First Report of Anthracnose of Mangifera indica Caused by Colletotrichum scovillei in China

Abstract

Mango anthracnose caused by Colletotrichum spp. is a constraint for sustainable mango (Mangifera indica L.) production. During May 2013, anthracnose symptoms were detected on mango leaves (cultivar Tainong No. 1) in Guangxi, China, which appeared on tender leaves as point-sized, red-brown to black, sunken spots that enlarged to circular or irregular lesions with a red halo, turning yellow as the leaves became older. Under unfavorable conditions, spots turned black but did not enlarge; rather, diseased leaves frequently became distorted and wrinkled. Tissue pieces (5 × 5 mm) were cut from infected leaves and soaked in 75% ethanol for 10 s, followed by 2 min in 0.1% HgCl₂, rinsing with sterile water, and plating onto potato dextrose agar (PDA). Of the 65 Colletotrichum strains isolated during our 3-year survey (2011 to 2013), a novel Colletotrichum culture (strain QZ7L) was obtained from an infected leaf sample of Lingshan county (22°24′59″N, 109°17′27″E). The strain was purified by single-spore isolation and incubated on PDA at 25°C under continuous fluorescent light irradiation, producing white to pale gray colonies with dense aerial mycelia. The reverse side of the colony was pale yellowish to olive. Conidia were hyaline, unicellular, straight, cylindrical, with both ends slightly round or one end round and the other slightly pointed, measuring 7.6 to 15.8 (average 10.3) × 3.0 to 4.7 (average 3.8) µm (n = 50). Appressoria were single, subglobose, ovate to clavate, light brown to dark black, 5.9 to 10 (average 7.9) × 4.5 to 7.8 (average 5.7) µm (n = 50). Morphological characteristics of the strain matched those of Colletotrichum scovillei (Damm et al. 2012). DNA of strain QZ7L was amplified with primers for three DNA loci—the internal transcribed spacer region of ribosomal DNA and two genes (glyceraldehyde-3-phosphate dehydrogenase and actin) —using primer pairs ITS1/ITS4, GDF1/GDR1, and ACT-512F/ACT783R, respectively (Qin et al. 2018), and the resulting sequences were submitted to the European Nucleotide Archive with accession numbers LT632569, LT632591, and LT632580, respectively. A concatenated maximum likelihood phylogenetic tree was built using MEGA 6.06. Strain QZ7L clustered with C. scovillei, clearly separating from other Colletotrichum spp. Conidial suspensions (10⁶ spores/ml) were used to inoculate the entire surface of attached tender leaves (cultivar Tainong No. 1) using a sterilized paintbrush and incubated at ambient temperature. Symptoms appeared after 3 days and were similar to those observed on naturally infected plants. The uninoculated controls remained symptomless. C. scovillei was reisolated from the lesions of inoculated leaves, fulfilling Koch’s postulates. C. acutatum, C. gloeosporioides, C. asianum, C. fructicola, and C. siamense were reported as causal agents of anthracnose on mango in China (Hu et al. 2012; Qin et al. 2017, 2018). C. scovillei was reported as a pathogen causing diseases on pepper (Damm et al. 2012) and banana (Zhou et al. 2017). This is the first report of C. scovillei causing anthracnose on mango in China. Although C. scovillei was found to be a rare species of Colletotrichum responsible for anthracnose on mango in this work, a tracking survey on the pathogen should be done for sustainable production of mango in the future.