interbreed

from WordNet (r) 3.0 (2006)

interbreed
    v 1: breed animals or plants using parents of different races
         and varieties; "cross a horse and a donkey"; "Mendel tried
         crossbreeding"; "these species do not interbreed" [syn:
         {crossbreed}, {cross}, {hybridize}, {hybridise},
         {interbreed}]

from The Collaborative International Dictionary of English v.0.48

Interbreed \In`ter*breed"\, v. t. & i.
   To breed by crossing different stocks of animals or plants.
   [1913 Webster]