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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 (the disease is transmitted by seed) 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]
Bacterial leaf streak is a pathogen known to infect and damage wheat varieties. The pathogen has also been known to infect other small grain all cereal crops such as rice, barley and triticale. The strains of the pathogen are named differently according to the species they infect. It is one of the most destructive diseases in rice.[15] Resistant wheat cultivars offer the best protection against yield loss, but little is known about the inheritance of resistance.[12] The disease is most common on wheat and can be found on winter and summer wheat varieties.
Symptoms of this pathogen can be seen on the stem, leaves, and glumes. Stem symptoms are not always present, but can be seen as a dark brown to purple discoloration on the stem below the head and above the flag leaf. [14] In the early stages of the disease, translucent water soaked streaks can be seen on the leaves often accompanied by a shiny glaze or clumps of dried bacteria on the leaf surface. [8] These markings turn to brown lesions after just a few days, and may be surrounded by a lime green halo. Lesions can stretch the entire leaf blade. BLS exhibits similar symptoms to those of Septoria nodorum , a common fungal infection. A common sign that will distinguish this pathogen from Septoria nodorum is the lack of spores on the leaves, which appears as tiny black spots on the leaf surface with a Septoria infection. A cream to yellow colored bacterial ooze produced by BLS infected plant parts is also a distinguishing sign of the pathogen.[7] Infected glumes, known as black chaff, are darkened and necrotic. Severe symptoms will result in kernels that are discolored due to black and purple streaks. [9] Plants infected with bacterial leaf streak will exhibit an orange cast from leaf symptoms and suffer yield and quality loss.[14]
Bacterial leaf streak of wheat is a seed-borne disease and is primarily transported by seed, but can also be transmitted by plant-to-plant contact within its lifecycle. Epidemics are typically observed late in the growing season and in wet environments. Moisture facilitates the release of the pathogen from the inoculated seed, which leads to leaf colonization and invasion of tissue. Bacteria on the moist leaf surface enter through leaf openings, such as the stomata or wounds. Under moderately warm weather conditions (15-30 degrees Celsius) bacteria will begin to release and multiply in the plant parenchyma tissue.[4] The bacteria then inject a number of effector proteins into the plant with a Type 3 Secretion System (T3SS)[5]. The T3SS effectors in Xanthomonas are Transcription Activator-like effectors (TAL effectors). These TAL effectors activate the production of plant genes that are beneficial to bacterial infection.[1] The bacteria spreads and progresses vertically up the plant.[3] The bacterial masses cause elongated streaks along the veins of the plant. Water collection on leaves also leads to the spread of the organism, increasing the number of lesions on leaves. Rain, wind, insects, and plant-to-plant contact may spread the disease in the season and cause reinfection.[4] After the plant is harvested or dies, the bacteria may overwinter in the soil; although, its survival rate is much greater when crop debris is present. However, the bacteria cannot survive on decomposing matter alone and free bacteria cannot survive for more than 14 days in hot dry weather.[7] Bacteria is primarily spread by infected or contaminated seed.[10] In some cases, the bacterial will overwinter on other perennial plants and weeds.[4] Residual bacteria in the soil, debris or other plants may also cause new infection in clean seed.
