Biotic stress is stress that occurs as a result of damage done to an organism by other living organisms, such as bacteria, viruses, fungi, parasites, beneficial and harmful insects, weeds, and cultivated or native plants. It is different from abiotic stress, which is the negative impact of non-living factors on the organisms such as temperature, sunlight, wind, salinity, flooding and drought. The types of biotic stresses imposed on an organism depend the climate where it lives as well as the species' ability to resist particular stresses. Biotic stress remains a broadly defined term and those who study it face many challenges, such as the greater difficulty in controlling biotic stresses in an experimental context compared to abiotic stress.
The damage caused by these various living and nonliving agents can appear very similar. Even with close observation, accurate diagnosis can be difficult. For example, browning of leaves on an oak tree caused by drought stress may appear similar to leaf browning caused by oak wilt, a serious vascular disease caused by a fungus, or the browning caused by anthracnose, a fairly minor leaf disease.
Biotic stressors are a major focus of agricultural research, due to the vast economic losses caused to cash crops. The relationship between biotic stress and plant yield affects economic decisions as well as practical development. The impact of biotic injury on crop yield impacts population dynamics, plant-stressor coevolution, and ecosystem nutrient cycling.
Biotic stress also impacts horticultural plant health and natural habitats ecology. It also has dramatic changes in the host recipient. Plants are exposed to many stress factors, such as drought, high salinity or pathogens, which reduce the yield of the cultivated plants or affect the quality of the harvested products. Although there are many kinds of biotic stress, the majority of plant diseases are caused by fungi. Arabidopsis thaliana is often used as a model plant to study the responses of plants to different sources of stress.
Biotic stresses have had huge repercussions for humanity; an example of this is the potato blight, an oomycete which caused widespread famine in England, Ireland and Belgium in the 1840s. Another example is grape phylloxera coming from North America in the 19th century, which led to the Great French Wine Blight.
Losses to pests and disease in crop plants continue to pose a significant threat to agriculture and food security. During the latter half of the 20th century, agriculture became increasingly reliant on synthetic chemical pesticides to provide control of pests and diseases, especially within the intensive farming systems common in the developed world. However, in the 21st century, this reliance on chemical control is becoming unsustainable. Pesticides tend to have a limited lifespan due to the emergence of resistance in the target pests, and are increasingly recognised in many cases to have negative impacts on biodiversity, and on the health of agricultural workers and even consumers.
Due to the implications of climate change, it is suspected that plants will have increased susceptibility to pathogens. Additionally, elevated threat of abiotic stresses (i.e. drought and heat) are likely to contribute to plant pathogen susceptibility.
Many biotic stresses affect photosynthesis, as chewing insects reduce leaf area and virus infections reduce the rate of photosynthesis per leaf area. Vascular-wilt fungi compromise the water transport and photosynthesis by inducing stomatal closure.
Plants have co-evolved with their parasites for several hundred million years. This co-evolutionary process has resulted in the selection of a wide range of plant defences against microbial pathogens and herbivorous pests which act to minimise frequency and impact of attack. These defences include both physical and chemical adaptations, which may either be expressed constitutively, or in many cases, are activated only in response to attack. For example, utilization of high metal ion concentrations derived from the soil allow plants to reduce the harmful effects of biotic stressors (pathogens, herbivores etc.); meanwhile preventing the infliction of severe metal toxicity by way of safeguarding metal ion distribution throughout the plant with protective physiological pathways. Such induced resistance provides a mechanism whereby the costs of defence are avoided until defense is beneficial to the plant. At the same time, successful pests and pathogens have evolved mechanisms to overcome both constitutive and induced resistance in their particular host species. In order to fully understand and manipulate plant biotic stress resistance, we require a detailed knowledge of these interactions at a wide range of scales, from the molecular to the community level.
