The importance of maize in sub-Saharan Africa and the potential of quality protein
maize (QPM) to alleviate the nutritional gap caused by lack of access to adequate
protein rich foods were highlighted. Frustrations from complex inheritance systems of
the QPM trait leading to calls for more information on the inheritance and stability of
the QPM trait, fear of total loss of the QPM trait due to the recessive nature of the
opaque-2 gene to the wild type gene in normal endosperm maize when QPM and
normal endosperm maize coexist, lack of information on the nutritional value of
contaminated QPM grain, and poor linkages with the smallholder farmers were all
cited as drawbacks in the promotion and adoption of QPM. Therefore the objectives
of the study were:
1) To solicit the participation of smallholder farmers in the development and
setting up of QPM breeding goals, objectives and dissemination strategies;
2) To estimate general combining ability (GCA), specific combining ability (SCA)
and reciprocal cross effects on anthesis days, quality traits and grain yield
among the publicly available elite QPM inbred lines;
3) To compare experimental QPM hybrids with selected check cultivars, and
normal endosperm maize hybrids for grain yield performance and kernel
endosperm modification scores;
4) To evaluate QPM hybrids for grain yield and kernel endosperm modification
scores in selected sub-Saharan Africa target environments.
5) To determine the level of normal endosperm maize pollen contamination that
can occur in quality protein maize without loss of nutritional superiority;
6) To estimate the average levels and the patterns of foreign maize pollen
contamination in QPM crops coexisting with normal endosperm maize
varieties.
The contribution of smallholder farmers in setting breeding goals and dissemination
strategies for QPM was solicited. One major finding was that the kernel endosperm
qualities of landrace “Hickory King” need to be incorporated into new QPM varieties
so as to encourage adoption. Farmers preferred getting information on QPM varieties
through their local Agricultural Research and Extension (AREX) officers.
A diallel study of 36 F1 QPM hybrids and their reciprocals was conducted across
seven environments for agronomic traits and three environments for nutritional value
traits. There were significant differences for all traits analysed using Griffing Method 3
model 1. General combing ability effects were significant and important in the control
of anthesis days, kernel endosperm modification, protein content, tryptophan content,
and Quality Index (QI). Specific combining ability effects were highly significant and
important in the control of grain yield. There were significant SCA effects for anthesis
days and QI but the proportions were lesser than the corresponding GCA effects in
both traits. Kernel endosperm modification had significant GCA effects and
nonsignificant SCA effects.
Reciprocal-cross differences were significant for anthesis days, tryptophan content
and QI. Nonmaternal effects were significant for tryptophan content whilst both
maternal and nonmaternal effects were significant for QI and anthesis days.
Nonmaternal effects were relatively more important than maternal effects in all the
cases where there were significant reciprocal-cross differences. The cross with the
highest SCA effects for grain yield was CZL03016/CML144. The most desirable
cross with the lowest anthesis days was CZL03016/CML144 whilst the most
desirable inbred line with the lowest anthesis GCA effects was CZL03016. The
inbred line with the most desirable GCA effects for protein content, tryptophan
content and QI was CML264Q. Inbred line CML264Q crossed to CZL03016 had
significant SCA effects for QI. The most desirable GCA effects for kernel endosperm
modification were associated with inbred line CZL03016 followed by CZL01006.
Maternal effects for both tryptophan content and QI were associated with inbred line
CML264Q.
Genotype by environment interaction effects across all the seven environments were
significant for grain yield and kernel endosperm modification. Check hybrids
performed better than experimental hybrids for grain yield but were not different for
kernel endosperm modification. The normal endosperm maize hybrids were
significantly better for both grain yield and kernel endosperm modification. However,
in all the comparisons the best check or normal endosperm maize hybrid was not
significantly better than the best experimental or QPM hybrid, respectively. The most
desirable score for kernel endosperm modification was from the cross of CZL01006
to CZL03016 though not significantly different from the check hybrid with the best
score. AMMI1 was the best model for kernel endosperm modification scores and
AMMI2 was suitable for grain yield. Both environments and hybrids were diverse.
Grain yield of most hybrids was not stable with specific adaptation to environments.
The most stable hybrid with no specific adaptation was CML176/CML181f with a
mean yield of 6.51t ha-1.
The putative nutritional superiority of normal endosperm maize pollen contaminated
QPM as measured by the QI depended on the environmental conditions. The
moisture stressed environment (CIMMYT Harare) had a lower QI value (0.858) and a
lower tolerance to pollen contamination of 15.3% whereas the grain produced under
near to optimum growing conditions (ART farm) had a higher QI value (0.915) and a
higher tolerance to pollen contamination of 31.9% before total loss of nutritional
superiority. Thus contaminated QPM grain had nutritional superiority up to a certain
point before total loss of nutritional superiority.
Geostatistical analysis was used to determine the levels and patterns of pollen
contamination that occur when QPM and normal endosperm maize crops coexist
under conditions minimising both temporal and geographical isolation to the lowest
possible levels for the two independent crops. Higher pollen contamination levels
were restricted mostly to the sections of the QPM crop proximal to the rows of normal
endosperm maize crop, with the central parts of the QPM crops experiencing
relatively low levels of contamination. For the four experiments (QCS200711,
QCS200712, QCS200721 and QCS200722) in which the thresholds to nutritional
superiority were determined, 87.9%, 94.8%, 62.2% and 65.6% of the crop areas
passed for superior QPM grain, respectively. Estimates for average contamination
levels of homogenous mixtures of grain from each of the nine experiments were
below 20% contamination. The contamination levels were far less than previously
thought.
“Hickory King” kernel quality attributes were important in breeding QPM varieties for
the smallholder farmers. Parents of the 72 hybrids were diverse for the agronomic
characters studied and three of the experimental hybrids were found to be adapted
and comparable to the check varieties. Quality protein maize tolerance to foreign
pollen contamination without loss in nutritional superiority depended on growing
conditions. The coexistence of QPM and normal endosperm maize without total loss
of QPM nutritional superiority was feasible. / Thesis (PhD.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/5307 |
| Date | January 2008 |
| Creators | Machida, Lewis. |
| Contributors | Derera, John., Tongoona, Pangirayi. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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