A leaf spot is a limited, discoloured, diseased area of a leaf that is caused by fungal, bacterial or viral plant diseases, or by injuries from nematodes, insects, environmental factors, toxicity or herbicides. These discoloured spots or lesions often have a centre of necrosis. Symptoms can overlap across causal agents, however differing signs and symptoms of certain pathogens can lead to the diagnosis of the type of leaf spot disease. Prolonged wet and humid conditions promote leaf spot disease and most pathogens are spread by wind, splashing rain or irrigation that carry the disease to other leaves.
Citrus canker is a disease affecting Citrus species caused by the bacterium Xanthomonas. Infection causes lesions on the leaves, stems, and fruit of citrus trees, including lime, oranges, and grapefruit. While not harmful to humans, canker significantly affects the vitality of citrus trees, causing leaves and fruit to drop prematurely; a fruit infected with canker is safe to eat, but too unsightly to be sold. Citrus canker is mainly a leaf-spotting and rind-blemishing disease, but when conditions are highly favorable, it can cause defoliation, shoot dieback, and fruit drop.
Grape black rot is a fungal disease caused by an ascomycetous fungus, Guignardia bidwellii, that attacks grape vines during hot and humid weather. “Grape black rot originated in eastern North America, but now occurs in portions of Europe, South America, and Asia. It can cause complete crop loss in warm, humid climates, but is virtually unknown in regions with arid summers.” The name comes from the black fringe that borders growing brown patches on the leaves. The disease also attacks other parts of the plant, “all green parts of the vine: the shoots, leaf and fruit stems, tendrils, and fruit. The most damaging effect is to the fruit”.
Bacterial blight is a disease of barley caused by the bacterial pathogen Xanthomonas campestris pv. translucens. It has been known as a disease since the late 19th century. It has a worldwide distribution.
Xanthomonas campestris is a gram-negative, obligate aerobic bacterium that is a member of the Xanthomonas genus, which is a group of bacteria that are commonly known for their association with plant disease. This species includes Xanthomonas campestris pv. campestris, the cause of black rot in brassicas, one of the most important diseases of brassicas worldwide.
Pseudomonas viridiflava is a fluorescent, Gram-negative, soil bacterium that is pathogenic to plants. It was originally isolated from the dwarf or runner bean, in Switzerland. Based on 16S rRNA analysis, P. viridiflava has been placed in the P. syringae group. Following ribotypical analysis misidentified strains of Pseudomonas syringae pv. ribicola and Pseudomonas syringae pv. primulae were incorporated into this species. This pathogen causes bacterial blight of Kiwifruit.
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.
Halo blight of bean is a bacterial disease caused by Pseudomonas syringae pv. phaseolicola. Halo blight’s pathogen is a gram-negative, aerobic, polar-flagellated and non-spore forming bacteria. This bacterial disease was first discovered in the early 1920s, and rapidly became the major disease of beans throughout the world. The disease favors the places where temperatures are moderate and plentiful inoculum is available.
Xanthomonas arboricola is a species of bacteria. This phytopathogenic bacterium can cause disease in trees like Prunus, hazelnut and walnut.
Xanthomonas fragariae is a species of bacteria. It causes a leaf spot disease found in strawberries. The type strain is NCPPB1469 from Fragaria chiloensis var. ananassa.
Xanthomonas vasicola pv. vasculorum (Xvv) is a gram-negative rod-shaped bacterium which has a single polar flagellum. It is a plant pathogen, causing both bacterial leaf streak of maize (corn) and sugarcane gumming disease. One outbreak in eucalyptus has been reported. Under experimental conditions it can infect sorghum, oats and some grass species. It is not currently a quarantine pathogen in any country, but it has already spread outside its native range and is highly adaptable to different environments.
Elsinoë mangiferae, common name "mango scab", is also known Denticularia mangiferae or Sphaceloma mangiferae (anamorph). It is an ascomycete plant pathogen native to tropical regions and specific for survival on only one host, the mango. Originally described in 1943 from Florida and Cuba specimens, this pathogen has since spread worldwide and is becoming a pathogen of great concern for the mango industries in Australia and India. The species was first described formally in 1946.
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.
Banana Xanthomonas Wilt (BXW), or banana bacterial wilt (BBW) or enset wilt is a bacterial disease caused by Xanthomonas campestris pv. musacearum. After being originally identified on a close relative of banana, Ensete ventricosum, in Ethiopia in the 1960s, BXW emanated in Uganda in 2001 affecting all types of banana cultivars. Since then BXW has been diagnosed in Central and East Africa including banana growing regions of: Rwanda, Democratic Republic of the Congo, Tanzania, Kenya, Burundi, and Uganda.
Xanthomonas campestris pv. vesicatoria is a bacterium that causes bacterial leaf spot (BLS) on peppers and tomatoes. It is a gram-negative and rod-shaped. It causes symptoms throughout the above-ground portion of the plant including leaf spots, fruit spots and stem cankers. Since this bacterium cannot live in soil for more than a few weeks and survives as inoculum on plant debris, removal of dead plant material and chemical applications to living plants are considered effective control mechanisms.
Bacterial blight of cotton is a disease affecting the cotton plant resulting from infection by Xanthomonas axonopodis pathovar malvacearum (Xcm) a Gram negative, motile rod-shaped, non spore-forming bacterium with a single polar flagellum
Pecan scab is the most economically significant disease of pecan trees in the southeastern United States. Venturia effusa is a fungal plant pathogen that causes pecan scab. The fungus causes lesions and tissue death on pecan twigs, petioles, leaves, nuts and shucks beginning in early spring, with multiple cycles of infection repeating until late summer. Wind and rain spread the fungus to a susceptible host. Control of the disease is achieved by fungicide, sanitation and, in some cases, quarantine.
Xanthomonas axonopodis pv. manihotis is the pathogen that causes bacterial blight of cassava. Originally discovered in Brazil in 1912, the disease has followed the cultivation of cassava across the world. Among diseases which afflict cassava worldwide, bacterial blight causes the largest losses in terms of yield.
Bacterial wilt of turfgrass is the only known bacterial disease of turf. The causal agent is the Gram negative bacterium Xanthomonas translucens 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 leaf streak (BLS), also known as black chaff, is a common bacterial disease of wheat. The disease is caused by the bacterial species Xanthomonas translucens pv. undulosa. The pathogen is found globally, but is a primary problem in the US in the lower mid-south and can reduce yields by up to 40 percent.[6] BLS is primarily seed-borne and survives in and on the seed, but may also survive in crop residue in the soil in the off-season. During the growing season, the bacteria may transfer from plant to plant by contact, but it is primarily spread by rain, wind and insect contact. The bacteria thrives in moist environments, and produces a cream to yellow bacterial ooze, which, when dry, appears light colored and scale-like, resulting in a streak on the leaves. The invasion of the head of wheat causes bands of necrotic tissue on the awns, which is called Black Chaff.[14] The disease is not easily managed, as there are no pesticides on the market for treatment of the infection. There are some resistant cultivars available, but no seed treatment exists. Some integrated pest management (IPM) techniques may be used to assist with preventing infection although, none will completely prevent the disease.[2]
