First Report of <i>Mycoleptodiscus suttonii</i> Causing Foliar Lesions on <i>Pouteria reticulata</i> in Panama

Pouteria reticulata (Engl.) Eyma (Sapotaceae) is a tropical tree with edible fruit native to forests from Mexico into South America (Schroeder et al. 2019). In October 2019, seedlings of P. reticulata with a browning and softening of foliar tissue were collected from the lowland tropical forest of Barro Colorado Island (BCI), Panama. Three fungal isolates were recovered by plating surface-sterilized symptomatic leaf tissue on malt extract agar amended with 0.02% chloramphenicol (MEA+C; Spear and Broders 2021). Axenic cultures on MEA+C at 25°C in darkness had white mycelia with an effuse margin, becoming olivaceous buff in the center and paler to the periphery by day 3, and melanizing to an opaque olivaceous black by day 10. Colonies reached 70 to 75 mm diameter after 4 days with slightly elevated, hispid, gray aerial mycelium. Dark microsclerotia of variable shapes were visible within 7 days, ranging in size from 108 to 514 x 105 to 488 μM (average 296 × 259 μm, n = 15). No conidia were observed. These morphological characters match the description of Mycoleptodiscus suttonii Hern.-Restr., J.D.P. Bezerra &amp; Crous (Hernández-Restrepo et al. 2019). Representative isolate ERS19.42.Le.A was molecularly identified by sequencing the ITS (internal transcribed spacer region; primers ITS5/ITS4, White et al. 1990), TEF1-α gene (translation elongation factor 1-α; primers 983F/EF-gr, Rehner and Buckley 2005), and RPB2 gene (RNA polymerase II second largest subunit; primers RPB–5F2, fRPB2-7cR, Liu et al. 1999; Sung et al. 2007). Sequences were deposited in GenBank (MW775503.1 [ITS]; PZ347402 [TEF1-α]; PZ347403 [RPB2]). GenBank BLASTn searches revealed 99.49, 99.73, and 99.38% identity in the ITS (NR_164056.1, 589/592 nt), TEF1-α (MK495974.1, 739/741 nt), and RPB2 (MK492732.1, 795/800 nt) regions to the M. suttonii type specimen (CBS 276.72; Hernández-Restrepo et al. 2019). Pathogenicity was assayed on P. reticulata seedling leaves in the forest of BCI. We clipped polypyrene caps filled with MEA+C, either colonized by ERS19.42.Le.A or uncolonized (controls) to visibly healthy leaves. Seventeen seedlings received both treatments, with one treatment per leaf (some leaves were lost in a storm). Clip pressure caused minor foliar necrosis at cap edges in both treatments. Leaves were harvested 7 and 14 days post-inoculation, with no significant difference in lesion size between dates for either treatment. Pooling both harvests, leaves inoculated with ERS19.42.Le.A exhibited significantly larger lesions than the controls (n = 15 vs. 14, mean±SD = 21.8±39.2 vs. 4.4±5.0 mm 2 ; Welch’s t-test on log-transformed data: t(27) = 3.19, P = 0.004). Surface-sterilized leaf tissue was plated as described above. We successfully reisolated M. suttonii from all 15 inoculated leaves based on morphology and bidirectional Sanger sequencing of the ITS region (MCLab, San Francisco, CA). Previously, M. suttonii was isolated from a stem lesion on Sannantha virgata in Australia and the roots of Theobroma cacao in Brazil (Hernández-Restrepo et al. 2019). To our knowledge, this is the first report of M. suttonii infecting leaves of P. reticulata seedlings in Panama. The geographic and host ranges of M. suttonii merit attention due to its pathogenicity on this widespread and ecologically important tropical tree, and because the Sapotaceae family includes globally important food and cosmetic crops, highlighting potential impacts across natural systems and economically valuable plants.