Hafiz Naeem Asghar

The combined application of rhizobial strains and plant growth promoting rhizobacteria improves growth and productivity of mung bean (Vigna radiata L.) under salt-stressed conditions

Salinity stress induces higher levels of ethylene in plants in arid and semi-arid regions. This increased concentration of ethylene can be inhibited by using plant growth promoting rhizobacteria (PGPR) containing ACC-deaminase. A pot trial was conducted under salt-stressed conditions to evaluate the potential of combined application of Rhizobium phaseoli (M6 and M9), and PGPR (Pseudomonas syringae, Mk1; Pseudomonas fluorescens, Mk20 and Pseudomonas fluorescens Biotype G, Mk25) to improve the productivity of mung bean. The results showed that salinity stress decreased significantly mung bean growth, yield and physiological parameters but inoculation with either rhizobia or PGPR alone enhanced these parameters significantly. However, the combined application of rhizobia and PGPR was more effective for reducing the depressing effect of salinity on mung bean. Co-inoculation increased the shoot fresh weight (145%), root fresh weight (173%), number of pods plant−1(150%), pod fresh weight (182%), total dry matter (269%), relative water content (19%), water use efficiency (51%), potassium concentration in leaves (33%), sodium concentration in leaves (56%) and nitrogen concentration in grains of mung bean (99%), compared with the uninoculated control. The results imply that combined application of Rhizobium and Pseudomonas strains can improve the productivity of mung bean. Thus, these strains could be evaluated in intensive field trials for developing biofertilizers to improve the productivity of mung bean under salt-affected conditions.

Methods to Break Seed Dormancy of Rhynchosia capitata, a Summer Annual Weed

La dormancia seminal de las malezas es un rasgo significativo contribuyente a su tasa de supervivencia, puesto que ayuda a las malezas a evitar herbicidas y otras practicas de desmalezado junto con condiciones ambientales desfavorables. Investigamos los efectos de diferentes tratamientos para romper dormancia sobre la germinacion de Rhynchosia capitata, una maleza anual estival comun en Paquistan. Las semillas se sumergieron en tiourea, KNO3, HCl, HNO3 y H2SO4 y ademas fueron escarificadas mecanicamente (papel lija). Los resultados indicaron que las semillas de R. capitata muestran signos de dormancia fisica principalmente debido a impermeabilidad de su cubierta. Escarificacion mecanica y acida (inmersion de semillas en H2SO4 por 60 y 80 min y en HCl por 12 y 15 h) fueron muy eficientes para romper dormancia y promover germinacion. Las semillas sumergidas en HNO3 por 1 a 5 dias mostraron poco efecto, mientras diversas concentraciones de tiourea y KNO3 fueron inefectivas para romper dormancia seminal en R. capitata.

Precursor (L-tryptophan)-Inoculum ( Azotobacter ) Interaction for Improving Yields and Nitrogen Uptake of Maize

ABSTRACT Auxins produced in the rhizosphere as a result of precursor-inoculum interaction may affect plant growth. Auxin production by Azotobactercultures was measured {in vitro} in the presence and absence of L-tryptophan and the most prolific auxin-producing culture (Z4) was then selected. A field experiment was conducted to evaluate the effect of L-tryptophan (an auxin precursor) and Azotobacterapplication on the growth, yield, and nitrogen (N) uptake of maize crop. Five levels of L-tryptophan (10− 3–10− 7 M) were tested with and without Azotobacter inoculation in a fertilized (NPK: 150–100–100 kg ha− 1, respectively) field. Results revealed that application of L-tryptophan (L-TRP) or Azotobacter inoculation alone significantly affected the maize crop; however, their combined application produced more pronounced effects as compared with their separate application. Combined application of 10− 4 M L-TRP and Azotobacter significantly increased the grain yield (18.4%), fresh biomass (16.7%), 1000-grain weight (14.5%), and total nitrogen uptake (40%) compared with an untreated and uninoculated control. It is highly likely that the physiological response evoked is due to the presence of auxins produced in the rhizosphere of maize as a result of precursor-inoculum interaction.

