TEMPERATE MAIZE INBREDS DERIVED FROM TROPICAL GERMPLASM .1. TESTCROSSYIELD TRIALS

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