Plant Growth Regulation and Suppression of Sugarcane Fungal Diseases through Multi-stress tolerant Rhizobacteria

Abstract

Sustainability in agricultural development has emerged as one of the most significant concerns of the current era as 20–40% of the reduced crop yields and estimated losses of 40 billion dollars worldwide caused by phytopathogens consider the rising concern for food security. Among the possible disease control methods, biocontrol of phytopathogens by using plant growth promoting bacteria (PGPB) seems to be a good option for the development of eco-friendly, cost effective, and sustainable approaches. Keeping in mind this scenario the current study was designed and undertaken. In the study, 93 bacterial strains were finalized to evaluate their biocontrol activity along with plant growth promoting traits. Bacterial strains showed Indole acetic acid (IAA), phosphate solubilization, ammonia, siderophore, and hydrogen cyanide (HCN) production. Out of 93 strains, 10 strains that showed best plant growth promoting (PGP) traits and antagonistic activities were selected and noticed to be positive towards enzyme activities, and ACC deaminase and exopolysaccharide production (EPS) production. Of these, 9 bacterial strains belonged to the genus Bacillus whereas one was identified as Bravibacterium frigoritolerans (PM12). Multi-stress tolerance against heat, drought, salinity and heavy metals along with resistance to antibiotics was observed. Bacterial strain PM19 (Bacillus methylotrophicus) showed resistance against 14 out of 15 antibiotics. Bacillus siamensis (PM13) and Bacillus xiamenensis (PM14) showed prominent multi abiotic stress tolerance among others. All bacterial strains showed distinct inhibition coefficient values against fungal strains. In another experiment, characterization of biologically produced silver nanoparticles (AgNPs) by Xray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Diffused reflectance spectroscopy (DRS) and Scanning electron microscopy (SEM) confirmed the production of silver nanoparticles by bacterial supernatant, fungal supernatant and sugarcane husk solution. Among all, sugarcane husk based AgNPs showed significant antifungal properties as compared to others. In the second phase, a greenhouse study was performed to analyze plant growth promotion and control of fungal diseases Colletotricum falcatum (red rot) and Fusarium monilliforme (pokha boeng). All inoculated bacterial strains enhanced sugarcane plant growth and yield in sugarcane. Examination of growth parameter revealed that the application of bacterial strain Bacillus siamensis (PM13) significantly enhanced the plant growth parameters with increased percent values of 21.77, 33.66,23.38, 32.96, 16.9, 36.9 , 62.68, 62.27, 43.76, 38.73, 23.7 and, 40.9 for plant height, plant fresh weight, cane length, cane weight, cane diameter, root length, Chlorophyll a, Chlorophyll b, carotenoids, Brix, POL and CCS, 2 respectively, in comparison to the control plants without bacterial strains inoculation. Results of the greenhouse experiment against red rot disease of sugarcane showed that augmentation of Bacillus siamensis (PM13), Bacillus tequlensis (PM17), Bacillus xiamenensis (PM14) and Bravebacterium frigoritolerance (PM12) to S. officinarum suppressed the symptoms of fungal disease and its drastic effects on sugarcane growth (enhanced) and yield parameters. The bacterial strain, Bacillus siamensis (PM13), showed the highest values among all for growth enhancement and red rot disease suppression. Whereas, inoculation of Bacillus siamensis (PM13), B. tequlensis (PM17), Bacillus gibsonii (PM11) and Bacillus sp. (PM15) not only enhanced growth of the plants but also alleviated the pokha boeng disease. In this experiment, the highest plant growth parameters were noticed in sugarcane plants inoculated with Bacillus tequilensis, while the lowest disease severity index was observed in Bacillus siamensis (PM13) treated plants. Application of silver nanoparticle played a positive role to control both diseases with increased plant growth in two varieties of sugarcane (variety 1: CO1148, and variety 2: CSSG32). Sugarcane plants of variety 2 (CSSG32) responded better in both aspects (plant growth and disease control) after the application of silver nanoparticles. It appears that augmented production of antioxidative enzymes and proline content in the greenhouse studies may lead to the induced systemic resistance against red rot and pokha boeng disease of sugarcane. Role of B. xiamenensis (PM14) as plant growth promoting multi-stress tolerant antagonistic bacterium is perhaps a new finding in this study and has not been reported previously adding new knowledge to scientific information. In vitro and in vivo experiments revealed native microflora of sugarcane as the potential growth promoting and fungal disease control agents. The present study has the potential to be implemented in sustainable agricultural. Thus, the potential application of native bacteria with multi-stress tolerance and biocontrol abilities; along with biologically produced silver nanoparticles studied presently may pave an interesting avenue for food security by implementing ecofriendly strategy