Genetic and phytochemical mechanisms underlying resistance to coffee wilt disease (Fusarium xylarioides) in diverse Ethiopian Arabica coffee (Coffea arabica L.) genotypes

Coffee is Ethiopia’s leading export commodity and supports the livelihood of more than 15 million people. However, its production is constrained by several biotic factors, most notably coffee wilt disease (CWD), caused by Fusarium xylarioides. Although the use of resistant varieties is an effective management strategy, the limited availability of resistant genotypes and unclear resistance mechanisms have hindered its application. Therefore, this study was conducted to identify resistant genotypes, explore resistance mechanisms, and examine the association between disease severity and phytochemical compounds. A total of 112 genotypes (111 Arabica and one Robusta) were artificially inoculated and evaluated under greenhouse conditions at the Jimma Agricultural Research Center in 2023 and 2024 using a randomized complete block design with three replications. Disease severity percentage (DS%) and incubation period (IP) were recorded periodically to calculate the area under the disease progress curve (AUDPC). Spectrophotometry and HPLC were used to quantify total phenol content (TPC), antioxidant capacity (AO), chlorogenic acid (CGA), caffeine (CAF), and trigonelline (TRG) contents in stem and leaf samples taken from inoculated and non-inoculated seedlings. Results revealed wide continuous variation in DS% (2.63–95.83%), AUDPC, and IP, with broad-sense heritability exceeding 70% and high genetic advance, indicating that resistance is predominantly governed by polygenic control and responsive to selection. Seventeen resistant genotypes were identified, characterized by low AUDPC and prolonged IP, of which three (B-136/04, G-07/13, and B-03/04) were highly resistant. In most resistant genotypes, inoculation with Fusarium xylarioides increased TPC, AO activity, and CGA in seedling leaves, along with CGA and CAF in stems. Disease severity showed strong negative correlation with IP, CGA, TPC, and AO activity, suggesting potential for indirect selection. Overall, these findings highlight the defensive roles of phytochemicals and their potential as resistance markers, providing key insights for developing resistant varieties. Future studies should include enzymatic and mineral analyses of stem tissues under both controlled and field conditions to further identify the resistance mechanisms.