HETEROTIC GROUPING OF SELECTED INBRED LINES OF MAIZE (Zea mays L.) USING TWO TESTERS IN KIAMBU AND EMBU COUNTIES, KENYA
BY CHEMELI JANE (BSC. AGED) REG. NO. 156/CE/22771/2010
A thesis submitted in partial fulfillment of the requirements for the award of the degree of Master of Science (Genetics) in the School of Pure and Applied Sciences of Kenyatta University.
FEBRUARY 2016 ii
DECLARATION
This thesis is my original work and has not been presented for a degree or any other award in any other university. Chemeli Jane Signature------Date ------This thesis has been submitted for examination with our approval as the university supervisors. Dr. Fredrick Njoka Dean, School of Agriculture Embu University College Signature------Date ------Dr. Philip Leley Maize Breeder KALRO Muguga South Nairobi, Kenya Signature------Date ------
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DEDICATION
To my progenies; Amon, Allan, Alvin, Austin and Adalia. Also to my husband for his love and encouragement.
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ACKNOWLEDGEMENT
I am highly indebted to my supervisors, Dr. F. Njoka and Dr. P. K. Leley who I profoundly thank for their exemplary intellectual guidance and support during the entire degree course. This work could not have been accomplished without their concern, patience, understanding, moral and material support.
Much thanks go to Prof. Dauglas Ndiritu for the genetic courses he taught me prior to this project. Special thanks go to Dr. F. Njoka for his useful and critical deliberations on the research proposal, progress reports and research findings. Dr. P. K Leley provided the germplasm that were used in the research, to him am indebted. Dr. Kipchumba Chelimo of Georgia University and Dr. Elias Thuranira of NARES were a constant source of knowledge and skills in breeding experiments.
I am grateful to my course mate Jennifer Kariuki for the ideas shared and lessons learned. Her company and warmth in the course of the research made the going worthwhile.
I would also like to appreciate the assistance from KALRO stations in Muguga and Embu for providing the field where this study was carried out. Furthermore I cannot thank enough, the
KALRO staff; Peter Njoroge the senior technician at KALRO Muguga for his advice on randomization of the inbred lines, Ann Ndambuki and Florence Gatumu for taking good care of the trials, John Gaitho for providing transport logistics to the study areas. The constant encouragement from Stephen Gichobi the senior technician in the department of Plant Sciences of Kenyatta University cannot go unnoticed. To all the support staff of plant sciences and all those who were a constant source of knowledge and skills, I will always be grateful.
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TABLE OF CONTENTS TITLE...……………………………………………………………………………………………i
DECLARATION ...... ii
DEDICATION ...... iii
ACKNOWLEDGEMENT ...... iv
TABLE OF CONTENT ...... v
LIST OF FIGURES ...... viii
LIST OF TABLES ...... ix
LIST OF PLATES ...... xi LIST OF APPENDICES……………………………………..……………………………….…xii
DEFINITION OF TERMS……………………………………………………………………...xii
ACRONYMS AND ABBREVIATIONS ...... xv
ABSTRACT ...... xvii
CHAPTER ONE ...... 1
INTRODUCTION ...... 1 1.2 Global production of maize ...... 3 1.3 Maize production constraints ...... 4 1.4 problem Statement ...... 5 1.5 Justification of the study ...... 6 1.6 Null hypotheses ...... 6 1.7 General objective ...... 7 1.7.1 Specific objectives ...... 7
CHAPTER TWO ...... 8
LITERATURE REVIEW ...... 8 2.1 Biology of maize ...... 8 2.2 Maize breeding in Kenya ...... 10 vi
2.3 Heterotic Groups...... 16 2.4 Combining Ability ...... 18 2.5 Testers in breeding programs ...... 19
CHAPTER THREE...... 21
MATERIALS AND METHODS...... 21 3.1 Study area and materials ...... 21 3.1.1 Study area ...... 21 3.1.2 Study materials ...... 24 3.2 Experimental layout ...... 25 3.3 Planting and field management ...... 27 3.4 Data collected ...... 28 3.4.1 Plant height ...... 28 3.4.2 Ear height ...... 29 3.4.3 Moisture Content ...... 29 3.4.4 Disease scores ...... 29 3.4.5 Grain yield ...... 30 3.5 Data analysis...... 30
CHAPTER FOUR ...... 32
RESULTS AND DISCUSSION ...... 32 4.1 Single site analysis ...... 32 4.1.1 Embu County………………………………………………………………………….32 4.1.1.1 Agronomic traits of the crosses between inbred lines and two testers in Embu County ...... 32 4.1.1.2 Correlation between agronomic traits of crosses in Embu ...... 33 4.1.2 Muguga, Kiambu County……………………………………………………………..34 4.1.2.1: Agronomic traits of the crosses between inbred lines and two testers in Muguga, Kiambu county ...... 34 4.1.2.2: Correlation between agronomic traits in Muguga ...... 37 4.2 Multiple site analysis in Embu and Muguga………………………………………………37 4.2.1 Agronomic traits of crosses between inbred lines and two testers in Embu and Muguga ...... 37 4.2.2 Mean values of all the agronomic traits measured for the crosses in Embu and Muguga ...... 38 4.2.3 Line by tester analysis of plant height (PH cm), ear height (EH cm), yield (t ha-1 ), MSV and GLS in Embu and Muguga...... 39 4.2.4 Correlation between agronomic traits ...... 40 vii
4.3 Combining ability ...... 40 4.4 Heterosis for grain yield ...... 44 4.5 Heterotic groups ...... 45
CHAPTER FIVE ...... 47
DISCUSSION, CONCLUSION AND RECOMMENDTION ...... 47 5.1 Discussion…………………………………………………………………………………47 5.2 Conclusion ...... 49 5.3 Recommendation ...... 51
REFERENCES ...... 52
APPENDICES ...... 60
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LIST OF FIGURES
Figure 2.1: Cytoplasmic male sterility……………………………………………………….…15 Figure 3.1: Map of Kiambu county…………………………………………………………..…22
Figure 3.2: Map of Embu county.…...... 23 Figure 3.3: Experimental design………………………………………………………………..26
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LIST OF TABLES Table 1.1: World Top producer in 2012………………………………………………………….3 Table 1.2: Kenya‘s corn production in the last ten years in 1000 MT……………………………4 Table 3.1: Entry number and hybrids formed with MU021…………………………………….24 Table 3.2: Entry number and hybrids formed with MU022……………………………………..24 Table 3.3: Rating of maize streak virus………………………………………………………….29 Table 3.4: Rating of gray leaf spot………………………………………………………………29 Table 4.1: Mean values of test crosses and two testers for plant height (PH, cm), Ear height (EH,cm), yield (tha-1), MSV and GLS in Embu………………….……33 Table 4.2: Correlation coefficients of plant height (PH, cm), ear height (EH, cm), yield (tha-1), MSV and GLS in Embu……….………………………………...…….34 Table 4.3: Mean values of test crosses and two testers for plant height (PHcm), ear height (EH cm), yield (tha-1), MSV and GLS in Muguga…………………………....……………...35 Table 4.4: Mean performance and statistical significance for plant and ear height…………….36 Table 4.5: Phenotypic correlation between plant height, ear height, yield, MSV and GLS in Muguga………………………………………………………………….37 Table 4.6: Mean values of test crosses and two testers for plant height (PH, cm), Ear height (EH, cm), yield (tha-1), MSV and GLS in combined sites……...…….39 Table 4.7: Phenotypic correlation coefficient of plant height (PH cm), ear height (EH cm), MSV,GLS and yield t ha-1in Embu and Muguga combined…….……….40 Table 4.8: General combining ability (GCA) for inbred lines and two testers based on plan Height (PH, cm), ear height (EH, cm), yield (t ha-1), MSV and GLS in Embu…………………………………………………………...41 Table 4.9: General combining ability (GCA) for inbred lines and two testers based on plant height (PH, cm), ear height (EH, cm), yield (t ha-1), MSV and GLS in Muguga…………………………………………………………42 Table 4.10: Specific Combining ability (SCA) estimates for the test cross based on plant height (PH, cm), ear height (EH, cm), yield (tha-1), MSV, GLS in Embu……….…...……………………………………………………….43
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Table 4.11: Specific Combining Ability (SCA) estimates for the crosses based on plant height (PH, cm), and ear height (EH, cm) in Muguga…………………..44 Table 4.12: Percentage heterosis (%H) and specific combining ability (SCA) for yield……………………………………………………………………....……45 Table 4.13: Classification of germplasm into different heterotic groups based on SCA effect grain yield……………………………………..………………….46
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LIST OF PLATES
Plate 2.1: The male inflorescence ………………………………………………………….…… 9
Plate 2.2: The anthers………………………………………………………………………….….9
Plate 2.3: The female inflorescence……….……………………………………………………..10
Plate 3.1: Maize growing in one of the plots……………………………………………….……27
Plate 3.2: Researcher taking plant and ear height…………………………………………….....28
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LIST OF APPENDICES
Appendix 4.1: Mean squares for plant height (PH cm), ear height (EH cm), yield (t ha-1), MSV and GLS………………………………………….……… 60 Appendix 4.2: Mean squares for plant (PH cm) ear height (EH cm), yield (t ha-1), MSV and GLS in Muguga Kiambu county……………………60 Appendix 4.3: Kruskal-Wallis Test of MSV and GLS scores in Embu and Muguga………………………………………………………………………..61 Appendix 4.4: Mean squares for plant (PH cm) ear height (EH cm), Yield (t ha-1), MSV and GLS in Embu and Muguga……………..……………...... 61
Appendix 4.5: Mean squares of Line x tester analysis for plant (PH cm) ear height (EH cm), yield (t ha-1), MSV and GLS in Embu and Muguga…..…………………………………………………………………...61 Appendix 4.6: Mean squares of general/ specific combining abilities of inbred lines and hybrids quantitative traits in Embu and Muguga Kiambu counties…………………………………………………..62
xiii
DEFINITION OF TERMS
Heterosis: It is the superiority of F1 hybrids over both its parents. It is manifested as an increase in vigor, size, growth rate, yield and resistance to diseases.
Mid-parent heterosis: The average heterosis observed when two random population are crossed together.
High parent heterosis: The difference between the mean of the F1 hybrid and the mean of the highest performing parent making up the cross.
Heterotic Groups: A group of related genotypes from the same population which display similar combining ability effects when crossed with genotypes from other germplasm groups.
Heterotic pattern: Heterotic groups that complement each other. They are specific crosses between genotypes which show high levels of heterosis.
Combining ability: It is the value of a genotype based on the performance of their offspring produced in a definite mating system.
General combining ability: The average performance of a line in hybrid combinations expressed as a deviation from the overall mean of all crosses made from other parental lines.
Quantitatively, it measures the comparative performance of lines.
Specific combining ability: Instances where hybrid deviates from the expected value which is the sum of the general combining ability of the parent inbred lines included in the crosses.
Additive genes: It is a mechanism of quantitative inheritance such that the combined effects of genetic alleles at two or more loci are equal to the sum of their individual effects. It is a characteristic that governs general combining ability. xiv
Non additive gene effects: This is when the gene effects of the allelic pair do not sum up since members of the allelic pair are not expressed equally. It is associated with specific combining ability.
Testers: These are genotypes of good general combining ability and well defined heterotic groups, which are used for identifying and selecting superior genotypes to be used in breeding programs.
