Management of carrot Alternaria leaf blight (Alternaria dauci) with seed treatments in East Hararghe, Ethiopia

Carrot ( Daucus carota L.) is an important root crop, commonly affected by a seed borne Alternaria dauci that causes leaf blight. In Ethiopia no seed treatment study was conducted for the disease. Therefore Laboratory, pot and field/nursery experiments were conducted at Haramaya University during 2020 and 2021 with the aims to evaluate the effect of seed treatments on A. dauci infection, seed germination, seedling emergence and root yield using naturally-infected seeds of Haramaya I carrot variety. Infected seeds were treated with fungicides (carbendazim, copper hydroxide, imidalm), hot water, bleach (chlorox), and common salt (NaCl). Untreated naturally-infected carrot seeds used as a control. The treatments were arranged in a completely randomized design with four and three replications for laboratory and pot experiments, respectively. A randomized complete block design with three replications employed for field experiments. The treatments significantly (P≤0.001) reduced A. dauci infection and improved seed germination and seedling emergence over the untreated controls. Carbendazim-treated seeds had the lowest mean infection (1.5%), while untreated seeds had the highest (77%). The treatments reduced disease incidence, severity, and area under the disease progress curve. At 95 days after sowing, mancozeb-treated plots had the lowest mean severity (28.8%), while the highest 52.03% was in untreated plots. Root yield increased by 2.49 tons (bleach treatment) to 12.23 tons (carbendazim-treatment) per hectare compared to untreated control. Carbendazim, mancozeb, and imidalm effectively managed the seedborne A. dauci . Hot water, common salt, and bleach also reduced the pathogen and can be applied as alternative treatments to the fungicides. • Seed treatment study was conducted at Haramaya University Ethiopia, to control Alternaria dauci (a fungal pathogen causing carrot leaf blight disease). • The efficacy of the treatments was investigated using naturally A. dauci infected seeds. • While previous research focused on agar-based assays, this study provides a more realistic assessment. • Carbendazim, mancozeb, and imidalm fungicides highly reduced A.dauci infection of seeds and disease intensity. • These fungicides significantly enhanced seed performance and crop yield. • The non-fungicide treatments, hot water, salt and bleach also reduced A. dauci infection and increased carrot root yield.