First report of Fusarium fujikuroi causing root rot and seedling elongation of soybean in Indiana

Authors: Detranaltes, Christopher; Jones, Christopher; Cai, Guohong

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2021
Publication Date: 5/11/2021
Citation: Detranaltes, C.E., Jones, C.R., Cai, G. 2021. First report of Fusarium fujikuroi causing root rot and seedling elongation of soybean in Indiana. Plant Disease. https://doi.org/10.1094/PDIS-03-21-0570-PDN.
DOI: https://doi.org/10.1094/PDIS-03-21-0570-PDN

Interpretive Summary: Soybean is an important agriculture crop. Numerous pathogens cause diseases on soybean and affect yield and quality. The geographical range of pathogens changes constantly. Here we report a new pathogen, Fusarium fujikuroi, causing root rot and seedling elongation of soybean in Indiana. We completed the experiments confirming its pathogenicity. This pathogen has been previously reported causing soybean root rot in China, Korea and the state of Kansas. Knowledge of the expanded geographical distribution of this pathogen will provide insight in disease control.

Technical Abstract: n May and June of 2020, 127 soybean (Glycine max (L.) Merr) seedlings (V1-V3 stage) showing reduced vigor or crown lesions were collected at Purdue’s Agronomy Center for Research and Education in West Lafayette, Indiana. Two isolates (AC13 and AC18) of Fusarium fujikuroi [Sawada] Wollenw. (teleomorph Gibberella fujikuroi) were recovered from two seedlings displaying necrotic cotyledons and root rot. Surface sterilized root tissue was plated onto the semi-selective media DCPA (Andrews and Pitt 1986) and hyphal tips were transferred from emerging mycelia onto potato dextrose agar (PDA). Single spore cultures were then obtained and grown on PDA. Both isolates developed floccose white aerial mycelia with reddish-pink coloration in the media. On carnation leaf agar, macroconidia formed in orange sporodochia within 2 weeks in darkness. Macroconidia were 3-5 septate, measuring 26 – 41 × 2.5 – 3.7 µm (average 34.8 × 3.2 µm, n=40). Microconidia were abundant in chains and false heads forming on both mono- and polyphialides. These characteristics were consistent with species descriptions of F. fujikuroi (Leslie and Summerell 2006). For molecular identification, we amplified and sequenced the internal transcriber spacer (ITS) region using ITS1/ITS4 primers (White et al. 1990) (GenBank accessions MW463362/MW463363), the mitochondrial small subunit (mtSSU) rDNA using MS1/MS2 primers (White et al. 1990) (MW465310/MW465307), and the translation elongation factor 1-alpha (TEF1a) gene using 983F/1567R primers (Rehner and Buckley 205) (MW475297/MW475298). These sequences showed 100% identity to both F. proliferatum and F. fujikuroi. Species-specific forward primers Fuji1F and Proli1F were then used in combination with the common reverse primer TEF1R to amplify a region in the TEF1a gene (Amatulli et al. 2012). PCR with Proli1F/TEF1R primers failed under a variety of annealing temperatures while PCR with Fuji1F/TEF1R succeeded and the products were sequenced (MW475299/MW475300). Subsequent GenBank BLAST searches revealed 100% identity of both isolates to F. fujikuroi (MT448248.1). Pathogenicity test was conducted with isolate AC13 in the greenhouse following the protocol of (Ellis et al. 2013). Ten seeds (cv. Williams) each were used for inoculation and control, respectively, with one seed per cup. Root rot symptoms similar to those observed in the field were observed 14 days after planting on all inoculated plants but not on controls. Infected plants showed symptoms of pre-emergence damping off, reddish brown lesions on the tap and lateral roots, and root necrosis. Some seedlings also exhibited hyper-elongation of the stem tissue. F. fujikuroi was successfully reisolated from inoculated plants but not from controls and identified as described above. F. fujikuroi has been reported causing soybean root rot in China (Zhao et al. 2020), Korea (Choi et al. 2019), and the state of Kansas (Pedrozo et al. 2015). To our knowledge this is the first report of F. fujikuroi infecting soybeans in the state of Indiana. F. fujikuroi is known to cause bakanae disease in rice with a typical symptom being elongated seedings (Leslie and Summerell 2006). Pedrozo et al. (2015) reported that F. fujikuroi isolated from soybean caused seedling elongation in rice but not in soybean. The increased distribution and new host symptomology observed here warrants heightened attention for the control of this pathogen.