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ACRONYMS AND ABBREVIATIONS
ANOVA Analysis of Variance
CA Combining Ability
CIMMYT International Centre for Maize and Wheat Improvement
DMA Dry Matter Accumulation
ECA East and Central Africa
EH Ear height
FAO Food and Agriculture Organization
GCA General Combining Ability
GEI Genotype X Environment Interaction
GLS Gray Leaf Spot
IFPRI International Food Policy Research Institute
KALRO Kenya Agricultural and Livestock Research Organization
NARES National Agricultural and Livestock Research Systems
MSV Maize Streak Virus
MT Metric tons
MU 021 Muguga Inbred line No 21
MU 022 Muguga Inbred line No 22 xvi
OPV Open Pollinated Varieties
PH Plant height
RIBD Randomized Incomplete Block Design
SCA Specific Combining Ability
SSA Sub-Saharan Africa
USAID United State Agency for International Development
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ABSTRACT
Maize is an important staple food for most Kenyans. The increasing population trend in the face of declining yields in maize production has intensified food insecurity countrywide. The low grain yield can be attributed to foliar diseases mainly gray leaf spot and maize streak virus and expensive hybrid seeds. Hybrid testing is expensive and limited in number of hybrids that can be generated and tested each year. This has increased the need to improve maize production techniques to meet the high demand. Assigning germplasm into different heterotic groups is fundamental for exploitation of heterosis for hybrid development within a shorter period thus reducing the cost. The objectives of this study were to identify good hybrids based on grain yield data and other yield related traits, to estimate the specific combining ability and percentage heterosis of hybrids formed and identify lines with good combining that can be used as parents in hybrid combination and classify the selected KALRO lines into heterotic groups. Eleven inbred lines were crossed with two single cross testers MU021 and MU022 developed by Kenya Agricultural and Livestock Research Organization (KALRO) Muguga South and belonged to heterotic groups A and B respectively. Line by tester design was used for making crosses. Twenty two crosses were evaluated in a randomized incomplete block design (RIBD) with two replications during the long rainy seasons between March and November 2012.The study was carried out in two different sites, at KALRO Muguga South and KALRO Embu. The parameters measured included plant height (cm), ear height (cm) and grain weight per plot in grams. Disease scores for gray leaf spot (GLS) and maize streak virus (MSV) were recorded and analyzed using Kruskal-Wallis Test. Data collected on plant height, ear height and yield were analyzed by Analysis of Variance (ANOVA) using Genstat programme 2012 and means separation was done using Tukey‘s 95% confidence intervals. Heterosis, general combining ability (GCA) and specific combining ability (SCA) were calculated using line by tester analysis. GCA mean squares due to lines and testers were highly significant p< 0.01 for plant height and ear height. GCA effects indicated that V217-48, Z426-43Z387-4-1 and Z419-5Z443-3 were the best general combiners for grain yield. V131-303 showed significant negative GCA effects. The good yielders in Embu were Z426-43Z387-4-1 X MU021, Z419-5Z443-3 X MU022,V217-48 X MU021, V217-48 X MU022 S458-2-2-2 X MU022 and V131-201 X MU021. In Muguga, the best performance were EC573(R12) Cross combinations S458-2-2-2 X MU021 or S458-2-2-2 X MU022 did well in the two counties. Inbred lines; V217-48 and V265-4-1 were resistant to both maize streak virus and Gray leaf spot in Muguga while inbred lines: Z419-5Z443-3, S458-2-2-2 and V131-201 showed resistance to both MSV and GLS. Total GCA mean squares were greater than SCA mean squares (GCA/SCA ratios of >1) indicating a preponderance of additive over non additive gene action. The basis of grouping the germplasm into different heterotic groups was specific combining ability (SCA) effects for grain yield. V131-303, Z426-43Z387-4-1, V217-48 and V131-201 showed negative SCA effects for grain yield with MU022 and were place into heterotic group B. EC573(R12)C853-14, V265-4-1, Z419-5Z443-3, V217-5, V265- 80, REGN99/48-2 and S458-2-2-2 showed negative SCA effects for grain yield with MU021 and were placed into heterotic group A. The general, specific combining abilities and heterotic groups showed that these genotypes had a potential hybrids for advanced yield testing and subsequent release in the specific locations.
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CHAPTER ONE
INTRODUCTION
1.1 Origin and background of maize
Maize (Zea mays L.) is a member of the maydeae tribe of the grass family Poaceae. It has two close relatives, gamagrass and teosinde. Gamagrass (Tripsacum) grows wild in the Eastern and
Southern sections of the United States of America and in Central and South America (Benz,
2005). Species of Tripsacum with 18 and 36 pairs of chromosomes are known. Teosinte is native to Southern Mexico and Guatemala and is generally regarded as the closest relative of corn. The annual form of teosinte has 10 pairs of chromosomes, the same number as corn (Roney, 2009).
Corn crosses readily with teosinte while special techniques have been used to cross corn and gamagrass (Wilkes, 2004; Beadle, 1986). Two locations have been suggested for the origin of corn. These are (a) the highlands of Peru, Equador and Bolivia and (b) the region of Southern
Mexico and Central America (Weatherwax and Randolph, 1955; Matsuoka et al., 2003). Maize is monoecious with separate male (tassels) and female (ear) inflorescence on the same plant and with the ear producing seeds. Maize is a cross pollinating (allogamous) species such that a natural population is usually heterogeneous. Maize plant can grow up to 2.5-3.5 m high and produce 400-700 seeds on one ear. The maize kernel is a hard one seeded fruit called a caryopsis and consists of a pericarp, endosperm and germ or embryo (Kling and Edmeades, 1997). Maize completely depends on human husbandry (Galinat, 1988; Dowswell et al., 1996; Thomas et al.,
2005).
Maize has 20 chromosomes (n=10). Some maize chromosomes have chromosomal knobs (highly repetitive heterochromatic domains that stain darkly). These domains were used by Barbara
McClintock in the transposon theory of ―jumping gene‖ for which she won a Nobel prize in 1983
(Doebley, 2004).
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Maize is an important model organism for genetics (Ananiev et al., 1998). Primary sequencing of maize genome was completed in 2008 and published on 20th November 2009, ―The B73 Maize
Genome‖. The genome is made up of duplicated and reshuffled helitrons (group of rolling circle transposon). It contains 32,540 genes (Stinard et al., 2009).
Maize is an important staple food for more than 1.2 billion people in Sub-Saharan Africa (SSA) and Latin America (Smale and Jayne, 2004). All parts of the crop can be used for food and non- food products. Apart from being an important feed grain for livestock in industrialized countries (Lukuyu, 2000), maize is also the source of industrial products like protein corn, oil corn, corn for milling purposes for example brewers grit and flakes, hominy grit and corn meal.
In many cultures, corn meal (ground dried maize) is served as thick porridge. Pop corn and roasted dried maize ears with semi hardened kernels are served as snacks. It is baked to unleavened bread in Punjab region (Janice et al., 2010). In the chemical industry, starch is made into plastics, fabric adhesives. Corn steep liquor is used in biochemical industry and research as a culture medium for growing many kinds of micro-organisms (Ligget and Koffler, 1948). Feed maize is being used increasingly as biofuel and ethanol fuel likewise to maize cobs (Karl, 2012).
In 1993, Adrian Fisher introduced ‗Corn Maze‘ ornamental as a tourist attraction. Waxy corn contains a special type of starch which permits it to be used in the manufacture of adhesives, gum paper sizing and pudding (Winkel-Shirley, 2001).
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1.2 Global production of maize
Maize is widely cultivated throughout the world. Tropical maize is grown in warmer regions between the equator and 30o N and 30° S while temperate maize is grown in cooler regions beyond 34° N and 34° S ( Karim et al., 2000).
Table 1.1. World top maize producers in 2014
POSITION COUNTRY PRODUCTION (1000 MT) 1 United States 361091.00 2 China 215500.00 3 Brazil 75000.00 4 EU-27 74160.00 5 Ukraine 28450.00 6 Mexico 24000.00 7 Argentina 24000.00 8 India 22500.00 9 Canada 11500.00 10 Russian Federation 11325.00 11 South Africa 11300.00 19 Tanzania 5000.00 26 Uganda 2750.00 27 Kenya 2650.00
Source: USDA 2014 in (www.ers.usda.gov/datafiles/US-Bioenergy/Feedstocks/)
FAOGIEWS (2012) county brief on Kenya, provisionally put the aggregate cereal production at
3.3 million tones, slightly below the last five years average and 14% less than previous year‘s good output. Cereal import requirement for 2011/2012 marketing (July/June) were forecast at 2.1 million tones (about 26% up from last year), including 860,000 tones of maize, 830,000 tones of wheat and 400,000 tones of rice.
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Table 1.2: Kenya’s corn production in the last ten years in 1000 Metric tons (MT)
YEAR PRODUCTION PERCENTAGE GROWTH RATE 2005 2906 11.47 2006 3247 11.73 2007 2930 -9.76 2008 2367 -19.22 2009 2439 3.04 2010 3465 42.07 2011 3377 -2.54 2012 3390 0.38 2013 2800 -17.40 2014 2650 -5.36
Source United State Department of Agriculture 2014 in (www.indexmundi.com/agriculture/?commodity=cornαgraph=production)
1.3 Maize production constraints
Production of maize by smallholder farmers is very low in Kenya with yields averaging 1.5-2.6 tonnes per hectare (Nyoro et al., 2007). The major abiotic constraint is inadequate and erratic or unfavorable distribution of rainfall (Bonhof et al., 2001). Drought has been reported to be the most important challenge of maize production in SSA (Kassie et al ., 2012). Climate change is likely to lead to increase temperature by an average of 2.10c in SSA and water scarcity, particularly in Southern Africa, in the coming decades (Lobell et al ., 2011). Maize production in rural Africa is in small plots using negligible amount of inputs or no improved germplasm
(Morris, 1998). Difficult market conditions such as capital constraints and government control on market price has also contributed to decline in production (Anseeuw et al ., 2012)
Biotic factors like weeds e.g. striga (Kanampiu et al., 2002), diseases, such as maize cob rot
(Ajanga and Hillocks, 2000) and northern corn leaf blight (Schechert et al., 1999), pests such as maize stem borers are the major constrains. Other pests in SSA include ear borers, white grabs,
5 army worms, cutworms, grain moths, beetles, weevils and grain borers. Other maize diseases in
SSA include downy mildew, rust, leaf blight, stalk and ear rots, leaf spot and maize streak virus
(MSV) (Schechert et al., 1999; Ajanga and Hillocks, 2000).
In Kenya production has declined due to post election violence in 2008, high input costs, poor policy implementation, reliance on rain fed agriculture, poor research and extension services, poor land policies, poor storage facilities/drying facilities, poor quality seed, low utilization of improved practices, inaccessible markets by smallholders, weak producer organizations and weak human resource capacity (Sandra and Paul, 2011). In the year 2011-2012, Maize Lethal
Necrotic Disease was a major threat to maize production in South Rift, Kenya which is the bread basket of Kenya. A total estimate of 65,000 hectares of maize were affected in the year 2012
(FAO, 2012).
1.4 Problem statement
Maize breeding institutions have combined molecular markers with conventional breeding tools to improve production (CIMMYT, 1999). Despite this, Kenya faces acute shortage of maize
(FAOGIEWS, 2012). Genetic engineering has the potential to increase production and productivity in agriculture (FAO, 2003). Biotechnological approach could be used to produce seeds at a faster rate compared to conventional breeding but the seeds are expensive and cannot be afforded by the majority of the producers who are small scale farmers (Langyintuo et al.,2008). In marginal areas where yield levels are low and the price of hybrid is high compared to grain price, smallholder farmers find it profitable to use the Open Pollinated Varieties than to buy hybrid seeds every year (Pixley and Bazinger, 2001). Hybrid testing both private and public are expensive and limited in the number of hybrids that can be generated and tested each year.
Heterotic groups can therefore be established to facilitate breeding efforts (Troyer, 2006; Tracy
6 and Chandler, 2006). Hybrid seeds increased maize production in the first two decades after independence but this was thwarted by market liberalization and weakened producer incentives.
