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Genetic and economic value of a shuttle breeding programme for enhancing adaptability of tropical maize germplasm in South Africa.Musundire, Lennin. January 2013 (has links)
Maize is the principal crop for food security and livestock feed in South Africa. It is also an industrial crop and the produce is exported to many countries in the world. Therefore there is high seed demand which prompts competition for breeding productive hybrids. However direct introduction of tropical hybrids into the warm temperate South African environments has not been successful. Competitive advantages can be obtained by implementing a “shuttle breeding” programme whereby part of the breeding is done in Zimbabwe and South Africa to minimise research and production costs. Introgression of temperate germplasm in tropical elite inbred lines can also be pursued to obtain adapted hybrids. The aim of this study was therefore to assess the effectiveness of introgression of temperate germplasm into tropical elite maize inbred lines as a strategy to enhance adaptability of new hybrids to South Africa, and also to determine both breeding and economic value of a “shuttle breeding” programme. To this end, the introgressed inbred lines and their hybrid progenies were evaluated in South Africa to determine the effect of the selection environment on their performance and genetic variation. Both genetic and economic gains were evaluated with a view to make recommendations to the small and medium scale enterprises with interests in the market.
Introgression of temperate germplasm into tropical germplasm elite lines did not disrupt the heterotic groupings because most of the introgressed lines (86%) fitted into known existing heterotic groups. Only 14% of the introgressed lines did not show any inclination to towards the known heterotic clusters of their founder tropical parents. These lines were considered to be new recombinant inbred lines that showed little resemblance with their founder parents. Selection environment did not influence heterotic clustering of the introgressed lines, and genetic diversity was identified among introgressed lines developed in the same environment.
Genetic variation was observed for the major economic traits and heritability of 21% to 91%. The introgression was effective for improving grain yield potential and ear prolificacy. Spearman’s rank correlation analysis on grain yield and ear prolificacy data showed significant positive correlation between selection environments such as Ukulinga in South Africa and Kadoma Research Centre in Zimbabwe. Therefore Kadoma Research Centre will be recommended for use in breeding new maize germplasm lines for South Africa. Correlation among traits showed that ear prolificacy and plant height had significant (P<0.05) direct effects on grain yield thus direct selection of these traits will be emphasised in breeding new hybrids.
Introgression of temperate germplasm into tropical elite maize inbred lines was effective for improving their adaptation to warm temperate environments. Positive genetic gains of 5-58% were realised for grain yield potential and 26-46% for ear prolificacy. Whereas 1% to 37% gains were realised for secondary traits such as plant and ear height, anthesis and silking days there was barely any improvement for root and stalk lodging, and grain moisture content at harvest. However, introgressed lines displayed impressive performance per se and inter se indicating potential for commercial production. The new inbred line 71-DMLF7_88 combined early physiological maturity, high ear prolificacy and grain yield potential qualifying it as a perfect parent for the warm temperate environments. At least six hybrids were stable and adaptable while four were considered to be ideal genotypes relative to standard commercial hybrids such as PAN6Q445B which is a market leader. The exceptional hybrids, 12C20264, 12C22766, 13XH349 and 11C11774 will be advanced in South Africa.
The study also indicated significant economic gains when a shuttle programme is implemented to breed new hybrids following the introgression strategy. The “Shuttle breeding” programme attained a positive net present value (NPV) of $1, 834, 166. 00. This indicated an increase in shareholder value through an opportunity cost of 17% and 3% relative to conventional breeding programmes which are based in South Africa and Zimbabwe, respectively. Positive NPV and genetic gain achieved using the “shuttle breeding” programme makes it a viable option for small and medium scale seed companies with intention to breed and commercialise competitive products in South African.
