First report of Fusarium fujikuroi causing fruit rot in Persian lime ( Citrus × latifolia Tanaka) in São Paulo citrus belt

Persian lime (Citrus × latifolia Tanaka), also known as Tahiti lime, is a citrus species grown worldwide for fresh fruit consumption and industry purposes. In São Paulo citrus belt, Brazil, Persian lime accounts for 40,536 ha, corresponding to 88.07% of the area cultivated with lemons and acid limes (Fundecitrus, 2025). Fusarium fruit rot is considered a mild disease of citrus; however, it was recently reported as widespread in Bangladesh, causing significant postharvest losses (Hasam et al., 2023). In early July 2025, harvested Persian lime fruit intended for export to Europe exhibited high incidence of white mold at the stylar end in a packinghouse located in the municipality of Matão, São Paulo, Brazil (21.6036° S, 48.3644° W). In the packinghouse, 500 samples of fruit were assessed, of which 40% were symptomatic and consequently discarded as unmarketable. Sporodochial conidiophores, bearing terminal phialides, were observed in infected stylar tissues, indicating a Fusarium sp. as the causal agent. These structures were transferred to Petri dishes containing full-strength Potato Dextrose Agar (PDA). A single-spore isolate (LFN0501) was obtained on PDA, and colonies were white with a pale orange reverse. Microconidia (n = 50) were hyaline, oval to ellipsoidal, aseptate, and measured 14.43–17.87 × 3.93–6.21 µm (average: 15.96 × 5.30 µm). Macroconidia (n = 50) were falcate, moderately curved, 2–5 septate and measured 24.13–50.87 × 4.11–6.24 µm (average: 38.79 × 5.21 µm); the apical cell was blunt to slightly papillate, and the basal cell was foot-shaped or slightly notched. Chlamydospores were absent. DNA was extracted from aerial mycelium using the Wizard® Genomic DNA purification kit (Promega), following manufacturer’s instructions. The RNA polymerase II second largest subunit (rpb2) (Liu et al., 1999) and translation elongation factor 1-alpha (tef1) (O’Donnell et al., 1998) were amplified. Sequences were deposited in GenBank (PZ303406 and PZ303407) and showed highest similarity to F. fujikuroi, with 100% (941/941 bp – PP066121.1) and 99% (652/653 bp - MN958238.1) identity for rpb2 and tef1, respectively. The phylogenetic reconstruction placed strain LFN0501 with the F. fujikuroi reference strain (CBS22176). Pathogenicity tests used detached Persian lime fruit (n = 10) inoculated at the stylar end with 50 µL of a conidial suspension droplet (7 × 10⁴ spores/mL) collected from 7-day old colonies grown on full-strength PDA at 25 ± 2 °C and 12h light/dark photoperiod. Fruit were incubated at 25 ± 5 °C in the dark for 48 h using separated airtight plastic containers lined with moist paper towels and then transferred to a growth room set at 25 ± 5 °C and 12h light/dark photoperiod. Symptoms similar to those observed in the packinghouse developed five days after inoculation, whereas negative control fruit samples (n = 5) remained asymptomatic. Koch’s postulates were fulfilled by re-isolating the pathogen and confirming its identity through a new sequencing of the same gene regions. F. fujikuroi is widely implicated in citrus root rot, twig dieback and bark decay disease in China and Europe (Xiao et al., 2025; Sandoval-Denis et al., 2018) but has been rarely associated with fruit rot symptoms. To our knowledge, this is the first report of F. fujikuroi causing fruit rot in Persian lime in Brazil. We expect that this report will encourage researchers to more thoroughly investigate the pathogen etiology and provide useful information for this disease management in Brazil.