Application of synteny across Poaceae to determine the map location of a sugarcane rust resistance gene

A major rust resistance gene has been identified in a self-progeny of the s ugarcane cultivar R570. Until now, this gene was known to be linked to a ma rker revealed by the sugarcane probe CDSR29 but unassigned to any linkage g roup of the current genetic map. We used synteny relationships between suga rcane and three other grasses in an attempt to saturate the region around t his rust resistance gene. Comparison of sugarcane, sorghum, maize and rice genetic maps led to the identification of homoeologous chromosome segments at the extremity of sorghum linkage group D, rice linkage group 2, maize li nkage group 4 and in the centromeric region of maize linkage group 5. One h undred and eighty-four heterologous probes were selected and tested for cro ss-hybridization with sugarcane DNA; 106 produced a good hybridization sign al and were hybridized on 88 individuals of the R570 selfed progeny. Two hu ndred and seventeen single-dose markers were added to the R570 genetic map, of which 66% mapped to linkage group VII, together with the rust resistanc e gene. This gene has now been mapped to the end of a co-segregating group consisting of 19 RFLP markers. None of the mapped loci were located closer to the gene than CDSR29. The gene thus appears to reside at the edge of a " synteny cluster" used to describe the different sass genomes.