In general, the study revealed that introgression of temperate germplasm into tropical elite inbred lines using a “shuttle breeding” programme was effective for enhancing adaptability of tropical germplasm to the South African warm temperate environments. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
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Heterosis, genetic distance and path coefficient analysis in dent, flint and popcorn hybrids.Mhoswa, Lorraine. January 2013 (has links)
Maize (Zea mays L.) is one of the most important food crops in sub-Saharan Africa (SSA);
however its production is constrained by many factors. Grain yield is compromised by poor
genetic performance and poor agronomic management. This calls for need to develop
hybrids and exploiting heterosis of single crosses which are adapted to challenging
environments. Currently, there is no popcorn hybrids developed in South Africa which is
adapted to local conditions. As such, there is need to develop hybrids that cater for smallscale
farmers in marginal environments. The objectives of the study were to determine i)
standard heterosis, levels of variation and heritability for phenotypic traits in dent and flint
maize hybrids; ii) the association between genetic distances and phenotypic traits in dent and
flint maize hybrids; iii) mid-parent heterosis in popcorn hybrids, iv) the effect of secondary
traits on grain yield in dent, flint and popcorn hybrids; v) genetic diversity and the relationship
between traits in widely grown selected hybrids in Southern Africa; and vii) to compare
effectiveness of phenotypic analysis models for determining genetic distances between
hybrids. Popcorn, dent and flint hybrids were evaluated at two sites. The data was analysed
using SAS, Genstat and Power marker statistical packages. The results revealed that the
relationship between genetic distance and heterosis is dependent on the environment.
Hybrids in top 10 at both sites were different indicating that there was a significant genotype x
environment interaction. 13 new heterotic patterns that performed better than the controls can
be utilized in heterosis breeding; however there is need to test them in different environments
to check on their stability. Grain texture cannot be used to discriminate hybrids for yield
because all patterns of dent x dent, dent x flint and flint x flint were present in the top 10
hybrids. Lines DXL124 and DXL158 dominated parentage of the top 10 hybrid rank for yield
qualifying them as potential testers for specific combining ability in future studies. Heterosis in
popcorn hybrids that performed better than the mid-parent can be utilized in heterosis
breeding to exploit vigour, though there is need to test the hybrids in a number of different
environments. The main direct factors contributing to yield were ear prolificacy, ear aspect,
number of plants and shelling percentages qualifying them to be selected to boost grain yield.
Phenotypic data and 91 SNP markers were used to estimate the genetic distance between
the hybrids. The results indicated that hybrids that were in the same cluster belong to the
same brand and were related in origin and pedigree. Both molecular and phenotypic data
were effective in discriminating the hybrids into different clusters according to genetic
background. SNP markers revealed nine clusters of hybrids, 12-trait model revealed eight
clusters and five-trait model revealed six clusters at 85% genetic distance. The study
indicates strategies that can be adopted to boost grain yield in dent, flint and popcorn hybrids. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
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Genetic variation and associations among adaptive traits in a recombinant maize inbred line population.Sithole, Mxolisi Percival Sibongeleni. 05 November 2013 (has links)
Maize production in Africa is constrained by abiotic and biotic stresses. Breeders need to
have information on the nature of combining ability of parents, their traits and performance
in hybrid combination. This requires careful determination of genetic variability of parents,
and studying associations between grain yield and adaptive traits to breed superior cultivars
which are better able to withstand such stresses. Therefore, this study was aimed at
selecting parental testers with best combining ability in hybrid combination with
recombinant inbred lines (RILs); and studying the correlation between grain yield and its
components in eastern and western South Africa. It was also aimed at determining genetic
variation and associations among adaptive traits in hybrids involving RILs. The final
objectives of the study were to determine cultivar superiority of testcrosses involving RILs,
and to select the best cultivars within and across four different environments.
The 42 RILs were crossed to 9 Zimbabwean tropical testers resulting in 1009 hybrids with
sufficient seed for planting in trials. From these a sample of 87 hybrids with adequate seed
were selected and planted at four sites for combining ability analysis. The hybrids were
evaluated at four sites in two regions; western region (Potchefstroom research station) and
eastern region (Cedara, Ukulinga and Dundee research stations), during 2011/12 season.
The experiments were laid out as augmented alpha lattice design. Trials were managed in
accordance with production culture for each region. All quantitative data was subjected to
GenStat and SAS statistical softwares.
