Combining ability, Genetic Gains and Path Coefficient Analyses of Maize Hybrids developed from ...

172 Pages·2016·1.5 MB·English

by  Isack Mathew (214550352)

Combining ability, Genetic Gains and Path Coefficient Analyses
of Maize Hybrids developed from Maize Streak Virus and
Downey Mildew Resistant Recombinant Inbred Lines

Isack MATHEW

A dissertation submitted in partial fulfilment of the requirements for the degree of
Master of Science in Plant Breeding

School of Agricultural, Earth and Environmental Sciences
College of Agriculture, Engineering and Science
University of KwaZulu-Natal
Pietermaritzburg, South Africa
November 2015
GENERAL ABSTRACT

Farmers in SSA continue to obtain low yields (less than two tonnes per hectare) despite the
high potential yield (about 14 tonnes per hectare) that can be achieved. The development of
improved and high yielding hybrids can help to reduce this gap significantly. Characterisation
of maize inbred lines is crucial for developing high yielding maize hybrids. A line x tester
analysis involving 38 crosses generated by crossing 19 maize inbred lines with two tropical
testers was conducted for different agronomic traits. The maize inbred lines used in this study
were sampled from a bi-parental inbred population developed by a shuttle breeding program
at University of KwaZulu Natal. The objectives of the study were to estimate combining
ability of inbred lines and hybrids, to evaluate the performance of the hybrids in agronomic
traits and grain yield, to calculate breeding gains achieved through selection and to deduce
the relationship between secondary traits and grain yield. In total 50 hybrids, including
control hybrids were evaluated in the trial. The hybrids were planted in the summer season of
2014/15 under rainfed conditions at three sites, Cedara, Dundee and Ukulinga in five metre
row plots and replicated twice in 5X10 alpha lattice design under recommended agronomic
practices for maize. Data was collected using a CIMMYT protocol and subjected to statistical
analyses using ANOVA and REML packages in GENSTAT 14th edition and PATHSAS
macros in SAS 9.3 computer software. The results showed varying performances between the
lines, crosses and control hybrids at the different sites. Inbred lines DMSR-8, DMSR-13,
DMSR-30 and DMSR-35-5 were shown to have good combining ability while DMSR-21 and
DMSR-73 showed positive specific combining ability. Selection across sites improved grain
yield by 9.32% over the population mean and by 10.22% and 12.73% at Cedara and Dundee,
respectively over commercial hybrids. Ranking by mean yield identified hybrids 15XH16,
15XH20 and 15XH28 at Cedara, Dundee and Ukulinga respectively, as the highest yielding
hybrids for that particular environment. GGE biplot and AMMI analyses revealed that
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hybrids 15XH10, 15XH13, 15XH20, 15XH25, 15XH28, 15XH34 and 15XH39 were the
most stable hybrids. Secondary traits were found to be associated with grain yield potential of
hybrids. Ear prolificacy had the most important relationship with grain yield and was
recommended for selection in grain yield improvement programs.
Keywords: Combining ability, genetic gains, genotype X environment interaction, line X
tester, path coefficient analysis.

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DECLARATION

I, Isack MATHEW, declare that:

1. The research presented in this dissertation, except where otherwise indicated, is my
original research.
2. This dissertation has not been submitted for any degree or examination at any other
university.
3. This dissertation does not contain other scientists‘ data, pictures, graphs or other
information, unless specifically acknowledged as being sourced from other scientists.
4. This dissertation does not contain other scientists‘ writing, unless specifically
acknowledged as being sourced from other scientists. Where other written sources
have been quoted, then:
a) Their words have been re-written, but the general information attributed to
them has been referenced;
b) Where their exact words have been used, their writing has been placed in
italics and inside quotation marks and referenced.
5. This dissertation does not contain text, graphics or tables taken from the internet, unless
specifically acknowledged, and the source being detailed in the dissertation and in the
references section.
……………………………………………
Isack MATHEW (Candidate)

As supervisor I agree to submission of the dissertation

Professor John Derera
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ACKNOWLEDGEMENTS

The Generation Challenge Program is acknowledged for funding prior development of lines
used in this study. I would like to acknowledge my supervisor Prof J. Derera for his guidance
and support. Jaysh Singh, a big thumbs up to you. A lot of gratuity to the support staff at
Ukulinga for taking care of the trials and data collection at Ukulinga and Cedara. The staff at
Dundee is also appreciated for managing trials. A big thank you to Onismo Muzah for
helping in data collection in the sun and rain. Dr. Bezuidenhout at Cedara and Mr Kunz at
UKZN Agromet are acknowledged for providing access to weather data. I am indebted to Dr.
Gasura for his help in statistical analysis. My colleagues in office RS114 thank you for your
company and support. Everyone who has contributed to the success of this work is
appreciated. Special mention to Vince Ndou, a colleague and a friend, thanks a lot. A great
deal of appreciation to Faith Kudzai Tanyanyiwa for moral support on too many days when it
felt so overwhelming.
I am forever grateful to Elizabeth and Stephen for all their support. Thank you and I love
you! My brother and sisters for all your great love and affection. Thanks to my mom for her
never ending prayers! I needed them every day of the journey.
Above all, I am grateful to God Almighty for everything that I am and ever will be.