Isolating, screening and applying chromium reducing bacteria to promote growth and yield of okra (Hibiscus esculentus L.) in chromium contaminated soils

Hexavalent chromium [Cr (VI)], extensively used in different industries, is one of the most toxic heavy metals. The Cr (VI) reducing bacteria could be helpful in decreasing its toxic effects. The present study was conducted to evaluate the potential of Cr (VI) reducing bacteria to improve growth and yield of okra (Hibiscus esculentus L.) in Cr-contaminated soils. Most of the selected bacterial isolates significantly increased the growth and yield of okra. Maximum response was observed in the plants inoculated with the isolate K12 where plant height, root length, fruit weight and number of fruits per plant increased up to 77.5 percent, 72.6 percent, 1.4 fold and 2.9 fold, respectively. Moreover, inoculation with bacteria caused significant decrease in Cr (VI) concentration in soil and plant parts across all treatments. The maximum decrease of 69.6, 56.1 and 40.0 percent in Cr (VI) concentrations in soil, plant vegetative parts and plant reproductive parts, respectively, was observed in the treatment inoculated with the strain K12. Based on amplification, sequencing and analysis of 16S rDNA sequence, the strain K12 was found belonging to genus Brucella and was designated as Brucella sp. K12. These findings suggest that the strain K12 may serve as a potential bioresource to improve crop production in Cr-contaminated soils.

Plant–Microbe Interactions for Sustainable Agriculture: Fundamentals and Recent Advances

Coordinated interactions between plants and microbes have supreme importance for improving plant growth as well as maintaining proper soil conditions. Rhizosphere interactions that are based on complex exchange are more complicated than those occurring above soil surface or non-rhizosphere soil. Among diverse microbial population, plant growth promoting rhizobacteria (PGPR) gain special attention owing to their multifarious functional characters like effective root colonization, hormone production, solubilization of nutrients, and production of certain enzymes that are beneficial for sustainable agriculture. An understanding about their ecology, growth-promoting traits, mechanisms of action, and their application for plant growth stimulation has key importance for maximum utilization of this naturally occurring population. The present review highlights the importance of PGPR for enhancing crop production. The mechanisms of plant growth promotions as well as effectiveness of PGPR under different environments have been discussed. The effectiveness of multistrain inocula over single strain has been explained with examples. Also, the limitations related to the use of bacterial inoculants under natural field conditions and some important basics related to their formulation and commercialization have been discussed.

Judicious use of kinetin to improve growth and yield of rice in nickel contaminated soil.

ABSTRACT The present study was conducted to evaluate the effect of kinetin on growth and yield of rice in the presence and absence of nickel contamination. Rice seedlings were dipped in kinetin solution (10−3, 10−4 and 10 M−5) for 2 hours and transplanted in pots having soil contaminated with nickel sulfate @ 130 mg kg−1. Experiment was laid out according to completely randomized design with four replications. Results revealed that kinetin significantly improved growth and yield of rice grown in nickel contamination. Kinetin @ 10−4 M showed maximum improvement in plant height, paddy yield, 1000 grain weight, number of tillers and panicles up to 9.76, 15.72, 11.77, 11.87, and 10.90%, respectively, as compared to plants grown in contaminated soil without kinetin. Kinetin also improved the uptake of nutrients (NPK) in straw and grain of plants grown in Ni contaminated soil. Plants treated with kinetin had more concentration of Ni in shoot but less in grain compared to plants grown in Ni contaminated soil without application of kinetin. The application of kinetin can reduce stress effect on plants through improvement in the biomass of plant. This strategy could be used to increase the phytoextraction of Ni from the contaminated soil.

Germination ecology of Rhynchosia capitata: an emerging summer weed in Asia

Rhynchosia capitata is becoming an increasing problem in summer crops, such as cotton, soybean, pearl millet and mungbean in many Asian countries. Laboratory and greenhouse studies have been conducted to determine the effects of several environmental factors on seed germination patterns and seedling emergence of R. capitata. We investigated whether the diverse ecological factors such as temperature, light, salinity, moisture stress, pH, and soil depth affected germination and seedling emergence of R. capitata. Germination increased as temperature increased from 25 oC and significantly reduced at 45 oC. Presence or absence of light did not influence germination. Germination of R. capitata was sensitive to increased salt and moisture stress, as well as to seed burial depth. Only 48% of seeds germinated at 150 mM salt concentration compared to 100% in control (distilled water). Similarly, 15% of seeds germinated at an osmotic potential of ‑0.8 MPa compared to 88% at ‑0.2 MPa. The optimum pH for seed germination of R. capitata was 7 (98% germination), but the seeds also germinated at lower level of pH 5 (85%) and at higher level of pH 10 (75%). In seed burial trial, maximum seedling emergence of 93% occurred at 2 cm depth, and seedling did not emerge from a depth of 12 cm. The high germination ability of R. capitata under a wide range of ecological factors suggests that this species is likely to be the one to cause more problems in a near future, if not managed appropriately.

