Yield Potential of Tropical Hybrid Maize Derivatives

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Abstract
In an effort to enhance the germplasm base of the U.S. maize (Zea mays L.) crop an adaptation program was initiated in 1975. A group of nine 100% tropical hybrids were crossed in all possible combinations, without reciprocals. Progeny from each cross were sib mated for six generations with selection for earliness, low plant and ear height, tassel and silk synchronization, lodging resistance, and prolificacy. Following sib mating, selection continued through two generations of setting. All generations were grown in Raleigh, NC. In 1983 34 selected inbred lines were crossed onto two Corn Belt single cross testers, (A632Ht ✕ B73) and (Mo17 ✕ H95 ✕ H993). The number of entries representing each cross varied greatly depending upon response to selection. The testcrosses were divided into two groups by tester and combined with eight commercial check hybrids to form two tests. The tests were grown at three locations in 1984 and 1985, with three replications at each location. Testcrosses developed from 100% tropical inbred lines crossed with elite U.S. materials were agronomically competitive with commercial U.S. hybrids. The inbreds are adapted to the southern USA and flower about 1 wk later than B73. Plant height and grain moisture of the testcrosses were all within the range of the commercial checks. About 25% of the testcrosses had yields comparable to the commercial checks. The inbreds are relatively insensitive to photoperiod as a result of the apparent presence of complementary genetic systems for photoperiod sensitivity among the different tropical materials.