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

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such a major drawback under ?¡rore ideal c<strong>on</strong>diti<strong>on</strong>s in whíeh<br />

the growing seas<strong>on</strong> is not generally terninated abruptly by<br />

envir<strong>on</strong>mental stresses¡ nevertheless, Iateness is not a<br />

desirable trait <strong>and</strong> <strong>on</strong>e suspects the naterial would have to<br />

be improved for this parameter as wel1.<br />

The ability <str<strong>on</strong>g>of</str<strong>on</strong>g> a genotype such as Minn6þ_62 to resp<strong>on</strong>d<br />

to high Levels <str<strong>on</strong>g>of</str<strong>on</strong>g> nitrogen fertilizer obviously reste in its<br />

capabillty <str<strong>on</strong>g>of</str<strong>on</strong>g> producing a rarge rìumber <str<strong>on</strong>g>of</str<strong>on</strong>g> spikes under these<br />

more optimal growing c<strong>on</strong>dlti<strong>on</strong>s. One could then specuJ.ate<br />

that this factor, combined with the kernel weight inadequacy<br />

<strong>and</strong> the negative associati<strong>on</strong> between spi.ke size <strong>and</strong> kernel<br />

wel-ght, suggests the ideal genotype for optimum growing<br />

c<strong>on</strong>diti<strong>on</strong>s might be <strong>on</strong>e which bas the abÍlity to produce<br />

large numbers <str<strong>on</strong>g>of</str<strong>on</strong>g> tíllers, thereby producing a larger number<br />

<str<strong>on</strong>g>of</str<strong>on</strong>g> spikes per unit area; but these spikes shourd have fewer<br />

kerneLs each Ín order to naintaÍn anð./or achieve adequate<br />

kernel size.<br />

0n the other h<strong>and</strong> this type <str<strong>on</strong>g>of</str<strong>on</strong>g> approach may be too<br />

simplistlc <strong>and</strong> rather unrealistic, particularly if taken to<br />

the extreme. îhere has in fact been an intensive effort to<br />

increase the graln nur¡ber per spike in seni_dwarfs, in<br />

general negating the above proposal" perhaps it then might<br />

be wise to produce hybrids with parents which have large,<br />

pì-ump grain <strong>and</strong> select intensively in the segregating<br />

populati<strong>on</strong>s for the most d.esirable combinati"<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the yield<br />

c<strong>on</strong>p<strong>on</strong>ents <strong>and</strong> <str<strong>on</strong>g>height</str<strong>on</strong>g>.<br />

2I2

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