When trying to solicit authors for this book it became apparent that the
causal factors for heterosis at the physiological and biochemical level
are today almost as obscure as they were 30 years ago. Though
biometrical-genetical analyses point to dispersion of complementary
genes - not overdominance - as the major cause of the phenomenon, plant
breeders' experience still suggests a cautious, pragmatic approach to
the dominance-overdominance controversy in breeding hybrid cultivars.
Thus we are faced with a striking discordance between our limited
comprehension of the causal factors and mechanism of heter- osis on the
one hand, and the extensive agricultural practice of utiliza- tion of
hybrid vigor on the other. Such utilization is the result of the
economic value of hybrid combinations displaying superior yields and
qualities as well as stability of performance, of benefits derived in
breeding programs, and of the enhanced varietal protection of
proprietary rights. No comprehensive and critical analysis of the
phenomenon of heterosis in economic plants has been published for the
last three decades since the now classical book Heterosis, edited by J .
W. Gowen (Iowa State College Press, Ames, Iowa, 1952). The present book
attempts to fill the gap and to assess the status of our present knowl-
edge of the concept, the basis, the extent, and the application of
heterosis in economic plants.