In order for a plant to defend itself against biotic stress, it must be able to differentiate between an abiotic and biotic stress. A plants response to herbivores starts with the recognition of certain chemicals that are abundant in the saliva of the herbivores. These compounds that trigger a response in plants are known as elicitors or herbivore-associated molecular patterns (HAMPs). These HAMPs trigger signalling pathways throughout the plant, initiating its defence mechanism and allowing the plant to minimise damage to other regions.These HAMPs trigger signalling pathways throughout the plant, initiating its defence mechanism and allowing the plant to minimise damage to other regions. Phloem feeders, like aphids, do not cause a great deal of mechanical damage to plants, but they are still regarded as pests and can seriously harm crop yields. Plants have developed a defence mechanism using salicylic acid pathway, which is also used in infection stress, when defending itself against phloem feeders. Plants perform a more direct attack on an insects digestive system. The plants do this using proteinase inhibitors. These proteinase inhibitors prevent protein digestion and once in the digestive system of an insect, they bind tightly and specifically to the active site of protein hydrolysing enzymes such as trypsin and chymotrypsin. This mechanism is most likely to have evolved in plants when dealing with insect attack.
Plants detect elicitors in the insects saliva. Once detected, a signal transduction network is activated. The presence of an elicitor causes an influx of Ca2+ ions to be released in to the cytosol. This increase in cytosolic concentration activates target proteins such as Calmodulin and other binding proteins. Downstream targets, such as phosphorylation and transcriptional activation of stimulus specific responses, are turned on by Ca2+ dependent protein kinases. In Arabidopsis, over expression of the IQD1 calmodulin-binding transcriptional regulator leads to inhibitor of herbivore activity. The role of calcium ions in this signal transduction network is therefore important.
Calcium Ions also play a large role in activating a plants defensive response. When fatty acid amides are present in insect saliva, the mitogen-activated protein kinases (MAPKs) are activated. These genes when activated, play a role in the jasmonic acid pathway. The jasmonic acid pathway is also referred to as the Octadecanoid pathway. This pathway is vital for the activation of defence genes in plants. The production of jasmonic acid, a phytohormone, is a result of the pathway. In an experiment using virus-induced gene silencing of two calcium-dependent protein kinases (CDPKs) in a wild tobacco ( Nicotiana attenuata), it was discovered that the longer herbivory continued the higher the accumulation of jasmonic acid in wild-type plants and in silenced plants, the production of more defence metabolites was seen as well as the decrease in the growth rate of the herbivore used, the tobacco hornworm (Manduca sexta). This example demonstrates the importance of MAP kinases in plant defence regulation.
Plants are capable of detecting invaders through the recognition of non-self signals despite the lack of a circulatory or immune system like those found in animals. Often a plant's first line of defense against microbes occurs at the plant cell surface and involves the detection of microorganism-associated molecular patterns (MAMPs). MAMPs include nucleic acids common to viruses and endotoxins on bacterial cell membranes which can be detected by specialized pattern-recognition receptors. Another method of detection involves the use of plant immune receptors to detect effector molecules released into plant cells by pathogens. Detection of these signals in infected cells leads to an activation of effector-triggered immunity (ETI), a type of innate immune response.
Both the pattern recognition immunity (PTI) and effector-triggered immunity (ETI) result from the upregulation of multiple defense mechanisms including defensive chemical signaling compounds. An increase in the production of salicylic acid (SA) has been shown to be induced by pathogenic infection. The increase in SA results in the production of pathogenesis related (PR) genes which ultimately increase plant resistance to biotrophic and hemibiotrophic pathogens. Increases in jasmonic acid (JA) synthesis near the sites of pathogen infection have also been described. This physiological response to increase JA production has been implicated in the ubiquitination of jasmonate ZIM domains (JAZ) proteins, which inhibit JA signaling, leading to their degradation and a subsequent increase in JA activated defense genes.
