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Agronomic aspects of recent developments in a protein quality maize (Zea mays L.) breeding programFoster, A. M. January 1987 (has links)
No description available.
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Physiological and gene expression responses to water stress in drought tolerant and drought sensitive maize cultivars.O'Regan, Brian Patrick. January 1996 (has links)
Physiological characteristics of the response to water stress of two maize cultivars, the
one drought resistant (PAN473) and the other drought sensitive (SR52), were compared.
Mature plants were grown in one of two treatments, control and water stress. The drought
resistant cultivar had a higher growth rate and a greater amount of roots in the lower soil levels
than the drought sensitive cultivar in the water stress treatment. There was no difference
between the cultivars in physiological characteristics in the control treatment, but in the water-stress
treatment the drought resistant cultivar had a higher transpiration rate during the onset
of water stress, and higher relative water content and levels of abscisic acid and proline
throughout the period of water stress. A comparison between the cultivars in their gene
expression response was done to determine if a correlation could be made with the difference
in physiological response. A differential screening of water stress cDNA libraries identified nine
different cDNA species which gave a signal with the water stress probe but not the control
probe. Three of these cDNAs were represented by more than one cDNA clone. The cDNAs
occurred in both libraries, therefore there was no difference between the cultivars in the
presence or absence of the water stress responsive genes. The three genes represented by these
cDNAs were named rws7, rws16 and rws5. All three genes showed increased transcription in
response to water stress in whole plants, and to desiccation and osmotic stress of detached
leaves. No increase in transcription was found in response to exogenously applied abscisic acid
or proline. No difference between the cultivars was observed in the pattern of transcription
response. Two of the three cDNA species that are represented more than once were
sequenced. Rws7 had an open reading frame. A BLAST search found no homologous amino
acid sequences, but the characteristics of the polypeptide suggest that it is a dehydrin. Rws 16
had a partial coding sequence. A BLAST search found two homologous amino acid sequences,
and both were chloride channel proteins. The remaining seven cDNA species were sequenced
at their 5' ends, and no complete homologous nucleotide sequences were found. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1996.
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Quantitative genetic analysis of agronomic and kernel endosperm traits in quality protein maize (QPM) and investigations of the putative nutritional value of contaminated QPM crops.Machida, Lewis. January 2008 (has links)
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.
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Development and application of SNP marker for low phytic acid gene (Ipa1-1) with studies on the effect of low phytic acid on seed germination, vigour and yield in maize.Naidoo, Roobavathie. January 2010 (has links)
Maize grain contains high levels of phytic acid which chelates iron, zinc and other micronutrients as it passes through the digestive systems of monogastric consumers reducing their bioavailability. Breeding for low phytic acid (LPA) content to improve micronutrient bioavailability is hampered by a tedious and destructive colorimetric method on the grain, low yields compared to the wild-types and reduced seed germination and vigour of LPA mutants. Breeding for LPA therefore should also incorporate breeding for improved germination and vigour in the mutants. Molecular markers to speed up the selection process and studies on gene action and combining ability for germination, vigour and yield parameters of the LPA mutants in combinations with other different maize germplasm will speed up breeding for this trait. The objectives of this study were: to develop a molecular marker linked to the lpa1-1 gene and apply this marker for foreground selection in a backcross breeding programme and to use amplified fragment length polymorphism (AFLP) markers for background selection to recover the recurrent parent genome to speed up the backcrossing process; to study gene action and combining ability for seed germination, vigour and yield from diallel crosses involving LPA mutants, QPM and normal endosperm maize inbred lines by replicated laboratory seed tests ( standard germination test and accelerated aging test) and field evaluations in South Africa and Zimbabwe.
