Plant Breeding

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varieties - indeed, new species - by
crossbreeding between species. This is because hybrids are often polypoid.
Polyploidy, as we know, can occur naturally in the wild. Some species of
cotton that we grow are polypodies that probably arose originally by
accidental crosses between different species of cotton.

But breeders do not have to rely on accidents. They can attempt to
produce fertile polypodies by crossbreeding between different species. One
early attempt to produce another hybrid species was made in 1927 by the
Russian geneticist G. D. Karpechenko, who crossbred two quite distantly
related species, a radish and a cabbage. Each species has eighteen
chromosomes (nine pairs); the hybrids had the same number (nine radish
chromosomes and nine cabbage chromosomes) and were sterile. However, some
polyploids arose by chance. These had thirty six chromosomes (nine pairs
of radish, and nine pairs of cabbage), and were fertile. Unfortunately,
the hybrid was not ...

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