Pratibha Vyas

The present study is aimed at evaluating biocontrol and growth-promoting potential of volatile organic compound (VOC) producing bacterial endophytes against Sclerotinia sclerotiorum in Helianthus annuus L. Two isolates SEB6 and SEB23, exhibiting fungal growth inhibition of 23.75 and 20.0%, respectively, in a dual-plate assay and 76.5 and 35.4%, respectively, in broth were identified by morphological features, biochemical tests, matrix-assisted laser desorption/ionization time of flight mass spectroscopy and 16S rRNA gene sequencing as Bacillus safensis and Serratia liquefaciens. Scanning electron microscopy revealed that fungal growth was inhibited by bacterial antagonists by rupturing, breaking, and shrinking of fungal hyphae. Additionally, the antagonists exhibited phosphate solubilization, and auxins, ammonia, and lipase production. Both strains produced various volatile organic compounds as detected by gas chromatography–mass spectrometry, including 26 VOCs in Bacillus safensis SEB6 and 16 in Serratia liquefaciens SEB23. The compounds 1-docosene, isopropyl myristate, 1,2-benzenedicarboxylic acid, octadecene, diethyl phthalate, glycerin, triacetin, and tetradecane were the common VOCs produced by both the strains. Colonization of plant tissues, as evident by scanning electron microscopy analysis, validated the endophytic nature of both the strains. The pot trial revealed that the combined application of both the strains decreased the disease severity by 88.9% and significantly improved the vigor index, plant growth, total phenol content, and chlorophyll content over control treatment. The maximum increase in N, P, and K contents of 1.73, 0.54, and 6.8%, respectively, was obtained with the treatment BsSEB6 + SlSEB23 in the presence of the fungal pathogen. To the best of our knowledge, this paper for the first time reports the production of 3-pentadecylphenol by the antagonistic Bacillus safensis strain.

Millets are an abundant source of micronutrients with great variability and are known as Miracle Grains/Nutri-cereals. Biofortification by plant growth promoting bacteria in millet cultivars with increased levels of iron (Fe) and zinc (Zn) can significantly reduce the prevalence of their deficiencies which are common in developing countries that rely mostly on cereals for their nutritional needs and dietary energy. This paper reviews the importance of PGPR in enhancing the availability of zinc and iron in millets through mineral solubilization via siderophore production. This results in acidification of soil by releasing organic acids that binds to cations thus making them available to the plant.

Ensuring food security for the growing global population is a major concern, particularly while striving towards enhancing the world’s food systems without compromising environmental sustainability. Conventional agricultural practices are majorly dependent on artificial fertilizers, which have various environmental and human health issues. Phosphorus is a major macronutrient for plant growth and development, but it is subject to tremendous losses in terms of immobilization, leaching, and erosion. Cognizant of this, environmentalists and sustainability researchers have focused more on modern approaches. Biofertilizers, plant breeding, and smart fertilizers have the potential to transform agricultural practices and offer answers to both immediate and long-term issues. Biofertilizers, consisting of the formulations of plant growth-promoting microorganisms, enhance plant growth and improve crop yield through direct or indirect mechanisms. Plant breeding mainly targets identifying genes linked to phosphorus efficiency traits, and breeding methods to enhance the phosphorus use efficiency of plants. Smart fertilizers are new technologies, including controlled and slow-released fertilizers, bioformulation fertilizers, and nano-fertilizers, to increase nutrient use efficiency and crop yield sustainably, thus minimizing health risks and other environmental issues. The major key barrier to preventing the widespread use of plant breeding and smart fertilizers in agriculture is the high cost of the material. This chapter explores the use of biofertilizers, innovative plant breeding methods, and smart fertilizers in contemporary agricultural practices to promote more sustainable and efficient food production systems.