A co-dominant single nucleotide polymorphism (SNP) marker which detects the transition base change of C/T nucleotides was developed from the gene sequence to identify the lpa1-1 trait. The 150 bp lpa1-1 SNP marker was validated by forward and reverse DNA sequencing of the parental amplification products which confirmed the C to T base change resulting in the LPA phenotype. The lpa1-1 SNP marker was used for foreground selection in 250 BC(2)F(1) progenies of CM 32 (LPA) x P 16 as the recurrent parent. This SNP marker was used to genotype the lines into homozygous dominant (wild type) and homozygous recessive (LPA) genotypes by their melting profiles and heterozygous genotypes by the normalised difference plots using high resolution melt (HRM) analysis. Seventeen heterozygous and 11 homozygous recessive lines were identified for background selection by fingerprinting with AFLP markers to determine the amount of recurrent parent (P 16) genome present. There were six EcoRI/MseI primer combinations tested with 277 data points scored (84% polymorphism rate). The amount of recurrent parent (P 16) genome recovered ranged from 62% to 92% with 13 lines showing greater than 83% of the recurrent parent genome.
The effects of diallel crosses generated between four LPA, three QPM and three normal endosperm maize lines were determined for seed germination and vigour using the standard germination and accelerated aging seed tests under laboratory conditions in accordance
with the procedures of the International Seed Testing Association. The specific combining ability (SCA) effects and general combining ability (GCA) effects were significant for the seed germination and vigour traits, indicating that genes with non-additive and additive effects were important in controlling these traits. However, the SCA effects were greater than GCA effects suggesting that genes with non-additive effects were predominant. The LPA parents showed reduced vigour compared to the normal and QPM inbred lines under both conditions, with LPA lines CM 31 and CM 32 showing stress tolerance. There were some combinations involving LPA lines, such as LPA x normal, LPA x QPM and LPA x LPA that retained high vigour and high germination rates under accelerated aging conditions, suggesting that they could be stress-tolerant..
A 10 x 10 diallel involving four LPA, three QPM and three Nm inbred lines was evaluated in replicated trials across six environments. Results show that both additive and non-additive gene effects were significant for resistance to northern corn leaf blight (NCLB), grey leaf spot (GLS) and Phaeosphaeria leaf spot (PLS) diseases. The additive gene effects were predominant for the yield and associated secondary traits such as days to mid-pollen shed (DMP), days to mid-silking (DMS), ear per plant (EPP) and grain moisture content (GMC) and grain yield. The LPA lines were early flowering and had quick grain dry down rate but all showed undesirable negative and significant GCA effects for yield. The yield of the LPA x LPA, LPA x Nm and LPA x QPM group of crosses was lower than the check hybrids by about 32 to 67% showing the need for yield improvement of the LPA combinations.
An eight x eight diallel involving two LPA and six normal endosperm lines was evaluated over two seasons in five locations with two replications for grain yield components and foliar diseases. There was significant additive and non-additive gene action for both seed germination and vigour traits with predominance of non-additive gene effects. Both additive and non-additive gene effects were significant for yield and associated traits such as anthesis dates and number of ears per plant. However, the additive gene action was predominant for yield and associated traits. Generally the LPA lines and their combinations showed lower germination and vigour. The LPA line, CM 32 showed stress tolerance under accelerated aging conditions. There were three LPA x Nm crosses that showed improvements to the means of seed germination and vigour and yield traits. Results indicated that there was not any significant correlation between yield and seed germination and between yield and vigour. Yield was, however, significantly and positively correlated with anthesis dates and GMC, indicating that higher yield was associated with longer growing cycles.
This study was able to successfully develop and apply the lpa1-1 SNP marker for foreground selection and AFLP markers for background selection in a backcross breeding programme. Problems of low seed germination, seedling vigour and grain yield of LPA lines and their combinations were confirmed. However results also indicated some potential of combining the LPA and QPM traits in a single cultivar. In general, procedures such as reciprocal recurrent selection, that emphasise both GCA and SCA effects would be recommended to improve seed germination, seedling vigour and yield in developing varieties with LPA trait. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2010.
