Soil microorganisms with potential for alleviation of abiotic stresses in combination with plant growth promotion would be extremely useful tools in sustainable agriculture. To this end, the present study was initiated where forty-five salt tolerant bacterial isolates with ability to grow in high salt medium were obtained from the rhizosphere of Triticum aestivum and Imperata cylindrica. These bacteria were tested for plant-growth-promoting rhizobacteria traits in vitro such as phosphate solubilization, siderophore, ACC deaminase and IAA production. Of the forty-five isolates, W10 from wheat rhizosphere and IP8 from blady grass rhizosphere, which tested positive in all the tests were identified by morpholological, biochemical and 16SrDNA sequencing as Bacillus safensis and Ochrobactrum pseudogregnonense respectively and selected for in vivo studies. Both the bacteria could promote growth in six varieties of wheat tested in terms of increase in root and shoot biomass, height of plants, yield, as well as increase in chlorophyll content. Besides, the wheat plants could withstand water stress more efficiently in presence of the bacteria as indicated by delay in appearance of wilting symptoms increases in relative water content of treated water stressed plants in comparison to untreated stressed ones, and elevated antioxidant responses. Enhanced antioxidant responses were evident as elevated activities of enzymes such as catalase, peroxidase, ascorbate peroxidase, superoxide dismutase and glutathione reductase as well as increased accumulation of antioxidants such as carotenoids and ascorbate. Results clearly indicate that the ability of wheat plants to withstand water stress is enhanced by application of these bacteria which also function as plant growth promoting rhizobacteria.

Aim:  To evaluate Ochrobactrum anthropi TRS‐2 isolated from tea rhizosphere and its talc based formulation for growth promotion and management of brown root rot disease of tea. Methods and Results:  Ochrobactrum anthropi TRS‐2, isolated from tea rhizosphere could solubilize phosphate, produce siderophore and IAA in vitro and also exhibited antifungal activity against six test pathogens. Application of an aqueous suspension of O. anthropi to the rhizosphere of nursery grown tea seedlings of five varieties of tea (TV‐18, T‐17, HV‐39, S‐449, UP‐3 and) led to enhanced growth of the treated plants, as evidenced by increase in height, in the number of shoots and number of leaves per shoot. Treatment with O. anthropi also decreased brown root rot of tea, caused by Phellinus noxius. Multifold increase in activities of chitinase, β‐1,3‐glucanase, peroxidase and phenylalanine ammonia lyase in tea plants was observed on application of O. anthropi to soil followed by inoculation with P. noxius. A concomitant increase in accumulation of phenolics was also obtained. Further, talc based formulation of O. anthropi was prepared and its survival determined every month up to a period of 12 months. Ochrobactrum anthropi could survive in the formulation up to a period of 9 months with a concentration of 7·0 log10 CFU g−1, after which there was a decline. Talc formulation was as effective as aqueous suspensions in both plant growth promotion and disease suppression. Conclusion:  Ochrobactrum anthropi, either in aqueous suspension or as talc formulation induced growth of tea plants and suppressed brown root rot disease. It induced defense responses in tea plants. Significance and Impact of the Study:  Ochrobactrum anthropi and its talc based formulation can be considered as an addition to available plant growth promoting rhizobacteria (PGPR) currently being used for field application. The present study offers a scope of utilizing this bacterium for growth promotion and disease management which would help in reduction of the use of chemicals in tea plantations.

Serratia marcescens (TRS-1), either as aqueous suspensions or in bioformulations of sawdust, rice husk and tea waste, promoted growth in tea seedlings as evidenced by increase in height, emergence of new leaves and branches, as well as increase in leaf biomass. Survival of S. marcescens in soil after application was determined by ELISA and Dot-Blot using PAb raised against the bacterium. S. marcescens solubilized phosphate in vitro and in vivo. Following application of the bacterium, soil P content decreased, root and leaf phosphate increased, and soil phosphatase activities were enhanced. The bacterium was antagonistic to a number of fungal pathogens in vitro. It also reduced brown root rot of tea caused by Fomes lamaoensis. Significant increase in phenolics, as well as peroxidase, chitinase, b-1,3-glucanase and phenylalanine ammonia-lyase, were observed in tea plants on application of S. marcescens alone or followed by F. lamaoensis.

