| Advance-cycle breeding is restricting the gennplasm base for U.S. maize (Zea Mays L.). Incorporating tropical germplasm into U.S. breeding pools could broaden the maize germplasm base, while providing favorable alleles for yield and disease resistance. Knowing quantitative trait loci (QTL) for disease resistance can enhance gain by permitting selection in the absence of disease expression. In addition, accounting for spatial variability can improve the precision of breeding value estimates.;Recombinant inbred (RI) lines were derived from a cross between NC300, a temperate-adapted, all-tropical line, and B104, a Stiff-Stalk-synthetic line. The RI lines were toperossed to the tester FR615.FR697. Resistance QTL for Southern Rust (rust) (Puccinia polysora) were mapped in the toperosses, while Gray Leaf Spot (GLS) (Cercospora zeae-maydis ) resistance QTL were mapped in both the RI lines and toperosses. A major rust-resistance gene and three GLS QTL corresponded to regions mapped in prior populations, and the tropical parental allele, NC300, increased resistance at three of these four loci. Three flowering time QTL corresponded to GLS QTL positions, and in each case the resistance allele was associated with increased maturity.;A SAS program, entitled SPATIALPRO, was developed to implement spatial analytical techniques. The program optimizes several spatial models for each trait and environment combination, and chooses a preferred model based on a specified criterion. Results from the preferred model are outputted into SAS data sets.;A long term breeding effort was initiated in 1975 to adapt and enhance tropical germplasm. Founder germplasm included seven tropical hybrids. At least five cycles of S1 recurrent selection (RS) for grain yield has been practiced on two populations derived from these hybrids. Studies were conducted to quantify the progress of S1 RS, and determine if this is a reasonable approach, or if it needs modification. S1 RS per se increased grain yield linearly within each population, but the yield responses across the cycle-toperosses to LH132.LH51 are half the average annual gains of U.S. commercial breeding activities. Predicted yield responses to S1 topeross recurrent selection for the two populations are substantially more promising in maintaining relevancy, and appears to be a more favorable method of enhancement. |
