Gene interaction of induced intermedium mutations of two‐row barley: I. Double mutant recombinants

From 69 induced intermedium mutants isolated from three Svalöf commercial varieties of two‐row spring barley, ‘Bonus’, ‘Foma’, and ‘Kristina’, and localized to 9 different int loci, double mutant recombinants were available in 1384 of the 1879 possible combinations among non‐allelic mutants. These double mutant segregates, without exception, showed an apparent, strong degree of synergistic intreraction between mutant genes that by themselves cause rather modest changes in the normal two‐row spike. They rank in three groups in their spike development: six‐rowed. irregular, and deformed. There are apparent differences, not only among int loci, but also among alleles in the ability to co‐operate for six‐rowed spikes in double mutants. A complex pattern of factors promoting the six‐rowed spike development in double mutants is indicated: the ranking among phenotypes for individual int alleles; the particular int locus serving as partner to a series of alleles to form double mutants; the state of the allele, as more flexible or more rigid. Success seems to depend on the particular constellation of loci and alleles.