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

maturity and days in post-anthesis parameters, and the other
agrononic eharacters in this study are interesting, part_
ícularly as they tend not to agree with previous reports.
Past evidence has suggested early heading j-s assoeiateil with
early maturity and hence lower yíeld. On the other hand, it
has been postulated that a 1ong post_fertÍlÍzation period
should Lead to hígher yie3.ds through more kernel deve lopment.
îhe evÍdence <strong>of</strong> thls stud.y supports the latter hypothesis.
The results suggest that the breeder should attempt to
select llnee which head earty but do not necessarÍly mature
early, in an attempt to rnaxímÍz e the grãin development
period. Obviously one must be aware <strong>of</strong> the problems associated
with "late" rnaturity, particularly in ryestern canada,
and lengthening the post-anthesis period by means <strong>of</strong> later
maturity may be undesírable. One would have to arbÍtrarily
choose an optimum maturity dåte and attempt to achieve a
rnaxÍmurn post-anthesis period by combining that with the
earllest heading possible .
In view <strong>of</strong> the positive association found between days
to heading and maturity, perhaps 'rearly,r by rtlate erosses
would give rlse to larger numbers <strong>of</strong> lines with varior¡s
combinations <strong>of</strong> headi.ng time and maturity, and a broad range
<strong>of</strong> post-anthesis periods. The post-anthesis periods would
also oceur at slÍghtly different tines <strong>of</strong> the growing season¡
With this type <strong>of</strong> nateriaL one could perhaps better define
the relati.onships involved and deternine, not only the ideal
length <strong>of</strong> the grain deveropment period, but also defíne which
L97