Septoria araujiae: Phylogeny, pathogenicity, and host specificity of a fungal pathogen with potential as a biocontrol agent for moth plant

Native to South America, moth plant (Araujia hortorum, Apocynaceae) is an invasive vine that threatens natural ecosystems and agriculture in many parts of the world. Biological control studies involving fungal pathogens have primarily focused on the rust Puccinia araujiae, but other aggressive pathogens exist that may show potential as complementary agents. In its native range in Argentina, plants were quite frequently observed with severe leaf and fruit damage caused by a fungal disease. The pathogen associated with this disease was isolated and identified as Septoria araujiae based on morphological analyses. Multilocus analyses allowed the first phylogenetic placement of this species within the genus. Koch’s postulates were fulfilled through inoculation experiments, confirming S. araujiae as the causal agent. The pathogen exhibited a hemibiotrophic life cycle, with an extended asymptomatic phase followed by a necrotrophic stage that led to severe defoliation. Host specificity experiments revealed a narrow host range, with susceptibility largely confined to species within the subtribe Oxypetalinae. These findings contribute new insights into the diversity, ecology, and host interactions of Septoria species and highlight the potential of S. araujiae as a biological control agent for A. hortorum.