ABSTRACT
The genetic variability among ten (10) accessions of Sphenostylis stenocarpa from three states and National Centre for Genetic Resources and Biotechnology Moor Plantation, Ibadan, Nigeria were assessed using sodium dodecyl polyacrylamide gel electrophoresis (SDS – PAGE). There were variations in the banding patterns of the accessions and polymorphism was also observed. Twelve polypeptide bands were obtained ranging from 9KDA to 219KDa. The Unweighted Pair Group Method with Mean Algorithm (UPGMA) dendrogram grouped the ten accessions into two clusters and six groups. Some accessions appeared in the same group, while others were observed to be in different groups. The proximate and nutritional analysis also detected variations. A strong and positive correlation was observed among some of the attributes studied. The principal component analysis also showed some variation among the accessions. The highest variability was observed in the ash content which shows that ash content could be a major indicator for nutritional variability in these 10 accessions followed by the Vitamin B2 in the second component.
CHAPTER ONE
INTRODUCTION
African Yam Bean (AYB) (Sphenostylis stenocarpa Ex. A. Rich, Harms) is an underutilized food leguminous crop of the family Fabaceae, sub family Papilionoideae (Azeke et al., 2005; Moyib et al., 2008). The domestication, cultivation and distribution of the crop are very evident in the tropics and Africa where it had been reported to exhibit very high diversity (Okpara et al., 1997). The distribution of the crop according to Genetic Resources Information Network (GRIN), (2009), includes the following countries within the tropical regions of Africa: Chad and Ethiopia (Northeast tropical Africa); Kenya, Tanzania and Uganda (East tropical Africa); Burundi, Central African Republic and Democratic Republic of Congo (Central tropical Africa); Cote d’voire, Ghana, Guinea, Mali, Niger, Nigeria and Togo (West tropical Africa) etc.
Nigeria is very significant in AYB production where extensive cultivation had been reported in the Eastern, Western and Southern areas of Nigeria (Saka et al.,
2004). AYB thrives in weathered soils where the rainfall can be extremely high. It grows well even in acidic and highly leached sandy soil of the humid low land tropics (Uguru et al., 2001).
The plant is an annual, with climbing, vine-like stems that require staking; the stem is often reddish in colour. In Nigeria, it is usually grown in association with yams, maize, cassava, etc., so that the same stake of the yam serves as support for both crops. It is cultivated mainly for home consumption and only about 30%
of the dry grain produced is sold. It is also planted for soil restoration (Saka et al., 2004). The seed is planted at the base of yam mounds in June or July. Germination is hypogeal and takes about 5 days after planting. It begins flowering at about 80-120 days and set fruits from late September and October. The large bright coloured (purple) flowers result in long linear pods that could house about 20 seeds and they vary in size, shape, colour, etc. Pods start maturing about 150 days after sowing. The tubers which develop more slowly than the flowers, normally take 5 to 8 months to swell to harvestable size. Most are dug up towards the end of the rainy season. AYB seeds can be brown, white, speckled etc, with a hilum having a dark brown border (Klu et al.,2001)(plate 2).
Plate 1: African yam bean plant
Plate 2: Diversity in colour, colour pattern structure of African yam bean
The seed grains and the tubers are the two major organs of immense economic importance as food for Africans. This indigenous crop has huge potential for food security in Africa. In West Africa, the seeds are preferred to the tubers but the tubers are relished in East and Central Africa (Potter, 1992). The crop replaces cowpea in some parts of Southwestern Nigeria (Okpara and Omaliko, 1995). Another positive contribution of the crop to food security is the presence of lectin in the seeds, which could be a potent biological control for most leguminous pests.
Apart from the production of two major food substances, the content of the protein in both tubers and seeds is comparatively higher than what could be obtained from most tuberous and leguminous crops (Nwokolo, 1996). The protein in the tuber of the crop is more than twice the protein in sweet potato (Ipomea batatas) or Irish potato (Solanum tuberosum) and higher than those in yam and cassava (Amoatey et al., 2000). Amino acid values in the seeds of the crop are higher than those in pigeon pea, cowpea and bambara groundnut (Uguru et al., 2001). The protein content in AYB seeds ranges between 21% and 29%, while that of the tuber ranges between 11% and 19% (NAS, 1979). The content of crude protein in AYB seeds is lower than that in soybean, but the amino acid spectrum indicated that the level of most of the essential amino acids especially lysine, methonine, histidine and iso-leucine in the crop is higher than those in other legumes including soybean (National Research Council, Washington,
2007). Generally, the amino acid profile of AYB compares favourably with whole hen’s eggs and most of them meet the daily requirement of the Food and
Agricultural Organization (FAO) and World Heath Organization (WHO) (Ekop,2006).
It produces an appreciable yield under diverse environmental conditions (Schippers, 2000). The plant is a good source of protein, fibre and carbohydrate. It is rich in minerals such as K, P, Mg, Ca, Fe and Zn, but low in Na and Cu. It also contains some anti-nutrients, such as trypsin inhibitor, phytate, tannin, oxalate and other alkaloids (Fasoyiro et al., 2006).
