ABSTRACT Low maize (Zea mays L.) yields and the impacts of climate change on maize production hig... more ABSTRACT Low maize (Zea mays L.) yields and the impacts of climate change on maize production highlight the need to improve yields in eastern and southern Africa. Climate projections suggest higher temperatures within drought-prone areas. Research in model species suggests that tolerance to combined drought and heat stress is genetically distinct from tolerance to either stress alone, but this has not been confirmed in maize. In this study we evaluated 300 maize inbred lines testcrossed to CML539. Experiments were conducted under optimal conditions, reproductive stage drought stress, heat stress, and combined drought and heat stress. Lines with high levels of tolerance to drought and combined drought and heat stress were identified. Significant genotype x trial interaction and very large plot residuals were observed; consequently, the repeatability of individual managed stress trials was low. Tolerance to combined drought and heat stress in maize was genetically distinct from tolerance to individual stresses, and tolerance to either stress alone did not confer tolerance to combined drought and heat stress. This finding has major implications for maize drought breeding. Many current drought donors and key inbreds used in widely grown African hybrids were susceptible to drought stress at elevated temperatures. Several donors tolerant to drought and combined drought and heat stress, notably La Posta Sequia C7-F64-2-6-2-2 and DTPYC9-F46-1-2-1-2, need to be incorporated into maize breeding pipelines.
Characterization of genetic diversity is of great value to assist breeders in parental line selec... more Characterization of genetic diversity is of great value to assist breeders in parental line selection and breeding system design. We screened 770 maize inbred lines with 1,034 single nucleotide polymorphism (SNP) markers and identified 449 high-quality markers with no germplasm-specific biasing effects. Pairwise comparisons across three distinct sets of germplasm, CIMMYT (394), China (282), and Brazil (94), showed that the elite lines from these diverse breeding pools have been developed with only limited utilization of genetic diversity existing in the center of origin. Temperate and tropical/subtropical germplasm clearly clustered into two separate groups.
Background: Northern corn leaf blight (NCLB) caused by Exserohilum turcicum is a destructive dise... more Background: Northern corn leaf blight (NCLB) caused by Exserohilum turcicum is a destructive disease in maize. Using host resistance to minimize the detrimental effects of NCLB on maize productivity is the most cost-effective and appealing disease management strategy. However, this requires the identification and use of stable resistance genes that are effective across different environments. Results: We evaluated a diverse maize population comprised of 999 inbred lines across different environments for resistance to NCLB. To identify genomic regions associated with NCLB resistance in maize, a genome-wide association analysis was conducted using 56,110 single-nucleotide polymorphism markers. Single-marker and haplotype-based associations, as well as Anderson-Darling tests, identified alleles significantly associated with NCLB resistance. The single-marker and haplotype-based association mappings identified twelve and ten loci (genes), respectively, that were significantly associated with resistance to NCLB. Additionally, by dividing the population into three subgroups and performing Anderson-Darling tests, eighty one genes were detected, and twelve of them were related to plant defense. Identical defense genes were identified using the three analyses. Conclusion: An association panel including 999 diverse lines was evaluated for resistance to NCLB in multiple environments, and a large number of resistant lines were identified and can be used as reliable resistance resource in maize breeding program. Genome-wide association study reveals that NCLB resistance is a complex trait which is under the control of many minor genes with relatively low effects. Pyramiding these genes in the same background is likely to result in stable resistance to NCLB.
Abstract Maize (Zea mays L.) yields in southern Africa are low, due largely to drought and low-N ... more Abstract Maize (Zea mays L.) yields in southern Africa are low, due largely to drought and low-N stress. Selection of stress-tolerant genotypes by CIMMYT is conducted indirectly under managed stress conditions, although the selection efficiency of this approach is not ...