Petroleum Hydrocarbons-Contaminated Soils: Remediation Approaches

Petroleum, the backbone of today’s mechanized society, now has become a threat to environment due to extraction and transportation. Accidental oil spills occur regularly at many locations throughout the world. Contamination of soil and water resources with petroleum oil and its products has become a serious problem due to carcinogenic and mutagenic compounds. Efforts are now focused on seeking potential remediation techniques for cleanup of petroleum hydrocarbons-contaminated soils in a cost effective and eco-friendly way. Various physical, chemical and biological remediation strategies have been used to restore contaminated soils. However, plant assisted bioremediation of petroleum hydrocarbons-contaminated soil is getting more attention as compared to sole use of either microorganisms or plants. The challenging task for such efforts to be successful is not only the survival of microorganisms upon their inoculation into hostile contaminated environment but also positive plant-microbe interactions. Bacteria having ACC-deaminase enzymes are considered helpful for plants in stressed environment. We have discussed that use of bacteria equipped with dual traits of bioremediation potential and ACC-deaminase activity in association with plants can be a good approach for remediation of petroleum hydrocarbons-contaminated soil.

Phytoremediation of Light Crude Oil by Maize (Zea mays L.) Bio-Augmented with Plant Growth Promoting Bacteria

ABSTRACT The aim of this study was to evaluate the converged effect of maize and plant growth promoting bacteria on degradation of petroleum hydrocarbons under axenic conditions. Artificially spiked sand with 10 g kg−1 light crude oil was planted with maize alone and in combination with eight bacterial isolates having plant growth promotion and bioremediation potential to observe the dissipation of petroleum hydrocarbons. Results showed remarkable suppression of maize growth and biomass production due to phytotoxicity of the crude oil contamination. However, bio-augmentation of plants with bacteria having ACC-deaminase activity significantly compensated the reduction in plant growth compared to uninoculated plants. The results revealed that plants bio-augmented with PM32Y exhibited significant increase in root length (75%), plant height (74%), and biomass (67%) as compared to uninoculated plants after 60 days of planting. The same bacterium in convergence with maize caused 43% degradation of petroleum hydrocarbons as compared to the unplanted and uninoculated control. Amplification, sequencing and phylogenetic analysis of 16S rRNA gene sequence identified PM32Y bacterium as Bacillus subtilis strain. It is concluded that bio-augmentation of plants with plant growth promoting bacteria having bioremediation potential and ACC-deaminase activity can successfully be used in phytoremediation of petroleum hydrocarbons.

Prospects of Bacterial-Assisted Remediation of Metal-Contaminated Soils

Industrial revolution resulted in plenty of contaminants in the environment. Several organic and inorganic pollutants have adversely affected soils and water resources, causing serious health issues in humans. Among inorganic contaminants heavy metals are of prime importance as they are nondegradable in the environment. Arsenic, cadmium, chromium, cobalt, copper, lead, mercury, selenium, zinc, and other metals originating from various point and nonpoint sources are contaminating natural resources. Elevated concentrations of poisonous metals are not only disturbing soil health and microbial ecology but also decreasing crop production and global food security. Entry of metal pollutants into the food chain is dangerous for human health. Serious efforts are needed to mitigate rising threats of metal contamination. Physical, chemical, and biological approaches can be used to remediate such type of pollutants. However, bioremediation is considered as a promising technique, being cost effective and environment friendly with minimum adverse effects, esthetic advantages, and long-term applicability. Phytoremediation is a type of bioremediation to remove toxic metals from soil through hyperaccumulation or phytostabilization in plant cells. Generally, higher contents of toxic metals in soil and water result in more uptake by roots and more translocation toward shoots, causing interference in metabolism and reduced growth. Successful phytoremediation is limited to the plant types, tolerance to the high metal concentrations, accumulation rate, growth rate, adaptability, and biomass production. Metal-tolerant bacteria can help plant to tolerate metal stress via different mechanisms involved including production of different hormones such as auxins, cytokinin, and gibberellic acid or suppressing stress-induced enzymes such as plant ethylene level. This chapter reviews possible interactions between plant and bacteria to make situations more conducive for remediation of metal-contaminated soil. The chapter also covers different strategies/mechanisms adopted by plants and bacteria to mitigate toxic effect of metals on plant growth in metal-contaminated soils.