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POSTERS: Disease Detection and Diagnosis II

P-166 - Identification and pathogenicity of Diplodia mutila causing stem blight of blueberry cv. Brigitta in Maule Region, Chile

Tuesday, August 5, 2025
9:30 AM - 10:15 AM HST
Location: Exhibit Hall 3
Abstract Text: In January 2023, five bushes of 12-year-old blueberry cv. Brigitta, from a commercial plantation in Longaví, Maule region, was submitted to the Lab of Fruit Pathology at the University of Talca. A field incidence of 8% was assessed across the 5 ha, based on visual symptoms. Symptoms included decline, basal canker, stem and cane blighted (red flagging). Diseased stems were disinfected and internal tissues were placed on PDA plus 0.1% Igepal. Four isolates developed white to white-grey fast-growing colonies with abundant aerial mycelium, with abundant aggregated black pycnidia. Conidia were one-cell, hyaline, thick-walled, ellipsoidal to cylindrical. To determine the species level, isolates were amplified and sequenced using the internal transcribed spacer (ITS1-5.8S-ITS2) region, a portion of the beta-tubulin (BT) and part of the translation elongation factor 1-a (TEF) genes, respectively. The sequences showed a 99% similarity compared to sequences of D. mutila CBS 112553 ex-type. Phylogenetic tree based on concatenated sequences of the three isolates using the maximum parsimony method were grouped in the same clade with CBS 112553 ex-type. Pathogenicity tests using D. mutila isolates on blueberry of five-year-old cv. Brigitta showed necrotic lesions and dieback symptoms on stems inoculated with conidial suspension or mycelial plugs. D. mutila was reisolated (100%) and reidentified using morphological characteristics and sequencing of ITS region, fulfilling Koch’s postulates. This is the first report of D. mutila causing Botryosphaeria stem blight in Chile and worldwide.