The results from combining ability study indicated that the line general combining ability
(GCA) effects played a non-significant role (p > 0.05) in determining grain yield, grain
moisture and anthesis date, while they were significant (p ≤ 0.05) for the other traits such as
ear prolificacy. The tester main effects were significant for all the traits except ear
prolificacy and plant height. Results also revealed that all the traits were controlled by both
additive and non-additive genes, where additive gene action had the most contribution to
the traits. The non-additive gene action played a minor role suggesting the total GCA effects
attributed to both lines and testers predominantly higher over the specific combining ability
(SCA) for all traits. In general the additive effects were preponderant over the non-additive
gene effects. One cross (L114 x T12) had a significant and positive SCA effect for grain yield.
The correlation between grain yield and secondary traits (number of ears per plant, grain
moisture content, ear height, plant height, ear position and anthesis date) suggested that
indirect selection can be employed to enhance grain yield by breeding for these particular
adaptive traits. Path analysis showed that plant height had the highest direct and indirect
effect on grain yield indicating its importance among other secondary traits for grain yield
enhancement. Phenotypic coefficient of variation (PCV) was higher than genotypic
coefficient of variation (GCV) for all the studied traits across all the four environments. All
the traits displayed high heritability at Potchefstroom except anthesis date which was highly
heritable at Ukulinga. Cedara was the second best site for heritability of all the traits except
for the number of ears per plant. The genetic advance for grain yield was the highest at
Cedara followed by Potchefstroom, Dundee and Ukulinga. The hybrids exhibited different
patterns of variation and distribution for all the traits. This indicated that selection
strategies to exploit GCA should be emphasised.
Association studies among grain yield and secondary traits such as ear length, number of
ears per plant, plant height, anthesis date, silking date and ear leaf area revealed that there
were significant phenotypic correlations between grain yield and secondary traits, and
among the secondary traits. Ear length had the highest direct effect on grain yield at
Ukulinga; number of ears per plant had the highest direct effect on grain yield at Cedara and
Potchefstroom; whereas plant height had the highest direct effect on grain yield at Dundee.
Grain yield was least affected by indirect factors at all the sites except Ukulinga, where
anthesis date had the highest indirect effect on grain yield through silking date followed by
plant height through leaf area. The study reveals that there is significant variation among
the hybrids for mean performance, indicating that there is opportunity for selection. Overall
the findings suggest that direct selection would be appropriate to enhance grain yield. Path
analysis revealed that plant height had the highest direct and indirect effects on grain yield,
indicating that plant height can be further exploited as the main trait in future breeding programmes for grain yield increment.
Hybrid 10MAK10-1/N3 was the best hybrid at Ukulinga in terms of grain yield, relative yield
and economic traits. Whereas hybrid T17/L83 was the best hybrid at Cedara in terms of
grain yield and relative yield; however, T11/L102 was selected as the most elite hybrid with
respect to grain yield, relative yield and economic traits. Hybrid T3/L48 was identified as thebest hybrid at Dundee with respect to grain yield, relative yield and prolificacy. At Potchefstroom the standard check PAN6611 was identified as the best hybrid in terms of grain yield and relative yield followed by developmental hybrid T1/L28; however,
developmental hybrid T1/L28 was the best in terms of earliness, prolificacy and ear aspect.
Stability coefficients and cultivar superiority index across the sites revealed that four
developmental hybrids were identified as best hybrids and they performed better than the
standard check. These hybrids will be recommended for further testing in advanced trials.
With respect to cultivar superiority, the desired hybrids are required to combine high grain
yield with economic and adaptive traits such as high ear prolificacy, low grain moisture, and
low ear aspect score (desired) for them to adapt to production environments in South
Africa. There was significant variation among the top 25 yielding hybrids. At least 5 hybrids
combined high grain yield with the desired complimentary adaptive traits such as quick
moisture dry down, prolificacy and ear aspect. The results showed that there is variation in
the performance of high yielding genotypes within all the sites, and that agronomically superior cultivars can be identified.
The study shows that there is significant variation among the RILs since they interacted
differently with the 9 tropical testers. Even among the top 25 selections of RILs in each
environment there was still variation for combinations of the desired traits. Significant
associations among grain yield and other economic and adaptive traits were observed with
implications for breeding strategy. Above all the significant variation gives large score for future breeding of new unique lines. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
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