Assessment of IAA synthesis by endophytic bacteria in Vanda (Orchidaceae)

Abstract

Vanda is an important economic orchid, and some interesting species originated in Thailand. Several factors involved in the growth and development of orchids include nutrition, environmental conditions, plant hormones, and endophytic microorganisms. Endophytic microorganisms influence the germination and adaptation of orchids in various environmental conditions. However, endophytic bacteria in Vanda are rarely reported. Therefore, this research aimed to study isolated endophytic bacteria in Vanda tissue that can produce indole-3-acetic acid (IAA) and affect the growth and development of this plant. An IAA synthetic efficiency assessment of 14 of 208 isolates was done on culturing media with and without L-tryptophan. Without L-tryptophan, isolate 1L1 produced the most IAA (37.75 mg IAA L-1); whereas, with L-tryptophan, isolate 2R13 produced the most IAA (152.63 g IAA L-1). The endophytic bacteria colonies varied in color (brown, white, pink, or yellow), form (circular or irregular), elevation (flat, raised, convex, or umbonate), surface (smooth or matte), margins (undulate, entire, or filiform), and ooze. In addition, morphological assessment of endophytic bacteria found that nine isolates had a coccus shape, and five isolates had a rod shape. The Gram staining test showed that 13 isolates were Gram-negative, and one isolate, 3R14, was gram-positive. From this research, the results confirmed that there were 14 endophytic bacteria isolates that could synthesize IAA for Vanda.