ABSTRACT
Nsukka yellow pepper genotypes were evaluated in 2009 and 2010 planting seasons to determine the pattern of genetic variability in its population. The initial collection comprising eighteen genotypes were assembled from the local farmers and evaluated in 2009 planting season. Forty nine promising genotypes were selected on individual plant basis and re-evaluated in 2010 planting season. The results of the performance of the genotypes in both years showed that there was considerable variability in the population with respect to qualitative and quantitative traits. The high coefficients of variation observed in most of the quantitative traits showed that there is a wide scope for improvement in the germplasm. The results of the principal component analysis (PCA) in 2009 planting season revealed that, the first four principal components accounted for 80.87% of the total variation in the population. The number of fruits per plant, total fruit weight and fruit yield were identified as the most effective traits for genotype detection and discrimination. The results of the cluster analysis based on the traits associated with the first and second principal components classified the eighteen genotypes into three groups, A, B, C and an outlier (Ny-15). The groups had a coefficient of similarity of about 0.850. A comparison of the cluster means showed that Cluster A comprised six genotypes characterized with moderate fruit yield; Cluster B had eight genotypes endowed with early flowering and poor fruit yield; cluster C consisted of three genotypes with high potentials for fruit set and yield. The outlier, showed the best adaptation with respect to all the traits studied. Similarly, the 2010 data were also subjected to PCA, the results showed that the first four principal components explained 73.19% of the total variation in the population and implicated the fruit girth, number of primary branches per plant, number of fruits per plant, total fruit weight and fruit yield as the most discriminatory traits accountable for the genetic divergence in the germplasm. The scatter plot based on the traits associated with the first two principal components differentiated the forty nine genotypes into four clusters, A, B, C and D. Cluster A comprised 21 genotypes with average performance in yield; cluster B consisted of 3 genotypes characterized with tall plants, early flowering and poor yield. Cluster C had 23 genotypes associated with moderate yield, while cluster D comprised two genotypes endowed with the best agronomic and yield potentials. The results of the correlation analysis showed that, number of fruits per plant had highly significant correlation with fruit yield in 2009, whereas the associations between yield and the other remaining traits were positive but non-significant. In 2010 however, all but fruit length and plant height significantly correlated with fruit yield. The path coefficient analysis implicated number of fruits per plant and average fruit weight as having highest direct positive effects on fruit yield in both years. Analysis of the biochemical composition of five promising Nsukka yellow pepper genotypes showed a wide range of variation for ascorbic acid from 183.0-400.0 mg/100g, while a lower variation was observed for capsaicin, ranging from 0.32 mg/100g in Ny-08-2 to 0.405 mg/100g in Ny-15-3. Thirty nine genotypes with promising agronomic and breeding potentials were selected for further breeding work.
TABLE OF CONTENTS
Title page – – – – – – – – – – i
Certification – – – – – – – – – – ii
Dedication – – – – – – – – – – iii
Acknowledgement – – – – – – – – – iv
List of co-authored articles from this work – – – – – – v
Table of Contents – – – – – – – – – vi
List of Tables – – – – – – – – – – vii
List of Figures – – – – – – – – – – ix
List of plates – – – – – – – – – – x
Abstract – – – – – – – – – – xi
Introduction – – – – – – – – – – 1
Literature Review – – – – – – – – – 5
Materials and Methods – – – – – – – – 22
Results – – – – – – – – – – – 34
Discussion – – – – – – – – – – 77
Conclusion – – – – – – – – – – 93
References – – – – – – – – – – 95
Appendices – – – – – – – – – – 107
CHAPTER ONE
INTRODUCTION
The production of indigenous vegetables is an important component of the subsistence farming system generally practiced in West Africa. Among the important vegetable crops commonly cultivated in Nigeria, pepper occupies the third position after onion and tomato (Uzo, 1984). It is an ancient vegetable crop whose production is presently on the increase. Peppers are cultivated for the fruits which are consumed fresh or in dried forms. It is an indispensable spice commodity and an integral component of many cuisines in the world due to its appealing flavor, taste and pungency (Bosland and Votava, 2000). Pepper accounts for 20% of the average daily vegetable in-take either as soups or as condiments in the diets of Nigerians (Erinle, 1989).
