First Report of <i>Melampsora ferrinii</i> on <i>Salix babylonica</i> in Australia

In June and July 2025, symptoms of willow rust were observed on weeping willows (Salix babylonica) across New South Wales (NSW), Australia. Affected trees had a slightly chlorotic appearance, with masses of orange to yellow uredinia on the underside of leaves and occurring on most leaves on sampled trees. Samples from Sydney and regional NSW (Bathurst and Orange) were collected when yellow to orange uredinia were abundant on the abaxial surface of infected leaves. Microscopic examination confirmed urediniospores were globose, subglobose or ovoid, evenly echinulate, 13–28 x 12–17 µm with walls of 1.7-2.4 µm (n=15) and matched the description of numerous Melampsora species described from Salix (Toome and Aime 2015). Molecular identification was undertaken following the methods described by Toome and Aime (2015), apart from the DNA extraction which was performed using the Qiagen DNeasy® Plant Mini Kit as per the manufacturer’s instruction. Subsequent PCR and sequencing targeted the internal transcribed spacer (ITS) and the large ribosomal sub-unit (28S) using primers RustITS1F–RustITS2R and Rust2inv–LR6, respectively (Toome and Aime 2015). A BLASTn analysis against the NCBI Eukaryota nucleotide (nt_euk) database revealed the samples shared a high sequence similarity with vouchered specimens of Melampsora ferrinii (e.g., ITS, 100% to M. ferrinii HMJAU 8956 OR612063; LSU, 100% to PUR N6740 [holotype] KJ136564). Sequences produced in this study were ultimately compared with other published Melampsora sequences reported globally to confirm the identification and included M. laricis-populina as the outgroup. Phylogenetic analysis was performed in Geneious Prime® using the Mafft alignment and RAxML plugins. All samples collected in this study formed a well-supported clade with M. ferrinii, confirming these as the first records of this species for Australia. The examined specimens were deposited in the NSW Plant Pathology and Mycology Herbarium (DAR87600–DAR87606) and sequences submitted to GenBank (ITS, PX232779–PX232785; LSU, PX232786–PX232792). Previously, only M. coleosporioides had been reported from weeping willow in Australia, and M. epitea on other Salix species, based on morphological characterisation (Marks and Walker 1972, Walker 1978). Based on the spread of our detections, from Sydney and regional NSW, it is likely that M. ferrinii is already well established in Australia. It is possible that M. ferrinii has in fact been present since the first records of willow rust in the 1970s. This hypothesis follows the observations made by Toome and Aime (2015) who revised the status of Melampsora on weeping willows in the United States based on molecular analysis, and is further supported by the numerous reports of M. ferrinii on S. babylonica that have since followed from other parts of the world, including Chile (Zapata 2016), China (Ji et al. 2024) and Iran (Abbasi et al. 2024). Further research is needed to understand the distribution of M. ferrinii across Australia. We intend to address this by revisiting historical collections and surveying for willow rust in future seasons, keeping in mind that new aecial hosts have also been reported and could introduce an alternative pathway to assess the spread and distribution (Peng et al. 2022, Lee et al. 2024).