PHENOTYPIC AND GENOTYPIC VARIATIONS IN COWPEA (Vigna unguiculata L. Walp) GENOTYPES IN NIGER STATE, NIGERIA

ABSTRACT

Cowpea production is faced with a number of constraints which results into low grain and fodder yields. The study was carried out to determine variation in yield with its component traits in different cowpea accessions. Twenty genotypes of Cowpea were evaluated in two locations (Minna and Kontagora) in a randomized completely block design (RCBD) and replicated three times. Some of the parameters that were collected include plant height at first branching, number of branches at 3,6and 9 weeks, days to first flowering and poding, pod length, leaf area and biomass weight. Results revealed that, there was wide variation among the genotypes. Genotype 11D-15-40 recorded a higher grain yield (689.8kg/ha) in Kontagora while  genotype  99K-57-3-2-1  recorded  a  higher  grain  yield  (282.7kg/ha)  in  Minna. Kontagora environment recorded a higher performance than Minna environment. However, the cowpea genotypes showed wider variability in Kontagora environment as shown by Boxplot for seed yield. Genotypes 04K-267-8, 10K-816-1, 98K-1092-1and 100K-817-3 were better in Kontagora, while genotypes 12K-261, 12K-632, TVU-408, IT10K-827-7 and 99K-57-3-2 1 in Minna as indicated by genotype plus genotype by environment interaction (GGE) biplot. From the study, cowpea would be better produced in Kontagora than Minna.

CHAPTER ONE

1.0        INTRODUCTION

1.1       Background to the Study

Cowpea (Vigna unguiculata (L). Walp) is a dicotyledonous plant belonging to the family Fabaceae and sub-family Fabiodeae. It is grown extensively in the low lands and mid-altitude regions of Africa (particularly in dry savannah) sometimes as sole crop but more often intercropped with cereals such as sorghum or millet (Agbogidi, 2010a). Cowpea grain contains about 28.4 % protein, fat 1.9%, fibre 6.3%, thiamine 0.00074%, riboflavin 0.00042%, and niacin 0.00281%. It is also a genuine African crop for hay and forage production (Chinma et al., 2008). Cowpea has been referred to as ‘poor man’s meat’ (Fall et al., 2003) and its young leaves and pods contain vitamins and minerals. About 5.4 million tonnes of dried cowpea are produced worldwide, with Africa producing close to 5.2 million tonnes of cowpea. Nigeria, being the largest producer and consumer of cowpea, accounts for approximately 61% of production in Africa and 58% worldwide. Africa exports and import negligible amounts. Approximately 11 million hectares are harvested worldwide, 97% of which is in Africa. Nigeria alone harvests 4.5 million hectares yearly (FAO, 2011). The crop can be harvested in three stages: while the pods are dry, mature and green and young and green (IITA, 2009).

It was estimated that 3.3 million tonnes of cowpea dried grains were produced worldwide in year 2000. Of this, Nigeria produced 2.1 million tonnes which ranked her the world’s largest producer. This was followed by Niger and Mali with approximately 650,000 and 110,000 tonnes respectively (Adegbite and Amusa, 2008). It was also estimated that cowpea was cultivated on a total land area of 9.8 million hectares,  out  of  which  about  9.3  million  hectares  is  found  in  West  Africa.

Additionally, the world average yield was 337 kg per hectare while Nigeria and Niger had 417 kg per hectare and 171 kg per hectare as average yield, respectively (IITA, 2004). Though, it sounds thrilling, the unfortunate side of this reported statistics is that it is based on improved cowpea lines which have slowly reduced the genetic diversity of the landraces (Udensi et al., 2012). Every stage in the life cycle of cowpea has at least a major insect pest that affects it from vegetative to reproductive stage. Aphids  (Aphis  craccivora  Koch.) attack  cowpea especially in  the seedling stage, flower thrips  (Megalurothrips sjostedti  Trybom) attack  cowpea at  flowering,  pod borer (Maruca vitata Fabricus) attack cowpea at flowering and also pod formation, numerous pod sucking bugs at poding, and the weevil (Callosobruchus maculatus Fabricus) attack mature cowpea in the field and during seed storage. Since cowpea is grown mainly in the dry savannah areas with no  irrigation facilities, intermittent rainfall especially early in the season has adverse effects on the growth of the crop, although hampered by frost. All of these factors, singly or combined, are responsible for the low grain yield, estimated at approximately 350 kg per hectare that farmers in sub-Saharan Africa obtain from their cowpea fields (IITA, 2009).

