THE EFFECT OF COMBINING SCALD RESISTANCE GENES ON DISEASE LEVELS, YIELD AND QUALITY TRAITS IN BARLEY

Pairwise combinations of genes for resistance to scald in barley were developed using linked isozyme markers to test whether such combinatio ns conferred improved resistance to the pathogen, Rhynchosporium secal is. The resistance genes originally derived from Hordeum vulgare ssp. spontaneum. The combinations were bred into an essentially similar gen etic background because the scald-susceptible, Australian barley culti var 'Clipper' was the recurrent backcross parent in their ancestry. In field tests of the recombinants over 2 years, disease levels were low er in three of six doubly resistant lines than in backcross lines carr ying a single resistance gene, which in turn were less diseased than e ither 'Clipper' or recombinants that lacked the marked resistance gene s. All resistant lines significantly outyielded 'Clipper' but did not themselves differ significantly. Lines resistant to scald had signific antly higher grain size and grain weight. Gains for malt yield of abou t 1% were detected in the higher disease environment. Resistance was n ot accompanied by any obvious ''cost'' in terms of yield or quality. P rotection against scald is therefore a significant requirement for new malting barley cultivars in scald-prone areas.