Role of Bacilli in phytohormone production in rice and grain under different doses of vegetative and generative fertilizer

Abstract

Importance of the work: The use of plant-growth-promoting bacteria inoculant is a sustainable option to promote rice plant growth and improve the yield. Integrating these bacteria resulting with chemical fertilization may be another relevant option.
Objectives: To assess the physiological responses of Pathum Thani 1 rice under the co-application of different fertilizers and plant growth-promoting bacteria.
Materials & Methods: A pot experiment was conducted to assess plant growth-promoting ability under different vegetative fertilizers, generative fertilizers and bacteria inocula. The pot experiment was a 2×2×5 factorial experiment in a completely randomized design.  Plants were measured for endogenous phytohormones—indole-3-acetic acid (IAA), gibberellic acids (GAs) and salicylic acid (SA)—, macronutrients—nitrogen (N), phosphorous (P) and potassium (K)—and their yield parameters were evaluated.
Results: Significant (p < 0.05) increases were observed in the inoculated Pathum Thani 1 rice grain yield (18.16–32.77 g/pot), panicle number (19.50–31.25 panicles/pot), tiller number (28.50–45.88 tillers/pot) and plant height (103.34–120.52 cm). Significant (p < 0.05) endogenous IAA and SA level changes were observed compared to the uninoculated control. GAs were only significantly (p < 0.05) increased in the vegetative phase and not in the generative phase (p > 0.05) compared to the uninoculated control. A significant (p < 0.05) effect in P and K accumulation was observed in plant tissue, but not in N accumulation.
Main finding: Additions of plant growth-promoting bacteria Lysinibacillus sp. N5 or Bacillus sp. N7 were the best options to enhance rice growth and yield the most. In addition, adding bacteria decreased the dose of fertilizer required to obtain a higher rice yield. Furthermore, adding bacteria enhanced P and K but not N in the soil under various fertilizer doses, implying that N was in excess for plant growth. Finally, adding bacteria enhanced endogenous phytohormones, such as IAA, GAs and SA, in plant tissue.