Role of PGPR on the physiology of sunflower irrigated with produced water containing high total dissolved solids (TDS) and its residual effects on soil fertility

The synergistic interaction effect between biochar and plant growth-promoting rhizobacteria on beneficial microbial communities in soil

Excessive use of chemical fertilizers and extensive farming can degrade soil properties so that leading to decline in crop yields. Combining plant growth-promoting rhizobacteria (PGPR) with biochar (BC) may be an alternative way to mitigate this situation. However, the proportion of PGPR and BC at which crop yield can be improved, as well as the improvement effect extent on different eco-geographic region and crops, remain unclear. This research used cabbage [Brassica pekinensis (Lour.) Rupr.] as the target crop and established as treatment conventional fertilization as a control and a 50% reduction in nitrogen fertilizer at the Yunnan-Guizhou Plateau of China, adding BC or PGPR to evaluate the effects of different treatments on cabbage yield and the soil physicochemical properties. Specifically, high-throughput sequencing probed beneficial soil microbial communities and investigated the impact of BC and PGPR on cabbage yield and soil properties. The results revealed that the soil alkaline hydrolyzable nitrogen (AH-N), available phosphorus (AP), and available potassium (AK) contents were higher in the BC application than in control. The BC application or mixed with PGPR significantly increased the soil organic matter (OM) content (P<0.05), with a maximum of 42.59 g/kg. Further, applying BC or PGPR significantly increased the abundance of beneficial soil microorganisms in the whole growth period of cabbage (P<0.05), such as Streptomyces, Lysobacter, and Bacillus. Meanwhile, the co-application of BC and PGPR increased the abundance of Pseudomonas, and also significantly enhanced the Shannon index and Simpson index of bacterial community (P<0.05). Combined or not with PGPR, the BC application significantly enhanced cabbage yield (P<0.05), with the highest yield reached 1.41 fold of the control. Our research indicated that BC is an suitable and promising carrier of PGPR for soil improvement, combining BC and PGPR can effectively ameliorate the diversity of bacterial community even in acid red soil rhizosphere, and the most direct reflection is to improve soil fertility and cabbage yield.

Microbial regulation of plant secondary metabolites: Impact, mechanisms and prospects

Plant secondary metabolites possess a wide range of pharmacological activities and play crucial biological roles. They serve as both a defense response during pathogen attack and a valuable drug resource. The role of microorganisms in the regulation of plant secondary metabolism has been widely recognized. The addition of specific microorganisms can increase the synthesis of secondary metabolites, and their beneficial effects depend on environmental factors and plant-related microorganisms. This article summarizes the impact and regulatory mechanisms of different microorganisms on the main secondary metabolic products of plants. We emphasize the mechanisms by which microorganisms regulate hormone levels, nutrient absorption, the supply of precursor substances, and enzyme and gene expression to promote the accumulation of plant secondary metabolites. In addition, the possible negative feedback regulation of microorganisms is discussed. The identification of additional unknown microbes and other driving factors affecting plant secondary metabolism is essential. The prospects for further analysis of medicinal plant genomes and the establishment of a genetic operation system for plant secondary metabolism research are proposed. This study provides new ideas for the use of microbial resources for biological synthesis research and the improvement of crop anti-inverse traits for the use of microbial resources.

Functional traits and phylogenetic analysis of top-soil inhabiting rhizobacteria associated with tea rhizospheres in North Bengal, India

