Management of Seed Quality of Cowpea

Cowpea, Vigna unguiculata (L.) Walp. is the major legume crop in Africa. It is the main protein supply of half of the population in sub-Saharan Africa.

Nigeria is the most populous country in West Africa, and also produces the largest amount of cowpea. Its urban population is growing in leaps and bounds, and thus, it is also importing a lot of cowpea from all its neighbours.

Cowpea also referred to as beans is being eaten by about 400 million people in the tropics e as part of their daily diet. It is often referred to as ‘meat of the poor’, because beans provide highly nutritious food, containing protein, fibre, complex carbohydrates, vitamins, and micronutrients. Beans also provide income for millions of people, particularly in Africa and Latin America.

Cowpea is indigenous to sub-Saharan Africa (SSA), is grown on about 14 million ha worldwide, with over 84% of these areas in SSA. Between 1985 and 2007, the rate of growth was 4.5% in land area planted to cowpea, 4.5% in grain yields/ha, and 5.9% in quantity of cowpea produced. These data indicate that the increase in the quantity of grain produced over the period resulted mainly from an expansion in the land area and less from an improved yield/unit area. In well-managed experimental stations, yields of up to 2 t/ha can be obtained but globally the average yield is about 450 kg/ha.

Cowpea (Vigna unguiculata (L.) Walp) is considered as one of the vegetable crops which have an importance for local consumption. Studies have shown that losses on legumes during post-harvest, drying and storage are significantly high. This is due to pod shattering in the field, poor drying systems, insects damages, mould, insect and/or disease infestation that normally starts in the field and proceeds into storage. Legume may receive improper care on the farm or in temporary storage and become heavily invaded by hidden storage fungi. Upon transfer to another storehouse, it may spoil more rapidly than really sound legume. Invasion by storage fungi may occur very shortly after harvest.

Conducive growth of fungi takes place during storage due to lack of storage facility and good packaging materials. These factors provide proper environment for successful establishment of fungi on food commodities. As fungi are serious parasites of stored grains, therefore their encroachment can results severe damage like decrease germinability, discoloration of the embryo, heating and mustiness, loss in weight etc. In addition, fungi can degrade the tissue of foodstuff that results to bad taste and decrease nutritious value.

Storage of cowpea has always been limited by pests and diseases leading to their deterioration. The major constraints to cowpea storage are insect pest and fungal diseases which cause variety of losses, which includes decrease in germinability, discoloration, heating and mustiness, and change in taste. Examples of fungi that cause this include; Aspergillus flavus and Aspergillus fumigatus. The fungi associated with stored foods and agricultural commodities have been classified into two types namely, the field and storage fungi. Most of the storage fungi are moulds. Although, grains naturally acquire a mould flora in the field and after harvest, they are normally of little consequence unless the environmental conditions favour fungal growth. Thus, poor storage conditions predispose grains to fungal spoilage, this being exacerbated by insect damage. Climatic conditions in the tropical countries often provide ideal conditions for high mould growth which develop on or within seeds at moisture contents within the storage container. Therefore, for efficient storage of cowpea, control measures must be adopted through the use of good storage containers, use of conventional chemicals, and use of plant materials.

People use different storage containers to store cowpea, with the common ones being polythene bags, sacks, plastic and tins. In addition, most household add pesticide e,g Phostoxin and fungicide to the stored cowpea in order to control pest and diseases. The indiscriminate use of these chemicals may cause health and environmental hazards. Therefore, the use of eco-friendly substances such as plant parts is necessitated. Various plants are known to have antimicrobial properties and these are used as promising biocontrol agents. Recently Alkhail (2005) showed that aqueous extracts of plants viz., Allium sativum, Cymbopogon proxims, Carum carvi, Azadirachta indica and Eugenia caryophyllus had strong antifungal activity against fungi viz., Fusarium oxysporum, Botrytis cinerea and Rhizoctonia solani. Most botanical pesticides are known to be general bio-cides or bio-irritants.

Therefore, any method of storage, which is aimed at preventing or retarding the invasion of these fungi and creating unfavourable conditions for their growth and multiplication will help in improving the quality of seed.