Cowpea  has  the  largest  usable  protein  content  of  all  cultivated  legumes  and  is arguably one of the most important plant protein sources as a valuable and dependable commodity crop for farmer and grain traders (Nwosu et al., 2013). With an annual worldwide estimated production of about 4.5 million metric tons, cowpea provides food for several millions of people in developing world (FAO, 2002). Cowpea is grown mostly by poor farmers in the developing countries with over 80% of the production coming from the savannas of tropical Africa. In the past decades though, advances in crop development have opened opportunities for its production in wet agro-ecologies (Nwofia et al., 2012).

1.2       Statement of the Research Problem

One of the major global challenges of the millennium is food security and how to address  the  phenomenon  of  malnutrition  among  the  teeming  and  ever  rising population of poor rural dwellers of the third world countries. In the wake of climate changes, fluctuating global economy and intensification of low-input agricultural production which has led to a rapid increase in soil degradation and nutrient depletion in many parts of sub-Saharan Africa, constituting serious threats to food production and food security, there is need to promote crops that could fix into global nutrient requirements.  One of such  crops  is  cowpea.  Cowpea production  is  faced  with  a number of constraints which are biotic and abiotic that resulted into low grain and fodder yield. In most West African countries, development and release of improved varieties that adapts well and yield better have been slow in getting to the farmers (FAO, 2000). Development of cultivars with early maturity, acceptable grain quality, resistance to  diseases  and  pests  is  necessary to  overcome the  ever-growing food shortage (Ehlers and Hall, 1997). Hence, there is need to generate more information on variability among the existing germplasm and cultivars and also broadening the gene pool of the crop for selection and development of more improved varieties not just in yield but with better nutritional values.

1.3       Justification of the Study

Successful conservation of germplasm largely depends on the understanding of the diversity within the species (Karuri et al., 2010). Germplasm with wider genetic base provides buffer and resilience against climatic and other environmental changes and ensures sustainable food security. The presence of genetic variability among crop genotypes depicts the richness of the genepool  and assures plant breeders of the possibilities of combating subsequent food security crisis for the crop. Moreover, understanding the nearness and diverseness of genotypes within the same species is an important  primary knowledge  to  guide  selection  and  improvement  in  a  breeding programme. In essence, diversity leads to the identification of superior genotypes which may be recommended as cultivar and identification of genotypes with desirable phenotypic traits for selection as parents for eventual breeding  and improvement programmes. Cowpea comes first ahead of other arable food legumes in the sub- Sahara Africa. The recent annual global production of cowpea approximates 3.3 million tons; Central and West Africa region are the major areas of its cultivation (CGIAR, 2011). While it is chiefly a vegetable and grain crop for human who values it as a nutritional supplement to cereals and an extender of animal proteins, it provides a very safe fodder for livestock animals. Cowpea has vast utility in the food culture of both man and animal (Fang et al., 2007).

The study of variability and diversity in accessions of cultivated crops could provide vital information for the establishment of breeding programme, especially when intraspecific hybridization are necessary for the incorporation of new features or for mapping purposes. Assessment of genetic diversity and variability in cowpea would enhance development of cultivars  for adaptation to specific production  constrain. Therefore, sufficient information is necessary on genetic variability among the available germplasm to formulate and accelerate breeding programme. Previous workers have reported on genetic variability among different varieties of cowpea (Nwosu et al., 2013) and a number of reports on the nutrient analysis (Mamiro et al., 2011; Odedeji and Oyeleke, 2011).

1.4       Aim and Objectives of the Study

The aim of this study was to estimate the extent of genetic variability for the yield and its component traits among some selected cowpea genotypes.

The objectives were to;

i.      determine yield with its component traits in different cowpea accessions.

ii.         evaluate the performance of cowpea genotypes across environments and to identify better cowpea genotypes for yield trials.

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