TEMPERATE MAIZE INBREDS DERIVED FROM TROPICAL GERMPLASM .1. TESTCROSS YIELD TRIALS

Tropical maize (Zea mays L.) has been suggested as a germplasm source to improve yield and disease resistance for U.S. breeding programs. Our objective was to compare the performance of testcrosses between tropical-derived Lines and an elite U.S. tester with the performance of adapted commercial hybrids. A group of 190 lines was derived from seven tropical commercial hybrids and intercrosses among them using two cycles of pedigree selection for adaptation to North Carolina. Ear-to-row sib-mating and selfing were used to develop the Lines. Visual selection of each generation concentrated on silk-tassel synchrony, earliness, standability, lower ear height, and ear quality. No selection for combining ability was made during line development. Lines were topcrossed onto the public U.S. single cross B73Ht/Mo17Ht. Test-crosses were evaluated in yield trials at three locations during 2 yr. Among 190 testcrosses, 16 were within the LSD (0.05) of the commercial checks for yield, standability, and grain moisture. Most genetic variation for yield, standability, and grain moisture was accounted for by differences among pedigrees rather than differences among lines within a pedigree. Seventeen testcrosses yielded more than the tester, B73Ht/Mo17Ht. The inbreds B73 and Mo17 represent two dominant heterotic groups utilized by U.S. maize breeders. Since tropical-derived lines appear to combine well with B73/Mo17, they could be used as a source of disease resistance for either heterotic group. In addition, they have potential to enhance the combining ability of inbreds representing these two heterotic groups.