First Report of Peduncle Dieback of Rose Caused by Colletotrichum gloeosporioides in Korea

Abstract

Roses are an ornamental crop and grown commercially as cut flowers. They are also used in the perfume, jam, and jelly industry. Dieback of rose is a major disease caused by different types of fungi including Lasiodiplodia pseudotheobromae, Acremonium sclerotigenum, Coniothyrium fuckelii, and Botrytis cinerea (Mirtalebi et al. 2016; Wee at al. 2017). Severe peduncle dieback of rose was observed in a garden Sngju, South Korea, in August 2018. Typical symptoms are characterized by progressive death of peduncle from the flower bud. The presumptive causal agent was isolated from infected tissue. Small sections of peel (2 × 2mm) were cut from the margin of infected tissue and disinfected with 0.5% NaOCl for 1 min, followed by rinsing in sterile water. A disinfected section of infected tissue was blotted dry, placed on potato dextrose agar (PDA), and incubated at 25°C in the dark. Two pure isolates (ICKR1 and ICKR2) were obtained by transferring newly emerging hyphal tips to the new fresh PDA plates. Colonies on PDA were creamy white with small black perithecia produced across the colony after 3 weeks. Asci were eight-spored, clavate to cylindrical, and 57.6 to 83.5 × 9.2 to 14.6 μm (mean ± SD = 70.1 ± 9.2 × 12.1 ± 1.35 μm) (n = 35). Ascospores were hyaline, unicellular, curved or straight with round ends, and 15.2 to 30.8 × 5.2 to 8 μm (mean ± SD = 21.4 ± 3.6 × 6.40 ± 0.8 μm) (n = 30). The morphology of asci and ascospores overlapped with the previous morphological description of Glomerella cingulata (teleomorph of C. gloeosporioides) (Ireland et al. 2008; Weir et al. 2012). Only a few conidia were produced on PDA, which were hyaline, cylindrical, straight with one or both ends rounded, and 18.8 to 24.6 × 5.9 to 6.8 μm (mean ± SD = 21.45 ± 1.9 × 6.3 ± 0.45 μm) (n = 20). Appressoria were brown and unlobed. Molecular analysis was reformed using the internal transcribed spacer (ITS) region of rDNA and partial GAPDH, TUB2, CHS-1, ACT, and CAL genes sequence data. The complete ITS region and partial GAPDH, TUB2, CHS-1, ACT, and CAL genes were amplified using ITS1F/ITS4, BT2a/BT2b, ACT-512F/ACT-783R, CHS-79F/CHS-345R, ACT-512F/ACT-783R, and CL1C/CL2C primer sets, respectively (Weir et al. 2012), and sequenced. The resulting sequences were deposited in GenBank (accession nos. LC469311 to LC469322). Phylogenetic analysis (maximum likelihood and neighbor joining) using MEGA 6 software delineated the present isolates from rose as Colletotrichum gloeosporioides. Pathogenicity tests were conducted on small twigs of rose containing at least one bud. Ten twigs were washed in tap water, disinfected with 90% ethanol, rinsed with distilled water, and prepared for inoculation. Each prepared twig was put in a plastic tube containing distilled water. The conidial suspension (1 × 10⁶ conidia /ml) of ICKR1 isolate was sprayed over six twigs. Another four twigs received distilled water and served as control. Both treated and control twigs containing tubes were place in a tube holder rack and incubated at 25°C and 16 h/6 h light/dark. After 12 days, typical dieback symptoms appeared on inoculated twigs, whereas control twigs remained asymptotic. The causal agent was reisolated and identified as C. gloeosporioides and confirmed Koch’s postulates. C. gloeosporioides is a ubiquitous pathogen on a wide range of crops and is responsible for anthracnose. C. gloeosporioides has been reported as the causal agent of Eucalyptus dieback in South Africa and tip dieback of Lygodium microphyllum and L. japonicum in Australia (Ireland et al. 2008; Smith et al. 1998). To our knowledge, this is the first report of dieback of rose caused by C. gloeosporioides in Korea.