3. Results
Results of ANOVA combined over the years revealed significant year effect for all measured traits except number of
ears per plant under well-watered condition (Table 2).
Genotype year interaction was significant only for days to
silking and ear aspect under well-watered and leaf death score
under drought stress (Table 2). Hybrids differed significantly
in grain yield performance and for all other measured traits
under both irrigation treatments (Table 2).
The means and statistics of grain yield (GY) of the top 10
and bottom 10 hybrids and the checks under well-watered and
drought stress conditions are presented in Table 3. Under
drought stress, GY ranged between 444 and 3022 kg ha 1
whereas under full irrigation it varied from 3827 to
8887 kg ha 1 (Table 1). The trial mean yield of 1868 kg ha 1
under drought represented only 23% of the trial mean yield
(6119 kg ha 1) under well-watered conditions. Hence, the
drought tolerance index (DTI), which is an indicator of hybrid
yield loss due to drought stress, ranged between 54 and 90%
with an average of about 70% (Table 3).
The yield rank of hybrids from the four source combinations
under both irrigation treatment conditions did not follow a
similar trend (Table 3). Under drought stress, the
exotic exotic sets of inbreds and adapted exotic sets of
inbreds produced hybrids with higher mean grain yield than
exotic adapted and adapted adapted hybrids.
Adapted exotic hybrid combinations were less variable in
comparison with their counterparts from exotic exotic
crosses (Table 3). The adapted exotic hybrids had a yield
advantage of 28% over exotic adapted hybrids. Under wellwatered condition, the adapted exotic hybrids produced the
highest mean yield of 6703 kg ha 1, and had yield advantages
of 9% over the exotic exotic hybrids and 14% over the hybrid
checks (Table 3). The adapted adapted crosses produced the
lowest average yield under both irrigation treatments (Table 3).
Under drought stress, the adapted exotic and exotic exotic
hybrids silked 2 days earlier than other sets of hybrids. Both
adapted exotic and exotic exotic hybrids had an average
score of 3 for ear aspect and recorded an average of 0.8 for
number of ears per plant, ratings that are better than other
hybrid combinations. Other measured traits followed similar
patterns under well-watered condition (Table 3).
Grain yield under drought stress condition had significant
and positive (r ¼ 0.5; P < 0.0001) correlation with yield under
well-watered condition. Under both irrigation conditions, grain