The increasing frequency of dry periods in many regions of the world and the problems associated with salinity in irrigated areas frequently result in the consecutive occurrence of drought and salinity on cultivated land. Currently, 50% of all irrigation schemes are affected by salinity. Nutrient disturbances under both drought and salinity reduce plant growth by affecting the availability, transport, and partitioning of nutrients. However, drought and salinity can differentially affect the mineral nutrition of plants. Salinity may cause nutrient deficiencies or imbalances, due to the competition of Na+ and Cl– with nutrients such as K+, Ca2+, and NO. Drought, on the other hand, can affect nutrient uptake and impair acropetal translocation of some nutrients. Despite contradictory reports on the effects of nutrient supply on plant growth under saline or drought conditions, it is generally accepted that an increased nutrient supply will not improve plant growth when the nutrient is already present in sufficient amounts in the soil and when the drought or salt stress is severe. A better understanding of the role of mineral nutrients in plant resistance to drought and salinity will contribute to an improved fertilizer management in arid and semi-arid areas and in regions suffering from temporary drought. This paper reviews the current state of knowledge on plant nutrition under drought and salinity conditions. Specific topics include: (1) the effects of drought and salt stress on nutrient availability, uptake, transport, and accumulation in plants, (2) the interactions between nutrient supply and drought- or salt-stress response, and (3) means to increase nutrient availability under drought and salinity by breeding and molecular approaches.

https://mediatum.ub.tum.de/doc/1304727/file.pdf

Drought and salinity: A comparison of their effects on mineral nutrition of plants

Previous studies have described the development of control methods against bacterial wilt diseases caused by Ralstonia solanacearum. This review focused on recent advances in control measures, such as biological, physical, chemical, cultural, and integral measures, as well as biocontrol efficacy and suppression mechanisms. Biological control agents (BCAs) have been dominated by bacteria (90%) and fungi (10%). Avirulent strains of R. solanacearum, Pseudomonas spp., Bacillus spp., and Streptomyces spp. are well-known BCAs. New or uncommon BCAs have also been identified such as Acinetobacter sp., Burkholderia sp., and Paenibacillus sp. Inoculation methods for BCAs affect biocontrol efficacy, such as pouring or drenching soil, dipping of roots, and seed coatings. The amendment of different organic matter, such as plant residue, animal waste, and simple organic compounds, have frequently been reported to suppress bacterial wilt diseases. The combined application of BCAs and their substrates was shown to more effectively suppress bacterial wilt in the tomato. Suppression mechanisms are typically attributed to the antibacterial metabolites produced by BCAs or those present in natural products; however, the number of studies related to host resistance to the pathogen is increasing. Enhanced/modified soil microbial communities are also indirectly involved in disease suppression. New promising types of control measures include biological soil disinfection using substrates that release volatile compounds. This review described recent advances in different control measures. We focused on the importance of integrated pest management (IPM) for bacterial wilt diseases.

https://www.jstage.jst.go.jp/article/jsme2/advpub/0/advpub_ME14144/_pdf

Recent trends in control methods for bacterial wilt diseases caused by Ralstonia solanacearum

Water, the most important component of life, is rapidly becoming a critically short commodity for humans and crop production. Limited water supply is one of the major abiotic factors that adversely affect agricultural crop production worldwide. Drought stress influences the normal physiology and growth of plants in many ways. It results in an increase of solute concentration outside the roots compared to the internal environment of the root and causes reverse osmosis. As a result, the cell membrane shrinks from the cell wall and may eventually lead to death of the cell. Water stress tends to shrink away from the interface with water-absorbing roots, creating a gap in the soil-plant-air continuum. As the plant continues to lose water via transpiration, water is drawn from root cells resulting in shrinkage of cell membranes and results in decreased integrity of the cell membrane and the living cell may be destroyed. Drought stress inhibits photosynthesis in plants by closing stomata and damaging the chlorophyll contents and photosynthetic apparatus. It disturbs the balance between the production of reactive oxygen species (ROS) and the antioxidant defence, causing accumulation of ROS which induces oxidative stress to proteins, membrane lipids and other cellular component. Mineral elements have numerous functions in plants including maintaining charge balance, electron carriers, structural components, enzyme activation, and providing osmoticum for turgor and growth .In this paper, an overview of some macronutrients (nitrogen, phosphorus, potassium, calcium and magnesium), micronutrients (Zinc, Boron, Copper) and silicon has been discussed in detail as how these nutrients play their role in decreasing the adverse effects of drought in crop plant.

/pdf/role-of-mineral-nutrition-in-alleviation-of-drought-stress-2g2yiban45.pdf

Role of Mineral Nutrition in Alleviation of Drought Stress in Plants

Allelopathy and Exotic Plant Invasion: From Molecules and Genes to Species Interactions

A combined application of biochar and phosphorus alleviates heat-induced adversities on physiological, agronomical and quality attributes of rice

A healthy soil acts as a dynamic living system that delivers multiple ecosystem services, such as sustaining water quality and plant productivity, controlling soil nutrient recycling decomposition, and removing greenhouse gases from the atmosphere. Soil health is closely associated with sustainable agriculture, because soil microorganism diversity and activity are the main components of soil health. Agricultural sustainability is defined as the ability of a crop production system to continuously produce food without environmental degradation. Arbuscular mycorrhizal fungi (AMF), cyanobacteria, and beneficial nematodes enhance water use efficiency and nutrient availability to plants, phytohormones production, soil nutrient cycling, and plant resistance to environmental stresses. Farming practices have shown that organic farming and tillage improve soil health by increasing the abundance, diversity, and activity of microorganisms. Conservation tillage can potentially increase grower’s profitability by reducing inputs and labor costs as compared to conventional tillage while organic farming might add extra management costs due to high labor demands for weeding and pest control, and for fertilizer inputs (particularly N-based), which typically have less consistent uniformity and stability than synthetic fertilizers. This review will discuss the external factors controlling the abundance of rhizosphere microbiota and the impact of crop management practices on soil health and their role in sustainable crop production.

