Hexastichon and intermedium mutants in barley

Homozygous intermedium mutations from two-row barley are generally characterized by their lateral florets being of increased size and fertility. Median florets develop normally. Sixty allelism-tested intermedium mutations represent nine different gene loci, each locus possessing a particular type of lateral floret development. The intermedium character is usually recessive. Two cases of dominant mutations have been recorded. The F2 generation of certain loci primarily give rise to double-recessive hexastichon plants (for instance int-c x int-d). Other locus combinations give rise, in individual progenies, to double-recessive hexastichon or irregular and deformed F2 plants (for instance int-a x int-c), and others, finally, produce double-recessive irregular and deformed F2 plants exclusively and no hexastichons (for instance int-a x int-e). Hexastichon types, consequently, may arise in two ways: (1) by direct mutation in the two-row locus of distichon types (V→v), and (2) as double-recessives in the second generation of hybrid combinations of special intermedium loci and alleles.