First Report of <i>Fusarium incarnatum</i> Causing Postharvest Rot of Tomato in China

In November 2023, postharvest fruit rot was observed on tomatoes (Solanum lycopersicum) stored at room temperature in Baoding City, China (38°N, 115°E). Disease incidence was 15% (45 of 300 fruit) based on the inspection of three cartons. Initial symptoms appeared as irregular, water-soaked lesions at the pedicel junctions. These were followed by the development of white to light gray mycelium, which led to the decay of internal tissues. Diseased marginal tissues (5×5 mm) were surface-sterilized in 75% ethanol for 3 min and then in 2% sodium hypochlorite for 90 s, rinsed three times with sterile water, placed onto potato dextrose agar (PDA), and incubated at 26°C for 5 days in darkness. Three isolates (E1-E3) with similar morphological characteristics were obtained. E1 was selected for further study based on its pathogenicity and typical morphology. On PDA, it produced dense white mycelium. Colonies turned orange-yellow with a cream reverse after 7 days. On carnation leaf agar (CLA), septate conidiophores that branched from the main hyphae bore clusters of phialides. Macroconidia were slightly curved, mostly 3- to 5-septate, with a foot-shaped basal cell and a tapered apex. They measured 20.9 - 40.7 × 3.5 - 5.1 μm (n = 100). Microconidia were fusoid to ovoid and 0- to 1-septate, measuring 11.4 - 20.5 × 1.0 - 3.3 μm. No chlamydospores were observed. Based on these morphological characteristics, the isolate was putatively identified as Fusarium sp. (Leslie and Summerell 2006).The genomic DNA of isolate E1 was extracted for molecular identification. The ITS region and EF-1α gene were amplified using primer pairs ITS1/ITS4 (White et al. 1990) and EF-1/EF-2 (O'Donnell et al. 1998). The resulting sequences (ITS: PQ351301; EF-1α: PV131710) were 100% (546/546 bp) and 99.3% (710/715 bp) identical to those of the Fusarium incarnatum ex-type strains MZ466406 and OP105211, respectively. Phylogenetic analysis confirmed E1 as F. incarnatum. To test pathogenicity, tomato fruit (five fruit per treatment with three replicates) were wound-inoculated with E1 conidial suspension (104 spores/mL), with sterile water serving as the control. Inoculated fruit developed water-soaked lesions with white mycelia within 5 days at 25 °C and 85% RH, whereas all controls remained asymptomatic. The fungus reisolated from lesions matched E1 in both morphology and molecular characteristics, thereby fulfilling Koch's postulates. To our knowledge, Fusarium luffae has been reported to cause fruit rot on cherry tomato during growth in China (Sun et al. 2024). However, this is the first report of F. incarnatum causing postharvest fruit rot on tomato in China. This finding will inform future control strategies.