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University of Zambia (2007)

Combining ability for early maturity in maize (Zea mays L) under drought and low nitrogen conditions

Ndhlela, Thokozile

Titre : Combining ability for early maturity in maize (Zea mays L) under drought and low nitrogen conditions

Auteur : Ndhlela, Thokozile

Université de soutenance : University of Zambia

Grade : Master of Science in Agronomy 2007

Résumé
The unpredictable rainfall patterns increased the demand for early maturing maize cultivars. The two most limiting production constraints in maize are drought and low nitrogen. In most national breeding programs in Southern Africa there are no early maturing testers for use in the early phases of breeding. This study was conducted with a view to validate the suitability of CML509/CML505 as a tester for the identification of early maturing inbred lines with a potential in the development of drought and low nitrogen resistant hybrid cultivars. Fifty inbred lines were crossed to this and other two testers, CML312/CML442 and CML395/CML444, for comparison. The research assessed the relative importance of general and specific combining ability effects (GCA and SCA) for grain yield (GY), days to anthesis (AD), anthesis-silking interval (ASI),plant height (PH), ear-height (EH), ears per plant (EPP), root-lodging (RL) and husk cover (HC), of the fifty inbred lines. The three-way hybrids were evaluated under low nitrogen, drought and optimum conditions.The testers grouped the lines into different heterotic groups with CML509/CML505 proving to be a good early maturing single cross tester for heterotic group A after it managed to group most of the lines that were originally in group A into the same group again. The inbred lines were grouped into heterotic groups by the three testers using the SCA effects for GY. A total of ten lines were grouped into an unidentified group after they exhibited negative SCA effects with a group A and group B tester respectively. General combining ability and SCA analysis showed that additive genetic variance was more important for grain yield and days to anthesis, a proxy parameter for maturity. This has an implication on the breeding strategy in that the parents with good GCA can be crossed and early testing of genotypes becomes more effective and promising hybrids can be identified and selected based on their prediction from GCA effects. The tester, CML505/CML509, showed good GCA effects for most of the traits. The line LF47 had the best GCA effect for GY (0.60 t ha"1) and LF49 had the poorest GCA effect for GY (-0.62 t ha1). The mean days to anthesis of the crosses with CML509/CML505 were 61.8 days and mean grain yield was 8.9 t ha"1 under, optimum conditions. CML509/CML505 also showed fairly good heterosis with most of the lines under both drought and low nitrogen conditions.

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