An Evaluation of Aluminum Tolerant Pseudomonas aeruginosa A7 for In Vivo Suppression of Fusarium Wilt of Chickpea Caused by Fusarium oxysporum f. sp. ciceris and Growth Promotion of Chickpea

Evaluating the potential of Acinetobacter calcoaceticus in alleviation of aluminium stress in Triticum aestivum

Soil contamination with toxic heavy metals [such as aluminum (Al)] is becoming a serious global problem due to the rapid development of the social economy. Although plant growth-promoting rhizo-bacteria (PGPR) are the major protectants to alleviate metal toxicity, the study of these bacteria to ameliorate the toxic effects of Al is limited. Therefore, the present study was conducted to investigate the combined effects of different levels of Acinetobacter calcoaceticus (5 ppm and 10 ppm) of accession number of MT123456 on plant growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress and response of antioxidant compounds (enzymatic and nonenzymatic), and their specific gene expression, sugars, nutritional status of the plant, organic acid exudation pattern and Al accumulation from the different parts of the plants, which was spiked with different levels of Al [0 µM (i.e., no Al), 50 µM, and 100 µM] using aluminum sulfate [Al2(SO4)3] in wheat (Triticum aestivum L.). Results from the present study revealed that the Al toxicity induced a substantial decreased in shoot length, root length, number of leaves, leaf area, shoot fresh weight, root fresh weight, shoot dry weight, root dry weight, chlorophyll-a, chlorophyll-b, total chlorophyll, carotenoid content, net photosynthesis, stomatal conductance, transpiration rate, soluble sugar, reducing sugar, non-reducing sugar contents, calcium (Ca2+), magnesium (Mg2+), iron (Fe2+), and phosphorus (P) contents in the roots and shoots of the plants. In contrast, increasing levels of Al in the soil signifcantly (P < 0.05) increased Al concentration in the roots and shoots of the plants, phenolic content, malondialdehyde (MDA), hydrogen peroxide (H2O2), electrolyte leakage (EL), fumaric acid, acetic acid, citric acid, formic acid, malic acid, oxalic acid contents in the roots of the plants. Although, the activities of enzymatic antioxidants such as superoxidase dismutase, peroxidase, catalase, ascorbate peroxidase and their specific gene expression in the roots and shoots of the plants and non-enzymatic such as phenolic, favonoid, ascorbic acid, and anthocyanin contents were initially increased with the exposure of 50 µM Al, but decreased by the increasing the Al concentration 100 µM in the soil. Addition of A. calcoaceticus into the soil signifcantly alleviated Al toxicity effects on T. aestivum by improving photosynthetic capacity and ultimately plant growth. Increased activities of antioxidant enzymes in A. calcoaceticus-treated plants seem to play a role in capturing stress-induced reactive oxygen species as was evident from lower levels of MDA, H2O2, MDA, and EL in A. calcoaceticus-treated plants. Research findings, therefore, suggested that A. calcoaceticus application can ameliorate Al toxicity in T. aestivum seedlings and resulted in improved plant growth and composition under metal stress as depicted by balanced exudation of organic acids.

The occurrence of banana Fusarium wilt aggravates antibiotic resistance genes dissemination in soil

The spread of antibiotic resistance genes (ARGs) and subsequent soil-borne disease outbreaks are major threats to soil health and sustainable crop production. However, the relationship between occurrences of soil-borne diseases and the transmission of soil ARGs remains unclear. Here, soil ARGs, mobile genetic elements and microbial communities from co-located disease suppressive and conducive banana orchards were deciphered using metagenomics and metatranscriptomics approaches. In total, 23 ARG types, with 399 subtypes, were detected using a metagenomics approach, whereas 23 ARG types, with 452 subtypes, were discovered using a metatranscriptomics method. Furthermore, the metagenomics analysis revealed that the ARG total abundance levels were greater in rhizospheres (0.45 ARGs/16S rRNA on average) compared with bulk (0.32 ARGs/16S rRNA on average) soils. Interestingly, metatranscriptomics revealed that the total ARG abundances were greater in disease-conducive (8.85 ARGs/16S rRNA on average) soils than disease suppressive (1.45 ARGs/16S rRNA on average) soils. Mobile genetic elements showed the same trends as ARGs. Network and binning analyses indicated that Mycobacterium, Streptomyces, and Blastomonas are the main potential hosts of ARGs. Furthermore, Bacillus was significantly and negatively correlated with Fusarium (P < 0.05, r = -0.84) and hosts of ARGs (i.e., Mycobacterium, Streptomyces, and Blastomonas). By comparing metagenomic and metatranscriptomic analyses，this study demonstrated that metatranscriptomics may be more sensitive in indicating ARGs activities in soil. Our findings enable the more accurate assessment of the transmission risk of ARGs. The data provide a new perspective for recognizing soil health, in which soil-borne disease outbreaks appear to be associated with ARG spread, whereas beneficial microbe enrichment may mitigate wilt disease and ARG transmission.

