Identification of Fusarium armeniacum Causing Fusarium Head Blight and Crown Rot on Winter Wheat ( Triticum aestivum ) in China

Fusarium head blight (FHB) and Fusarium crown rot (FCR) are the two devastating wheat diseases worldwide. In May 2023 and 2024, we recorded disease incidences of 13 to 20% for FHB and 6 to 11% for FCR, respectively, in the Huanghuai wheat-growing region of China (Zhang et al. 2024). Affected tissue fragments (5 mm) or symptomatic kernels were surface-sterilized in 1% NaClO for 2 min, rinsed twice with sterile distilled water, air-dried, and plated on potato dextrose agar (PDA) plates. The plates were incubated at 25 °C for 3 days. Pure cultures were obtained by monoconidial and hyphal tip isolation. Colonies resembling Fusarium were further identified to species level by molecular characterization. Among the collection, nine isolates from Henan Province (3 from FHB-affected plants in Anyang, 6 from FCR-affected plants in Xinyang) were identified as Fusarium armeniacum. On PDA, F. armeniacum produced abundant aerial mycelium, accompanied by orange-to-pink pigments (Figure 1). On carnation leaf agar (CLA), macroconidia were falcate, elongated, and distinctly curved, predominantly with 3 to 5 septa, a long curved apical cell, and a foot-shaped basal cell, measuring 17.4 ± 4.9 × 3.7 ± 0.5 μm (n = 150). Microconidia were ovoid to ellipsoid or cylindrical, straight to slightly curved, measuring 9.1 ± 1.6 × 3.4 ± 0.6 μm (n = 150) (Figure 1). Partial sequences of the translation elongation factor 1-α (TEF), RNA polymerase II (RPB2), and calmodulin (CAM) genes from three representative isolates (HN7-8, HN9-5, HN9-9) were sequenced as described (O’Donnell et al. 2000, 2022) and deposited in GenBank under accession numbers PX684571–PX684573 (TEF), PX684574–PX684576 (RPB2), and PX684577–PX684579 (CAM). BLAST analysis on the Fusarioid-ID database revealed that the TEF sequences of HN7-8, HN9-5, and HN9-9 shared 99.85%, 100%, and 99.85% identity with those of F. armeniacum isolate LC2809 (accession no. MW620070). For RPB2 and CAM, all three isolates exhibited 100% similarity to F. armeniacum isolate LC2809 (RPB2, accession no. MW474595) and isolate CBS485.94 (CAM, accession no. PQ240137). Phylogenetic analysis confirmed these isolates as F. armeniacum (Figure 2). For FHB verification, wheat spikes (cv. Ji-29) were inoculated by injecting 10 μL of a spore suspension (106 spores/ml) of isolates HN6-1 and HN7-8 into a central floret of each spike in April 2025 under natural field conditions, during the anthesis of wheat in Zhuanghang Town, Shanghai. Inoculated spikes were covered with plastic bags for 48 h to maintain humidity, spikes inoculated with sterilized water served as controls. For FCR verification, mycelial plugs from the margin of 3-day-old cultures of isolates HN9-5 and HN9-9 were placed around the coleoptiles of individual potted wheat seedlings (cv. Zheng-1860), and then maintained in a climate incubator at 25 °C under a 12-h photoperiod, with blank PDA plugs served as controls. Each inoculation treatment included fifteen replicates. After 14 days, inoculated plants exhibited symptoms of FHB or FCR respectively, whereas mock-inoculated controls remained healthy (Figure 1). The pathogen was successfully re-isolated from symptomatic tissues and subsequently confirmed as F. armeniacum by both morphological and molecular characterization, thereby fulfilling Koch’s postulates. To our knowledge, this is the first report of F. armeniacum causing wheat FHB and FCR in China, further surveillance of its geographical distribution and incidence is warranted.