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Optimisation of the randomly amplified polymorphic DNA (RAPD) technique for the characterisation of selected South African maize (Zea mays L.) breeding material.Edwards, Nicola Rachel. 23 October 2013 (has links)
Maize (Zea mays L.) is an important agronomic crop with the maize industry forming an
important component of the South African economy. Considerable effort has been directed
towards the genetic improvement of maize through both conventional breeding and
biotechnology. Genotype identification by DNA fingerprinting is becoming an important activity
in plant breeding. A widely used molecular based and relatively inexpensive method for DNA
fingerprinting is the randomly amplified polymorphic DNA (RAPD) technique. The RAPD
technique was tested in this study for its potential use in maize breeding programmes. Initial
results using the technique showed a low degree of reproducibility, therefore both the DNA
isolation and RAPD protocols were extensively optimised. DNA quality and quantity, and choice
of Taq polymerase buffer were three of the variables found to be influential in ensuring
reproducibility. The ability of the RAPD technique to characterise seven maize genotypes was
evaluated. Sixty random oligonucleotide primers were screened. Forty two primers scored a
total of 233 fragments (an average of 5.5 per primer), but not all primers gave reproducible
profiles. Eighteen primers scored a total of 110 loci for the presence (1) and absence (0) of DNA
fragments. RAPD markers were able to distinguish between all seven genotypes with five primers
producing specific fragments for four genotypes. Genetic similarity matrices were calculated
using two software programmes i.e. Genstat 5™ release 4.1 (1993) and PAUP (Phylogenetic
Analysis Using Parsimony) 4.0 beta version (Swafford, 1998). Cluster analysis was used to
generate dendrograms to visualise the genetic relationships of the seven maize genotypes (only
minor differences were observed between the Genstat or PAUP method of analysis). Genetic
diversity ranged from 0.62 to 0.96. The estimation of genetic relationship was in accordance with
the presumed pedigree of the genotypes showing that the RAPD technique demonstrates potential
for genome analysis of maize. The applicability of the technique for marker assisted selection was
also evaluated. Near-isogenic lines (NILs) for leaf blight (Helminthosporium spp.) were screened
for polymorphisms using a total of 120 primers. Ten primers identified polymorphisms between
the NILs. Four primers produced five polymorphic fragments present in the resistant inbred
K0315Y and absent in the susceptible inbred D0940Y. A small F2 population of 14 individuals
was produced by selfing the F1 of a cross between K0315Y and D0940Y. To speed up the generation time, the F1 and F2 plants were cultured by embryo rescue from 18d old harvested
seed. One fragment of 627 base pairs produced by primer OPB-01 (5' GTTTCGCTCC 3')
showed a 3: 1 segregation in the small F2 population and was considered putatively linked to the
HtN gene for leaf blight resistance. This study shows that the RAPD technique does have
application in maize breeding programmes. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2000.
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Responsividade e estabilidade da produção de grãos de milho: relações com caracteres relacionados à tolerância a estresses abióticos e heranças / Maize grain yield responsiveness and stability: relationships with traits related to abiotic stresses tolerance and inheritanceCarneiro, Otávio Luiz Gomes 09 August 2018 (has links)
Os principais caracteres a serem considerados em programas de melhoramento de milho visando tolerância a estresses abióticos são: prolificidade (PRO), intervalo de florescimento (IF), número de ramificações do pendão (NRP) e stay green (SG). Diversos autores sugeriram que esses caracteres podem estar relacionados à estabilidade da produção de grãos. Ademais, apesar da importância da responsividade e estabilidade da produção de grãos para a seleção de cultivares, há poucos relatos sobre a herança desses parâmetros, com resultados controversos. Os objetivos desse estudo foram investigar a relação entre a estabilidade e os caracteres relacionados à tolerância a estresses abióticos e a herança dos parâmetros responsividade e estabilidade da produção de grãos de milho. Foram avaliados dois Grupos de híbridos simples de milho: Grupo I (GI) consituído por 100 híbridos e o Grupo II (GII) por 48 híbridos, os quais foram