Lack of information and awareness of the new varieties affected farmers‘ adoption of the new hybrid varieties (Muyanga and Jayne, 2006). Liquidity constraints due to lack of access to credit facilities in the late 1990s caused reluctance in adoption of productivity enhancing technologies such as improved maize varieties and fertilizer application (Simtowe and Zeller, 2006). It is with this view that the study grouped the selected KALRO inbred lines into heterotic groups on the basis of yields and come up with hybrid varieties that are adapted to the selected environment thus reducing the time that each hybrid would take to be developed.
1.5 Justification of the study
Twentieth century corn breeders have spent vast resources developing inbred lines that when tested in hybrid combinations, produce high yielding hybrids (Troyer, 2006).The international
Maize and Wheat Improvement Center (CIMMYT) has developed and released maize inbred lines suitable to the various ecological zones. However, information about their combining ability and the best hybrid combination is not available furthermore; there are no uniform heterotic groups known for the newly developed inbred lines.
1.6 Null hypotheses
i. There is no significant difference in yield performance among the selected KALRO inbred lines in Embu and Kiambu counties.
ii. There is no significant variation in the combining ability of the selected KALRO inbred lines with the two testers
iii. The selected KALRO inbred lines are not heterotic to the two testers.
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1.7 General objective
To determine the combining ability and the best hybrids basing on yield of the selected lines from KALRO and assign them into heterotic groupings.
1.7.1 Specific objectives
i. To identify good hybrids based yield and other yield related traits.
ii. To estimate the specific combining ability and percentage heterosis of the hybrids formed and identify lines with good combining ability that can be used as parents in hybrid combinations. iii. To classify the selected KALRO inbred line into heterotic groups.
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CHAPTER TWO
LITERATURE REVIEW
2.1 Biology of maize
Maize is a tall determinate annual plant producing large, narrow, opposing leaves (about a tenth as wide as their height), borne alternately along the length of a solid stem. The stem has internodes and taper at the tip. Fibrous roots develop from the lower nodes of stem below ground level while prop roots are produced by the lower two nodes. Maize is a monoecious plant. The male inflorescence (tassels) crown the plant at the stem apex (Plate 2.1) while the female inflorescence (cobs or ears) are borne at the apex of condensed, lateral branches protruding from leaf axils (Plate2.3) (Doebley, 2004). It is an allogamous plant that propagates through seeds produced predominantly by cross pollination and depends mainly on wind borne cross pollination.
The staminate produces pairs of free spikelets each enclosing a fertile and a sterile floret (Plate
2.2). The anther develops four loculi, each one containing a central row of archeosporial cells that give rise to sporogenous tissue. After several weeks the mother cells are in the meiotic stages. Microspores are organized around four nuclei and become mature pollen grains. The amount of pollen produced by a tassel is estimated to be 25 million pollen grains (Kling and
Edmeades, 1997). Maize in the field shed pollen for thirteen days, each silk receives an average of thirteen pollen grains per day. The pistillate produces pairs of spikelets on the surface of a highly condensed rachis. Each spikelet encloses two fertile florets, one of whose ovaries will mature into a maize kernel once sexually fertilized (Sleeper and Poehlman, 2006). The individual maize grain is a caryopsis, a dry fruit containing a single seed fused to the inner tissues of the
9 fruit case. The seed contain a germ which consists of a radical and an attached seed leaf (Kling ich consists of a radical and an attached seed leaf (Klingand Edmeades, 1997).
Plate 2.1: The male inflorescence. Source: Biological drawings by Mackean, D. G.
Plate 2.2: The anthers. Source: Biological drawings by Mackean, D. G.
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Plate 2.3: The female inflorescence. Source: Biological drawings by Mackean, D. G.
2.2 Maize breeding in Kenya
In Kenya, maize breeding activities are mainly carried out by the National Agricultural Research
Systems (NARES) (Nyoro, 2002). The International Center for maize and Wheat Improvement
(CIMMYT) and a few private companies (CIMMYT, 2004). Their main activities include: conservation by periodic rejuvenation in the breeding nursery, improvement by recurrent
11 selection procedures of the basic breeding stock i.e. Kitale synthetic 11 (KS11) and Ecuador 573
(EC 573); monitoring progress in recurrent selection populations and evaluating with a view to commercially release of semi-elite and super elite hybrid combination in the form of, single, three-way, double varietal and top crosses (Smale and Jayne, 2003). Sources of seeds in the rural community are farmers and gardeners who save seeds from the previous crop every year.
In the high yielding zone almost all farmers purchase hybrid seed every year (DeGroote et al.,
2001). Kenya Seed Company has produces certified seeds suitable for all the agro-ecological zones in the East and Central Africa (ECA). The Kenyan maize varieties comprise white semi- dent grains and have been bred and selected for a wide range: Highland varieties include, H 614,
H 624, H 626, H 627, H 629 and H 9401. Medium altitude varieties are: H 513, H 515 and H
516. H 624 is grown in the transitional zone. Lowland agro-Ecozone varieties include Pwani hybrids (PH1 and PH4) while the dry land agro-Ecozone varieties are Katumani composite B
(Shiluli et al., 2000). The Insect Resistant Maize for Africa (IRMA) project implemented by
KALRO and CIMMYT uses biotechnology to develop crop varieties that are resistant to stem borers. With the introduction of maize hybrids and related technologies, maize registered a tremendous increase in yields between 1964 and 1975 often dubbed ―Kenya‘s Green
Revolution‖. However Karugia and Kosura (2005), noted that, this early promise was lost in the
1980s and since then achieving the increase in the productivity has been an elusive goal.
Systematic germplasm improvement program was initiated by the government of Kenya in 1955 when it hired M. N. Harrison a plant breeder to develop late maturing maize hybrids. Crosses of
KSII with Ecuador 573 and Costa Rica 76 yielded 40% more than the best parent, KSII. Based on this information H611 (KSII X Ecuador 573) was released in 1964 (Harrison, 1970). A double cross, H622, and a three-way hybrid 632 were released for commercial production in
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1965. Hybrid maize production in Kenya has become popular in high and medium potential areas. However, open pollinated varieties (OPVs) yielding 4-24 % higher than commercial hybrid H625 have recently been identified (Mwenda, 1986; Ochieng, 1986). Between 1965-
1989, eleven high altitude maize hybrids were released with 30-33% yielding advantage over the local maize. Katumani Composite A (KCA) and (KCB) were the first to be released for the marginal regions and were released in 1966 and 1968 respectively. Dry land composite (DC1) was later released in 1989. Embu program released medium maturing H511 and H512 in 1968 and 1970 respectively (Allan, 1971). H600 are late maturing varieties suitable for the Kenyan highland, the medium maturing H500 hybrids are for medium altitude region. Open pollinated composites and synthetics are suitable for drier lowland. More than forty varieties have been released in Kenya since 1961 (KARI, 2003).
Heterosis or hybrid vigour is the better performance of hybrid relative to the parents and the outcome of the genetic and phenotypic variation (Miranda, 1999). It refers to the superiority of first filia (F1) over the standard commercial check variety; hence it is also called economic superiority over checks (Sharief et al., 2000). Generally heterosis is manifested as an increase in vigor, size, growth rate and yield. This superiority is estimated over the average of the two parents (the mid parent value). The manifestation of heterosis depends on the genetic divergence of the two parental populations (Hallauer and Miranda, 1988). The effective use of heterosis involves the development of populations with high combining ability (Vasal et al., 1992; Fan et al., 2004)
In maize, inbred lines are low yielding while hybrids show a high degree of heterosis for yield as well as other agronomic traits like plant height and days to maturity (Duvick, 1999). However,
13 high yielding hybrids also owe their high yield levels to other non heritable factors like environmental conditions (Chapman et al., 2000).
Two major types of heterosis have been defined according to the type of parents involved in making the hybrids (Lamkay and Edwards, 1999). These are mid-parent or average heterosis and high parent heterosis or better parent heterosis. Mid-parent heterosis is the heterosis observed when two random populations are crossed together and is used for selecting populations for recurrent selection programs to determine the amount of relationship among cultivars. This is the one commonly used and the formula for the condition necessary for heterosis of quantitatively inherited traits given by (1981) is as follows:
H=∑ dy2
H-Mid-parent (average heterosis) d- Is the effects due to dominance y2- Is the square of the difference in allele frequency between the lines or populations, it determines the amount of heterosis expressed in the cross.
The difference in the allele frequency and the dominance of loci of inbred lines and cultivars are generally not known. Therefore experimental data obtained from hybrids and their respective parents are the only sources available to determine the lls of heterosis expressed in hybrids
(Falconer, 1981).
High parent heterosis is the difference between the mean of the highest F1 hybrid and the mean of the highest performing parent making up the hybrid. It is also referred to as Heterobeltosis
(Lamkay and Edwards, 1999). It is from these measurements of heterosis that heterotic
14 relationships are determined. The hybrid should perform over both its parents for heterosis to be of any value to the breeder, but in some cases the hybrid may be inferior to the weaker parent.
Heterobeltosis = (F1-BP) / BP ×100
BP – mean of better parent
Hybrid corn was the first generation progeny from a cross involving inbred lines. Breeding of hybrid corn involved (a) development of inbred lines by controlled self pollination, (b) determination of inbred lines to be combined into productive crosses, thus single and double crosses are produced and (c) commercial utilization of the crosses for seed production (Airy,
1959). An inbred line is developed by self pollination and selection until homozygous plants are obtained. This requires five to seven generations of controlled pollination (Jenkins, 1936,
Sprague, 1942). A single cross is the hybrid progeny from across between two inbred lines.
Single cross plants are heterozygous for all the genes by which the two inbred lines differ. A double cross is the hybrid progeny from a cross between two heterozygous single cross parents.
The double cross seed is produced on a single cross plant that has been pollinated by a second single cross. It is the hybrid seed that is usually sold to the farmer.
Inbred seeds used in production of single cross seed are increased in an isolated field with open pollination. Double cross therefore requires four separate isolate fields to produce four inbred lines needed for one double cross hybrid. Adequate isolation fields are required. To reduce the number of isolated fields, a male parent that produces heavy pollen and sheds it freely is used; increasing the number of border rows with pollen parents reduce the distance needed for isolation and the fertile tassels are removed before pollen is shed.
15
Hybrid corn seed may be produced without detasseling by utilizing cytoplasmic male sterility
(Matus—Cadis, 2003). This is a cytoplasm with plasmogenes which cause abortion of pollen.
The expression of cytoplasmic male sterility may be affected by particular genes in chromosomes called restorer genes. They restore fertility cytoplasmic male sterile plants.
A X B C X D
Male sterile male fertile male fertile male fertile
AB Male sterile X CD male fertile Either C or D has pollen restoring gene
ABCD 50 % male fertile
if either C or D has restorer gene
Figure 2.1: cytoplasmic male sterility. Source: (Matus-Cadis, 2003)
Inbred lines are then combined into single or double crosses after testing their combining abilities in a top cross. A top cross is a testcross between inbred line and an open pollinated variety, a single cross or some testers. It measures the GCA of inbred lines being tested. The inbred lines with good GCA as determined by the top cross test are then grown in single cross yield test to determine the SCA of particular hybrid combinations.
Yield stability in a genotype is the ability of that genotype to have uniform yield regardless of environmental effects while adaptability is the ability of a variety to provide stable and high
16 yield under different environmental conditions (Becker, 1981). Since maize displays orderly sequence of yield components, indirect selection can be used by searching improved yield components.
