Neem

Neem (Azadirachta indica (A. Juss))

Distribution: A native to India and Burma, neem trees are only suited to the tropical and semi-tropical regions. Through introduction the tree has spread to Asia, Africa, the Americas, Australia and the islands of the south Pacific. It is present mainly in the drier (arid) tropical and subtropical zones. Mountainous areas are generally avoided.

Botanical characteristics: Neem is a fast growing tree that can reach a height of 15-20 m. Under favourable conditions up to approximately 35-40 m. It is an evergreen but under severe conditions it may shed most or nearly all of its leaves. The branches are wide spread. The fairly dense crown is roundish or oval and may reach the diameter of 15-20 m in old, free-standing specimens.

The trunk is relatively short, straight and may reach a girth of 1.5-3.5 m. The bark is hard, fissured or scaly, and whitish-grey to reddish-brown. The sap wood is greyish-white and the heart wood reddish when first exposed to the air becoming reddish-brown after exposure. The root system consists of a strong taproot (can be twice as long as the height of the tree) and well developed lateral roots.

The unpaired, pinnate leaves are 20-40 cm long and the medium to dark green leaflets (which number up to 31) are about 3-8 cm long. The terminal leaflet is often missing. The petioles are short. Very young leaves are reddish to purplish in colour. The shape of mature leaflets is more or less asymmetric and their margins are dentate with the exception of the base of their basiscopal half, which is normally very strongly reduced and cuneate.

The flowers (white and fragrant) are arranged axillary, normally more-or-less drooping panicles which are up to 25 cm long. The inflorescences, which branch up to the third degree, bear 150-250 flowers. An individual flower is 5-6 mm long and 8-11 mm wide. Protandric and bisexual flowers and male flowers exist on the same individual (polygamous).

The glabrous fruits are olive-like drupes which vary in shape from elongate oval to nearly roundish, and when ripe are 1.4-2.8 x 1.0-1.5 cm. The fruit skin (exocarp) is thin and the bitter-sweet pulp (mesocarp) is yellowish-white and very fibrous. The mesocarp is 0.3-0.5 cm thick. The white, hard shell (endocarp) of the seed encloses one, rarely two or three, elongated seeds (very often referred to as “seed kernels” or kernels) having a brown testa.

Ecology: The neem tree is famous for its drought resistance. Normally it thrives in areas with sub-arid to sub-humid conditions, with an annual rainfall between 400 and 1200 mm. It can grow in regions with an annual rainfall below 400 mm, but in such cases it depends largely on the ground water levels. Neem can grow in many different types of soil, but it thrives best on well drained deep and sandy soils. (pH 6.2-7.0). It is a typical tropical/subtropical tree and exists at annual mean temperatures between 21-32 °C. It can tolerate high to very high temperatures. It doesn't tolerate temperature below 4 °C (leaf shedding and death may ensue).

A multipurpose tree: The beneficial properties of the neem tree have been part of Indian folklore for thousands of years. Dubbed 'the village pharmacy', it has numerous medicinal properties, aiding conditions ranging from digestive disorders to diabetes and from high cholesterol to cancer. For many of the medicinal properties mentioned, no scientific data exists, but the fame is based on traditional knowledge (Ayurvedic medicine) or anecdotal stories. Besides its use in traditional Indian medicine the Neem tree is of great importance for its anti-desertification properties and possibly as a good CO₂ sink.

Of primary interest to research scientists is its activity as an insecticide. Many of the tree's secondary metabolites have biological activity, but azadirachtin is considered to be of the most ecological importance. Studies have shown a wide spectrum of activity and species affected. Research has increased in the past few years as the desire for safe pest control methods increases and it becomes apparent that this tree will be able to play a role in integrated pest management systems.

Useful books:

• Gahukar, R. T. (1995) Neem in plant protection. Nagpur, India, Agri-Horticultural Publishing House. vii + 165 pp. ISBN 81-900392-0-2

• Boa, E. R. (1995) A guide to the identification of diseases and pests of neem (Azadirachta indica). Bangkok, Thailand, FAO Regional Office for Asia and the Pacific (RAPA). 71 pp.

• Schmutterer, H. (Editor) (1995) The neem tree Azadirachta indica (A. Juss.)and other meliaceous plants: sources of unique natural products for integrated pest management, medicine, industry and other purposes. Weinheim, Germany, VCH Verlagsgesellschaft mbH. xxiii + 696 pp. ISBN 3-527-30054-6

• Tewari, D. N. (1992) Monograph on neem (Azadirachta indica A. Juss.).Dehra Dun, India, International Book Distributors. vi + 279 pp. ISBN 81-7089-1752

• Vietmeyer, N. D. (Director) (1992) Neem: a tree for solving global problems. Report of an ad hoc panel of the Board on Science and Technology for International Development, National Research Council. Washington, DC, USA,National Academy Press. ix + 141 pp. ISBN 0-309-04686-6

• Jacobson, M. (Editor) (1989) The neem tree. Boca Raton, Florida, USA, CRC Press, Inc. 178 pp.

Useful links:
http://www.neemfoundation.org/
http://www.fao.org/forestry/FOR/FORM/FOGENRES/Inn/neem.stm
platformagenttechnologie (http://www.platformgentechnologie.nl/patents/euro_pat_office/parents/neem_final_backgrounder_nl.shtml/)