Colletotrichum fructicola Causes Necrotic Leaf Lesions in Avocado (Persea americana) in Amazonas, Peru: First Record and In Vitro Control Using Piper Essential Oils

Anthracnose is one of the most destructive diseases of avocado worldwide; however, foliar infections remain poorly documented in Peru. We investigated the etiology of necrotic leaf lesions observed in avocado plantations in Amazonas and assessed the in vitro antifungal activity of two Piper essential oils (EOs). Incidence was quantified in a 420-tree plot (n = 150 plants). Two representative isolates (MGS03, MGS04) were obtained from symptomatic leaves and characterized by morphology and multilocus sequencing (ITS, CHS-1, ACT, and TUB2). Maximum-likelihood phylogeny within the C. gloeosporioides species complex clustered with C. fructicola. Pathogenicity tests on detached leaves (unwounded inoculation) reproduced field symptoms and fulfilled Koch’s postulates. The antifungal activity of Piper carpunya and P. aduncum EOs (50–1000 µL L−1) was evaluated using poisoned-medium assays, revealing a strong dose-dependent inhibition of mycelial growth. Inhibition reached >89.8% at 500 µL L−1 and ~100% at 1000 µL L−1, with P. aduncum showing slightly higher activity. This study provides the first confirmed record of C. fructicola associated with necrotic leaf lesions in avocado in Peru and demonstrates the promising antifungal potential of Piper EOs as eco-friendly candidates for anthracnose management.