avaliados respectivamente em 12 e 28 ambientes. Esses híbridos foram avaliados seguindo delineamento látice 10 x 10 e 7 x 7, compreendendo os 100 e 49 híbridos simples, respectivamente, com duas repetições por ambiente. Para completar o delineamento látice no GII, um híbrido simples comercial foi adicionado aos demais híbridos. Utilizando técnicas uni e multivariadas, as correlações entre os caracteres envolvendo tolerância a estresses abióticos, isto é, PRO, IF, NRP e SG, e os parâmetros de estabilidade apresentaram baixas magnitudes e, de forma geral, não diferiram de zero. Esses resultados indicaram que a estabilidade da produção de grãos e os caracteres relacionados à estresses abióticos são provavelmente independentes. Os resultados das análises dialélicas da responsividade e estabilidade mostraram que a contribuição da capacidade específica de combinação foi superior à capacidade geral de combinação para ambos os parâmetros nos dois Grupos de híbridos. Desta forma, os efeitos gênicos não aditivos (dominância e epistasia) foram mais importantes que os efeitos aditivos para a responsividade e estabilidade da produção de grãos. Apesar de os híbridos selecionados apresentarem os caracteres relacionados à tolerância a estresses abióticos de forma desejada e, assim, possivelmente reduzirem as flutuações da produção de grãos devido principalmente às instabilidades de precipitação, esses não possuem relação direta com os parâmetros de estabilidade. De qualquer forma, é importante que esses caracteres estejam inseridos nos programas de melhoramento de milho visando obter cultivares tolerantes a esses tipos de estresses. Também, a maior importância dos efeitos não aditivos em relação aos efeitos aditivos no controle da responsividade e estabilidade possui uma série de implicações para os programas de melhoramento de milho, uma vez que a seleção deverá ser realizada em cruzamentos de linhagens e não nas performances das linhagens per se. / The main traits considered in maize breeding programs aiming tolerance to abiotic stresses are: prolificacy (PRO), anthesis-silking interval (ASI), number of tassel branches (TB) and stay green (SG). Several authors have suggested that these traits would be related to maize grain yield stability. In addition, despite the importance of grain yield responsiveness and stability for the cultivars selection, there are few reports about the inheritance of these parameters, and they usually have controversial results. The objectives of this study were to investigate the relationship between stability and traits related to tolerance to abiotic stresses and the inheritance of maize grain yield responsiveness and stability parameters. Two groups of maize single-crosses were evaluated: Group I (GI) consisted of 100 single-crosses and Group II (GII) of 48 single-crosses, respectively evaluated in 12 and 28 environments. These hybrids were evaluated following a 10 x 10 and a 7 x 7 lattice designs comprising the 100 and 49 single-crosses, respectively, with two replications per environment. To complete the lattice design in GII a commercial single-cross was added to entries. Using univariate and multivariate techniques, the correlations between the traits involving abiotic stress tolerance, i.e., PRO, ASI, TB and SG, and stability parameters presented low magnitudes and, in general, did not differ from zero. These results indicated that grain yield stability and traits related to abiotic stresses tolerance are likely independent. The diallel analyses results of responsiveness and stability showed that the contribution of the specific combining ability was higher than the general combining ability for both parameters in the two Groups of single-crosses. Therefore, the non-additive genetic effects (dominance and epistasis) were more important than the additive effects for the grain yield responsiveness and stability. Although the selected single-crosses have the traits related to abiotic stresses tolerance in a desired way and possibly reduce grain yield fluctuations due mainly to precipitation instabilities, they are not directly related to the stability parameters. However, it is important that these traits be included in maize breeding programs in order to develop cultivars that are tolerant to these types of stresses. Additionally, the greater importance of non-additive effects than additive effects on responsiveness and stability control have several implications for maize breeding programs, since selection should be assessed in crosses of inbred lines and not in lines per se performance.