Molecular characterization of open-pollinated maize varieties (OPVs) is fundamentally important i... more Molecular characterization of open-pollinated maize varieties (OPVs) is fundamentally important in maize germplasm improvement. We investigated the extent of genetic differences, patterns of relationships, and population structure among 218 diverse OPVs widely used in southern and eastern Africa using the model-based population structure, analysis of molecular variance, cluster analysis, principal component analysis, and discriminant analysis. The OPVs were genotyped with 51 microsatellite markers and the fluorescent detection system of the Applied Biosystems 3730 Capillary Sequencer.
Despite numerous published reports of quantitative trait loci (QTL) for drought-related traits, p... more Despite numerous published reports of quantitative trait loci (QTL) for drought-related traits, practical applications of such QTL in maize improvement are scarce. Identifying QTL of sizeable effects that express more or less uniformly in diverse genetic backgrounds across contrasting water regimes could significantly complement conventional breeding efforts to improve drought tolerance. We evaluated three tropical bi-parental populations under water-stress (WS) and well-watered (WW) regimes in Mexico, Kenya and Zimbabwe to identify genomic regions responsible for grain yield (GY) and anthesis-silking interval (ASI) across multiple environments and diverse genetic backgrounds.
A total of 550 maize inbred lines collected from global breeding programs were evaluated for drou... more A total of 550 maize inbred lines collected from global breeding programs were evaluated for drought resistance under both well-watered and water-stressed environments. The evaluation was based on multiple measurements of biomass taken before and after the drought stress was applied using the normalized difference vegetation index (NDVI), along with other selection criteria including anthesis-silking interval, leaf senescence, chlorophyll content, root capacitance, final grain yield, and grain yield components. Kernel weight was the most stable trait under drought stress. Correlations between the primary trait (grain yield) and the secondary traits, except the root capacitance and ASI under water-stressed condition, were all significant. Root capacitance had relatively low heritability and low genetic correlation with other drought resistance criteria, and is not recommended as a drought resistance criterion. Significant reduction of NDVI values measured in the afternoon when the leaves became rolling, compared to those measured in the morning when the leaves were open, provides a reliable index for leaf rolling, which however was not significantly correlated with grain yield. NDVIs measured across different developmental stages were highly correlated with each other and with most of the secondary traits as well as, grain yield, indicating that NDVI can be used as a secondary trait for large-scale drought resistance screening. Regression models built based on non-yield drought criteria and yield components explained about 40% and 95% of the variation for the grain yield, respectively. Some maize lines developed in China for temperate regions showed strong drought resistance comparable to tropical maize lines when tested under tropical condition, indicating that temperate lines with a wide adaptability can be used in drought resistance breeding for both temperate and tropical environments.
ABSTRACT To develop stable and high-yielding maize (Zea mays L.) hybrids for a diverse target pop... more ABSTRACT To develop stable and high-yielding maize (Zea mays L.) hybrids for a diverse target population of environments (TPE), breeders have to decide whether greater gains result from selection across the undivided TPE or within more homogeneous subregions. Currently, CIMMYT subdivides the TPE in eastern and southern Africa into climatic and geographic subregions. To study the extent of specific adaptation to these subregions and to determine whether selection within subregions results in greater gains than selection across the undivided TPE, yield data of 448 maize hybrids evaluated in 513 trials across 17 countries from 2001 to 2009 were used. The trials were grouped according to five subdivision systems into climate, altitude, geographic, country, and yield-level subregions. For the first four subdivision systems, genotype x subregion interaction was low, suggesting broad adaptation of maize hybrids across eastern and southern Africa. In contrast, genotype x yield-level interactions and moderate genotypic correlations between low-and high-yielding subregions were observed. Therefore, hybrid means should be estimated by stratifying the TPE considering the yield-level effect as fixed and appropriately weighting information from both subregions. This strategy was at least 10% better in terms of predicted gains than direct selection using only data from the low- or high-yielding subregion and should facilitate the identification of hybrids that perform well in both subregions.
