Influence of Testers and Watering Regimes on Combining ability and Heterosis of Maize Top Crosses


Thirty-six top crosses of white maize were produced as the combinations of four male testers and nine newly
developed inbreds as female parents. The four testers included an inbred, a single cross, a three-way cross, and
a synthetic variety. The parents and crosses were evaluated in two separate field irrigation trials to explore the
extent of general combining ability and heterosis of crosses using narrow, medium, and broad base testers under
normal and stressed watering regimes. Watering regimes and genotypes as sources of variation of combined
analysis were highly significant for all traits. The (Parents vs. Crosses) with watering regimes interaction possessed
highly significant mean squares for dates of tasseling and silking. Significant negative GCA effects were recorded
for tasseling date and silking date under both conditions. The grain yield of crosses varied differently between
regimes. Two testers (I.272 and G.2) and two lines (I.276 and I.278) recorded significant negative GCA effects (favorable)
for dates to tasseling (TD) and silking (SD) under both watering regimes. The SC.10 (as tester) and three
female lines (I.274, I.277, and I.281) exhibited significant positive (unfavorable) GCA effects on flowering dates under
both conditions. Variable GCA effects for ASI were observed among the tested maize genotypes, particularly
under normal conditions. However, under-stressed one, all tested genotypes showed insignificant GCA effects
for ASI except I.272, which may be shorted the ASI. Out of thirty-six top crosses, thirty and twenty-eight crosses
recorded significantly unfavorable (favorable) heterosis under normal irrigated trial comparing to twenty-two, and
twenty-one crosses in stressed watering regime for TD and SD, respectively. However, for ASI, eleven and nine
crosses were significantly showed favorable flowering intervals than corresponding mid-parents under normal and
stressed conditions respectively. For grain yield per plot about 25% significant superiority in performance of all
top crosses over corresponding mid-parents was recorded under either normal or stress conditions. The investigated
ten inbred lines may be of great benefit for hybrid water-saving maize breeding program. Narrow genetic
base tester (I.272) resulted in favorable heterosis of crosses and could be recommended in advanced generations
of homozygosity, whereas mostly based ones may be valid for screening during the first generations of selfing.


Maize, Combining ability, Heterosis, Watering Regimes

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