ASSESSMENT OF GENETIC (VIA PROTEIN ELECTROPHORESIS) AND NUTRITIONAL VARIABILITIES AMONG TEN ACCESSIONS OF SPHENOSTYLIS STENOCARPA (HOCHT. EX. A. RICH) HARMS

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.

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