**Abstract**

Neglected and underutilized crops (NUS) are those crops that are entirely ignored or little attention is paid to them by agriculture researchers, plant breeders and policy-makers. There has been renewed interest in NUS as many of these varieties and species, along with a wealth of traditional knowledge are being lost at an alarming rate. This chapter provides an overview of underutilized legumes in Sub-Saharan Africa (SSA). There is a recognized need to explore the diversity of indigenous micro symbionts associated with underutilized legumes. The biochemical mechanism in legumes remains elusive to date as evidence is mounting for allelopathic inhibition of nitrifying microorganisms by root exudation of phenolic compounds. A cross-sectional study was undertaken to explore the potential relationship between enzymatic processes of certain legumes and high tolerance to drought stresses, high biomass productivity, erosion control and dune stabilization and general soil health. Pigeon pea among other legumes have a huge untapped potential for improvement of both in quantity and quality of production in Africa.

**Keywords:** NUS, PGPR, PGPF, African legumes, pigeon pea, food security

#### **1. Introduction**

*Cajanus cajan* (L.) Millsp. (*C. cajan*) (Family: Fabaceae) also known as pigeon pea, is a famous food and cover/forage crop bearing a high amount of key amino acids like methionine, lysine and tryptophan [1]. It is one of the key promising sources of antioxidants and key enzyme inhibitors that can be exploited for future bioproduct development in tropical and subtropical regions in the world. This legume is one of the underutilized species in sub-Saharan Africa. Other economically important legumes include sword beans (*Canavalia ensiformis*), Bambara groundnut (*Vigna subterranea*), and Lima beans (*Phaseolus lunatus*) among several others [2, 3]. Neglected and underutilized species (NUS) has been a question of great interest in a wide range of fields.

The role of NUS in fighting poverty, hunger and malnutrition has received increased attention across several disciplines in recent years. There has been a growing recognition of the vital links between NUS, nutritional diversity, food sustainability and wealth creation. One well-known study that is often cited in research on NUS is that of Padulosi [2], who defined NUS as those species which are entirely ignored by agricultural researchers, plant breeders and policymakers. It is a widely held view that NUS is not traded as commodities. Agricultural species that are not among the major staple crops often come under the heading of 'neglected and underutilized species' (NUS) and are sometimes called 'orphan' crops.

If [2]'s findings are accurate, many of these varieties and species, along with a wealth of traditional knowledge about their cultivation and use, are being lost at an alarming rate. Evidence suggest that nearly 30,000 edible plant species have been identified, of which over 7000 plant species have been used in the history of civilization to meet food requirements [4]. Recent trends in NUS have led to a proliferation of studies as researchers have shown an increased interest in these species. It was established that barely 150 species are commercially cultivated and, of these, just 103 crops provide up to 90% of the calories in the human diet.

Several divergent accounts of NUS have been proposed, creating numerous controversies. The relationship between crop diversity, dietary diversity, nutrition and health has attracted conflicting interpretations from the scientific community. NUS offers opportunities to enrich diets with healthier food (particularly legumes, fruits and vegetables). The gradual shift from diets based on local foods to a 'Western-style' diet, high in fats, salt, sugar and processed foods, increases the incidence of non-communicable diseases, such as diabetes, obesity, heart disease and certain types of cancer.

African legumes can contribute significantly to the dietary supply of nutrients especially protein, essential amino acids, dietary fiber, vitamins, and minerals in the diet. However, compared to the well-known pulses, like the common bean, oilseed legumes, soybean, the African legumes are greatly underutilized and under-researched [5].

Numerous studies have attempted to explain the consistent contribution of NUS in fighting poverty, hunger and malnutrition and in generating income in both domestic and international markets [6–10]. This chapter examines the relationship between the biochemical mechanism through the enzymatic processes resulting to allelopathic inhibition of nitrifying microorganisms by root exudation of phenolic compounds in pigeon peas and related legumes. These could be exploited for future bio-product development to bring about sustainable crop production and to also ameliorate the effect of both biotic abiotic stresses to boost yield and restore depleted soil nutrients.

#### **1.1 Neglected and underutilized legumes in Sub-Saharan Africa**

Previous studies of NUS have established that in some countries like the Côte d'Ivoire, a considerable variety of minor leafy vegetables, legumes and vegetable crops are utilized and appreciated for their rich nutritional value. In the same way, minor forest and timber forest species are collected from the wild in Ghana which is utilized in developmental projects in the country such as housing construction, furniture and other arts and crafts. In the same vein, sword beans (*C. ensiformis*) are common food crops in the region. Similarly, in East Africa however, demand for leafy green vegetables is ever more recognized due to their nutritive value. In Uganda on the other hand, despite disregard on the part of stakeholders more especially the agricultural research and development programs, poor communities continue to grow and market miscellaneous underutilized species which are locally processed in form of artifacts and are mainly exported around the globe. NUS also serves as an alternative food source and is equally exploited for ornamental and medicinal value, generating significant income for some populations in West Africa. The use of some NUS is also significant in Malawi, particularly about Bambara groundnut (*V. subterranea*), sorghum, finger millets and pearl millets. In Nigeria,

#### *Enzymatic Processing of Pigeon Pea Seed Increased Their Techno-Functional Properties DOI: http://dx.doi.org/10.5772/intechopen.101406*

NUS such as fonio (*Digitaria exilis*, *Digitaria iburua*), Ethiopian tef (*Eragrotis tef*), Lima beans (*P. lunatus*), Pigeon peas (*C. cajan*) and *V. subterranea*, *Crotalaria* spp. and *Solanum nigrum*. Zimbabwe reports significant use of NUS, especially finger and pearl millets [2, 3].
