First Report of Anthracnose Caused by Colletotrichum spaethianum on Allium ledebourianum in India

Allium ledebourianum (Ledebour chive) is known for its culinary, medicinal, and ornamental properties. During the rainy season (June to September) of 2015 and 2016, symptoms similar to anthracnose were observed on 40 to 50% of A. ledebourianum plants in the wild allium repository at Indian Council of Agricultural Research–Directorate of Onion and Garlic Research, Rajgurunagar, Pune, India. Leaves of infected plants exhibited brown, necrotic, elliptical lesions measuring 10 to 50 mm in length. Acervuli with prominent setae had developed within lesions in concentric rings. In humid weather (>75% relative humidity) constant enlargement of lesions toward the leaf ends resulted in complete leaf necrosis. Small (5-mm²) sections of leaf tissue at the edge of lesions were excised and surface disinfested with 1% NaOCl for 2 min, rinsed three times in sterile distilled water, blotted dry with sterile blotter paper, and plated on Sabouraud dextrose agar for 4 days at 25 ± 2°C and 12-h photoperiod. Three isolates (AAL-1, AAL-2, and AAL-3) were recovered from infected plants. Initially, colonies were white and later turned to pale gray, salmon-colored masses of conidia, acervuli and black sclerotia-like bodies were observed embedded in the medium. Microscopically, conidia were hyaline, single-celled, curved or slightly curved with a rounded apex and a truncate base, measuring 12.5 to 19.0 (15.4 ± 1.55) µm in length and 2.9 to 4.4 (3.1 ± 0.43) µm in width. Conidia contained one oil globule either at the center or the end. Acervular conidiomata were covered with abundant, dark-brown setae having an acute tip, two to four septa, and 55.0 to 96.3 µm in length. Appressoria were dark brown, either single or in loose groups, irregularly shaped, 6.0 to 11.0 μm long, and 4.8 to 7.9 μm wide. The characteristics were consistent with Colletotrichum spaethianum (Allesch.) Damm, P.F. Cannon & Crous (Damm et al. 2009). The internal transcribed spacer (ITS) region of rDNA, a partial sequence of actin (ACT), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene were amplified with ITS1 and ITS4, ACT-512F and ACT-783R, and GDF1 and GDR1 primers, respectively (Damm et al. 2009). The ITS sequence (MG650112) shared 99% similarity with C. spaethianum from alfalfa (KX364060) in the GenBank. The ACT gene (MG738716) and GAPDH gene (MG733341) showed 97 and 98% identity with C. spaethianum from Atractylodes japonica (KT122853) and Hemerocallis spp. (JQ400010), respectively. For pathogenicity tests, 45-day-old plants (n = 5) were sprayed with conidia suspension (10⁶ conidia/ml) and control plants with sterilized water and kept separately in a growth chamber at 25°C, 85% relative humidity, and a 12-h photoperiod. Symptoms consistent with anthracnose as outlined above developed 10 days postinoculation, whereas control plants were symptomless. The fungus was reisolated from the symptomatic leaves and confirmed as C. spaethianum. Recently, C. spaethianum causing anthracnose of A. fistulosum was documented from Brazil (Santana et al. 2016). To our knowledge, this is the first report of C. spaethianum causing anthracnose on A. ledebourianum in India.