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

## TL;DR

This study identifies rust-causing pathogens in sugarcane and finds many Erianthus arundinaceus clones resistant to brown rust, including some without the known resistance gene.

## Contribution

The study reveals new resistance sources in E. arundinaceus and suggests the presence of unknown resistance genes for brown rust.

## Key findings

- 17.9% of samples were infected with Puccinia melanocephala and 34.8% with Puccinia kuehnii.
- 61 E. arundinaceus clones showed high resistance to brown rust, some lacking the Bru1 gene.
- 13 offspring and 6 backcross parents of the 'ROC' series carried the Bru1 resistance gene.

## Abstract

Sugarcane rust diseases are caused by Puccinia melanocephala (brown rust) and Puccinia kuehnii (orange rust), and significantly threaten the sustainable and stable development of the global sugarcane industry. Erianthus arundinaceus within the Saccharum 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 E. arundinaceus clones and their offspring (F1 and backcross with modern sugarcane varieties) is limited. In this study, a total of 201 leaf samples from Saccharum 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 P. melanocephala and P. kuehnii, respectively. Additionally, 12.9% of the samples were infected by both pathogens. A total of 88 clones of E. arundinaceus offspring and the parents plus 3 additional E. arundinaceus 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 E. arundinaceus and 6 backcross parents of the “ROC” series exhibited the major resistance gene (Bru1) for brown rust. Unexpectedly, the Bru1 gene was absent in 42 clones that were resistant to brown rust, suggesting that other resistance genes for brown rust likely exist in E. arundinaceus and their offspring. Our results offer some significant genetic resources for developing sugarcane cultivars with resistance against rust.