Effects of reduced plant height on breeding requirements and ...

densities, to facilitate the seleetion <strong>of</strong> sufficient numbers
<strong>of</strong> appealing short statured types ín order to make progress
toward improved agronomic performance. Iêrger populations
would also be required by the breeder desiring to seLect
intermediate <strong>height</strong> genotypes, sÍnce these were arso shown
to occu¡ at a lower frequency than tatt segregates,
An additional problem with the material investígated
was the apparent linkage between shorteneai stature and late
heading and maturity, whfch was probably partially responsible
for the strong assocíation <strong>of</strong> <strong>reduced</strong> <strong>plant</strong> <strong>height</strong> with re-
duced kernel size and plumpness. lhis rateness 'n,as associated
with an observed slow and prostrate early growth habit" The
kernel parameters suffered in the shoz,t material, partÍc ular_
1y among early maturing lines and those showing high yield
leveLs. some lines dltt not suffer these kerne f síze problerns,
but these were most <strong>of</strong>ten lower yielders, The lower yieì.d
resulted from the production <strong>of</strong> fewer spi.kes per unit area¡
the yield component by which the better yielders apparently
achieved that yíeld" The number <strong>of</strong> kernels per spike was not
a sígnificant problem since parentaL genotypes had adequate
spike size" The semi-dwarf parent, Miruób_62, was below
optínunr i.n kernel size.
Based on the associatÍons shown, a specíal effort may
be required to irnprove kerneL size in semi-dwarf segregates
by intensive selection for inprovement throughout the
segregating generations among large nunbers <strong>of</strong> semi_dwarf
l1nes. îhe ease <strong>of</strong> visual selection for <strong>plant</strong> <strong>height</strong>