Fungal Pathogens of Opuntia spp. cladodes and their Control Using Commercial Fungicides

Abstract

Cladodes of Opuntia spp. are affected by diverse fungal pathogens that cause important yield losses. This study aimed to isolate, identify, and evaluate the pathogenicity of fungi associated with diseased cladodes and to assess the efficacy of three commercial fungicides; AZOXI 25 SC, ORTIVA TOP, and AGRIZOLE, applied at 0.5, 1.0, 1.5, and 2.0 L hL⁻¹ under laboratory (27±2 °C ) and screenhouse (25±4 °C) conditions. Six fungal isolates; Alternaria sp., Fusarium sp., Rhizopus sp., Aspergillus sp., Cladosporium sp., and Penicillium sp. were recovered from symptomatic cladodes and identified based on morphological characteristics. Pathogenicity tests confirmed lesion development for all isolates, with lesion diameters increasing from 20.0 to 45.2 mm for Alternaria sp., 22.1 to 50.1 mm for Fusarium sp., 18.3 to 38.6 mm for Rhizopus sp., 25.0 to 55.4 mm for Aspergillus sp., 21.5 to 40.7 mm for Cladosporium sp., and 17.8 to 35.4 mm for Penicillium sp. Disease incidence at 30 days ranged from 88.6% (Rhizopus sp.) to 95.4% (Fusarium sp.), and all fungi were successfully reisolated, fulfilling Koch’s postulates. In vitro antifungal activity increased with fungicide concentration; at 0.5 L hL⁻¹, antifungal index (AI) values ranged from 24.8-37.4% for AZOXI 25 SC, 33.1-45.6% for ORTIVA TOP, and 20.5-36.8% for AGRIZOLE, increasing to 71.7-77.3%, 74.1-78.4%, and 71.2-76.8%, respectively, at 2.0 L hL⁻¹. Screenhouse trials conducted 20 days post-inoculation showed reductions in lesion severity from 3.1-3.6 to 1.1-3.0, accompanied by marked decreases in disease incidence: Alternaria sp. (45.3-3.4%), Fusarium sp. (50.2-4.1%), Rhizopus sp. (55.2-6.1%), Aspergillus sp. (41.9-1.6%), Cladosporium sp. (50.2-4.2%), and Penicillium sp. (53.9-5.2%). Overall, AZOXI 25 SC, ORTIVA TOP, and AGRIZOLE effectively reduced fungal growth, lesion severity, and disease incidence, providing practical management options for fungal diseases of Opuntia spp.