First Report of Mango Anthracnose Caused by <i>Colletotrichum plurivorum</i> in China

Mango (Mangifera indica L.), is an important tropical fruit crop in China (Shu et al., 2020). Anthracnose caused by Colletotrichum spp. is a serious threat to production (Li et al., 2019). In April 2024, irregular curly lesions with black necrotic spots were observed on mango leaves in Hainan province, China (18.456936°N, 109.831150°E). Symptoms progressed along margins of young leaves. Disease incidence was 20% in the affected 5-ha orchard. Twenty symptomatic samples were collected; six leaves with typical anthracnose lesions were used for isolation. Tissue samples (5 mm²) from lesion margins were surface-sterilized (75% ethanol for 1 min, 0.5% NaOCl for 30 s), rinsed thrice with sterile water, and plated on potato dextrose agar (PDA) with chloramphenicol. Three representative isolates (24MGC68-1, -2, -3), selected from four isolates obtained from six mango leaves (66.7% isolation rate), were purified by hyphal tipping. After 4 days on PDA at 28°C, all exhibited light gray aerial mycelia. The colonies were white to pale gray with dense aerial mycelia that presented a similar appearance on the reverse side. The conidia of isolates were cylindrical, smooth-walled, and hyaline, ranging from 13.4 - 16.7 × 5.1 - 6.1 µm (n=100). The appressoria of isolates are loosely distributed, ranging in color from pale to medium-brown, with smooth walls, nearly spherical to oval shape, and intact or lobed margins, mean ± SD = 2.78 ± 0.63 × 3.26 ± 0.75 µm, Length/Width ratio = 1.17 (n=20). These morphological characteristics were similar to Colletotrichum spp. as previously described (Damm et al. 2019). For molecular identification, partial sequences of the internal transcriptional spacer (ITS), actin (ACT), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH), beta-tubulin (TUB2) and histone H3 (HIS3) were sequenced using specific primers (Damm et al., 2019, Weir et al., 2012). All sequences (GenBank accessions: PX232777–PX232778, PX243752–PX243759, PQ803202, PQ738182, PQ807008, PV862204–PV862205) showed more than 99% similarity with C. plurivorum strain LP13-2 (accession: OM432472, OM472173, OM655153, OM662296, OM655179). Based on these morphological and molecular analyses, isolates were identified as C. plurivorum. In the pathogenicity test, nine healthy mango plants with tender leaves were sprayed with a conidia suspension (106 conidia/ml) prepared from 5-day-old colonies of 24MGC68-2. Three control plants were treated with sterile distilled water. Necrotic lesions developed on inoculated plants within 3-7 days post-inoculation, whereas control plants remained asymptomatic. This experiment was repeated twice under the same conditions. To confirm pathogenicity, C. plurivorum was re-isolated from the margins of necrotic tissues on inoculated plants. No pathogens were isolated from the asymptomatic control plants after surface sterilization and culturing on PDA. The re-isolated strain exhibited identical morphological and molecular characteristics to the original isolate, thereby fulfilling Koch’s postulates. Although C. plurivorum has been reported on Mangifera indica in Brazil (Damm et al., 2019), this study provides the first confirmed record of C. plurivorum causing mango anthracnose in China.