The availability of dense molecular markers has made possible the use of genomic selection (GS) f... more The availability of dense molecular markers has made possible the use of genomic selection (GS) for plant breeding. However, the evaluation of models for GS in real plant populations is very limited. This article evaluates the performance of parametric and semiparametric models for GS using wheat (Triticum aestivum L.) and maize (Zea mays) data in which different traits were measured in several environmental conditions. The findings, based on extensive cross-validations, indicate that models including marker information had higher predictive ability than pedigree-based models. In the wheat data set, and relative to a pedigree model, gains in predictive ability due to inclusion of markers ranged from 7.7 to 35.7%. Correlation between observed and predictive values in the maize data set achieved values up to 0.79. Estimates of marker effects were different across environmental conditions, indicating that genotype 3 environment interaction is an important component of genetic variability. These results indicate that GS in plant breeding can be an effective strategy for selecting among lines whose phenotypes have yet to be observed.
Striga hermonthica (Del.) Benth. and Striga asiatica
(L.) Kuntze severely affect maize (Zea mays ... more Striga hermonthica (Del.) Benth. and Striga asiatica (L.) Kuntze severely affect maize (Zea mays L.) production in sub-Saharan Africa. A single Striga plant produces a large number of seeds that form a bank of viable but dormant seed in the soil until they get a chemical signal from suitable maize host roots. Imidazolinone-resistant (IR) open-pollinated maize varieties (OP Vs) developed for Striga control were tested in diverse environments in four countries of eastern Africa in 2004. The objective of the study was to assess the agronomic performance of IR maize and genotype environment interactions (GE) for grain yield (GY) and the number of emerged Striga plants across 17 environments under Strigainfested and Striga-free conditions. In the combined analysis of variance across Striga-infested and Striga-free locations, mean squares for genotypes and GE were significant for most measured traits. The best IR maize variety (STR-VE-216) outyielded the Striga-tolerant and commercial genotypes by 113 and 89%, respectively, under Striga-infested conditions. IR OP Vs supported significantly fewer emerged Striga plants relative to the check varieties. Under Striga-free conditions, IR OP Vs showed GY advantage over commercial varieties. Under Striga-infested conditions genotypic variance ( 2 G ) was larger than genotype location variance ( ´ 2 G L ) for GY and number of emerged Striga plants at 12 wk after planting. The genetic correlations among locations under Striga-infested conditions were high (0.990), suggesting little GE between most environments used. Cluster analysis of genotypes under Striga-infested locations revealed two major groups that separated the IR OP Vs from the check varieties. The outstanding performance of selected IR OP Vs indicates that their use for Striga control would reduce the Striga seed bank while benefiting farmers with high GY
There are 84 distinct cultivars of highland bananas ( Musa spp.) in Uganda, grouped in five clone... more There are 84 distinct cultivars of highland bananas ( Musa spp.) in Uganda, grouped in five clone sets and it is not known which among these are female fertile. The objective of the study reported herein was to identify female fertile highland bananas that can be used in a cross breeding program and to determine the influence of pistil morphological traits on seed set. Seventy eight cultivars were screened for female fertility using pollen from 'Calcutta 4' and thirty-three cultivars representing the major variability of highland bananas were selected for studying pistil morphological traits to establish their relationship with seed yield. The clone sets and cultivars were highly significantly (P<0.0001) different in seed set rates but between-clone effects were higher than within-clone effects. Number of seeds was significantly negatively correlated with style length, ovary length and diameter of the style base. Path analysis indicated a high residual, suggesting that th...
Additional index words. breeding, heterosis, Mycosphaerella fi jiensis, Radopholus similis herita... more Additional index words. breeding, heterosis, Mycosphaerella fi jiensis, Radopholus similis heritance to facilitate and accelerate breeding. This provided a justification for investment in the development of diploid breeding stocks as pursued by major programs worldwide .