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Responsividade e estabilidade da produção de grãos de milho: relações com caracteres relacionados à tolerância a estresses abióticos e heranças / Maize grain yield responsiveness and stability: relationships with traits related to abiotic stresses tolerance and inheritanceOtávio Luiz Gomes Carneiro 09 August 2018 (has links)
Os principais caracteres a serem considerados em programas de melhoramento de milho visando tolerância a estresses abióticos são: prolificidade (PRO), intervalo de florescimento (IF), número de ramificações do pendão (NRP) e stay green (SG). Diversos autores sugeriram que esses caracteres podem estar relacionados à estabilidade da produção de grãos. Ademais, apesar da importância da responsividade e estabilidade da produção de grãos para a seleção de cultivares, há poucos relatos sobre a herança desses parâmetros, com resultados controversos. Os objetivos desse estudo foram investigar a relação entre a estabilidade e os caracteres relacionados à tolerância a estresses abióticos e a herança dos parâmetros responsividade e estabilidade da produção de grãos de milho. Foram avaliados dois Grupos de híbridos simples de milho: Grupo I (GI) consituído por 100 híbridos e o Grupo II (GII) por 48 híbridos, os quais foram avaliados respectivamente em 12 e 28 ambientes. Esses híbridos foram avaliados seguindo delineamento látice 10 x 10 e 7 x 7, compreendendo os 100 e 49 híbridos simples, respectivamente, com duas repetições por ambiente. Para completar o delineamento látice no GII, um híbrido simples comercial foi adicionado aos demais híbridos. Utilizando técnicas uni e multivariadas, as correlações entre os caracteres envolvendo tolerância a estresses abióticos, isto é, PRO, IF, NRP e SG, e os parâmetros de estabilidade apresentaram baixas magnitudes e, de forma geral, não diferiram de zero. Esses resultados indicaram que a estabilidade da produção de grãos e os caracteres relacionados à estresses abióticos são provavelmente independentes. Os resultados das análises dialélicas da responsividade e estabilidade mostraram que a contribuição da capacidade específica de combinação foi superior à capacidade geral de combinação para ambos os parâmetros nos dois Grupos de híbridos. Desta forma, os efeitos gênicos não aditivos (dominância e epistasia) foram mais importantes que os efeitos aditivos para a responsividade e estabilidade da produção de grãos. Apesar de os híbridos selecionados apresentarem os caracteres relacionados à tolerância a estresses abióticos de forma desejada e, assim, possivelmente reduzirem as flutuações da produção de grãos devido principalmente às instabilidades de precipitação, esses não possuem relação direta com os parâmetros de estabilidade. De qualquer forma, é importante que esses caracteres estejam inseridos nos programas de melhoramento de milho visando obter cultivares tolerantes a esses tipos de estresses. Também, a maior importância dos efeitos não aditivos em relação aos efeitos aditivos no controle da responsividade e estabilidade possui uma série de implicações para os programas de melhoramento de milho, uma vez que a seleção deverá ser realizada em cruzamentos de linhagens e não nas performances das linhagens per se. / The main traits considered in maize breeding programs aiming tolerance to abiotic stresses are: prolificacy (PRO), anthesis-silking interval (ASI), number of tassel branches (TB) and stay green (SG). Several authors have suggested that these traits would be related to maize grain yield stability. In addition, despite the importance of grain yield responsiveness and stability for the cultivars selection, there are few reports about the inheritance of these parameters, and they usually have controversial results. The objectives of this study were to investigate the relationship between stability and traits related to tolerance to abiotic stresses and the inheritance of maize grain yield responsiveness and stability parameters. Two groups of maize single-crosses were evaluated: Group I (GI) consisted of 100 single-crosses and Group II (GII) of 48 single-crosses, respectively evaluated in 12 and 28 environments. These hybrids were evaluated following a 10 x 10 and a 7 x 7 lattice designs comprising the 100 and 49 single-crosses, respectively, with two replications per environment. To complete the lattice design in GII a commercial single-cross was added to entries. Using univariate and multivariate techniques, the correlations between the traits involving abiotic stress tolerance, i.e., PRO, ASI, TB and SG, and stability parameters presented low magnitudes and, in general, did not differ from zero. These results indicated that grain yield stability and traits related to abiotic stresses tolerance are likely independent. The diallel analyses results of responsiveness and stability showed that the contribution of the specific combining ability was higher than the general combining ability for both parameters in the two Groups of single-crosses. Therefore, the non-additive genetic effects (dominance and epistasis) were more important than the additive effects for the grain yield responsiveness and stability. Although the selected single-crosses have the traits related to abiotic stresses tolerance in a desired way and possibly reduce grain yield fluctuations due mainly to precipitation instabilities, they are not directly related to the stability parameters. However, it is important that these traits be included in maize breeding programs in order to develop cultivars that are tolerant to these types of stresses. Additionally, the greater importance of non-additive effects than additive effects on responsiveness and stability control have several implications for maize breeding programs, since selection should be assessed in crosses of inbred lines and not in lines per se performance.
