First report of Colletotrichum truncatum causing anthracnose of dragon fruit (Hylocereus spp.) in India

Dragon fruit (Hylocereus spp.) is gaining popularity due to high net return, medicinal importance and ability to survive under less water and poor quality soils. In year 2020 and 2021, H. undatus and H. polyrhizus plants at research field of ICAR-National Institute of Abiotic Stress Management, Baramati (18°09'30.62″N, 74°30'08″E) were affected with anthracnose disease. Out of 340 plants, 60 were symptomatic, showed disease severity up to 25 to 30%. Intermittent raining in July to September and untimely rain in November, 2021 favored the disease. Infected cladodes showed reddish to dark-brown, sunken lesions, with chlorotic haloes later converted to mature necrotic patches with prominent black acervuli. On fruits, small, light brown spots quickly turned to sunken water-soaked lesions with concentric rings of black acervuli. Infected stems were collected randomly from different plants. For pathogen isolation, lesion edge tissues (5 to 10 mm2) were excised and disinfected with 1% Sodium hypochlorite (2 min) followed by triple rinsed with sterilized water and plated on potato dextrose agar (PDA) amended with Streptomycin sulphate (30 mg/L) for 4 days at 27 ± 2°C with a 12 h photoperiod. Purified colonies of three isolates 2CT, 6CT, D6CT were obtained from successive isolation attempts. Colonies were round with smooth margins, initially pale white mycelia that changed to dark gray with pinkish-orange conidial masses. Average colony diameter was 58.3 mm at 7 DAI. Conidia were single-celled, hyaline, slightly curved, tapered tip and truncate base, with an oil globule at center. Average conidia size (n=50) was 25.7 (±2.3) μm × 3.7 (±0.2) μm, L/W ratio=6.9. Conidia were initiated from an acervular conidiomata with intermittent dark brown, septate, straight, pointed setae 114 (±35) μm long × 4.5 (±1.1) μm wide. Appressoria were dark brown, lobate or round, mostly in groups, measuring 11 (±2.4) × 6.6 (±0.8) μm. Morphological characters were consistent with Colletotrichum truncatum (Schwein.) Andrus & W.D. Moore (Damm et al. 2009). For molecular identity of three isolates, partial internal transcribed spacer (ITS) region, actin, β-tubulin (TUB2) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) genes were amplified with ITS1/ITS4, ACT512F/ACT783R, BT2A/BT2B, and GDF1/GDR1 primers, respectively. Sequences were deposited in GenBank (ITS: OK639098 to OK639100; Actin: OM927967, OM927968, ON099061; TUB2: OM927969, ON099062, ON099063; GAPDH: ON099064, ON099065). A maximum likelihood phylogenetic tree based on all sequenced loci in MEGA11 shows the clustering of present isolates in the C. truncatum clade. For pathogenicity, 4 month old unwounded stems of H. undatus and H. polyrhizus were inoculated with a spore spray (1x106/ml conidia) of C. truncatum. For each isolate, three plants were inoculated. Plants inoculated with sterilized water represented the negative control. Inoculated and control plants were kept separately at 25 ± 2°C temperature and >85% relative humidity. Inoculated plants showed minute, sunken, water soaked, reddish brown spots which were converted to sunken patches with black acervuli at 15 DAI. No symptoms were observed in the negative control. Pathogenicity test was repeated twice and the pathogen was re-isolated from symptomatic stems showed similar morphology with C. truncatum. Based on morphological and molecular characteristics and pathogenicity test, pathogen identified as C. truncatum. Previously, dragon fruit anthracnose caused by C. truncatum was reported from China (Guo et al. 2014) and Malaysia (Vijaya et al. 2015). To our knowledge, this is the first report of C. truncatum cause of dragon fruit anthracnose in India. Detailed pathogen diagnostics may help in formulating effective, on time, appropriate disease management strategies.