| dc.description.abstract | Maize is the staple crop for most farmers in the arid and semi arid areas of the tropics.
Drought and low soil fertility are major limiting factors in maize production in these areas.
Research emphasis has been placed at developing early maturing quality protein maize (QPM)
varieties that can yield well under water-limited conditions and low nitrogen stress
experienced in drier mid-altitude areas of this region. The general objective of this study was
to assess the general combining ability present in CIMMYT's early QPM maize lines and
specific combing ability of single crosses under drought stress, low nitrogen and well-watered
conditions and group the lines in known heterotic groups. Two studies were conducted.
In the first study, 13 inbred lines were crossed in a diallel. Hybrids were evaluated under
managed drought, random stress and low nitrogen stress and well watered conditions at six
locations. The objective was to evaluate their performance, estimate GCA and SCA effects
and determine the phenotypic correlations between grain yield and agronomic traits. Inbred
line 1 and 2 had high, positive and significant (P < 0.05) GCA effects for grain yield under all
well-watered conditions and managed drought stress. This suggesting that these inbred lines
have the potential to be used as parents for developing good hybrids for well-watered
conditions as well as drought-stressed environments. Entry 42 was consistent in its top
performance for grain yield under all conditions tested. Phenotypic correlations between grain
yield across well-watered conditions were positive and significant (P < 0.001) for days to
anthesis, plant height and ear height. Under the three stress conditions, the correlation between
anthesis silking interval and ears per plant was negative and significant (P < 0.05) indicating a reduced anthesis-silking interval which resulted in an increased number of ears under stress
conditions.
In the second study, lines were crossed with two inbred line testers. The FI hybrids were
evaluated under six locations to estimate general combining ability and specific combining
ability effects under drought stress and well watered conditions, and group them into known
heterotic groups. Inbred line 45 had high, significant and positive GCA effect for grain yield
under managed drought stress and across well-watered conditions. Lines with good GCA in
each heterotic group may be used in recycling inbred lines. Based on SCA effects for grain
yield, the two inbred line testers grouped 29 lines into heterotic group B, 25 inbred lines into
heterotic group A and 11 into heterotic group AB. Entries 55, 60, 87 and 113 were the top
performers in terms of grain yield both under managed drought and across well-watered conditions. | en |