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Recurrent selection for drought tolerance in Maize (Zea mays L. and study of heterotic patterns of maize populations from Eastern Kenya.January 2007 (has links)
There are few maize varieties that are drought tolerant in semi-arid eastern Kenya and farmer perceptions of drought tolerant maize cultivars have not been studied in this region. Farmers in this region use maize landraces that have not been studied for their potential future hybridization. The main objectives of this study were therefore to: (i) study farmer perceptions of drought and preference for maize varieties, (ii) improve drought tolerance in maize populations in the semi-arid eastern Kenya using S1 family recurrent selection, and (iii) classify maize landraces according to their heterotic patterns. A participatory rural appraisal (PRA) was conducted in Machakos and Makueni districts in semi-arid eastern Kenya. A total of 175 farmers were involved in focus group discussions. An open ended questionnaire and a checklist were used to guide the farmers during the discussion sessions. Scoring and ranking techniques were used to assess farmers’ preferences of maize varieties and constraints to maize production. The farmers grew maize as their major crop followed by beans. Nearly 60% of the farmers grew local maize landraces, whose seed they recycled from season to season; 40% grew improved varieties, but mainly composites rather than hybrids. The key farmers’ criteria for choosing a maize variety in order of importance were drought tolerance, early maturity, high yield, and disease resistance. The major constraints to maize production were drought, lack of technical know-how, pests, poor soils, and inadequate seed supply. Maize traits preferred by farmers in a drought tolerant variety included high yield, recovery after a dry spell and the stay green characteristic. Two maize landrace populations MKS and KTU from semi-arid eastern Kenya and three CIMMYT populations V032, ZM423, and ZM523 were subjected to two cycles of S1 progeny recurrent selection for drought tolerance in yield and traits indicative of drought tolerance were measured during flowering and grain filling from February 2005 to September 2007. Evaluation to determine selection gains was done in one trial replicated five times. It was laid out as a 4x4 lattice design and drought was imposed at reproductive stage by withholding irrigation one week before flowering and resumed during grain filling. The trial was repeated under well-watered conditions which served as a control experiment. After two cycles of selection under drought stress conditions, KTU population had a realized gain in yield of 0.2 t ha-1, MKS population 1.2 t ha-1 and ZM423 0.4 t ha-1, whereas in V032 and ZM523, grain yield reduced by 1.1 t ha-1 and 0.6 t ha-1, respectively. Under well watered conditions, the realized gains in grain yield were positive in all the populations except V032, where there was a reduction of 0.1 t ha-1. Selection increased the genetic variability and heritability estimates for yield in S1 lines of MKS and ZM423 populations, but decreased in KTU, V032 and ZM523 populations. The research to identify heterotic patterns was undertaken using ten maize landraces from the semi-arid eastern Kenya, six maize landraces from coastal Kenya, and three maize populations from CIMMYT. These populations were planted at Kiboko Research Farm during the short rains of October-December 2005 and crossed to two population testers, Embu 11 and Embu 12. The evaluation of the test crosses was done during the long rains of March-June 2006. Percentage heterosis for yield ranged from -17.7% to 397.4%, -79.4 to 22.2% for anthesis-silking interval, -23.9% to 29.2% for ear height, -0.1 to 1.1 for ear diameter, -7.1 to 21.2% for ear length and -5.9% to 30.3% for plant height. iii General combining ability (GCA) effects were significant (p=0.05) for all the traits, while specific combining ability (SCA) effects were not significant (p>0.05), implying that variation among these crosses was mainly due to additive rather than nonadditive gene effects. Since SCA was not significant (p>0.05) for yield, maize populations were classified based on percentage heterosis for yield alone. The maize populations therefore, were grouped into three different heterotic groups P, Q and R. Twelve landrace populations and two CIMMYT populations showed heterosis with Embu 11 and no heterosis with Embu 12 were put in one group P. Two landrace populations that showed no heterosis with either tester were put in group Q. Two landrace populations and one CIMMYT population showed heterosis with both testers were put in group R. None of the populations showed heterosis only with Embu 12 and no heterosis with Embu 11. The main constraint to maize production was drought and the farmers preferred their landraces whose seed they recycled season to season. After two cycles of recurrent selection, the landrace populations showed improved progress in yield. Thus, further selection will be beneficial in the populations where genetic variability increased. Therefore, these populations can further be improved per se and released as varieties and/or incorporated into the existing maize germplasm to broaden their genetic base, given that their heterotic patterns have been identified. Considering that farmers recycle seed, breeding should be towards the development of open-pollinated varieties which are drought tolerant. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.
