University of Massachusetts
Eastern Agricultural Center
The ub gene (unbranched tassel) for increasing productivity
--Walton C. Galinat
Productivity in corn has increased over the millenia by several structural changes including (1) an increase in the photosynthetic area above the ear; (2) an increase in the storage capacity of the ear as a whole; (3) an increase in femaleness including tassel reduction; (4) an increase in the precociousness of female development together with its consequence, the extent of husk enclosure.
Under the present system of high density planting of about 26,000 plants/acre, further increases in the photosynthetic area above the ear by increases in the number and size of leaves can be dangerous during years of drought stress. Losses from crop failure during one bad year would not be compensated for by an accumulation of small increases that only occur under ideal conditions.
Increases in the storage capacity of the ear may remain unfulfilled as barren cobs at high density planting. Increased productivity by means of increased femaleness is independent of the stress problems from high plant density. A shift in the reproductive investment of resources (photosynthate) from the tassel and pollen production into ear development has become at least an unconscious part of breeding programs for increased yields. But having recognized this, why not make use of the ub gene for unbranched or reduced tassels in order to partition more resources and productivity into the ear? The gene is simply inherited and it is usually expressed as a recessive gene showing some incomplete dominance in certain crosses. For maximum increases in ear productivity, the ub gene should probably occur in both parents of an Fl hybrid.
But there is a pollination problem in crossing fields with reduced or unbranched tassels in the male rows, especially when only 20% of the rows serve as the pollinators. Work is underway to determine if a certain recessive gene for a ramosa tassel (ra-D) on a plant with a normal ear can increase pollen shed from an otherwise genetically unbranched (ub) tassel.
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