<i>Fusarium</i> <i>oxysporum</i> and <i>Fusarium falciforme</i> Cause Root Rot of <i>Ormosia hosiei</i> Seedlings in Guizhou Province, China

Ormosia hosiei Hemsl. & E. H. Wilson is a precious timber and endemic tree species in China (Lin et al., 2023). From May to July 2025, a root rot disease was observed in an O. hosiei nursery located in Huishui Country (26.07°N, 106.39°E) and Guiyang City (26.38°N, 106.37°E) of Guizhou Province, respectively. Diseased seedlings exhibited wilting, leaf chlorosis and drop, blackened roots, and subsequent mortality (Fig. 1a, b). Disease incidence was approximately 43% of 500 plants. In July 2025, pieces of blackened roots from symptomatic seedlings were removed, disinfected in 3% sodium hypochlorite for 30 s and in 75% alcohol for 60 s, rinsed three times in sterile distilled water, embedded in potato dextrose agar (PDA) medium, and incubated at 28°C in the dark for 5 d. Isolations resulted in two colony morphologies (white peripheries with purple or orange centers) and fifteen single spores of each colony type were retained. One single-spore isolate from each colony type were examined for identification (CHF2-8 and CHF2-24 from purple and orange colonies, respectively). Microconidia of CHF2-8 and CHF2-24 were rice grain-shaped and were 7.8 to 9.2 and 7.7 to 8.5 μm, respectively. Sickle-shaped macroconidia were only observed on CHF2-24 and were 25.3 to 43.6 (n=50) (Fig 1g, i). These morphological characteristics were consistent with Fusarium spp. (Wang et al., 2022). DNA from the isolates was extracted using the CTAB method. The internal transcribed spacer (ITS), translation elongation factor 1-alpha (TEF-1α) and second largest subunit of RNA Polymerase II (RPB2) regions were then amplified using the primers ITS1/ITS4, Ef1/Ef2 and 5F2/7cR, respectively (White et al., 1990; O'Donnell et al., 1998; Liu et al., 1999). The amplified products were sequenced. The number of base pairs matching showed that isolate CHF2-8 had the highest identity with F. oxysporum (ITS: PQ285819, 517/517; TEF-1α: KY081518, 675/676; RPB2: ON693001, 946/946); isolate CHF2-24 had the highest identity with F. falciforme (ITS: PV549582, 499/500; TEF-1α: PQ632709, 701/702; RPB2: OQ928397, 901/901). Sequences from isolates CHF2-8 and CHF2-24 were deposited in GenBank (ITS: PV960582 and PV960583; TEF-1α: PV990108 and PV990111; RPB2: PV990109 and PV990110). Phylogenetic analysis using the maximum-likelihood method showed that isolate CHF2-8 clustered with the F. oxysporum clade, and isolate CHF2-24 clustered with the F. falciforme clade (Fig 2). For pathogenicity tests, we used healthy, 3-month-old O. hosiei seedlings that had been cultivated in autoclaved soil, with the mixture ratio of forest topsoil, nutrient soil, and vermiculite set at 5:2:1. A 20-mL aliquot of a spore suspension (2.0 × 105 conidia/mL) of isolates CHF2-8 and CHF2-24 was applied to the stem base of plants in nine pots each, respectively. Sterile water was applied to non-inoculated plants. Plants were maintained in a greenhouse at 28°C at 60% humidity and 12 h photoperiod. Forty-five days after inoculation, wilting, leaf chlorosis and drop were observed on inoculated plants and not on non-inoculated plants (Fig 1c–e). Conidial and colony morphologies recovered from inoculated plants matched the identity of the isolates recovered from field-collected plants, fulfilling Koch’s postulates. To our knowledge, this is the first report of these pathogens causing root rot of O. hosiei in China. These findings provide a foundation for developing management strategies against this root rot disease.