Hybrids for wide adaptations are selected by looking for non-crossover Genotype x Environment
Interaction (GEI) or preferably the absence of GEI (Matus-Cadiz, 2003). Several methods have been used to evaluate stability of characters of different hybrids. Mani and Singh (1999), studied yield stability in twelve maize hybrids over three diverse environments. The composite Navin followed by double top cross hybrid EHF-1121 was found to be the most stable genotype with respect to yield but stability parameter was found to exploit interaction effect of hybrids grown in diverse environments (Kana and Miller, 1984).
Consolidated breeding programmes evaluate correlation and interrelationship among grain yield and its components (Maniyannan, 1998). Kernel yield was found to be positively and significantly correlated with plant height (Ahmed and Hassanein, 2001). Genetic correlation analysis elaborates the degree of association among important quantitative traits but does not give a rule on how much a character contributes towards the expression of the other character(s) in a plant population. Grain yield is positively and genetically correlated with plant and ear height (Martin and Russell, 1984), but Rather et al. (1999), reported the association between plant heights with grain yield as non-significant.
2.3 Heterotic groups
According to Warburton et al. (2002), heterotic group is a group of related or unrelated genotypes from the same or different population which display similar combining ability effects when crossed with genotypes from other germplasm groups. A heterotic pattern is a specific pair of heterotic groups or lines, which express high heterosis in hybrid combination (Warburton et
17 al., 2002). Heterotic groups are important as they allow exploitation of germplasm in a hybrid- breeding program. Some methods that can be employed in identifying heterotic groups include making crosses in a diallel fashion, making crosses in the North Carolina Design II (Robinson et al., 1958) mating design and using DNA markers to classify the germplasm (Melchinger, 1999).
A heterotic group contains different genotypes, which show similar heterosis because of similar allelic frequencies thus broad sources of germplasm are represented (Fan et al., 2009). It is made up of a set of inbred lines that have similar performance when crossed with inbred lines from another heterotic group. Inbred lines within a heterotic group are related due to advanced cycle breeding. Classifying inbred lines into heterotic groups is critical in determination of potential usefulness of the lines for the development of high yielding hybrids and synthetic varieties.
According to Warburton et al. (2002), this has not been maximized in the tropics thus; a high level of diversity has made it relatively difficult to find uniform heterotic groups.
Heterotic patterns can be analyzed either by crossing the germplasm in question with a common tester which are known to be of different heterotic patterns, using molecular markers or by crossing the germplasm in a diallel mating system (Basbag et al., 2007). To assign germplasm into heterotic patterns, Reif et al.(2005), suggested two strategies to be used: A higher mean heterosis and hybrid performance; reduced specific combining ability (SCA) variance and a lower ratio of SCA to general combining ability (GCA) variance.
CIMMYT developed a number of heterotic groups from some of the broad groups to suit its lowland and tropical, subtropical and highland maize breeding programs (CIMMYT, 1999). In
Eastern and Southern Africa, the heterotic groups are based on Southern Cross (SC), Salisbury white (N3), K64r/m162w and Natal Potchefstroom Pear Elite Selection (NPPES) varieties
18
(CIMMYT, 1999). In Kenya KSII and EC573 are sources of inbred lines for maize hybrid development for highlands categorized as pool A and B for medium zone (KARI, 2003).
2.4 Combining ability
After an inbred is developed, it is crossed with other inbreds and its productivity in single and double cross combinations is evaluated. The ability of an inbred to transmit desirable performance to its hybrid progenies is referred to as its combining ability (CA) (Kumar et al.,
2007). Combining ability tests are necessary since it is not possible to predict the performance of hybrids from visually assessing or measuring their per se performance or of the component inbred lines or genotypes. Information on combining ability of germplasm under evaluation can also help in the exploitation of heterosis. Combining ability of inbred lines is determinant of the potential usefulness of an inbred line in the hybrid combinations and the final evaluation of inbred lines can be best determined by hybrid performance (Sharma et al., 2005).
The average performance of a particular inbred line in a series of hybrid combinations is known as its general combining ability (GCA) (Kumar et al., 2007). It is expressed as a deviation from the overall of all crosses made from other parental lines in a Diallel cross (Falconer, 1981).
These deviations can either be positive or negative. A positive deviation can be favorable or unfavorable on the trait under consideration. Negative values are not desirable for yield traits but they are favorable for days to anthesis where earliness is significantly important (Venkatesan et al., 2007). Generally, GCA is primarily associated with alleles which are additive in their effects.
Additive effects are predictable portion of the genetic effects and are therefore useful to plant breeders (Baloch et al., 2010). The GCA tests are used preliminary for screening of lines from a larger number of lines in a breeding program. They are also used to identify the type of a gene action governing traits of interest (Falconer and Mackay, 1989). A high GCA estimate is
19 indicative of additive gene action. Genotypes with poor GCA are discarded. The GCA effects quantitatively measure the comparative performance of parents and cross combinations in relation to one another (Zehui et al., 2000). Any particular cross has an expected value, which is the sum of the GCA of the two parental lines. The cross may deviate from the expected value to a greater or lesser extent and this deviation is called the SCA of the two lines in the combination
(Falconer, 1989, Vacaro et al., 2002). SCA is defined as instances in which certain hybrid combinations are either better or poorer than would be expected on the average performance of the parent inbred lines included in the cross (Sprague and Tatum (1942). The SCA is attributed to non-additive gene portion of the total genetic effects (Sprague and Tatum, 1942).
The SCA is used to indicate the value of superior genotype combinations especially in the intra group crosses; it represents final stage in selection of inbred lines as it identifies specific inbred lines to use in hybrid formation and to determine heterotic relationship among different genotypes. Lines from different heterotic groups, which give high positive SCA estimates, are said to be complimentary to each other (Hallauer and Miranda, 1981).
2.5 Testers in breeding programs
Testers are genotypes of good GCA and well defined heterotic groups, which are used for identifying and selecting superior genotypes to be used in breeding programs (Melania and
Carena, 2005). They are very important in determining the heterotic alliance of new inbred lines as well as evaluating the breeding values of genotypes for population improvement.
Inbred lines, single cross hybrids or heterogeneous materials can be used as testers. Rawlings and
Thompson (1962), pointed out that a good tester should be able to discriminate good from bad genotypes and provide information that classifies the merit of lines and maximizes the genetic
20 gains. It should be poor in the traits for which the lines are to be analyzed but should have broad adaptation to the target environment.
The procedure for identifying superior genotypes by using testers, involves evaluation of testcrosses for GCA effects. The choice of what type of tester (broad based or narrow based) to use in a breeding program depends on the availability of the testers, type of materials under tests and type of hybrids for which the lines are to be used (Parentoni et al., 2001). In selecting for
GCA, a broad based heterogeneous population is used as a tester and when selecting for SCA, a narrow genetic base (inbred or single cross) is used (Hallauer and Miranda, 1988).
The productiveness of an inbred line is determined by its ability to transmit desirable genes to its hybrid progenies (CA) (Pixley and Banziger, 2002). The genetic basis of a germplasm, its interaction with environment, correlation studies among various quantitative characters in crop studies, combining ability and heterosis are of great importance to a plant breeder for selection and breeding different varieties of maize with increased yield potential.
The study was carried out to evaluate the yield components of different maize inbred lines when hybridized with two testers. Correlation analysis of the traits was carried out and combining ability analysis was calculated according to Singh and Chaudhary (1985). Based on heterosis and specific combining ability, the inbred lines were placed in heterotic groups.
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CHAPTER THREE
MATERIALS AND METHODS
3.1 Study area and materials
3.1.1 Study area
The experiment was undertaken in Muguga, Kiambu County and Embu (Embu County) both on
KALRO farms. Muguga lies at latitude 1o 131 South, longitude 36o 381 East at an altitude of
2096 meters above sea level. It recieves bimodial rainfall between March and May and between
October and November with annual rainfall above 1500 mm per annum. It has a mean temperature of 16.8 oC. It falls under the agro-ecological zone AEZs 2-4 in the Central Kenya highlands (Plate 3.1). Embu lies at latitude 0o 321 South and longitude 37o 271 East with an altitude of 1560 meters above sea level (Jaetzold and Schimidt, 1983) (Plate 3.2). Embu has bimodal rainfall with annual precipitation of about 995 mm. This permits the growing of two
o crops per year. Temperature range from 10.8 to 20.9 C. It falls under agro-ecological zone III
(LH3). The main soil types are well drained Nitisol with relative fertile status d to its volcanic origin (Jaetzold and Schimidt, 1983).
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FURE 3.1: Map of Kiambu County.
Source: Google map 2015.
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FIGURE 3.2: Map of Embu County.
Source: Google map 2015.
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3.1.2 Study materials
The genotypes for this study were derived from Central nursery developed by CIMMYT at
KALRO Kiboko and supplied by KALRO Muguga South. The eleven genotypes were hybridized with two testers MU021 and MU022 (Tables 3.1, 3.2) in the long rains of 2012.
Table 3.1: Entry number and hybrids formed with MU021
Entry No Inbred line Hybrid 1 V131-303 MU021 X V131-303 3 EC573(R12)C853-14 MU021 X EC573(R12)C853-14 5 V265-4-1 MU021 X V265-4-1 7 Z426-43,Z387-4-1 MU021 X Z426-43,Z387-4-1 9 Z419-5, Z443-3 MU021 X Z419-5 Z443-3 11 V217-5 MU021 X V217-5 13 V265-80 MU021 X V265-80 15 REGN99/48-2 MU021 X REGN99/48-2 17 V217-48 MU021 X V217-48 19 S458-2-2-2 MU021 X S458-2-2-2 21 V131-201 MU021 X V131-201
Table 3.2: Entry number and hybrids formed with MU022
Entry No Inbred line Hybrid 2 V131-303 MU022 X V131-303 4 EC573(R12)C853-14 MU022 X EC573(R12)C853-14 6 V265-4-1 MU022 X V265-4-1 8 Z426-43,Z387-4-1 MU022 X Z426-43,Z387-4-1 10 Z419-5, Z443-3 MU022 X Z419-5 Z443-3 12 V217-5 MU022 X V217-5 14 V265-80 MU022 X V265-80 16 REGN99/48-2 MU022 X REGN99/48-2 18 V217-48 MU022 X V217-48 20 S458-2-2-2 MU022 X S458-2-2-2 22 V131-201 MU022 X V131-201
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3.2 Experimental layout
The experimental design was an alpha lattice design for incomplete blocks of 6 x 4 with two replications at each of the two sites (Figure 3.1). The plots consisted of 3 rows of 11 hills spaced at 0.75 m apart and the in-row spacing was 0.25 m. The plot area measured 6.1875 m2 (0.75 x 3) x (0.25 m x 11 plants) and each had 33 plants, giving a total population of 53,333 plants ha-1.
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Figure 3.3: Experimental design
27
Plate 3.1: Maize growing in plot 1(entry 12)
3.3 Planting and field management
Planting at Muguga was carried on 10/04/2012 at the onset of the long rains of 2012; while in
Embu was on 10/05/2012. Ploughing of the field was carried out using a tractor-drawn heavy disc plough and it was harrowed twice. A pre-marked chain was used to mark stations at a spacing of 0.75 m between the rows and 0.25 m within the rows. A compound fertilizer, Di- ammonium phosphate was applied at a recommended rate of 80 kg P2O5 per hectare at planting.
Three weeks after emergence hand hoeing was carried out to control weeds. Another hand hoeing was carried out after four weeks. Top dressing was done using calcium ammonium nitrate
(CAN 26 % N) eight weeks after planting and after thinning at a rate of 200 kg/ha. Maize stalk borer was controlled using Oermethrin 5 % dust applied into the funnel of each plant. Harvesting was carried out on 2/10/2012 at Muguga and on 10/10/2012 at Embu.
