Xuejun Zhang

Belonging to Enterobacteriaceae. Bacteria are straight rod-shaped. 0.5 ~ 1.0× 1.0 ~ 3.0 (micron), single or opposite, sometimes short chain. Gram staining reaction was negative, with periflagellar movement (except 1 species). Facultative anaerobic, some species grow weakly anaerobic. The optimum growth temperature is 27 ~ 30℃, and the highest is 32 ~ 40℃. Oxidase is negative and contact enzyme is positive. Fructose, galactose, D- glucose, B- methylglucoside and sucrose can produce acids. Acetic acid, fumaric acid, gluconic acid, malic acid and succinic acid are all acceptable, but benzoic acid, oxalic acid and propionic acid cannot be used as carbon and energy sources. The molar percentage of G+C in DNA is 50 ~ 58. The typical species is Erwinia amyloliquefaciens.

Most species of Erwinia are plant pathogens, which cause plant necrosis, ulcer, wilting, leaf spot, gummosis and soft rot. Some of them are epiphytes on the surface of plants or as secondary fungi on diseased spots, and there are 1 species of summer spores parasitic on Puccinia graminis. The main plant pathogens in China are Phytophthora chrysanthemi, bacterial basal rot of rice and Erwinia carota, such as Cruciferae plants such as Chinese cabbage and potato soft rot. Corn bacterial wilt and pear fire blight are foreign quarantine objects in China.

1882, a member of Erwinia piricola was discovered in Burrill, USA, and was named micrococcus amyloliquefaciens at that time. 1889 was confirmed to be 1 plant pathogenic bacteria, named Bacillus amyloliquefaciens. Then similar bacteria were found on carrots, potatoes, starfish taro and other plants. 1920, American bacteriologist C.E.A.Winslow and others merged all bacteria with periflagellate and founded the genus Erwinia, which belongs to the bacterial family. 1923, 1 version of Berger's bacterial identification manual (hereinafter referred to as Berger's manual) separated the plant pathogenic bacteria from Erwinia, and independently established a new genus of 1. That is, phytomonas. 1937, the Bacillus family was abolished, and Erwinia belongs to the newly established Enterobacteriaceae family, which is still in use today. However, there is great heterogeneity among members of this genus, and there is great controversy on the classification of this genus. There are three main viewpoints. From 65438 to 0945, Erwinia can be divided into two genera according to the nutritional requirements of each member and the pathogenic characteristics to plants. Erwinia is limited to those members who cause plant necrosis and wilting, have a narrow range of carbon sources and need organic nitrogen to grow; However, members with strong pectinase activity, extensive nutrition utilization and causing plant soft rot have been established as a new genus, namely pectinase. Because there are species between the above two groups of bacteria, and some species have the same characteristics as Erwinia but cannot cause soft rot, this view has not been adopted. ② Erwinia has 1 genus. From 1968 to 1969, Day proposed to divide Erwinia into three groups, namely, amyloidomycetes, herbaceous fungi and carrot soft rot. This method is simple, practical and convenient, so it is widely used. This classification system was adopted by the eighth edition of Berger's Manual (1974). ③ Plant pathogenic bacteria belong to the same group as other bacteria. With the development of modern classification methods, it has been suggested that members of Erwinia should be divided into Enterobacter, Salmonella and Endophyte according to numerical classification, systematic classification, molecular hybridization and homology analysis of DNA fragments, regardless of the pathogenicity of each member in the genus. This view needs a comprehensive and systematic study. In the Berger Handbook of Systematic Bacteriology 1 volume, the classification system of the eighth edition of Berger Handbook is basically maintained, and the members of Erwinia are recorded as *** 15 species and 2 subspecies. Among them, two varieties of Erwinia carota rose to subspecies, and two varieties of Erwinia carota rose to species respectively. According to the classification system in the 8th edition of Berger's Manual, the subgenus and subgenus of Erwinia are identified in Table 1 ~ 4 respectively.

