Submitted to: Plant Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/1999
Publication Date: N/A
Interpretive Summary: The barley disease scald is caused by the fungal pathogen Rhynchosporium secalis. Scald lowers quality characteristics and yield of this crop. The challenge faced by geneticists seeking to improve scald resistance in barley is that the fungal pathogen that causes scald can rapidly overcome any given individual scald resistance gene. One method to make scald resistance genes more effective over a longer period of time is to combine them together in combination. In this research, the field effectiveness of a new barley scald resistance gene, Rrs14, was demonstrated. In consecutive years of field trials, visual scald damage was reduced between 80% and 88% in a barley line harboring this new scald resistance gene when compared to a scald-sensitive control barley cultivar. To facilitate breeding efforts with this new scald resistance gene, a molecular marker for Rrs14 was identified that can predict its presence with over 98% accuracy. The marker's presence can be assessed in one of three possible formats, which increases its utility. This research also confirmed that Rrs14 is on barley chromosome 5H, to which no other scald resistance genes have been assigned. With this marker, it will be substantially easier for breeders to combine Rrs14 with any other barley scald resistance gene in a single barley cultivar, in order to improve the longevity of scald resistance in barley.
Technical Abstract: The scald susceptible barley cultivar Clipper and a third-backcross (BC3) line homozygous for the Rrs14 scald resistance gene that originally came from Hordeum vulgare ssp spontaneum were grown in replicated field trials. The level of resistance that Rrs14 confers against field populations of the pathogen Rhynchosporium secalis, the causal agent of scald disease, was evaluated. The Rrs14 BC3-line exhibited 80% and 88% less leaf damage than Clipper in 1995 and 1996 respectively. Given this effectiveness of Rrs14, research was undertaken to identify a linked marker locus suitable for indirect selection of Rrs14. Based on linkage to a set of previously mapped loci, Rrs14 was positioned to barley chromosome 1H between the seed storage protein (hordein) loci Hor1 and Hor2, approximately 1.8 cM from the latter locus. The Hor2 locus is thus an ideal codominant molecular marker for Rrs14. The tight linkage between Rrs14 and Hor2 and the availability of alternative biochemical and molecular techniques for scoring Hor2 genotypes, permits simple indirect selection of Rrs14 in barley scald resistance breeding programs.