Asghari Bano

The stimulatory effects of L-tryptophan and plant growth promoting rhizobacteria (PGPR) on soil health and physiology of wheat

During the present study, Pseudomonas moraviensis and Bacillus cereus, were isolated from rhizosphere soil of halophytic weed (cenchrus ciliaris L.) of Khewra salt range, and used as bioinoculants. The plant growth promoting rhizobacteria (PGPR) were applied to wheat (Triticum aestivum) by seeds soaking, and aqueous solution of tryptophan was added to the rhizosphere soil at 1ug/L, after seed germination. Experiment was conducted at Quaid-e-Azam University Islamabad both in pots (filled with sterilized soil) under axenic condition and in field under natural condition, for two consecutive years. The inoculation of Pseudomonas moraviensis and Bacillus cereus, significantly increased the organic matter, P, K, Ca, and NO 3 -N availability of soil. The inoculation of these PGPR positively enhanced growth and physiology of treated plants, and this affect was further augmented in the presence of tryptophan. Addition of tryptophan with Pseudomonas moraviensis and Bacillus cereus increased the fresh weight, proline contents and activities of antioxidant enzymes significantly over control. Added tryptophan with both PGPR, improved the number of plants at yield and seeds establishment by improving number of seeds/spike and spike length. Effects of PGPR inoculation alone and with tryptophan were more pronounced in pots grown plants. It is inferred from the results, that tryptophan addition is a competent source for increasing potential of PGPR, thereby improving wheat growth, and physiology.

Alleviation of heavy metals toxicity by the application of plant growth promoting rhizobacteria and effects on wheat grown in saline sodic field

ABSTRACT The aim of the study was to determine tolerance of plant growth promoting rhizobacteria (PGPR) in different concentrations of Cu, Cr, Co, Cd, Ni, Mn, and Pb and to evaluate the PGPR-modulated bioavailability of different heavy metals in the rhizosphere soil and wheat tissues, grown in saline sodic soil. Bacillus cereus and Pseudomonas moraviensis were isolated from Cenchrus ciliaris L. growing in the Khewra salt range. Seven-day-old cultures of PGPR were applied on wheat as single inoculum, co-inoculation and carrier-based biofertilizer (using maize straw and sugarcane husk as carrier). At 100 ppm of Cr and Cu, the survival rates of rhizobacteria were decreased by 40%. Single inoculation of PGPR decreased 50% of Co, Ni, Cr and Mn concentrations in the rhizosphere soil. Co-inoculation of PGPR and biofertilizer treatment further augmented the decreases by 15% in Co, Ni, Cr and Mn over single inoculation except Pb and Co where decreases were 40% and 77%, respectively. The maximum decrease in biological concentration factor (BCF) was observed for Cd, Co, Cr, and Mn. P. moraviensis inoculation decreases the biological accumulation coefficient (BAC) as well as translocation factor (TF) for Cd, Cr, Cu Mn, and Ni. The PGPR inoculation minimized the deleterious effects of heavy metals, and the addition of carriers further assisted the PGPR.

Effects of exogenously applied salicylic acid and putrescine alone and in combination with rhizobacteria on the phytoremediation of heavy metals and chickpea growth in sandy soil

ABSTRACT The present attempt was made to study the role of exogenously applied salicylic acid (SA) and putrescine (Put) on the phytoremediation of heavy metals and on the growth parameters of chickpea grown in sandy soil. The SA and Put were applied alone as well as in combination with plant growth promoting rhizobacteria (PGPR). The PGPRs, isolated from the rhizosphere of chickpea, were characterized on the basis of colony morphology and biochemical traits through gram staining, catalase and oxidase tests, and identified by 16S-rRNA gene sequencing as Bacillus subtilis, Bacillus thuringiensis and Bacillus megaterium. The chickpea seeds were soaked in 24 h old fresh cultures of isolates for 2–3 h prior to sowing. The growth regulators (PGRs), SA and Put (150 mg/L), were applied to the seedlings as foliar spray at three-leaf stage. The result revealed that plants treated with SA and Put alone or in combination with PGPRs, significantly enhanced the accumulation of heavy metals in plant shoot. PGPR induces Ni accumulation in sensitive variety and Pb in both the varieties, the PGR in combination augment the bioremediation effects of PGPR and both sensitive and tolerant variety showed significant accumulation of Ni, Cd, and Pb. SA was more effective in accumulating Ni and Cd whereas, significant accumulation of Pb was recorded in Put. PGPRs further augmented the PGRs induced accumulation of heavy metals and macronutrients in chickpea shoot and in rhizosphere. SA increased the proline content of tolerant variety while decreasing the lipid peroxidation and proline content of the sensitive variety but decreased the stimulating effect of PGPR in proline production. Interactive effects of PGPR and PGRs are recommended for inducing phytoremediation in chickpea plants under drought stress.

