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Ethan Flores
Ethan Flores

Blackleg ((NEW))



Blackleg is an infectious, non-contagious disease caused by Clostridium chauvoei. Infection occurs when animals ingest bacterial spores while grazing. The bacterial spores penetrate the intestine and are disseminated via the bloodstream to the skeletal muscle, where the spores remain dormant. Following an event that causes low oxygen conditions (i.e. bruising or damage to the muscle) in infected tissue, the spores germinate, multiply and produce toxin that results in muscle necrosis and hemorrhage. The animals affected by blackleg are usually well fed animals between 6 months and 2 years of age. The cause of death in affected cattle is usually acute toxemia. The course of the disease is often between 12-48 hours and clinical signs are often absent; however, animals may exhibit signs of lameness, tachycardia, fever, anorexia, rumen stasis and lethargy. Blackleg is primarily a disease of pastured cattle with the majority of the cases occurring during the summer months.




blackleg


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Throughout 2017, the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) diagnosed a significantly increased number of blackleg cases. Although a cause for the increased incidence of cases has not been conclusively determined, a possible explanation are the environmental changes that resulted from the unusual weather conditions experienced during 2017. Specifically, it is speculated that the extreme amounts of rain and flooding associated with Hurricane Harvey and the subsequent dry conditions worked to stir up the soil leading to exposure of deeply hidden bacterial spores.


The affected animals presented to TVMDL for necropsy ranged in age from 4 months to up to 1 year of age. The gross lesions included variably sized areas of skeletal muscle that was dark red and contained gas bubbles (necrotizing myositis). Due to the intramuscular gas bubbles, affected sections of skeletal muscle would often float in formalin. Most of the affected animals had a concurrent fibrinous pericarditis and necrotizing myocarditis. The skeletal muscle and myocardial lesions typically had the faint to pervasive odor of rancid butter. The diagnosis of blackleg was based on the characteristic gross lesions and a positive fluorescent antibody test results on affected tissues. The cases of blackleg at TVMDL appeared to peak after Hurricane Harvey and continued through December 2017.


However, L. maculans is the virulentA form which causes infection (and can result in a disease) More species causing blackleg that infects canola from the seedling stage onward. It progressively damages the crop as the season progresses, by girdling stems and restricting moisture and nutrient uptake, and eventually leading to yield loss. Leptosphaeria maculans was first detected in 1975 in north east Saskatchewan and in 1987 in Ontario. Since then L. maculans has become widespread throughout western and eastern Canada.


It is not unusual to observe blackleg symptoms in canola crops, even when resistant cultivarsCultivars are variants in a species developed through the intervention of humans (despite the term 'variety' often being incorrectly used to describe this). Cultivars can be open-pollinated type, hybrid, synthetic, composite, etc. More are grown. It is important to be familiar with blackleg symptoms, the disease cycle, and to know the disease management practices that prevent yield and seed quality losses.


The L. maculans fungus overwinters on infected canola residue. The spores produced from diseased stubble, especially the infected lower stem and upper root pieces, are the major source of the pathogenA disease-causing organism (such as a fungus or bacteria). More that contributes to widespread field infection and yield loss. In the spring, the fungus produces fruiting bodies, called pseudotheciaFruiting bodies produced by fungus which cause disease (as the L. maculanspseudothecia can be produced on infected canola residue, which can then infect live canola plants nearby). It is plural for pseudothecium. More and pycnidiaA type of fruiting body (produced by a pathogen, such as the blackleg-causing Leptosphaeria maculans pathogen) that appears as pepper-like spots (which are spore-bearing structures) within lesions. More, on infected canola residue. PseudotheciaFruiting bodies produced by fungus which cause disease (as the L. maculanspseudothecia can be produced on infected canola residue, which can then infect live canola plants nearby). It is plural for pseudothecium. More may continue to be produced on infected residue for several years, or until the infected residue breaks down.


