Diallel crosses among maize lines with emphasis on resistance to foliar diseases

Ten elite maize (Zea mays L.) lines were crossed in a complete diallel sche me and the single-cross hybrids obtained were assessed at four experimental stations of the Agronomic Institute of Campinas, in Sao Paulo State, Brazi l. The experiments were set up in a randomized complete block design with t hree replications, including four commercial checks. The experimental plots consisted of two 5-m rows spaced at 0.9 m, with a total of 50 plants. The traits assessed included: days to mid-tassel pollen shed (DPS), plant heigh t (PH), ear height (EH), grain yield, corrected for a 50-plant stand and 14 % moisture (GY corr.), and resistance to Phaeosphaeria maydis and Puccinia polysora. General and specific combining ability effects (GCA and SCA) were determined. There was extensive genetic variability among hybrids with the best hybrids (HS 04 x 10 and HS 10 x Il) not differing from the commercial checks. The Lines with the greatest potential for hybrid synthesis include d: L10, L11 and L13, because they had higher GCA for yield, moderate resist ance to Tt maydis and reduced EH. The greatest contribution to reduction of the Phaeosphaeria stain was obtained with L5. The magnitude of the GCA rel ative to the total variation indicated that additive effects predominated f or resistance to P. maydis and P. polysora. Significant SCA (P < 0.01) was also found, indicating dominance effects as well.