**Genetic Diversity of Nigerian Cashew Germplasm**

Olawale Mashood Aliyu

*Department of Cytogenetics and Genome Analysis Institute of Plant Genetics and Crop Research (IPK), Gatersleben Germany* 

#### **1. Introduction**

162 Genetic Diversity in Plants

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> Cashew (*Anacardium occidentale* L) is a tropical tree nut crop that is native to tropical South American countries around Bolivia, Brazil, Peru and West Indies (Nakasone & Paull, 1998; Samal et al., 2003), with the Amazonia forest of Brazil being the centre of origin (Mitchell & Mori, 1987). Recent archeological data from 47-million year old lake sediment in Germany has shown evidence of earlier distribution of cashew in Europe during the Tertiary period, thus, suggesting bio-geographic link between America and Africa continents in the distribution of genus *Anacardium* (Manchester et al., 2007). Since the introduction of the modern cashew into Africa and Asia continents about five centuries ago, the crop has spread widely and these new areas have become the centre of diversity of cashew today. Cashew has now become important commodity export crop in the third world countries like Benin Republic, Cote d'Ivore, Guinea Bissau, Ghana, India, Mozambique, Nigeria, Philippines, Srilanka,Tanzania and Vietnam.

> Cashew is a drought resistance and evergreen perennial small tree plant with dense foliage and can grow as high as 15 meters or more. It is a member of *Anacardiaceae* family with about 75 genera and 700 species (Nakasone & Paull, 1998). Other members of the family *Anacardiaceae* include mango and pistachio. Out of the eight species identified in the genus *Anacardium*, only cashew (*occidentale*) is of economic importance because of its edible hypocarp (apple) and nutritious kernel from the drupaceous nut (Fig. 1). Cashew tree is mostly single-stemmed with umbrella-shaped canopy and the flowering is normally preceded by vegetative growth flush at the end of wet season in the southern hemisphere. The flowers comprise of male and hermaphrodite types in varying proportion and are produced at the end of new shoots in the periphery of the tree canopy. And because of the sticky nature of the cashew pollens, the plant tends more to insect pollination, with some low degree of selfing (Northwood, 1966; Masawe, 1994; Feitas & Paxton, 1996, Aliyu, 2008). The kidney shaped nut (drupe) attached to the swollen hypocarp (pseudo-fruit or apple) is the true biological fruit of the cashew tree (Fig. 1). The kernel, eaten as dessert is the most nutritional part of the cashew and important delicacy because of it high protein and low cholesterol fat. It contains about 47% fat and oil, 21% protein and 22% carbohydrates (Fetuga et al. 1975; Nayar, 1998) and 82% of this fat is unsaturated that helps in reducing body cholesterol level. Structurally, the kernel is protected by a hard shell or endocarp and a

spongy mesocarp which contains some acidic oil called cashew nut shell liquid (CNSL). The liquid has been reported for a number of potential industrial uses e.g. for brake linings, paints and vanishes etc. The juice derived from the fresh cashew apples contains high content of vitamin C, about three times higher than in citrus and pawpaw. This characteristic informed fresh consumption of cashew apples by many people, but unfortunately, this pseudo-fruit can only be kept afresh for a short time after harvesting because of it high sucrose content that aid rapid degradation (rotten).

Fig. 1. The most economic products of cashew tree (i.e. hypocarps or apples, the nuts and its derivative kernels after shelling). (Fruit photo from Topper et al., 2001).
