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tassel signals

Irvin C Anderson ianderso at iastate.edu
Thu May 7 15:38:36 EST 1998

The tassel, as the terminal vegetative growing point, produces IAA, etc.
that promotes internode elongation and thereby uses most of the plants
energy for vegetative growth during the same period that the ear (as a
lateral branch) must also grow to the silking stage by the time of
anthesis.  The level of IAA produced by leaves is inadequate for internode
elongation: it is only after tassel initiation at V6 and nearly V9 before
the tassel-growing point is large enough to produce significant IAA for
rapid internode elongation. So, you can imagine how much energy is required
to produce the internodes plus about 5% free sucrose as an osmoticum in the
stalk by anthesis.  Both tassel size and concentration of IAA vary in
inbreds. Present day hybrid have smaller tassel and I expect lower IAA

A long time ago I grew 23 inbred lines from a population of maybe 400 lines
that Dr Hallauer had measured tassel size.  Tassel size varied from 2.5 to
10 grams dry weight.  I grew the lines at densities of 25 and 50 thousand
plant /ha. Plant with very small tassels yielded 1.4 times more grain/ha at
50 than at 25 whereas those with large tassels yielded 0.7 as much at 50 as
at 25.  Most of the lines fit the regression line very well.

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