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3.4 Data collected
Field data for plant height (PH cm), ear height (EH cm), disease scores for Gray leaf spot
(GLS) and Maize Streak Virus (MSV), was recorded for nine sampled plants per plot. Some derived traits such as yield per hectare (at 12.5 % moisture adjustment) were calculated using
Field book software (Vivek et al., 2007).
3.4.1 Plant height
The distance between the base and the insertion of the first tassel branch of each plant was measured in (cm) using a ruler at physiological maturity (Plate 3.4).
Plate 3.2: Researcher taking plant height and ear height
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3.4.2 Ear height
Ear height was measured as the distance between the base of the plant to the insertion of the lowest ear of the same plant using a ruler at physiological maturity (Plate 3.4).
3.4.3 Moisture content
Moisture content from each plot was determined using appropriate moisture meter at physiological maturity during harvesting. Recorded moisture content was utilized in adjustment of grain yield per plot and per hectare to 12.5% moisture content.
3.4.4 Disease scores
Disease scores for maize streak virus (MSV) and GLS were scored during the grain filling stage at a scale of 1-5 as shown in Tables 3.3 (Mesfin et al., 1992) and 3.4 (Kinyua et al., 2010).
Table 3.3 Rating of maize streak virus (modified from Mesfin et al., 1992)
Rate Observed plant symptom 1 Very few streaks or no symptoms. Symptoms only observed by close inspection inform of specks with no subsequent development 2 Light streaking- Clearly visible but limited symptoms, spots or streaks developing on several leaves. Young leaves have less symptoms 3 Moderate streaking; Many long streaks homogenous distribution until plant maturity 4 Severe at least 60 % of leaf area uniformly over all leaves and the whole plant 5 Very severe streaking: 70 % of the leaf area or more affected with stunting
Table 3.4 Rating of grey leaf spot (Kinyua et al., 2010)
Rate Observed Plant Symptom 1 Traces of small lesion or no symptoms 2 Small regular elongated brown-gray necrotic spots growing parallel to veins 3 Lesions reach 3.0 cm x 0.3 cm on lower leaves spreading upwards on plant during the season. 4 Severe at least 60 % leaves infected. 5 8-9 leaves infected translating to 75 % leaves covered with dark, grayish- brown rectangular lesions. Very severe.
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3.4.5 Grain yield
Yield per plot was calculated from shelled grain per plot adjusted to 12.5 % moisture and converted to tones per hectare (t ha-1).
3.5 Data analysis
Data collected was subjected to analysis of variance (ANOVA) using Genstat 2012 program.
Data from the two sites was analyzed separately and combined analysis for the two sites was also carried out. Means were separated using Tukey‘s 95 % confidence intervals. The mean values of inbred lines and F1 were used to calculate combining abilities and assess the gene effects for grain components as proposed by Singh and Chaudhary (1985). The GCA for each parent
(inbred line/ tester) was estimated as the mean of all crosses involving that parent (inbred line/ tester) minus the overall mean. The SCA was estimated as mean of a cross minus mean of all inbred line crosses involving that line, mean of all testers cross involving that tester and the overall mean.
Estimation of GCA effects according to Singh and Chaudhary (1985). The statistical model used for line x tester analysis was:
GCA lines:
gi = xi…/tr- x…/ltr
where, l = number of lines
t = number of testers
r = number of replications
g = general combining ability effects for cross i
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xi is the grand total of lines for cross i
x… grand total crosses
Testers:
GCA (testers)
gt= x.j./lr- x…/ltr x.j is the grand total of testers for cross i
Estimation of SCA effects using Singh and Chaudhary (1985) statistical model.
Sij= xij./r- xi../tr – x.j./lr +x…/ltr
Sij= specific combining ability effects for cross i
Xij = is the grand total for cross i
Tukey‘s correlation coefficient (r) was calculated among the different traits measured from all the nine center plants per plot.
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CHAPTER FOUR
RESULTS AND DISCUSSION
4.1 Single site analysis
4.1.1 Embu County
4.1.1.1 Agronomic traits of the crosses between inbred lines and two testers
There were highly significant differences among test crosses at (p<0.01) for plant height
(PH), ear height (EH) and yield (t ha-1) (Appendix 4.1). There were no significant
differences among test crosses at (p<0.05) for Gray leaf Spot (GLS) and Maize streak virus
(MSV)(Appendix 4.3). Table 4.1 shows the mean values of all the agronomic traits
measured for all the crosses and the two testers. There was a large variability for plant
height (PH), ear height (EH) and yield (t ha-1). However there was a small variability for
MSV and GLS. The plant height means ranged from 168.5 cm (Entry 2) to 236 cm (Entry
4). The mean plant height for the tester MUO21 (check) was 222 cm and tester MUO22
(check) was 204 cm. Crosses with MUO22 showed both the highest and the shortest mean
heights for plant height which were V131-303×MUO22 and EC573 (R12) C853-14×MUO22
respectively. The mean ear heights ranged from 61 cm (Entry 2) to 125 cm (Entry
15).Crosses with MUO21 had the highest ear height while the crosses with MUO22 had the
lowest ear height. REGN99/48-2 × MUO21 showed the highest ear height while V131-
303×MUO22 showed the lowest ear height. The mean yield ranged from 4.4 t ha-1(V131-
303×MUO22) (Entry 2) to 8.75 t ha-1 (V217-48 × MU021) (Entry 17). Z426-43,Z387-4-
1×MU021 showed the second highest yield of 8.19 t ha-1 (Entry 7).
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Table 4.1: Mean values of test crosses and two testers for plant height (PH cm), Ear height (EH cm), yield (tha-1), MSV and GLS Entry Test Crosses PH(cm) EH(cm) YIELD(t/h GLS MSV a) 1. V131-303×MU021 213.5±16.5 101.5±13.5 6.98±0.25 1.25±0.25 1.0±0 2 V131-303×MU022 168.5±20.5 61±10 4.4±1.72 1.0±0 1.0±0 3 EC573(R12)C85314×MU021 209.5±3.5 108±7 6.96±0.91 1.0±0 1.0±0 4 EC573(R12)C85314×MU022 236±18 119.5±26.5 5.59±0.27 1.25±0.25 1.0±0 5 V265-4-11×MU021 205.5±9.5 95.±7.5 4.82±0.63 1.25±0.25 1.0±0 6 V265-4-11×MU021 195.5±1.5 92±4 6.72±0.83 1.5±0 1.0±0 7 Z426-43,Z387-4-1×MU021 221.5±27.5 114±12 8.19±0.89 1.0±0 1.0±0 8 Z426-43,Z387-4-1×MU022 204±7 94±1 6.33±0.23 1.0±0 1.0±0 9 Z419-5 Z443-3×MU021 211.5±16.5 115.5±14.5 6.74±0.24 1.0±0 1.0±0 10 Z419-5 Z443-3×MU022 228±4 110±1 8.1±0.54 1.0±0 1.0±0 11 V217-5×MU021 213.5±16.5 107.5±9.5 6.48±0.60 1.0±0 1.0±0 12 V217-5×MU022 214.5±3.5 100.5±4.5 6.93±0.22 1.25±0.25 1.0±0 13 V265-80×MU021 211±1 106.5±5.5 6.1±0.08 1.0±0 1.0±0 14 V265-80×MU022 227±17 104.5±17.5 6.36±0.35 1.0±0 1.0±0 15 REGN 99/48-2×MU021 226±21 125±27 6.46±1.55 1.0±0 1.0±0 16 REGN 99/48-2×MU022 210±12 102.5±13.5 6.9±0.18 1.25±0.25 1.0±0 17 V217-48×MU021 207.5±19.5 100.5±8.5 8.75±.0.10 1.0±0 1.0±0 18 V217-48×MU022 232±15 101±13 7.44±1.73 1.0±0 1.0±0 19 S458-2-2-2×MU021 229±22 121±12 7±1.05 1.0±0 1.0±0 20 S458-2-2-2×MU022 221.5±4.5 96.5±4.5 7.12±0.67 1.0±0 1.0±0 21 V131-201×MU021 197±24 83.5±13.5 7.12±0.42 1.0±0 1.0±0 22 V131-201×MU022 195.5±16.5 77±7 6.31±0.18 1.0±0 1.0±0 23 MU021 222±8 121±6 6.8±0.57 1.0±0 1.0±0 24 MU022 204±15 88±14 7.77±0.75 1.0±0 1.0±0 MEAN 212.7 101.8 6.77 1.073 1.0 LSD 39.8 33.56 2.317 0.3034 1.0
4.1.1.2 Correlation between agronomic traits of crosses
Plant height (0.3639) and ear height (0.2649) had a significant positive correlation with yield while GLS (-0.2034) showed a significant negative correlation. Ear height (0.8567) showed a significant positive correlation with plant height while GLS (-0.0097) had a non significant negative correlation with plant height. However MSV had no correlation with all the studied traits (Table 4.2).
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Table 4.2: Correlation coefficients of plant height (PH cm), ear height (EH cm), yield (tha- 1), MSV and GLS Trait Correlation coefficient PH - EH 0.8567 - MSV 0 0 - GLS -0.0097 0.0775 0 - Yield 0.3639 0.2649 0 -0.2034 PH EH MSV GLS
4.1.2 Muguga, Kiambu County
4.1.2.1 Agronomic traits of the crosses between inbred lines and two testers
There were highly significant differences among test crosses at (p<0.01) for plant height (PH cm), ear height (EH cm) and yield (tha-1) (appendix 4.2). There was no significant differences among test crosses at (p<0.05) for (MSV) and GLS (Appendix 4.3).
There was a large variability for plant height (PH), ear height (EH) and yield (tha-1).