During the growing season, the pathogenA disease-causing organism (such as a fungus or bacteria). More also produces another type of fruiting body called pycnidiaA type of fruiting body (produced by a pathogen, such as the blackleg-causing Leptosphaeria maculans pathogen) that appears as pepper-like spots (which are spore-bearing structures) within lesions. More that appear as pepper-like spots within lesions. From the pycnidiaA type of fruiting body (produced by a pathogen, such as the blackleg-causing Leptosphaeria maculans pathogen) that appears as pepper-like spots (which are spore-bearing structures) within lesions. More ooze masses of tiny spores called pycnidiosporesMasses of tiny spores (such as those from the blackleg-causing Leptosphaeria maculans pathogen, the which ooze out from pycnidia in a viscous pink liquid). More. These spores spread short distances by rain splash and wind, and cause secondary infection within a crop. Infected stubble can continue to produce pycnidiosporesMasses of tiny spores (such as those from the blackleg-causing Leptosphaeria maculans pathogen, the which ooze out from pycnidia in a viscous pink liquid). More for three to five years.


Seedling infection may arise from infected seed or from airborne and rain-splashed spores. Plants infected at this stage are usually the most severely affected and may be lost or stunted. Seed-treated certified seed can control seed-borne blackleg infection, which will reduce the chance of new pathogenA disease-causing organism (such as a fungus or bacteria). More races being introduced to the field with the seed. Newer seed treatments protect the cotyledon to one-leaf stage from airborne blackleg infection, but do not protect plants from later infection by airborne spores.


Climate has an impact on blackleg incidence and severity. Regions with warm, humid conditions and frequent rain showers tend to have higher incidence and severity of blackleg. Warm, dry conditions slow disease development, while prolonged moist weather favours rapid spread and development. However, the disease is present in drier regions of the Prairies and can be a problem, even in dry years, provided early season showers occur to disperse the spores for initial infection.


Infection of canola is due to ascosporesMicroscopic asexual spores that typcially become airborne. More and pycnidiosporesMasses of tiny spores (such as those from the blackleg-causing Leptosphaeria maculans pathogen, the which ooze out from pycnidia in a viscous pink liquid). More of the pathogenA disease-causing organism (such as a fungus or bacteria). More, whose production and dispersal depends on environmental factors such as rain and wind. Therefore, the severity of blackleg disease can vary between regions and years. AscosporesMicroscopic asexual spores that typcially become airborne. More are responsible for the spread of new races of the pathogenA disease-causing organism (such as a fungus or bacteria). More, as these are wind-borne and can move relatively long distances (at least 10 kilometres). Although most blackleg infection comes from canola residue within the same field, ascosporesMicroscopic asexual spores that typcially become airborne. More and even some pycnidiosporesMasses of tiny spores (such as those from the blackleg-causing Leptosphaeria maculans pathogen, the which ooze out from pycnidia in a viscous pink liquid). More that become air-borne after rain-splash may land on canola or volunteer canola plants in nearby fields to begin new infections. In the management of blackleg disease, it is recommended that canola crops in western Canadian should be separated from fields that were planted to canola the previous year by at least 50 to 100 metres.


Research at the University of Manitoba found that peak ascospore and pycnidiospore dispersal was associated with rain events. Peak ascospore dispersal occurred several hours after rainfall of greater than two millimetres and persisted for approximately three days after such events. Peak pycnidiospore dispersal occurred during the same time as the rainfall. Spores are spread by wind, with more spores carried in the direction of prevailing winds. PycnidiosporesMasses of tiny spores (such as those from the blackleg-causing Leptosphaeria maculans pathogen, the which ooze out from pycnidia in a viscous pink liquid). More were found to travel further than first thought (45 metres) and may even move by wind. The research also found that on days without rain, air temperature and relative humidity (RH) had an effect on spore dispersal. More ascosporesMicroscopic asexual spores that typcially become airborne. More and pycnidiosporesMasses of tiny spores (such as those from the blackleg-causing Leptosphaeria maculans pathogen, the which ooze out from pycnidia in a viscous pink liquid). More were trapped between 9:00 pm and 4:00 am, when temperatures were between 13 to 18 degrees Celsius and RH was greater than 80 per cent, than at other times of the day, on days without rain 3.


Research from the University of Alberta/Alberta Agriculture & Forestry found that for every unit of increase in disease severity, a 17.2 per cent loss in plant seed yield can be expected 4. Pod number and seed yield both declined linearly as blackleg severity increased. An updated yield loss model from the University of Alberta indicated that yields dramatically decrease when disease severity is equal to or greater than a rating of two 5. Use the online too to calculate your blackleg yield loss. 041b061a72


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