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.

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 150mM 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.

The pre-symbiosis of arbuscular mycorrhizal fungi (AMF) is induced by the production of specific plant root exudates. Mycorrhizal fungi symbiotic relationships have many benefits to the plants. These benefits include, improved plant growth and developments, and enhanced plant tolerance to several diseases. Over the pre-symbiotic phase, the root releases essential metabolites necessary for fungal growth and root colonization. Root exudates compounds were reported and identified by several researchers. Root exudates have sugar, amino acids, proteins, carbon, some lipophilic compounds, flavonoids, and other bio-molecules. These compounds were presented as a critical and fundamental signal in plant, fungal and microbe bio-communications in the soil. Root-microbe interactions are continuous occurrences in the biological active soil zone. Mycorrhizal fungi bio-interaction can be classified as positive (symbiotic) to the host or could be negative to the plant. Root exudates may act as messengers that communicate and initiate biological and physical interactions between soil organisms and roots. The currentreview will illustrate the role of root exudates in mycorrhizal fungi association, the major components of root exudates and more focus on the disease control by root exudates derived from plants mycorrhizosphere. Key words: Mycorrhizal fungi, exudates, bio-communications, root, add volatiles, non-volatiles.