First Report of Mango Stem-End Rot caused by Aspergillus tubingensis in Yunnan Province, China

Mango (Mangifera indica L.) is the second-largest fruit crop in Yunnan province, China with a planting area of 114,700 hectares and an annual production of 1.329 million tons in 2021(Wang et al.2023), and has become a vital industry driving local economic growth in tropical area. However, a destructive post-harvest disease of mango fruit, Stem-End Rot (SER), poses a serious threat to the industry. On 22 July, 2023, 50 intact mangoes (cv. San Nian) were harvested from three orchards in Xishuangbanna (21°08′N 101°50'), China and stored in room temperature (24-28℃). After 5 d, 72% of the fruit developed typical SER symptoms. Initially, small brown to black lesions emerged near the stem end of the fruit, and expanded rapidly into the flesh tissue. Ten mango fruit were soaked in 75% ethyl alcohol for 3 min, then disinfected with 3% sodium hypochlorite for 30 s, and rinsed with sterile water. After drying on sterile filter paper, 0.5 cm×0.5 cm tissues were cut from the lesion margin of fruits with typical SER symptoms and cultured on PDA plates, in the dark at 28 ℃ for 5 d (Tovar-Pedraza et al.2020). Pure cultures were obtained by the single-spore isolation method (Tao et al.2024), and 48 isolates showed 3 distinct morphologies after cultivation on PDA, which were initially identified as Aspergillus tubingensis, Botryosphaeria dothidea and Colletotrichum asianum by ITS and Apmat sequencing. These A. tubingensis isolates (n=13), as a noncommon SER pathogen, formed dense, brown, powdery aerial mycelial colonies on PDA. There were brown and black conidiophore heads, and smooth and transparent conidia, scattered on the hypha mass after 10 to 15 d. The top of the conidiophores swells and forms spherical conidia with a diameter of 2.85-4.42 μm, growing in a chain-like manner at the end of the columnar body. All 13 isolates were used for a preliminary pathogenicity test. BNXJ-3, with the highest virulence, was selected for further identification. ITS (the internal transcribed spacer region) and β-TUB (beta-tubulin) of BNXJ-3 were amplified, sequenced and deposited in GenBank (ITS: PV915572, β-tub: PX262636). The ITS and β-TUB sequences of BNXJ-3 showed 98.94% (558/564) and 98.95% (470/475) identity to those of A. tubingensis CBS13448T (ex-type strain, ITS: AJ223853，β-tub: AY820007), respectively. BNXJ-3 was clustered with the A. tubingensis CBS13448T clade using MEGA 7.0.21 (maximum likelihood method). Combined with morphological characteristics(Pan et al. 2024), BNXJ-3 was identified as A. tubingensis. Pathogenicity was tested by needle-inoculating mycelial plugs near the pedicel and equatorial region of 12 non-infected mango fruit (cv. San Nian ) following Feng et al.(Feng et al.2023). Sterile PDA on three mangoes was used as a control. Inoculated fruit were incubated at 28 °C and 95% ± 3% relative humidity, with three replicates per treatment and three independent experimental runs. Typical SER symptoms were observed 7 d after inoculation, whereas the control group remained asymptomatic. The strain reisolated was identified as A. tubingensis by ITS and β-TUB sequencing in accordance with Koch's postulates. This is the first report of A. tubingensis causing SER disease on mangoes. The study broadens our understanding of the different pathogenic species associated with SER in mangoes and provides a solid scientific foundation for developing targeted management strategies against A. tubingensis-induced SER disease.