Quercus myrsinifolia Blume is a resilient evergreen oak in Korea, valued for landscape stabilization, dense wood, and wildlife-supporting acorns. Trunk canker symptoms were observed on 5 of 25 Q. myrsinifolia trees (20% incidence) at the Chonnam National University Arboretum, Gwangju, Korea (35°10′21. 32″ N, 126°53′58. 56″ E), in August 2024. The symptoms included bark cracking, sunken lesions, and localized necrosis, with 8% of the infected trees showing severe symptoms such as dieback and wilting. Ten samples of bark and cambial tissue showing active canker lesions were collected from five symptomatic Q. myrsinifolia trees. Tissues were surface-sterilized with 5% sodium hypochlorite for 3 min, rinsed thrice, cut into 5–6 mm² sections, placed on potato dextrose agar (PDA) with streptomycin (0. 02 g L⁻¹), and incubated at 25°C in the dark. After 5–7 days, fungal isolates with distinct colony morphologies were hyphal tipped and grown on PDA plates. A total of 15 isolates: including 10 Lasiodiplodia sp. , three Botryosphaeria sp. and two Diaporthe sp. were isolated from 10 different samples, but only Lasiodiplodia sp. , was consistently isolated from all samples. One representative isolate of Lasiodiplodia sp. (Qm24₁Lp) was selected for identification and pathogenicity testing. Qm24₁Lp colonies grew rapidly within seven days, producing dark olivaceous mycelium, black pycnidia, and conidia that changed from hyaline to pigmented and striate as they matured. For sporulation, the isolate was cultured on PDA at 25°C under a 12 h near-UV light/dark cycle (Sangeetha et al. 2012). As the conidia matured, they appeared as dark brown, single-septate, and longitudinally striate (12. 5 ± 0. 5 × 1. 8 ± 0. 2 μm). Molecular identification of Qm24₁Lp was performed using three gene regions: the internal transcribed spacer (ITS; ITS5F/ITS4), translation elongation factor-1-α (tef1-α; EF1-688F/TEF1-1251R and TEF1-728F/EF1-986), and beta-tubulin (tub2; BT1a/BT1b and BT12a/BT2b) (Luo et al. 2024). Sequence of Qm24₁Lp were deposited into GenBank (ITS: PV583398; tef1-α: LC871488; and tub2: LC871489). BLAST analysis revealed 100% identity for the ITS region (EF622077; 310/310 bp), 99% for the tef1-α gene (EF622057; 281/282 bp), and 100% for the tub2 gene (EU673111; 250/250 bp) with the ex-type strain CBS 116459 of L. pseudotheobromae (Alves et al. 2008). Concatenated ITS, tef1-α, and tub2 sequences of Qm24₁Lp were analyzed by the maximum-likelihood method in MEGA X (1, 000 bootstrap), and also clustered the isolate with ex-type L. pseudotheobromae strain CBS 116459 (Wu et al. 2021). Qm24₁Lp was confirmed for pathogenicity based on Koch’s postulates. Six healthy 3-year-old Q. myrsinifolia seedlings were slightly wounded, and three were inoculated with 5-mm mycelial plugs of Qm24₁Lp and three with sterile PDA (control), and sealed with Parafilm. After six weeks, inoculated seedlings developed dark lesions and cracks around the wound sites, while controls remained healthy. The experiment was repeated twice under greenhouse conditions, and L. pseudotheobromae was re-isolated from symptomatic tissues, confirming its pathogenicity. Although Lasiodiplodia species have been reported to infect several woody species in Korea (Nam et al. 2016), this is the first record of L. pseudotheobromae as a pathogen of Q. myrsinifolia, as confirmed from the search of USDA Fungal Databases. The findings offer an important baseline information for monitoring and managing this emerging disease and about the pathogenicity of L. pseudotheobromae.
Choub et al. (2026) studied this question.