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

xvii i
occurred for yield, but the se¡ni-dwarfs tended to perform
better under more optitnu t growing cond.itions, ie. better
weed control, moisture and fertility.
One semi-dwarf and one ta1l genotype were tested at
three locations to determine the effects <strong>of</strong> altered <strong>plant</strong>
density on relative performance. Again no significant
inieractions occurred for yie1d, ho¡/ever, there was a ten-
dency for the semi-dwarf to show relatively greater improve-
ment than the tâll as <strong>plant</strong> density i-ncreased. The seraj--
dwarf showed a negative response to adverse growing
conditions.
The semi-dwarfs studied appeared to achieve yield
improvernents via increases in the nunber <strong>of</strong> spikes per unit
area and kernels per spike, at the expense <strong>of</strong> kernel weíght.
îhe ínterre lationships <strong>of</strong> these yield components are discussed
with particular reference to the semi-dwarfs, as are methods
for developing high yielding semi-dwarfs with an improved
bâlance among the yíeld components.
Pre liminary research was conducted to detêrmíne the
relati-onships <strong>of</strong> <strong>plant</strong> <strong>height</strong> with coleoptile length, root
system size and growth rate, energence rate and abiÌity.
Plant heíght was poÊitively associated with coleoptile
length. Shorter genotJ4)es appeared to have snalLer, slower
growÍng root systerns. Emergence rate a¿d ability were not
affected b). <strong>reduced</strong> <strong>height</strong>. these paraneters were all
positively associated with kerael size.