First Report of Angiopsora paspalicola Causing Leaf Rust on Paspalum conjugatum in Malaysia

Paspalum conjugatum (family Poaceae), locally known as buffalo grass, is a perennial weed that can be found in rice field, residential lawn, and sod farm in Malaysia (Hakim et al. 2013; Uddin et al. 2010). In September 2022, buffalo grass with rust symptoms and signs was collected from the lawn located in Universiti Malaysia Sabah in the province of Sabah (6°01′55.6″N, 116°07′15.7″E). The incidence was 90%. Yellow uredinia were observed primarily on the abaxial surface of the leaves. As the disease progressed, leaves were covered with coalescing pustules. Microscopic examination of pustules revealed the presence of urediniospores. Urediniospores were ellipsoid to obovoid in shape, with yellow contents, 16.4 to 28.8 × 14.0 to 22.4 μm, and echinulate, with a prominent tonsure on most of the spores. A fine brush was used to collect yellow urediniospores, and genomic DNA was extracted as described by Khoo et al. (2022a). The primers Rust28SF/LR5 (Aime et al. 2018; Vilgalys and Hester 1990) and CO3_F1/CO3_R1 (Vialle et al. 2009) were used to amplify partial 28S ribosomal RNA (28S) and cytochrome c oxidase III (COX3) gene fragments following the protocols of Khoo et al. (2022b). The sequences were deposited in GenBank under accession numbers OQ186624 to OQ186626 (985/985 bp) (28S) and OQ200381 to OQ200383 (556/556 bp) (COX3). They were 100% similar to Angiopsora paspalicola 28S (MW049243) and COX3 (MW036496) sequences. Phylogenetic analysis using maximum likelihood based on the combined 28S and COX3 sequences indicated that the isolate formed a supported clade to A. paspalicola. Kochʼs postulates were performed with spray inoculations of urediniospores suspended in water (10⁶ spores/ml) on leaves of three healthy buffalo grass leaves, whereas water was sprayed on three additional buffalo grass leaves, which served as controls. The inoculated buffalo grass was placed in the greenhouse. Symptoms and signs similar to those of the field collection occurred after 12 days of inoculation. No symptoms occurred on the controls. To our knowledge, this is the first report of A. paspalicola causing leaf rust on P. conjugatum in Malaysia. Our findings expand the geographic range of A. paspalicola in Malaysia. Albeit P. conjugatum is a host of the pathogen, the host range of the pathogen especially in Poaceae economic crops needs to be studied. Weed management could be an effective way to eliminate inoculum sources of A. paspalicola.