PHYSIOLOGICAL AND MORPHOLOGICAL ADAPTATION OF A HIGH CONTENT AZADIRACHTIN IN THAI NEEM (AZADIRACHTA SIAMENSIS VAL.) TO FIELD TRIAL

Neem tree is well known as a natural bio-pesticide source to protect cultivated plant from insects. Azadirachtin belongs to the group of limonoids and is a secondary metabolite accumulating in the seed of neem tree, especially in the form of azadirachtin-A. The lack of high azadirachtin-A accumulation clones, however, is a limitation in the use of the initial material as a bio-pesticide on an industrial scale. The aim of this research was to determine the content of azadirachtin-A in clones of Thai neem and to intensively study the physiological and morphological adaptation of neem in the field prior to seed production. Eleven clones of Thai neem (A. siamensis Val.) seeds, including SP48, PR10, PR13, PR15, SP01, SP20, SP25, V58, V100, V122 and V141 were harvested from mature trees grown in field sites. The azadirachtin-A contents in the dry seeds were extracted, purified and then assayed. The top-four clones of a high azadirachtin-A content were then cultivated in a field trial for physiological and morphological adaptation. Four-clones SP01, V141, V122 and V58, were classified as rich in azadirachtin-A. The azadirachtin-A content in those clones was significantly higher (2–3-fold) than in the control (SP48). Physiological and morphological adaptations of a one-year plantation were evaluated. The physiological characteristics in terms of net-photosynthetic rate (NPR), stomatal conductance (G), transpiration rate (E), and water use efficiency (WUE) in all clones showed no differences when compared with a control clone (SP48). Similarly, morphological characteristics, including plant height, stem circumference, and bush diameter, were not-significantly different from controls. This means that these clones have a high adaptive ability to field trial environments.