Halophyte root powder: an alternative biofertilizer and carrier for saline land

ABSTRACT The present investigation was based on the hypothesis that the endophytes residing in the roots of halophytes have better adaptation to saline conditions. Six halophytic herbs were collected from Khewra salt range (EC = 4.7 dS m−1 and SAR = 25.7). From these herbs, root pieces of Cenchrus ciliaris were shade dried; finely ground to powder and three plant growth promoting rhizobacteria (PGPR), Bacillus cereus, Pseudomonad moraviensis, and Stenotrophomonas maltophilia, were isolated. Root powder in sterilized and unsterilized forms was added in the saline-sodic field on wheat and mixed with soil in pot experiment with induced NaCl (150 mM). Sterilized root powder increased organic matter NO3-N and P contents of soil and leaves, fresh weight, sugar content, and yield attributes. The root powder application in unsterilized form significantly decreased EC, SAR, and Na content of field soil with concomitant increase in soil and leaves K, P, and NO3-N. The farmer’s benefit was increased by 33% at yield. Root powder-induced salt tolerance was mediated by the PGPR (residing inside the root) through increased growth and better physiological adaptations. It is inferred that root powder harboring the PGPR may be an alternative to biofertilizer with longer shelf life and may also serve as carrier for the preparation of effective biofertilizer for saline land using other PGPR bio-inoculants.

Pseudomonas putida improved soil enzyme activity and growth of kasumbha under low input of mineral fertilizers

ABSTRACT Effective management of the nutrients and enzyme activity in the soil is necessary for maximum crop growth and productivity. However, the excessive use of chemical fertilizers (CFs) not only adversely affects the soil nutrient status and soil physicochemical properties but also aids pollution to the ecosystem. The objective of present study was to investigate the effect of single as well as combined applications of phosphate-solubilizing bacteria and agrochemicals on important soil enzyme activities and their impact on the growth of kasumbha (safflower). Pseudomonas putida (P. putida;106 cells/mL) was applied as seed inoculation prior to sowing, and CFs were applied as full, half, and quarter doses during sowing to modulate the growth of kasumbha host plants. P. putida in combination with half dose of CFs (PH) increased the soil urease and phosphatase activities, while P. putida combined with quarter dose of CFs (PQ) augmented the soil invertase activities. Moreover, the PQ treatment exhibited the maximum colony-forming units of P. putida. Leaf chlorophyll, carotenoids, protein contents, and root lengths were increased by PH treatment. Whereas, shoot length and leaf area were improved by PH and PQ treatments, respectively. Leaf protease activity was enhanced by P. putida in combination with full dose of CFs and PQ treatments, while leaf phosphate contents were significantly improved by PQ treatment. It can be concluded that P. putida in combination with half as well as quarter doses of CFs is a promising approach for the improvement of soil enzyme activities and growth of kasumbha and replacing 50% of the use of CFs.

Correction: Rhizoremediation of petroleum hydrocarbon, prospects and future

Correction for ‘Rhizoremediation of petroleum hydrocarbon, prospects and future’ by Asim Shahzad et al., RSC Adv., 2016, 6, 108347–108361.

