Geographic and genetic identification of RppS, a novel locus conferring broad resistance to southern corn rust disease in China

Southern corn rust, a devastating fungal disease of maize, can cause significant loss of grain yield during intermittent outbreak. Growing resistant varieties is the most cost-effective way to manage southern rust in field corn. However, the prevalence of incomplete resistance owing to rapid evolution of pathogen warrants the necessities of discovering new resistant resources. To this end, the disease occurrence of 15 maize inbred lines in response to southern rust was examined in fields located in tropical, subtropical and temperate regions respectively. Overall, the character of resistance or susceptibility was rather steady among locations for most of inbred lines although infrequent variations existed. A tropical inbred line, SCML205, displayed fully resistant response in all the locations tested. By contrast, Jing24, W1636, Zheng58, W541 and G10-2426 exhibited completely susceptible response. A 3:1 segregation ratio of resistance to susceptibility was identified in the progeny of F2 population generated from the cross of SCML205 × Jing24, demonstrating SCML205 harbors a single dominant resistant gene. Allelism test was performed to confirm the resistance conferred by a novel locus, which was designated as RppS. Genetic mapping were conducted to locate RppS to the distal arm of chromosome 10S, a region close to other resistant genes known so far. Together, our survey of the resistance to southern rust in numerous inbred lines leads to the identification of a novel resistant gene, which would be tremendously valuable for plant breeding.