The species as a crop is less susceptible to pests and diseases compared with most legumes; this quality may be due to the inherent lectin in the seed of the crop (Dukes, 1981). Omitogu et al. (1999) observed that the lectin in the seed of the crop is a promising source of a biologically potent insecticide against field and storage pest of legumes. The inclusion of the lectin extract from AYB in the meal for three cowpea insect pests, namely; Maruca vitrata, Callosobruchus maculates and Clavigralla tomentosicollis gave a mortality rate greater than 80% after 10 days (Okeola et al., 2001).
Over time, some conditions have negatively influenced the productivity and acceptability of the crop among cultivators, consumers and research scientists. Notable among these are:
1. The hardness of the seed coat which makes a high demand on the cost and time of cooking. It lasts for about 4-6hrs.
2. The agronomic demand for stakes and long maturation period.
3. Flatulence and diarrhoea are common discomforts after the consumption of AYB (Adewale et al., 2013).
The photoperiodic sensitivity of the crop seems to compound the above disadvantages as it confines the cultivation and production of the crop to one season in the year. However, a concerted crop breeding research programmes may overcome these problems (Okpara et al., 1997). The plant has very high ability to fix nitrogen. It is, therefore, an important crop with merit and significant for land reclamation (Assefa et al., 1997). The species has the following common names: Haricot igname in French (Duke, 1981), Yam pea in the United Kingdom (Terrell, 1985). It is known as Akirerku, Kulege, Sese, Pemp in West Africa. In Nigeria, its local names include; Agima, Azama, Ijiriji, Girigiri, Okpodudu etc (NAS, 1979). The plant is found in the following states in Nigeria: Enugu, Anambra, Imo, Delta, CrossRiver, Edo, Ondo, Ogun, Oyo, Benue, Akwa-Ibom, Rivers, Ebonyi and AbiaStates (Okoye, 1991).
African Yam Bean is used extensively in various dietary preparations and has potential for supplementing the protein requirement of many families throughout the year. The seeds may be eaten alone or in soups and commonly served with yam, maize or rice. In Ghana, the seed is processed into flour and used for pudding or fortified with cassava. The water drained after boiling the beans is drunk by lactating mothers to increase breast milk production (Klu et al., 2001). In Togo, Ghana and Nigeria, paste made from the seeds of AYB is used as a cure
for stomach aches and when the paste is mixed with water it is traditionally used for the treatment of acute drunkenness. There might be pharmacological evidence for the use of AYB in treating such conditions (Asuzu, 1986).
Underutilized crops are indigenous, relatively common in specific areas, accessible, well-adapted, easy and cheap to produce and culturally linked to the people who use them traditionally (Jaenicke et al., 2009). The landraces of these species are cultivated less than in the past and are rarely found in urban markets. They cannot compete with crops which now dominate world’s food. They are hardly represented in ex situ gene banks, so efforts to characterize them depend on the limited available and loosely representative diversity (Padulosi et al.,
2004). The AYB plant has been relegated to an unimportant position as it is grown predominantly by the older generation of farmers (Saka et al., 2004). The bulk of the genetic resources of this crop are in the hands of these farmers, which threatens its survival. There is therefore, a need for germplasm collection, characterization and conservation of Sphenostylis stenocarpa to prevent it from being lost. Information provided by characterization can be useful in identifying promising AYB genotypes that could be recommended directly to farmers and other end users and also for incorporation into breeding activities for further improvement. Traditionally, genetic variability analysis of AYB has been done with easily distinguishable phenotypic traits. Knowledge of genetic diversity of the plant will be useful in facilitating the development of large number of new varieties through hybridization (Ajibade et al., 2005). Recent advances in biotechnology and data analysis have resulted in powerful techniques that can be
used for characterization and evaluation of germplasm collections to provide further information on diversity within and among the accessions (Panella et al.,
1992).
Protein markers can be used effectively to study the genetic variation of germplasm for its utilization in crop breeding programmes (Akande, 2011). Seed protein patterns obtained by sodium dodecyl suplphate polyacrylamide gel electrophoresis (SDS-PAGE) have been used successfully in plant breeding programmes (Rao et al., 1992). Therefore, the study was undertaken to assess genetic variabilities among ten accessions of Sphenostylis stenocarpa (from NACGRAB and 3 states in Nigeria) based on SDS-PAGE.
The objectives of the study include the following
1. To assess the nutritional variability among ten accessions of Sphenostylis stenocarpa
2. To evaluate the genetic diversity and relationship among ten accessions of Sphenostylis stenocarpa with the aid of protein electrophoresis.
This material content is developed to serve as a GUIDE for students to conduct academic research
ASSESSMENT OF GENETIC (VIA PROTEIN ELECTROPHORESIS) AND NUTRITIONAL VARIABILITIES AMONG TEN ACCESSIONS OF SPHENOSTYLIS STENOCARPA (HOCHT. EX. A. RICH) HARMS>
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