Maize is susceptible to biotic and abiotic stresses. The most important abiotic stresses in Afric... more Maize is susceptible to biotic and abiotic stresses. The most important abiotic stresses in Africa are drought and low soil fertility. Aflatoxin contamination is a potential problem in areas facing drought and low soil fertility. Three studies were conducted to evaluate maize germplasm for tolerance to stress. In the first study, fifteen maize inbred lines crossed in a diallel were evaluated under drought, low N stress, and well-watered conditions at six locations in three countries to estimate general (GCA) and specific combining ability (SCA), investigate genotype x environment interaction, and estimate genetic diversity and its relationship with grain yield and heterosis. GCA effects were not significant for grain yield across environments. Lines with good GCA effect for grain yield were P501 and CML258 across stresses. Lines CML339, CML341, and SPLC7-F had good GCA effects for anthesis silking interval across stresses. Additive genetic effects were more important for grain yield...
Maize is grown in most regions of Uganda. Aflatoxin contamination of maize occurs in Uganda but t... more Maize is grown in most regions of Uganda. Aflatoxin contamination of maize occurs in Uganda but there is lack of information on the distribution of Aspergillus flavus in major maize production regions of the country. The objective of this study was to determine the incidence and severity of Aspergillus flavus in major maize growing regions of Uganda. Hierarchical sampling procedure was used to randomly collect maize samples from all different fields in 16 districts in two cropping seasons of 2013. Samples were assayed for A. flavus incidence and severity. Results revealed significant (P<0.001) variation among regions and districts within regions for A. flavus incidence and severity. The highest A. flavus incidence and severity were recorded for Pallisa (74.2% and 4.8, respectively), one of the leading maize producing districts in Uganda. Among regions, the highest A. flavus incidence and severity were registered in eastern region at 62.4% and 4.6 respectively. These results revea...
Genomic prediction is a new method that uses markers across the whole genome to predict individua... more Genomic prediction is a new method that uses markers across the whole genome to predict individual breeding values at an early growth stage. One of the applications of genomic prediction in plant breeding is to help the breeder select beneficial crosses to create the next generation. The aim of this study was to investigate the genomic prediction accuracy of the diverse population of CIMMYT's East African maize breeding program. The genotypic dataset contains 2022 lines and 66K SNP markers from genotyping by sequencing. The phenotypic data consists of yield evaluations from 154 trials. Genomic prediction was done in two steps: first the BLUP for each line was estimated by considering trial, block and tester effects. In the second step direct genomic values (DGVs) were predicted from BLUPs using ridge regression (rrBLUP). Cross validation was used to estimate the accuracies and it was repeated 50 times. In each cross validation a random 30% of the lines were considered the test p...
ABSTRACT Low maize (Zea mays L.) yields and the impacts of climate change on maize production hig... more ABSTRACT Low maize (Zea mays L.) yields and the impacts of climate change on maize production highlight the need to improve yields in eastern and southern Africa. Climate projections suggest higher temperatures within drought-prone areas. Research in model species suggests that tolerance to combined drought and heat stress is genetically distinct from tolerance to either stress alone, but this has not been confirmed in maize. In this study we evaluated 300 maize inbred lines testcrossed to CML539. Experiments were conducted under optimal conditions, reproductive stage drought stress, heat stress, and combined drought and heat stress. Lines with high levels of tolerance to drought and combined drought and heat stress were identified. Significant genotype x trial interaction and very large plot residuals were observed; consequently, the repeatability of individual managed stress trials was low. Tolerance to combined drought and heat stress in maize was genetically distinct from tolerance to individual stresses, and tolerance to either stress alone did not confer tolerance to combined drought and heat stress. This finding has major implications for maize drought breeding. Many current drought donors and key inbreds used in widely grown African hybrids were susceptible to drought stress at elevated temperatures. Several donors tolerant to drought and combined drought and heat stress, notably La Posta Sequia C7-F64-2-6-2-2 and DTPYC9-F46-1-2-1-2, need to be incorporated into maize breeding pipelines.
Characterization of genetic diversity is of great value to assist breeders in parental line selec... more Characterization of genetic diversity is of great value to assist breeders in parental line selection and breeding system design. We screened 770 maize inbred lines with 1,034 single nucleotide polymorphism (SNP) markers and identified 449 high-quality markers with no germplasm-specific biasing effects. Pairwise comparisons across three distinct sets of germplasm, CIMMYT (394), China (282), and Brazil (94), showed that the elite lines from these diverse breeding pools have been developed with only limited utilization of genetic diversity existing in the center of origin. Temperate and tropical/subtropical germplasm clearly clustered into two separate groups.
