Heterosis in
maize hybrids: Fact or artifact
J.A.W. Ochieng
Heterosis (hybrid vigor) is defined as the superior
performance of the hybrid cross over the mid-parental value.
For topcross progenies, using a common tester, heterotic level narrows
down to the performance of the female parent relative to the hybrid.
Topcross hybrids of maize were evaluated for heterosis in a replicated
trial at two sites in one season following standard agronomic practices for
Kenyan highlands. The
tester (male parent) was an improved maize population at cycle 10, whilst the
female parents were either landraces, improved populations or inbred lines.
Mid-parent heterosis was computed for grain yield (T Ha-1), ear height
(meters) and days to 50% anthesis. Statistically
significant differences (p< 0.05) among varieties were observed for all
traits, except plant stand. Heterosis
varied among hybrids for the three traits.
Heterosis was positive for grain yield and ear height, but negative for
number of days to 50% anthesis. There
was a range in variation of heterosis levels for grain yield, ear height and
days-to-anthesis. For grain
yield, high percent heterosis was associated with those topcross hybrids in
which the female parent was an inbred line or an ill-adapted landrace,
implying that the high value was an artifact of the low yield potential of the
landraces or inbred line cross, compared to the hybrid.
Generally, percent heterosis for yield was lower in the hybrids in
which the female parent was either a single cross or population well-adapted
to the highlands and in this latter case, heterosis was considered a genetic
fact.
