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 newlydeveloped inbreds as female parents. The four testers included an inbred, a single cross, a three-way cross, anda synthetic variety. The parents and crosses were evaluated in two separate field irrigation trials to explore theextent of general combining ability and heterosis of crosses using narrow, medium, and broad base testers undernormal and stressed watering regimes. Watering regimes and genotypes as sources of variation of combinedanalysis were highly significant for all traits. The (Parents vs. Crosses) with watering regimes interaction possessedhighly significant mean squares for dates of tasseling and silking. Significant negative GCA effects were recordedfor tasseling date and silking date under both conditions. The grain yield of crosses varied differently betweenregimes. 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 threefemale lines (I.274, I.277, and I.281) exhibited significant positive (unfavorable) GCA effects on flowering dates underboth conditions. Variable GCA effects for ASI were observed among the tested maize genotypes, particularlyunder normal conditions. However, under-stressed one, all tested genotypes showed insignificant GCA effectsfor ASI except I.272, which may be shorted the ASI. Out of thirty-six top crosses, thirty and twenty-eight crossesrecorded significantly unfavorable (favorable) heterosis under normal irrigated trial comparing to twenty-two, andtwenty-one crosses in stressed watering regime for TD and SD, respectively. However, for ASI, eleven and ninecrosses were significantly showed favorable flowering intervals than corresponding mid-parents under normal andstressed conditions respectively. For grain yield per plot about 25% significant superiority in performance of alltop crosses over corresponding mid-parents was recorded under either normal or stress conditions. The investigatedten inbred lines may be of great benefit for hybrid water-saving maize breeding program. Narrow geneticbase tester (I.272) resulted in favorable heterosis of crosses and could be recommended in advanced generationsof homozygosity, whereas mostly based ones may be valid for screening during the first generations of selfing