Application of Plant Growth Promoting Bacillus thuringiensis as Biofertilizer on Abelmoschus esculentus Plants under Field Condition

Changes in Biologically Active Compounds in Pinus sylvestris Needles after Lymantria monacha Outbreaks and Treatment with Foray 76B

Due to climate warming, the occurrence of Lymantria monacha outbreaks is predicted to become more frequent, causing repeated and severe damage to conifer trees. Currently, the most effective way to control the outbreaks is aerial spraying with the bioinsecticide Foray 76B. The present study aimed to determine the impact of both: (i) L. monacha outbreaks and (ii) treatment with Foray 76B on tree resistance through the synthesis of polyphenols (TPC), flavonoids (TFC), photosynthetic pigments (chlorophyll a and b, carotenoids), lipid peroxidation (MDA), and soluble sugars (TSS) in Pinus sylvestris needles. Samples were collected from visually healthy (control), damaged/untreated, and damaged/Foray 76B-treated plots in 2020 and 2021 (following year after the outbreaks). The results revealed that L. monacha outbreaks contributed to the increase in TPC by 34.1% in 2020 and 26.7% in 2021. TFC negatively correlated with TPC, resulting in 17.6% and 11.1% lower concentrations in L. monacha-damaged plots in 2020 and 2021, respectively. A decrease in MDA was found in the damaged plots in both 2020 and 2021 (10.2% and 23.3%, respectively), which was associated with the increased synthesis of photosynthetic pigments in 2021. The research results also showed that in the following year after the outbreaks, the increase in the synthesis of photosynthetic pigments was also affected by the treatment with Foray 76B. Moreover, the increase in the synthesis of TPC and photosynthetic pigments in the damaged plots in 2021 illustrates the ability of pines to keep an activated defense system to fight biotic stress. Meanwhile, a higher synthesis of photosynthetic pigments in Foray 76B-treated plots indicates a possible effect of the treatment on faster tree growth and forest recovery after L. monacha outbreaks.

Plant growth-promoting rhizobacterial biofertilizers for crop production: The past, present, and future

Recent decades have witnessed increased agricultural production to match the global demand for food fueled by population increase. Conventional agricultural practices are heavily reliant on artificial fertilizers that have numerous human and environmental health effects. Cognizant of this, sustainability researchers and environmentalists have increased their focus on other crop fertilization mechanisms. Biofertilizers are microbial formulations constituted of indigenous plant growth-promoting rhizobacteria (PGPR) that directly or indirectly promote plant growth through the solubilization of soil nutrients, and the production of plant growth-stimulating hormones and iron-sequestering metabolites called siderophores. Biofertilizers have continually been studied, recommended, and even successfully adopted for the production of many crops in the world. These microbial products hold massive potential as sustainable crop production tools, especially in the wake of climate change that is partly fueled by artificial fertilizers. Despite the growing interest in the technology, its full potential has not yet been achieved and utilization still seems to be in infancy. There is a need to shed light on the past, current, and future prospects of biofertilizers to increase their understanding and utility. This review evaluates the history of PGPR biofertilizers, assesses their present utilization, and critically advocates their future in sustainable crop production. It, therefore, updates our understanding of the evolution of PGPR biofertilizers in crop production. Such information can facilitate the evaluation of their potential and ultimately pave the way for increased exploitation.

Effects of biofertilizer on soil microbial diversity and antibiotic resistance genes

Spread of antibiotic resistance or the presence of antibiotic resistance genes (ARGs) in pathogens is a globally recognized threat to human health. Numerous studies have shown that application of organic fertilizers may increase the risk of ARGs, however, the risk of resistance genes associated with biofertilizers is largely unknown. To investigate whether biofertilizer application introduces ARGs to the soil, we used high-throughput quantitative polymerization chain reaction (HT-qPCR) to explore the effect of biofertilizer application over three years on soil ARGs in three orchards with different locations in China. Redundancy analysis showed specific and significant differences in the beta diversity of soil bacteria and fungi between treatments (fertilizer vs. no fertilizer). One-way ANOVA analysis revealed findings of the main driver of the significant difference in microbial community structure between fertilizer and control treatment was the change in soil properties following the application of biofertilizer. A total of 139 ARGs and 27 MGEs (mobile genetic elements), and 46 ARGs and 6 MGEs from 11 major taxa were detected in biofertilizer and soil samples, respectively. Only the samples from Guangxi had significant differences in the detected number of ARGs and MGEs between fertilization and control. Through structural equation modeling (SEM), we found that soil properties indirectly affected ARGs by shaping bacterial diversity, while bacterial abundance directly affected ARGs. Biofertilizer application did not significantly alter the relative abundance of ARGs in soil due to the complexity of the soil environment and competition between exogenous and native microorganisms. This study provided new insights into the spread of the antibiotic resistome of the soil through biofertilizer applications.

