In Vitro Evaluation of Different Fungicides Against Hard Rot Pathogen of Annona muricata L.

Postharvest fungal diseases remain a major constraint to the production, storage, and marketing of Annona muricata L. (soursop), causing significant economic losses through reduced fruit quality and shelf life. This study evaluated the in vitro efficacy of three commercial fungicides against Colletotrichum gloeosporioides associated with hard rot of soursop fruits. Diseased fruits exhibiting characteristic hard rot symptoms were collected from Ado-Ekiti, Nigeria, and the pathogen was isolated on Sabouraud Dextrose Agar (SDA). Pure cultures were obtained through subculturing and evaluated using the poisoned food technique. Three fungicides—Ridomil Gold® (Metalaxyl-M + Mancozeb), Tandem® (Copper (I) oxide + Metalaxyl), and Z-Force® (Mancozeb 80% WP)—were incorporated into SDA at varying concentrations, after which fungal radial growth was monitored daily under laboratory conditions. Fungicidal efficacy was assessed based on mycelial growth rate and percentage inhibition relative to the untreated control. The untreated control recorded the highest radial growth (14.11 mm day⁻¹), confirming the aggressive growth of the pathogen in the absence of fungicidal treatment. Ridomil Gold® exhibited the greatest inhibitory effect, achieving 86.2% and 90.2% inhibition at 5 and 6 g L⁻¹, respectively, and complete (100%) inhibition at 7 and 9 g L⁻¹. Z-Force® produced moderate inhibition at lower concentrations but completely suppressed fungal growth at 5 g L⁻¹. Tandem® reduced mycelial growth substantially, reaching a maximum inhibition of 83.8%, but failed to achieve complete inhibition within the concentration range evaluated. The findings demonstrate that fungicide efficacy varies with formulation and concentration, with Ridomil Gold® proving the most effective against C. gloeosporioides under in vitro conditions. The study provides baseline information for the chemical management of soursop hard rot and highlights the need for greenhouse and field evaluations to validate laboratory findings before large-scale application.

Keywords: Annona muricata; Colletotrichum gloeosporioides; Fungicide efficacy; Hard rot; Postharvest disease management.