COMBINING ABILITY OF EARLY AND INTERMEDIATE MAIZE (Zea mays L.) INBRED LINES FOR DROUGHT TOLERANCE USING LINE BY TESTER ANALYSIS

ABSTRACT
Maize (Zea mays L.) is an annual plant belonging to the family (Graminae or Poaceae). It is a major cereal crop in West Africa, accounting for slightly over 20% of all food crops produced for domestic production in the sub-region. It is one of the most important cereals in Ghana, which is cultivated in all the agro-ecological zones. The objectives of this study were to estimate the general and specific combining ability effects of the inbred lines, determine the mode of gene action controlling grain yield and drought tolerance. A study was undertaken to assess the combining ability of 17 early and 26 intermediate maize inbred lines and one check for each genotypic group for drought tolerance using line by tester (line x tester) analyses. This trial was conducted in the screen house of the Department of Horticulture, KNUST in 2016. A randomized complete block design with three replications was used in the experiment. Some inbred lines with desirable general combining ability (GCA) effects for the studied traits were identified under drought-stress condition. For early maize genotypes inbred lines L1 followed by L4 were best general combiners for number of kernel row per ear, number of kernels per row, cob weight and grain yield under drought-stress condition. For intermediate maize genotypes under drought-stress condition, the line L4 was best general combiner for grain yield, cob weight, number of kernel rows per ear and ear diameter for their positive and significant GCA effects. These lines could be selected for their good traits to develop high yielding hybrids and for further exploitation in a breeding programme. Hybrid combination, L7 x T2 and L8 x T1 under well-watered condition and L6 x T2 under drought-stressed condition for intermediate maize genotypes were good specific combiners for grain yield while, for early maize genotypes, crosses were not significant for yield under well-watered and drought-stress conditions. The low ratio of 2gca/ 2sca, in the current study showed the preponderance of non-additive gene actions for almost all the traits for early and intermediate maize genotypes. The inbred lines L1 (S6-15-22) and L4 (CML538) for early maize maturity genotypes and L4 (CML502) for intermediate maize maturity genotypes were identified as best general combiners that can withstand drought-stress. These lines showed positive and significant GCA effects for yield and yield-related traits under drought-stress condition. The cross L6 X T2 was identified as good specific combiners that can withstand drought-stress for the positive and significant SCA effect for grain yield and yield-related traits under drought-stress condition.


Positive and significant mid-parent heterosis was observed under drought-stress condition for early and intermediate maize maturity genotypes. The crosses L2 X T1 and L3 X T2 observed high mid-parent heterosis for early and intermediate maturity genotypes, respectively. Generally, the results of the current study identified crosses with good level of heterosis, inbred lines with good GCA effects and cross combinations with desirable SCA effect for the traits studied. The results indicate the possibility of developing desirable cross combinations through crossing and or recombination of inbred lines with desirable traits of interest. Hence, the information from this study could be useful to researchers who would like to develop high yielding varieties of maize under drought-stress condition.


TABLE OF CONTENTS
ABSTRACT
LIST OF ABBREVIATIONS

CHAPTER ONE
1.0 INTRODUCTION

CHAPTER TWO
2.0 LITTERATURE REVIEW
2.1 Botany and description of maize
2.2 Importance of maize
2.3 World maize production
2.4 Challenges of drought to maize production
2.5 Drought stress effects on maize
2.6 Adaptation of maize to drought
2.6.1 Strategy to drought adaptation or tolerance
2.6.2 Drought escape
2.6.3 Drought tolerance
2.7 Inbred lines development
2.8 Concept of line x tester analysis and combining ability
2.8.1 Line x tester analysis
2.8.2 Combining ability
2.9 Heterosis

CHAPTER THREE
3.0 MATERIALS AND METHODS
3.1 Experimentation site
3.2 Experimental materials
3.3 Design and Experimental management
3.4 Soil sampling and analyses
3.5 Planting
3.6 Irrigation schedule
3.7 Fertilizer application
3.8 Statistical analyses
3.8.1 Analysis of variance
3.8.2 Combining ability analysis
3.8.3 Genetic components
3.8.4 Proportional contribution of lines, testers, and line by tester interaction to the total variation
3.8.5 Heterosis

CHAPTER FOUR
4.0 RESULTS
4.1 Soil analysis
4.2 Analyses of Variance (ANOVA)
4.2.1 Early maturity maize genotypes
4.2.2 Intermediate maturity maize genotypes
4.3 Estimates of general combining ability effects
4.3.1 Early maturity maize genotypes
4.3.2 Intermediate maturity maize genotypes
4.4 Specific combining ability effects
4.4.1 Early maturity maize genotypes
4.4.2 Intermediate maturity maize genotypes
4.5 Estimates of genetic component and proportional contribution to the total variances
4.5.1 Early maturity maize genotypes
4.5.2 Intermediate maturity maize genotypes
4.6 Mean performances of genotypes and heterosis
4.6.2 Intermediate maturity maize genotypes

CHAPTER FIVE
5.0 DISCUSSION
5.1 Analyses of variance for early and intermediate maturity maize genotypes
5.2 General combining  ability  effect  for  early  and  intermediate  maturity  maize genotypes
5.3 Estimates of specific combining ability for early and intermediate maturity maize genotypes
5.4 Estimates of genetic component and contributions to the total variances for early and intermediate maturity maize genotypes
5.5 Mean performances and heterosis for early and intermediate maturity maize genotypes

