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.