Background: Northern corn leaf blight (NCLB) caused by Exserohilum turcicum is a destructive dise... more Background: Northern corn leaf blight (NCLB) caused by Exserohilum turcicum is a destructive disease in maize. Using host resistance to minimize the detrimental effects of NCLB on maize productivity is the most cost-effective and appealing disease management strategy. However, this requires the identification and use of stable resistance genes that are effective across different environments. Results: We evaluated a diverse maize population comprised of 999 inbred lines across different environments for resistance to NCLB. To identify genomic regions associated with NCLB resistance in maize, a genome-wide association analysis was conducted using 56,110 single-nucleotide polymorphism markers. Single-marker and haplotype-based associations, as well as Anderson-Darling tests, identified alleles significantly associated with NCLB resistance. The single-marker and haplotype-based association mappings identified twelve and ten loci (genes), respectively, that were significantly associated with resistance to NCLB. Additionally, by dividing the population into three subgroups and performing Anderson-Darling tests, eighty one genes were detected, and twelve of them were related to plant defense. Identical defense genes were identified using the three analyses. Conclusion: An association panel including 999 diverse lines was evaluated for resistance to NCLB in multiple environments, and a large number of resistant lines were identified and can be used as reliable resistance resource in maize breeding program. Genome-wide association study reveals that NCLB resistance is a complex trait which is under the control of many minor genes with relatively low effects. Pyramiding these genes in the same background is likely to result in stable resistance to NCLB.
Abstract Maize (Zea mays L.) yields in southern Africa are low, due largely to drought and low-N ... more Abstract Maize (Zea mays L.) yields in southern Africa are low, due largely to drought and low-N stress. Selection of stress-tolerant genotypes by CIMMYT is conducted indirectly under managed stress conditions, although the selection efficiency of this approach is not ...
Molecular characterization of open-pollinated maize varieties (OPVs) is fundamentally important i... more Molecular characterization of open-pollinated maize varieties (OPVs) is fundamentally important in maize germplasm improvement. We investigated the extent of genetic differences, patterns of relationships, and population structure among 218 diverse OPVs widely used in southern and eastern Africa using the model-based population structure, analysis of molecular variance, cluster analysis, principal component analysis, and discriminant analysis. The OPVs were genotyped with 51 microsatellite markers and the fluorescent detection system of the Applied Biosystems 3730 Capillary Sequencer.
Despite numerous published reports of quantitative trait loci (QTL) for drought-related traits, p... more Despite numerous published reports of quantitative trait loci (QTL) for drought-related traits, practical applications of such QTL in maize improvement are scarce. Identifying QTL of sizeable effects that express more or less uniformly in diverse genetic backgrounds across contrasting water regimes could significantly complement conventional breeding efforts to improve drought tolerance. We evaluated three tropical bi-parental populations under water-stress (WS) and well-watered (WW) regimes in Mexico, Kenya and Zimbabwe to identify genomic regions responsible for grain yield (GY) and anthesis-silking interval (ASI) across multiple environments and diverse genetic backgrounds.
