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Arabidopsis thaliana, the thale cress, mouse-ear cress or arabidopsis, is a small flowering plant native to Eurasia and Africa. A. thaliana is considered a weed; it is found along the shoulders of roads and in disturbed land.
Monoculture is the agricultural practice of growing a single crop, plant, or livestock species, variety, or breed in a field or farming system at a time. Polyculture, where more than one crop species is grown in the same space at the same time, is the alternative to monoculture. Monoculture is widely used both in industrial farming and in organic farming. It has allowed farmers to increase efficiency in planting, managing, and harvesting but it can also increase the risk of diseases or pest outbreaks.
Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between unicellular and/or multicellular organisms other than by the ("vertical") transmission of DNA from parent to offspring (reproduction). HGT is an important factor in the evolution of many organisms.
In biology, polymorphism is the occurrence of two or more clearly different morphs or forms, also referred to as alternative phenotypes, in the population of a species. To be classified as such, morphs must occupy the same habitat at the same time and belong to a panmictic population.
Vitis labrusca, the fox grape, is a species of grapevines belonging to the Vitis genus in the flowering plant family Vitaceae. The vines are native to eastern North America and are the source of many grape cultivars, including Catawba, Concord, Delaware, Isabella, Niagara, and many hybrid grape varieties such as Agawam, Alexander and Onaka. Among the characteristics of this vine species in contrast to the European wine grape Vitis vinifera are its "slip-skin" that allows the skin of the grape berries to easily slip off when squeezed, instead of crushing the pulp, and the presence of tendrils on every node of the cane. Another contrast with European vinifera is the characteristic "foxy" musk of V. labrusca, best known to most people through the Concord grape. This musk is not related to the mammalian fox, but rather to the strong, earthy aromas characteristic of the grapes that were known by early European-American settlers in the New World. The term "foxy" became a sort of catchall for the wine tasting descriptors used for these American wines that were distinct from the familiar flavors of the European viniferous wines.
A pathosystem is a subsystem of an ecosystem and is defined by the phenomenon of parasitism. A plant pathosystem is one in which the host species is a plant. The parasite is any species in which the individual spends a significant part of its lifespan inhabiting one host individual and obtaining nutrients from it. The parasite may thus be an insect, mite, nematode, parasitic Angiosperm, fungus, bacterium, mycoplasma, virus or viroid. Other consumers, however, such as mammalian and avian herbivores, which graze populations of plants, are normally considered to be outside the conceptual boundaries of the plant pathosystem.
Genetically modified crops are plants used in agriculture, the DNA of which has been modified using genetic engineering methods. Plant genomes can be engineered by physical methods or by use of Agrobacterium for the delivery of sequences hosted in T-DNA binary vectors. In most cases, the aim is to introduce a new trait to the plant which does not occur naturally in the species. Examples in food crops include resistance to certain pests, diseases, environmental conditions, reduction of spoilage, resistance to chemical treatments, or improving the nutrient profile of the crop. Examples in non-food crops include production of pharmaceutical agents, biofuels, and other industrially useful goods, as well as for bioremediation.
Moisture stress occurs when the water in a plant's cells is reduced to less than normal levels. This can occur because of a lack of water in the plant's root zone, higher rates of transpiration than the rate of moisture uptake by the roots, for example, because of an inability to absorb water due to a high salt content in the soil water or loss of roots due to transplantation. Moisture stress is more strongly related to water potential than it is to water content.
Lactuca serriola, also called prickly lettuce, milk thistle, compass plant, and scarole, is an annual or biennial plant in the dandelion tribe within the daisy family. It has a slightly fetid odor and is commonly considered a weed of orchards, roadsides and field crops. It is the closest wild relative of cultivated lettuce.
Raoul A. Robinson was a Canadian/British plant scientist with more than forty years of wide-ranging global experience in crop improvement for both commercial and subsistence agriculture. He is best known for his application of system theory to crop pathosystems and the elucidation of the concepts of horizontal and vertical resistance and their implication on breeding for durable resistance.
The gene-for-gene relationship was discovered by Harold Henry Flor who was working with rust of flax. Flor showed that the inheritance of both resistance in the host and parasite ability to cause disease is controlled by pairs of matching genes. One is a plant gene called the resistance (R) gene. The other is a parasite gene called the avirulence (Avr) gene. Plants producing a specific R gene product are resistant towards a pathogen that produces the corresponding Avr gene product. Gene-for-gene relationships are a widespread and very important aspect of plant disease resistance. Another example can be seen with Lactuca serriola versus Bremia lactucae.
In genetics, the term horizontal resistance was first used by J.E. Vanderplank to describe many-gene resistance, which is sometimes also called generalized resistance. This contrasts with the term vertical resistance which was used to describe single-gene resistance. Raoul A. Robinson further refined the definition of horizontal resistance. Unlike vertical resistance and parasitic ability, horizontal resistance and horizontal parasitic ability are entirely independent of each other in genetic terms.
Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all living organisms are made up of cells that process hereditary information encoded in genes, which can be transmitted to future generations. Another major theme is evolution, which explains the unity and diversity of life. Finally, all living organisms require energy to move, grow, and reproduce, as well as to regulate their own internal environment.
Marker assisted selection or marker aided selection (MAS) is an indirect selection process where a trait of interest is selected based on a marker linked to a trait of interest, rather than on the trait itself. This process has been extensively researched and proposed for plant and animal breeding.
Genetic pollution is a controversial term for uncontrolled gene flow into wild populations. It is defined as "the dispersal of contaminated altered genes from genetically engineered organisms to natural organisms, esp. by cross-pollination", but has come to be used in some broader ways. It is related to the population genetics concept of gene flow, and genetic rescue, which is genetic material intentionally introduced to increase the fitness of a population. It is called genetic pollution when it negatively impacts on the fitness of a population, such as through outbreeding depression and the introduction of unwanted phenotypes which can lead to extinction.
Rhizobacteria are root-associated bacteria that form symbiotic relationships with many plants. The name comes from the Greek rhiza, meaning root. Though parasitic varieties of rhizobacteria exist, the term usually refers to bacteria that form a relationship beneficial for both parties (mutualism). They are an important group of microorganisms used in biofertilizer. Biofertilization accounts for about 65% of the nitrogen supply to crops worldwide. Rhizobacteria are often referred to as plant growth-promoting rhizobacteria, or PGPRs. The term PGPRs was first used by Joseph W. Kloepper in the late 1970s and has become commonly used in scientific literature. PGPRs have different relationships with different species of host plants. The two major classes of relationships are rhizospheric and endophytic. Rhizospheric relationships consist of the PGPRs that colonize the surface of the root, or superficial intercellular spaces of the host plant, often forming root nodules. The dominant species found in the rhizosphere is a microbe from the genus Azospirillum. Endophytic relationships involve the PGPRs residing and growing within the host plant in the apoplastic space.
Plant disease resistance protects plants from pathogens in two ways: by pre-formed structures and chemicals, and by infection-induced responses of the immune system. Relative to a susceptible plant, disease resistance is the reduction of pathogen growth on or in the plant, while the term disease tolerance describes plants that exhibit little disease damage despite substantial pathogen levels. Disease outcome is determined by the three-way interaction of the pathogen, the plant and the environmental conditions.
Plant breeding is the science of changing the traits of plants in order to produce desired characteristics. It has been used to improve the quality of nutrition in products for humans and animals. The goals of plant breeding are to produce crop varieties that boast unique and superior traits for a variety of agricultural applications. The most frequently addressed traits are those related to biotic and abiotic stress tolerance, grain or biomass yield, end-use quality characteristics such as taste or the concentrations of specific biological molecules and ease of processing . Plant breeding can be accomplished through many different techniques ranging from simply selecting plants with desirable characteristics for propagation, to methods that make use of knowledge of genetics and chromosomes, to more complex molecular techniques. Genes in a plant are what determine what type of qualitative or quantitative traits it will have. Plant breeders strive to create a specific outcome of plants and potentially new plant varieties, and in the course of doing so, narrow down the genetic diversity of that variety to a specific few biotypes.
The Vertifolia effect is a well documented phenomenon in the fields of plant breeding and plant pathology. It is characterized by the erosion of a crop’s horizontal resistance to disease during a breeding cycle due to the presence of strong vertical resistance, characterized by the presence of R genes. This effect was observed in late blight of potato. This phenomenon was first described by J.E. Van der Plank in his 1963 book Plant Disease: Epidemics and Control. Van der Plank observed that under artificial selection the potato variety Vertifolia had stronger vertical resistance to the potato late blight pathogen, Phytophthora infestans, as measured by the presence of specific R genes. However, when the pathogen overcame these R genes Vertifolia exhibited a greater loss of horizontal resistance than varieties with fewer R genes and lower vertical resistance. This effect suggests that when a pathogen evolves an avirulence gene to counteract a variety’s R gene, that variety will be more susceptible to the pathogen than other varieties.
The study of gene-for-gene interactions uncovers genetic components, evolutionary impacts, and ecological/economic implications between rust fungi and plants. Rust fungi utilize the gene-for-gene interaction to invade host plants. Conversely, host plants utilize the gene-for-gene interaction to prevent invasion of rust fungi.
References
- ↑ Vanderplank, J.E. (1963) Plant Diseases: Epidemics and Control. Academic Press, New York and London, 349pp.
- ↑ Robinson, Raoul A. (1976) Plant Pathosystems. Springer-Verlag, Berlin, Heidelberg, New York, 184pp.
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