Identification of Thalictrum squarrosum as an alternate host for Puccinia triticina and pathogen analysis of Thalictrum squarrosum rust

<i>Puccinia triticina</i> (<i>Pt</i>) is a heteroecious fungus needing two different plants as primary and alternate hosts throughout its life cycle. <i>Thalictrum</i> spp. were first identified as alternate hosts of <i>Pt</i> in 1921, and over 100 species have been identified. However, within China, only <i>T. petaloideum</i> L., <i>T. minus</i> L., <i>T. minus</i> var. <i>hypoleucum</i> and <i>T. baicalense</i> have been reported as alternate hosts of <i>Pt</i>. During the six-year (2015-2018, 2023-2024) field surveys in Zhangbei County (41.26°N, 115.14°E), Zhangjiakou City, Hebei Province, our research team found rust disease on <i>T. squarrosum</i>. This persistent infection phenomenon aroused our interest in investigating the role of <i>T. squarrosum</i> in the sexual reproduction of <i>pt</i>. To clarify whether <i>T. squarrosum</i> can serve as an alternate host for <i>Pt</i> and to analyze the source of the pathogen, this study used artificial inoculation experiments and molecular identification techniques. The results of the artificial inoculation experiments showed that the basidiospores of <i>Pt</i> could infect <i>T. squarrosum</i>, and produce pycnia on the adaxial surface of the leaf. Subsequently, aecia were produced on the abaxial side of the leaf after artificial fertilization, and the mature aecia produced aeciospores. The aeciospores were then inoculated into susceptible wheat varieties and the wheat showed typical symptoms of wheat leaf rust. These results confirmed that <i>T. squarrosum</i> could serve as an alternate host for <i>Pt</i>. For molecular identification, 20 single-aecium samples of <i>T. squarrosum</i> were selected. Based on sequence alignment of their ITS regions and phylogenetic analysis, it was shown that rust on <i>T. squarrosum</i> could be caused by infection of <i>Pt</i> from wheat or the species complex of <i>P. recondita</i>. Our study provides new insights into the sexual cycle of <i>Pt</i> in China and provides a scientific basis for studying the evolution of <i>Pt</i> virulence and optimizing control methods for wheat leaf rust.