First Report of Fusarium nirenbergiae Causing Rot of Potato in China
Authors: Li Linxuan , Wen Lina , Zhu Tingting , Ren Maozhi 
Published: January 2025

Potato (Solanum tuberosum L.) is the third largest food crop globally following rice and wheat, which is consumed by more than 1 billion people worldwide (FAO 2024). In October 2022, tuber rot of potato (cv. Chuanyu-50) was observed in three adjacent indoor storage areas (about 1000 m2 per area) in Sichuan, China (103°10′ E, 30°54′ N), with an average incidence rate of 12%. Symptoms included tuber shrinkage, rot, and brown flesh. White hyphae were visible on the surface of the severely decayed tubers. Fifteen diseased tubers were collected from three areas (five per area). They were rinsed with sterile water and cut into pieces (3-5 mm thick, two pieces per tuber) at the boundary of the symptomatic area. The pieces were surface sterilized in 75% ethanol for 1 min, rinsed five times with sterile water, placed on potato dextrose agar (PDA), and incubated at 27°C in the dark. After 7 days, 24 of 30 isolates generated white to pale pink aerial hyphae on PDA. Macroconidia on carnation leaf agar were falcate, hyaline, one to five septate, and averaged 22 to 50 μm in length. Microconidia were hyaline, 0–1-septate, ellipsoidal to falcate, and smooth- and thin-walled. Chlamydospores were globose to subglobose, and 4–6 µm in diameter. These characteristics align with the description of Fusarium (Leslie and Summerell 2006; Lombard et al. 2019). Sequences of the translation elongation factor 1 alpha (TEF1-α) (O’Donnell et al. 1998), internal transcribed spacer (ITS) (Badotti et al. 2017), and RNA polymerase II second largest subunit (RPB2, primers 5F2/7CR) (Liu et al. 1999 ) from three representative isolates DR-1, DR-5 and DR-6 were amplified, sequenced and deposited in GenBank (TEF1-α: PP795695, PP795696, and PP795697; ITS: PP794584, PP794585, and PP794586; RPB2: PP998061, PP998062, and PP998063). Polyphasic identification of the TEF1-α, ITS, and RPB2 sequences from the DR-1 showed 99.84%, 100%, and 99.54% similarity with sequences of F. nirenbergiae strain CBS 130301 (NRRL 26374) (GenBank nos. MH485017, MH865885, and MH484926) in the FUSARIOID-ID database, respectively. Phylogenetic analysis of the concatenated TEF1-α and RPB2 sequences using the maximum likelihood method assigned these isolates to the F. nirenbergiae clade. Pathogenicity tests were conducted on potato tubers (cv. Chuanyu-50). The epidermis of each tuber was slightly wounded using a sterile blade. Conidial suspension (1×106 conidia/ml; approximately 10 μl per tuber) of the isolate DR-1 was point-inoculated into the wounded tubers. Twenty tubers were inoculated with the DR-1 conidial suspension, while five noninoculated potato tubers injected with sterilized water as controls. Meanwhile, another isolate DR-5 was also point-inoculated into tubers in the same manner. After inoculation, the potato tubers were kept in a moist chamber at 25°C. All inoculated tubers rotted and turned brown with white hyphae after 15 days, and the necrotic area ranged from 40% to 60% in the inoculated tubers. However, the controls remained healthy. The pathogen was reisolated from the inoculated tissues but not from the control tubers. All pathogens reisolated from 10 inoculated tubers were F. nirenbergiae, and the identity was confirmed as described above. The experiments were repeated three times with similar results. To our knowledge, this is the first report of F. nirenbergiae causing rot of potato in China. These results will contribute to developing control strategies for F. nirenbergiae-induced potato disease.