hybrid vigor

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Increased vigor or other superior qualities arising from the crossbreeding of genetically different plants or animals.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A property of some hybrids that are more likely to outperform either purebred parent in surviving.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (genetics) the tendency of a crossbred organism to have qualities superior to those of either parent