Since the initiation of a product oriented breeding programme aimed at improving maize for
drought prone mid altitudes of southern Africa, CIMMYT developed several inbred lines and
single cross hybrids using pedigree selection methods, with emphasis on earliness, drought
and low nitrogen stress tolerance. This resulted in increased volumes of seed inventories.
Sixteen inbred lines and 71 single cross hybrids were crossed to three (single cross) testers,
CML312/CML442 and CML505/CML509 (heterotic group A) and CML395/CML444
(heterotic group B) and evaluated as two separate experiments for general and specific
combining ability in contrasting environments (optimal, managed drought and nitrogen
stressed). The objective was to asses the relative importance of general combining ability
(GCA) and specific combining ability (SCA) in identifying promising early maturing maize
lines, single crosses and testers that could tolerate drought and nitrogen stress conditions,
thus simulating prevailing conditions in most resource poor farmersâ fields in the mid
altitude environments of southern Africa.
The first experiment consisted of 48 experimental crosses and 24 additional crosses. Six
trails were planted in a lattice (Alpha 0,1) with eight plots per incomplete block. The second
experiment consisted of 213 experimental crosses and additional 27 double crosses and
synthetics. Five trials were planted in a lattice (Alpha 0,1) with 12 plots per incomplete
block. Trials were planted under optimal conditions at ART farm, Rattray Arnold and
Kadoma, nitrogen stressed conditions at Harare and drought stressed conditions at Chiredzi
in Zimbabwe in 2006.
Data was collected on grain yield (GY), anthesis dates (AD), anthesis silking interval (ASI),
plant heights (PH), ears per plant (EPP), and leaf senescence (SEN). Data was analysed first
according to Lattice (alpha 0.01) design using computer software Fieldbook, for the general
performances of all crosses for all traits. Line x tester analysis for general combining ability and specific combining ability was performed using SAS and AGROBASE II computer
software. The first experiment identified heterotic group B line 15 as superior with a GCA value of
0.56. The line had a SCA value of 0.21 with early maturing (heterotic group A tester)
CML505/CML509. The hybrid had grain yield of 7.9t/ha and 1.3t/ha across optimal and
stress environments respectively and was early maturing (69 days) (silking anthesis days).
In the second set of materials heterotic group A single crosses 51, 37, 55, and 7 had good
general combining ability above 0.64. Heterotic group B single crosses 11, 38, 39 and 22 had
good specific combing ability with CML505/CML509. The hybrid combinations ranged
between 6.1-7.4 t/ha across optimal environments and 0.8-1.4 t/ha across stressed
environments. These hybrids were very early (AD 64-66 days), could be evaluated in wide
environments for GCA with heterotic group A lines and single crosses in order to identify an
early maturing group B tester. CML505/CML509 classified the early maturing lines and
single crosses into heterotic groups better than CML312/CML442.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ufs/oai:etd.uovs.ac.za:etd-04082009-143814 |
| Date | 08 April 2009 |
| Creators | Mawere, Sebastian Shangwa |
| Contributors | Prof MT Labuschagne |
| Publisher | University of the Free State |
| Source Sets | South African National ETD Portal |
| Language | en-uk |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.uovs.ac.za//theses/available/etd-04082009-143814/restricted/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University Free State or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
Page generated in 0.0122 seconds