Synchytrium gangeticum, sp. nov., associated with wart disease on Andrographis paniculata, with polygenic phylogeny of family Synchytriaceae

A novel Synchytrium species, Synchytrium gangeticum, sp. nov. (Chytridiomycota: Synchytriaceae), is described as the causal agent of wart disease in Andrographis paniculata (a medicinally important herb) in northern India. Synchytrium gangeticum exhibits host specificity toward A. paniculata, inducing the formation of small, raised, red/brown galls on leaves and stems, with rapid spread observed during early rainy seasons. The microscopic analysis revealed distinct spore morphology and gall development, characteristic of a long-cycled Synchytrium species. It is distinguished by unique resting spore dimensions (90–170 µm) and sporangium size (40–70 µm) and produces uniflagellate zoospores measuring 1–3 µm. Phylogenetic analyses, based on rDNA gene cluster (internal transcribed spacer [ITS], 18S, and 28S), positioned S. gangeticum closest to Synchytrium collapsum, but with significant morphological, and genetic divergence. This study presents the first comprehensive description of a Synchytrium species pathogenic to A. paniculata, providing insights into its host specificity, life cycle, and phylogenetic relationship within the genus.