Astragalus schanginianus (Fabaceae), a perennial herbaceous plant native to Xinjiang, plays a key role in natural grassland ecosystems through nitrogen fixation and soil stabilization (Flora of China). In August 2023, root rot was observed in a natural grassland survey in Fuyun County (89°52'11.37"N, 47°13'24.45"E), China. Disease symptoms were observed on all surveyed plants (100% incidence, n = 15), which exhibited browning of the inner root tissues. Five diseased plants were randomly selected for tissue isolation. Root segments (3 mm3) were surface-disinfested (75% ethanol for 30 s, 1% NaClO for 60 s), rinsed three times with sterile water, dried with sterile filter paper, and subsequently cultured on potato dextrose agar (PDA) at 25°C, with three plates per plant and five explants per plate. Strains LYZ1593 and LYZ1594, which were isolated from different individual plants and exhibited consistent colony morphology, were purified by single-spore isolation for further study. On PDA, the isolates developed abundant white aerial mycelium and produced rose-colored diffusible pigmentation in the agar. Macroconidia were hyaline, slender, straight to slightly curved, 3 - 5 septa, measuring 28.6 ± 6.4 × 4.8 ± 0.8 μm (n = 30). Microconidia were fusiform, hyaline, 0 - 1 septum, measuring 9.1 ± 1.3 × 2.4 ± 0.4 μm (n = 30). Chlamydospores were globose, smooth-walled, formed in chains, measuring 9.7 ± 1.4 × 9.0 ± 2.3 μm (n = 15). Conidiogenous cells were monophialides. Based on these morphological characteristics, the fungus was provisionally identified as a Fusarium sp. (Lesli et al., 2006). For molecular identification, the ITS, RPB2, and EF1α genes were amplified with primers ITS1/ITS4 (White et al., 1990), fRPB2-5F/fRPB2-7cR (Liu et al., 1999), and EF1/EF2 (O'Donnell et al., 1998), respectively. The obtained sequences were compared against the FUSARIOID-ID database and revealed 100% identity of all three loci with F. acuminatum strain LC5227. A maximum-likelihood tree from concatenated sequences (MEGA7, Tamura et al., 2016) grouped the strains within F. acuminatum with 100% bootstrap support (1000 replicates). Sequences were deposited under accession numbers PX570701 to PX570702 (ITS); PX516689 to PX516690 (RPB2); and PX548366 to PX548367 (EF1α). Pathogenicity was assessed using the wound-free root dip method, sterile A. schanginianus seedlings (1 cm root length) were immersed in conidial suspension (1×10⁷ conidia/mL) of the representative strain LYZ1593 for 1 h, then transplanted into pots with a sterilized loam soil (dry-heat sterilized at 169°C for 2 h), with five seedlings per pot. Four pots per treatments (inoculated/control) were used, with two experimental replicates. Plants were maintained at 25 ± 2°C with 70% relative humidity. At 10 days post-transplanting, 20% of inoculated plants died, and by 30 days, all inoculated seedlings exhibited brown root lesions, while controls remained asymptomatic. The fungus reisolated from infected roots matched F. acuminatum morphologically and molecularly, fulfilling Koch’s postulates. To our knowledge, A. schanginianus has only been reported to be infected by Microsphaera astragali (Amano, 1986). This study represents the first report of F. acuminatum causing root rot in A. schanginianus, broadening our understanding of root rot pathogens in natural grassland legumes. This finding has implications for disease management in native plant communities.
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