Blueberry is also called huckleberry， which is a perennial shrub fruit tree in Vaccinium of Ericaceae. The fruit is round or oblate， and has blue skin. Because of its unique fruit flavor and rich nutritional value， it is loved by people and has high economic value[1]. The blueberry planting industry in the United States started early， and large-scale blueberry planting has been realized in the 1930s[2]. The introduction and planting of blueberry only started in the 1980s in China， and the localization of blueberry was successfully carried out in the 1990s， forming relatively complete industrial development[3]. Up to 2017， the blueberry planting area in China has reached 55 900 hm2. The rapid development of the blueberry planting industry has brought huge economic benefits， but the accompanying blueberry disease problem has become increasingly prominent and needs to be solved urgently. There are many types of blueberry diseases， including 7 fungal diseases， namely， dry fruit， gray mold， shoot blight， leaf spot， anthracnose， leaf rust and stem canker， 3 types of virus diseases， namely， blueberry scorch and tomato ringspot virus and blueberry red ringspot virus， 3 kinds of physiological diseases， namely， iron deficiency， magnesium deficiency and boron deficiency， 10 kinds of insect pests， namely blueberry bud mite， cabbage aphid， green peach aphid， fruit fly， Buzura thiberaria Oberthur， Prodenia litura， Adoroetus tenuimaculatus waterhouse， wireworm， mole cricket， flatheaded borer[4]. Among all the blueberry diseases mentioned above， the most serious and common one is blueberry canker caused by fungus. Studies at home and abroad have found that there are many pathogens that can cause blueberry canker， mainly Botryosphaeria dothidea in Botryosphaeria， which is widely distributed all over the world， and is a common pathogen， saprophytic fungus and endophytic fungus of monocot， dicot and gymnosperm[5]. The genus Botryococcus can cause many fruit tree diseases， producing leaf spots， withering and necrosis of branches， canker on branches and stems， fruit and seed rot and other symptoms， leading to weak growth of fruit trees， decline in the quantity and quality of fruits. When the disease is severe， it can cause trees to die and cause serious economic losses[6-9].
　　Symptoms of Blueberry Canker
　　Blueberry canker is mainly caused by Botryosphaeria， which mainly damages one-year branches. Many studies in the past believed that the fungi infect plants through wounds and pruning parts. However， with the deepening of research， many experiments have shown that the pathogen of blueberry canker is not limited to infection through wounds， but can also infect plants by entering directly through plant stomata and natural openings in vivo[10]. When blueberry canker occurs， hygrophanous red spots are first formed on the stems or branches. At first， the lesions are small but develop rapidly. The lesions change from reddish brown to black， irregular in shape， and the boundary between disease and health is obvious. The surface of the xylem of the injured branch turns brown or yellowish brown， and the tissue is necrotic. Sometimes it is only a few centimeters， and sometimes it spreads to the entire branch. When the climate is hot， the affected leaves turn brown; and at the later stage of the disease， black particles can be seen with naked eyes on the diseased spots， which are the acervuli of blueberry canker， and you will see the distribution of white mycelia inside the diseased branches at this period[11-13]. With the extension of disease spots， the shoots wither， which gradually leads to the death of the whole plant in the later stage[14]. The mortality of infected plants in the rhizomes is higher， and the upper buds will die when the diseased spots expand to surround the branches for 1 week. 　　Occurrence Law of Blueberry Canker
　　The pathogen of blueberry canker is a parasitic pathogen. It does not develop to disease when it initially infects blueberry plants， but exists in the form of endophytes. Therefore， many blueberry plants do not show symptoms in appearance but are actually infected by pathogenic bacteria. When the temperature of the planting environment is too low and the humidity is too high， the blueberry canker pathogen is very easy to infect the plants. When the branches and leaves of the plants are too dense， the growth of the plants is poor， and the roots and leaves are damaged during transplanting， the blueberry canker disease can be aggravated. During the latent infection period of pathogenic bacteria， the pathogenic bacteria first colonize the host plant tissues， and then infect the plant branches when the temperature and humidity are appropriate. The infection becomes more serious when the environment is humid[15]. A large number of conidia of Botryococcus will grow on infected branches of blueberry plants after overwintering. After the spores are released， they can spread to many parts of the plant and other plants with the help of airflow， rainwater， and irrigation water. Seeds and agricultural operations can also carry the pathogen[16]. After infecting the plant， the hyphae of the pathogenic fungus can quickly colonize the plant’s xylem， tracheids， ducts and other types of cells. The peak period of disease occurrence is from May to June with high temperature and humidity[17-18]. Plants are more susceptible to blueberry canker in a planting environment with higher humidity and lower temperature. Some blueberry varieties are more likely to infect blueberry canker due to their biological characteristics. Factors such as planting techniques and nursery planning can also affect the incidence of blueberry canker[19].
　　Control of Blueberry Canker
　　At present， domestic research on blueberry canker is not common. The existing research on control of blueberry canker is mainly the aetiological research and disease-resistant breeding research of blueberry canker. At present， the prevention and control of blueberry canker mainly adopts chemical control， selection of disease-resistant varieties， cultivation of disease-free and strong seedlings， optimization of cultivation sites and cultivation methods[20-22]. The current research has summarized the symptoms， rules and conditions of blueberry canker in more detail， and put forward the planting theory of rational planting and cultivation of disease-free seedlings. China has successfully developed a variety of disease-resistant blueberry strains to prevent blueberry canker， which has played a very good role. In terms of pathogenic biology research， there are also many reports on the occurrence of blueberry canker and prevention and treatment techniques. Jiang et al.[23] introduced the symptoms， conditions and prevention methods of blueberry canker in detail， and provided guidance on the prevention and control of blueberry canker in many aspects， so as to curb the harm caused by blueberry canker. 　　Prospects
　　As one of the most common and serious diseases in the blueberry planting industry， blueberry canker is difficult to prevent and control in production. Among the many prevention and control methods for blueberry canker， chemical control and selection of disease-resistant varieties are most easily accepted by the public， but both of the two methods have some disadvantages. On the one hand， the selection and breeding of disease-resistant varieties takes a long time and problems such as resistance degradation exists， so achieve the expected disease prevention effect cannot be achieved. On the other hand， a large amount of chemical pesticides can easily cause environmental pollution and disrupt ecological balance[24-25]. Therefore， we should strengthen the comprehensive prevention and monitoring and early warning of blueberry diseases， and carry out in-depth research on blueberry disease prevention and control measures to achieve the purpose of efficient prevention and control and increase economic benefits.
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　　Editor： Yingzhi GUANG  Proofreader： Xinxiu ZHU