Identification of Causal Agents of Rust of Saccharum spp. and Assessment of Resistance to Brown Rust in Erianthus arundinaceus Clones and Their Offspring

Sugarcane rust diseases are caused by <i>Puccinia melanocephala</i> (brown rust) and <i>Puccinia kuehnii</i> (orange rust), and significantly threaten the sustainable and stable development of the global sugarcane industry. <i>Erianthus arundinaceus</i> within the <i>Saccharum</i> complex is a potential germplasm resource for sugarcane breeding and is characterized by its tolerance of infertile land, drought, and diseases. However, the research on resistance to rust in <i>E. arundinaceus</i> clones and their offspring (F1 and backcross with modern sugarcane varieties) is limited. In this study, a total of 201 leaf samples from <i>Saccharum</i> spp. hybrids with rust symptoms were collected and screened for disease occurrence. PCR detection revealed that 17.9% and 34.8% of the samples were infected by <i>P. melanocephala</i> and <i>P. kuehnii</i>, respectively. Additionally, 12.9% of the samples were infected by both pathogens. A total of 88 clones of <i>E. arundinaceus</i> offspring and the parents plus 3 additional <i>E. arundinaceus</i> were selected for the identification of brown rust resistance by an artificial inoculation method. Among them, 61 clones displayed high resistance to brown rust. Molecular detection showed that 13 offspring of <i>E. arundinaceus</i> and 6 backcross parents of the "ROC" series exhibited the major resistance gene (<i>Bru1</i>) for brown rust. Unexpectedly, the <i>Bru1</i> gene was absent in 42 clones that were resistant to brown rust, suggesting that other resistance genes for brown rust likely exist in <i>E. arundinaceus</i> and their offspring. Our results offer some significant genetic resources for developing sugarcane cultivars with resistance against rust.