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A comparative analysis of conventional and marker assisted selection methods in screening for resistance to maize (Zea mays L.) streak virus disease.Abalo, Grace. January 2006 (has links)
Maize (Zea mays L.) streak virus disease (MSD) is the most important virus disease in Africa but farmers are unaware of its status. A project was initiated to assess the current status of MSD and to breed for its resistance. Four populations comprised of two BC1F1 and two F2 progenies developed by backcrossing and selfing the F1 progenies of two crosses between a donor line (CMl 202) and two susceptible lines (CMl 321 and CMl 384) were developed. Conventional and molecular marker assisted selection (MAS) methods were used to screen for resistance to MSD in each of the four populations. To facilitate unbiased comparison, separate screening nurseries were established for MAS and conventional screening. The objectives of the study were five-fold; 1) to assess the status of
MSD in Uganda and understand farmers' preferences and varietal selection criteria for maize using a participatory rural appraisal (PRA), 2) to screen for MSD resistance in early generations of segregating maize populations using conventional method, 3) to screen for resistance to MSD using SSR marker assisted selection , 4) to compare the effectiveness of marker assisted selection and conventional methods for selection for resistance to MSD,
and 5) to compare costs associated with MAS and conventional selection methods.
Results of PRA showed that unreliable rainfall and insect pests were the dominant constraints to maize productivity in Uganda. Diseases were ranked fifth among the production constraints . Maize streak virus disease was considered the most important disease constraint. Farmers showed common preference for high yielding and early maturing cultivars. However, farmers had other special preferences which were diverse and included large, white and high test density kernels for marketing, and sweet taste,
particularly for home consumption. Farmers' research priorities included tolerance to drought, resistance to insect pests and diseases, sweetness, prolificacy, resistance to lodging, and drooping leaves because theyt cover the soil fast and prevent weed growth.
Conventional screening for resistance to MSD showed that backcross and selfing populations segregated in 1:1 and 3:1 Mendelian ratios confirming the presence of one major gene with simple inheritance . Severity and incidence of disease were positively correlated suggesting a non-reference by the insects. In the selfing populations, the presence of complete esistance against MSD was suggested because frequency distribution patterns were highly skewed in favour of resistance. There was a decrease in disease severities with selection from BC1F1 to BC2F1 and from F2 to F3 generations indicating that high response to selection was achieved. On the other hand, one marker, umc1917, consistently polymorphic and eo-dominant was selected and used in MAS protocol. Results showed that the observed outcomes fitted the expected ratio of 1:2:1 for a F2 population and 1:1 for a BC1F1 population (X2 not significant). Evaluation of F3 and
BC2F1 progeny selected using markers showed low disease severity suggesting that marker assisted selection was effective. However, the study showed that the presence of the O'Tl, was not consistent with symptom expression in the field.
Evaluation of lines in three-way crosses identified ten potential lines that were high yielding, highly resistant to MSD and stable across three locations. Both MAS and conventional selection were equally effective in identifying high yielding lines although resistance was higher under MAS.
Costs of MAS and conventional method varied depending on the units for
comparison. The total costs of conventional method were higher than that of MAS in both first and second selection cycles. Comparing costs per row for conventional and costs per plant or data point for MAS showed that conventional selection was 2.4 times more expensive than costs per sample for MAS. However, costs per plant for MAS were 6.6 times
higher than for conventional selection. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2006
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Investigation of heterotic patterns and genetic analysis of Downy mildew resistance in Mozambican lowland maize (Zea mays L.) germplasm.Fato, Pedro. January 2010 (has links)
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.
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