Plant pathology is the scientific study of diseases in plants caused by pathogens and environmental conditions. Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants. Not included are ectoparasites like insects, mites, vertebrate, or other pests that affect plant health by eating plant tissues. Plant pathology also involves the study of pathogen identification, disease etiology, disease cycles, economic impact, plant disease epidemiology, plant disease resistance, how plant diseases affect humans and animals, pathosystem genetics, and management of plant diseases.
Stewart's wilt is a serious bacterial disease of corn caused by the bacterium Pantoea stewartii. This bacterium affects plants, particularly types of maize such as sweet, flint, dent, flour, and popcorn. The disease is also known as bacterial wilt or bacterial leaf blight and has shown to be quite problematic in sweet corn. The disease is endemic in the mid-Atlantic and Ohio River Valley regions and in the southern portion of the Corn Belt.
Ralstonia solanacearum is an aerobic non-spore-forming, Gram-negative, plant pathogenic bacterium. R. solanacearum is soil-borne and motile with a polar flagellar tuft. It colonises the xylem, causing bacterial wilt in a very wide range of potential host plants. It is known as Granville wilt when it occurs in tobacco. Bacterial wilts of tomato, pepper, eggplant, and Irish potato caused by R. solanacearum were among the first diseases that Erwin Frink Smith proved to be caused by a bacterial pathogen. Because of its devastating lethality, R. solanacearum is now one of the more intensively studied phytopathogenic bacteria, and bacterial wilt of tomato is a model system for investigating mechanisms of pathogenesis. Ralstonia was until recently classified as Pseudomonas, with similarity in most aspects, except that it does not produce fluorescent pigment like Pseudomonas. The genomes from different strains vary from 5.5 Mb up to 6 Mb, roughly being 3.5 Mb of a chromosome and 2 Mb of a megaplasmid. While the strain GMI1000 was one of the first phytopathogenic bacteria to have its genome completed, the strain UY031 was the first R. solanacearum to have its methylome reported. Within the R. solanacearum species complex, the four major monophyletic clusters of strains are termed phylotypes, that are geographically distinct: phylotypes I-IV are found in Asia, the Americas, Africa, and Oceania, respectively.
Xanthomonas is a genus of bacteria, many of which cause plant diseases. There are at least 27 plant associated Xanthomonas spp., that all together infect at least 400 plant species. Different species typically have specific host and/or tissue range and colonization strategies.
Brenneria salicis is a Gram-negative bacterium that is pathogenic on plants.
Clavibacter michiganensis is an aerobic non-sporulating Gram-positive plant pathogenic actinomycete of the genus Clavibacter. Clavibacter michiganensis has several subspecies. Clavibacter michiganensis subsp. michiganensis causes substantial economic losses worldwide by damaging tomatoes and potatoes.
Curtobacterium flaccumfaciens is a Gram-positive bacterium that causes disease on a variety of plants. Gram-positive bacterium characteristics include small irregular rods, lateral flagella, the ability to persist in aerobic environments, and cells containing catalase. In the interest of studying pathogenicity in plants, the species Curtobacterium flaccumfaciens is broken down further into pathovars, which help to better describe the pathogen.
Bacterial wilt is a complex of diseases that occur in plants such as Cucurbitaceae and Solanaceae and are caused by the pathogens Erwinia tracheiphila, a gram-negative bacterium, or Curtobacterium flaccumfaciens pv. flaccumfaciens, a gram-positive bacterium. Cucumber and muskmelon plants are most susceptible, but squash, pumpkins, and gourds may also become infected.
Leifsonia xyli subsp. xyli is the bacterium that causes ratoon stunting disease, a major worldwide disease of sugarcane. It is Gram positive and grows slowly in the laboratory.
A wilt disease is any number of diseases that affect the vascular system of plants. Attacks by fungi, bacteria, and nematodes can cause rapid killing of plants, large tree branches or even entire trees.
