Judul: Penapisan Komunitas Bakteri Rizosfer secara In Planta untuk Meningkatkan Pertumbuhan Jagung di Lahan Kering
Abstrak: Indonesia has wide proportion of dryland and its potential for the development of a variety of important crops, such as maize. Increment of the dryland capacity is still constrained by various problems, among others, drought and low soil fertility. Microbial applications to increase the dryland productivity have been carried out. However, effective microbial inoculum for specific problems in the dryland should continue to explore. In this study, in planta screening was done to obtain potential rhizosphere bacterial community for growth promoting of maize in dryland. The dominant bacterial group from selected bacterial community was also analysed for plant growth promoting characteristics and its potency and role in the growth of maize in greenhouse. A total of 11 rhizosphere soil samples (TR A, TR B, C TR, TR D, TR E, F TR, TR G, H TR, TR I, J TR, and TR K) were collected from selected maize grown in two farm of dryland development located in Lombok, West Nusa Tenggara. In green house screening, a 100 g of each rhizosphere soil sample was added to maize growth medium. The results showed that TR D gave the best growth performance of maize. In the 50% water content of growing media, TR D treatment generally showed increased fresh weight of upper biomass (47.1%), dry weight of upper biomass (45.2%) and highest increase of root dry weight (33.4%). Based on cultivation method using four culture media showed that at least 22 bacterial isolates and 5.72 x 107 cells g-1 of soil were found in the TR D. Those number of isolate was higher compared with the others rhizosphere soil samples. T-RFLP analysis of bacterial community inhabitant of TR D showed that 8 T-RFs were detected based on metagenomic approach and 7 T-RFs based on cultivation-dependent approach. Those number of T-RF based on metagenomic approach was higher compared with the others communities in this study. Based on Shannon index, the diversity level of bacterial community of TR D was 1.6 in metagenomic and 1.58 in cultivation-dependent approach. The diversity level in metagenomic approach was higher compared with the others communities. The bacterial community structure of TR D included Burkholderiales, Pseudomonas, Bacillus, Candidatus, Alphaproteobacteria, Betaproteobacteria, Rhizobiales, Sinobactera-ceae, and Acidobacteria. Burkholderiales is the dominant group in metagenomic approach with eveness value was 45.83%. Pseudomonas sp. strain L485 is the dominant group in cultivation-dependent approach with eveness value was 42.88%. Pseudomonas sp. strain L485 also detected in metagenomic with eveness value was 17.38%. Based on estimation of the dominance and existence in metagenomic and cultivation-dependent approaches, Pseudomonas sp. strain L485 was chosed to plant growth promoting characteristics and tested for its ability to promote the growth of maize in the greenhouse. Pseudomonas sp. L485 is the maize rhizosphere bacteria producing indole acetic acid (IAA) and exopolysaccharide (EPS). The amount of IAA produced by this strain in King's broth medium supplemented with 5 ppm L-tryptophan was about 4.97 ppm when the cell density reached 3.74 x 1010 cells ml-1 and 11.95 ppm when the strain reached the stationary phase of growth. Approximately 0.058 mg EPS per mg of cell
Keyword: bacterial community, in planta, rhizosphere, maize, dryland, T-RFLP