IDENTIFICATION OF ENDOPHYTIC BACTERIA ASSOCIATED WITH N2 FIXATION AND INDOLE ACETIC ACID SYNTHESIS AS GROWTH PROMOTERS IN CURCUMA ALISMATIFOLIA GAGNEP.

Endophytic bacteria carrying out dinitrogen (N₂) fixation and indole acetic acid (IAA) synthesis were firstly identified in C. alismatifolia, a globally important flower crop. Their potential as growth promoters to stimulate the rapid growth of host plant was also examined. It will be beneficial to reduce the propagation period of tissue culture plantlets, and also utilize as a biofertilizer for rhizome production in the field. Seven endophytic bacteria were isolated from the leaf, four isolates from the leaf base, and two from the rhizome. ECS203, a gram-negative bacterium with a round shape, showed the highest N₂ fixation at 4.2 nmol C₂H₄/10⁶ cells/hr, and ECS202 showed the highest IAA synthesis at 296 μL μg ^{? 1} protein. Three selected isolates of N₂-fixing and IAA synthesizing endophytic bacteria, i.e., ECS202, ECS203, and ECS204, isolated from the leaf base, were used to reinoculate Curcuma plantlets derived from tissue culture. Then, plants were grown in sterilized sand for 2 months and weekly supplied with N-free nutrient solution. Plant growth, colonization, nitrogen fixation, and IAA synthesis were measured at two months after planting. The inoculated plants clearly showed a better performance of plant growth and yield in terms of the plant height, plant weight, leaf area, and diameter of new rhizomes compared with uninoculated plants. The chlorophyll content and N concentration of leaves and roots also increased in inoculated plants. Endophytic bacteria from inoculated plants colonized the roots, rhizome, and leaf base. Partial sequence analysis using 16S rDNA indicated that the isolate ECS202 corresponded to Sphingomonas pseudosanguinis (99.2% similarity over 1,371 bp), ECS203 to Bacillus drentensis (99.4% similarity over 1,450 bp) and ECS204 to Bacillus methylotrophicus (99.9% similarity over 13,06 bp).