Overall effects of combining ability of the best 20 maize inbred lines for selected traits of black hole resistance and grain yield under B. Specific effects of combining ability of the best 20 test crosses for selected traits of resistance to flow hole and grain yield under C.
Significance of maize in Kenya
Yet an estimated five million farmers in Kenya grow maize at least once a year on two out of three farms (Government of Kenya, 2009; Oscar, 2009). The highland tropics, humid transition zones and mid-altitude agro-ecological zones achieve high yields (>2.5 tonnes ha-1) and produce 80% of Kenya's maize (Government of Kenya, 2009; Oscar, 2009).
Maize production constraints in Kenya
Previous studies have shown a clear relationship between borer damage traits (leaf damage, number of exit holes, cumulative tunneling, number of dead hearts, etc.) and wheat yield losses (De Groote et al., 2004; Morais et al., 2012). The values of these losses provide a basis for setting research priorities to justify studies to understand the genetics of resistance to the root borer and selection for borer resistance in tropical maize.
The maize stem borer problem
Economic importance of stem borers
Problem statement and justification
Incidentally, the moisture transition agro-ecological zone has the highest adoption of improved maize varieties (95%) making this area a promising target for insect resistant varieties (De Groote et al., 2005). It provides inherent control without environmental concerns and that it is mostly compatible with other pest management approaches (Morais et al., 2012).
Research objectives, hypotheses, and structure of thesis
Knowledge of the genetics of stem borer resistance (Busseola fusca and Chilo partellus) is limited to a few crosses of maize inbred lines. These challenges can be attributed to the lack of resistant cultivars, limited genetic information on stem borer resistance, and limited information on response to selection for borer resistance.
Research hypotheses
Both line x tester analysis and divergent selection in populations were used in testing for gene action, skill combining, and recurrent selection of S1 progeny to predict genetic gain for stock borer resistance and grain yield between selection cycles. It is possible to detect resistance to stem borers, Busseola fusca and Chilo partellus in maize in greenhouse and laboratory trials using the loose leaf bioassay and whole plant bioassays in maize inbred lines included in this study.
Structure of thesis
Maize Technology Development and Transfer: A GIS Application for Research Planning in Kenya. CABI Publishing/CIMMYT/KARI, Wallingford, UK. Identification of corn borer resistance in transgenic inbred lines and maize hybrids with the GFM Cry1A gene.
Introduction
Maize in Kenya
- Maize production constraints in Kenya
- Biology of Busseola fusca
- Biology of Chilo partellus
The first concise information on the life cycle and the economy of Busseola fusca was carried out by Fuller in the 1900s (Kfir, 1997). The first concise information on the life cycle and the economy of Chilo partellus was carried out by Swinhoe in the 1900s (Kfir, 1997).
Geographical distribution of Busseola fusca and Chilo partellus stem borers
Economic importance of Busseola fusca and Chilo partellus
Management of the stem borers
However, its application is still limited due to the polygenic nature of the insect resistance trait, the limited understanding of its inheritance and the high costs associated with plant breeding (Hallauer et al., 2010). This will form the basis for a viable breeding strategy for the use of stem borer-resistant maize hybrids.
Breeding for resistance to maize stem borers
- Inheritance and combining ability for resistance to stem borers
Genetic components affecting quantitative or polygenic traits can be classified as additive, dominance, and epistasis variance (Falconer et al., 1996). Given that resistance to stem borer is a polygenic trait with low heritability (Falconer et al., 1996), recurrent selection methods would be most appropriate for the accumulation of alleles favorable for resistance.
Recurrent selection in maize
Recent studies in quantitative genetics theory suggest that S1 progeny recurrent selection can be used in breeding for resistance to stem borers in maize populations (Sandoya et al., 2010). The strategy is best given the low heritability of the polygenic traits that constitute stem borer resistance (Hallauer et al., 2010).
Line x tester mating design
With repeated selection of S1 offspring, the expected genetic variation, considering only additive genetic effects, is fourfold greater among half-sib families and twice greater among full-sib families (Sandoya et al., 2008; Hallauer et al., 2010). . Given that there are limited studies on the response of maize populations to selection for pest resistance, this study serves as a reference for determining the value of recurrent selection of S1 progeny to improve B.
Heterotic orientations in maize
- Determination of heterotic orientations
Characterization of the maize germplasm and its allocation in different heterotic orientations is useful to provide information about the genotypes (Hallauer et al., 2010). Several methods have been used in the allocation of maize lines in different heterotic orientations (Schnable et al., 2013).
Methods of screening maize germplasm for resistance to stem borers
- Screening methods and rating
- Leaf disk bioassays method
- Selection indices
- Genotype x Environment Interactions
Natural contamination may not be reliable due to lack of uniformity and seasonal variations that occur (Tefera et al., 2010). Several examples in the applications of selection indices with improvements in stem borer resistance and grain yield in maize have been reported in the literature (Ajala et al., 2010).