Rhizobacteria associated with cultivated crops are known to stimulate plant growth through various indirect or direct mechanisms. In recent years, the host list of plant growth promotion/promoting rhizobacteria has expanded to include bean, barley, cotton, maize, rice, vegetables, peanut, rice, wheat, and several plantation crops. However, interaction of rhizobacteria with tea plants of organic and conventional tea gardens is poorly understood. In the present study, rhizobacterial species associated with tea rhizosphere were isolated from 14 tea gardens located in North Bengal, India. In total, 16 rhizobacterial isolates isolated from collected soil samples were assessed for antagonistic and plant growth promotion/promoting activity under laboratory conditions. Molecular characterization based on sequencing of 16S rRNA gene revealed dominance of Bacillus with five species followed by Pseudomonas with two species. Interestingly, only one isolate was affiliated with actinobacteria, i.e., Microbacterium barkeri. Out of 16 isolates, isolates Bacillus subtilis OKAKP01, B. subtilis BNLG01, B. paramycoides BOK01, M. barkeri BPATH02, and Stenotrophomonas maltophilia BSEY01 showed highest growth inhibition against Fusarium solani (68.2 to 72.8%), Pseudopestalotiopsis theae (71.1 to 85.6%), and Exobasidium vexans (67.4 to 78.3%) causing respective Fusarium dieback, gray blight, and blister blight diseases in tea crop. Further, these five isolates also possessed significantly greater antifungal (siderophore producer, protease, chitinase, and cellulase activity) and plant growth promotion/promoting (indole-3-acetic acid production, ACC deaminase, ammonia, and phosphate solubilization) traits over other eleven rhizobacterial isolates. Therefore, these five isolates of rhizobacteria were chosen for their plant growth promotion/promoting activity on tea plants in nursery conditions. Results from nursery experiments revealed that these five rhizobacteria significantly improved growth rates of tea plants compared with the control. Therefore, this study suggests that these rhizobacteria could be used to formulate biopesticides and biofertilizers, which could be applied to sustainable tea cultivation to improve crop health and reduce disease attack.

Plant Growth-Promoting Rhizobacteria (PGPR) with Microbial Growth Broth Improve Biomass and Secondary Metabolite Accumulation of Cannabis sativa L

Plant growth-promoting rhizobacteria (PGPR) are a sustainable crop production input; some show positive effects under laboratory conditions but poorly colonize host field-grown plants. Inoculating with PGPR in microbial growth medium (e.g., King's B) could overcome this. We evaluated cannabis plant (cv. CBD Kush) growth promotion by inoculating three PGPR (Bacillus sp., Mucilaginibacter sp., and Pseudomonas sp.) in King's B at vegetative and flower stages. At the vegetative stage, Mucilaginibacter sp. inoculation increased flower dry weight (24%), total CBD (11.1%), and THC (11.6%); Pseudomonas sp. increased stem (28%) dry matter, total CBD (7.2%), and THC (5.9%); and Bacillus sp. increased total THC by 4.8%. Inoculation with Mucilaginibacter sp. and Pseudomonas sp. at the flowering stage led to 23 and 18% increases in total terpene accumulation, respectively. Overall, vegetative inoculation with PGPR enhanced cannabis yield attributes and chemical profiles. Further research into PGPR inoculation onto cannabis and the subsequent level of colonization could provide key insights regarding PGPR-host interactions.

Rhizobacteria of Bali With Obvious Growth-Promoting Properties on Corn (Zea mays L.)

Corn productivity in Indonesia is still relatively low compared with other countries. Therefore, it is necessary to increase the productivity of corn by using rhizobacteria, which have multiple traits. This study was conducted to obtain indigenous rhizobacteria of Bali that have multiple traits, can produce indoleacetic acid (IAA), fix nitrogen from atmosphere, produce siderophores, colonize roots, increase seed germination, and promote the growth of corn. Isolation of rhizobacteria was carried out from the rhizosphere of plants belonging to the Gramineae family that grows in Bali Island, Indonesia. Six isolates, namely, Sr3, Tb9, Rg1, Rg23, Al27, and Jg8, could produce IAA, fix nitrogen from the atmosphere, produce siderophores, and increased germination rate and vigor index of corn seedling. Among them, three isolates, namely, Rg1, Sr3, and Jg8, significantly (p &lt;0.05) increased the germination rate of corn seeds, increased vigor index, increased root dry weight and shoot dry weight of corn at the age of 7 days, and were able to colonize corn roots. Compared with the control, the rhizobacteria treatment increased the germination of corn seeds ranging from 5.04 to 13.05%. Based on the analysis of the 16S rRNA gene, it was found that these rhizobacteria species were Glutamicibacter nicotianae strain Rg1 (accession number OM349119), Brevibacillus invocatus strain Sr3 (accession number OM327515), and Micrococcus luteus strain Jg8 (accession number OM362349). Under a greenhouse condition, all the three isolates significantly (p &lt;0.05) increased nutrient uptake, the leaf chlorophyll content, net assimilation rate, and crop growth rate of corn when compared with control. These results suggested that these isolates of rhizobacteria obviously promoted the growth of corn and can be developed as biostimulant to promote the growth and increase the corn yield in Bali, Indonesia.