First report of Fusarium head blight of wheat caused by Fusarium brachygibbosum in China

Fusarium head blight (FHB) is a devastating wheat disease caused by several Fusarium species, which not only reduces yield but also contaminates grain with various mycotoxins (Al-Hashimi et al., 2025). In July 2024, a survey conducted across 32 fields in seven counties of Xinjiang, China, revealed an FHB incidence rate of approximately 43.75% (Zheng et al., 2025). Fourteen symptomatic wheat samples were collected from each field. Symptomatic seeds were surface disinfected sequentially with 75% ethanol and 0.1% sodium hypochlorite solution, rinsed three times with sterile distilled water, blotted dry on sterile filter paper, and plated onto potato dextrose agar (PDA) medium supplemented with streptomycin sulfate (Leslie and Summerell, 2006). Plates were incubated at 25 °C in darkness for 7 days. Fungal colonies exhibiting morphological characteristics of Fusarium spp. were purified by single-spore isolation and identified based on morphological features and DNA sequence analysis. Partial sequences of the internal transcribed spacer (ITS) region and translation elongation factor 1-alpha (TEF1-α) gene were amplified using primer pairs ITS1/ITS4 (White et al., 1990) and EF1/EF2 (O’Donnell et al., 1998). Results indicated that F. graminearum, F. avenaceum, and F. acuminatum associated with FHB in wheat in Xinjiang (Zheng et al., 2025). However, one isolate designated XJ-19-2, collected from Shihezi city, initially produced white to greyish-white colonies with floccose to cottony aerial mycelia on PDA. BLASTn analysis of the ITS and TEF1-α amplicon revealed more than 99% sequence identity with F. brachygibbosum (PX854928.1 and PX866700.1). Phylogenetic trees based on partial ITS and TEF1-α gene sequences (Fig S1.) were constructed using MEGA 7.0 (University Park, PA, USA) (Tirado-Ramirez et al., 2021). The isolate exhibited a radial growth rate of 2.33 cm/d at 25 ℃ in the dark, with the reverse side of colonies appearing pale beige to light yellow, displaying slightly darker pigmentation in the center that gradually faded toward the margin (Fig S2 A, B). After 3 days of incubation in liquid mung bean medium at 25 ℃, both macroconidia and microconidia were observed. Macroconidia (n = 50) were falcate to nearly straight, mostly 3–5-septate, measuring (15.7–38.7) μm × (3.65–4.99) μm, with slightly pointed to blunt apical cells and a short, distinct foot-shaped basal cell. Microconidia (n = 50) were oval, ellipsoidal to cylindrical, aseptate or occasionally 1-septate, measuring (5.27–13.6) μm × (2.21–3.83) μm (Fig S2 C). Pathogenicity tests were performed using the wheat cultivar Xindong 18, one of the predominant varieties grown in Xinjiang. At anthesis, the central floret of each of ten spikes was injected with 20 μL of a conidial suspension (106 macroconidia/mL), while control plants were inoculated with sterile distilled water. The proportion of diseased seeds per wheat head was assessed 21 days post-inoculation. Typical FHB symptoms were observed on inoculated spikes, with 28.6% of spikes infected by XJ-19-2 at 21 days (Fig S2 D), whereas no symptoms developed in water-inoculated controls. The same fungus was re-isolated from symptomatic grains. To the best of our knowledge, this is the first report of FHB of wheat caused by F. brachygibbosum in China.