However, there was a small variability for MSV and GLS. The plant height means ranged from
217.5 cm (V131-303 X MU021) (Entry 1) to 283 cm (EC573 (R12)C853-14 X MU021) (Entry
3).The plant height mean for the two testers (checks) showed an insignificant variability (275.5 cm (MU021) and 274.5 (MU022). The mean ear heights ranged from 82 cm (Z426-43, Z387-4-1
X MU022) (entry 8) to 132 cm (EC573(R12)C853-14 X MU021) (entry 3). Tester MU022 had a lower mean height of 99 cm. The mean yield ranged from 4.62 t ha-1 (V131-303 X MU022)
(entry 2) to 7.81 t ha-1 (REGN 99/48-2 X MU021 (entry 15) respectively. The highest scores for
MSV was 2±1 (EC537 (R12) C853-14 X MU022) (entry 4) and (Z426-43,Z387-41 X MU022)
(entry 8), while for GLS was 1.5±0.5 showed by crosses (Z419-5,Z443-3 X MU021) (entry 9),
(REGN99/48-2 X MU021) (entry 15) and (S458-2-2-2 X MU022) (entry 20) (Table 4.3)
35
Table 4.3: Mean values of test crosses and two testers for plant height (PH cm), Ear height (EH cm), yield (tha-1), MSV and GLS in Muguga Entry Test Crosses PH EH YIELD MSV GLS 1 V131-303×MU021 217.5±2 85.5±1.5 5.31±0.79 1±0 1.25±0.25 2 V131-303×MU022 223.5±7.5 76±0 4.62±0.47 1.5±0.5 1±0 3 EC573(R12)C853-14×MU021 283±14 132±0 7.34±0.95 1.25±0.25 1.250.25± 4 EC573(R12)C853-14×MU022 266.5±14.5 107.5±13.5 6.79±0.64 2±1 1±0 5 V265-4-11×MU021 245±4 100±8 4.5±0.38 1±0 1.25±0.25 6 V265-4-1×MU022 227.5±0.5 79.5±2.5 5.44±0.71 1±0 1±0 7 Z426-43,Z387-4-1×MU021 263±10 110±5 5.87±0.75 1.75±0.75 1±0 8 Z426-43,Z387-4-1×MU022 222.5± 1.5 82 ± 2 4.89 ±0.11 2 ± 1 1.5 ±0 9 Z419-5, Z443-3×MU021 258±5 107.5±0.5 6.94±0.02 1.5±0.5 1.5±0 10 Z419-5, Z443-3×MU022 254±14 92±6 5.78±0.32 1±0 1.25±0.25 11 V217-5×MU021 242.5±3.5 106±3 6.29±0.16 1±0 1.25±0.25 12 V217-5×MU022 238.5±17.5 90±4 5.12±0.39 1.5±0.5 1.25±0.25 13 V265-80×MU021 249.5±8.5 97.5±9.5 6.66±0.44 1±0 1.25±0.25 14 V265-80×MU022 243±15 89±5 7.09±0.01 1.75±0.75 1±0 15 REGN 99/48-2×MU021 269±2 116±3 7.81±0.13 1±0 1.5±0 16 REGN 99/48-2×MU022 262±11 99±6 6.96±0.53 1.25±0.25 1±0 17 V217-48×MU021 244±2 113±8 5.68±0.27 1.5±0.5 1.25±0.25 18 V217-48×MU022 240.5±12.5 87.5±7.5 6.59±0.17 1.0±0 1±0 19 S458-2-2-2×MU021 267.5±12.5 109±14 7.33±0.97 1.75±0.75 1±0 20 S458-2-2-2×MU022 274.5±1.5 114±4 6.28±0.63 1.0±0 1.5±0 21 V131-201×MU021 255.5±8.5 110±11 7.07±0.56 1.0 ± 0 1.25 ±0.25 22 V131-201×MU022 243.5±2.5 86.5±0.5 5.27±0.32 1.75±0.75 1±0 23 MU021 275.5±3.5 126.5±2.5 7.29±0.21 1.5±0.5 1±0 24 MU022 274.5±5.5 99±1 6.53±0.55 1.75±0.75 1 ±0 MEAN 251.2 100.6 6.27 1.365 1.177 LSD 21.75 17.32 1. 8527 1.4221 0.4479
Table 4.4 shows mean separation in plant height. there were significant differences between 3
(EC573(R12)C853-14 and entries 9,21,10,13,5,17,22,14,11,2,18,6,2 and 8. However, there was no significant difference between entries 3 (EC573(R12)C853-14 x MU021), 23 (MU021), 20
(S458-2-2-2 x MU022), 24 (MU022), 15 (REGN99/48-2 X MU021), 19 (S458-2-2-2 x MU021),
4 (EC573(R12)C853-14 x MU022), 7 (426-43,Z387-4-1 x mu021) and entry 16 (REGN99/48-2
X MU022). All the other entries showed significant difference in height from the two testers
(table 4.4). The least significant difference (LSD) for ear height shown in (table 4.5) is 17.32.
36
Entries 3 (EC573(R12)C853-14 X MU021), 7 (Z426-43,Z387-4-1 X MU021), 15 (REGN99/48-
2 X MU021), 17 (V217-48 X MU021), 20 (S458-2-2-2 X MU022) and entry 21 (V131-201 x
MU021) were not significantly different from entry 23 (MU021), the tester. All entries except 2,
3 and 6 were significantly different from tester MU022 (entry 24). Turkey‘s protected LSD is not calculated for yield, MSV and GLS as the variance ratios for the entries were not significant
Table 4.4: Mean performance and statistical significance for plant height and ear height in Muguga Entries TEST CROSS PLANT HEIGHT EAR HEIGHT 3 EC573(R12)C853-14 X MU021 283a 132a 23 MU021 275.5ab 126.5ab 20 S458-2-2-2 X MU022 274.5ab 116abc 24 MU022 274.5ab 114bcd 15 REGN99/48-2 X MU021 269abc 113bcd 19 S458-2-2-2 X MU021 267.5abc 110bcd 4 EC573(R12)C853-14 XMU022 266.5abcd 110bcd 7 Z426-43,Z387-4-1 X MU021 263abcde 109cde 16 REGN99/48-2 XMU022 262abcde 107.5cde 9 Z419-5Z443-3 X MU021 258bcdef 107.5cde 21 V131-201 X MU021 255.5bcdef 106cdef 10 Z419-5Z443-3 X MU022 254bcdef 100cdefg 13 V265-80 X MU021 249.5cdefg 99cdefgh 5 V265-4-1 X MU021 245defgh 99cdefgh 17 V217-48 X MU021 244efghi 97.5defgh 22 V131-201 X MU022 243.5efghi 92efghi 14 V265-80 X MU022 243efghi 90fghi 11 V217-5 X MU021 242.5efghi 89fghi 12 V217-5 X MU022 238.5fghij 87.5ghi 18 V217-48 X MU022 230.5ghij 86.5ghi 6 V265-4-1 XMU022 227.5hij 85.5ghi 2 V131-303 X MU022 223.5hij 82hi 8 Z426-43,Z387-4-1 X MU022 222.5ij 79.5i 1 V131-303 X MU021 217j 76i Means followed by same letters do not have significant differences according to Tukey‘s 95% confidence intervals
37
4.1.2.2 Correlation between agronomic traits in Muguga
The phenotypic correlation between the traits plant height (PH), ear height (EH), yield (tha-1),
MSV and GLS are shown in Table 4.5. Plant height (0.5464) and ear height (0.5683) had a significant positive correlation with yield but MSV(-0.2626) and GLS (-0.1105) showed a significantly negative correlation with yield. MSV (-0.0682) was the only trait that showed an insignificant negative correlation with plant height while GLS had a positive non significant correlation to with plant height. MSV showed an insignificant negative correlation with all the traits.
Table 4.5 Phenotypic correlation between plant height, ear height, yield, MSV and GLS in Muguga
Trait Correlation coefficient (r) PH - EH 0.8226 - MSV -0.0682 -0.1642 - GLS 0.0421 0.1734 -0.1196 - YIELD 0.5464 0.5683 -0.2626 -0.1105 - PH EH MSV GLS YIELD P<0.05
4.2 Multiple site analysis in Embu and Muguga Stations
4.2.1 Agronomic traits of crosses between inbred lines and two testers
There were highly significant differences among test crosses at (p<0.01) for plant height (PH) and ear height (EH). There were significant differences among test crosses at (p<0.05) for yield
(appendix 4.4).
38
4.2.2 Mean values of all the agronomic traits measured for the crosses in Embu and Muguga
Table 4.6 shows the mean values of all the agronomic traits measured for all the crosses. There was a large variability for plant height (PH), ear height (EH) and yield in both sites. A non- significant variability for MSV and GLS was noted. The plant height mean ranged from 196 cm
(V131-303×MU022) (Entry 2) to 251.2 cm (EC573(R12) C853-14 x MU022) (Entry 4). The mean plant height for tester MU021 (check) was 248.7 cm which was the highest height of the mean heights from all crosses. The mean ear height ranged 68.5 cm (V131-303×MU022) to
120.5 cm (REGN99/148-2×MU021).Tester MU021 (check) had the highest ear height of 123.8 cm. Generally crosses with tester MU021 had higher grand mean ear heights than those with tester MU022.The mean yield ranged from 4.51 t ha-1 (V131-303×MU022) to 7.21 t ha-1 (V217-
48×MU021). Crosses with tester MU021 had the highest grand mean yield compared to the
-1 crosses with tester MU022.The crosses with high mean yield were 7.15 t ha (EC573[R12]C853-
14×MU021), 7.14 t ha-1 (REGN99/48-2×MU021), 7.17 t ha-1 (S458-2-2-2×MU021) and 7.1 t ha
-1 (V131-201×MU021).The highest mean for MSV scores was 1.38 (Z426-43 Z387-4-
1×MU021) and ( V265-80×MU022) while that for GLS was 1.25.
39
Table 4.6: Mean values of test crosses and two testers for plant height (PH cm), Ear height (EH cm), yield (tha-1), MSV and GLS in Embu and Muguga combined.
Entry TEST CROSSES PH EH YIELD MSV GLS 1 V131-303×MUO21 215.2±6.86 93.5±7.22 6.15±0.59 1.0±0 1.25±0.14 2 V131-303×MU022 196±18.21 68.5±5.95 4.51±0.73 1.25±0.25 1.0±0 3 EC573 (R12)C853-14×MU021 246.2±22.02 120 ± 7.49 7.15±0.89 1.13±0.13 1.13±0.13 4 EC573 (R12)C853-14×MU022 251.2± 12.91 113.5±12.63 6.1±0.45 1.5±0.5 1.13±0.13 5 V265-4-1×MU021 225.2±12.15 95.8±5.11 5.19±0.36 1.0±0 1.25±0.13 6 V265-4-1×MU022 211.5±9.26 85.8±4.09 6.08±0.58 1.0±0 1.25±0.14 7 Z426-43, Z387-4-1×MU021 242.2±16.92 112±5.43 7.03±0.82 1.38±0.38 1.0±0 8 Z426-43, Z387-4-1×MU022 213.2±6.09 88±3.58 5.61±0.43 1.5±0.5 1±0 9 Z419-5 Z443-3×MU021 234.7±15.16 111.5 ±6.36 6.84±0.11 1.25± 0.25 1.25 ± 0.14 10 Z419-5 Z443-3×MU022 241±9.57 101±5.76 6.94±0.72 1.0±0 1.13±0.13 11 V217-5×MUO21 228±10.87 106.8±4.09 6.38±0.24 1±0 1.13± 0.13 12 V217-5×MU022 226.5± 10.05 95.2 ±3.91 6.02±0.55 1.25±0.25 1.25 ± 0.14 13 V265-80×MUO21 230.2±11.65 102±5.18 6.38±0.24 1±0 1.13±0.13 14 V265-80×MUO22 235±10.34 96.8 ±8.67 6.72± 0.26 1.38 ±0.38 1 ± 0 15 REGN 99/48-2×MUO21 247.5±15.11 120.5±11.39 7.14±0.75 1±0 1.25±0.14 16 REGN 99/48-2×MU022 236±16.42 100.8 ± 6.12 6.93 ±0.23 1.13 ±0.13 1.13 ±0.13 17 V217-48×MUO21 225.7±13.23 106.8 ± 5.98 7.21 ±0.90 1.2 5±0.25 1.13 ±0.13 18 V217-48×MU022 231.2±7.98 94.2±7.26 7.02±0.75 1±0 1±0 19 S458-2-2-2×MUO21 248.2±15.17 115±8.87 7.17±0.59 1.38±0.38 1 ± 0 20 S458-2-2-2×MU022 248±15.42 105.2±5.62 6.7±0.45 1±0 1.25±0.14 21 V131-201×MUO21 226.2±19.83 96.8±10.44 7.1±0.29 1±0 1.13±0.13 22 V131-201×MUO22 219.5±15.44 81.8 ± 3.97 5.79±0.34 1.38±0.38 1.0 ± 0 23 MUO21 248.7±15.85 123.8 ± 3.10 7.04± 0.28 1.25±0.25 1.0± 0 24 MU022 239.2±21.37 93.5 ± 6.55 7.15±0.52 1.38±0.38 1.0 ±0 MEAN 232 101.2 6.52 1.18 1.13 LSD 31 25.98 2.03 1.0 0.387
4.2.3. Line by tester analysis
The analysis of variance of test crosses between the inbred lines and the two testers showed
significant differences for plant height, ear height and yield. The source of variation due to lines
was highly significant (p<0.01) for plant height and ear height. Yield was significant
(p<0.05).There was no significant difference of MSV and GLS (Appendix 4.4)
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4.2.4 Correlation between agronomic traits
The phenotypic correlation between plant height (PH cm), ear height (EH cm), yield (t ha -1),
MSV and GLS are shown in table 4.7. Plant height (0.177) showed appositive insignificant correlation with yield, ear height (0.389) had a positive significant correlation with yield. MSV and GLS were negatively correlated with yield. All the studied traits were positively correlated with plant height (Table 4.7).
