Identification of field resistance and molecular detection of the brown rust resistance gene Bru1 in new elite sugarcane varieties in China

Brown rust, caused by Puccinia melanocephala has become a serious problem for sugarcane production in China. Therefore, 50 new elite varieties bred by the Chinese Sugarcane System were screened for brown rust resistance and the presence of a major resistance gene, Bru1. Identification of field resistance and molecular detection of the brown rust resistance gene Bru1 in the 50 new elite varieties and 2 main cultivated varieties were carried out in 2014 and 2015 at regional experimental stations of the China Sugarcane System in Dehong and Baoshan, Yunnan Province, where the incidence of brown rust is particularly high. Resistance evaluations based on ratings of symptom severity resulting from field infection showed that 32 (64%) of the 50 new elite varieties were highly resistant (n = 13, 26%), resistant (n = 16, 32%) and moderately resistant (n = 3, 6%). Molecular detection identified Bru1 in 27 (54%) of these resistant varieties suggesting that brown rust resistance in these new elite varieties is primarily controlled by Bru1. The absence of Bru1 in the remaining five resistant suggested the presence of additional brown rust resistance genes. Two main cultivated varieties were highly resistant and Bru1-positive varieties. Different series differed in the frequencies of resistant and Bru1-positive varieties. Yunzhe series varieties had the highest frequency of resistant varieties (87.5%) and the highest frequency of Bru1-positive varieties (81.3%); In contrast, the Yuetang series varieties had the lowest frequency of resistant varieties (40%) and the lowest frequency of Bru1-positive varieties (30%). In this study, we defined the field resistance of 50 new elite varieties to brown rust, and determined the distribution of brown rust resistant gene Bru1 in different series varieties. These results will provide new options for commercial production with effective resistance to brown rust. Moreover, these new elite resistant varieties can be used for subsequent breeding and selection to produce agronomically superior varieties with effective brown rust resistance.