A total of 550 maize inbred lines collected from global breeding programs were evaluated for drou... more A total of 550 maize inbred lines collected from global breeding programs were evaluated for drought resistance under both well-watered and water-stressed environments. The evaluation was based on multiple measurements of biomass taken before and after the drought stress was applied using the normalized difference vegetation index (NDVI), along with other selection criteria including anthesis-silking interval, leaf senescence, chlorophyll content, root capacitance, final grain yield, and grain yield components. Kernel weight was the most stable trait under drought stress. Correlations between the primary trait (grain yield) and the secondary traits, except the root capacitance and ASI under water-stressed condition, were all significant. Root capacitance had relatively low heritability and low genetic correlation with other drought resistance criteria, and is not recommended as a drought resistance criterion. Significant reduction of NDVI values measured in the afternoon when the leaves became rolling, compared to those measured in the morning when the leaves were open, provides a reliable index for leaf rolling, which however was not significantly correlated with grain yield. NDVIs measured across different developmental stages were highly correlated with each other and with most of the secondary traits as well as, grain yield, indicating that NDVI can be used as a secondary trait for large-scale drought resistance screening. Regression models built based on non-yield drought criteria and yield components explained about 40% and 95% of the variation for the grain yield, respectively. Some maize lines developed in China for temperate regions showed strong drought resistance comparable to tropical maize lines when tested under tropical condition, indicating that temperate lines with a wide adaptability can be used in drought resistance breeding for both temperate and tropical environments.
ABSTRACT To develop stable and high-yielding maize (Zea mays L.) hybrids for a diverse target pop... more ABSTRACT To develop stable and high-yielding maize (Zea mays L.) hybrids for a diverse target population of environments (TPE), breeders have to decide whether greater gains result from selection across the undivided TPE or within more homogeneous subregions. Currently, CIMMYT subdivides the TPE in eastern and southern Africa into climatic and geographic subregions. To study the extent of specific adaptation to these subregions and to determine whether selection within subregions results in greater gains than selection across the undivided TPE, yield data of 448 maize hybrids evaluated in 513 trials across 17 countries from 2001 to 2009 were used. The trials were grouped according to five subdivision systems into climate, altitude, geographic, country, and yield-level subregions. For the first four subdivision systems, genotype x subregion interaction was low, suggesting broad adaptation of maize hybrids across eastern and southern Africa. In contrast, genotype x yield-level interactions and moderate genotypic correlations between low-and high-yielding subregions were observed. Therefore, hybrid means should be estimated by stratifying the TPE considering the yield-level effect as fixed and appropriately weighting information from both subregions. This strategy was at least 10% better in terms of predicted gains than direct selection using only data from the low- or high-yielding subregion and should facilitate the identification of hybrids that perform well in both subregions.
The availability of dense molecular markers has made possible the use of genomic selection (GS) f... more The availability of dense molecular markers has made possible the use of genomic selection (GS) for plant breeding. However, the evaluation of models for GS in real plant populations is very limited. This article evaluates the performance of parametric and semiparametric models for GS using wheat (Triticum aestivum L.) and maize (Zea mays) data in which different traits were measured in several environmental conditions. The findings, based on extensive cross-validations, indicate that models including marker information had higher predictive ability than pedigree-based models. In the wheat data set, and relative to a pedigree model, gains in predictive ability due to inclusion of markers ranged from 7.7 to 35.7%. Correlation between observed and predictive values in the maize data set achieved values up to 0.79. Estimates of marker effects were different across environmental conditions, indicating that genotype 3 environment interaction is an important component of genetic variability. These results indicate that GS in plant breeding can be an effective strategy for selecting among lines whose phenotypes have yet to be observed.
