Combining Ability Analysis for Early Maturity and Phaeosphaeria Leaf Spot Resistance in Regional Maize Germplasm
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Phaeosphaeria leaf spot (P. maydis Henn.) disease has the potential to cause substantial yield losses in maize (Zea mays L,). Maize is grown by smallholder farmers without fungicides; hence the need to breed for resistance in regional adapted germplasm. Sub-Saharan Africa has been characterised by low annual rainfall amounts. As such the demand for early maturing maize hybrids has been on the increase. No information is available on the combining ability of maize genotypes for Phaeosphaeria leaf spot resistance (PLS) and early maturity. In addition, there is virtually little information about the gene action determining PLS resistance in African maize germplasm. This study was therefore conducted to determine the combining ability of early maturity and PLS disease resistance in Sub-Saharan Africa maize germplasm. The maize inbred parents previously selected for their performance were crossed in a North Carolina Design II mating scheme. The twenty-five experimental hybrids that were generated were evaluated for general and specific combining abilities together with five check hybrids in a 5 x 6 rectangular lattice design during the 2006/7 summer season at two locations, Borrowdale and Kadoma in Zimbabwe. There was significant variation among hybrids (P < 0.05). General combining ability (GCA) effects were more important than specific combining ability (SCA) effects, reflecting the preponderance of additive gene action for days to maturity, Phaeosphaeria leaf spot disease resistance and grain yield. Results of GCA showed that E25 and E29 were the best general combiners for earliness (giving high negative GCA effects) at both locations. For PLS disease resistance, E31 and E18 were the best general combiners (giving high negative GCA effects), at Borrowdale and Kadoma, respectively. For SCA effects, the highest significant negative effect for earliness was shown by the crosses E28 x E29 and E32 x E25 at both locations. The highest SCA effect for PLS disease resistance was given by the cross E32 x E31 and E28 x E31 at Borrowdale and Kadoma, respectively. For grain yield, the highest SCA effects were given by E26 x E18 and E28 x E25 at Borrowdale and Kadoma, respectively. The hybrids showed a high range of performance for all characters investigated, and could be further exploited for their heterotic capacities and subsequent release in areas where PLS is prevalent. Early maturity and PLS disease resistance heritabilities were moderate (51 %) and high (68 %), respectively indicating that selection could be used to improve earliness and PLS resistance in this germplasm.