Groundnut (Arachis hypogaea L.) is an annual legume which is also known as peanut. It is the 13th most important food crop of the world. Today, groundnut is the world’s 4th most important source of edible oil and the 3rd most important source of vegetable protein in the world. Groundnut is cultivated in more than 100 countries in 6 continents and covers an area of 26.4 million hectares worldwide with a total production of 41.3 million metric tons, and an average productivity of 1.4 metric tons per hectare (FAO, 2014). Major groundnut producers in the world are: China, India, Nigeria, USA, Indonesia and Sudan. Developing countries account for 96% of the global groundnut area and 92% of the global production (FAO, 2014). Groundnut kernels are consumed directly as raw, roasted or boiled kernels or oil extracted from the kernel is used as culinary oil. Groundnut seeds contain high quality oil (50%), easily digestible protein (25%) and carbohydrates (20%). It is also used as animal feed and industrial raw material. These multiple uses of groundnut make it an excellent cash crop for domestic markets as well as for foreign trade in several developing and developed countries (Pandey et al., 2012).
Groundnut is affected by several diseases like leaf spots, collar rot, rust, bud necrosis and stem necrosis (Prasada et al., 2012). Apart from these, aflatoxin contamination is one of the major problems, produced in the infected groundnut seeds by Aspergillus flavus Link ex fries and Aspergillus parasiticus Speare, particularly at the end of season under drought conditions (Fountain et al., 2014). Aflatoxins, especially the most potent aflatoxin B1, are secondary metabolite produced by A. flavus. They are highly carcinogenic, immunosuppressive agents, highly toxic and fatal to humans and animals particularly affecting liver and digestive track (Wild and Gong 2010). These health problems are more severe in African communities due to exposure to aflatoxins throughout their lives (Wild and Gong 2010). There have been increasing reports of aflatoxin contamination in freshly harvested groundnuts in several countries of sub-Saharan Africa. Recently, 22–54% of groundnut samples collected during 2009 and 2010 from different groundnut growing areas in Nigeria showed >20 ng g−1 of aflatoxins (Waliyar et al., 2016). This contamination renders the commodity unfit for human consumption and unacceptable for trade in high-value markets. Therefore, aflatoxin contamination in groundnut as well as in maize has been considered as a major non-tariff barrier to international trade since agricultural products that exceed the permissible levels of contamination (4 to 20 ng/g) are banned. About $1.2 billion in commerce is lost annually due to aflatoxin contamination, with African economies losing $450 million each year (IITA, 2013).
Following the outbreak of aflatoxicosis and the enormous economic loss in the poultry industry of Britain in 1961, the Federal government of Nigeria, in order to protect her export trade initiated screening studies to determine the extent of aflatoxin contamination of groundnut and groundnut products (Halliday and Kazaure, 1967). McDonald and Harkness (1965) found aflatoxins in groundnut samples from Zaria, Kano and Mokwa, in Northern Nigeria. Bassir (1969) isolated aflatoxin B1 from various mouldy food materials offered for sale in Ibadan markets. Since then, toxigenic fungi and mycotoxins have been found in various foods and feedstuffs in many regions of Nigeria. Thus, mycotoxigenic fungi belonging to not less than forty