Striga hermonthica (Del.) Benth. and Striga asiatica
(L.) Kuntze severely affect maize (Zea mays ... more Striga hermonthica (Del.) Benth. and Striga asiatica (L.) Kuntze severely affect maize (Zea mays L.) production in sub-Saharan Africa. A single Striga plant produces a large number of seeds that form a bank of viable but dormant seed in the soil until they get a chemical signal from suitable maize host roots. Imidazolinone-resistant (IR) open-pollinated maize varieties (OP Vs) developed for Striga control were tested in diverse environments in four countries of eastern Africa in 2004. The objective of the study was to assess the agronomic performance of IR maize and genotype environment interactions (GE) for grain yield (GY) and the number of emerged Striga plants across 17 environments under Strigainfested and Striga-free conditions. In the combined analysis of variance across Striga-infested and Striga-free locations, mean squares for genotypes and GE were significant for most measured traits. The best IR maize variety (STR-VE-216) outyielded the Striga-tolerant and commercial genotypes by 113 and 89%, respectively, under Striga-infested conditions. IR OP Vs supported significantly fewer emerged Striga plants relative to the check varieties. Under Striga-free conditions, IR OP Vs showed GY advantage over commercial varieties. Under Striga-infested conditions genotypic variance ( 2 G ) was larger than genotype location variance ( ´ 2 G L ) for GY and number of emerged Striga plants at 12 wk after planting. The genetic correlations among locations under Striga-infested conditions were high (0.990), suggesting little GE between most environments used. Cluster analysis of genotypes under Striga-infested locations revealed two major groups that separated the IR OP Vs from the check varieties. The outstanding performance of selected IR OP Vs indicates that their use for Striga control would reduce the Striga seed bank while benefiting farmers with high GY
There are 84 distinct cultivars of highland bananas ( Musa spp.) in Uganda, grouped in five clone... more There are 84 distinct cultivars of highland bananas ( Musa spp.) in Uganda, grouped in five clone sets and it is not known which among these are female fertile. The objective of the study reported herein was to identify female fertile highland bananas that can be used in a cross breeding program and to determine the influence of pistil morphological traits on seed set. Seventy eight cultivars were screened for female fertility using pollen from 'Calcutta 4' and thirty-three cultivars representing the major variability of highland bananas were selected for studying pistil morphological traits to establish their relationship with seed yield. The clone sets and cultivars were highly significantly (P<0.0001) different in seed set rates but between-clone effects were higher than within-clone effects. Number of seeds was significantly negatively correlated with style length, ovary length and diameter of the style base. Path analysis indicated a high residual, suggesting that th...
Additional index words. breeding, heterosis, Mycosphaerella fi jiensis, Radopholus similis herita... more Additional index words. breeding, heterosis, Mycosphaerella fi jiensis, Radopholus similis heritance to facilitate and accelerate breeding. This provided a justification for investment in the development of diploid breeding stocks as pursued by major programs worldwide .
Maize is susceptible to biotic and abiotic stresses. The most important abiotic stresses in Afric... more Maize is susceptible to biotic and abiotic stresses. The most important abiotic stresses in Africa are drought and low soil fertility. Aflatoxin contamination is a potential problem in areas facing drought and low soil fertility. Three studies were conducted to evaluate maize germplasm for tolerance to stress. In the first study, fifteen maize inbred lines crossed in a diallel were evaluated under drought, low N stress, and well-watered conditions at six locations in three countries to estimate general (GCA) and specific combining ability (SCA), investigate genotype x environment interaction, and estimate genetic diversity and its relationship with grain yield and heterosis. GCA effects were not significant for grain yield across environments. Lines with good GCA effect for grain yield were P501 and CML258 across stresses. Lines CML339, CML341, and SPLC7-F had good GCA effects for anthesis silking interval across stresses. Additive genetic effects were more important for grain yield...
Maize is grown in most regions of Uganda. Aflatoxin contamination of maize occurs in Uganda but t... more Maize is grown in most regions of Uganda. Aflatoxin contamination of maize occurs in Uganda but there is lack of information on the distribution of Aspergillus flavus in major maize production regions of the country. The objective of this study was to determine the incidence and severity of Aspergillus flavus in major maize growing regions of Uganda. Hierarchical sampling procedure was used to randomly collect maize samples from all different fields in 16 districts in two cropping seasons of 2013. Samples were assayed for A. flavus incidence and severity. Results revealed significant (P<0.001) variation among regions and districts within regions for A. flavus incidence and severity. The highest A. flavus incidence and severity were recorded for Pallisa (74.2% and 4.8, respectively), one of the leading maize producing districts in Uganda. Among regions, the highest A. flavus incidence and severity were registered in eastern region at 62.4% and 4.6 respectively. These results revea...
