First Report of Postharvest Fruit Rot in Longan Caused by <i>Botrytis cinerea</i> in China

Longan (<i>Dimocarpus longan</i> Lour.), a Sapindaceae tropical fruit, is mainly cultivated in China, Thailand, and Vietnam. From 2015-2017, China dominated global production with 1,919.4 thousand metric tons annually (55.7% of total) (Rakariyatham et al., 2020). On Jan 5, 2025, soft rot of longan fruits (10% incidence) was found in the Fruit Wholesale Market of Qujing City (25.54°N, 103.80°E), Yunnan Province, China. The infected fruits exhibited brown epidermis with completely whitened and decayed internal tissues, accompanied by a fermented alcoholic odor. The margins of the infected fruits were cut into small pieces of 0.5 × 0.5 cm, soaked in 75% ethanol for 3 minutes, then rinsed 5 times with sterile water, and placed on potato dextrose agar (PDA), followed by incubation in the dark at 28 °C. After 24h, white mycelia emerged around the tissues, hyphal tip transfer method was used for strain purification on PDA. Four days later, the colony covered the entire 9-cm-diameter PDA and turned gray. Obvious gray sclerotia appeared in the center of the colony after 8 days. Scattered sclerotia appeared around the colony after 14 days. A large number of scattered grayish-black sclerotia were observed after 20 days. Six similar strains were isolated, with a representative isolate YC1126 subjected to morphological and molecular characterization. Morphological analysis revealed septate conidiophores with irregular inter-septal distances, apically branched to form grape-like conidial clusters. The conidia are unicellular, ovoid or ellipsoidal, with a size range of 5.1 to 9.3 μm × 6.5 to 15.4 μm (n = 50). The sclerotia are gray or grayish-black, round or irregular in shape, and the size 0.23 to 1.06 cm × 0.25 to 1.44 cm (n = 50). The morphological characteristics of this isolate are similar to <i>Botrytis cinerea</i> (Liu et al., 2024). Molecular identification was conducted by sequencing the internal transcribed spacer (ITS) region of rDNA and three nuclear protein-coding genes (glyceraldehyde-3-phosphate dehydrogenase [<i>G3PDH</i>], heat-shock protein 60 [<i>HSP60</i>], and DNA-dependent RNA polymerase subunit [<i>RPB2</i>]) using primers of ITS1/ITS4, G3PDHfor/G3PDHrev, HSP60for/HSP60rev, and RPB2for/RPB2rev, respectively (Staats et al., 2005). BLAST analysis showed that this isolate (GenBank accession nos. PQ857502, PV472625, PV472626, and PV472627 for ITS, <i>G3PDH</i>, <i>HSP60</i>, and <i>RPB2</i>, respectively) shared 99.89% to 100% identity with <i>Botrytis cinerea</i> (GenBank accession nos. PV230480 [515/515 bp], MF461628 [922/923 bp], MF461629 [1011/1011 bp], and MN159929 [1133/1133 bp], respectively). A maximum-likelihood and Bayesian posterior probability-based phylogenetic analyses with the concatenated sequences placed YC1126 in the clade of <i>B. cinerea</i>. Thus, isolate YC1126 was identified as <i>B. cinerea</i>. For pathogenicity test, 10 needle-wounded longan fruits were inoculated with 7-day-old fungal discs (with 10 unwounded as control), 10 wounded fruits with conidial suspension (1×10⁶ spores/mL) (with sterile water as control), then incubated at 28°C in the dark. The wounded fruits inoculated with fungal discs and conidial suspension showed the same disease symptoms as previously observed, while the two controls remained disease-free. The pathogen was re-isolated from the symptomatic fruits and was identified as <i>B. cinerea</i>, which fulfilled Koch's postulates. To the best of our knowledge, this is the first report of fruit rot in longan caused by <i>B. cinerea</i> in China.