Conclusions from the literature review
Variability for resistance to pink stem borer (Sesamia calamistis Hampson) and the sugarcane borer (Eldana saccharina Walker) in two tropical maize populations. Indirect response to selection for improving resistance to the Mediterranean corn borer (Sesamia nonagrioides Lef) in maize.
Introduction
In addition, farmers exchange maize germplasm in agroecologies, so the need to investigate the reaction of these tropical maize inbred lines to resistance to these borers becomes paramount. The objective of this study was to evaluate inbred lines of tropical maize for resistance to two B.
Materials and Methods
- Germplasm
- Experimental sites
- Experimental design and treatments
- Artificial infestation with insects
- Data collection and analysis
The ranking index is the average performance of each of the desired traits of each genotype, using the ranking of leaf feeding damage score, number of dead hearts, number of exit holes and cumulative trunk tunnel length. Where rP is the phenotypic correlation between traits X and Y, σP (X, Y) is the phenotypic covariance between trait of property Y.
Results
- Mean performance of maize inbred lines
- Stem borers resistance traits in different environments
- Correlations for stem borer resistance and agronomic traits
- Correlations between B. fusca and C. partellus borer resistance traits
- Heritability and genotypic and phenotypic correlations
Total number of plants showing number of exit holes per plant per trial due to B. There was no significant correlation between leaf feeding damage and the number of exit holes for B.
Discussion
The knowledge about genetic correlations between borer resistance traits is important to create selection criteria (Sujiprihati et al., 2003). Similar results have been reported indicating that selection based on these traits can lead to improvement in stem borer resistance (Munyiri et al., 2013).
Conclusion
Evaluation of maize (Zea mays L.) genotypes as components of integrated stem borer (Chilo partellus Swinhoe) management in the coastal region of Kenya. Proceedings of International Symposia on Methodologies for Developing Host Plant Resistance to Maize Insects.
Introduction
The x-line tester mating design has been applied to determine the pattern of gene action for stem borer resistance potential in maize (Sharma et al., 2007). The x-line tester continues to be applied in the determination of heterotic orientations in maize using different testers (Sanghera et al., 2012).
Materials and Methods
- Germplasm
- Experimental sites
- Experimental design and infestation
- Artificial infestation with insects
- Data collection and analysis
The number of dead hearts was determined as a percentage of the plants in the diagram, indicating death of the growing points. The clustering of lines into heterotic groups A (CML312/CML442) and B (CML395/CML444) depended on the direction of the specific combination ability, so that lines showing positive SCA with tester A were assigned to the opposite heterotic group B, and vice versa versa, while lines showing positive SCA for both were designated as AB group.
Results
- Genotype x environment interactions
- Trait variations under Busseola fusca infestation
- General combining ability effects
- Specific combining ability effects
- Heterotic orientations based on specific combining ability
- Heterosis of testcrosses relative to testers
- Relative standard heterosis
In Kakamega, positive (p≤0.05) GCA effects were detected for wheat yield for all 20 major lines except for line 5. Specific effects of combining ability of test crosses for selected traits of resistance to stem borer and yield of wheat under B.
Discussion
- Variations among lines and testcross hybrids
- General and specific combining ability
- Heterotic orientations of lines under B. fusca infestation
- Heterosis relative to testers
Both additive and non-additive gene effects have been reported in the literature for stem borer resistance, and grain yield and yield components for various crops (Udaykumar et al., 2013). At Embu, 12 and 8 lines revealed positive SCA estimates for grain yield with CML395/CML444 and CML312/CML442, respectively.
Conclusions
Studies of combining ability for yield and related traits in newly obtained inbred lines of maize (Zea mays L.). Association between parental genetic distance with heterosis and specific combining ability in quality protein maize.
Introduction
This mating scheme was applied to determine the possible gene action configuration for stem borer resistance in maize (Sharma et al., 2007). Populations and inbred lines or single cross hybrids were used as testers in the identification of hybrids for yield performance (Sanghera et al., 2012).
Materials and Methods
- Germplasm
- Experimental sites
- Experimental design and Treatments
- Artificial infestation with insects
- Data collection and analysis
The design was therefore used in the study to evaluate test cross hybrids in the target locations. Single crossover testers were used in the current study because the end product would be a three-way crossover.
Results
- Genotype x environment interactions
- Trait variations under Chilo partellus infestation
- General combining ability effects
- Specific combining ability effects
- Heterotic orientations of lines based on specific combining ability
- Heterosis of maize inbred lines relative to testers
At Kiboko, significant and desirable SCA effects (P≤0.05) on grain yield were detected for all test crosses with CML312/CML442. In Embu, 8 lines showed significant (p≤0.05) positive SCA effects for grain yield with CML395/CML444 and therefore targeted heterotic group A.
