Progress in Genetic Mapping of Sugarcane Smut Resistance

A Quantitative Trait Locus (QTL) mapping study is under way to analyse the genetic determinism underlying sugarcane smut resistance. A total of 1295 polymorphic AFLP markers have been generated on a population of 200 individuals derived from a cross between R 570 (resistant) and MQ 76/53 (highly susceptible). This population is under evaluation for its resistance to smut in the field over three successive crop cycles and in two different locations on Reunion island. Inoculation was performed by dipping three-bud cuttings in a spore suspension, and susceptible clones were regularly interspersed in the field to trigger the epidemy. Different inoculation methods were also compared in greenhouse trials. The bud puncture method appeared the most efficient and will be used for further greenhouse evaluations of the progeny. Detection of marker-trait associations has been performed and so far has indicated a complex determinism for smut resistance. Many markers are involved with little effects. Nevertheless, among other traits that were looked at, two putative major genes originating from MQ 76/53 have been tagged: a gene involved in the red color of the internode and a rust resistance gene. Locus specific markers, SSR markers from sugarcane and maize and sequences differentially expressed in response to challenge by smut (provided by the South African Sugar Association Experiment Station), will be mapped. This should help explain the genetic variation in smut resistance observed in the trials.