Biofertilizers and nanofertilizers for sustainable agriculture: Phycoprospects and challenges

Increased food demands and ceasing nutrient deposits have resulted in a great shortfall between the food supply and demand and would be worse in the years to come. Higher inputs of synthetic fertilizers on lands have resulted in environmental pollution, persistent changes in the soil ecology, and physicochemical conditions. This has greatly decreased the natural soil fertility thereby hindering agricultural productivity, human health, and hygiene. Bio-based resilient nutrient sources as wastewater-derived algae are promising as a complete nutrient for agriculture and have the potential to be used in soilless cultivations. Innovations in nano-fortification and nano-sizing of minerals and algae have the potential to facilitate nutrients bioavailability and efficacy for a multifold increase in productivity. In this context, various options on minerals nanofertilizer application in agricultural food production besides efficient biofertilizer have been investigated. Algal biofertilizer with the nanoscale application has huge prospects for further agriculture productivities and fosters suitable development.

Rhizospheric bacteria as potential biocontrol agents against Fusarium wilt and crown and root rot diseases in tomato

The discovery of novel biocontrol agents requires the continuous scrutiny of native microorganisms to ensure that they will be useful on a regional scale. The goal of the present work was to discover novel antagonistic bacteria against Fusarium oxysporum ff. spp. lycopersici race 3 (Fol R3) and radicis-lycopersici (Forl) causing Fusarium wilt disease and Fusarium crown and root rot of tomatoes, respectively. High-throughput liquid antagonism screening of 1,875 rhizospheric bacterial strains followed by dual confrontation assays in 96-well plates was used to select bacteria exhibiting > 50% fungal growth inhibition. In a second dual confrontation assay in 10-cm Petri dishes, bacteria showing > 20% Fol R3 or Forl growth inhibition were further screened using a blood hemolysis test. After discarding β-hemolytic bacteria, a seedling antagonistic assay was performed to select five potential antagonists. A phylogenetic analysis of 16S rRNA identified one strain as Acinetobacter calcoaceticus (AcDB3) and four strains as members of the genus Bacillus (B. amyloliquefaciens BaMA26, Bacillus siamensis BsiDA2, B. subtilis BsTA16 and B. thuringiensis BtMB9). Greenhouse assays demonstrated that BsTA16 and AcDB3 were the most promising antagonists against Fol R3 and Forl, respectively. Pathogen biocontrol and growth promotion mechanisms used by these bacteria include the production of siderophores, biofilm, proteases, endoglucanases and indole acetic acid, and phosphate solubilization. These five bacteria exerted differential responses on pathogen control depending on the tomato hybrid, and on the growth stage of tomatoes. We report for the first time the use of an Acinetobacter calcoaceticus isolate (AcDB3) to control Forl in tomato under greenhouse conditions.

Efficacy of nanoparticles as nanofertilizer production: a review

Owing to the ever-increasing demand for food, the growing global population has forced farmers to increase fertilizer use. The overall use of fertilizers increased by 13 times between 1950 and 2020, from 15 to 194 million tons. Due to the resource shortages of chemical fertilizers on the market, agricultural costs are rising drastically every day because they cause an adverse impact on the environment by releasing chemical particulates and run-off agriculture. Biofertilizers have thus become a safer supplement to increase crop production without doing any harm to the environment, as they are produced industrially from a selected community of microorganisms that either develop a mutually beneficial relationship with plants or are part of their rhizosphere. They still have some drawbacks, which led to the development of a new avenue for the application of nanotechnology-mediated nanofertilizers. Nanotechnology recommends significant prospects for tailoring nanofertilizer production. They are typically coated with desired chemical composition having controlled release and targeted delivery of effective nanoscale ingredients, ability to improve plant productivity and to minimize environmental pollutants. The present review focuses primarily on the usefulness of nanofertilizers, as well as its environmental and safety concerns. The research would also include useful knowledge related to the introduction of different forms of nanoparticles within the agricultural field, contributing to the opening of a new route to nanorevolution.