Rhizotrophs in Saline Agriculture

The rhizo-deposition provides energy and nutritional inputs to soil with selection of large and distinct community of metabolically active soil microbiota that carries many biochemical transformations. Positive effects of Rhizobium, Pseudomonas, Bacillus, and Azospirillum on the mitigation of salt stress in inoculated plants have been documented. However, information is scarce regarding the mode of action of the beneficial microbes in improving salt tolerance to host plants. This chapter deals with the salt tolerance potential of rhizobacteria and their mechanism in planta. It has been shown that cooperative microbial activities can be exploited as a low input biotechnology. Addition of osmoprotectants increases tolerance of the microbes to salt. Difference in the utilization of C/N sources also makes the difference in the salt tolerance of rhizobia. Field experiments should be conducted with plant growth-promoting rhizobacteria (PGPR) isolated from stressed areas. Furthermore, efficiency of growth regulators previously used to ameliorate salt stress should be monitored in combination with PGPR, which may be useful as future strategy to mitigate salt stress for agriculture productivity and environmental sustainability. The mechanism of salt tolerance in PGPR appears similar to that of growth regulators applied exogenously to plants.

l-tryptophan-assisted PGPR-mediated induction of drought tolerance in maize (Zea mays L.)

ABSTRACT Drought is an important abiotic stress that limits the plant growth and productivity. Present investigation was aimed that plant growth-promoting rhizobacteria (PGPR) isolated from moisture-stressed area impart drought tolerance in plants and tryptophan may improve their efficiency. Pseudomonas sp. (1), Bacillus cereus and Bacillus pumilus (B. pumilus) were isolated from maize rhizosphere grown in irrigated fields, semi-arid region and arid region, respectively. Proteus sp. and Pseudomonas sp. (2) were isolated from rice rhizosphere grown in irrigated fields and raised bed. B. pumilus produced 5× more abscisic acid (ABA) in culture media than Pseudomonas sp. (1) by the addition of l-tryptophan. These inoculants also modulated the phytohormone content of maize leaves in a pot experiment. Higher ABA was produced by the application of B. pumilus and Pseudomonas sp. (2), while indole 3-acetic acid and gibberellic acid were found higher in Pseudomonas sp. (1) and Proteus sp. treated plants. Addition of l-tryptophan increased the concentration of all phytohormones in soil and leaves of maize. Maximum increase in relative water content, osmotic potential, protein content and photosynthetic pigments was recorded in B. pumilus treated maize plants. Under irrigated condition, response of Pseudomonas sp. co-inoculated with B. pumilus from arid field superseded while under drought stress the effect of later predominated. Bacillus pumilus can be used in the formulation of biofertilizer to alleviate drought stress in arid and semi-arid regions.

Rhizoremediation of petroleum hydrocarbon, prospects and future

Oil refineries generate several tones of oily waste which is dumped in an open pit within the vicinity of oil field. The disposal or removal of such waste through excavation is costly and laborious. Therefore oil refineries are looking for rapid and economic methods to remediate such waste. Rhizoremediation is successfully adapted to remediation hydrocarbon contaminated soils by the oil refineries. This is a technique in which plants and microbes are used to remediate oily waste contaminated sites. The main aim of the study was to introduce an economic and rapid rhizoremediation technique to oil refineries in which plant and microbes are used to enhance the natural degradation process of oily sludge contaminated soils. The rhizosphere of oily sludge is composed of several genera of hydrocarbon degrading microbes naturally. When such microbes are inoculated to oily sludge rhizosphere are capable of degrading hydrocarbons more likely because of presence of root exudates that can provide enough carbon, nutrients and oxygen for microbes to increase in number thus accelerate the rate of degradation of hydrocarbons via β-oxidation. The use of microbes + plants to remediate oily sludge remained an area of interest by researchers over the last several years. Several laboratory scale and field trials have been conducted to evaluate the combine effect of hydrocarbon degrading microbes with plants to accelerate the natural rehabilitation process of oily sludge contaminated soils. However the mode of degradation of hydrocarbons in combination with plants and microbes remained an area of interest for scientist to remediate oily sludge contaminated soils. Oil refineries generate several tonnes of oily waste which is dumped in an open pit within the vicinity of oil field. The disposal or removal of such waste through excavation is costly and laborious. Therefore oil refineries are looking for rapid and economic methods to remediate such waste. Rhizoremediation is successfully adapted to remediation hydrocarbon contaminated soils by the oil refineries. This is a technique in which plants and microbes are used to remediate oily waste contaminated sites. The suitability of plant growth promoting rhizobacter and plant species to remediate oily sludge was discussed in detail in this review. The factors affecting the degradation of hydrocarbons and under oily sludge contaminated rhizosphere are also examined.