First Report of Paramarasmius palmivorus Causing Collar Rot of Solanum aethiopicum gilo in Ghana
Authors: Okorley Benjamin Azu , Brentu Francis Collison , Ravnskov Sabine , Offei Samuel K. 
Published: January 2025

African eggplant (Solanum aethiopicum gilo group) is a nutritious vegetable widely commercialized in Ghana. In the 2021 planting season (May-July), collar rot symptoms were observed on African eggplant on a farm at Domeabra, Legon, and Okumaning in the Central (N5° 48′ 11″, W1° 26′ 48″), Greater Accra (N5° 39′ 34″, W0° 11′ 34″) and Eastern (N6° 8′ 34″, W0° 55′ 59″) regions of Ghana, respectively. Disease incidence was 8-15% in the different farms. Infected plants showed gray-colored lesions at the collar region, soft root rot, and, eventually, wilted due to stem girdling. Thin mycelia were observed on the affected parts of the stem and roots. To identify the causal agent, small portions of diseased stem tissues were submerged in 2% NaOCl for 2 min and rinsed thrice in sterile distilled water (SDW). Next, they were transferred to PDA, amended with ampicillin (50 mg/ml), and then incubated at 25°C for 3 days. Twelve isolates purified by the hyphal-tip culture method were similar morphologically, fluffy with a smooth texture like fine chamois, initially cottony white, and turning pale orange at the center with aging. They were fast-growing, reaching 63.7 to 72.1 cm in diameter. Hyphae were hyaline, septate, branched, 1.4 to 3.1 µm in diameter. These morphological features resembled Paramarasmius sp., classified originally as Marasmius (Sharples) (Antonín et al., 2022). Genomic DNA was extracted from the mycelia of three isolates from the various sampling regions for molecular identification. Two rDNA regions, the internal transcribed spacer (ITS) and mitochondria small subunit (mtSSU), were amplified and sequenced using the ITS1/ITS4 and MS1/MS2 primers, respectively (White et al., 1990). BLASTn analysis of the ITS and the mtSSU sequences revealed a 99.9% and 99.8% identity to P. palmivorus (MN871733.1 and MN794124.1, respectively), further confirmed by phylogenetic analyses. To confirm pathogenicity, the inoculum was made by transferring mycelial plugs from three isolates into autoclaved millet grains, pre-soaked in SDW for 6 hrs. The cultures were incubated at 25 ± 1°C for 8 days, with regular shaking every 2 days to ensure uniform growth. Subsequently, fungal inoculation was made by placing three grains colonized by mycelia close to the stem base of a 21-day-old healthy seedling of African eggplant (cv. Kotobi) raised in pots filled with sterilized potting soil. Each fungal treatment consisted of six replicates of inoculated plants. Three plants were mock-inoculated with autoclaved grains to serve as control treatments, and the experiment was repeated twice. The plants were kept in a screen house with a 12/12 hrs light-dark cycle at 28 ± 3°C. Daily irrigation was done using SDW. Five days after inoculation, typical stem rot symptoms developed at the collar region, characterized by grey water-soaked lesions and thin white mycelium. Next, the seedlings toppled, wilted, and died within 7-14 days. No symptoms were observed in the mock-inoculated plants. The pathogen was reisolated from infected plants on PDA and confirmed as P. palmivorus according to the molecular approach outlined above. P. palmivorus has been recorded to cause bunch rot in oil palm and thread blight disease of cocoa in Ghana (Amoako-Attah et al., 2020). To our knowledge, this study is the first record of P. palmivorus affecting African eggplant in Ghana, and it emphasizes the need to control and determine the host range of this pathogen.