First Report of Fusarium nisikadoi Causing Pokkah Boeng Disease on Sugarcane in China

Pokkah boeng disease (PBD), caused by Fusarium spp., is an economically significant disease of sugarcane (Saccharum officinarum L.) worldwide and has occurred frequently in China. From 2022 to 2024, leaf samples exhibiting PBD symptoms were collected from major sugarcane-producing regions across China. A total of 181 Fusarium-like isolates were obtained from 203 symptomatic leaves using tissue isolation method and purified by single-spore isolation on potato dextrose agar (PDA). Three F. nisikadoi isolates of A9 (Longchuan County, Yunnan Province; 24°26′1.20″N, 98°35′16.27″E), SFQ5 (Fusui County, Guangxi Zhuang Autonomous Region; 22°31′51.25″N, 107°38′52.99″E), and SL4 (Leizhou City, Guangdong Province; 21°8′26.79″N, 109°59′16.43″E) were selected for detailed characterization. On PDA, colonies were white and floccose with pale yellow reverse. Microconidia were oval, aseptate, and measured 3.49–10.71 µm × 2.61–3.33 µm (n = 50). On carnation leaf agar (CLA), microconidia were clavate, 0–3-septate, and 3.36–19.96 µm × 2.51–4.83 µm (n = 50); macroconidia were slender, sickle-shaped, mostly straight, with 3–7 septa, and measured 44.35–57.96 µm × 2.48–4.19 µm (n = 50). Morphological features of these isolates matched the description of F. nisikadoi (Leslie and Summerell 2006). For further molecular identification, the translation elongation factor 1-alpha (TEF-1α) and RNA polymerase II second largest subunit (RPB2) genes were amplified and bidirectionally sequenced using primer pairs EF1/EF2 (O’Donnell et al. 1998) and fRPB2-7cf/fRPB2-11aR (O’Donnell and Cigelnik 1997), respectively. The resulting sequences were deposited in GenBank under accession numbers: TEF-1α for PV953863 (A9), PX990909 (SFQ5), PX990910 (SL4); RPB2 for PX056327 (A9), PX990907 (SFQ5), PX990908 (SL4). BLASTn analysis revealed that the TEF-1α sequences shared 100% identity with F. nisikadoi strain NRRL 25179 (GenBank MN193879), while RPB2 sequences showed 99.37–100% identity with the same reference strain (MN193907). Phylogenetic analysis was conducted in MEGA 6.0 using the neighbor-joining algorithm based on concatenated TEF-1α and RPB2 sequences. The three isolates grouped within a single well-supported clade alongside reference F. nisikadoi sequence (NRRL 25179) retrieved from GenBank. To fulfill Koch’s postulates, pathogenicity tests were conducted on 2-month-old sugarcane plants (cultivar LC05-136). Heart leaf of ten plants were inoculated by microinjection of a conidial suspension (1 × 10⁶ conidia/ml), while ten control plants received sterile water. Plants were maintained in a growth chamber at 28°C with a 12-h photoperiod and >90% relative humidity. Typical PBD symptoms including leaf distortion, chlorosis, and necrotic streaking, developed on all inoculated plants within 10 days post-inoculation, whereas the control plants remained asymptomatic. F. nisikadoi was consistently re-isolated from the symptomatic tissues of inoculated plants but not from controls, confirming its pathogenicity. Fusarium nisikadoi was originally described from bamboo and wheat in Japan (Nirenberg and Aoki 1997) and has not previously been associated with sugarcane. To our knowledge, this is the first report of F. nisikadoi causing pokkah boeng disease on sugarcane in China. Although detected at low frequency (1.66%) among Fusarium isolates, this species represents a newly recognized causal agent of PBD in Chinese sugarcane production systems.