The Collaborative International Dictionary of English v.0.48:

Hybridize \Hy"brid*i`ze\, v. t. [imp. & p. p. Hybridized; p.
   pr. & vb. n. Hybridizing.]
   To render hybrid; to produce by mixture of stocks.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hybridizing
    n 1: (genetics) the act of mixing different species or varieties
         of animals or plants and thus to produce hybrids [syn:
         hybridization, hybridisation, crossbreeding,
         crossing, cross, interbreeding, hybridizing]