Pepper belongs to the family, Solanaceae and the genus, Capsicum. According to Bosland et al. (1996), Mexico is the primary centre of diversity while, the secondary diversity centre exists in Guatemala. Of the thirty species recognized in this genus, only five have been domesticated (Bosland and Votava, 2000). Worldwide, the production of pepper has reached 21.3 million tonnes from an estimated area of 1.6 million hectares with China being the largest producer. Nigeria accounts for more than 50% of the 1 million tonnes believed to be produced in Africa (FAO, 2001). Therefore, Nigeria is one of the important countries in the world for pepper genetic resources given the different types that are presently cultivated.
For many years, the farmers in Nsukka agricultural zone have engaged in the cultivation of Nsukka yellow pepper and its production has been restricted to the zone. To date, there is no evidence that it has been cultivated on a commercial scale in any region outside the zone. Characterized with distinctive aroma and yellow colour (Uzo, 1979), Nsukka yellow pepper is highly cherished for its flavor in the preparation of some local dishes and has remained a major source of dietary vitamins and minerals. These two classic horticultural traits have endeared the crop to both urban and rural dwellers in Nigeria. Today, Nsukka yellow pepper has attained a premium status as a principal vegetable crop with great economic potentials to boost exports and meet domestic needs as well as create employment opportunities for many households especially amongst rural dwellers (Onwubuya et al., 2008).
In spite of the overwhelming economic importance of this crop, extensive literature search has shown that, no effort has been made to characterize Nsukka yellow pepper with a view to understanding the extent of genetic variability and the relationship among the existing lines as a basis for selection and improvement. Consequently, it has not benefitted from the amount of research attention accorded other vegetable crops such as tomato (Uguru and Onwubiko, 2002), and fluted pumpkin (Chukwurah and Uguru, 2010).
Information available indicate that, previous workers concentrated on its agronomy and yield attributes (Ekwu and Okporie, 2002, Echezona and Nganwuchu, 2006 and Abu and Uguru, 2006), whereas no attempt has been made to investigate the pattern of genetic variability especially in relation to genetic similarity among the existing genotypes. Although peppers naturally are autogamous plants (Allard, 1960), investigations in other Capsicum species have implicated tremendous variability and genetic divergence (Grubben and El Tahir, 2004; Abu and Uguru, 2006; Adetula and Olakojo, 2006; Del et al., 2007; Bozokalfa et al., 2009; Idowu-agida, 2009). Natural gene introgression is believed to be the prime force responsible for the high variability observed in this germplam (Grubben and El Tahir, 2004), and the amount of variation resulting from this activity in aboriginal populations such as Nsukka yellow pepper has not been investigated.
To undertake a successful breeding programme, the level of genetic variability inherent in the population must first of all be determined. This is important because the success of any selection programme depends on the degree of variability in the population since selection does not create variability but acts only on that which is already in existence. Therefore, a good estimate of variability in plant populations is extremely useful in selection studies.
Several methods have been proposed for determining genetic variability in pepper including molecular markers, total seed protein content, isoezymes profiles, and other DNA-based analyses. However, the morphological marker is the first step and the simplest approach towards genotype detection and species characterization (Smith and Smith, 1989). Agro-morphological traits have been successfully used for genetic diversity analysis in many agricultural crops (Aruah et al., 2010; Oyiga et al., 2010; Moukoumbi et al., 2011).
In general, yield constitutes the primary consideration for which many research efforts are envisaged. However, this trait is a complex one and as such it is controlled by a large number of contributing components that are interrelated (Griffing, 1956). Therefore, direct selection for yield may not be effective because there is always the risk of omitting some useful traits whose contributions through other traits might not be easily appreciated. Correlation coefficient could reveal the intensity of the association between two traits and improve the efficiency of selection effort. However, correlation coefficient alone may not be adequate since it only describes the mutual relationship between two variables without regard to causation. In order to have a clearer picture of yield components for a sound selection programme, it is important to partition the correlation coefficient into direct and indirect effects (Dewey and Lu, 1959). Presently, there is paucity of information on the traits that breeders can base their selection criteria on for yield improvement among Nsukka yellow pepper genotypes.
To date, limited information is also available on the aspect of biochemical attributes with respect to proximate composition and other phytochemicals in the aboriginal landraces which is also an important consideration that will complement phenotypic information in the development of breeding lines. The apparent lack of literature information on these aspects have created information gap among the existing Nsukka yellow pepper genotypes which the present study was therefore initiated to fill, with the following objectives:
- To characterise Nsukka aromatic yellow pepper with respect to qualitative and quantitative characters and biochemical attributes
- To determine the nature of association between yield and yield components
- To identify and select promising genotypes for future breeding programmes.
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