Azadirachtin levels in neem (Azadirachta indica A. Juss.) seed grown in Northern Australia

To help in establishing the viability of a commercial neem industry in Australia an understanding of the expected azadirachtin levels in the seed was needed. Between 1992 and 1994, four studies were set up to investigate the range of azadirachtin levels in trees grown in North Queensland and other Northern Australian sites. These studies included a general survey of ecotypes, a regional survey, a study of the variation of azadirachtin levels throughout the cropping season and a study of the annual variation. One hundred and forty five trees from of six ecotypes, all growing at a single site, were assayed for the azadirachtin content of their seed. Azadirachtin levels ranged between 0.35 and 0.89% of dried kernel. The average azadirachtin concentration did not vary significantly between ecotypes. However, the variation of individual trees within an ecotype was large. In the regional survey, 95 trees, growing in five regions of Queensland were assayed for seed azadirachtin levels. Azadirachtin levels varied significantly between sites, with Weipa having the highest and Redland Bay the lowest. However, azadirachtin levels also varied greatly within sites. The seasonal variation in seed azadirachtin levels from individual trees was measured over the cropping season in 1992 and 1993 to determine if early fruit had higher azadirachtin levels than late fruit. Nc significant pattern developed but the trend was for higher levels early in the season. Annual azadirachtin levels of individual trees were examined over two or three years to determine the fluctuations that could be expected from one year to the next. Azadirachtin levels fluctuated between years with high and low years being consistent across all the trees tested.