The Role of Plant Growth Promoting Rhizosphere Microbiome as Alternative Biofertilizer in Boosting Solanum melongena L. Adaptation to Salinity Stress

Improving soil fertility through dual inoculation with arbuscular mycorrhizal fungi and Rhizobium on a eutric cambisol cultivated with forage legumes in a semi-arid region

The Sub-Saharan region of southern Africa is characterized by high temperatures, low rainfall, and poor land-use management practices such as continuous cropping without replenishment of soil nutrients. The combination of these factors has resulted in nutrient depletion and land degradation. The current study aimed at investigating the effect of arbuscular mycorrhizal fungi (AMF) and Rhizobium bacteria inoculation on soil chemical properties in field-grown forage legumes, namely, Mucuna pruriens (mucuna), Lablab purpureus (lablab) and Vigna unguiculata (cowpea), in the semi-arid region of the Eastern Cape Province (South Africa). Forage legumes were inoculated with the AMF species Paraglomus occulum and the Rhizobia bacteria species Bradyrhizobium strain and grown for 120 days. Soil samples were collected in the following sequence: prior to planting, before flowering and after harvesting the forage legumes in each of the two seasons (2017/2018 and 2018/2019) and soil chemical properties were determined using standard procedures. The results showed that the addition of dual inoculation over time greatly improved soil chemical properties when compared to the control treatment. This was advocated by the significant (P ≤ 0.05) increase in soil pH, soil organic carbon, soil organic matter, total nitrogen, phosphorus, calcium, potassium, magnesium, sodium, sulfur and iron in soils. The concentration of cation exchange capacity was significantly (P ≤ 0.05) higher in cowpea treated with Rhizobium as compared to other treatment combinations. The control treatment of mucuna forage greatly improved the concentrations of manganese, boron, copper, molybdenum, and zinc over other treatment combinations only before the flowering stage. However, the concentrations of micronutrients were significantly higher on the treatment combination of lablab and single inoculation of AMF after harvesting. Generally, dual inoculation with AMF and Rhizobia enhanced soil properties when compared to a single inoculation or untreated control.

Unlocking the plant growth-promoting potential of yeast spp.: exploring species from the Moroccan extremophilic environment for enhanced plant growth and sustainable farming

In this study, we successfully isolated two distinct yeasts from Moroccan extreme environments. These yeasts were subjected to molecular characterization by analyzing their Internal Transcribed spacer (ITS) regions. Our research thoroughly characterizes plant growth-promoting abilities and their drought and salt stress tolerance. In a greenhouse assay, we examined the impact of selected yeasts on Medicago sativa's growth. Four treatments were employed: (i) control without inoculation (NI), (ii) inoculation with L1, (iii) inoculation with L2, and (iv) inoculation with the mixture L1 + L2. L1 isolated from Toubkal Mountain shared 99.83% sequence similarity to Rhodotorula mucilaginosa. Meanwhile, L2, thriving in the arid Merzouga desert, displayed a similar identity to Naganishia albida (99.84%). Yeast strains were tolerant to NaCl (2 M) and 60% PEG (polyethylene glycol P6000) in case of drought. Both strains could solubilize phsphorus, with L2 additionally demonstrating potassium solubilization. In addition, both strains produce indole acetic acid (up to 135 µl ml-1), have siderophore ability, and produce aminocyclopropane-1-carboxylic acid deaminase. Isolates L1 and L2, and their consortium showed that the single or combined strain inoculation of M. sativa improved plant growth, development, and nutrient assimilation. These findings pave the way for harnessing yeast-based solutions in agricultural practices, contributing to enhanced crop productivity and environmental sustainability.

Physiological and molecular insight of microbial biostimulants for sustainable agriculture

Increased food production to cater the need of growing population is one of the major global challenges. Currently, agro-productivity is under threat due to shrinking arable land, increased anthropogenic activities and changes in the climate leading to frequent flash floods, prolonged droughts and sudden fluctuation of temperature. Further, warm climatic conditions increase disease and pest incidences, ultimately reducing crop yield. Hence, collaborated global efforts are required to adopt environmentally safe and sustainable agro practices to boost crop growth and productivity. Biostimulants appear as a promising means to improve growth of plants even under stressful conditions. Among various categories of biostimulants, microbial biostimulants are composed of microorganisms such as plant growth-promoting rhizobacteria (PGPR) and/or microbes which stimulate nutrient uptake, produce secondary metabolites, siderophores, hormones and organic acids, participate in nitrogen fixation, imparts stress tolerance, enhance crop quality and yield when applied to the plants. Though numerous studies convincingly elucidate the positive effects of PGPR-based biostimulants on plants, yet information is meagre regarding the mechanism of action and the key signaling pathways (plant hormone modulations, expression of pathogenesis-related proteins, antioxidants, osmolytes etc.) triggered by these biostimulants in plants. Hence, the present review focuses on the molecular pathways activated by PGPR based biostimulants in plants facing abiotic and biotic challenges. The review also analyses the common mechanisms modulated by these biostimulants in plants to combat abiotic and biotic stresses. Further, the review highlights the traits that have been modified through transgenic approach leading to physiological responses akin to the application of PGPR in the target plants.

