The two-ranked or four-rowed ear of maize has always been reported as a recessive trait that is a common mutant or variant in eight-rowed maize. It is often unstable in expression in that only a portion of the ear, usually the upper part, will be four-rowed or with different ears on the same plant, one may be four-rowed and others eight-rowed. Seed from a four-rowed ear may produce eight-rowed ears and vice versa. The stunting of eight-rowed maize sometimes causes it to produce ears with only four rows.
As reported previously, we have stabilized the expression of two-ranking in maize through the transfer of a segment from Tripsacum chromosome 9 to the short arm of maize chromosome 2. In segregations with typical eight-rowed maize, two-ranking behaved as if controlled by a single recessive gene. But when hybrids of our two-ranking strains involved in our square-ear sweet corn breeding program were hybridized to our string cob inbred, W-401, the F1 hybrids were consistently two-ranked. Inbred W-401 was bred for a low condensation level approaching that of teosinte and similar to that of the oldest known archaeological maize cobs. Thus at this primitive state, two-ranking is dominant over four-ranking, as would be expected during the emergence of maize.
Walton C. Galinat
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