Mycorrhizal inoculation in neem (Azadirachta indica) enhances azadirachtin content in seed kernels

In view of the high mycorrhizal dependency of neem trees (Azadirachta indica), an experiment was conducted to study if Arbuscular Mycorrhizal (AM) inoculation can enhance the azadirachtin content in seed kernels of trees grown in the field. Azadirachtin is an important active ingredient in neem seed kernels based on which a large biopesticide industry has emerged in India and few countries in Europe and the USA. Inoculation of neem seedlings in the nursery with Glomus fasciculatum and Glomus mosseae resulted in increased height, dry weight, root colonization and phosphorus (P) content. In a separate experiment, field-grown neem plants inoculated in the nursery and during transplantation with Glomus fasciculatum were evaluated after 5 years. No significant differences were found in the tree height, girth at breast height (GBH) and fruit yield but oil percentage, total triterpenoids and azadirachtin content in kernels increased significantly as a result of AM inoculation. A similar enhancement in azadirachtin was noted with P application. These results open up possibilities of producing quality neem seed with high bioactive ingredients through AM inoculation.