• Energy Research

Siderophores are low molecular weight secondary metabolites produced by microorganisms under low iron stress as a specific iron chelator. In the present study, a rhizospheric bacterium was isolated from the rhizosphere of sesame plants from Salem district, Tamil Nadu, India and later identified as Bacillus subtilis LSBS2. It exhibited multiple plant-growth-promoting (PGP) traits such as hydrogen cyanide (HCN), ammonia, and indole acetic acid (IAA), and solubilized phosphate. The chrome azurol sulphonate (CAS) agar plate assay was used to screen the siderophore production of LSBS2 and quantitatively the isolate produced 296 mg/L of siderophores in succinic acid medium. Further characterization of the siderophore revealed that the isolate produced catecholate siderophore bacillibactin. A pot culture experiment was used to explore the effect of LSBS2 and its siderophore in promoting iron absorption and plant growth of Sesamum indicum L. Data from the present study revealed that the multifarious Bacillus sp. LSBS2 could be exploited as a potential bioinoculant for growth and yield improvement in S. indicum.

This review presents a comprehensive and systematic study of the field of bacterial plant biostimulants and considers the fundamental and innovative principles underlying this technology. Plant biostimulants are an important tool for modern agriculture as part of an integrated crop management (ICM) system; helping make agriculture more sustainable and resilient. Plant biostimulants contain substance(s) and/or microorganisms whose function when applied to plants or the rhizosphere, is to stimulate natural processes to enhance plant nutrient uptake, nutrient use efficiency, tolerance to abiotic stress, biocontrol, and crop quality. The use of plant biostimulants has gained substantial and significant heed worldwide as an environment-friendly alternative for sustainable agricultural production. Presently, there is an increasing curiosity of industry and researchers in microbial biostimulants especially, bacterial plant biostimulants (BPBs) to improve crop growth and productivity. The BPBs that are based on PGPR (plant growth-promoting rhizobacteria) play plausible roles to promote/stimulate the crop plant growth through several mechanisms that include, i) nutrient acquisition by nitrogen (N2) fixation and solubilization of insoluble minerals (P, K, Zn), organic acids and siderophores, ii) antimicrobial metabolites and various lytic enzymes, iii) action of growth regulators and stress-responsive/induced phytohormones, iv) ameliorating abiotic stress like drought, high soil salinity, extreme temperatures, oxidative stress, and heavy metals by using different modes of action, and v) plant defense induction modes. Presenting here is a brief review emphasizing the applicability of BPBs as an innovative exertion to fulfill the current food crisis.

Fuel contamination is a major issue that comes with the utilization of biodiesel. Microbial growth is one of the primary causes of contamination during fuel handling and storage. This work attempts to identify the types, shapes, and growth profiles of microorganisms on fuel samples. The morphology of microbial colonies is presented in order to analyze the potential of fuel contamination. The diesel, biodiesel, and blends are stored in stainless steel (SS) and glass tanks, where each is placed indoors and outdoors during the 90 days of storage time. The morphology of microbial colonies is observed through a microscope with a magnification of 1000× and the quantity is calculated by a digital colony counter. Microbial contamination in all samples is considered as high contamination where the Colony Forming Unit (CFU) is greater than 105 L-1. Colony forms are far more assorted in blends than in pure diesel (B0) and neat biodiesel (B100). The transformation of microbial colonies accelerates after 60 days of storage time. The results reveal that the number of bacterial colonies that grow in B20 is higher and more varied, nevertheless, the contamination in B100 is significantly higher. This is indicated by a 1.5-fold rise in B20 acidity and a 2.5-fold increase in water content compared to the initial condition.

