First report of Colletotrichum asianum causing mango anthracnose in Puerto Rico

Authors: Serrato Diaz, Luz; YAIR, ARON - Martex Farms; Ayala Silva, Tomas; Goenaga, Ricardo

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2025
Publication Date: 7/31/2025
Citation: Serrato Diaz, L.M., Yair, A., Ayala Silva, T., Goenaga, R.J. 2025. First report of Colletotrichum asianum causing mango anthracnose in Puerto Rico. Plant Disease. https://doi.org/10.1094/PDIS-01-25-0180-PDN.
DOI: https://doi.org/10.1094/PDIS-01-25-0180-PDN

Interpretive Summary: Mango (Mangifera indica), a major tropical fruit, suffers from a severe fungal disease called anthracnose (caused by Colletotrichum species) that rots fruit in eight days, drastically reducing its marketability. During a survey in Isabela, Puerto Rico, mango anthracnose on leaves was found on 18 varieties: Aman Dusheri, Cambodiana, Colombo Kidney, Fajri, Himsagar, Katar Rum Rung, Leyat, Langra, Mamou, Mulgoba, Nam tan teen, Osteen, Saigon, Sang tong, Suwon tip, Tete Nene, Sad Lim Pua and Tommy Atkins. Diseased leaves were analyzed in the lab, and three isolates of Colletotrichum asianum were identified through microscopy and DNA sequencing. Pathogenicity tests showed that all 18 varieties developed necrotic leaf spots after being sprayed with Colletotrichum fungal spores. On detached fruits, anthracnose lesions appeared as early as eight days after inoculations on Nam Doc Mai and 15 days on Keitt. Untreated leaves and fruits showed no symptoms. The fungus was confirmed through re-isolation and genetic testing, fulfilling Koch's postulates. C. asianum is known to cause mango anthracnose in other countries such as Brazil, China, Indonesia, Mexico, the Philippines, South Africa and Taiwan. This is the first report of C. asianum causing mango anthracnose in Puerto Rico. Identifying C. asianum as a causal agent of mango anthracnose is important to establish adequate control measures of this disease in Puerto Rico.

Technical Abstract: Mango (Mangifera indica) is one of the major tropical fruits traded worldwide. The mango industry faces anthracnose, a devastating fungal disease caused by Colletotrichum spp., that affects mango production and shelf life. This pathogen can result in complete rot of mangoes in less than 8 days, thus limiting its marketability. During a disease survey at the USDA-ARS mango backup germplasm collection in Isabela, Puerto Rico, mango anthracnose on leaves was found in the following varieties: Aman Dusheri, Cambodiana, Colombo Kidney, Fajri, Himsagar, Katar Rum Rung, Leyat, Langra, Mamou, Mulgoba, Nam tan teen, Osteen, Saigon, Sang tong, Suwon tip, Tete Nene, Sad Lim Pua and Tommy Atkins. Diseased pieces (1 mm2) of mango leaf tissues were surface disinfested and plated on potato dextrose agar (PDA) amended with 250 mg/L ampicillin and 60 mg/L streptomycin. Three isolates (MFANT6, MLANT2 and MLANT4) of Colletotrichum asianum were identified using taxonomic keys (Prihastuti et al. 2009; Weir et al. 2012) and through sequencing of the internal transcribed spacer (ITS), amplified from portions of the ß-tubulin (BT), Actin (ACT), and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) genes. The sequenced regions are represented in GenBank accession numbers: PQ811864, PQ811865 and PQ811866 for the ITS region; PQ815301, PQ815302 and PQ815303 for BT; PQ815278, PQ815279 and PQ815280 for ACT; and PQ815324, PQ815325 and PQ815326 for GADPH. A maximum likelihood tree was constructed with sequences of the three isolates mentioned above and sequences of the ex-type isolates of the C. gloeosporioides complex. The tree was rooted to C. boninense ex-types MAFF306094 and MAFF305972. All three isolates were clustered (Bootstrap = 99) to C. asianum ex-types ICMP18580 and ICMP18696 (Prihastuti et al. 2009). To characterize morphologically, colonies of C. asianum grown on PDA were grayish green with aerial mycelial growth and conidial masses. Conidia (n = 50) were 13.8 × 3.6 µm in length, single-celled, smooth-walled, hyaline, cylindrical and with obtuse ends. Acervuli and perithecia were absent in culture. Pathogenicity tests were conducted on non-detached leaves and on detached mango fruits. For non-detached leaves, two 15 years-old trees of the 18 varieties mentioned above, were used in the experiments. Twigs containing at least 10 healthy leaves were inoculated with approximately 10 ml of a suspension of 4.5 x 105 conidia/ml from 8 days-old pure cultures of C. asianum. Untreated controls were inoculated with sterilized distilled water only. Inoculated mango twigs were covered with plastic bags for 30 days to maintain humidity. Thirty days after inoculations (DAI), necrotic spots on leaves were observed in all inoculated varieties. For detached fruits, 12 healthy and surface-disinfested mango fruits of commercial varieties Keitt and Nam Doc Mai were inoculated with approximately 5 ml of a suspension of 4 x 105 conidia/ml from 8 days-old pure cultures of C. asianum. Untreated controls were inoculated with sterilized distilled water only. Inoculated fruits were placed in a plastic box for 8 days at room temperature. Anthracnose severity was evaluated at 8, 15, 20 and 25 DAI. Eight DAI, anthracnose sunken lesions were observed on Nam Doc Mai while lesions on Keitt were visible 15 DAI only. Untreated controls on both non-detached leaves and detached mango fruits had no symptoms of anthracnose, and no fungi were isolated from tissue. Colletotrichum asianum was reisolated from both leaf and fruit tissue and sequences of isolates recovered from pathogenicity test were grouped with original C. asianum isolates and C. asianum ex-types, fulfilling Koch’s postulates. Colletototrichum asianum has been reported causing mango anthracnose in Brazil, China, Indonesia, Mexico, Philippines, South Africa and Taiwan (Alvarez et al. 2020; Benatar, et al. 2021; Li et al. 201