First Report of Fusarium armeniacum Causing Fusarium Head Blight on Soft Red Winter Wheat in Illinois.

Abstract

In the summer of 2016, while surveying the diversity of the Fusarium head blight (FHB) causal agent on soft red winter wheat (Triticum aestivum) in Illinois, we identified hundreds of naturally infected plants in five locations. Samples with characteristic symptoms of FHB (bleaching, accompanied by pink/white mycelium) were collected one to three weeks after anthesis. The collected glumes and developing kernels were surface sterilized and plated on sterile media. Single conidia isolates were derived for further work. All isolates were deposited to the USDA-ARS Mycotoxin Prevention and Applied Microbiology Research Unit in Peoria, IL. Among the collection, isolate CMR105 showed characteristics of F. armeniacum growing on PDA with abundant white mycelia and pigments of orange to pink (Suppl. Figure 1B). The CMR105 macroconidia were prominently curved, long, and tapering with a distinct foot shape typical of F. armeniacum (Leslie and Summerell, 2006). CMR105 conidia were produced quickly and abundantly compared to typical isolates such as BMR001, which were rare and slow-growing. The translation elongation factor 1-alpha (EF1-α), RNA polymerase 2 (RPB2), β-tubulin, and the internal transcribed spacer (ITS) genes were sequenced from selected isolates, including CMR105. The resulting DNA sequences were trimmed and aligned using blast on the Fusarium ID database and NCBI's nr database. For all the genes, isolate CMR105 had a 99% or higher similarity to multiple F. armeniacum accessions (Suppl. Table 1). We then conducted a phylogenetic analysis using the DNA sequences of three concatenated genes (RPB2, β-tubulin, and ITS). A maximum likelihood tree supported that isolate CMR105 is F. armeniacum (Suppl. Figure 1E). Koch's postulates were carried out in greenhouse experiments on spring wheat cultivar 'Norm'. At anthesis, a spore suspension of 5 x 104 spores per ml was injected into the central spikelet of wheat heads. Three plants were inoculated per isolate and a mock control consisting of water. The inoculated plants were placed into a mist chamber for 48 hours. Symptoms consisting of premature bleaching of multiple spikelets and pink/white coloration were observed one-week post-inoculation. No symptoms were observed on the control. Two weeks post-inoculation, kernels from the wheat heads were collected, surface sterilized with 10% bleach, and plated on PDA. The recovered isolates showed similar colony morphology to the inoculum. Similar results were obtained on field inoculations on soft red winter wheat. F. armeniacum has been reported from the United States, Australia, South Africa, China, and Argentina (Kommedahl et al., 1979; Nichea et al., 2015). To date, F. armeniacum has been reported to cause seed and root rot on soybeans, has been recovered from asymptomatic corn, and more commonly found as a soil saprophyte (Ellis et al., 2012; Leslie and Summerell, 2006; Nichea et al., 2015). We have shown here for the first time that F. armeniacum also causes FHB on wheat in Illinois. In both field and greenhouse assays, our F. armeniacum strain was less aggressive than F. graminearum strains. Recently, F. armeniacum was reported to cause FHB on emmer and spring wheat in New York (Fulcher and Bergstrom, 2020). It is important to note that many species of the genus Fusarium cause FHB. In this report, we show evidence that F. armeniacum is another causal agent of FHB in Illinois and warrants further study and surveillance.