Influence of Fusarium virguliforme Temporal Colonization of Corn, Tillage, and Residue Management on Soybean Sudden Death Syndrome and Soybean Yield.

The asymptomatic host range of Fusarium virguliforme includes corn, a common crop rotated with soybean that we hypothesize may alter F. virguliforme population dynamics and disease management. A field-based approach explored the temporal dynamics of F. virguliforme colonization of corn and soybean roots under different tillage and residue managements. Experiments were conducted in Iowa, Indiana, Michigan, and Wisconsin, United States and Ontario, Canada from 2016 to 2018. Corn and soybean roots were sampled at consecutive timepoints between 1 and 16 weeks after planting. DNA was extracted from all roots and analyzed by real-time quantitative PCR for F. virguliforme quantification. Trials were rotated between corn and soybean, containing a two-by-two factorial of tillage (no-tilled or tilled) and corn residue (with or without) in several experimental designs. In 2016, low amounts (approximately 100 fg per 10 mg of root tissue) of F. virguliforme were detected in the inoculated Iowa, Indiana, and Michigan locations and noninoculated Wisconsin corn fields. However, in 2017, greater levels of F. virguliforme DNA were detected in Iowa, Indiana, and Michigan across sampling timepoints. Tillage practices showed inconsistent effects on F. virguliforme root colonization and sudden death syndrome (SDS) foliar symptoms among trials and locations. However, residue management did not alter root colonization of corn or soybean by F. virguliforme. Plots with corn residue had greater SDS foliar disease index in Iowa in 2016. However, this trend was not observed across the site-years, indicating that corn residue may occasionally increase SDS foliar symptoms depending on the disease level and soil and weather factors.

Economic Impact of Fluopyram-Amended Seed Treatments to Reduce Soybean Yield Loss Associated with Sudden Death Syndrome.

Soybean (Glycine max) sudden death syndrome (SDS), caused by Fusarium virguliforme, is a key limitation in reaching soybean yield potential, stemming from incomplete disease management through cultural practices and partial host resistance. A fungicidal seed treatment was released in 2014 with the active ingredient fluopyram and was the first chemical management strategy to reduce soybean yield loss stemming from SDS. Although farm level studies have found fluopyram profitable, we were curious to discover whether fluopyram would be beneficial nationally if targeted to soybean fields at risk for SDS yield loss. To estimate economic benefits of fluopyram adoption in SDS at-risk acres, in the light of U.S. public research and outreach from a privately developed product, we applied an economic surplus approach, calculating ex ante net benefits from 2018 to 2032. Through this framework of logistic adoption of fluopyram for alleviation of SDS-associated yield losses, we projected a net benefit of $5.8 billion over 15 years, considering the costs of public seed treatment research and future extension communication. Although the sensitivity analysis indicates that overall net benefits from fluopyram adoption on SDS at-risk acres are highly dependent upon the market price of soybean, the incidence of SDS, the adoption path, and ceiling of this seed treatment, the net benefits still exceeded $407 million in the worst-case scenario.

Direct colorimetric detection of unamplified pathogen DNA by dextrin-capped gold nanoparticles.

The interaction between gold nanoparticles (AuNPs) and nucleic acids has facilitated a variety of diagnostic applications, with further diversification of synthesis match bio-applications while reducing biotoxicity. However, DNA interactions with unique surface capping agents have not been fully defined. Using dextrin-capped AuNPs (d-AuNPs), we have developed a novel unamplified genomic DNA (gDNA) nanosensor, exploiting dispersion and aggregation characteristics of d-AuNPs, in the presence of gDNA, for sequence-specific detection. We demonstrate that d-AuNPs are stable in a five-fold greater salt concentration than citrate-capped AuNPs and the d-AuNPs were stabilized by single stranded DNA probe (ssDNAp). However, in the elevated salt concentrations of the DNA detection assay, the target reactions were surprisingly further stabilized by the formation of a ssDNAp-target gDNA complex. The results presented herein lead us to propose a mechanism whereby genomic ssDNA secondary structure formation during ssDNAp-to-target gDNA binding enables d-AuNP stabilization in elevated ionic environments. Using the assay described herein, we were successful in detecting as little as 2.94 fM of pathogen DNA, and using crude extractions of a pathogen matrix, as few as 18 spores/µL.