Studies regarding the upregulation of defensive chemicals have confirmed the role of SA and JA in pathogen defense. In studies utilizing Arabidopsis mutants with the bacterial NahG gene, which inhibits the production and accumulation of SA, were shown to be more susceptible to pathogens than the wild-type plants. This was thought to result from the inability to produce critical defensive mechanisms including increased PR gene expression. Other studies conducted by injecting tobacco plants and Arabidopsis with salicylic acid resulted in higher resistance of infection by the alfalfa and tobacco mosaic viruses, indicating a role for SA biosynthesis in reducing viral replication. Additionally, studies performed using Arabidopsis with mutated jasmonic acid biosynthesis pathways have shown JA mutants to be at an increased risk of infection by soil pathogens.
Along with SA and JA, other defensive chemicals have been implicated in plant viral pathogen defenses including abscisic acid (ABA), gibberellic acid (GA), auxin, and peptide hormones. The use of hormones and innate immunity presents parallels between animal and plant defenses, though pattern-triggered immunity is thought to have arisen independently in each.
The Agricultural Research Service (ARS) and various government agencies and private institutions have provided a great deal of fundamental information relating spectral reflectance and thermal emittance properties of soils and crops to their agronomic and biophysical characteristics. This knowledge has facilitated the development and use of various remote sensing methods for non-destructive monitoring of plant growth and development and for the detection of many environmental stresses that limit plant productivity. Coupled with rapid advances in computing and position locating technologies, remote sensing from ground-, air-, and space-based platforms is now capable of providing detailed spatial and temporal information on plant response to their local environment that is needed for site specific agricultural management approaches. This is very important in today's society because with increasing pressure on global food productivity due to population increase, result in a demand for stress-tolerant crop varieties that has never been greater.
Abiotic stress is the negative impact of non-living factors on the living organisms in a specific environment. The non-living variable must influence the environment beyond its normal range of variation to adversely affect the population performance or individual physiology of the organism in a significant way.Whereas a biotic stress would include living disturbances such as fungi or harmful insects, abiotic stress factors, or stressors, are naturally occurring, often intangible and inanimate factors such as intense sunlight, temperature or wind that may cause harm to the plants and animals in the area affected. Abiotic stress is essentially unavoidable.
Abiotic stress affects animals, but plants are especially dependent, if not solely dependent, on environmental factors, so it is particularly constraining. Abiotic stress is the most harmful factor concerning the growth and productivity of crops worldwide. Research has also shown that abiotic stressors are at their most harmful when they occur together, in combinations of abiotic stress factors.Aglandau
The Aglandau is one of the more important of approximately a hundred cultivars of olives in France. It is grown primarily in Provence, but also as far away as Azerbaijan and Ukraine. The 'Aglandau' is primarily used for production of oil, but can also be eaten. When used as table olives, the fruit is normally called Beruguette. The oil is highly valued for its fruity taste.Biotic component
Biotic components, or biotic factors, can be described as any living component that affects another organism or shapes the ecosystem. This includes both animals that consume other organisms within their ecosystem, and the organism that is being consumed. Biotic factors also include human influence, pathogens, and disease outbreaks. Each biotic factor needs the proper amount of energy and nutrition to function day to day.
Biotic components are typically sorted into three main categories:
Producers, otherwise known as autotrophs, convert energy (through the process of photosynthesis) into food.
Consumers, otherwise known as heterotrophs, depend upon producers (and occasionally other consumers) for food.
