Tomato (Solanum lycopersicum L.) is a fruit of great economic value that is grown worldwide. In November 2022, fruit rot symptoms were observed in cherry tomatoes (cv. Qianxi) in Jinan City of Shandong Province, China. Six cherry tomato samples (four symptomatic and two asymptomatic) were collected from commercial fields (approximately 1.2 ha) where the incidence of the disease ranged from 5 to 10%. The core and surface of the infected fruit were colonized and covered with white mycelia. Tissue pieces (5 mm × 5 mm) from the junction of healthy and diseased samples were surface-disinfected with 75% ethanol for 3 min, followed by 10% sodium hypochlorite for 5 min, and washed three times with sterile water. Tissue pieces were cultured on potato dextrose agar (PDA containing 200 mg/L timentin) at 28°C for five days. Four fungal isolates with similar morphological characteristics were obtained from each sample. Two representative isolates were collected and purified using the single-spore method. After five days on PDA at 28°C, FL1 and FL2 colonies showed abundant white to cream colored aerial mycelia with an average growth rate of 5 mm/day. On carnation leaf agar, FL1 was characterized by falcate macroconidia with pronounced dorsiventral curvature containing three to eight tapered apical cells and foot-shaped basal cells ranging in size from 25 to 74 μm × 3.6 to 6.8 μm (n=50). Microconidia and chlamydospores were not observed. These morphological characteristics were consistent with the description of F. luffae (Wang et al. 2019). DNA was extracted using the CTAB method. The nucleotide sequences of the translation elongation factor 1-α gene (TEF1) and the second largest RNA polymerase II subunit (RPB2) were amplified using specific primers EF1/EF2 and RPB2F/R, respectively (O'Donnell et al. 1998, 2010). FL1 and FL2 sequences were deposited in GenBank (TEF1: OQ427345 and OQ427346, RPB2: OQ427347 and OQ427348). Polyphasic identification indicated 100% similarity of FL1 and FL2 to F. luffae. A combined dataset of TEF1 and RPB2 was aligned using MAFFT v.7, and phylogenetic analysis was performed in MEGA v.7.0 using the maximum likelihood method. The cherry tomato isolates (FL1 and FL2) clustered together with the F. luffae reference strain NRRL31167 (100% bootstrap) and were identified on a morphological and molecular basis as F. luffae belonging to the Fusarium incarnatum-equiseti species complex. F. luffae was the only pathogen recovered from the infected fruit. To test for pathogenicity, healthy cherry tomato fruit were inoculated in a greenhouse (28°C, 12/12 h light/dark cycle, 90% relative humidity), six by wounded inoculation and six by nonwounded inoculation) with 10 μL conidial suspensions of isolate FL1 at 1 × 106 conidia/mL. Six wounded-treated cherry tomato fruit were used for the control. All cherry tomatoes were kept in a growth chamber at 28℃ with 90% relative humidity. After seven days, the inside of the wound inoculated fruit began to rot, expanding toward the surface and producing white mycelia. Two diseased cherry tomatoes were randomly selected for tissue isolation and F. luffae was re-isolated showing the same morphology as the FL1 isolate, thus fulfilling Koch's postulates. The nonwounded inoculated fruits and control cherry tomatoes remained asymptomatic with no pathogens recovered. This indicates that the wound is an important way for F. luffae to invade tomato, and fruit rot is caused by F. luffae's infection of tomato. To the best of our knowledge, F. luffae has caused fruit rot in muskmelon (Zhang et al. 2022), but this is the first report of fruit rot disease in cherry tomatoes caused by F. luffae in China. Since cherry tomatoes are an important commercial crop in China, F. luffae infection has the potential to pose a threat to the industry.
Keywords: Fusarium luffae; cherry tomato; fruit rot.