Seed yield and azadirachtin content of Azadirachta indica in four ecosystems of southwest China

Azadirachta indica (neem) is a globally recognized plant resource suitable for the development of botanical insecticides, and its seeds have been promoted as an industrial source for the manufacture of biopesticides. The purpose of this study was to evaluate the yield potential of neem seeds and azadirachtin from four ecosystems of southwest China during the periods of 2008 (Year 1) and 2009 (Year 2). The results showed that each ecosystem in Year 1 had higher neem seed production, while each ecosystem in Year 2 had markedly higher contents of azadirachtin A (azA) and total azadirachtin A and B [az(A + B)]. There were significant differences (P < 0.05) between the four ecosystems in the mean tree height (H), mean tree basal diameter (BD), and mean tree canopy diameter (CD) during the two consecutive years, but no significant differences were found in the weight of per seed (SW), the length/width ratio of seeds (RLW), or the kernel percentage (KP). The seed yield per hectare was significantly (P < 0.05) higher for the trees in the tropical sub-humid region (Yuanyang), with a maximum of 1763.4 kg ha−1 in Year 1 and an average of 1650.3 kg ha−1 for the two years, than those in the subtropical arid (Yuanmou) and semi-arid (Yuanjiang) regions. The content and yield of az(A + B) for the seeds produced in the tropical semi-arid region (Gejiu) were the highest, with respective average values of 8.2 g kg−1 and 5.84 kg ha−1 throughout the two evaluation years. Compared with the other three locales, the trees from the subtropical arid region (Yuanmou) produced significantly (P < 0.05) lower seed yield and az(A + B) yield in the drought year of 2009.