Salinity is a major problem affecting crop production all over the world: 20% of cultivated land in the world, and 33% of irrigated land, are salt-affected and degraded. This process can be accentuated by climate change, excessive use of groundwater (mainly if close to the sea), increasing use of low-quality water in irrigation, and massive introduction of irrigation associated with intensive farming. Excessive soil salinity reduces the productivity of many agricultural crops, including most vegetables, which are particularly sensitive throughout the ontogeny of the plant. The salinity threshold (ECt) of the majority of vegetable crops is low (ranging from 1 to 2.5 dS m−1 in saturated soil extracts) and vegetable salt tolerance decreases when saline water is used for irrigation. The objective of this review is to discuss the effects of salinity on vegetable growth and how management practices (irrigation, drainage, and fertilization) can prevent soil and water salinization and mitigate the adverse effects of salinity.

Soil Salinity: Effect on Vegetable Crop Growth. Management Practices to Prevent and Mitigate Soil Salinization

Use of plant growth promoting rhizobacteria (PGPRs) with multiple plant growth promoting traits in stress agriculture: Action mechanisms and future prospects

Does plant-Microbe interaction confer stress tolerance in plants: A review?

Thirty crop species provide 90% of our food, most of which display severe yield losses under moderate salinity. Securing and augmenting agricultural yield in times of global warming and population increase is urgent and should, aside from ameliorating saline soils, include attempts to increase crop plant salt tolerance. This short review provides an overview of the processes that limit growth and yield in saline conditions. Yield is reduced if soil salinity surpasses crop-specific thresholds, with cotton, barley and sugar beet being highly tolerant, while sweet potato, wheat and maize display high sensitivity. Apart from Na+ , also Cl- , Mg2+ , SO4 2- or HCO3 - contribute to salt toxicity. The inhibition of biochemical or physiological processes cause imbalance in metabolism and cell signalling and enhance the production of reactive oxygen species interfering with cell redox and energy state. Plant development and root patterning is disturbed, and this response depends on redox and reactive oxygen species signalling, calcium and plant hormones. The interlink of the physiological understanding of tolerance processes from molecular processes as well as the agronomical techniques for stabilizing growth and yield and their interlinks might help improving our crops for future demand and will provide improvement for cultivating crops in saline environment.

Salinity and crop yield

There has been many recent studies on the use of microbial antagonists to control diseases incited by soilborne and airborne plant pathogenic bacteria and fungi, in an attempt to replace existing methods of chemical control and avoid extensive use of fungicides, which often lead to resistance in plant pathogens. In agriculture, plant growth-promoting and biocontrol microorganisms have emerged as safe alternatives to chemical pesticides. Streptomyces spp. and their metabolites may have great potential as excellent agents for controlling various fungal and bacterial phytopathogens. Streptomycetes belong to the rhizosoil microbial communities and are efficient colonizers of plant tissues, from roots to the aerial parts. They are active producers of antibiotics and volatile organic compounds, both in soil and in planta, and this feature is helpful for identifying active antagonists of plant pathogens and can be used in several cropping systems as biocontrol agents. Additionally, their ability to promote plant growth has been demonstrated in a number of crops, thus inspiring the wide application of streptomycetes as biofertilizers to increase plant productivity. The present review highlights Streptomyces spp.-mediated functional traits, such as enhancement of plant growth and biocontrol of phytopathogens.

https://www.mdpi.com/1422-0067/19/4/952/pdf

Plant Growth Promoting and Biocontrol Activity of Streptomyces spp. as Endophytes.

Soil salinity: A serious environmental issue and plant growth promoting bacteria as one of the tools for its alleviation.

