Cashew: History, Evolutionary Origin, Genetic Resources, Improvement and Advances in Breeding

Cashew (Anacardium occidentale L.) is one of the most potential tropical nut trees, which belongs to the order Sapindales and family Anacardiaceae with 860 known species. The genus Anacardium is naturally distributed mostly in the tropics due to its long association with man. Amazonia has been considered the primary centre and Planalto of Brazil as the secondary centre of diversity. The presence of the highest number of wild species in northeast Brazil suggests that Anacardium genus, and A. occidentale, may have originated from this site. A. occidentale was the only species in the genus that has been introduced outside of the New World due to its economic importance. However, in recent times other species like A. excelsum, A. giganteum, A. spruceanum, A. humile, have shown economic potential. Cashew is believed to have been domesticated in northern part of South America and/or Caribbean or southern Mexican region. Regarding the presence of cashew in India, it is commonly mentioned that it was Portuguese travellers who introduced cashew nuts into India from Brazil in the sixteenth century. Contrary to the archaeological depiction of cashew fruit and plant in ancient monuments of India and in ancient writings indicating its ancient pre-Columbian presence. Cashew has naturalized in the coastal areas of India and has established itself all over South India, and possibly in many other tropical countries of Africa and Asia. It is now widely cultivated in most states of India belonging to both western and eastern coastal regions. Cashew is an evergreen tree bearing nuts that grows in latitude 15° north and south of the equator. The true fruit of cashew is the cashew nut, which is kidney shaped measuring 2–3 cm in length with a hard outer shell attached to a long, fleshy stalk, called cashew apple. Cashew is a source of food, income, industrial raw materials and foreign exchange for many African, Asian and Latin American countries. Products like roasted kernels, kernel oil, cashew nut shell liquid (CNSL), juice, jam and alcohol are derived from nuts and apples. The architecture of the tree makes it a leading tree crop for the recovery of land area by preventing desertification and soil erosion. Most importantly, cashew nut is the most profitable part of the tree, providing foreign exchange earnings to the producer countries. Realising the economic and nutritional value of cashew nut, all the cashew-growing countries started several research programmes in the field of cashew including germplasm collection, its use in crop improvement programmes, diversity studies, development of new high-yielding varieties etc. In India, so far 63 high-yielding varieties were released for commercial cultivation by the Directorate of Cashew Research, Puttur, and various agricultural universities. New approaches such as molecular breeding strategies and genomic studies are being integrated into crop improvement programmes of this crop.