The co‐operation between intermedium genes and the six‐row gene hex‐v in a six‐row variety of barley

The interactive competence of the genes promoting lateral floret development in the successful Svalöf six‐row variety ‘Agneta’ was studied. In this variety, genes for enhanced development of lateral florets occur not only at the six‐row locus hex‐v, but also at a recessive intermedium locus, int‐c. Three int‐c mutants, c 5 , c 13 , and c 29 , were crossed to ‘Agneta thus there was no dominant normal allele at int‐c present in the crosses, whereas the hex‐v locus would segregate for the normal and the six‐row allelic states. F 2 data for lateral floret characters (awn length, fertility, seed size) were contrasted to standards considered to provide the phenotypic spectra corresponding to the different genotypic constituents of the F 2 segregations (two‐row variety, VV CC; int‐c mutants, Wcc; six‐row mutant, vv CC; and six‐rowed variety ‘Agneta’, vv cc). The analyses of observed data in relation to expectations on various hypotheses for interaction between hex‐v and int‐c led to the following main conclusions. The degrees of phenotypic enhancement may differ among characters of lateral floret development and among int‐c mutant genes. There are no indications that the int‐c allele present in ‘Agneta’ is the superior enhancer of the hex‐v gene v A in this variety. Nor can we presume that v A is a superior six‐row gene. Most probably, it would pay the efforts in a plant‐breeding program with six‐row barley to try various constellations of hex‐v and int‐c mutants.