Neem (Azadirachta indica A.]uss., Family: Meliaceae, Subfamily: Meliodeae, Order, Meliales) is an evergreen tree native to the Indian subcontinent. It also grows widely in several other countries in Asia, Australia, Africa and Central and South America. The tree grows on almost all kinds of soils, including saline, alkali, and other wastelands. It grows as an avenue, ornamental and agroforestry plantation or as a shade tree along roadsides.
For centuries, neem has been held in high esteem by Indians for its medicinal and insecticidal properties. Various tree pans have been employed to obtain medicinal preparations used in Ayurvedic and Unani systems of medicines. There is hardly a disease where the use of neem is not mentioned.
It has been an age-old practice to place dried leaves between folds of clothes to ward off moths, insects and other pests in stored rice, wheat and other grains. It is now considered to hold great potential as a pest-control agent for use in agriculture.
Due to ever-increasing public concerns about the harmful effects of toxic synthetic pesticides, neem-based products have virtually taken centrestage as possible alternatives. The problems associated with synthetic pesticides, such as pest resistance, environmental contamination, toxic residues in food, feed and fibre, chronic toxicity, disruption of non-target organisms, etc., are practically non-existent with biopesticides based on neem.
Initial studies on neem were focused on the manurial, soil conditioning and pesticide value of its cake. By 1960, chemists established that its bioactive principles were extractable in organic solvents. The water suspension of neem seed kernel was observed to be antifeedant against the migratory and desert Locusts, Locusta migratoria and Schistocerca gregaria. Neem is a renewable source of various useful products. It finds application in medicines, soap making, pest control, nitrification inhibition, slow nutrient release manure, cattle feed and fuel, energy etc.
It has emerged as the singlemost important source of pesticides and allied products. All parts of the tree, such as leaf, flower, fruit, seed, kernel, bark, wood, and twig, are biologically active, the maximum activity being associated with the seed kernel. Biopesticides based on neem are endowed with features of diverse activity and relative safety to nontarget organisms. In agriculture, neem products are valued for their effect as slow N-release materials and as nitrification inhibitor also.
The observations of the scientists on the neem’s activity initially received a lukewarm response from the international community. While validation trials carried out by different national and international groups yielded inconsistent results, confirmation of the activity by Prof. H. Schmutterer’s group in Germany sparked the interest of international community on this wonderful tree.
The tree’s international recognition was borne out by a publication, ‘Neem: A Tree for Solving Global Problems’ published by the National Academy of Sciences, USA, in 1992. Neem contains a large number of chemically diverse and structurally complex bioactive tetranortriterpenoids commonly referred to as C-seco meliacins or limonoids. It does not knockdown or kill the insect instantaneously like most neurotoxic insecticides. Instead, it elicits physiological and behavioral responses in insects, which lead to their death.
The Indian Agriculture Research Institute (IARI) has contributed enormously in the last four decades to the research and development of neem. The chemists joined hands with biologists in unraveling the multifarious actions of neem. Extraction and isolation protocols for various bioactive neem constituents were established for the first time in most of the cases.
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