First Report of Colletotrichum scovillei Causing Anthracnose Fruit Rot on Pepper in Ontario, Canada.

Abstract

Anthracnose fruit rot affecting field peppers (Capsicum annuum L.) has been reported in Ontario, Canada, leading to significant crop losses of up to 80% over the past three years. Ten symptomatic fruits per field, exhibiting one or more soft, sunken lesions covered with salmon-colored spore masses (Fig. S1), were collected from one and two Banana pepper fields in August 2022 and 2023, respectively, all located in southwestern Ontario. Small sections of diseased tissue (0.5 cm in length) from lesion edges underwent surface sterilization and plated on 2% potato dextrose agar (PDA, Difco) supplemented with kanamycin (50 mg liter-1), neomycin sulfate (12 mg liter-1) and streptomycin sulfate (100 mg liter-1), and incubated at 22°C for 7 days in the dark. Fifteen fungal colonies were isolated and purified using the hyphal tipping method. All fungal isolates showed a pale gray colony morphology with a faint salmon tint on PDA (Fig. S1). Conidia, produced on PDA after incubating the 15 isolates at 22°C for 17 days in the dark, were hyaline, aseptate, smooth-walled, cylindrical with obtuse ends (Fig. S1), and measured 9.4 to 15.0 × 2.7 to 4.8 µm (mean ± standard deviation of 145 conidia = 11.3 ± 1.2 μm × 3.7 ± 0.5 μm), the typical morphology of Colletotrichum species (Damm et al. 2012). Internal transcribed spacer (ITS), actin (ACT), chitin synthase 1 (CHS-1), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), glutamine synthetase (GS), histone H3 (HIS3) and beta-tubulin 2 (TUB2) gene regions of all isolates were amplified and sequenced with primers ITS1/ITS4, ACT-512F/ACT-783R, CHS-79F/CHS-345R, GDF1/GDR1, GSF1/GSR1, CYLH3F/CYLH3R and Bt2a/Bt2b and deposited in GenBank (Accession Nos. ITS: PP060584 to PP060596; ACT, CHS-1, GAPDH, GS, HIS3 and TUB2: PP085919 to PP086005), respectively. The sequences were 100% identical to Colletotrichum scovillei strains from different hosts and countries (ITS: PP079643; ACT: MN718468; CHS-1: MN718466, GAPDH: MN718465.1, HIS3: MT592502, TUB2: MK462971). The maximum likelihood-based phylogenetic analysis of ITS, ACT, CHS-1, GAPDH, GS, HIS3, and TUB2 concatenated sequences was conducted using IQ-TREE 2.2.2.7 (Minh et al. 2020). All isolates from this study were grouped with high bootstrap support values with the holotype C. scovillei CBS 126529 (Fig. S2). Living cultures of these isolates were deposited in the Canadian Collection of Fungal Cultures (DAOMC 252833 to 252847). Pathogenicity was tested by inoculating 4 Banana (cv. Jumbo Stuff) and 4 Bell (cv. Archimedes) pepper fruits with 10 μl droplet of a 1 × 105 conidia ml-1 suspension of each isolate onto a wound made with a sterile pipette tip. Eight control fruits were mock-inoculated with sterilized water. Nine days post-inoculation, necrotic lesions measuring 24.7 ± 0.3 mm on Bell and 27.9 ± 0.2 mm on Banana peppers were observed. Colletotrichum scovillei was re-isolated from all symptomatic fruits, and its species identity was confirmed through morphology, fulfilling Koch's postulates. Control fruits remained symptom-free, and no fungi were isolated from them. This is the first report of C. scovillei in Canada. Previously identified as a pathogen causing anthracnose on peppers in eastern Asia, the United States, Brazil, and Kosovo (Farr and Rossman 2024; Xhemali et al. 2023), its emergence in Ontario raises significant concerns for pepper crops. Additional research is essential to better understand the epidemiology of the disease and develop effective phytosanitary strategies for control.