First Report of Tobacco Fusarium Root Rot Caused by <i>Fusarium solani</i> in Fujian Province, China

Tobacco (Nicotiana tabacum L.) is one of the most important economic crops in China. In the recent years, tobacco root rot disease has severely broken out in Taining area (26.33°N, 116.53°E), Fujian Province, China. Particularly, in May 2025, severe root rot symptoms occurred in the “Cui Bi-1” variety of flue-cured tobacco, a commercially cultivar developed in China, in some of the tobacco fields in this region. A total of 18 hectares were planted, and root rot affected 15 hectares of those fields. Typical disease symptoms include plant stunting, withering of dark-brown lower leaves, appearance of rotting roots, and deterioration inside the plant stem. Under high humidity and temperature conditions, the infection initiates at the plant roots, progresses to the plant stem and leaves, and ultimately leads to the plant death. Tissues of infected stems and roots were dissected and cut into small pieces, sterilized with 75% ethanol for 30 s, and then washed five times with sterile distilled water. Tissue pieces were then plated onto potato dextrose agar (PDA) and incubated at 28°C for 3 days. Most colonies on PDA medium appeared as white to pale yellow flocculent aerial mycelium on the agar plate. The five-day-old, cultured mycelium on PDA was collected, suspended in sterile distilled water, and filtered through a piece of filter cloth. Conidia observation reveals that the spores were slightly curved, featuring two to five septa, which is consistent with the description of Fusarium solani (Leslie and Summerell 2006). The collected conidia were capable of rapidly germinating into hyphae even in sterile distilled water within 2 hours. Then a single spore (named as TN-1) was isolated for subsequent molecular analyses. The nuclear ribosomal internal transcribed spacer ITS, translation elongation factor TEF-1α and the second largest subunit of RNA polymerase II RPB2 (Vettraino et al., 2009) region DNA were amplified and sequenced. The amplified sequences from TN-1 were aligned in NCBI GenBank, and the results showed the obtained ITS (PX830036), TEF-1α (PX842327) and RPB2 (PX842328) sequences were 97.45%, 95.32% and 97.81% identical to the corresponding DNA sequences of F. solani strains in GenBank (ITS: MH582400, 496/509 identities; TEF-1α: MH582420 652/684 identities; and PRB2: MH582410, 803/821 identities). The phylogenetic analysis using combined ITS-TEF-1α-RPB2 sequences confirmed TN-1 clustering to F. solani. Pathogenicity studies were conducted to verify the isolated TN-1. Conidia of TN-1 (1×106 spores/ml) was injected into the root area of the tobacco seedling. The infected tobacco seedlings were cultured at 28°C with a 12h photoperiod. After 5 days, the infected seedlings showed a withering symptom, and the lower leaves showed symptoms of wilting, whereas the control seedlings did not. Previously, it was reported that a case of Fusarium root rot on tobacco in China is caused by F. solani (Wang et al. 2025). To our knowledge, this is the first report of a new F. solani strain causing severe root rot on tobacco in Fujian province. The isolation and identification of the new F. solani as a root rot agent might provide important insights for clarifying the outbreak principle of this devastating tobacco disease and are also important for developing new strategies to control its spread.