Decomposers, otherwise known as detritivores, break down chemicals from producers and consumers (usually antibiotic) into simpler form which can be reused.Bouteillan
The Bouteillan is a cultivar of olives grown primarily in Provence. Originally from the town of Aups in the Var département, it is today grown also in Australia and the United States. It is mostly used for the production of oil. The Bouteillan is vulnerable to certain pests, but has a good resistance to cold.Cailletier
The Cailletier, also known in English by the Italian name Taggiasca, is a cultivar of olives grown primarily in the Alpes-Maritimes region near Nice and the Riviera di Ponente, Italy. It is best known under the name Niçoise, which signifies its curing method, in which form it is an important ingredient in the salade niçoise. It can also be used for the production of oil. This cultivar is particularly susceptible to the olive fruit fly.Cayon olive
The Cayon is a cultivar of olives grown primarily in the Var region of southern France. It is used primarily for the production of olive oil. The Cayon is highly valued for its role as a pollinator of other olive varieties.Dehydrin
Dehydrin (DHN) is a multi-family of proteins present in plants that is produced in response to cold and drought stress. DHNs are hydrophilic and reliably thermostable. They are stress proteins with a high number of charged amino acids that belong to the Group II Late Embryogenesis Abundant (LEA) family. DHNs are primarily found in the cytoplasm and nucleus but more recently, they have been found in other organelles, like mitochondria and chloroplasts. DHNs are characterized by the presence of Glycine and other polar amino acids. All DHNs contain at least one copy of a consensus 15-amino acid sequence. This segment, also known as the K-segment, has the sequence EKKGIMDKIKEKLPG. However, an inspection of a range of other reported dehydrin sequences shows that its conservation is not absolute." Dehydration-induced proteins in plants were first observed in 1989, in a comparison of barley and corn cDNA from plants under drought conditions. The protein has since been referred to as dehydrin and has been the identified as the genetic basis of drought tolerance in plants. However, the first direct genetic evidence of dehydrin playing a role in cellular protection during osmotic shock was not observed until 2005, in the moss, Physcomitrella patens. In order to show a direct correlation between DHN and stress recovery, a knockout gene was created, which interfered with DHNA’s functionality. After being placed in an environment with salt and osmotic stress and then later being returned to a standard growth medium, the P. patens wildtype was able to recover to 94% of its fresh weight while the P. patens mutant only reached 39% of its fresh weight. This study also concludes that DHN production allows plants to function in high salt concentrations. Another study found evidence of DHN’s impact in drought-stress recovery by showing that transcription levels of a DHN increased in a drought-tolerant pine, Pinus pinaster, when placed in a drought treatment. However, transcription levels of a DHN decreased in the same drought treatment in a drought-sensitive P. pinaster. Drought-tolerance is a complex trait, thus that it cannot be genetically analyzed as a single gene trait. The exact mechanism of drought tolerance is yet to be determined and is still being researched. One chemical mechanism related to DHN production is the presence of the phytohormone ABA. One common response to environmental stresses is the process known as cellular dehydration. Cellular dehydration induces biosynthesis of abscisic acid (ABA), which is known to react as a stress hormone because of its accumulation in the plant under water stress conditions. ABA also participates in stress signal transduction pathways ABA has been shown to increase the production of DHN, which provides more evidence of a link between DHN and drought tolerance.There are other proteins in the cell that play a similar role in the recovery of drought treated plants. These proteins are considered dehydrin-like or dehydrin-related. They are poorly defined, in that these dehydrin-like proteins are similar to DHNs, but are unfit to be classified as DHNs for varying reasons. They are found to be similar in that they respond to some or all of the same environmental stresses that induce DHN production. In a particular study dehydrin-like proteins found in the mitochondria were upregulated in drought and cold treatments of cereals. Dehydrins have been reported to confer resistance against fungal infections and over-expression of dehydrins provide protection under abiotic and biotic stress conditions.Evogene
Evogene Ltd. (Hebrew: אבוג'ן) is an Israeli company engaged in research and development for improving crop quality, productivity and economics, through application of plant genomics, for the food, feed and biofuel industries. The Company has strategic collaborations with world-leading agricultural companies to develop improved seed traits in relation to yield and a-biotic stress (such as tolerance to drought), and biotic stress (such as resistance to disease), in key crops as corn, soybean, wheat and rice.Fertilizer burn
Fertilizer burn is defined as leaf scorch resulting from over-fertilization, usually referring to excess nitrogen salts.Fertilizer burn is the result of desiccation of plant tissues due to osmotic stress, creating a state of hypertonicity.
Fertilizers vary in their tendency to burn roughly in accordance with their salt index.Functional Plant Biology
Functional Plant Biology is an international peer-reviewed scientific journal published by CSIRO Publishing. The journal publishes papers of a broad interest that advance knowledge on mechanisms by which plants operate and interact with their environment. Of specific interest are mechanisms and signal transduction pathways by which plants adapt to extreme environmental conditions such as high and low temperatures, drought, flooding, salinity, pathogens, and other major abiotic and biotic stress factors.
