A hybrid corn variety is the cross of two inbred lines,
each of which may have one or more desirable charac
teristics lacked by the other or which complement the
other. The hybrid progeny of the ?rst generation is
designated F1. In the development of hybrids only the
F1 hybrid plants are sought. The F1 hybrid is more
vigorous than its inbred parents. This hybrid vigor, or
heterosis, can be manifested in many ways, including
increased vegetative growth and increased yield.
The development of a hybrid corn variety involves
three steps: (1) the selection of superior plants from
various germplasm pools; (2) the sel?ng of the superior
plants for several generations to produce a series of
inbred lines, which although different from each other,
each breed true and are highly uniform; and (3) crossing
the selected inbred lines with unrelated inbred lines to
produce the hybrid progeny (F1). During the inbreed
ing process the vigor of the lines decreases. Vigor is
restored when two unrelated inbred lines are crossed to
produce the hybrid progeny (F1). An important conse
quence of the homozygosity and homogeniety of the
inbred lines is that the hybrid between any two inbreds
will always be the same. Once the inbreds that give the
best hybrid have been identi?ed, the hybrid seed can be
reproduced inde?nitely as long as the homogeneity of
the inbred parents is maintained.