Rice is a crop that is consumed as a staple food by the majority of the people in the world and therefore failure in rice crops, due to any reason, poses a severe threat of starvation. Rice blast, caused by a fungus Pyricularia oryzae, has been ranked among the most threatening plant diseases of rice and it is found wherever rice is grown. All of the rice blast disease management strategies employed so far have had limited success and rice blast has never been eliminated from rice fields. Hence, there is a need to look for the best remedy in terms of effectiveness, sustainability, and organic nature of the method. This study was aimed at determining the plant growth-promoting and fungicidal effects of a mixture of Piper caninum and Piper betle var. Nigra leaves extracts and rhizobacteria. Gas chromatography–mass spectrophotometry (GC-MS) analysis of a mixture of leaves extracts of these plants revealed the presence of new bioactive compounds such as alpha.-gurjunene, gamma.-terpinene, and ethyl 5-formyl 3-(2-ethoxycarbonyl) in a mixture of leaves extracts of P. caninum and P. betle var. Nigra. The mixture of these extracts reduced the intensity of blast disease, inhibited P. oryzae, and improved the growth, yield, and quality of Bali rice. All treatments comprising of different concentrations of a mixture of leaves extracts of P. caninum and P. betle var. Nigra plus rhizobacteria exhibited biocontrol and bioefficacy. However, a 2% concentration of a mixture of these leaves extracts with plant growth-promoting rhizobacteria (PGPR) exhibited potent inhibition of growth of P. oryzae, a significant reduction in the intensity of blast disease, and a maximum increase in growth, yield, and quality of Bali rice. In the 15th week, the intensity of blast disease decreased from 80.18% to 7.90%. The mixture of leaves extract + PGPR also improved the height of the plant, the number of tillers, number of leaves, number of grains per panicle, number of heads per panicle, and the full-grain weight per clump. Applications of various concentrations of a mixture of leaves extracts + PGPR resulted in improvement in the potential yield of rice, however, the application of 2% extracts + PGPR gave the highest potential yield of 5.61 tha−1 compared to the low yields in the control and other treatments. The high grain yield observed with the treatment was caused by the low intensity of blast disease. This treatment also strengthened the stem and prevented the drooping of the plant and improved the quality of rice grain.

Bali is a world tourist destination and has many natural resources that need to be developed to support the tourism sector. One of the local Bali resources that has the potential to be developed to support tourism and food is the local red Bali rice. This local Balinese rice is a characteristic of the ecotourism area of the Jatiluwih village of Tabanan, Bali. Balinese rice is grown with inorganic pesticides and there is an urgent need to develop organic pesticides as a sustainable approach to rice farming. In this regard, extracts of piper plants can serve as the best and greenest biopesticides as plant growth-promoting rhizobacteria (PGPR), and compost functions as organic fertilizer. The present research aimed to evaluate PGPR, compost, and the synergistic biopesticidal effects of extracts of three piper plants, namely Piper caninum, Piper betle var. Nigra, and Piper betle, against blast disease in Bali red rice plants. The results showed that the synergistic action of PGPR, compost, and crude extract of piper plant provided an inhibitory activity against blast disease in rice plants where the greatest inhibition was found in a mixture of the three extracts with an inhibition of 50 cm. This shows that the mixed compounds of the three piper extracts work synergistically in suppressing blast disease; in addition, PGPR also exhibited a positive impact on the growth of red rice because PGPR produce growth hormones and various antifungal metabolites that help the plant growth and induce systemic resistance against phytopathogens. The active principles were identified as citronella, trans-geraniol, and 4.6-dipropyl-nonan-5-one. A combination of these extracts with compost and PGPR showed potential antifungal activity against blast disease at a concentration of 2%. This application also promoted the growth of Bali red rice. There is a significant increase in the number of leaves and the number of tillers, where the height is inversely proportional to the higher the extract up to 2%, as the height of the red Bali rice plant decreases. This is good because it reduces the red Bali rice stalks’ possibility of falling during small production. The piper extract mixture at a concentration of 2% had the highest effect on grain production/tonne (6.59 tonne/ha) compared to the control at only 3.21–3.41 tonnes/ ha. The 2% concentration of the extracts from the mixture of the three pipers has the highest effect on growth and red Bali rice production, and provides the greatest obstacle to the intensity of blast disease in red Bali rice.