Associative diazotrophic bacteria from forage grasses in the Brazilian semi-arid region are effective plant growth promoters

Abstract

The study of plant growth-promoting bacteria (PGPB) can identify outstanding bacteria for crops. For forage grasses adapted to drylands, the selection of PGPB can increase the field performance of pastures. The aim of this study was to isolate, and characterise at molecular, biochemical and symbiotic levels, diazotrophic bacteria obtained from buffel grass (Cenchrus ciliaris), sorghum (Sorghum bicolor) and Tifton 85 (Cynodon spp.) from Brazilian semi-arid region fields. Field-grown plants were collected, and the roots were surface-disinfected, crushed and inoculated in a semi-solid medium. After the formation and confirmation of microaerophilic pellicles, the bacteria were isolated and purified. All bacterial isolates were subjected to nifH gene amplification and identified by their partial 16S rRNA gene sequences. The bacteria were evaluated for the production of auxins and siderophores, calcium phosphate solubilisation, and diazotrophic ability as ‘in vitro’ plant growth-promotion traits. A plant inoculation assay was conducted to assess the plant growth-promotion abilities of the bacterial isolates. Twenty-one bacterial isolates harboured the nifH gene (nifH+), among which nine were obtained from sorghum, eight from buffel grass, and four from Tifton 85. The bacterial isolates were classified as Bacillus (8), Stenotrophomonas (7), Agrobacterium (4), Cellulomonas (1) and Paenibacillus (1). All were shown to be auxin producers, with 14 isolates showing diazotrophic capacity ‘in vitro’. Fourteen isolates increased plant N content, but the bacterial strains ESA 392 and ESA 398 (Bacillus), ESA 397 and ESA 407 (Stenotrophomonas), and ESA 401 (Agrobacterium) were shown to promote both plant growth and N nutrition. These strains are candidates for further assays to evaluate their agronomic performance under field conditions, aiming inoculant production for forage grasses in drylands.

Positive Effects of Organic Substitution in Reduced-Fertilizer Regimes on Bacterial Diversity and N-Cycling Functionality in Greenhouse Ecosystem

“…A similar situation of increased Flavobacterium , Aeromonas , Citrobacter , Pseudochrobactrum and Stenotrophomonas abundances after fertilizer input reduction with partial organic material substitution was also observed. Previous studies reported that Flavobacterium , Citrobacter and Stenotrophomonas degrade organic matter, are involved in N cycling (such as promoting nutrient cycling and enhancing soil N) and are enriched when organic materials were introduced into the soil [ 45 , 80 , 81 , 82 ], which explained their higher abundances in treatments with continuous C input (2/4 CN + 2/4 MN and 2/4 CN + 2/4 SN) in this study. A higher C/N ratio in the input fertilizer was selected for bacterial assemblage according to the ecological function and adaptation to the surrounding environment [ 83 ].…”

Bacilli Rhizobacteria as Biostimulants of Growth and Production of Sesame Cultivars under Water Deficit

“…Significant effects of water restriction on sesame were observed with a reduction in shoot dry mass, plant height, number of capsules per plant, and sesame productivity from the thirtieth day after planting [ 38 ]. ESA 13 already proved to be an efficient plant growth promoter for rice ( Oryza sativa ) [ 6 ], while ESA 402 showed positive effects on sorghum under full irrigation [ 40 ] and water deprivation conditions [ 7 ]. The results observed for the sesame genotypes in the present study agree with the potential of both bacilli to compose multi-crop inoculants for drylands.…”

“…The Bacillus spp. strains ESA 13 [ 6 ], ESA 402 [ 7 , 40 ], and ESA 441 [ 68 ] were obtained from the “Coleção de Culturas de Micro-organismos de Interesse Agrícola da Embrapa Semiárido” (Embrapa Semiárido, Petrolina-PE, Brazil). They were streaked in LB solid medium (Luria Bertani) and incubated for 24 h at 28 °C.…”

Beneficial Plant-Associated Microorganisms From Semiarid Regions and Seasonally Dry Environments: A Review

“…Furthermore, Santana et al (2020) showed that Enterobacter sp., Bacillus sp., and Rhizobium sp., isolated from T. spicata , were also able to improve some plant growth and gas exchange parameters in sorghum growing under drought conditions ( Tables 1 , 2 ). Although these bacterial groups have already been shown to be efficient inoculants for sorghum ( da Silva et al, 2018 ; Antunes et al, 2019 ), their ability to attenuate the adverse effects of drought and promote sorghum growth under drought had not been revealed. Interestingly, these T. spicata isolates showed diazotrophic capacity in a culture medium supplemented with up to 1.27 mol L –1 NaCl ( Table 1 ; Fernandes-Júnior et al, 2015 ), which suggests that the beneficial effects of BNF may be supported around the plant environment under water-deficit conditions.…”