First Report of Thread Blight Disease Caused by <i>Ceratobasidium niltonsouzanum</i> on <i>Coffea arabica</i> in Peru

Thread blight of coffee is commonly attributed to Corticium koleroga. However, similar symptoms can also be caused by Ceratobasidium spp. and Marasmius spp. (de Melo et al. 2018; Lima et al. 2019; Huamán-Pilco et al. 2021). We report Ceratobasidium niltonsouzanum on coffee in Peru, suggesting that “thread blight” symptoms may have different aetiologies and warrant local surveys. In early 2024, symptoms of thread blight disease were observed on coffee plants (Coffea arabica cv. Catimor) in commercial plantations in Rodríguez de Mendoza, Amazonas, Peru (6.56°S, 77.22°W; 1573 m above sea level). Affected plants exhibited necrotic foliar lesions and white, thread-like fungal structures connecting the leaves and branches (Figure 1). Diseased tissues were surface-sterilized and plated on potato dextrose agar (PDA), from which four isolates (ECA-100, ECA-113, ECA-115, ECA-116) were purified using the single-hyphal tip technique (Huamán-Pilco et al. 2023). Colonies were initially white and cottony, becoming cream to light brown with age (Figure 2). Microscopic examination of the microcultures showed hyaline, septate hyphae exhibiting right-angle branching, characteristic of Ceratobasidium species. However, no basidia formation was detected (Figure 3). Genomic DNA was extracted from PDA-grown mycelium and hyphal threads using a Wizard DNA kit (Promega, USA), and the ITS region (ITS1–5.8S–ITS2) was amplified using primers ITS1F/ITS4. Sequencing (Macrogen, South Korea) and BLASTn analysis of the ITS sequences revealed 99.5%–99.7% identity with Ceratobasidium niltonsouzanum sequences from Brazil (Figure 4) (de Melo et al. 2018), identifying the isolates to species. Sequences were deposited in GenBank under Accession Nos. PV544844, PV544845, PV544846 and PX271061. Pathogenicity was confirmed by inoculating four healthy coffee plants with 7-day-old PDA cultures using sterile toothpicks colonised by the fungus; control plants received sterile toothpicks. Fifteen days post-inoculation, inoculated plants developed necrotic foliar lesions with thread blight symptoms, while control plants remained symptomless. Ceratobasidium niltonsouzanum was re-isolated from symptomatic tissues, fulfilling Koch's postulates (Figure 5). Ceratobasidium niltonsouzanum has been reported previously on various tropical crops in Brazil and yerba mate (Ilex paraguariensis) Argentina (de Melo et al. 2018; Lima et al. 2019), but not on coffee in Peru. To our knowledge, this is the first record of Ceratobasidium niltonsouzanum causing thread blight on Coffea arabica in Peru. Our findings highlight the need for local surveys also considering the as yet unreported but globally widespread Corticium koleroga to clarify aetiology and guide epidemiology and management. The authors gratefully acknowledge the Laboratorio de Investigación en Sanidad Vegetal (LABISANV) of the Universidad Nacional Toribio Rodríguez de Mendoza de Amazonas (UNTRM). The authors declare no conflicts of interest.