Genomic prediction is a new method that uses markers across the whole genome to predict individua... more Genomic prediction is a new method that uses markers across the whole genome to predict individual breeding values at an early growth stage. One of the applications of genomic prediction in plant breeding is to help the breeder select beneficial crosses to create the next generation. The aim of this study was to investigate the genomic prediction accuracy of the diverse population of CIMMYT's East African maize breeding program. The genotypic dataset contains 2022 lines and 66K SNP markers from genotyping by sequencing. The phenotypic data consists of yield evaluations from 154 trials. Genomic prediction was done in two steps: first the BLUP for each line was estimated by considering trial, block and tester effects. In the second step direct genomic values (DGVs) were predicted from BLUPs using ridge regression (rrBLUP). Cross validation was used to estimate the accuracies and it was repeated 50 times. In each cross validation a random 30% of the lines were considered the test p...
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Papers by Dan Makumbi
(L.) Kuntze severely affect maize (Zea mays L.) production
in sub-Saharan Africa. A single Striga plant
produces a large number of seeds that form a bank
of viable but dormant seed in the soil until they get
a chemical signal from suitable maize host roots.
Imidazolinone-resistant (IR) open-pollinated maize
varieties (OP Vs) developed for Striga control were
tested in diverse environments in four countries of
eastern Africa in 2004. The objective of the study
was to assess the agronomic performance of IR
maize and genotype environment interactions
(GE) for grain yield (GY) and the number of emerged
Striga plants across 17 environments under Strigainfested
and Striga-free conditions. In the combined
analysis of variance across Striga-infested and
Striga-free locations, mean squares for genotypes
and GE were significant for most measured traits.
The best IR maize variety (STR-VE-216) outyielded
the Striga-tolerant and commercial genotypes by
113 and 89%, respectively, under Striga-infested
conditions. IR OP Vs supported significantly fewer
emerged Striga plants relative to the check varieties.
Under Striga-free conditions, IR OP Vs showed
GY advantage over commercial varieties. Under
Striga-infested conditions genotypic variance ( 2
G )
was larger than genotype location variance ( ´ 2
G L )
for GY and number of emerged Striga plants at 12
wk after planting. The genetic correlations among
locations under Striga-infested conditions were
high (0.990), suggesting little GE between most
environments used. Cluster analysis of genotypes
under Striga-infested locations revealed two major
groups that separated the IR OP Vs from the check
varieties. The outstanding performance of selected
IR OP Vs indicates that their use for Striga control
would reduce the Striga seed bank while benefiting
farmers with high GY
(L.) Kuntze severely affect maize (Zea mays L.) production
in sub-Saharan Africa. A single Striga plant
produces a large number of seeds that form a bank
of viable but dormant seed in the soil until they get
a chemical signal from suitable maize host roots.
Imidazolinone-resistant (IR) open-pollinated maize
varieties (OP Vs) developed for Striga control were
tested in diverse environments in four countries of
eastern Africa in 2004. The objective of the study
was to assess the agronomic performance of IR
maize and genotype environment interactions
(GE) for grain yield (GY) and the number of emerged
Striga plants across 17 environments under Strigainfested
and Striga-free conditions. In the combined
analysis of variance across Striga-infested and
Striga-free locations, mean squares for genotypes
and GE were significant for most measured traits.
The best IR maize variety (STR-VE-216) outyielded
the Striga-tolerant and commercial genotypes by
113 and 89%, respectively, under Striga-infested
conditions. IR OP Vs supported significantly fewer
emerged Striga plants relative to the check varieties.
Under Striga-free conditions, IR OP Vs showed
GY advantage over commercial varieties. Under
Striga-infested conditions genotypic variance ( 2
G )
was larger than genotype location variance ( ´ 2
G L )
for GY and number of emerged Striga plants at 12
wk after planting. The genetic correlations among
locations under Striga-infested conditions were
high (0.990), suggesting little GE between most
environments used. Cluster analysis of genotypes
under Striga-infested locations revealed two major
groups that separated the IR OP Vs from the check
varieties. The outstanding performance of selected
IR OP Vs indicates that their use for Striga control
would reduce the Striga seed bank while benefiting
farmers with high GY