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

such a major drawback under ?¡rore ideal conditions in whíeh
the growing season is not generally terninated abruptly by
environmental stresses¡ nevertheless, Iateness is not a
desirable trait and one suspects the naterial would have to
be improved for this parameter as wel1.
The ability <strong>of</strong> a genotype such as Minn6þ_62 to respond
to high Levels <strong>of</strong> nitrogen fertilizer obviously reste in its
capabillty <strong>of</strong> producing a rarge rìumber <strong>of</strong> spikes under these
more optimal growing condltions. One could then specuJ.ate
that this factor, combined with the kernel weight inadequacy
and the negative association between spi.ke size and kernel
wel-ght, suggests the ideal genotype for optimum growing
conditions might be one which bas the abÍlity to produce
large numbers <strong>of</strong> tíllers, thereby producing a larger number
<strong>of</strong> spikes per unit area; but these spikes shourd have fewer
kerneLs each Ín order to naintaÍn anð./or achieve adequate
kernel size.
0n the other hand this type <strong>of</strong> approach may be too
simplistlc and rather unrealistic, particularly if taken to
the extreme. îhere has in fact been an intensive effort to
increase the graln nur¡ber per spike in seni_dwarfs, in
general negating the above proposal" perhaps it then might
be wise to produce hybrids with parents which have large,
pì-ump grain and select intensively in the segregating
populations for the most d.esirable combinati"on <strong>of</strong> the yield
conponents and <strong>height</strong>.
2I2