By Metin Turan, Nurgül Kıtır, Ülker Alkaya, Adem Günes, Şefik Tüfenkçi, Ertan Yıldırım and Emrah Nikerel

Plant Growth Promoting Rhizobacteria (PGPR) are beneficial soil bacteria that can live either symbiotically with plants at rhizosphere or as endophytes living on or inside of the host plants. There are two main mechanisms via PGPR contribute to the plant growth. Direct mechanism consists of phytohormone production (i.e. auxins (IAA), cytokinins and gibberellins), biological nitrogen fixation, solubilizing inorganic phosphates, mineralizing organic phosphate and producing organic matter such as amino acids. As indirect mechanisms, PGPR aid plants in combat against the pathogen microorganisms by means of stimulating the disease-resistance mechanism of plants, promote favorable symbiosis, decontaminate the soil of xenobiotics. PGPR can also help plants to cope against abiotic stress by lowering ethylene levels, or against pathogenic microorganism by means of secreting antibacterial/antifungal substances. Exact mechanisms of PGPR characteristics which stimulate the plant growth or product formation are still under investigation, yet in agriculture, PGPR are used as environmental friendly biofertilizers, biocontrol agents or biostimulants. These beneficial bacteria are usually introduced to the plants either in powder or liquid form or the seeds are covered with the inoculants before sowing. Plants are subject to many different environmental elements. Abiotic factors such as drought or water stress have been one of the main plant growth limiting factors. Agricultural PGPR application is an alternative solution against loss due to the environmental stresses, since breeding a plant with stress resistance trait is a very long and tricky process due to the fact that such traits are controlled by multiple genes. PGPR phytohormone and enzyme (i.e. ACC deaminase) production can decrease the stress levels of plants while enhancing the root structures.

Part of the book: Plant Growth

The Role of Soil Beneficial Bacteria in Wheat Production: A Review

By Ramazan Çakmakçı, Metin Turan, Nurgul Kıtır, Adem Güneş, Emrah Nikerel, Bahar Soğutmaz Özdemir, Ertan Yıldırım, Murat Olgun, Bülent Topçuoğlu, Şefik Tüfenkçi, Mehmet Rüştü Karaman, Leyla Tarhan and Negar Ebrahim Pour Mokhtari

Free-living plant growth-promoting rhizobacteria (PGPR) have favourable effect on plant growth, tolerance against stresses and are considered as a promising alternative to inorganic fertilizer for promoting plant growth, yield and quality. PGPR colonize at the plant root, increase germination rates, promote root growth, yield, leaf area, chlorophyll content, nitrogen content, protein content, tolerance to drought, shoot and root weight, and delayed leaf senescence. Several important bacterial characteristics, such as biological nitrogen fixation, solubilization of inorganic phosphate and mineralization of organic phosphate, nutrient uptake, 1-aminocydopropane-1-carboxylic acid (ACC) deaminase activity and production of siderophores and phytohormones, can be assessed as plant growth promotion traits. By efficient use, PGPR is expected to contribute to agronomic efficiency, chiefly by decreasing costs and environmental pollution, by eliminating harmful chemicals. This review discusses various bacteria acting as PGPR, their genetic diversity, screening strategies, working principles, applications for wheat and future aspects in terms of efficiency, mechanisms and the desirable properties. The elucidation of the diverse mechanisms will enable microorganisms developing agriculture further.

Part of the book: Wheat Improvement, Management and Utilization

Peat Use in Horticulture

By Nurgul Kitir, Ertan Yildirim, Üstün Şahin, Metin Turan, Melek Ekinci, Selda Ors, Raziye Kul, Hüsnü Ünlü and Halime Ünlü

Peat is a spongy substance which is an effect of incomplete decomposition of plant residues in different stages of decomposition. Between the several organic matters which are used as substrate for horticultural plants cultivation in soilless conditions, peat is the unabandonable ingredient for mixtures for commercial production of plants. Peat is used in horticulture as a component of garden plant substrates, in agriculture for the production of garden soil and as an organic fertilizer, and in balneology as a material for baths and wraps. The use of peat for agriculture and horticulture is determined by the following quality parameters: the degree of decomposition, ash content, pH, the presence of carbonates, the density of the solid phase, bulk density, and porosity. As an organic material, the peat forms in the acidic, waterlogged, and sterile conditions of fens and bogs. The conditions seem like the development of mosses. The plants do not compose as they die. Instead of this, the organic matter is laid down and accumulates in a slow time as peat due to the oxygen deficiency in the bog. This makes peat a highly productive growing medium. In the present novel review, we discuss the peat use in horticulture.

Part of the book: Peat

Melatonin: Role in Increasing Plant Tolerance in Abiotic Stress Conditions

By Raziye Kul, Aslıhan Esringü, Esin Dadasoglu, Üstün Sahin, Metin Turan, Selda Örs, Melek Ekinci, Guleray Agar and Ertan Yildirim

Nowadays, due to the environmental stress factors that limit the production of crops, it has become very difficult to find suitable areas to enable the plant to reach its optimum product potential. Abiotic stress is very effective in decreasing agricultural production. Factors such as drought, salinity, high and low temperature, flood, radiation, heavy metals, oxidative stress, and nutrient deficiency can be considered as abiotic stress factors, and these sources of stress negatively affect plant growth, quality and productivity. Melatonin (MEL) was first identified in plants in 1995 and is increasingly becoming important for its role and effects in the plant system. MEL has been shown to have a substantial role in plant response to growth, reproduction, development, and different stress factors. In addition to its regulatory role, MEL also plays a protective role against different abiotic stresses such as metal toxicity, temperature, drought, and salinity. In plants, an important role of MEL is to alleviate the effects of abiotic stresses. In this review, the effects of MEL on plant growth, photosynthetic activity, metabolism, physiology, and biochemistry under abiotic stress conditions as a plant growth regulator will be examined.