Multifaceted Impacts of Plant-Beneficial Pseudomonas spp. in Managing Various Plant Diseases and Crop Yield Improvement

The modern agricultural system has issues with the reduction of agricultural productivity due to a wide range of abiotic and biotic stresses. It is also expected that in the future the entire world population may rapidly increase and will surely demand more food. Farmers now utilize a massive quantity of synthetic fertilizers and pesticides for disease management and to increase food production. These synthetic fertilizers badly affect the environment, the texture of the soil, plant productivity, and human health. However, agricultural safety and sustainability depend on an ecofriendly and inexpensive biological application. In contrast to synthetic fertilizers, soil inoculation with plant-growth-promoting rhizobacteria (PGPR) is one of the excellent alternative options. In this regard, we focused on the best PGPR genera, Pseudomonas, which exists in the rhizosphere as well as inside the plant's body and plays a role in sustainable agriculture. Many Pseudomonas spp. control plant pathogens and play an effective role in disease management through direct and indirect mechanisms. Pseudomonas spp. fix the amount of atmospheric nitrogen, solubilize phosphorus and potassium, and also produce phytohormones, lytic enzymes, volatile organic compounds, antibiotics, and secondary metabolites during stress conditions. These compounds stimulate plant growth by inducing systemic resistance and by inhibiting the growth of pathogens. Furthermore, pseudomonads also protect plants during different stress conditions like heavy metal pollution, osmosis, temperature, oxidative stress, etc. Now, several Pseudomonas-based commercial biological control products have been promoted and marketed, but there are a few limitations that hinder the development of this technology for extensive usage in agricultural systems. The variability among the members of Pseudomonas spp. draws attention to the huge research interest in this genus. There is a need to explore the potential of native Pseudomonas spp. as biocontrol agents and to use them in biopesticide development to support sustainable agriculture.

Screening Biocontrol Agents for Cash Crop Fusarium Wilt Based on Fusaric Acid Tolerance and Antagonistic Activity against Fusarium oxysporum

Fusarium wilt, caused by Fusarium oxysporum, is one of the most notorious diseases of cash crops. The use of microbial fungicides is an effective measure for controlling Fusarium wilt, and the genus Bacillus is an important resource for the development of microbial fungicides. Fusaric acid (FA) produced by F. oxysporum can inhibit the growth of Bacillus, thus affecting the control efficacy of microbial fungicides. Therefore, screening FA-tolerant biocontrol Bacillus may help to improve the biocontrol effect on Fusarium wilt. In this study, a method for screening biocontrol agents against Fusarium wilt was established based on tolerance to FA and antagonism against F. oxysporum. Three promising biocontrol bacteria, named B31, F68, and 30833, were obtained to successfully control tomato, watermelon, and cucumber Fusarium wilt. Strains B31, F68, and 30833 were identified as B. velezensis by phylogenetic analysis of the 16S rDNA, gyrB, rpoB, and rpoC gene sequences. Coculture assays revealed that strains B31, F68, and 30833 showed increased tolerance to F. oxysporum and its metabolites compared with B. velezensis strain FZB42. Further experiments confirmed that 10 µg/mL FA completely inhibited the growth of strain FZB42, while strains B31, F68, and 30833 maintained normal growth at 20 µg/mL FA and partial growth at 40 µg/mL FA. Compared with strain FZB42, strains B31, F68, and 30833 exhibited significantly greater tolerance to FA.