<i>Fusarium</i> <i>moricola</i> sp. nov. Within the <i>Fusarium tricinctum</i> Species Complex Causing Bud Blight of Mulberry in Hubei, China

Mulberry (Morus spp.) has been cultivated for silkworm rearing for thousands of years in Asia. In February 2023, a bud blight disease was observed in Wuhan, Hubei Province, China (30°25′37″N, 113°57′39″E), affecting 12% of 2-year-old ‘YSD10’ mulberry trees. Symptoms included brown blight around winter buds with dense orange clusters, bud death due to necrosis, and progressive branch dieback from coalescing lesions. Symptomatic tissues (5× 5 mm) were excised from lesions margins, surface-sterilized (75% ethanol for 30 s, 2.5% sodium hypochlorite for 2 min), rinsed thrice with sterile water, and plated on potato dextrose agar (PDA). Three isolates (Cd5, Cd10, and Cd11) were single-spore purified. On PDA at 25°C for 7 days, they formed sparse white mycelia with pale/reddish-orange pigment, growing 4.25–4.79 mm day-1. Microconidia were scarce, fusiform, oval, or obovoid. Macroconidia were fusiform, with slightly curved apical cells and foot-shaped basal cells, with 1-5 septa: 1-septate (12.7–30.4 × 2.4–3.6, avg. 22.3 × 3.0 μm), 3-septate (29.7–42.6 × 2.7–3.7, avg. 35.3 × 3.2 μm), 5-septate (39.2–53.2 × 3.2–4.5, avg. 47.3 × 3.7 μm) (n =30). Mesoconidiophores emerged laterally from aerial hyphae, simple or branched. Chlamydospores were globose to subglobose, intercalary, solitary or in chains, 3.8–6.0 μm in diameter (avg. 4.6 μm, n = 30). For molecular identification, ribosomal internal transcribed spacers (ITS), translation elongation factor 1α (EF-1α), RNA polymerase II largest subunit (RPB1), and second largest subunit (RPB2) were amplified using primers ITS1/ITS4 (White et al. 1990), EF1H/EF2T (O’Donnell et al. 1998), Fa/G2R (O'Donnell et al. 2010), and fRPB2-7cF/RPB2-11aR (Liu et al. 1999), respectively. Sequences were deposited in GenBank (ITS: PQ034582-PQ034584, EF-1α, RPB1, RPB2: PQ014390-PQ014398). Maximum-likelihood phylogenetic analysis (MEGA7) showed the three strains formed a distinct clade outside known Fusarium tricinctum species complex (FTSC), with 100% bootstrap support. Based on morphological and molecular characteristics (Crous et al. 2021), they are propose as a new species, Fusarium moricola sp. nov. Koch’s postulates were fulfilled using healthy 35-day-old mulberry seedlings and one-year-old ‘YSD10’ winter stems. For seedling inoculation, each strain was tested on three seedlings. Needle-wounded plants were sprayed with107conidia ml-1 (5 ml/plant), maintained humidity at 25 °C under an 18/6 h light/dark. For stems inoculation, buds of surface sterilization stems were wounded, ~ 1 cm of epidermis below each bud was excised, and each bud was wrapped in 5-layer sterilized toilet paper saturated with 3 ml of 105 conidia ml-1, then incubated at 25°C in darkness. Each strain was tested on three stems (5 buds/stem). Controls were treated with sterile water. At 7 days post-inoculation (dpi), brown lesions appeared on inoculated seedling nodes. At 14 dpi, inoculated stems developed orange sporodochia and brown discoloration matching field symptoms. Controls were asymptomatic. Fungi with identical morphology to the original isolates were reisolated from symptomatic tissues of both tests. Mulberry bud (twig) blight has been attributed to Fusarium lateritium f.sp. mori (Vajna 2000). To our knowledge, this is the first report of a novel Fusarium species within FTSC causing mulberry bud blight. The identification of this pathogen provides a basis for developing effective control strategies.