Unraveling the Life Cycle of Nyssopsora cedrelae : A Study of Rust Diseases on Aralia elata and Toona sinensis .

Rust disease poses a major threat to global agriculture and forestry. It is caused by types of Pucciniales, which often require alternate hosts for their life cycles. Nyssopsora cedrelae was previously identified as a rust pathogen on Toona sinensis in East and Southeast Asia. Although this species had been reported to be autoecious, completing its life cycle solely on T. sinensis , we hypothesized that it has a heteroecious life cycle, requiring an alternate host, since the spermogonial and aecial stages on Aralia elata , a plant native to East Asia, are frequently observed around the same area where N. cedrelae causes rust disease on T. sinensis . Upon collecting rust samples from both A. elata and T. sinensis , we confirmed that the rust species from both tree species exhibited matching internal transcribed spacer (ITS), large subunit (LSU) rDNA, and cytochrome oxidase subunit III (CO3) mtDNA sequences. Through cross-inoculations, we verified that aeciospores from A. elata produced a uredinial stage on T. sinensis . This study is the first report to clarify A. elata as an alternate host for N. cedrelae , thus providing initial evidence that the Nyssopsora species exhibits a heteroecious life cycle.