Abstract

Aqueous neem (Azadiracta indica) leaf extract was tested for its effect on Casuarina equisetifolia seed germination capacity, growth of Frankia and on some dominant rhizosphere microorganisms under casuarinas grown in soil contaminated with sewage water. Analysiswas carried out to determine the main micro- and macroelement content of different extract amounts. The addition of extract amount between 10- 20 µl per 10 ml medium (1- 2 µl ml^-1) selectively stimulated Frankia growth and inhibited other non- beneficial bacteria and fungi in the rhizosphere such as Bacillus subtilis, Drechslera sp and Curvularia lunata. Slight increase was observed in Casuarina seed germination capacity with 1- 2 Μ ml^-1 of the extract, but with no significant differences, indicating at least no negative effect of the extract on seed germination. According to the results and as the roots and leaves of both Casuarina and neem release their active components in soil, and according to previous recommendations, we suggest a significant synergistic effect between Casuarina, rhizosphere microorganisms and neem trees for the benefits of Casuarina nodulation, growth performance and nitrogen fixation.

Key words: Neem, Casuarina, aqueous extract, Frankia, rhizospheric microorganisms.