in: BACTERIAL PRACTICES IN AGRICULTURE, Fatih Çığ, Editor, İksad Yayınevi, Ankara, pp.3-55, 2021
There is a growing interest in the use of plant-associated microorganisms, which play a central role in soil and plant health, as well as plant nutrition through carbon and nutrient cycling, and are becoming increasingly important for agricultural sustainability. Beneficial, free-living, rhizosphere and root-colonizing bacteria that stimulate plant growth, increase yield, and reduce stress are generally considered plant growth-promoting rhizobacteria (PGPR). PGPR enhance plant growth by a wide variety of mechanisms like biological N2- fixation, solubilization and mineralization of organic/inorganic P, K, Zn and Fe, production of siderophore, ammonia, salycylic acid, and phytohormones like indole acetic acid (IAA), cytokinins, gibberellins, ethylene, certain volatiles etc., producing plant growth regulators and volatile organic compounds, recycling of essential elements and uptake of essential nutrients from the soil, organic matter mineralization, rhizosphere engineering, soil structure formation, containing of 1- aminocyclopropane-1-carboxylate (ACC) deaminase, lowering of plant ethylene level, quorum sensing signal interference and reducing biofilm formation, degrading organic pollutants, improving plant-microbe symbioses, and indirectly acting as a biocontrol agents by mechanisms such as producing siderophores, β-1,3-glucanase, chitinases, antibiotics, fluorescent pigment and cyanide, and inducing systemic resistance. The use of free-living beneficial bacteria as an important agricultural input to increase crop production requires the selection of competent rhizobacteria with plant growth promoting properties.
Tea is a popular herb grown commercially in more than 50 countries in well-distributed rainy, hot, and humid climates, well-drained, deep, fairly loamy, acidic and lime-free soils, and its shoot used as a beverage. Since it increases leaf yield, tea needs more nitrogen compared to other plants and its requirement has increased year after year. In addition, fertilizers may not be effective in this regard due to runoff and leaching under the high rainfall tea ecosystem. In long-term continuous cropping tea garden systems, tea bushes grow very close together and root secretions can accumulate from all sides in the rhizosphere, causing a significant inhibitory effect, even some nutrient content accumulates in the soil, soil quality in the root zone decreases and tea growth is inhibited. Soil quality, fertility and health of tea plantation systems, especially biological parameters, depend on agricultural management practices, and long-term overuse of inorganic fertilizers adversely affects them. The inoculum efficiency of microbial products, which play an important role in sustainable agriculture, varies depending on a number of factors such as soil mineral content, type of crop and competition with native strains. As an alternative, the use of bacterial inoculants can contribute to increasing agricultural productivity and solving environmental problems by reducing the use of chemical, environmental pollution and production costs if the selected and developed bacterial inoculants are efficient. This review discusses various microorganisms especially bacteria, their ecology, isolation, characterization, strategies, principles, future aspect, nutrient uptake and use efficiency, microbial diversity and rhizosphere microbe interactions in tea cropping systems, processes involved in the efficiency, and applications for tea and future directions.