Table 4.7: Phenotypic correlation between plant height (PH cm), ear height (EH cm), yield (t ha-1), MSV and GLS in Embu and Muguga combined
Trait Correlation coefficient PH - EH 0.593 - MSV 0.230 -0.108 - GLS 0.157 0.043 0.06 - YIELD 0.177 0.389 -0.237 -0.192 PH EH MSV GLS
There was significant difference among the lines, testers and their F1 hybrid in the traits studied in the Embu and Muguga (Appendix 4.4).
4.3 Combining ability
The best general combiner for plant height was Z419, Z443-3 (+20.75), while for ear height were
EC573(R12) C853-14 and REGN99/48-2 both with GCA of +12.25 and a negative GCA for yield. The best GCA for yield was V217-48 (1.40). V131-201 (-0.215) is the best general combiner for MSV. Five lines were good general combiners for GLS; V131-201, Z419-5, Z443-
3, V217-48, S458-2-2-2 and V131-201, all the five lines had a GCA of 0.08 (Table 4.8)
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Table 4.8: General combining ability (GCA) for inbred line based on plant height (PH, cm), ear height (EH, cm), yield (t ha-1), MSV and GLS in Embu county LINE TRAITS PH (cm) EH (cm) Yield (t ha-1) MSV GLS V131-303 -23 -20.25 -1.01 +0.20 +0.05 EC573(R12)C853-14 +8.75 +12.25 -0.71 -0.05 +0.04 V265-4-1 -13.5 -9.75 -0.93 +0.38 +0.30 Z426-43,Z387-4-1 -1.25 +2.5 +0.56 +0.07 +0.08 Z419-5, Z443-3 +20.75 +11.25 +0.78 -0.05 -0.08 V217-5 0 +2.5 +0.01 +0.13 +0.65 V265-80 +5.0 +4 -0.22 +0.25 -0.08 REGN99/48-2 +4.0 +12.25 -0.26 -0.02 +0.05 V217-48 +5.75 -0.75 +1.40 +0.03 -0.08 S458-2-2-2 +11.25 +7.25 +0.36 -0.09 -0.08 V131-201 -17.75 -21.25 +0.02 -0.22 -0.08 MU021 +1.95 +5.07 +0.02 -0.09 -0.03 MU022 -1.95 -5.27 -0.12 -0.09 -0.03
The best general combiner for plant height and ear height in Muguga was EC573(R12)C853-14 with a GCA of; (+25.659 and +20.23 respectively). The best general combiner for yield was
REGN 99/48-2 with a GCA of +1.18. V265-4-1 (-0.34) was the best general combiner for MSV.
The following five lines were best general combiners for GLS; EC573(R12)C853-14, V265-4-
1,V265-80, V217-48 and V131-201. All the five inbred lines had a negative GCA of -0.09
(Table 4.9).
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Table 4.9: General combining ability (GCA) for inbred line based on plant height (PH, cm), ear height (EH, cm), yield (t ha-1), MSV and GLS in Muguga, Kiambu county
LINE TRAITS PH (cm) EH (cm) Yield (t ha-1) MSV GLS V131-303 -28.84 -18.77 -1.25 -0.09 +0.16 EC573(R12)C853-14 +25.66 +20.23 +0.86 +0.28 -0.09 V265-4-1 -12.84 -9.77 -0.74 -0.34 -0.09 Z426-43,Z387-4-1 -6.34 -3.52 -0.83 +0.53 +0.03 Z419-5, Z443-3 +6.91 +0.23 +0.15 -0.09 +0.16 V217-5 -8.59 -1.52 -0.51 -0.09 +0.03 V265-80 -2.84 -6.27 +0.66 +0.03 -0.09 REGN99/48-2 +16.41 +7.98 +1.18 -0.22 +0.03 V217-48 -11.84 +0.73 -0.08 -0.09 0.09 S458-2-2-2 +21.91 +11.98 +0.59 +0.03 +0.03 V131-201 +0.41 -1.27 +0.04 +0.03 -0.09 MU021 +4.91 +8.53 -0.32 -0.09 +0.03 MU022 -4.91 -8.34 -0.32 -0.09 -0.03
Table 4.10: shows the Specific combining ability of hybrids in Embu. The best specific combiner for plant height (+20.55) and ear height (+14.98) was V131-303 x MU021. The second best specific combiner hybrid for both plant height and ear height was EC573(R12)C853-14 X
MU022 with SCA of +15.21 and +11.02 respectively.V131-303 x MU021 (+1.18) was the best specific combiner for yield. (Table 4.10).
43
Table 4.10: Specific Combining ability (SCA) estimates for hybrids based on plant height (PH, cm), ear height (EH, cm), yield (tha-1), MSV and GLS in Embu
HYBRID PH (cm) EH (cm) Yield (t ha-1) MSV GLS V131-303 x MU021 +20.55 +14.96 +1.18 +0.16 +0.09 V131-303 x MU022 -20.55 -14.98 -1.18 -0.16 -0.09 EC573(R12)C853-14 x MU021 -15.21 -11.02 -0.01 -0.09 -0.03 EC573(R12)C853-14 x MU022 +15.21 +11.02 +0.01 +0.09 +0.03 V265-4-1 x MU021 +3.05 -5.52 -1.05 -0.09 -0.03 V265-4-1 x MU022 -3.05 +5.52 +1.05 +0.09 +0.03 Z426-43,Z387-4-1 x MU021 +6.80 +4.73 +0.83 +0.03 -0.03 Z426-43,Z387-4-1 x MU022 -6.80 -4.73 -0.83 -0.03 +0.03 Z419-5 Z443-3 x MU021 +4.80 -2.27 -0.73 +0.03 +0.09 Z419-5 Z443-3 x MU022 -4.80 +2.52 +0.73 -0.03 -0.09 V217-5 x MU021 -2.46 -1.77 -0.33 -0.09 -0.16 V217-5 x MU022 +2.46 +1.77 +0.33 +0.09 +0.16 V265-80 x MU021 -9.96 -4.27 -0.49 +0.03 -0.03 V265-80 x MU022 +9.96 +4.27 +0.49 -0.03 +0.03 REGN99/48-2 x MU021 +6.05 +5.96 -0.08 -0.09 -0.03 REGN99/48-2 x MU022 -6.05 -5.98 +0.08 +0.09 +0.03 V217-48 x MU021 -14.21 -5.52 +0.55 +0.03 -0.03 V217-48 x MU022 +14.21 +5.52 -0.55 -0.03 +0.03 S458-2-2-2 x MU021 +1.80 +6.98 -0.16 +0.03 +0.09 S458-2-2-2 x MU022 -1.80 -6.98 +0.16 -0.03 -0.09 V131-201 x MU021 -1.21 -2.02 +0.30 +0.03 +0.09 V131-201 x MU022 +1.21 +2.02 -0.30 -0.03 -0.09
In Muguga, the best specific combiner for plant height was Z426-43,Z387-4-1 X MU021
(+15.34) while the best specific combiner for ear height was S458-2-2-2 X MU022 (+10.84).
The highest SCA effect observed for grain yield was V217-48 X MU022 (+0.78). (Table 4.11).
44
Table 4.11: Specific Combining ability (SCA) estimates for hybrids based on plant height (PH, cm), ear height (EH, cm), yield (tha-1), MSV, and GLS in Muguga, Kiambu county.
Hybrid PH (cm) EH (cm) YIELD (t-ha-1) MSV GLS V131-303 x MU021 -8.16 3.76 +0.03 -0.16 -0.16 V131-303 x MU022 +8.16 +3.59 -0.03 +0.16 +0.16 EC573(R12)C853-14 x MU021 +3.34 +3.75 -0.04 -0.28 +0.09 EC573(R12)C853-14 x MU022 -3.34 -4.41 +0.04 +0.28 -0.09 V265-4-1 x MU021 +3.84 +1.75 -0.28 +0.09 +0.09 V265-4-1 x MU022 -3.84 -1.91 +0.28 -0.09 -0.09 Z426-43,Z387-4-1 x MU021 +15.34 +5.50 +0.17 -0.03 -0.28 Z426-43,Z387-4-1 x MU022 -15.34 -5.66 -0.17 +0.03 +0.28 Z419-5,Z443-3 x MU021 -2.91 -0.76 +0.26 +0.16 +0.09 Z419-5,Z443-3 x MU022 -2.91 +0.53 -0.26 -0.16 -0.09 V217-5 x MU021 -2.91 -0.51 +0.27 -0.16 -0.03 V217-5 x MU022 +2.91 +0.34 -0.27 +0.16 +0.03 V265-80 x MU021 -1.66 -4.26 -0.53 -0.28 +0.09 V265-80 x MU022 +1.66 +4.09 +0.53 +0.28 -0.09 REGN99/48-2 x MU021 -1.41 -0.01 +0.11 -0.03 +0.22 REGN99/48-2 x MU022 +1.41 -0.16 -0.11 +0.03 -0.22 V217-48 x MU021 +1.84 +4.25 -0.78 +0.16 +0.09 V217-48 x MU022 -1.84 -4.41 +0.78 -0.16 -0.09 S458-2-2-2 x MU021 -8.41 -11.01 +0.21 +0.47 -0.28 S458-2-2-2 x MU022 +8.41 +10.84 -0.21 -0.47 +0.28 V131-201 X MU021 +1.09 +3.25 +0.58 -0.28 +0.09 V131-201 x MU022 -1.091 -3.41 -0.58 +0.28 -0.09
All the traits showed significant mean squares of the general and specific combining abilities The
GCA effects were more than the SCA effects. The GCA effects were more than the SCA effects for Plant height and yield but equal for ear height and GLS. SCA mean squares were more than
GCA mean squares for MSV (Appendix 4.5)
4.4 Heterosis for grain yield
The percentage heterosis (% H) and specific combining ability (SCA) value for yield are shown in Table 4.12. Generally all the hybrids formed with MU022 showed higher heterosis compared with hybrids formed with tester MU021 except V265-4-1 X MU022 (-14.97). Percentage heterosis for yield ranged from -36.92 to 5.79 with the hybrid V131-303 X MU022 having the
45 highest negative percentage heterosis over better parent. Generally, all the hybrids showed significant negative (p< 0.05) % H for yield with the exception of S458-2-2-2 X MU021 and
V131-201 X MU022 which showed significant positive (p <0 05) % H.
Table 4.12: Percentage heterosis (%H) and specific combining ability (SCA) for yield in Embu and Muguga, Kiambu counties combined.
Line %H Yield Yield SCA MU021 MU022 MU021 MU022 V131-303 -13.98 -36.92 +1.18 -1.18 EC573 (R12)C853-14 0 -13.43 -0.01 +0.01 V265-4-1 -27.41 -14.97 -1.05 +1.05 Z426-43,Z387-4-1 -1.4 -2.1538 +0.83 -0.83 Z419-5,Z443-3 -4.34 -21 -0.73 +0.73 V217-5 -10.77 -15.804 -0.33 +0.33 V265-80 -10.77 -6.0139 -0.49 +0.49 REGN99/48-2 -0.139 -3.0769 -0.08 +0.08 V217-48 -0.839 -1.818 +0.55 -0.55 S458-2-2-2 0.2797 -6.294 -0.16 +0.16 V131-201 -0.6993 5.79 +0.30 -0.30
4.5 Heterotic groups
The lines showing negative SCA effects with tester MU021and positive with MU022 were put in heterotic group A. These were; EC573(R12)C853-14, V265-4-1, V265-80, V217-5, S458-2-2-2.