Part of the book: Abiotic and Biotic Stress in Plants

How Abiotic Stress Conditions Affects Plant Roots

By Raziye Kul, Melek Ekinci, Metin Turan, Selda Ors and Ertan Yildirim

Roots are generally subject to more abiotic stress than shoots. Therefore, they can be affected by such stresses as much as, or even more, than above ground parts of a plant. However, the effect of abiotic stresses on root structure and development has been significantly less studied than above ground parts of plants due to limited availability for root observations. Roots have functions such as connecting the plant to the environment in which it grows, uptaking water and nutrients and carrying them to the above-ground organs of the plant, secreting certain hormones and organic compounds, and thus ensuring the usefulness of nutrients in the nutrient solution. Roots also send some hormonal signals to the body in stress conditions such as drought, nutrient deficiencies, salinity, to prevent the plant from being damaged, and ensure that the above-ground part takes the necessary precautions to adapt to these adverse conditions. Salinity, drought, radiation, high and low temperatures, heavy metals, flood, and nutrient deficiency are abiotic stress factors and they negatively affect plant growth, productivity and quality. Given the fact that impending climate change increases the frequency, duration, and severity of stress conditions, these negative effects are estimated to increase. This book chapter reviews to show how abiotic stress conditions affect growth, physiological, biochemical and molecular characteristics of plant roots.

Part of the book: Plant Roots

Introductory Chapter: Plant Roots – Underground Treasure

By Ertan Yildirim

Part of the book: Plant Roots

Plant Root Enhancement by Plant Growth Promoting Rhizobacteria

By Metin Turan, Tuba Arjumend, Sanem Argın, Ertan Yildirim, Hikmet Katırcıoğlu, Burak Gürkan, Melek Ekinci, Adem Güneş, Ayhan Kocaman and Parisa Bolouri

Soil microorganisms perform a variety of functions, some of which are extremely helpful to the maintenance of ecological sustainability. Bacteria thriving in the plant rhizosphere drive plant development through a variety of ways, which are referred to as PGPRs (plant growth-promoting rhizobacteria). Despite the fact that there are many different types of PGPRs, their significance and applications in sustainable agriculture are still debated and limited. The performance of PGPRs vary, which might be related to a variety of environmental conditions that impact their development and proliferation in plants. PGPR is a nonpathogenic, friendly bacterium that stimulates plant development by altering hormone concentrations and nutritional needs, as well as mitigating stress-related damage. PGPRs colonize root hairs and lateral roots in plants, where they may exhibit their beneficial characteristics. Rhizobacteria that promote plant development have the ability to control root system architecture (RSA), as well as the vegetative growth and physiology of the entire plant. The generation of hormones like Indole acetic acid (IAA) by PGPR has long been linked to RSA effects. This book chapter reviews the effects of PGPRs on the growth, the physiological, biochemical, and molecular characteristics of plant roots as well as the mechanisms involved.

Part of the book: Plant Roots

Principles of Irrigation Management for Vegetables

By Selda Ors, Ustun Sahin, Melek Ekinci, Metin Turan and Ertan Yildirim

Vegetables have a very high percentage of water content. Some of the vegetables, such as cucumber, tomato, lettuce, zucchini, and celery contain over ninety-five percent of water. As a result of the high-water content in the cells, they are extremely vulnerable plants to water stress and drought conditions. Their yield and quality are affected rapidly when subjected to drought. Therefore, irrigation is essential to the production of most vegetables in order to have an adequate yield with high quality. However, over-irrigating can inhibit germination and root development, decrease the vegetable quality and post-harvest life of the crop. Determination of suitable irrigation systems and scheduling to apply proper amount of water at the correct time is crucial for achieving the optimum benefits from irrigation. This determination requires understanding of the water demand of the vegetable, soil characteristics, and climate factors. All these factors have major impact for the success and sustainability of any vegetable irrigation. This section contains fundamentals of water requirements on different vegetables and summarizes important issues related to soil, water, and vegetable growth relations together with irrigation management concept by evaluating the challenging issues on the selection of proper irrigation system, suitable irrigation timing, and other parameters to increase vegetable yield in an irrigated agriculture.

Part of the book: Vegetable Crops

Seeds of Resilience: Physiology and Mechanisms of Hardseededness

By Sıtkı Ermis, Eren Özden and Ertan Yıldırım

Physical dormancy, also known as hardseededness or seed coat impermeability, is a condition that occurs when a seed’s coat becomes impermeable, preventing the entry of water, gases, and other external factors. This impermeability serves as a protective mechanism, delaying germination until suitable conditions are met. Factors influencing hard seed formation fall into two categories: internal and external. Internal factors pertain to plant-specific traits, such as species and seed morphology. Genetic variations and seed coat characteristics play a role in shaping hard seed formation. External factors, based on environmental conditions, also influence seed development. Soil nutrient availability, water supply, humidity, temperature, and light conditions impact seed coat permeability and germination. Additionally, the timing of seed maturity, drying, and storage conditions can contribute to hard seed formation. The interplay of these factors determines a plant’s tendency to produce hard seeds. Overcoming dormancy caused by seed coat impermeability involves various methods, including physical, chemical, and mechanical approaches. These methods enhance water and gas permeability, facilitating germination. The choice of method depends on seed characteristics and desired outcomes in breaking dormancy. This section emphasizes the impact of hardseededness on seed quality and the application of methods to enhance germination, underscoring its significance in seed science.

Part of the book: Seed Biology