CHAPTER SIX
6.0 CONCLUSIONS AND RECOMMENDATIONS
REFERENCES


CHAPTER ONE
1.0 INTRODUCTION
Maize (Zea mays L.) is an annual plant belonging to the family Graminae or Poaceae (Sprague and Dudley, 1988). It is a major cereal crop in West Africa, accounting for slightly over 20% of all food crops produced for domestic consumption in the sub-region (IITA, 2000). It is cultivated in all the agro-ecological zones of Ghana (Fening et al., 2011). Worldwide, maize is currently the third most traded cereal, after wheat and rice, with more than 160 million hectares cultivated every year (FAOSTAT, 2010). The production was estimated to be 985 million tons for the 2012/2013 season an increase of 9% from 2011/2012 (Brandt, 2013).

According to Badu-Apraku et al. (2011), in West and Central Africa (WCA), maize is consumed directly and serves as major staple diet for some 200 million people, providing about 15% of the total caloric intake of rural and urban consumers, while in developed countries, it is mainly used as livestock feed (DuPlessis, 2003). Industrially, maize is used to produce alcohol, starch, pulp, abrasive, and oil in the pharmaceutics and recently for fuel production (Morris, 2007; Acharya and Young, 2008).

The demand for maize in developing countries is expected to be about 504 million tons by 2020 and this is expected to exceed the demand for both wheat and rice (IFPRI, 2000). To meet this demand, there is a need for increased maize production in the developing countries while maintaining the same land resources since population growth and environmental conditions limit the opportunity for increasing maize area (Pingali and Pandey, 2001). The need to increase maize production in developing countries is challenged by a number of constraints including both abiotic and biotic stresses. Among the major abiotic stresses limiting tropical maize production are drought and low soil fertility. Drought is known to cause substantial reduction in the economic yield of crop plants, a major threat to food security, sustainability of production systems, and the well-being of people living in drought-prone areas. It adversely affects the lives of 2.6 billion people (43% of the world population) that are engaged in agriculture (Saxena et al., 2002). Possibly due to climate change, drought effects on maize production are generally severe in the dry Savanna zone of West Africa (Fajemisin et al., 1985). This is because rainfall in this region is irregular in terms of timing (can start early or very late in the season), quantity (some times less than 600 mm/annum) and distribution (could be poorly distributed) (Izge and Dugje, 2011). Most tropical maize is produced under rain fed conditions, and in area where drought is considered to be the most important abiotic constraint to production (CIMMYT, 1999).

Drought at any stage of crop development affects production, but grain yield losses can be greater if the drought stress occur at the most drought-sensitive stage of crop growth, such as flowering and grain filling. Drought stress can reduce yield by 50% when it occurs at flowering period, by 21% when it happens at the grain filling stage (Denmead and Shaw, 1960), and by 90% when it strikes from few days before tassels emergence to the beginning of grain filling (NeSmith and Ritchie, 1992).

Drought would intensify in the years ahead in response to climate change (Acquaah, 2012), Therefore, the survival of resource-poor, small scale maize growers in sub Saharan Africa who cultivate drought-susceptible maize varieties with little or no access to irrigation facilities has become a great challenge.


According to FAO (2006) and Derera et al. (2008), additional irrigation could possibly improve maize production in drought prone areas but in general, most rain fed farmers are resource poor, smallholders, and have a limited capacity to adopt high-input technologies (Bänziger and Diallo, 2001; FAO, 2006). A better approach to help these resource poor subsistence farmers is by using varieties that tolerate or escape the periodic droughts which befall the region.

One of the most important conditions for identifying high yielding hybrids is the information about parents’ genetic structure and their combining ability (Ceyhan, 2003). The choice of selection and breeding method to be used for genetic improvement of crop plants therefore, will depend on the magnitude of genetic variability and the nature of gene action leading the inheritance of desirable traits (Aminu and Izge, 2013).

Line x tester analysis method (Kempthorne, 1957) is a tool widely used by plant breeders to generate reliable information on the general and specific combining ability effects and aids in selecting desirable parents and crosses. This method has been used in maize breeding by several workers and continues to be applied in quantitative genetic studies in maize (Rawlings and Thompson, 1962; Joshi et al., 2002; Sharma et al., 2004). The effectiveness of this method depends mainly upon the type of tester used in the evaluation. According to Hallauer (1975), a suitable tester should be simple in use, provide information that correctly classifies the relative merit of lines, and increases the genetic gain. Although, it is difficult to identify testers having all these characteristics, it can help to provide information to estimate the combining ability and also the type of gene action involved in the expression of yield and yield related traits.

Therefore, in the present study, the main objective was to undertake analysis of 17 early and 26 intermediate maize inbred lines for grain yield and drought tolerance. The specific objectives were to:

assess the general and specific combining ability of the parents and hybrids for yield and drought tolerance,

determine the nature of gene action controlling the traits of yield and drought tolerance of the inbred lines;

identify parents and hybrids that can withstand drought stress, and

estimate heterosis for yield and drought stress.

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Item Type: Ghanaian Postgraduate Material  |  Attribute: 134 pages  |  Chapters: 1-5
Format: MS Word  |  Price: GH50  |  Delivery: Within 30Mins.
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