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Leaf spots are visible symptoms of virus infections on plants, and are referred to as systemic symptoms. [7] In systematic virus infections leaf spots caused by viruses show a loss of green colour in leaves, due to chlorosis which is a repression of chlorophyll development. [ 1 ]
Symptoms of infection include a downward curling of the leaves, leaf tip dieback, stunting, necrosis of growing leaf tips, sunken 'chicken pox-like' spots on leaves (often with a surrounding halo), stem death and yellowing. [7] Since these symptoms are so generic, extreme caution must be taken when introducing new plants to your greenhouse.
The term "necrosis" came about in the mid-19th century and is commonly attributed to German pathologist Rudolf Virchow, who is often regarded as one of the founders of modern pathology. [2] Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated digestion of cell components.
Overview of signal transduction pathways involved in apoptosis. Cell death is the event of a biological cell ceasing to carry out its functions. This may be the result of the natural process of old cells dying and being replaced by new ones, as in programmed cell death, or may result from factors such as diseases, localized injury, or the death of the organism of which the cells are part.
Elm yellows is a plant disease of elm trees that is spread by leafhoppers or by root grafts. [1] Elm yellows, also known as elm phloem necrosis, is very aggressive, with no known cure. Elm yellows occurs in the eastern United States, and southern Ontario in Canada. It is caused by phytoplasmas which infect the phloem (inner bark) of the tree. [2]
Liquefactive necrosis (or colliquative necrosis) is a type of necrosis which results in a transformation of the tissue into a liquid viscous mass. [1] Often it is associated with focal bacterial or fungal infections, and can also manifest as one of the symptoms of an internal chemical burn . [ 2 ]
Necroptosis is a programmed form of necrosis, or inflammatory cell death. Conventionally, necrosis is associated with unprogrammed cell death resulting from cellular damage or infiltration by pathogens, in contrast to orderly, programmed cell death via apoptosis. Nemosis is another programmed form of necrosis that takes place in fibroblasts. [18]
In some cases, commonly in more susceptible hosts, stem and fruit spots can occur as a result of infection as well. These leaf spots cause a reduction in plant photosynthetic surface area. While usually harmless, severe causes of these leaf spots can lead to defoliation, twig dieback, tissue necrosis, and loss of marketable fruit. [2]