INHERITANCE AND CHROMOSOME LOCATIONS OF SCALD-RESISTANCE GENES DERIVED FROM IRANIAN AND TURKISH WILD BARLEYS

A set of advanced backcross barley lines derived from crosses between cv Clipper and different Iranian and Turkish wild barleys, which are h omozygous for particular isozyme-marked donor intervals, was screened for resistance to barley scald. Eight lines that consistently exhibite d scald resistance were identified, and genetic analysis indicated tha t single dominant genes encoded resistance in five of the lines, singl e recessive genes were present in two lines, and a pair of unlinked, d ominant genes encoded the resistance in the last line. Linkage between the scald-resistance gene and the isozyme marking the introgressed do nor chromosome interval was detected in four lines, allowing the chrom osome locations of these resistance genes to be determined. One such r esistance gene resides on barley chromosome 5, to which no other scald -resistance genes have been mapped; this gene has been designated Rrs1 4. A survey of the effectiveness of the eight resistance genes against a set of virulent pathotypes of the scald pathogen revealed that four of the lines were completely resistant to all of them. In two instanc es, the recovery of more than one scald-resistance gene from a single original donor parent could be demonstrated. These scald-resistance ge nes should provide additional opportunities for breeding programs that aim to develop scald-resistant barley cultivars.