Black rot, caused by the bacterium Xanthomonas campestris pv. campestris (Xcc), is considered the most important and most destructive disease of crucifers, infecting all cultivated varieties of brassicas worldwide. This disease was first described by botanist and entomologist Harrison Garman in Lexington, Kentucky, US in 1889. Since then, it has been found in nearly every country in which vegetable brassicas are commercially cultivated.
Beet vascular necrosis and rot is a soft rot disease caused by the bacterium Pectobacterium carotovorum subsp. betavasculorum, which has also been known as Pectobacterium betavasculorum and Erwinia carotovora subsp. betavasculorum. It was classified in the genus Erwinia until genetic evidence suggested that it belongs to its own group; however, the name Erwinia is still in use. As such, the disease is sometimes called Erwinia rot today. It is a very destructive disease that has been reported across the United States as well as in Egypt. Symptoms include wilting and black streaks on the leaves and petioles. It is usually not fatal to the plant, but in severe cases the beets will become hollowed and unmarketable. The bacteria is a generalist species which rots beets and other plants by secreting digestive enzymes that break down the cell wall and parenchyma tissues. The bacteria thrive in warm and wet conditions, but cannot survive long in fallow soil. However, it is able to persist for long periods of time in the rhizosphere of weeds and non-host crops. While it is difficult to eradicate, there are cultural practices that can be used to control the spread of the disease, such as avoiding injury to the plants and reducing or eliminating application of nitrogen fertilizer.
Blackleg is a plant disease of potato caused by pectolytic bacteria that can result in stunting, wilting, chlorosis of leaves, necrosis of several tissues, a decline in yield, and at times the death of the potato plant. The term "blackleg" originates from the typical blackening and decay of the lower stem portion, or "leg", of the plant.
Bacterial wilt of turfgrass is the only known bacterial disease of turf. The causal agent is the Gram negative bacterium Xanthomonas campestris pv. graminis. The first case of bacterial wilt of turf was reported in a cultivar of creeping bentgrass known as Toronto or C-15, which is found throughout the midwestern United States. Until the causal agent was identified in 1984, the disease was referred to simply as C-15 decline. This disease is almost exclusively found on putting greens at golf courses where extensive mowing creates wounds in the grass which the pathogen uses in order to enter the host and cause disease.
Bacterial Wilt of Carnations is a bacterial disease caused by the plant pathogen Paraburkholderia caryophylli. Previously, named Pseudomonas caryophilli, the pathogen is an aerobic gram negative bacteria known for only being capable of entering its host through wounds. Once inside the host, it colonizes the vascular system and roots causing symptoms such as, internal stem cracking, yellowing of the leaves, wilting, and the development of cankers. As a bacterial disease, Bacterial Wilt of Carnations can also be characterized by signs such as bacterial streaming, and bacterial ooze.
Rathayibacter toxicus is a phytopathogenic bacterium known for causing annual ryegrass toxicity (ARGT) commonly found in South and Western Australia.
Xanthomonas oryzae pv. oryzae is a bacterial pathovar that causes a serious blight of rice, other grasses, and sedges.
Ralstonia pseudosolanacearum is a soil-borne bacterium. It is a vascular phytopathogen that infects host plants through the root system causing wilting disease that causes loss in a wide range of crops. R. pseudosolanacearum is Gram negative and was originally identified as Ralstonia solanacearum, however, in 2014 Safni et al. proposed a taxonomic revision of the Ralstonia solanacearum species complex to reclassify phylotype strains, including R. pseudosolanacearum.
Clavibacter nebraskensis is a species of bacteria in the genus Clavibacter. It causes wilt and blight in maize, called Goss's wilt.
Clavibacter sepedonicus is a species of bacteria in the genus Clavibacter. C. sepedonicus is a high-profile alien plant pathogen of A2 Quarantine status affecting only potatoes. It causes a disease in potatoes known as 'ring rot' due to the way it rots vascular tissue inside potato tubers It is present in parts of Europe but is under statutory control under 'Council Directive 93/85/EEC' of 4 October 1993 on the control of potato ring rot. This means that if an outbreak occurs, the outbreak must be controlled and if possible the disease has to be eradicated. If necessary, prohibitions are put into place to prevent further spread.
