Prevalence of the Crayfish Plague Pathogen Aphanomyces astaci in Invasive American Crayfishes in the Czech Republic

Abstract:  In Central Europe invasive North American crayfishes are carriers of the oomycete Aphanomyces astaci, which causes crayfish plague. This lethal disease currently represents one of the major threats to native European crayfishes. We used molecular methods—species-specific amplification and sequencing of the pathogen DNA—to investigate the prevalence of individuals latently infected with A. astaci in 28 populations of two invasive American crayfish species (6 of the signal crayfish [ Pacifastacus leniusculus ] and 22 of the spiny-cheek crayfish [ Orconectes limosus ]) in the Czech Republic. The pathogen occurred in 17 investigated populations. We recorded a high variation in positive reactions, ranging from 0% to 100%, in populations of O. limosus . In P. leniusculus, however, only one individual out of 124 tested positive for the pathogen. There was a clear relationship between the water body type and pathogen prevalence in O. limosus . Infection ratios in isolated standing waters were usually low, whereas in running waters, pathogen prevalence often exceeded 50%. Other evaluated characteristics of potential plague pathogen carriers (size, sex, and the presence of melanized spots in the cuticle) seemed to be unrelated to infection. Our data suggest that in contrast to other European countries, O. limosus seems to be the primary reservoir of crayfish plague in the Czech Republic. Although all populations of alien American crayfishes may be potential sources of infections and should be managed as such, knowledge on the prevalence of the plague pathogen at various localities may allow managers to focus conservation efforts on the most directly endangered populations of native crayfishes.     

Understanding the Causes of Disease in European Freshwater Crayfish

Abstract:  Native European freshwater crayfish (Astacida, Decapoda) are under severe pressure from habitat alteration, the introduction of nonindigenous species, and epizootic disease. Crayfish plague, an acute disease of freshwater crayfish caused by the fungus-like agent Aphanomyces astaci , was introduced into Europe in the mid-nineteenth century and is responsible for ongoing widespread epizootic mortality in native European populations. We reviewed recent developments and current practices in the field of crayfish pathology. The severity of crayfish plague has resulted in an overemphasis on it. Diagnostic methods for detecting fungi and fungal-like agents, and sometimes culturing them, are frequently the sole techniques used to investigate disease outbreaks in European freshwater crayfish. Consequently, the causes of a significant proportion of outbreaks are undetermined. Pathogen groups well known for causing disease in other crustaceans, such as viruses and rickettsia-like organisms, are poorly understood or unknown in European freshwater crayfish. Moreover, the pathogenic significance of some long-known pathogens of European freshwater crayfish remains obscure. For effective management of this culturally significant and threatened resource, there is an urgent need for researchers, diagnosticians, and resource managers to address the issue of disease in European freshwater crayfish from a broader perspective than has been applied previously.     

影响甜菜黑腐丝囊霉的几种生态学和生物学因子

通过对河西灌区甜菜(Beta vulgaris L.)黑腐病(Sugar Beet Black Rot)为期3a的研究，探讨了甜菜栽培品种与病害发病率及病原菌黑腐丝囊霉（Aphanomyces cochlioides)分离频率的关系以及3种环境因子即温度、pH值、不同天然培养基与甜菜黑腐丝囊霉的关系。结果表明：各栽培品种在田间的发病率与室内病原分离频率不同，其中工农2号田间发病率为1．3％，室内分离频率为93％，工农5号分别为1％和7．2％，宁甜301分别为2％和6．1％，工农2号具有更大的耐病性；甜菜黑腐丝囊霉的生长温度范围为5—30℃，最适温度为25—27℃，对高温敏感，33℃为其致死温度；甜菜黑腐丝囊霉可在pH3．5—11范围内生长，最适pH为5—9．9；甜菜黑腐丝囊霉在PDA、玉米粉琼脂、甜菜汁、麦芽糖—胨、麦芽糖酵母汁及燕麦琼脂培养基上均可生长，其中在甜菜汁培养基上生长最好．图4表3参11