Introgression of a Large Effect QTL for Smut Resistance Inherited from S. spontaneum

Smut caused by Sporisorium scitamineum is a major sugarcane disease that can cause considerable yield losses. Sugarcane resistance to smut has been demonstrated to be heritable although the genetic determinants of this resistance are unknown. Studies involving modern cultivars have shown inheritance to be highly quantitative with many small effect QTL (9% variation explained) contributing to resistance. Introgression from wild species has long been of interest to sugarcane breeders to increase the genetic diversity of modern cultivars as only a small number of original progenitor clones are believed to have contributed to the ancestry of sugarcane. S. Spontaneum is widely recognised as imparting a range of important traits to modern sugarcane cultivars such as adaptation to environmental stresses, ratooning performance and resistance to diseases. An introgression program was started in Australia with the introduction of 43 biparental crosses between sugarcane and Saccharum spontaneum. These populations were evaluated for performance in field trials and for disease resistance. Progeny from a cross between a BC1 S. spontaneum clone and a sugarcane cultivar were found to segregate for resistance to smut. AFLP, SSR and DArT markers have been used to map this population and QTL analysis has identified a major effect that varies from 36% to 45% variation explained depending on year. This population is being screened across a sugarcane SNP chip to improve the resolution of the genetic map. Further crossing is being carried out to introgress this region into commercial cultivars.