Addition of Soil Protists Enhances Performance of Agrochemical Seed Treatments

Chemicals are an integral part of modern agriculture, and are applied through a variety of methods. Some agrochemicals applied for crop protection function by absorption through the root before translocation to the rest of the plant. To be absorbed by the root, the agrochemical must first be transported through the soil, often by water. Some agrochemicals suffer from poor water-based soil transmission due to their chemical properties, limiting their application as a traditional seed treatment. Two such agrochemicals are chlorantraniliprole and spinosad. Soil protists are an important component of the soil microbial community. Certain soil protists have been previously shown to facilitate transport and targeted delivery of suspended particles and cells through soil and microfluidic devices. We provide practical evidence that a soil protist, Colpoda sp., when co-inoculated with an agrochemical seed treatment, can substantially and robustly reduce subsequent pest feeding damage compared with the agrochemical alone. Using maize (Zea mays L.) and fall armyworm, Spodoptera frugiperda (J. E. Smith, 1797) (Lepidoptera: Noctuidae), in a plant damage assay, we directly compare pest feeding damage and mortality in plants that received no additional treatment, only protists, only agrochemical, and co-inoculation of agrochemical with protists. We discover for both agrochemicals tested, the co-inoculation of protists with the agrochemical increases protection in leaves when the efficacy of the agrochemical alone declines. Protist amendment is a simple, natural, inexpensive, chemical-free, soil-based transport enhancer that thus may be widely useful in a variety of contexts including more sustainable and cost-effective integrated pest management. ImportancePest resistance, regulatory pressure, and environmental concerns are limiting many classes of pesticides which can be effectively used to protect valuable crops from pests. Other classes of pesticides, however, are limited by physical characteristics - water solubility or octane-water partition coefficient (KOW) fall outside the limit for an effective seed coating, or the per-unit cost is high enough to discourage broad application. Here, we provide data which supports the co-inoculation of a high value, low solubility, high KOW pesticides with a naturally-occurring soil protist as a seed treatment can enhance crop protection relative to the pesticide alone. This co-formulation reduced feeding damage by up to 30% compared with the pesticide alone. Co-inoculation of crop-protecting agrochemicals with natural soil protists may be employed as a more sustainable agriculture biotechnology, enabling the use of classes of agrochemicals which may not otherwise show sufficient performance for use as a seed treatment.