result in economic profit to growers in years when weather conditions are not conducive to SDS development. In addition, ILeVO treatments are known to cause phytotoxicity in soybean seedlings, which can negatively impact root growth and sometimes reduce yield (Budi, 2020). Phytotoxicity problems are also known to occur with other fungicides, such as Topguard (flutriafol). Although this fungicide is labeled for SDS, it is not used by growers due to the lack of a safe application method that prevents plant stand loss from phytotoxicity. In this proposal, we hypothesize that treating seeds with a reduced rate of fungicide, in combination with another antimicrobial treatment, would reduce the risk of phytotoxicity without compromising SDS control.
Nanotechnology is being explored as a pesticide delivery system that can enhance the efficacy of pesticide and reduce pesticide use. Nano-emulsion is widely used to encapsulate biopesticides such as essential oils. With this technology, pesticides are encapsulated in nano-emulsions which have droplet size within ranges of 1~100 nanometers. These nano-emulsions provide many advantages, including increased stability, controlled release and higher absorption rates of the encapsulated active compounds. Due to these benefits, nano-emulsions have been widely applied as vehicles for delivery of active compounds in several fields, including drugs, food, and agriculture. Unfortunately, not all compounds can be nano-encapsulated because of their chemical structure or properties. The fungicides in ILeVO, Saltro, and Topguard cannot be nano-encapsulated due to their extremely low water or oil solubility. For that reason, we are proposing to use nano-encapsulated biopesticides as the antimicrobial treatment to combine with the reduced rate of commercially fungicides.
Biopesticides are materials with pesticidal properties that originate from plants, animals, and microorganisms. They are promising crop protection options because they are safer and more environmentally friendly than their chemical counterparts. Plant essential oils are a type of biopesticide that has shown effectiveness against several plant pathogens and pests. For example, lemongrass oil reduced Fusarium solani growth in vitro, reduced root rot incidence by up to 45% in petri dish assays, and doubled soybean root length and shoot length in greenhouse assays (Eke et al. 2020). Thymol essential oil was also effective in inhibiting F. solani in petri dish assays (Kong et al. 2021). Although we are not aware of studies on the effectiveness of these essential oils specifically against SDS, these are promising results since F. solani is a closely related species to F. virguliforme. In addition, lemongrass and thymol essential oils have been effective in reducing disease caused by several other plant pathogens, including Phytophthora root rot in curcubits (Amini et al. 2016) and bacterial pustule in soybean (Kumari et al., 2018), respectively.
Nano-encapsulation of biopesticides can increase their efficacy by up to ~20% (Kah et al., 2018), reduce their cost, protect them from adverse environmental conditions (Blanco-Padilla et al., 2014) and allow better control of their release (Mossa et al., 2018). Nanocellulose is an organic nanomaterial that is nontoxic, biodegradable, and an effective nanoencapsulation agent for natural antimicrobials, drugs, and bioactive compounds. Due to the increasing demand for soy-based products, large amounts of soybean residues are generated every year (Costa et al., 2015; Li et al., 2019). Soybean residues have a cellulose content of up to 50% and are therefore great, low-cost sources of nanocellulose. We propose to use nanocellulose derived from soybean residues to encapsulate the biopesticides in this study.
Goal: The overall goal of this project is to enhance soybean productivity, profitability and environmental sustainability by combining fungicide seed treatments with nano-encapsulated biopesticides using soybean residue-derived nanocellulose as carriers.