Relationship between epiphyte, rot, necrosis and wilting of leaves and plants-+-production of yellow pigment+-pectinase activity -D need growth factor-characteristic grass flora of starch decomposition flora in carrot soft rot area

Table 1 Main identification characteristics of three groups of Erwinia *

*+:positive; -:negative; D: negative or positive (the same below)

Identification characteristics of six kinds of Erwinia amylolytic flora

Table 3 Species identification of Erwinia herbaceous flora

Table 4 Species identification characteristics of Erwinia carota soft rot flora

Loquat disease

Loquat disease

Cao ruobin

More than 40 species are known in the world, and more than 30 species have been reported from 199 1 in China. The main diseases are anthracnose, gray leaf spot and early defoliation (including anthracnose, angular leaf spot, leaf blight, flax leaf blight and so on). ).

anthrax

Distributed in the provinces south of the Yangtze River, it mainly harms flower heads, near-mature and mature fruits, and also seriously harms seedlings in South China. Make the ear brown and wither, the fruit rot or shrink into hard fruit, the seedling tip wither and the leaves fall early. The pathogen is Syringa, belonging to Ascomycetes and Coccidae. Colletotrichum gloeosporioides is a semi-ignorant fungus belonging to Cercospora. Mycelia overwinters on diseased branches or hard fruits, and conidia are produced in the next spring, causing initial infection, and then spread through rain and insects. The prevention and control of the disease is to clear the garden in winter, cut off the hard fruits in early spring, remove the diseased fruits in time at the beginning of the disease, and spray Tobuzine or Bordeaux solution one month before the fruits are colored.

Gray spot disease

Common in loquat producing areas, sometimes infringing on fruits. Diseases on leaves are nearly round, large, light brown to grayish white, causing early defoliation. The pathogen is paecilomyces aegypti. , belonging to Alternaria. In Zhejiang, the variety Jiao Jia and its hybrid with 52 have strong disease resistance, poor soil, poor drainage and poor cultivation management. Pathogens overwinter on diseased leaves with conidia and hyphae, and conidia spread by wind and rain in the next spring. Control measures include: strengthening orchard management, applying more chemical fertilizers, popularizing strong trees, and spraying thiophosphate or Bordeaux solution on orchards with serious diseases after new leaves grow.

Early deciduous leaves

It is distributed in all producing areas, and it has the greatest impact when seedlings die. It mainly includes anthracnose, angular leaf spot, leaf blight and flax leaf blight, which are round, polygonal or irregular, gray to brown, with or without dark edges or wheel lines on loquat leaves, producing small black particles (pathogen conidia or no conidia) or gray to black mold (pathogen conidiophore and conidia). In severe cases, a large number of fallen leaves are caused, which greatly affects growth. The pathogen of angular leaf spot is Pseudocercospora loquat, and the pathogen of leaf spot is Clasterosporium eriolotryae Hara loquat, both of which are semi-fungi and filamentous fungi. Spot disease is loquat, Hemiptera, Coccoidea; Flaxseed leaf blight belongs to Hemiptera, Loquat, Nilapidospora. In Zhejiang, the variety Wuer is resistant to angular leaf spot, and Jiao Jia crosses Wuer to resist angular leaf spot. The infection process, disease cycle and disease control are basically the same as those of gray spot disease.

Other common diseases of loquat are shown in the table below.

Other common diseases of loquat

Hop disease

Hop disease

Ji xiuqin

Hops, also known as hops, are native to America, Europe and West Asia, and are cultivated in China and other countries in the world. There are nearly 30 known hop diseases in the world, and more than 10 have been found in China. Among them, there are 8 fungal diseases, bacterial diseases 1 species, nematodes 1 species, viroid diseases 1 species, 8 viral diseases and 3 physiological diseases. 1905, the damage of downy mildew was first discovered in Japan, and later reported in North America, Britain, Germany and China.

