Fusarium nirenbergiae L. Lombard & Crous

Fusarium nirenbergiae L. Lombard & Crous, Persoonia 41: 29 (2018) Fig. 27 Description. Pathogenic to spring onion (Allium fistulosum) and causes yellowing, curling, and wilting of leaves, often accompanied by basal rot and reddish-brown discoloration of the roots and bulb plate. Sexual morph not observed. Conidiophores on aerial mycelium unbranched or slightly branched, comprise terminal or intercalary monophialides, often reduced to single phialides. Aerial phialides, subulate to subcylindrical, smooth, thin-walled, 9–23 × 1.5–2.5 µm, with unnoticeable or absent periclinal thickening. Aerial conidia formed in small false heads on the tips of the phialides, 0–1 - septate 0 - septate conidia: 5–9 × 2–4 μm (mean = 8 × 3 μm, n = 20), 1 - septate conidia: 9–14 × 2–4 μm (mean = 12 × 3 μm, n = 20). Macroconidia falcate, curved dorsoventrally, with apical cell blunt to papillate, curved, basal cell blunt to foot-like, hyaline, smooth, and thin-walled, 3–5 - septate: 3 - septate conidia: 31–41 × 3.5–4 μm (mean = 35 × 4 μm, n = 20), 4 - septate conidia: 35–45 × 3–5 μm (mean = 38 × 4 μm, n = 20), 5 - septate conidia: 42–55 × 3–4 μm (mean = 50 × 4 μm, n = 20). Sporodochia and chlamydospores were not observed. Culture characteristics. Colonies on PDA reach 65 mm in diameter after 7 days of growth at 25 ° C in the dark, white to pale vinaceous, with abundant aerial mycelium and filiform margins. Reverse is pale vinaceous. Material examined. Thailand • Chiang Rai Province, Mueang Chiang Rai District, Doi Hang, on spring onion (Allium fistulosum), February 2023, Maryam Fallahi, dried culture MF 112-2 (MFLU 24-0251), living culture MFLUCC 24-0248. Notes. In the phylogenetic tree generated for Fusarium oxysporum species complex, strain MFLUCC 24-0248 clustered with the ex-type strain of Fusarium nirenbergiae (CBS 840 88) with 68 % ML, 73 % IQ bootstrap support, and 0.99 BYPP (Fig. 25). The base pair differences between F. nirenbergiae strains MFLUCC 24-0248 and CBS 840 88 revealed a 0.16 % (1 / 612 bp) difference in tef 1 and a 0.57 % (5 / 876 bp) difference in rpb 2. The sequence data of rpb 1 is not available for F. nirenbergiae (CBS 840 88). Fusarium nirenbergiae (MFLUCC 24-0248) did not produce sporodochia or chlamydospores; however, the ex-type strain of F. nirenbergiae did produce both structures. (Lombard et al. 2019). Phylogenetically, F. nirenbergiae is closely related to F. curvatum; however, they are distinguished based on morphology and molecular analysis (Lombard et al. 2019). Fusarium nirenbergiae is globally recognized as a causative agent of wilting on various hosts (Lombard et al. 2019; Aiello et al. 2021). To the best of our knowledge, this study represents the first report of Fusarium wilt on spring onion caused by F. nirenbergiae.