Molecular determination of RSD and the Bru 1 gene in commonly used sugarcane ( Saccharum officinarum ) breeding parents in China

Ratoon stunting disease (RSD) and brown rust are major plant diseases that disrupt sugarcane production. Identifying disease-resistant parental lines offers an efficient strategy for controlling these diseases in sugarcane. The aim of this study was to clarify the occurrence of RSD and the distribution of the major brown rust resistance gene Bru 1 among commonly used sugarcane breeding parents in China. We used PCR assays for the molecular detection of RSD and Bru 1 in 255 sugarcane breeding parents collected from the National Germplasm Repository of Sugarcane of China (2019–2020). RSD was detected in 68.6% of the parental lines, indicating that commonly used sugarcane breeding parents in China are severely infected by RSD. However, 80 of the tested lines were RSD negative, indicating these parental lines had good resistance to RSD. The RSD incidence rate varied between different parental line series: VMC had the lowest RSD frequency (40.0%) and Guitang had the highest frequency (84.6%), indicating that the VMC series had good resistance levels to RSD and that a high proportion of parental lines were RSD resistant. Bru 1 was present in 87 of the 255 tested parental lines, with greatest frequency detected in the ROC series (71.4%) and lowest frequency detected in the CP series (21.6%). These results indicate that Bru 1 is a major source of brown rust resistance in commonly used sugarcane breeding parents in China, with important implications for brown rust resistance breeding programs in sugarcane. Overall, these results provide a reference for selecting appropriate breeding lines that are resistant to RSD and brown rust, offering guidance for effective disease control in sugarcane.