Soil salinity severely affects plant growth and development and imparts inevitable losses to crop productivity. Increasing the concentration of salts in the vicinity of plant roots has severe consequences at the morphological, biochemical, and molecular levels. These include loss of chlorophyll, decrease in photosynthetic rate, reduction in cell division, ROS generation, inactivation of antioxidative enzymes, alterations in phytohormone biosynthesis and signaling, and so forth. The association of microorganisms, viz. plant growth‐promoting rhizobacteria, endophytes, and mycorrhiza, with plant roots constituting the root microbiome can confer a greater degree of salinity tolerance in addition to their inherent ability to promote growth and induce defense mechanisms. The mechanisms involved in induced stress tolerance bestowed by these microorganisms involve the modulation of phytohormone biosynthesis and signaling pathways (including indole acetic acid, gibberellic acid, brassinosteroids, abscisic acid, and jasmonic acid), accumulation of osmoprotectants (proline, glycine betaine, and sugar alcohols), and regulation of ion transporters (SOS1, NHX, HKT1). Apart from this, salt‐tolerant microorganisms are known to induce the expression of salt‐responsive genes via the action of several transcription factors, as well as by posttranscriptional and posttranslational modifications. Moreover, the potential of these salt‐tolerant microflora can be employed for sustainably improving crop performance in saline environments. Therefore, this review will briefly focus on the key responses of plants under salinity stress and elucidate the mechanisms employed by the salt‐tolerant microorganisms in improving plant tolerance under saline environments.

Abiotic stresses affect plants in different ways and are causes of reduction in crop productivity. In order to increase crop productivity it becomes necessary to evolve efficient low-cost technologies for abiotic stress management. Soil microorganisms, surviving in the soil under extreme conditions, have shown great properties, which, if exploited can serve agriculture for increasing and maintaining crop productivity. While it is well established that beneficial soil microorganisms can promote growth and increase productivity through mechanisms such as nutrient mobilization, hormone secretion and disease suppression, it is also becoming increasingly clear that their effects may be more far-reaching. Several studies have reported that soil microorganisms may have mechanisms for alleviation of abiotic stresses in plants such as water and temperature stress, salinity, heavy metals etc. Some of these include tolerance to salinity, drought (Azospirillum sp., Pseudomonas syringae, P. fluorescens, Bacillus sp.) and nutrient deficiency (Bacillus polymyxa, Pseudomonas alacaligenes). Other than bacteria, salinity- and drought-tolerant isolates of Trichoderma harzianum and the effect of other strains of Trichoderma in amelioration of such abiotic stresses have also been reported. Arbuscular mycorrhizal fungi (Glomus mosseae, G. etunicatum, G. intraradices, G. fasciculatum, G. macrocarpum, G. coronatum etc.) help in alleviating abiotic stresses in different crops by enhancing nutrient uptake (phosphorus, nitrogen, magnesium and calcium), biochemical (accumulation of proline, betaines, polyamines, carbohydrates and antioxidants), physiological, molecular and ultra-structural changes. In the present chapter, we attempt an overview of current knowledge on how plant-rhizobacteria, plant-Trichoderma as well as plant-mycorrhiza interactions help in alleviating abiotic stress conditions in different crop systems, which can be used for sustainable agriculture.

Fusarium causing disease in maize is probably the one of the most serious diseases among the crop plants all over the world. It not only damages the maize plant, reduces its potential yield and its nutritional values but imposes threatening to the human life through the induction of mycotoxin development. F. graminearum and F. moniliforme syn. Fusarium verticillioides are two important maize pathogens that cause substantial damage to its ear, stalk and foliage, causing contamination of grains with mycotoxins. Since conventional methods of controlling the diseases including the chemical methods proved not enough for total control of the disease with creating situation even worse for our surroundings, the application of PGPR and PGPF can play significant role to control the damage caused by Fusarium.

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