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Anacardium occidentale L., the cashew nut tree, has its probable origin in Brazil in north-eastern South America. There are eight species in the genus. Anacardium refers to the shape of the fruit (‘Ana’ = upwards/opposite ‘cardium’ = heart). Cashew is a woody, evergreen tree with a dome-shaped spreading habit and grows to a height of up to 10–15 m. The branches of older trees almost touch the ground (Fig. 2.1.1a). Young leaves are reddish-brown to green, gradually turning dark green as they mature. Flowers are produced in loose panicles at the end of the branches (Fig. 2.1.1b). The cashew is andromonoecious; on each panicle, perfect and staminate flowers are produced (Johnson, 1973; Ohler, 1979). It is cross-pollinated (Wait and Jamieson, 1986) by insects (Reddi, 1992). Cashew has a chromosome number of 2n = 42; however, the ploidy is unclear (Purseglove, 1968).

Fig. 2.1.1. (a) Dome-shaped spreading habit of cashew tree. It grows 10–15 m in height. The branches of older trees almost touch the ground. (b) Flowers produced in loose panicles at the end of the branches in andromonoecious inflorescences, with each panicle bearing perfect and staminate flowers.

Normally, trees growing under favourable conditions can produce their first crop after 6 years when grown from seedlings; however, grafted plants are known to yield in 3 years. The kidney-shaped nut is attached to the fruit-like pear-shaped cashew ‘apple’ which is the enlarged and swollen fruit stalk. The true fruit is the nut composed of a hard, greyish-brown pericarp. The seed is enclosed in the nut and consists of two cotyledons and the embryonic axes covered by the seedcoat.

Cashew is a hardy tropical tree, can tolerate a range of soils and environments and can survive with as little as 750 mm of rain per annum. It has a well-developed and fast-growing root system with a network of primary and secondary roots.

In its native habitat, it extends into semi-arid regions where the daily maximum temperatures are >40°C. It is well suited for wasteland reclamation and is an ideal crop for afforestation (Nayar, 1983; Sastry and Kavathekar, 1990). Temperature is reported to be critical for bud sprouting and shoot elongation. A two-step temperature regime is recommended by Aliyu (2005) for induction of bud sprouts and shoot elongation. The first step for induction of buds occurs at temperatures <35°C, followed by increased temperatures that favour optimal shoot elongation. De Figueirêdo et al. (2014) have performed a life cycle assessment of cashew to quantify the impact of environmental factors, i.e. farm soil conditions, farm management practices, fertilization regime, disease and pest management practices to improve cashew crop and its products.

Cashew is a nut crop of major importance, grown in >30 tropical countries and producing four valuable commercial products: cashew nuts, cashew apple, gum and wood (de Figueirêdo et al.,2014). Cashew trees were introduced to East Africa and India from Brazil by Portuguese colonizers and missionaries between 1563 and 1578 (Rao et al., 1988; Uji et al., 1991). It spread from coastal South India to other growing regions (De Castro, 1994). Certain selections that have adapted to coastal India have improved performance in terms of number of flowers, higher panicle length, nut inflorescence number, yield of nuts/plant and weight of the nuts (Hanumanthappa et al., 2014). According to the Global Statistical Review (2015–2016) of the International Nut and Dried Fruit Council (2016), India led the global production of cashew in 2016 with 172,719 MT (kernel basis) or 23% of global production. It is closely followed by Côte d’Ivoire (171,111 MT), which increased its production by 55% in a single season and reflects a 3% increase in global production. Vietnam is the third largest producer with 113,095 MT or 15% of global production. The global production of cashews in 2016 was 738,861 MT.

The kernels are a rich source of ascorbic acid and vitamin B complex (Vijaykumar, 1991; Gopalan and Vijaykumar, 1992). By-products of cashew, i.e. cashew apple and cashew nut shell liquid (CNSL) are important in local and international markets. CNSL, a naturally occurring phenol, present in the honeycomb structure (mesocarp) between the outer shell (epicarp) and the inner shell (endocarp) of the cashew nut, is used as raw material for several polymer-based industries, e.g. paints, varnishes, industrial and decorative laminates, brake lining and rubber compounding resins and foundry chemicals (Kamath, 1956; Ohler, 1979). It is also used in dentistry to inhibit tooth decay and cavities (D’Souza et al., 1996). The cashew tree gum has antimicrobial and insecticidal properties (Marques et al., 1992). Cashew processing industries, globally, are an important source of wage employment for rural women and also self-employment through micro-enterprises (Jeeva, 2013). The cashew industry in India generates >400,000 jobs annually in remote areas with 95% of them being carried out by rural women (Patil, 2015).