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DEDICATIONS

To God Almighty, who enables me. He is my Strength, Shield and Sanctuary.
To my late father, for seeing it first. My father taught me to rise against all odds and
adversity.
To my family, for all your love. My mum, Julie Lyness, Elizabeth, Mary, Moses and Nastasia
have always stood by me. I love you all

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Table of Contents

GENERAL ABSTRACT ......................................................................................................... ii
DECLARATION .................................................................................................................... iv
ACKNOWLEDGEMENTS .................................................................................................... v
DEDICATIONS ...................................................................................................................... vi
Table of Contents ................................................................................................................ vii
List of Tables ..................................................................................................................... xiii
List of Figures ...................................................................................................................... xv
List of Acronyms and Abbreviations ................................................................................. xiii
Chapter 1 : General Introduction ............................................................................................... 1
1.1. Introduction ................................................................................................................. 1
1.2. Importance of Maize ................................................................................................... 1
1.3. Overview of Production Constraints ........................................................................... 2
1.4. Prospects of Crop Improvement ................................................................................. 3
1.5. Problem Statement ...................................................................................................... 4
1.6. Significance of the Study ............................................................................................ 4
1.7. Research Goals and Objectives ................................................................................... 5
1.7.1. Goal of the Study ................................................................................................. 5
1.7.2. Specific Objectives .............................................................................................. 5
1.8. Research Hypotheses .................................................................................................. 6
1.9. Structure of Dissertation ............................................................................................. 6
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Chapter 2 : Literature Review .................................................................................................... 8
2.1. Introduction ................................................................................................................. 8
2.2. Importance of Superior Seed....................................................................................... 8
2.3. Line X Tester Analysis ............................................................................................... 9
2.4. Combining Ability .................................................................................................... 10
2.4.1. General Combining Ability (GCA) ................................................................... 11
2.4.2. Specific Combining Ability (SCA) ................................................................... 11
2.5. Importance of Tester Lines ....................................................................................... 12
2.6. Application of Combining Ability ............................................................................ 13
2.6.1. Prediction of Hybrid Performance ..................................................................... 13
2.6.2. Evaluation of Inbred Lines ................................................................................ 13
2.6.3. Determination of Gene Action ........................................................................... 14
2.7. Genetic Gains ............................................................................................................ 15
2.7.1. Genetic Gains Achieved in Grain Yield over the years ..................................... 16
2.7.2. Some Genetic Gains Achieved in Secondary Traits over the years .................. 17
2.8. Factors Influencing Genetic Gains Achieved through Selection .............................. 19
2.8.1. Selection Pressure .............................................................................................. 19
2.8.2. Heritability and Genetic Variance ..................................................................... 19
2.8.3. Genetic Variability ............................................................................................. 20
2.8.4. Genotype X Environment (GXE) Interactions .................................................. 20
2.8.5. Heterosis ............................................................................................................ 23
2.8.6. Transgressive Segregation ................................................................................. 23
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2.9. Measuring Genetic Gains .......................................................................................... 24
2.10. Correlation, Regression and Path Coefficient Analyses ........................................... 25
2.10.1. Grain Yield and its Relationship with Secondary Traits ................................... 26
2.10.2. Importance of Secondary Traits ......................................................................... 28
2.10.3. Efficiency of Selecting Secondary Traits in Grain Yield Improvement ............ 30
2.11. Summary and Conclusion ......................................................................................... 31
Chapter 3 : Materials and Methods .......................................................................................... 33
3.1. Introduction ............................................................................................................... 33
3.2. Description of Germplasm ........................................................................................ 33
3.3. Description of Sites ................................................................................................... 37
3.4. Experimental Layout and Crop Management ........................................................... 39
3.5. Data Collection ......................................................................................................... 40
3.6. Data Analyses ........................................................................................................... 42
3.6.1. Mean Performance .................................................................................................... 42
3.6.1.1. Grain Yield ........................................................................................................ 42
3.6.1.2. ANOVA and Mean Separation Test .................................................................. 43
3.6.1.3. Frequency Distribution and Mean Ranking ....................................................... 44
3.6.2. Line X Tester Analysis ............................................................................................. 44
3.6.2.1. ANOVA ............................................................................................................. 44
3.6.2.2. General Combining Ability (GCA) ................................................................... 45
3.6.2.3. Specific combining ability (SCA) ..................................................................... 45
3.6.3. Genetic Gains ............................................................................................................ 46
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3.6.3.1. Phenotypic and Genotypic Variances ................................................................ 46
3.6.3.2. Broad-sense Heritability .................................................................................... 47
3.6.3.3. Coefficients of Variation ................................................................................... 47
3.6.3.4. Predicted Genetic Gain ...................................................................................... 48
3.6.3.5. Estimation of Realised Genetic Gains ............................................................... 48
3.6.4. Relation between Grain Yield and Secondary Traits ................................................ 50
3.6.4.1. Correlation Analysis .......................................................................................... 50
3.6.4.2. Regression Analysis ........................................................................................... 50
3.6.4.3. Path Analysis ..................................................................................................... 51
3.6.5. Genotype X Environment Interaction ....................................................................... 51
3.6.5.1. Additive Main Effects and Multiplicative Interaction Analysis (AMMI) ......... 51
3.6.5.2. Genotype and Genotype X Environment Interaction Analysis (GGE) ............. 52
3.6.5.3. Cultivar Superiority Index ................................................................................. 52
3.6.5.4. Cultivar Stability and Mean Rank Analysis ...................................................... 53
Chapter 4 : Results ................................................................................................................... 54
4.1. Analysis of Variance ................................................................................................. 54
4.2. Frequency Distribution ............................................................................................. 56
2.3. Mean Performance of the Hybrids ............................................................................ 62
2.4. Line X Tester Analysis ............................................................................................. 64
2.5. Combining Ability .................................................................................................... 65
2.6. Genetic Gains ............................................................................................................ 70
2.7. Relationship between Grain Yield and Secondary Traits ......................................... 79
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