Abstract
Ten elite maize (Zea mays L.) lines were crossed in a complete diallel scheme and the single-cross hybrids obtained were assessed at four experimental stations of the Agronomic Institute of Campinas, in São Paulo State, Brazil. The experiments were set up in a randomized complete block design with three 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 height (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 11) not differing from the commercial checks. The lines with the greatest potential for hybrid synthesis included: L 10, L 11 and L 13, because they had higher GCA for yield, moderate resistance to P. maydis and reduced EH. The greatest contribution to reduction of the Phaeosphaeria stain was obtained with L 5. The magnitude of the GCA relative to the total variation indicated that additive effects predominated for resistance to P. maydis and P. polysora. Significant SCA (P < 0.01) was also found, indicating dominance effects as well.
Highlights
The high incidence of leaf disease in maize crops in some areas of south central Brazil has led breeders to develop cultivars resistant to the main pathogens involved
Little has been published on the inheritance or genetic potential of maize disease resistance, except for downy mildew caused by Peronosclerospora sorghi (Lima et al, 1982), northern corn leaf blight caused by Exserohilum turcicum (Narro León, 1996) and southern corn rust caused by Puccina polysora (Fantin et al, 1993)
Ten elite maize lines were crossed in a complete diallel design to estimate the general and specific combining abilities and the respective yield and resistance to two leaf diseases, caused by Phaeosphaeria maydis and Puccinia polysora, of the single-cross hybrids
Summary
The high incidence of leaf disease in maize crops in some areas of south central Brazil has led breeders to develop cultivars resistant to the main pathogens involved. Lima et al (1996) have studied different maize lines and populations to identify the sources of resistance to several leaf diseases. Ten elite maize lines were crossed in a complete diallel design to estimate the general and specific combining abilities and the respective yield and resistance to two leaf diseases, caused by Phaeosphaeria maydis and Puccinia polysora, of the single-cross hybrids.
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