THE EXACT origin of neem is uncertain, but today it is found almost everywhere in the tropical belt. Some say neem is native to the entire Indian subcontinent, but others expand this to dry forest areas throughout south and southeast Asia, including Pakistan, Sri Lanka, Thailand, Malaysia and Indonesia.

Indian neem was introduced in Africa early this century by Brig-Gen. Frederick Guggisberg, governor of what is now called Ghana. Neem can now be found in more than 30 countries, including Fiji, the Philippines, the Caribbean, Mauritius and Latin America. Neem can also be found in southern USA and about 50,000 neem trees have been planted in Mecca, Saudi Arabia, to protect Haj pilgrims from the fiery desert sun.

Because neem's spread is so extensive, considerable genetic variation in the species can be expected. But, Christel Palmberg-Lerche, FAO's chief of forest resources development, explained, "Due to the reputedly short life of the seeds, no systematic collections of germplasm covering the full range of the species have been carried out. Such collections would be of the greatest importance to adequately evaluate genetic variations in the species".

In India, seeds have been collected from about 20 centres scattered in eight states by the Indian Council of Forestry Research and Education (ICFRE) in Dehradun. ICFRE director D N Tewari reports the seeds collected varied in weight and length. Samples from Rajasthan and Haryana are more potent than those obtained from other parts of the country, but it is not known whether this is because of environmental or genetic variation.

Efforts to collect neem germplasm have begun in Thailand in collaboration with the DANIDA Forest Seed Centre because of fears that neem germplasm may be getting eroded. Two varieties of neem have been identified in Thailand, one of which is similar to the Indian neem. Changing cropping patterns are reducing the area for neem plantations in Thailand. Rice fields are being converted to plantations of sugarcane and, in dryer areas, of cassava, leaving little room for such trees as neem that were traditionally grown on field boundaries to provide fuel and other needs.