BREEDING MAIZE (ZEA MAYS L.) HYBRIDS WITH COMBINED TOLERANCE TO STRIGA HERMONTHICA AND LOW SOIL NITROGEN FOR THE NORTHERN SAVANNA ZONES OF GHANA
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Date
2019-06
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KNUST
Abstract
Maize is an important staple crop widely produced and consumed in West and Central
Africa (WCA). Low soil nitrogen (low-N), recurrent drought and Striga hermonthica
infestation are major constraints to maize production and productivity in WCA. The
specific objectives of this study were to (i) determine genetic diversity among 100
selected set of maize inbred lines using Simple Sequence Repeat (SSR) and Single
Nucleotide Polymorphism (SNP) markers (ii) classify the selected set of inbred lines
into heterotic groups using the general combining ability effect of multiple traits
(HGCAMT) method, SSR and SNP markers, and to compare effectiveness of the
different methods in grouping the inbred lines, (iii) determine the combining ability and
heterosis for grain yield and agronomic traits of the selected set of inbred lines under
Striga infestation, low-N and optimal growing conditions, (iv) determine the grain yield
potential and yield stability of hybrids derived from the selected inbred lines under
Striga infestation, low-N and optimal growing conditions.
Substantial genetic and phenotypic variability existed among the inbred lines used in
this study for grain yield, Striga resistance/tolerance and low-N tolerance. Although
SSR markers used in this study were highly informative, the use of large number of
SNP markers made the SNP comparable with the SSR for genetic diversity analysis,
and better than SSR in cluster and population structure analyses. Genetic analysis of
150 hybrids derived from the North Carolina Mating Design II revealed significant
differences among the hybrids for grain yield, Striga resistance and low-N tolerance.
General combining ability and SCA mean squares were significant for grain yield and
most traits under optimal, Striga-infested and low-N environments and across
environments, indicating that both additive and non-additive gene actions were
important in the inheritance of the traits. The inheritance of grain yield under low-N
and across environments were controlled largely by additive gene action, while the
inheritance of grain yield under optimal and Striga-infested environments were
controlled largely by non-additive gene action. Non-additive gene action largely
modulated the inheritance of almost all traits measured under Striga-infested
environments, except for Striga damage syndrome rating at 8 WAP. The SNP genetic
distance based heterotic grouping method was identified as the most efficient in
grouping the inbred lines into heterotic groups.
The yield response and stability analyses of the 150 hybrids and six local checks over
10 contrasting environments indicated that 62% of the hybrids had average stability
across environments, while 8% had above average stability and were adapted
specifically to either Striga-infested or low-N environments. The hybrids TZdEI 215 x
TZdEI 192, TZEI 378 x TZdEI 215 and TZEI 3A x TZdEI 192 were the highest yielding
and most stable across environments. They are recommended for further testing and
commercialization in the savanna zones of Ghana and other countries in WCA.
Description
A THESIS SUBMITTED TO THE DEPARTMENT OF CROP AND SOIL
SCIENCES,IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY IN PLANT BREEDING