In this project work, the most efficient storage material and/or container will be evaluated.

Aim / General objective

To determine the effects of different containers and botanicals in the management of seed quality of cowpea (Vigna unguiculata (L.) Walp).

Specific objectives

To evaluate the effects of the different storage materials on the seed health and storability potentials of Cowpea.

To assess the potency of the different botanicals as biopesticides on the seed borne storage.

Identify the appropriate storage container and botanical for the maintenance of the seed health of Cowpea over the period of storage.

Compare the effects of the botanicals with a standard synthetic fungicide on the incidence and severity of seed borne fungi of cowpea stored in different materials/containers.

Literature review

There is a large morphological diversity found within the crop, and the growth conditions and grower preferences for each variety vary from region to region (Padulosil and Ng, 1997). However, as the plant is primarily self-pollinating its genetic diversity within varieties is relatively low (Egbadzor et al., 2014). Cowpeas can either be short and bushy (as short as 20 centimetres (7.9 in)) or act like a vine by climbing supports or trailing along the ground (to a height of 2 metres (6.6 ft)) (Sheehan 2012; National Research council 2016). The tap root can penetrate to a depth of 2.4 metres (7.9 ft) after eight weeks (Davis, 1991).

The size and shape of the leaves varies greatly, making this an important feature for classifying and distinguishing cowpea varieties (Pottorff et al., 2012). Another distinguishing feature of cowpeas are the long 20–50 centimetres (7.9–19.7 in) peduncles which hold the flowers and seed pods. One peduncle can support four or more seed pods (Davis, 1991). Flower colour varies through different shades of purple, pink, yellow and white and blue (National Research council 2016).

Seeds and seed pods from wild cowpeas are very small (Davis, 1991), while cultivated varieties can have pods between 10 and 110 centimetres (3.9 and 43.3 in) long (Rawal, 1975). A pod can contain 6–13 seeds that are usually kidney shaped, although the seeds become more spherical the more restricted they are within the pod (Sheahan 2012; Davis 1991). Their texture and colour is very diverse. They can have a smooth or rough coat, and be speckled, mottled or blotchy. Colours include white, cream, green, red, brown and black or various combinations (Davis, 1991).

Africa was suggested as the centre of origin of cowpea (Richard, 1847). This assumption was not contested because wild cowpea plants have been found in tropical Africa and Madagascar (Steele, 1976), 1 where it was presumably domesticated subsequent to the Neolithic age (Vanderborght, 2001). Pasquet (1991) suggested that the most likely progenitor of domesticated cowpea is V. unguiculata ssp. unguiculata var. spontanea. For determining the precise domestication site and the cowpea diversity centres, several studies have been performed in the last decades, although a conclusive result has been difficult to reach. Several hypotheses have been proposed for cowpea domestication, such as Ethiopia (Steele 1976; Vavilov 1926; Pasquet 2000), West Africa (Murdock 1959; Faris 1965; Rawal 1975; Vaillancourt and Weeden 1992; Ng 1995), and Eastern and Southern Africa (Baudoin and Marechal, 1985). Coulibaly et al., (2002) using amplified fragment length polymorphisms (AFLPs) and morphologic data, concluded that the wild species was originated from Eastern Africa. In this case, domestication should have occurred in North-Eastern Africa and the domesticated plant was then probably dispersed to Western Africa. According to Ng and Padulosi, (1988) West Africa appears to be the centre of diversity of cultivated forms. A ‘diffuse’ domestication in the African savannah after the dispersal of cereals was also hypothesized (Steele 1986; Garba and Pasquet, 1988). This last hypothesis was presented by Harlan (1971), who considered that the cowpea was domesticated in the African Non-Center. Whatever the place of domestication, cowpea is an ancient legume that was domesticated by African gatherers, cultivators and farmers from its wild forms in Africa dating back to Neolithic times (Ba et al., 2004). During the Neolithic period, the cowpea was first introduced into India, which was then considered a secondary centre of cowpea genetic diversity (Pant et al., 1982). The spread of cowpea in Asia occurred at the end of Neolithic period (thirdmillennium BC), where the subspecies asparagus bean or yardlong (V. unguiculata ssp. sesquipedalis) is still cultivated for long immature pods (Xu et al., 2011), as well as in America between the 16th and 17th centuries (AD) (Padulosi and Ng, 1997). Although some reports suggest that cowpea has been cultivated in Europe at least since the 18th century BC and possibly from prehistoric times onward (Coulibaly et al., 2002; Tosti and Negri, 2002 ), others suggest that it was only introduced in Europe around 300 BC, where it still remains as a minor crop in the southern part (Badiane et al., 2014). From Europe, more specifically from Portugal and Spain, this legume was exported in the 17th century to the New World (Badiane et al., 2014; Fang et al., 2007). Another important result was obtained by Fang et al., 2007 who provided evidence for the common origin of cowpea germplasm from Asia and North America different from the West Africa. However, such studies have mostly used breeding lines and, consequently, the introgression of extra regional germplasm could have occurred. Huynh et al., 2013 analysing a worldwide collection of cowpea landraces and African ancestral wild cowpeas by using more than 1200 single nucleotide polymorphism (SNP) markers, confirmed that accessions from Asia and Europe were more related to those from western Africa, whereas accessions from Americas appeared to be more closely related to those from Eastern Africa.

