In Southern Africa and Mozambique, tropical lowland accounts for 22% and 65%,
respectively, of area under maize production, but grain yield is compromised by downy
mildew disease (DM, which is caused by Peronosclerospora sorghi (Weston and Uppal)
Shaw), and lack of appropriate varieties, especially hybrids. Among other factors,
productivity can be enhanced by deploying DM resistant hybrids, which are higher yielding
than open pollinated varieties. Development of a viable hybrid-breeding programme
requires knowledge of genetic effects governing yield and DM resistance in inbreds, and
effective germplasm management requires heterotic groups and heterotic patterns to be
established. In addition, knowledge of farmer-preferred traits is required. Currently, such
information is not available to the hybrid-breeding programme in Mozambique. The
objectives of this study were, therefore; i) to identify farmers’ preferred variety traits and
major production constraints, ii) to determine combining ability effects of inbred maize S4
lines for grain yield and DM resistance, iii) to determine heterotic groups and heterotic
patterns among the elite inbred maize lines, and iv) to investigate gene effects governing
resistance to DM in breeding source inbred maize lines from the breeding programme in
Mozambique.
During 2007/08, 142 households were involved in a survey conducted in three
districts representing two maize agro-ecological zones in Mozambique. Formal surveys and
informal farmer-participatory methods were employed and data subjected to analysis in the
SPSS computer programme. Results indicated that there was a low utilization of improved
varieties, especially hybrids, with grain yield estimated at 0.7 t ha-1. Farmers were aware of
the major production constraints and could discriminate constraints according to their
importance for their respective communities. For the lowland environment, farmers
identified downy mildew, drought, and cutworm and stem borer damage as the main
constraints. In contrast, for the high altitude environments, they ranked ear rot, seed and
fertilizer availability, turcicum leaf blight, grey leaf spot diseases and low soil fertility among
the major constraints limiting productivity. The most important variety selection criteria were
grain yield, short growth cycle, white and flint grain with stress tolerance to drought, low soil
fertility, diseases, and grain weevils. These afore mentioned traits, would be priority for the
breeding programmes for the lowland and mid altitude environments in Mozambique.
To determine combining ability for downy mildew resistance, heterotic groups and
heterotic patterns, two testers (open-pollinated varieties) ZM523 (Z) and Suwan-1 (S), were
crossed with 18 lines to generate 36 top crosses for evaluation. Crosses were evaluated at
two sites under DM. Preponderance of GCA effects indicated that additive gene effects were
more important than non-additive gene effects in governing both grain yield and downy
mildew resistance in the new maize lines. Based on specific combining ability (SCA) data,
lines for yield were classified into two heterotic groups, S and Z; whereas based on
heterosis data, lines were fitted into three heterotic groups (S, Z and SZ).
Further heterotic patterns and gene action for yield were determined by subjecting
nine inbred lines and the two testers, S and Z, to an 11 x 11 diallel-mating scheme. The
diallel crosses, three hybrid checks and the two testers were evaluated in six environments
in Mozambique. Results revealed that non-additive gene effects were predominant for yield
components. In addition, high levels of heterosis for yield was observed and three heterotic
groups identified (Z, S and S/Z), and five exceptional heterotic patterns among the inbred
elite maize lines were observed. Topcrosses with yield levels comparable to single cross
hybrids were also identified, and these would be advanced in the testing programme with
potential for deployment as alternative cheaper and sustainable technology to conventional
hybrids for the poor farming communities in Mozambique.
To determine gene effects for downy mildew resistance in potential breeding lines,
two maize populations were derived from crosses between downy mildew susceptible line
LP67, and resistant lines DRAC and Suwan-L1. To generate F2 and backcross progenies
(BCP1 and BCP2), F1 progenies were self-pollinated and simultaneously crossed to both
inbred parents (P1 and P2). All the six generations (P1, P2, F1, F2, BCP1, and BCP2) of
the populations were evaluated at two sites under downy mildew infection. A generation
mean analysis was performed in SAS. It was revealed that downy mildew resistance was
influenced by genes with additive and dominance effects, plus different types of epistatic
effects such as additive x additive, and dominance x dominance. Overall results indicated
that genes with predominantly non-additive effects controlled resistance in DRAC, whereas
resistance in Suwan-L1 was largely influenced by additive gene effects. These findings
have serious implications on the effective use of these downy mildew resistance sources in
breeding programmes that aim to generate varieties with downy mildew resistance.
Overall, results suggested that inbreeding and selection within heterotic groups,
followed by hybridization between inbreds within and across heterotic groups would be
effective to generate new hybrids. The breeding programme will consider development of
conventional hybrids, such as single crosses and three way crosses, and top crosses.
Implications of the findings of the study and recommendations are discussed. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/5037 |
| Date | January 2010 |
| Creators | Fato, Pedro. |
| Contributors | Derera, John., Tongoona, Pangirayi. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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