Z419-5,Z443-3 and REGN99/48-2. They belong to the same heterotic group with tester MU021
(heterotic group A) while lines V131-303, Z426-43,Z387-4-1, V217-48 and V131-201 had negative effects with tester MU022 but positive SCA with tester MU021 hence belong to the same heterotic group as MU022 (heterotic group B), (Table 4.13).
46
Table 4.13: Classification of germplasm into heterotic groups based on SCA effects for grain yield. Entry MU021 MU022 Heterotic group V131-303 1.1832 -1.1832 B EC573 (R12)C853-14 -0.0118 0.0118 A V265-4-1 -1.0543 1.0543 A Z426-43,Z387-4-1 0.8282 -0.8282 B Z419-5,Z443-3 -0.7318 0.7318 A V217-5 -0.3268 0.3268 A V265-80 -0.4918 0.4918 A REGN99/48-2 -0.0818 0.0818 A V217-48 0.5507 -0.5507 B S458-2-2-2 -0.1618 0.1618 A V131-201 0.2982 -0.2982 B
47
CHAPTER FIVE
DISCUSSION, CONCLUSION AND RECOMMENDATION
5.1 Discussion
Significant differences were observed among the inbred lines, the testers and their F1 hybrids for the traits studied, indicating the presence of genetic differences among the genotypes. Plant and ear height were strongly correlated with grain yield. This agrees with Martin and Russel (1984),
Burak and Magoja (1991) and Singh and Dash (2000). The inbred lines with positive GCA in height which contributed positively to yield included Z419-5, Z443-3, V217-48 and S458-2-2-2 in Embu but in Muguga, they were EC573(R12 ) C853-14,Z419-5,Z443-3, REGN99/48-2 and
S458-2-2-2.The tallest hybrid in both sites did not produce highest yields. This could be explained by the fact that yield is a complex trait determined by factors that are genetic, environmental or both. The best general combiner for plant height in Embu was Z419-5, Z443-3.
The best specific combiner hybrid for plant height in Embu was V131-303 X MU021 but in
Muguga it was Z426-43,Z443-3 X MU021.
Plant height is an indicator of vigour of the plant. A vigorous plant is expected to make better production of assimilate which could lead to higher yield. According to Machado et al. (2002), plant height explained 61 % of the grain yield in corn. The average height of a maize plant is 2.5 m though some natural strains can grow to 12 m high (Karl, 2013). The mean plant height of genotypes in Embu was 212.7 cm and 251.2 cm for Muguga.
The ears should develop in the mid section of the plant between the stem and leaf sheath. High ear height subjects maize to lodging (Karl, 2007). The mean ear height in Embu was 101.8 cm while in Muguga it was 100.6 cm.
48
The GCA and SCA effects were significant for all the characters indicating the importance of both additive and non additive gene effects in their inheritance. This in agreement with reports of
Malla et al. (2009). The (GCA/SCA ratios of >1) in plant height and yield indicate preponderance of additive genes in controlling these traits.In Embu the best general combiner for yield was V217-48 and the best specific combiner was V131-303 X MU021. In Muguga the best general combiners for yield was REGN 99/48-2 and the hybrid with the best specific combining ability was V217-48 X MU022. Sprague and Tatum (1942), explained the importance of GCA in preliminary screening of lines from a large number of lines in a breeding program. SCA represent the final stage in selection of inbred lines.
In the present study, cross combinations generated from parents having different types of GCA effects either positive significant, negative significant and non significant positive or negative and their corresponding SCA effects were observed. Almost all types of parental combinations for combining ability produced hybrids with positive and significant SCA for grain yield. The best general combiner for yield in Embu was V217-48 but was not the best specific combiner.
Parents of low GCA still produced high and positive SCA, V131-303 had a high negative GCA but produced the highest positive SCA value in combination with tester MU021 which had a higher positive GCA. These findings are in agreement with those of Venkatesan et al. (2007),
Rosamma and Vijayakumar (2005), Shanthi et al. (2003) and Sharma et al. (2005). The above study revealed that there is no direct relation between GCA effects of parents and SCA effects of hybrids. For the low x low GCA combinations that produced hybrids with high and positive
SCA, it can be attributed to over-dominance or epistatic gene action. High x low GCA combinations with positive SCA can be attributed to additive and dominance gene action. GCA is due to additive gene action where as SCA is mostly due to over-dominance.
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The study showed that, plant height, ear height and grain yield were governed by non additive gene action since crosses of parents of low GCA still produced high and positive SCA. It was observed that high x low combiners were the best combinations V131-303 X MU021. Tester
MU021 had a positive GCA but V131-303 had the lowest and negative GCA but produced the highest positive SCA effects. The germplasm were classified into heterotic groups A and B basing on the SCA effects on yield. Similar findings on heterotic groupings were reported by
Mosisa et al. (1996), Santos et al. (2001), Pswarayi and Vivek, (2004) and Menkir et al. (2004).
5.2 Conclusion
Morphological traits related to yield showed significant difference across the sites. It is therefore possible to select hybrids for wide adaptations by looking for non cross-over Genotype X
Environmental interaction (GEI) or preferably the absence of GEI. The correlation analysis showed positive relationship between plant height and ear height with yield but the various heights of the different genotypes had different contribution towards the yield (Table 4.10). Most hybrids had a mean of over 200cm which is within the recommended plant height for grain yield.
The GCA and SCA effects were significant for plant and ear height, as well as yield indicating the importance of both additive and non additive gene effects in their inheritance. In Embu the best general combiner for yield was V217-48 and the best specific combiner wasV131-303 X
MU021. In Muguga the best general combiners based on yield was REGN 99/48-2 and the hybrid with the best specific combining ability for yield was V217-48 X MU022. High yielding hybrids in Embu were Z426-43 Z387-4-1 X MU021, Z419-5Z443-3 X MU022, V217-48 X
MU021, V217-48 X MU022, S458-2-2-2 X MU022 and V131-201 X MU021. In Muguga, the best were EC573(R12)C853-14 X MU021; REGN99/48-2 X MU021 and S458-2-2-2 X
MU021. The lines selected for Muguga combined well only with tester MU021 while in Embu,
50 the lines combined well with the two testers. Hybrid combination S458-2-2-2 with any of the testers did well across the sites.
The productivity of an inbred line is determined by its ability to transmit desirable genes to its hybrid progenies. The hybrids showed both positive and negative SCA effects. The positive SCA effects implied that there was positive interaction between the two parents. Such gene interaction leads to the expression of heterosis. An inbred line that expressed negative SCA effects when crossed to a tester implied that they belonged to the same heterotic group. In order to maximize the genetic diversity and therefore heterosis during hybrid development, one parent should come from the inbred lines belonging to heterotic group A, while the other parent should be from inbred line belonging to heterotic group B. In the case of development of synthetic varieties, inbred lines belonging to the same group should be used. Testers can therefore provide precision in discrimination against the lines.
Negative GCA effects for disease scores indicate resistance. The following inbred lines had negative GCA effects for Maize streak virus in Embu: EC573(R12)C853-14; Z419-5,Z443-3,
REGN99/48-2, S458-2-2-2, V131-201 and tester MU021. Negative GCA effect for GLS was shown by the following inbred line: Z419-5,Z443-3, V265-80, V217-48, S458-2-2-2, V131-201 and tester MU021. In Muguga the lines that showed negative GCA effects for MSV were: V131-
303, V265-4-1, Z419-5,Z443-3, V217-48, REGN 99/48-2 and the two testers. The lines that showed negative GCA effects for GLS were as follows: EC573(R12)C853, V265-4-1, V265-80,
V217-48, V131-201 and tester MU022. It is possible to develop disease resistant varieties for both Embu and Muguga.
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5.3 Recommendation
Inbred lines Z426-43Z387-4-1, Z419-5Z443-3, V217-48, S458-2-2-2 and V131-201 can
further be developed for farmers in Embu.
Three inbred lines that showed high yields in Muguga are EC373(R12)C853-14,
REGN99/48-2 and S458-2-2-2.These can further be developed and released to farmers in
Muguga.
Based on this study inbred line S458-2-2-2 should be recommended for further evaluation
and eventually released to farmers in the two counties.
V217-48 and V265-4-1 which were resistant to the two foliar diseases and out-
performed the two checks in yield should be included in the development of high yielding
disease resistant varieties in Muguga.
In Embu, Z419-5Z443-3, S458-2-2-2 and V131-201 showed resistance to both MSV and
GLS and therefore should be included in the development of resistance varieties in Embu.
There is need to further study the materials for stability of characters studied and
eventually release to farmers in the two counties.
52
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APPENDICES
Appendix 4.1: Mean squares for plant height (PH cm), ear height (EH cm) and yield (t ha- 1), in Embu MEAN SQUARES Source df PH(cm) EH(cm) Yield(tha-1) Replications 1 2730.1 1323 0.789 Treatments 23 442.3** 451.6** 1.879* Error 23 19.24 16.23 1.12 Cv % 19.24 15.9 16.6 Overall mean 212.7 101.8 6.77 *, ** significant at p<0.05 and p<0.01 level respectively; ns = non significant
Appendix 4.2: Mean squares for plant (PH cm) ear height (EH cm), and yield (t ha-1), in Muguga Kiambu county
MEAN SQUARES Source of Variance df PH EH YIELD Replication 1 1430.1 320.33 0.0065 Treatment 23 699.1** 428.66** 1.6016* Error 23 10.51 8.37 0.898 CV% 4.2 8.3 14.3 Overall mean 251.2 100.6 6.27 *,** significant at p<0.05 and p<0.01 level respectively.ns-non significant
Appendix 4.3: Kruskal-Wallis Test of MSV and GLS scores in Embu and Muguga
EMBU MUGUGA MSV GLS MSV GLS Chi-square 0.000 27.348 14.161 27.736 df 21 21 21 21 p-value 1.000 0.241 0.922 0.226
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Appendix 4.4: Mean squares for plant (PH cm) ear height (EH cm), and yield (t ha-1) in Embu and Muguga.
Source of variation MEAN SQUARES Df PH EH YIELD Replications 1 4056.0 1472.7 0.33 Sites 1 35728.2** 30.4ns 5.93 * Treatments 23 792.7** 697.4** 2.03*
Site.treatments 23 348.8** 182.9ns 1.45 Error 15.41 12.91 1.009 CV % 6.6 12.8 15.5 Overall mean 232.2 101.2 6.52
*,** Significant at p<0.05 and p<0.01 level respectively.
Appendix 4.5: Mean squares of Line x tester analysis for plant (PH cm) ear height (EH cm), yield (t ha-1), MSV and GLS in Embu and Muguga.
MEAN SQUARES Source Df PH EH YIELD MSV GLS Replication 1 2730.84 1323 1.053 1 1.161 Line 10 527.068** 586** 2.061* 1* 0.0534* Tester 1 15.364** 1223.273** 0.5021* 1* 0.0511* Line x Testers 10 377.614** 218.173** 1.803* 1* 0.0261* Residual 23 370.083 235.87 1.608 1 0.031
*,** Significant at p<0.05 and p<0.01 level respectively.
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Appendix 4.6: Mean squares of general/ specific combining abilities of inbred lines and hybrids quantitative traits in Embu and Muguga Kiambu counties
MEAN SUM OF SQUARES Source of df PH EH(cm) t ha-1 MSV GLS Variance (cm) GCA lines 10 665.5* 198* 760.23** 198** 197.997** SCA 22 198.03* 198* 198** 200.19** 197.999** Error 66 80.7 55.66 12.18 13.71 5.61 GCA/SCA ratio 3.361 1 3.84 0.989 0.999
*,** Significant at p<0.05 and p<0.01 level respectively.