The Origin of the Problem: Characterization of Paraguayan , Causal Agent of Septoria Leaf Spot of Stevia, Based on Multilocus Sequence Analysis.

Septoria leaf spot is a significant disease affecting cultivated stevia, potentially reducing yields by > 50%. The disease is caused by , first identified in 1978 in Japan as a new pathogen of stevia. Understanding the origin of could clarify how it spread to new production areas. To investigate this, 12 isolates of sp. were obtained from stevia's native range in the Amambay forests and field plantings in Paraguay from 2018 to 2020. These isolates underwent colony morphology and molecular characterization of , , , , , , and loci. GenBank sequences from isolates collected in France, Japan, and the United States were included. Multilocus sequence phylogenetic analysis generated a maximum likelihood (ML) tree. The morphological characteristics of Paraguayan isolates were similar to those of previously reported type cultures from Japan. The ML analysis showed that Paraguayan isolates formed a monophyletic group with isolates from France, Japan, and the United States. During blotter tests, pycnidia and cirri of were observed on multiple stevia seed surfaces from different sources. Further characterization confirmed viable pathogenic conidia of . This observation suggests that could be associated with stevia seed, possibly spreading from the center of origin to other countries. This research is the first to genetically characterize from Paraguay and propose its potential spread mechanism from the center of origin to the rest of the world.