A chitinolytic actinomycete Streptomyces vinaceusdrappus S5MW2 was isolated from water sample of Chilika lake, India and identified using 16S rRNA gene sequencing It showed in vitro antifungal activity against the sclerotia producing pathogen Rhizoctonia solani in a dual culture assay and by chitinase enzyme production in a chitin supplemented minimal broth Moreover, isolate S5MW2 was further characterized for biocontrol (BC) and plant growth promoting features in a greenhouse experiment with or without colloidal chitin (CC) Results of greenhouse experiment showed that CC supplementation with S5MW2 showed a significant growth of tomato plants and superior disease reduction as compared to untreated control and without CC treated plants Moreover, higher accumulation of chitinase also recovered in the CC supplemented plants Significant effect of CC also concurred with the Analysis of Variance of greenhouse parameters These results show that the a marine antagonist S5MW2 has BC efficiency against R solani and chitinase enzyme played important role in plant resistance

Chitinolytic Streptomyces vinaceusdrappus S5MW2 isolated from Chilika lake, India enhances plant growth and biocontrol efficacy through chitin supplementation against Rhizoctonia solani.

In vitro biocontrol activity of halotolerant Streptomyces aureofaciens K20: A potent antagonist against Macrophomina phaseolina (Tassi) Goid.

A total of 66 actinomycetes isolates were isolated from mangroves of Andhra Pradesh, India, using various enrichment techniques and pretreatments. The samples were collected from Coringa mangrove ecosystem and pre-treated by enrichment with CaCO3, sodium dodecyl sulphate and phenol, plated on the media supplemented with cycloheximide (50 mg/ml), nystatin (25 mg/ml) and nalidixic acid (50 mg/ml). The population count of actinomycetes fluctuated from 1.9 x 10(5) to 8.0 x 10(5)/g soil. Out of the isolated 66 actinomycetes, 8 isolates possessing plant growth promoting potential were further studied and characterized by physiological and biochemical traits and identified by 16S rRNA gene sequencing as different species of Streptomycetes genera.

Isolation and Characterization of Streptomycetes with-Plant Growth Promoting Potential from Mangrove Ecosystem.

Disease-causing plant pathogens are a major threat to crop productivity, resulting in huge production loss for major agricultural crops. To manage and minimize these losses, farmers mainly rely on chemical control methods and frequently use pesticides and fungicides. Many of these chemicals are highly toxic and detrimental to the agro-environment as well as to human health. In addition, it has been reported that such frequent use of chemicals causes resistance-development in the pathogens. The search for alternative eco-friendly disease management practices has led us towards the use of actinobacteria as biocontrol agents (BCA). Actinobacteria are gram positive saprophytic bacteria and are present in high population densities in soil. Actinobacteria have received special attention as biocontrol agents due to their capability to produce numerous useful and diverse bioactive compounds, such as antibiotics and extracellular enzymes. Several strains of actinobacteria have been reported to control plant disease and promote plant growth as well. Exploitation of actinomycete strains with biocontrol and plant growth-promoting potential is the best approach for plant disease management in a sustainable manner. This chapter provides a brief insight into actinobacteria: their occurrence, importance, and their role in nature. A discussion about the role of actinobacteria as BCA, mechanism of biocontrol, antibiotics and extracellular enzymes produced, with the evaluation of actinobacteria as potential bio-inoculants as well as future prospects, is also included in order to explore the maximum benefit to eco-friendly sustainable agricultural systems.

Pooja Shrivastava

Papers

Soil salinity: A serious environmental issue and plant growth promoting bacteria as one of the tools for its alleviation.

Chitinolytic Streptomyces vinaceusdrappus S5MW2 isolated from Chilika lake, India enhances plant growth and biocontrol efficacy through chitin supplementation against Rhizoctonia solani.

In vitro biocontrol activity of halotolerant Streptomyces aureofaciens K20: A potent antagonist against Macrophomina phaseolina (Tassi) Goid.

Isolation and Characterization of Streptomycetes with-Plant Growth Promoting Potential from Mangrove Ecosystem.

Actinobacteria: Eco-Friendly Candidates for Control of Plant Diseases in a Sustainable Manner