Hybrids vs OP varieties [Was: Genetic engineering is a Good Thing?]
msachs at uiuc.edu
Mon Sep 21 14:28:58 EST 1998
In article <0$rICJAbKeB2EwMO at upthorpe.demon.co.uk>, Oz
<Oz at upthorpe.demon.co.uk> wrote:
> In article <A6589F7E4E3DD211AA7F0000C0E21BD57F0F29 at aricrmntnews.isd.dpi.
> qld.gov.au>, Ian Staples <ianst at refer.to.signature.au> writes
> >The advantage of hybrids is not necessarily simply yield _per se_.
> >A major factor is that hybrids derived from inbred lines are
> >genetically uniform, which usually results in a more uniform phenotype.
> >As a result you get consistent quality, uniform ripening, easier and
> >more efficient harvesting, and similar benefits.
> Why was this a problem for maize, but not for wheat and barley (and most
> crops in fact) that breed pretty true?
Maize and its ancestor are naturally out-crossers (separate male and
female flowers coupled with wind pollination), while wheat and barley and
relatives are naturally selfers. Maize is naturally very polymorphic and
loses vigor as it becomes inbred. With OPVs and land races, virtually
every plant in a farmer's field is genetically different, so wind
pollination maintains polymorphism and vigor in subsequent generations.
With hybrids, the farmer's field is, at best, limited to two alleles for
each gene. So, each subsequent generation would be more and more inbred
and there is very noticeable loss in yield after only one generation. It
took special efforts to breed maize inbred lines that produced decently
enough so that they could be used as economically viable parents of
hybrids. Wheat, barley, etc. were always selected as inbreds, and
required no special breeding efforts to go from polymorhic lines to
inbreds. So, while there is somewhat of a heterotic boost for hybrid
wheat, it is not as significant as in maize.
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