Abstract:
Certain groups of bacteria live in rhizosphere are beneficial for plant growth,
protect from disease and abiotic stress. Therefore, this group of bacteria are
called plant growth promoting rhizobacteria (PGPR). Megathyrsus maximus
is a grass species, commonly found in Sri Lanka, is used as a fodder grass.
This grass grows well under very harsh conditions and in nutrient poor soils.
One of the reasons may be due to the microbial communities living in the root
system which support acquiring minerals thereby capable to withstand under
stress conditions. Therefore, the main objective of this study was to isolate
bacteria from the rhizosphere of M. maximum and characterize the traits that
are important for plant growth. In total, 36 bacterial isolates were isolated from
exo-rhizosphere and six bacterial isolates from endo-rhizosphere. Differential
abilities of bacterial isolates in nitrogen fixation, capacities of Zn, K and
phosphates solubilizations, and IAA production in vitro were investigated in
this study. Five exo-rhizospheric and one endo-rhizospheric isolate (E6) were
found as good Zn solubilizers in ZnO and ZnCO3 supplied as insoluble Zn
sources. It was found that R19 showed significantly higher Zn solubilizing
activity (100.78 mg/L) in ZnO supplemented broth whereas R24 showed the
highest value (133.06 mg/L) in ZnCO3 supplemented medium. Out of them
three isolates were able to solubilize potassium in mica supplemented medium
and the highest potassium solubilization was reported by R24 (23.41 mg/L)
followed by E6 (21.81 mg/L). R19, R24 and E6 showed the highest phosphate
solubilizing index. In total, seven isolates showed significantly higher nitrogen
fixing ability in NFb medium. The highest amount of IAA (39.37 mg/L) was
produced by bacterial isolate R24, followed by E6 (7.43 mg/L) and R8 (7.289
mg/L). According to our knowledge this is the first report of isolation and
characterization of PGPR bacteria from grass species solubilizing Zn,
potassium and phosphate along with other plant growth promoting traits such
as nitrogen fixation and IAA production in Sri Lanka. These bacteria would
be best candidates to develop as biofertilizers to be used in agriculture
specially for fodder production.
