LAUSR

Mango (Mangifera indica L.) is considered one of the most important tropical or subtropical fruit crops (Nelson et al.2008). China is the second-largest producer of mango (Kuhn et al. 2017). In June 2021, postharvest stem-end rot disease was observed on Narcissus mango (about 20% of the fruits showed similar symptoms of infections) in local agricultural market of Guangzhou, China. Black rot symptomatic lesions were observed on the fruit surface, which initially started from the stem end and progresses into decay, turning brown. To isolate and identify the pathogen, small pieces (3-5 mm2) were excised from the lesion margins of the fruits (n=54), which were surface sterilized by 1% NaOCl (1 min), 70% ethanol (30 s) and then washed twice with sterile distilled water. After sterilization, the tissues were cultured on potato dextrose agar (PDA). Three morphologically similar isolates (SXM-1/2/3) were obtained and the representative isolate SXM-1 was analyzed. Colonies surface initially had white-gray moderate aerial mycelia, in reverse umber with patches of pale luteous to luteous. On malt extract agar (MEA) surface dirty white, reverse greyish sepia with patches of sienna. Conidiomata pycnidia, black, erumpent to superficial on PDA, globose with neck, ostiole exuding cream conidial droplets; Conidiophores hyaline, smooth, 1-3-septate, branched, densely aggregated, cylindrical, straight to sinuous, 22-42 × 2.8-3.7 µm. Alpha conidia (n = 50) aseptate, hyaline, smooth, fusiform to somewhat short cylindrical, 3.2-11 ×1.3-3.5 µm. Beta conidia (n = 30) hyaline, smooth, curved or hamate 14.8-33.6 × 1.1-2.6 μm. According to morphological characterization, the representative isolate SXM-1 was similar to Diaporthe pseudomangiferae CBS 101339 (Gomes et al. 2013). For molecular identification, the internal transcribed spacer (ITS) region, histone H3 (HIS) and β-tubulin (TUB) genes (White et al. 1990; Carbone et al. 1999; Glass et al.1995) were amplified and sequenced, which were deposited in GenBank (ON243823, ON254656, ON254655). BLASTN analysis revealed that DNA sequences of the isolates (SXM-1/2/3) showed 99% identity with those of D. pseudomangiferae (MG576128.1, KC344149, MN329124.1), respectively. A phylogenetic tree analysis based on the concatenated sequences confirmed the isolates as D. pseudomangiferae. Pathogenicity tests were made with the representative isolate SXM-1. Healthy fruits were inoculated with 5 mm mycelial discs of the representative isolate SXM-1 after being wounded with a needle or non-wounded, control fruits were inoculated with sterilized PDA plugs. All inoculated and control fruits were incubated in the dark at 26°C for 7 days post-inoculation. Control fruits remained asymptomatic, whereas inoculated fruits were dark brown necrotic lesions with a roughly circular shape around the inoculation sites. Pathogenicity tests were performed in triplicate. The pathogenic isolates were successfully reisolated, thus confirming Koch's postulates. D. pseudomangiferae was associated with fruit peel of mango in Mexico and the Dominican Republic, and it has also been reported to cause inflorescence rot, rachis canker, and flower abortion in mango (Gomes et al. 2013; Serratodiaz et al. 2014). To our knowledge, this is the first report of D. pseudomangiferae causing postharvest stem-end rot of mango fruits in China. This finding suggests that D. pseudomangiferae is a potential problem for mango fruit production in China, and it is important to establish an adequate and effective control management of this disease. References: Nelson, S. C. 2008.Mango Anthracnose (Colletotrichum gloeosporiodes). Publication PD-48. Cooperative Extension Service, College of Tropical Agriculture and Human Resources, University of Hawai'i at Manoa, U.S.A. Kuhn, D. N., et al. 2017. Front. Plant Sci. 8:577. White, T. J., et al. 1990. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego. Carbone, I., et al. 1999. Mycologia. 91:553. Glass, N. L., et al. 1995. Appl. Environ. Gomes R. R., et al. 2013. Persoonia. 1:31. Serratodiaz, L. M., et al. 2014. Plant Dis. 98:1004. * These authors contributed equally to this work and should be considered co-first authors. The authors declare no conflict of interest. Keywords: Stem-end rot, Diaporthe pseudomangiferae, Mango, China.