1.0 Introduction and literature review
The rhizosphere is a term first described by Lorenz Hiltner in 1904 an agronomist and plant physiologist. He referred to it as the region of the soil that is directly influenced by plant root, he further stated that this zone is marked with greater microbial activities than the bulk soil (surrounding soil away from the root) (Hiltner, 1904). Further study on the rhizosphere revealed that it consistof a gradient in chemical, biological and physical properties that varies radially and longitudinally moving along the plant root to the bulk soil (McNear, 2013).This difference in gradient gave rise to the three distinct sections of the rhizosphere which includethe endorhizosphere, the rhizoplane, and the ectorhizosphere (Lynch, 1987).The process of seeds germination and development of root system through the soil results in the loss of organic materials which provide the driving force for the presence of active microbial populations around the root, known as the rhizosphere effect (Whipps, 1990; Morgan and Whipps, 2001).
This soil environment is highly favourable to microorganisms making it very active, as very significant interactions occur among the plant, soil, and microorganisms. The microorganisms present in the rhizosphere compete for available resources such as water, nutrients and space.They sometimes develop a very close relationship so as to improve their competitiveness and overcome their competitors (Hartmann et al., 2009). The rhizosphere harbours a great number of microbes which include bacteria, fungi, nematodes, protozoa, algae and microarthropods (Raaijmakers and Weller, 2001). These organisms play vital roles in the development and growth of the plant and function of the plant root system they inhabit (Kent and Triplett, 2002). The association that occur between microorganisms and their host plant has several effectswhich might be beneficial, neutral, or harmful to the plant, depending on the type of microorganisms and plants involved and on the present condition of the soil environment (Bais et al., 2006). The occurrence of these diverse significant activities makes this zone unique in the soil as an environment.
Pepper (hot and sweet) is a vegetable crop that belongs to the Solanaceae family, genus Capsicum. Capsicum annuum is a medium hot, cayenne-type chilli pepper commonly called cow horn. The curved peppers resemble a cow’s horn, hence the name, Capsicum annuum. It has its origins in South and Central America, the West Indies and Mexico. The very hot varieties of pepper (Chilies) have a high content of the alkaloid capsaicin (C18H2703) a chemical compound that accounts for the heat in chilli pepper which imparts the pungency or spicy taste.They are known to be 15 – 20 cm long and mature from green to red. The plant is around 1 meter tall. Harvest is 75 days after repotting.
In Nigeria pepper is an integral part of almost all dishes due to its peculiar inherent qualities, as such its absence in a particular food makes it seem incomplete. According to the report of Erinle, (1989); and Alegbejo, (2002) tha in Nigeria the amount of pepper consumed is about 20% of the average vegetable that is consumed by one person in day. It is used extensively in food flavouring, for spicing meat and fishes, for decoration, and addition of colour to food such as jellof rice and moi- moi in the daily diet of over 120 million Nigerians despite their socioeconomic status. It is used in the preparation of soup and stew, which are among the major essential complements of staple foods based on cereals and root crops and also forms remedies for toothache and sore throat (Leung and Foster, 1996; Bosland, 1994). Peppers are also important sources of nutrient in the body for boosting immunity and maintaining good health.
1.2 The Rhizosphere
Rhizosphere is a term used to describe the region of the soil that surrounds the root surface of the plant and under the influence of plant exudates produced by the root as well as the presence inhabiting microorganisms (Hutsch et al 2002). Studies have shown that the population of microorganisms in a teaspoon of soil is more when compared to the population of people on the earth; the rhizosphere has a capacity of 1000-2000 times this value, which gives it a higher population size (McNear, 2013).
Considering a general perspective, three distinct components are recognized in the rhizosphere (Lynch, 1987 andMcNear, 2013), the rhizosphere, the rhizoplane, and the root itself (figure 1). The rhizosphere also known as endorhizosphere is the inner part of the rhizosphere inhabited by microorganisms that is under the influence of root released organic compounds. The middle part of the rhizosphere is called rhizoplane. It is the plant root surface that is having strongly adhering root particles. The third part which is the root itself is also known as ectorhizosphere. This is the outermost zone that extends to the bulk soil (Efretuei and Filed, 2016).