First Report of Rust Caused by Cerotelium fici on Ficus carica L. in Korea.

Abstract

Fig (Ficus carica L.) belonging to the Moraceae family is cultivated worldwide, with its primary production areas located in the Mediterranean region (Tous and Fergusen 1996). Yeongam-gun is a significant region for fig cultivation in Korea, accounting for 42% of the country's total fig cultivation area with approximately 1,400 fields (453ha, production yield 6000 tons). In July to November 2023, we observed severe rust disease in four fig orchards in Yeongam-gun (34°42'52.2"N, 126°31'32.16"E). The disease had affected 70% of the fig cultivation area (cv. Masui Dauphine). The area of each field is approximately 0.33~0.66ha, and 5 samples were collected from each field. Pustules of the pathogen were found in all samples. The diseased plants were deposited in the herbarium of the National Institute of Agricultural Sciences, Wanju, Korea (Specimen No. Cero_001). The initial symptoms were observed as chlorotic spots on the adaxial surface of the leaves, which developed into necrotic areas surrounded by chlorotic halos. Over time, dark brown spots were observed on the adaxial surface of the leaves, and abundant reddish-brown pustules were visible on the abaxial surface. Almost all leaves with these symptoms fell prematurely. Microscopic observation revealed that the urediniospores (n>50) were ellipsoidal, globose, obovoidal, or angular in shape, yellowish to faintly orange in color, sized 19.5-39.9 × 10.1-27.5 μm and had a wall thickness of 0.6-1.5 μm (average 1 μm). Telia were not observed. These morphological characteristics were comparable with that of Cerotelium fici (Gardner, 1997; Latinovic et al., 2015). For molecular analysis, genomic DNA was extracted from 3 to 5 samples, and the internal transcribed spacer region 2 (ITS2) and the large subunit (LSU) were amplified and sequenced using primer set: Rust2inv (Aime, 2006) and LR6 (Vilgalys and Hester, 1990). Furthermore, approximately 660 bp of the cytochrome c oxidase subunit III (COX3) gene was amplified and sequenced with CO3_F1 and CO3_R1 primers (Vialle et al., 2009). The obtained sequences were deposited in NCBI GenBank (GenBank accession no. PP491072 to PP491074 and PP491079 to PP491081). Phylogenetic tree analysis using the maximum likelihood method identified the isolate as Cerotelium fici. Pathogenicity test was conducted either by placing or by rubbing symptomatic leaf pieces on healthy leaves (5 leaves/plant) of three-year-olds fig plants (cv. Masui Dauphine) in a greenhouse in Wanju-gun, Jeonbuk special self-governing province. Healthy and symptom free leaf pieces were used for control. Two plants per treatment were used and the experiment repeated twice. The typical symptoms of fig rust disease were observed two weeks after inoculation in both methods. Control leaves were symptomless. C. fici was successfully reidentified from symptomatic tissues of inoculated leaves, fulfilling Koch's postulates and confirmed as a causal agent of fig rust. Fig rust caused by C. fici has been reported in New Zealand, Montenegro, Hawaii and other tropical regions (McKenzie, 1986). To our knowledge, this is the first report of fig rust in Korea caused by Cerotelium fici. It is believed that this will be helpful in research on the management of fig rust disease.