We found that phytopathogens such as P. carotovorum resisted the effects of azadirachtin more strongly than plant growth-promoting bacteria such as Rhizobium sp. (Table 3). Furthermore, the sporulation of T. asperellum was delayed by treatment with 0.4 mgmL-1 or more of azadirachtin, though the same was not true for F. Oxysporum (data not shown). Additionally, T. asperellum prevalence in the rhizosphere and root nodules was significantly reduced when plants were treated with 1.25 or 2.5 µgmL-1 azadirachtin (Figure 2 and 3). These results suggest that the use of azadirachtin in agriculture suppresses some plant growth-promoting bacteria, resulting in the loss of phytopathogen control or an imbalance of microbial soil ecology, eventually leading to the increased prevalence of various plant diseases. Additionally, in the BS pots, plants treated with 2.5 µgmL-1 azadirachtin had lighter roots and shoots than the control (Table 2). Similarly, the amount of root nodules and T. asperellum in the rhizospheres of plants treated with neem extract was less than that of the control (Figure 2 and 3). This also suggests that neem extract suppresses the growth of some plant growth-promoting bacteria. However, the long-term use of neem extract enhanced the growth of microorganisms in the soil and rhizosphere (Table 1 and Figure 1). This implies that, in agricultural usage, neem extract was safer for the soil ecosystem than azadirachtin.