Variable responses on early development of shallot (Allium ascalonicum) and mustard (Brassica juncea) plants to Bacillus cereus inoculation

ABSTRACT

Aim: Auxin, a phytohormone secreted by plant growth-promoting rhizobacteria is one of the direct mechanisms vital for plant growth promotion. A laboratory experiment was conducted to observe the effect of IAA-producing and non-IAA-producing diazotroph Bacillus cereus strains on early growth of shallot (Allium ascalonicum) and mustard (Brassica juncea) plants. Methodology and Results: Treatments evaluated were as follows Control = uninoculated, no inoculation, UPMLH1 = IAA-producing B. cereus UPMLH1, and UPMLH24 = non-IAA-producing B. cereus UPMLH24. Inoculation with IAA-producing B. cereus UPMLH1 significantly increased shallot adventitious roots (root number and length) and shoot growth (19 to 54% increment). Inoculation of non-IAA-producing B. cereus UPMLH24 did not significantly improve growth of adventitious roots of shallot as compared to uninoculated control, except its shoot (up to 40% increase). However, primary roots and shoot growth of mustard plants significantly increased through inoculation with IAA-producing and non-IAA-producing strains (14 to 73% increment). Conclusion, Significance and Impact of Study The results indicated that exogenous IAA secreted by B. cereus UPMLH1 might have play an important role in inducing roots of shallot bulbs and it may have a variable promotional effect depending on plant species.