Soil Health and Sustainable Agriculture

Arbuscular mycorrhizae fungi (AMF) are the symbiotic fungi that predominate in the roots and soils of agricultural crop plants. The AMF form beneficial symbioses in most terrestrial ecosystems and crop production systems. Ninty percent of land plant species are colonized by one or more of the mycorrhizal fungi species ranging from flowering to non flowering plants, while only a few plant families do not form this association. The relationship between mycorrhiza and plant is very widely spread among terrestrial vascular plants. The AMF must have a host to complete its life cycle and this association has been found to be mutually beneficial; thus, the fungus assists the plant in mineral nutrients uptake, while the plant supplies the fungus with carbon as a result of this relation. The negative-antagonistic interaction of AMF with various soilborne plant pathogens is the reason for their use as a bio-control agents. Many workers have observed an antagonistic effect of AMF against some fungal pathogens.

/pdf/mycorrhizal-fungi-as-a-biocontrol-agent-29aaqen1qr.pdf

Mycorrhizal fungi as a biocontrol agent.

Interactive effects of phosphorus (P) with in vitro-induced water deficit (using sorbitol and mannitol) were studied on African violet (Saintpaulia ionantha) whole-plant microculture. Sorbitol and mannitol significantly reduced (more negative) the cell sap osmotic potential. Increased P was very effective in increasing (less negative) the osmotic potential of cell sap under the imposed water deficit treatments. On the other hand, induced water deficit significantly reduced shoot growth (shoot height and dry mass), and root number and length, whereas P mitigated these adverse effects and improved shoot and root growth. Cultures exposed to water deficit at 150 mM sorbitol and mannitol experienced some physiological disorders (about 10% shoot tip browning, 15% stem basal-end browning) and 20% chlorosis. Physiological disorders and chlorosis were totally mitigated with increased P to 1.0 or 2.0 mM. Phosphorus concentration in shoot tissues was decreased with water deficit in the medium and enhanced by elevated P in the medium. Ex vitro survival percentages increased in plantlets that experienced in vitro water deficit with sorbitol and mannitol at 50 to 100 mM and P at 1.0 to 2.0 mM. We conclude that P is a key factor to regulate cell osmotic potential and growth under in vitro induced water deficit. On the other hand, microculture level is a very effective alternative for the study of plant response and tolerance to water deficit and its interaction with nutrient availability in the root zone.

Phosphorus regulates osmotic potential and growth of African violet under in vitro‐induced water deficit

Interactive effects of increased phosphorus (P) with salinity were studied at the microculture level of African violet (Saintpaulia ionantha) Increased P from 05 to 20 mM in the medium was very effective to mitigate the adverse effects of increased NaCl salinity (00, 50, 75, 100 mM) Growth (shoot height, and dry mass) was significantly reduced with increased salinity, whereas increasing P improved growth with elevated salt concentrations Leaf osmolarity was decreased (more negative) with salinity effect and it was increased (less negative) by P treatments Percent ash was increased with salinity and it was not highly affected by P Root number and root length were significantly reduced with increased salinity and improved with increased P The percentage of shoot content of nitrogen (N), P, calcium (Ca), potassium (K), and magnesium (Mg) were reduced with elevated salinity level and this reduction was less as P concentration increased in the medium Sodium (Na) was significantly increased with impos

Increased phosphorus mitigates the adverse effects of salinity in tissue culture

Ralstonia solanacearum (race 3 biovar 2) is a bacterial wilt causal agent of many plant species. Infects (potatoes Solanum tuberosum, eggplant Solanum melongena, peppers Capsicum annuum, tomatoes Lycopersicon esculentum, geraniums, Geranium carolinianum, ginger Zingiber officinale and a few weed species including bittersweet Celastrus orbiculatus, nightshade Solanum karsense and stinging nettle Urtica dioica. Ralstonia solanacearum can be infectious in the soil for years in the presence of a host. Race 3 biovar 2 is most commonly transmitted by contaminated soil, equipment, water and insect, or by transplantation of infected seeds or seedlings. Management requires use of resistance cultivars, clean and certified seed, good cultural practices, some chemicals fumigation, antagonistic microbes as a biological control like (Mycorrhizal fungi, Streptomyces sp. and Tricoderma sp.) transgenic resistant plant, cropping systems, soil amendments, integrated control, genetically engineered antagonistic and virulent mutants of R. solanacearum.

/pdf/ralstonia-solanacearum-the-bacterial-wilt-causal-agent-3gg2lh1xym.pdf

Monther Mohumad Tahat

Papers

Soil Health and Sustainable Agriculture

Mycorrhizal fungi as a biocontrol agent.

Phosphorus regulates osmotic potential and growth of African violet under in vitro‐induced water deficit

Increased phosphorus mitigates the adverse effects of salinity in tissue culture

Ralstonia solanacearum: the bacterial wilt causal agent.