Diversity and Pathogenicity of Fungi Associated with Dieback and Trunk Cankers in Pecan Orchards of Sonora, Mexico

Pecan (Carya illinoinensis) is a major economic crop in Mexico. The states of Chihuahua and Sonora contribute approximately 80% to the national production. Recently, symptoms of trunk diseases, including necrotic lesions in the xylem, cankers, dieback, and shoot blights, have been observed in pecan orchards in Sonora. This study aimed to determine the presence and identity of fungi responsible for these symptoms. A survey was conducted between 2021 and 2022 in 11 orchards near Hermosillo, Sonora. Fungi were isolated from necrotic tissue on potato dextrose agar medium, yielding approximately 150 isolates. Based on colony morphology, 50 isolates were selected for molecular characterization using the translation elongation factor 1 alpha (tef-1α) gene, the nuclear ribosomal DNA-internal transcribed spacer (ITS), and, for some isolates, the β-tubulin gene. The fungi identified included Pseudofusicoccum stromaticum, Lasiodiplodia exigua, L. brasiliensis, Diaporthe caatingaensis, Eutypella microtheca, and several Fusarium species. The optimal growth temperature for most isolates was 30°C, while none exhibited growth at 40°C, although some Lasiodiplodia and Pseudofusicoccum isolates showed limited growth at 37°C. Following pathogenicity studies, the Lasiodiplodia species produced the largest lesions on pecan cultivar Wichita, followed by P. stromaticum and E. microtheca, which exhibited intermediate virulence. The least virulent were D. caatingaensis and Fusarium spp. isolates. This study contributes to understanding the phytosanitary status of pecan orchards in Mexico and lays the groundwork for developing management strategies to control these fungi.