The disease can tolerate warm or freezing temperature,[2] but favorable conditions for the disease include wet and humid weather. Irrigated fields provide a favorable environment for the disease.[14] The disease has become quite prevalent in semi-tropical regions, but can found all over the world where wheat is grown.[13] Strong winds that blow soils help contribute to the spread of disease. When the spread is initiated by wind blown soil particles, symptoms will be found most readily towards the edges of the field.[6]
Bacterial leaf streak of wheat is not easily prevented, but can be controlled with clean seed and resistance. Some foliar products, such as pesticides and antibiotic compounds, have been tested for effectiveness, but have proven to have insignificant outcomes on the bacterial pathogen. Using clean seed, with little infection, has yielded effective results for researchers and producers. The pathogen, being seed-borne, can be controlled with the elimination of contaminated seed. However, clean seed is not always a sure solution. Because the pathogen may still live in the soil, the use of clean seed is only effective if both the soil and seed are free of the pathogen. Currently, there are no successful seed treatments available for producers to apply to wheat seed for the pathogen. Variety resistance is another option for control of the disease. Using cultivars such as Blade, Cromwell, Faller, Howard or Knudson, which are resistant to BLS may reduce the impact of the disease and potentially break the disease cycle. Avoiding susceptible cultivars such as Hat Trick, Kelby, and Samson may also reduce the presence of the disease and reduce the amount of bacterial residue in the soil.[6] Using integrated pest management techniques such as tillage to turn over the soil and bury the infection as well as rotating crops may assist with disease management, but are not a definitive control methods.[9] Depending on conditions, the bacteria may survive for up to 81 months.[4] Because the bacteria is moisture driven, irrigation may also increase the risks of BLS infection.[8]
Bacterial leaf streak is a major bacterial disease of wheat. Yield losses are normally less than 10%, but can be up to 40%. The loss in yield is due to lower weight of the seed rather than lack of production. Risk of damages due to bacterial leaf streak is variable, but should not be overlooked because there is always a chance of an epidemic. Research is still being done on the pathogen, specifically on finding resistant strains. Farmers should avoid planting susceptible cultivars, and avoid infected seed in order to ensure there will be no infection of the pathogen.[4] This disease can survive in freezing to warm climates, threatening wheat populations throughout the world.
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.
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.
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.
Alternaria triticina is a fungal plant pathogen that causes leaf blight on wheat. A. triticina is responsible for the largest leaf blight issue in wheat and also causes disease in other major cereal grain crops. It was first identified in India in 1962 and still causes significant yield loss to wheat crops on the Indian subcontinent. The disease is caused by a fungal pathogen and causes necrotic leaf lesions and in severe cases shriveling of the leaves.
Zymoseptoria tritici, synonyms Septoria tritici, Mycosphaerella graminicola, is a species of filamentous fungus, an ascomycete in the family Mycosphaerellaceae. It is a wheat plant pathogen causing septoria leaf blotch that is difficult to control due to resistance to multiple fungicides. The pathogen today causes one of the most important diseases of wheat.
Urocystis agropyri is a fungal plant pathogen that causes flag smut on wheat.
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.
Ascochyta is a genus of ascomycete fungi, containing several species that are pathogenic to plants, particularly cereal crops. The taxonomy of this genus is still incomplete. The genus was first described in 1830 by Marie-Anne Libert, who regarded the spores as minute asci and the cell contents as spherical spores. Numerous revisions to the members of the genus and its description were made for the next several years. Species that are plant pathogenic on cereals include, A. hordei, A. graminea, A. sorghi, A. tritici. Symptoms are usually elliptical spots that are initially chlorotic and later become a necrotic brown. Management includes fungicide applications and sanitation of diseased plant tissue debris.
Xylophilus ampelinus is a species of bacteria that can cause plant disease. It is available from the NCPPB in the United Kingdom and other international culture collections such as ICMP in New Zealand, and LMG/BCCM in Belgium.
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.
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.
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.
Xanthomonas oryzae pv. oryzae is a bacterial pathovar that causes a serious blight of rice, other grasses, and sedges.
Bacterial blight of soybean is a widespread disease of soybeans caused by Pseudomonas syringaepv. glycinea.
Xanthomonas campestris pv. juglandis is an anaerobic, Gram negative, rod-shaped bacteria that can affect walnut trees though the flowers, buds, shoots, branches, trunk, and fruit. It can have devastating effects including premature fruit drop and lesions on the plant. This pathogen was first isolated by Newton B. Pierce in California in 1896 and was then named Pseudomonas juglandis. In 1905 it was reclassified as Bacterium juglandis, in 1930 it became Phytomas juglandis, and in 1939 it was named Xanthomas juglandis. The International Standards for Naming Pathovars declared it to be named Xanthomonas campestris pv. juglandis in 1980. There have been recent proposals to change the name once again to Xanthomonas arboricola pv. juglandis, but this has not yet been universally accepted.