Discussion
- Genetic variation
- General and specific combining ability
- Heterotic orientations of maize inbred lines under C. partellus infestation 117
In the current study, the significant difference between mean squares between lines, testers, lines x testers for stem borer resistance traits and grain yield showed their suitability for combining ability studies. Both additive and non-additive gene effects have been reported in the literature for grain yield and yield components for different crops (Sanghera et al., 2012; Schnable et al., 2013).
Introduction
Leaf screening bioassays have been used as a rapid method for screening materials in a wide range of horticultural and agronomic crops against pests and diseases, including Bt cassava, beans, maize (Mugo et al., 2001; Murenga et al. ., 2011; González et al., 2013). To reliably predict resistance to stem borers, isolated leaf bioassay conditions must be favorable for optimal plant growth and healthy neonates (Tefera et al., 2010).
Materials and Methods
- Germplasm
- Experimental design and Treatments
- Data collection
- Greenhouse evaluations
- Laboratory evaluations
- Data analysis
The use of isolated leaf bioassays for the artificial screening of maize genotypes for stem borer resistance may be a practical alternative approach. Appropriate fertilizers, weeding and irrigation were applied as recommended for the greenhouse (Murenga et al., 2004).
Results
- Trait variations in the greenhouse
- Trait variations in the laboratory
- Rank selection indices in the greenhouse and laboratory
- Correlations among traits in the greenhouse and laboratory
- Evaluation of the maize inbred lines in the greenhouse
- Evaluation of the maize inbred lines in the laboratory
- Partitioning of damage effects under B. fusca and C. partellus infestation
Similar significant (r=0.458, p≤ 0.01) correlations were detected between leaf feeding damage in the greenhouse and the leaf area damaged in the laboratory (Table 5.3). Correlation coefficients based stem borer damage parameters in the greenhouse and laboratory trials at KARI.
Discussion
Conclusion
Expected responses to selection for resistance to pink stem borer (Sesamia calamistis Hampson) and sugarcane borer (Eldana saccharina Walker) in two maize populations. Mechanisms and genetic diversity for host plant resistance to spotted stem borer, Chilo partellus in sorghum, Sorghum bicolor.
Introduction
The S1 progeny recurrent selection scheme is characterized by additive genetic effects that are more important than non-additive genetic effects in stem borer resistance in maize populations (Sandoya et al., 2008; Schnable et al., 2013). Various successful cases of its use in various crops against pests and diseases have been reported (Ordas et al., 2009).
Materials and methods
- Germplasm
- Experimental sites
- Formation of S1 progenies
- Multi-site evaluation of the cycle 0 and the advanced cycles
- Artificial infestation with insects
- Data collection
- Data analysis
Susceptible offspring were used as controls. The recombination involved planting the S1 seed from ear to row and hand pollination using bulk pollen was performed with one half pollinating the other to ensure random mating. Recombination involved planting the S1 seed from ear to row and hand pollination using bulk pollen was performed with one half pollinating the other to ensure random mating.
Results
- Trait variations in cycles under C. partellus infestation
- Trait variations in cycles under B. fusca infestation
- Mean performance of cycles of two maize populations
- Genetic gains from selection in cycles
- Broad sense heritability estimates
- Correlations of selected traits and grain yield
In the CML444/MBR/MDR C3Bc population, net genetic gain in grain yield was 25%, cumulative stem tunneling -57%, number of exit holes -69% and leaf feeding injury score 10%. In the CML444/MBR/MDR C3Bc population, net genetic gain in grain yield was 36%, cumulative stem tunneling -24%, number of exit holes -15% and leaf feeding injury score -29%.
Discussion
Similar results regarding estimates of gains under yield selection have been reported in the literature (Ana Paula et al., 2013; Liberatore et al., 2013). Similar results have been reported under maize population cycles (Sandoya et al., 2008; Ana Paula et al., 2013).
Conclusion
Maize genotypes identified with resistance to spotted stem borer, Chilo partellus and favorable agronomic traits. Mapping QTL for resistance to the Mediterranean maize borer attack using the interbred B73 x Mo17 (IBM) population of maize.
Introduction
Summary of key research findings and implications for breeding
- Genetic variation for stem borer resistance
- Combining ability and heterotic orientation under Busseola fusca infestation
- Response of maize populations to S1 progeny recurrent selection
In addition, they combined high level of resistance to Busseola fusca with high wheat yield potential. The leaf disc bioassay method was evaluated for its efficiency for screening maize genotypes for resistance to the stem borers Busseola fusca and Chilo partellus in tropical inbred maize lines in the greenhouse and laboratory.
General observations on stem borer resistance
The findings of the completed study indicate that high variation of germplasm exists for resistance to Busseola fusca and Chilo partellus stem borers. The study identified hybrids with a high yield advantage over commercial hybrids indicating significant progress in breeding for resistance to Busseola fusca and Chilo partellus.