Overview of biofertilizers in crop production and stress management for sustainable agriculture

With the increase in world population, the demography of humans is estimated to be exceeded and it has become a major challenge to provide an adequate amount of food, feed, and agricultural products majorly in developing countries. The use of chemical fertilizers causes the plant to grow efficiently and rapidly to meet the food demand. The drawbacks of using a higher quantity of chemical or synthetic fertilizers are environmental pollution, persistent changes in the soil ecology, physiochemical composition, decreasing agricultural productivity and cause several health hazards. Climatic factors are responsible for enhancing abiotic stress on crops, resulting in reduced agricultural productivity. There are various types of abiotic and biotic stress factors like soil salinity, drought, wind, improper temperature, heavy metals, waterlogging, and different weeds and phytopathogens like bacteria, viruses, fungi, and nematodes which attack plants, reducing crop productivity and quality. There is a shift toward the use of biofertilizers due to all these facts, which provide nutrition through natural processes like zinc, potassium and phosphorus solubilization, nitrogen fixation, production of hormones, siderophore, various hydrolytic enzymes and protect the plant from different plant pathogens and stress conditions. They provide the nutrition in adequate amount that is sufficient for healthy crop development to fulfill the demand of the increasing population worldwide, eco-friendly and economically convenient. This review will focus on biofertilizers and their mechanisms of action, role in crop productivity and in biotic/abiotic stress tolerance.

An Insight into Abiotic Stress and Influx Tolerance Mechanisms in Plants to Cope in Saline Environments

Simple Summary

This review focuses on plant growth and development harmed by abiotic stress, primarily salt stress. Salt stress raises the intracellular osmotic pressure, leading to hazardous sodium buildup. Plants react to salt stress signals by regulating ion homeostasis, activating the osmotic stress pathway, modulating plant hormone signaling, and altering cytoskeleton dynamics and cell wall composition. Understanding the processes underlying these physiological and biochemical responses to salt stress could lead to more effective agricultural crop yield measures. In this review, researchers outline recent advances in plant salt stress control. The study of plant salt tolerance processes is essential, both theoretically and practically, to improve agricultural output, produce novel salt-tolerant cultivars, and make full use of saline soil. Based on past research, this paper discusses the adverse effects of salt stress on plants, including photosynthesis suppression, ion homeostasis disturbance, and membrane peroxidation. The authors have also covered the physiological mechanisms of salt tolerance, such as the scavenging of reactive oxygen species and osmotic adjustment. This study further identifies specific salt stress-responsive mechanisms linked to physiological systems. Based on previous studies, this article reviews the current methodologies and techniques for improving plant salt tolerance. Overall, it is hoped that the above-mentioned points will impart helpful background information for future agricultural and crop plant production.

Abstract

Salinity is significant abiotic stress that affects the majority of agricultural, irrigated, and cultivated land. It is an issue of global importance, causing many socio-economic problems. Salt stress mainly occurs due to two factors: (1) soil type and (2) irrigation water. It is a major environmental constraint, limiting crop growth, plant productivity, and agricultural yield. Soil salinity is a major problem that considerably distorts ecological habitats in arid and semi-arid regions. Excess salts in the soil affect plant nutrient uptake and osmotic balance, leading to osmotic and ionic stress. Plant adaptation or tolerance to salinity stress involves complex physiological traits, metabolic pathways, the production of enzymes, compatible solutes, metabolites, and molecular or genetic networks. Different plant species have different salt overly sensitive pathways and high-affinity K⁺ channel transporters that maintain ion homeostasis. However, little progress has been made in developing salt-tolerant crop varieties using different breeding approaches. This review highlights the interlinking of plant morpho-physiological, molecular, biochemical, and genetic approaches to produce salt-tolerant plant species. Most of the research emphasizes the significance of plant growth-promoting rhizobacteria in protecting plants from biotic and abiotic stressors. Plant growth, survival, and yield can be stabilized by utilizing this knowledge using different breeding and agronomical techniques. This information marks existing research areas and future gaps that require more attention to reveal new salt tolerance determinants in plants—in the future, creating genetically modified plants could help increase crop growth and the toleration of saline environments.