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Plant disease triangle. Epidemiology is the study of factors affecting the outbreak and spread of infectious diseases. [11] A disease triangle describes the basic factors required for plant diseases. These are the host plant, the pathogen, and the environment. Any one of these can be modified to control a disease. [12]
Plant diseases are diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). [1] Organisms that cause infectious disease include fungi , oomycetes , bacteria , viruses , viroids , virus -like organisms, phytoplasmas , protozoa , nematodes and parasitic plants . [ 2 ]
Physiological plant disorders are caused by non-pathological conditions such as poor light, adverse weather, water-logging, phytotoxic compounds or a lack of nutrients, and affect the functioning of the plant system. Physiological disorders are distinguished from plant diseases caused by pathogens, such as a virus or fungus. [1]
Such diseases were originally thought to be caused by viruses, which, like phytoplasmas, require insect vectors and cannot be cultured. Viral and phytoplasmic infections share some symptoms. [ 5 ] In 1967, phytoplasmas were discovered in ultrathin sections of plant phloem tissue and were termed mycoplasma-like organisms due to their ...
Diseases caused by P. syringae tend to be favoured by wet, cool conditions—optimum temperatures for disease tend to be around 12–25 °C (54–77 °F), although this can vary according to the pathovar involved. The bacteria tend to be seed-borne, and are dispersed between plants by rain splash.
Important diseases caused by phytomyxeans include club root in cabbage and its relatives, and powdery scab in potatoes. [4] These are caused by species of Plasmodiophora and Spongospora, respectively. [5] The vegetative form is a multinucleate cell, called a plasmodium. This ultimately divides to form new spores, which are released when the ...
In order for heteroplasmy to occur, organelles must contain a genome and, in turn, a genotype. In animals, mitochondria are the only organelles that contain their own genomes, so these organisms will only have mitochondrial heteroplasmy. In contrast, photosynthetic plants contain mitochondria and chloroplasts, each of which contains plastid ...
In humans, as in most eukaryotes, the 18S rRNA is a component of 40S ribosomal subunit, and the 60S large subunit contains three rRNA species (the 5S, 5.8S and 28S in mammals, 25S in plants). 60S rRNA acts as a ribozyme, catalyzing peptide bond formation, while 40S monitors the complementarity between tRNA anticodon and mRNA. [citation needed]