The current Editor-in-Chief is Sergey Shabala (University of Tasmania).Lucques
The Lucques is a cultivar of olives grown primarily in Languedoc in France. It is primarily used as a green table olive. It can also produce high quality oil, but this is hard to extract. Though vulnerable to certain pests, it is relatively resistant to cold and drought.MAPK networks
Mitogen-activated protein kinase (MAPK) networks are the pathways and signaling of MAPK, which is a protein kinase that consists of amino acids serine and threonine. MAPK pathways have both a positive and negative regulation in plants. A positive regulation of MAPK networks is to help in assisting with stresses from the environment. A negative regulation of MAPK networks is pertaining to a high quantity of reactive oxygen species (ROS) in the plant.Olivière
The Olivière is a cultivar of olives grown primarily in the Pyrénées-Orientales region of southern France, where it is the most prevalent variety of olives. It is highly valued for its exceptionally high tolerance to cold. The Olivière is primarily used for oil, and even though the fruit yields a low percentage, the trees carry large quantities of olives, and the oil is of high quality.Picholine
The Picholine is a French cultivar of olives. It is the most widely available cultivar in France. Though originally from Gard in southern France, it is today grown all over the world. The Picholine is best known as a cocktail olive, though it is also used to make olive oil. It is the most common variety of olive used for oil from Morocco.Productivity (ecology)
In ecology, productivity refers to the rate of generation of biomass in an ecosystem. It is usually expressed in units of mass per unit surface (or volume) per unit time, for instance grams per square metre per day (g m−2 d−1). The mass unit may relate to dry matter or to the mass of carbon generated. Productivity of autotrophs such as plants is called primary productivity, while that of heterotrophs such as animals is called secondary productivity.Sabine olive
The Sabine is a cultivar of olives grown primarily in Corsica. In the Balagne region of Haute-Corse it is the main variety. The olive yields an exceptionally high amount of oil; more than 30%. Vulnerable to certain biological pests, it is relatively tolerant of cold. The Sabine olive variety should not be confused with the olive oil produced in the Sabina region of Italy.Salonenque
The Salonenque, carrying the name of Salon-de-Provence, is a cultivar of olives grown primarily in Provence. Though it is used for producing oil, and gives a good yield, it is valued primarily as a table olive. It is produced as a so-called cracked olive, which means that the fruit is cracked to speed up the curing process.Tanche
The Tanche, probably the best known French olive cultivar, is grown primarily in the Drôme and Vaucluse regions of southern France. It is often referred to as a perle noire, the "Black Pearl of Provence". The Tanche is said to have been introduced to France by the Greeks of Massilia, around the fourth century BC.Tree care
Tree care is the application of arboricultural methods like pruning, trimming, and felling/thinning in built environments. Road verge, greenways, backyard and park woody vegetation are at the center of attention for the tree care industry. Landscape architecture and urban forestry also set high demands on professional tree care. High safety standards against the dangers of tree care have helped the industry evolve. Especially felling in space-limited environments poses significant risks: the vicinity of power or telephone lines, insufficient protective gear (against falling dead wood, chainsaw wounds, etc.) and narrow felling zones with endangered nearby buildings, parking cars, etc.. The required equipment and experience usually transcends private means and is often considered too costly as a permanent part of the public infrastructure. In singular cases, traditional tools like handsaws may suffice, but large-scale tree care usually calls for heavy machinery like cranes, bucket trucks,harvesters, and woodchippers.
Road side trees are especially prone to biotic stress by exhaust fumes, toxic road debris, soil compaction, and drought which makes them susceptible to fungal infections and various plant pests. When tree removal is not an option, because of road ecology considerations, the main challenge is to achieve road safety (visibility of road signs, blockage-free lanes, etc.) while maintaining tree health.