rubro-oculata also differed from that of two greenhouse epyphites (A. papillosa and Dendrobium moschatum (Buch.–Ham.) Swartz.) ( Tsavkelova et al., 2004). Therefore, orchid bacterial communities vary depending on the species or the root type. This diversity may be due to the composition of the root exudates. Orchids are known to produce various phenolic compounds and phytoalexins, which were shown to suppress a number of different microorganisms ( Stoessl and Arditti, 1984). Plant exudates also supply the rhizosphere with tryptophan that is the main precursor in microbial IAA biosynthesis ( Kravchenko et al., 2004). IAA producing bacteria transform it into auxin, increasing its exogenous level.