The present study was designed to check the ability of cyanogenic antagonistic bacterial endophytes to produce volatile organic compounds and enhance growth of sunflower under Sclerotinia sclerotiorum stress. Forty endophytic bacteria were isolated and screened for antagonism against Sclerotinia sclerotiorum. Out of 40 endophytes, two isolates SEB1 and SEB21 exhibited fungal growth inhibition of 30.0 and 36.6%, respectively, in dual plate assay and 78.7 and 82%, respectively, in liquid media. Scanning electron microscopy showed rupturing, breakage and shrinkage of the fungal hyphae in the presence of the antagonistic bacterial strains. In addition, the bacterial strains also exhibited phosphate solubilization, and production of hydrogen cyanide, siderophores, auxins, ammonia, lipase and cellulases. The isolates were identified as Sphingobacterium solani SEB1 and Pseudomonas sp. SEB21 by 16S rRNA gene sequencing. GCMS analysis confirmed the presence of dimethyl-sulfone, phenol, 3-hexadecene, 2,4-ditertbutylphenol, 1-docosene, 1-octadecene, 2,4-dimethylphenylimino-4-nitrophenyl, nonylcyclopropane 1-nonadecene, octacosane, n-octadecanol, isopropyl myristate, 3-hexadecene, 7,9-di-tert-butyl-1-oxosiro-4,5-deca-6,9-diene, 3,5-bis (1,1-dimethylethyl)-phenol, isopropyl myristate, 7,9-ditert-butyl-1-oxospiro (4,5) deca-6,9-diene-2,8-dione, 1-tricosene and octacosanol as major volatile organic compounds produced by the bacterial strains. SEM analysis showed colonization of plant tissues by both the bacterial strains validating their endophytic nature. The bacterial treatments showed disease control up to 88.9% and significantly improved vigor index, plant growth, total phenol and chlorophyll content over the uninoculated control in sunflower grown under greenhouse conditions. The treatment SsSEB1+PspSEB21 in the presence of the fungal pathogen showed 1.41%, 0.47% and 6.8% N, P and K content in plants, respectively, which was the highest among all the treatments. Further field-level evaluations are recommended to validate the effectiveness of Sphingobacterium solani SEB1 and Pseudomonas sp. SEB21 as biological control agents. Sphingobacterium solani as a biocontrol agent and a plant growth-promoting endophyte is reported here for the first time.

In the present study, a liquid formulation(s) containing two phosphate-solubilizing Bacillus licheniformis PRPSB ₁₀ and Pseudomonas putida PRPSB ₃₈ has been developed and tested for its efficacy to improve growth, yield, and nutrient content of potato ( Solanum tuberosum L.) under integrated nutrient management system. These two phosphate-solubilizing strains, isolated from potato rhizosphere showed high phosphate-solubilizing efficiency, with solubilization index of 6.1 and 5.8, respectively, on modified Pikovskaya agar. The strain PRPSB ₁₀ solubilized 659.9, 202.0, and 113.7 μg ml ⁻¹ of tricalcium phosphate, rock phosphate, and iron phosphate, respectively, while the strain PRPSB ₃₈ solubilized 457.4, 187.9, and 80.0 μg ml ⁻¹ of the same substrates, respectively, after 5 days of incubation in NBRIP broth. Among the different cell protectants tested, 0.1% carboxymethyl cellulose (CMC) was found to be the best for B. licheniformis PRPSB ₁₀ while 5 mM trehalose was best suited for P. putida PRPSB ₃₈ maintaining the cell viability ~10 ⁸ CFU ml ⁻¹ up to 1 year under ambient storage conditions. Two-year field evaluations of the liquid formulation in potato variety Kufri Pukhraj with different P dosages revealed a significant improvement in plant growth, phosphorus content, tuber yield and soil fertility over the respective control treatment with an average increase of 16.2% in yield over control. Economic analysis further indicated mean net returns of ₹44,876 ha ⁻¹ and an improved benefit-cost ratio of 2.52 compared with the uninoculated control. The results indicated that the developed liquid PSB formulation exhibited excellent stability, effectively enhanced yield and phosphorus availability highlighting its potential to be used as a liquid biofertilizer for improving potato productivity and maintaining soil health.

The study aimed at selecting salt-tolerant endophytic bacteria with the ability to improve growth, proline content, and antioxidant enzymes in Avena sativa (Oat) under salinity. Of 43 endophytic bacteria isolated from various Oat tissues on nutrient agar with 2.5% NaCl, all produced ammonia and auxins. Additionally, 30.2% solubilized phosphate, 83.7% solubilized ZnO, 4.6% solubilized Zn₃(PO₄), 7.0% solubilized ZnCO₃, 69.8% produced siderophores, and 2.3% produced HCN. These isolates also differed in their ability to exhibit growth at different NaCl levels (5–15%). Dendrogram that was generated based on plant growth-promoting traits and salinity tolerance exhibited three clusters and four independent branches. Out of thirteen bacterial isolates selected based on plant growth-promoting traits and salinity tolerance, five isolates showed significantly higher radicle and plumule length of Oat over control on water agar plates. Two promising isolates evaluated for growth promotion, antioxidant, and osmoprotectant activities in two salt-resistant (OL-14, OL-1876-2) and two susceptible (UPO-212, OL-1971) Oat genotypes under salinity in pots significantly enhanced plant height, dry weight, proline content, superoxide dismutase, peroxidase, and catalase activities over the uninoculated control. The SEM analysis showed the colonization of plant tissues by these bacterial strains validating their endophytic nature. Isolates were characterized based on polyphasic approach exhibiting maximum similarity to Bacillus inaquosorum O₃SE₂ and Bacillus safensis O₄SE_1. Salinity-tolerant plant growth-promoting B. inaquosorum and B. safensis as endophytes associated with Avena sativa L. are reported for the first time.