First report of <i>Ceratobasidium</i> sp. causing root rot of <i>Crotalaria juncea</i> in Mexico

Crotalaria juncea (Fabaceae), also known as sunn hemp or Indian hemp, is a warm-season legume grown cover crop that provides nitrogen and organic-matter to soils, prevents weed growth suppresses nematode populations (Meagher et al., 2019). In September 2021, root rot symptoms were observed in fields distributed Cocula, Guerrero, Mexico. Diseased plants showed reduced growth, rot, chlorosis, wilting (Fig. 1). The disease incidence was estimated be up 40%. For fungal isolation, diseased roots surface sterilised with 2% sodium hypochlorite for two minutes, rinsed distilled water twice blotted dry on sterile filter paper. Small fragments of placed potato dextrose agar (PDA) medium incubated at 25°C darkness five days. Ceratobasidium-like colonies obtained consistently 10 isolates purified by the hyphal-tip method. Fungal PDA white initially 2) then turned brown, raised, entire undulated edges. Septate hyphae hyaline, 4.2-6.7 μm width, smooth, branched right angles septum near point branching. Microscopic examination lactophenol blue staining nuclei per cell. morphological features resembled those Ceratobasidium spp. (Gonzalez 2016; Ferreira 2021). Four representative selected molecular analysis pathogenicity tests. deposited Culture Collection Phytopathogenic Fungi Colegio Superior Agropecuario del Estado de Guerrero (Accession Nos. CSAEG28–CSAEG31). identification, genomic DNA from each extracted mycelia following CTAB method, internal transcribed spacer (ITS) region partial sequences second largest subunit RNA polymerase II (rpb2) gene amplified sequenced primer pairs ITS5/ITS4 (White 1990) RBP2-980F/RPB2-7cR (Liu 1999), respectively. GenBank OM677842-OM677845 ITS OL677498-OL677501 rpb2). Phylogenetic analyses performed using Maximum Likelihood method rpb2 Additionally, phylogenetic data anastomosis groups (AGs) sp. generated. trees inferred grouped four CSAEG28–CSAEG31 within clade high bootstrap support 3). tree AGs into distinct other but closely related AG-L 4). All these results this study belong new AG tests, 5-mm-diameter plugs margin seven-day-old seedlings (21 days old) replicates isolate. Control inoculated plug. kept greenhouse where temperature ranged 25 30°C. Root appeared after 12 5), whereas control remained symptomless. test similar results. reisolated infected found morphologically identical used inoculation, thus fulfilling Koch's postulates. have been reported members Fabaceae, including Arachis hypogaea, Glycine max, Trifolium subterraneum, Vigna sinensis (Farr & Rossman, 2023). This first report causing Mexico worldwide. According our observations, serious threat health plants.