Plant Disease Resistant Varieties Genetic Resources
Obtaining disease-resistantSeveral means of obtaining disease-resistant plants are commonly employed alone or in combination. These include introduction from an outside source, selection, and induced variation. All three may be used at different stages in a continuous process; for example, varieties free from injurious insects or plant diseases may be introduced for comparison with local varieties. The more promising lines or strains are then selected for further, and they are further improved by promoting as much variation as possible through or special treatment. Finally, selection of the plants showing greatest promise takes place. Developing disease-resistant plants is a continuing process.Special treatments for inducing changes include the application of mutation-inducing chemicals and irradiation with. These treatments commonly induce genetic changes, but, occasionally, ones also may occur.Methods used in breeding plants for resistance are similar to those used in breeding for other characters except that two organisms are involved—the host plant and the pathogen.
Thus, it is necessary to know as much as possible about the nature of inheritance of the resistant characters in the host plant and the existence of physiological races or strains of the pathogen. The use of in developing disease-resistant plantsThe techniques of can be used to manipulate the genetic material of a cell in order to produce a new characteristic in an organism. Genes from plants, microbes, and animals can be recombined ( ) and introduced into the living cells of any of these organisms.that have had genes from other species inserted into their genome (the full complement of an organism’s genes) are called. The production of pathogen-resistant transgenic plants has been achieved by this method; certain genes are inserted into the plant’s genome that confer resistance to such pathogens as viruses, fungi, and insects. Transgenic plants that are tolerant to and that show improvements in other qualities also have been developed. About the release of transgenic plants into the exists, and measures to safeguard the application of this technology have been adopted.
In the several federal agencies, such as the, the, and the, regulate the use of genetically engineered organisms. As of 2016, more than 457 million acres (185 million hectares) worldwide were planted with. Among the most successful GM crops are corn (maize), soybeans, and cotton, all of which have proved valuable to farmers with respect to producing increased yields and having economic advantages. Classification of plant diseases by causal agentPlant diseases are often classified by their physiological effects or symptoms.
Many diseases, however, produce practically identical symptoms and signs but are caused by very different microorganisms or agents, thus requiring completely different control methods. Classification according to symptoms is also inadequate because a causal agent may induce several different symptoms, even on the same plant organ, which often intergrade. Classification may be according to the species of plant affected. Host indexes (lists of diseases known to occur on certain hosts in regions, countries, or continents) are valuable in. When an apparently new disease is found on a known host, a check into the index for the specific host often leads to identification of the causal agent. It is also possible to classify diseases according to the essential process or function that is adversely affected.
The best and most widely used classification of plant diseases is based on the causal agent, such as a noninfectious agent or an infectious agent (i.e., a, or ). Noninfectious disease-causing agentsNoninfectious diseases, which sometimes arise very suddenly, are caused by the excess, deficiency, nonavailability, or improper balance of light, air circulation, water, or essential soil elements; unfavourable soil moisture-oxygen relations; extremes in soil acidity or alkalinity; high or low temperatures; injury; other poisonous chemicals in air or soil; changes in soil grade; girdling of; mechanical and electrical agents; and compaction. In addition, unfavourable preharvest and storage conditions for fruits, vegetables, and nursery often result in losses. The effects of noninfectious diseases can be seen on a variety of plant species growing in a given locality.
Many diseases and injuries caused by noninfectious agents result in heavy loss but are difficult to check or eliminate because they frequently reflect ecological factors beyond human control. Symptoms may appear several weeks or months after an environmental disturbance.Injuries incurred from accidents, poisons, or adverse environmental disturbances often result in damaged tissues that weaken a plant, enabling bacteria, fungi, or viruses to enter and add further damage. The cause may be obvious ( or ), but often it is obscure. Symptoms alone are often unreliable in identifying the causal factor.
Plant Disease Resistant Varieties Genetic Resources List
A thorough examination of recent weather patterns, the condition of surrounding plants, cultural treatments or disturbances, and soil and water tests can help reveal the nature of the disease. Adverse environmentHigh may corn, cotton, and bean leaves and may induce formation of at the soil surface of tender flax, cotton, and peanut plants. Frost injury is relatively common, but temperatures just above freezing also may cause damage, such as net (localized tissue death) in potato tubers and “silvering” of corn leaves. Isolated, thin-barked trees growing in northern climates and subjected to frequent thawing by day and freezing by night may develop dead bark cankers or vertical frost cracks on the south or southwest sides of the trunk.
Alternate freezing and thawing, heaving, low air moisture, and smothering under an ice-sheet cover are damaging to alfalfa, clovers, strawberries, and grass on golf greens. Legume crowns commonly split under these conditions and are invaded by decay-forming fungi.The and dry that often accompany high temperatures cause stunting, wilting, blasting, marginal of leaves, and of shoots. Leaf is common on trees in exposed locations following hot, dry, windy weather when water is lost from leaves faster than it is absorbed by roots. Leaf scorch and sudden flower drop are common indoor plant problems because the humidity in a home, an apartment, or an office is usually below 30 percent.
Similar symptoms are caused by a change in soil grade, an altered water-table level, a compacted and shallow soil, paved surface over tree roots, temporary flooding or a waterlogged (oxygen-deficient) soil, girdling tree roots, salt spray near the ocean, and an injured or diseased root system. Injured plants are often very susceptible to air and soil pathogens and secondary invaders.of and is prevalent when soil moisture and temperature levels fluctuate widely and is low.Poor aeration may cause blackheart in stored potatoes. Accumulation of certain gases from the respiration of in storage may produce apple scald and other disorders.All plants require certain mineral elements to develop and mature in a healthy state.
Such as, and are required in substantial quantities, while micronutrients or such as, and are needed in much smaller quantities.
Lavender Plant Varieties
The relationship between a plant and a pest1 is very complex. The ability of a pest to cause disease in a plant depends on environmental conditions, the properties of the organism itself and the capacity of the plant to defend itself. Varieties within a plant species can differ in their ability to defend themselves. Under different climatic conditions the interaction between the same plant and pest may have different outcomes.Pathogens are known to develop and form new biotypes – pathotypes, races or strains that can cause damage to plants, which remain unaffected by the original form of the pathogen. Resistance is the ability of a plant variety to restrict the growth and development of a specified pathogen or the damage they cause when compared to susceptible plant varieties under similar environmental conditions and pathogen pressure.
Resistant varieties may exhibit some disease symptoms or damage under heavy pathogen pressure. Consistent terminologyTo promote consistency in the terminolgy used to describe the reaction of a plant to a pest, the ISF Vegetable and Ornamental Crops Section has adopted a set of agreed. The paper defines two levels of resistance. Company claims on the level of resistance are based on tests carried out with well-characterized isolates of a pest in controlled environmental conditions. An isolate is a population of (micro) organisms that has been obtained in pure culture from a field, from another location or in a laboratory, and that has been characterised using differential hosts.
A characterised isolate is representative of a biotype, pathotype, race or strain of a pest and will not have any characteristic differentiating it from another isolate of the same biotype, pathotype, race or strain. The definition paper is also available in the following languages;,.Seed companies are also encouraged to use uniform codes for pests affecting vegetable and cereal crops in catalogues and other communication with customers – see.Resistance genes may be effective against all or some biotypes, pathotypes, races or strains of a pest, and the emergence of new biotypes, pathotypes, races or strains is not uncommon. To identify and distinguish different isolates within a species plant pathologists use different methods including ‘differential hosts’ – see. Isolates that after characterization do not match an already described pathotype, biotype, race or strain of the pest are designated as a new biotype, pathotype, race or strain following proof that it is established in nature in a scientific publication.