First Report of Wilt Caused by Fusarium nirenbergiae on tomato (Solanum lycopersicum) in China.

In May 2024, Fusarium wilt was observed in a tomato field in Weifang City, Shandong Province (36°54'6.876" N, 118°51'17.003" E) with an incidence of approximately 32%. The typical symptoms of the disease included leaf wilting and light brown or dirty white elongated lesions on one side of the stem. Three diseased plants were collected and labeled as FQKW24-1-FQKW24-3. Stem tissues with lesions were cut into 5 mm pieces and then surface sterilized with 75% ethanol for 45 s and 3% NaClO for 1 min. After triple rinsing with sterile distilled water, the tissue were transferred on potato dextrose agar (PDA) and incubated in darkness at 25°C for 5 days. After purification using hyphal-tip method (Leslie and Summerell. 2006), 9 isolates with consistent colony morphology were obtained. The representative strains FQKW24-1A and FQKW24-2A were selected for morphological identification. The colonies exhibited white or pale vinaceous center, with a floccose texture and abundant aerial mycelium. Reverse white or pale vinaceous in the center, lacking diffusible pigment. Microconidia on synthetic nutrient poor agar (SNA) were ellipsoidal to falcate, measuring 7.3 - 13.7 (x̄=10.1) × 2.7 - 4.7 (x̄=3.7) μm and 8.9 - 18.7(x̄=13.0) ×3.3 - 5.9 (x̄=4.6) μm for FQKW24-1A and FQKW24-2A, respectively. On carnation leaf agar (CLA), macroconidia were falcate, 3-5 septate, 33.9-50.4 (x̄=41.6) × 5.6 - 3.2 μm (x̄=4. 6) and 35.5 - 57.7 (x̄=44.7) × 3.6 - 5.8 (x̄=4.8) μm for FQKW24-1A and FQKW24-2A, respectively. The translation elongation factor 1-alpha gene (tef1), calmodulin (cmdA), and RNA polymerase II second largest subunit (rpb2) were amplified according to Wang et al. (2019). Sequences of tef1, cmdA, and rpb2 (PV018785-PV018793) of the isolates FQKW24-1A, FQKW24-2A and FQKW24-3A were submitted to GenBank. Alignment analysis of these sequences revealed similarities of 99.8% (614/615), 99.4% (871/876) and 99.8% (601/602) with the ex-type culture of F. nirenbergiae CBS 840.88 for tef1, rpb2 and cmdA, respectively. Phylogeny inferred based on the combined cmdA, tef1 and rpb2 sequences using PhyloSuite software, showed the three isolates and F. nirenbergiae were clustered into one branch. Based on morphology and phylogenetic analyses, the isolates were identified as F. nirenbergiae. Pathogenicity tests were conducted twice in an artificial climate box (12-h photoperiod at 25 °C, RH 80%) on 15-20 cm tomatoes seedlings with the pot culture. Plants were grown in sterilized soil and separately inoculated in pots with 20 ml of F. nirenbergiae spore suspension (106 conidia/ml). Control plants were mock-inoculated with water. Each treatment contained 10 plants. The first symptoms appeared 20 days after inoculation, which were a characteristic yellowing and wilting of foliage, falling off from bottom to upward. Within 3 months, stem tissues of the inoculated plants exhibited typical symptoms similar to those observed in the field. The controls remained healthy. To fulfill Koch's postulates, fungi reisolated from symptomatic plants were confirmed as F. nirenbergiae by TEF sequences. F. nirenbergiae causes tomato wilt in the United States and the Netherlands (Lombard, et al. 2019), passion fruit wilt in Italy (Aiello, et al. 2021) and potato/saffron rot in China (Li et al. 2025; Mirghasempour et al. 2022). To our knowledge, this is the first report of F. nirenbergiae causing wilt of tomato in China. These findings aid in developing control strategies for F. nirenbergiae tomato infections.