Cowpea (Vigna unguiculata (L). Walp.), is a member of the leguminosae family that is native to Africa. It is an annual legume, and commonly referred to as southern pea, black eye pea, crowder pea, lubia, niebe, coupe or frijole. The history of cowpea dates to ancient West African cereal farming, 5 to 6 thousand years ago, where it was closely associated with the cultivation of sorghum and pearl millet. A survey of the germplasm accessions from Nigeria, Niger, Burkina Faso and Ghana showed greater diversity than accessions from other areas in Africa (Ng and Maréchal, 1985), leading to the conclusion that West Africa was the primary centre of domestication’.

According to FAOSTAT, about 96% of the total world production of cowpea is produced in Africa. Most this production comes from West Africa with Nigeria being the highest producer in this region.

According to IITA, Cowpea’s high protein content, its adaptability to different types of soil and intercropping systems, its resistance to drought, and its ability to improve soil fertility and prevent erosion makes it an important economic crop in many developing regions. The sale of the stems and leaves as animal feed during the dry season also provides a vital income for farmers.

Under conditions of subsistence agriculture, the average yield of dry seed normally ranges between 100 and 300 kg per hectare. Compared to yields of modern soybean (3,000 kg per hectare and up), peanut (2,000), or even cowpea grown on experiment stations and in countries such as India (at least 2,000), this is an appalling level Much of the difference is due to the fact that cowpea occupies only a small part of each hectare of the mixed cropping system. But some is due to the particular types used by Africa’s subsistence farmers. Those traditionally selected plants may be very clever at dodging their enemies but from a productivity standpoint, they aren’t very good. Whatever the climate, locale, or cultivation method, insects are the major constraint. In the lowland tropics the effect can be so devastating that overcoming them could send grain production soaring 20 fold or more, according to literature reports. But it is not an easy task. Africa has at least 15 major and more than 100 minor insect pests that challenge cowpea. By comparison with the insect onslaught, diseases are less troublesome, but that’s not saying much. Fungi sometimes cause terrible damage, especially in the wetter areas. Devastating attacks are not unknown in the drier areas as well.

Even when the harvest is in hand, the farmer’s fight for her food is far from over. Certain insects make their living on cowpeas in storage. Cowpea weevil and bruchid beetle are the major threat here. They begin infesting the plant in the field, but really capitalize when the seeds are crammed together in a grain bin or silo. There in weevil heaven each female produces 20 ravenous larvae every 3 or 4 weeks, so within a few months nearly every seed has a neat hole drilled in its side. And within six months little that is edible remains. Food prepared with even partially infested grain tastes bad, and selling seed exhibiting even a few of the telltale beetle holes is difficult. In Nigeria it has been estimated that some 30,000 tons of cowpea grain are lost annually, most of it during storage.