Species and distribution

Hop diseases mainly include downy mildew, root cancer, root rot and so on.

downy mildew

Now it has been widely distributed in more than 20 countries such as China, Japan, Britain, the United States, Germany, France and the former Soviet Union. At present, except Xinjiang, all producing areas in China are damaged to varying degrees, and sometimes the yield is reduced by 60% ~ 70%, which seriously affects the yield and quality of hops. The pathogen is Pseudoperonospora harzianum, which belongs to oomycetes and downy mildew. It mainly harms leaves, branches and cones. The diseased leaf spots are polygonal, yellow-green to yellow-brown, with dark gray mold layers clustered on the back of the leaves, that is, pathogenic sporangia and sporangia. Sporangium germinates at 17 ~ 18℃ for 2 ~ 3 hours, producing swimming spores for infection. Wet conditions such as low temperature, rainstorm and fog and continuous cropping are very beneficial to the occurrence of leaf spot diseases such as downy mildew, and the epidemic of the disease is closely related to the atmospheric temperature and humidity of that year. The pathogen overwinters in the roots of diseased plants with mycelium and a small amount of oospores, which becomes the source of infection at the beginning of the following year.

Crown gall disease

It mainly damages the rhizome, expands into a pale yellow tumor with dark cracks on the surface, and is dark brown and dry in autumn and winter, with soft texture. Pathogens overwinter in the skin or soil of cancer tissues. This disease is caused by Agrobacterium tumefaciens. The thallus is stalk-shaped, with 1 ~ 4 periflagella. The colonies on the culture medium were white and Gram staining was negative.

root rot

Found in Beijing, Inner Mongolia, Gansu and other provinces during 1992. The pathogen is Fusarium oxysporum, belonging to the order Oncospora. It will lead to wilting of stems and leaves, rot of stems and roots, and browning of pith. Others, such as virus-like disease (Hsd), were discovered in Fukushima Prefecture, Japan by 1952. The disease dwarfs plants, hinders their growth and makes their leaves smaller and turn yellow-green. Cysticercosis was first discovered in Britain in 1934, and then occurred in 3 1 countries such as Germany, Belgium and the United States, as well as in 15 provinces and cities such as Liaoning, Jilin and Heilongjiang in China. The pathogen is metacercaria.

In addition, in China, the diseases that harm the mosaic, stem and whole plant of beer depend on Verticillium inkense and Botrytis cinerea. , cercospora antwerp, ringspot disease (ascohyta humili kab. Etbub), powdery mildew (Sphaerotheca humili(DC. ) burr. ), Rhizoctonia solani, Spodoptera albicans. , mosaic virus (HpMV), chlorotic virus (HpCV), chlorotic ringspot virus (HpRSV), hemp leaf chlorosis virus (HpLCV), hop leaf rosette virus (HpLRV), necrotic mosaic virus (HpNV), ringspot virus (HPRSV), yellow net virus. Physiological diseases include leaf deformation, cluster top, flower withered, sugar disease, sunburn and so on caused by boron deficiency.

disease control

In view of the different diseases of hops in different places, we must first strictly import quarantine to prevent the introduction of foreign diseases; Seeds must be soaked or dressed with chemicals such as metalaxyl, wanjunqing, streptomycin, mercuric chloride and K84 biological agent; In cultivation, the nursery should be clean and disease-free, seedlings should be grafted by bud grafting, diseased bodies should be removed, diseased stubble should be dug up, cultivation management should be strengthened, and disease-resistant varieties should be selected. Pay attention to pesticide protection at the early stage of the disease, cut off diseased tumors in time when cutting buds, smear and disinfect with mercuric chloride water or streptomycin and lime milk, and use metalaxyl, chlorothalonil, zineb, ethyl phosphate, mancozeb or Bordeaux mixture to prevent and control other serious diseases.

Apple silver leaf disease

Apple silver leaf

Li Zhixing

Fungal diseases of silver-leaf apple branches are caused by the invasion of Actinidia purpurea.

Distribution and harm

It has been reported in Japan, France, Britain and New Zealand, but the disease has not been found in most fruit areas in the United States, and it has not been found in the old apple producing areas in Liaoning and Jiaodong Peninsula in China, while the new apple producing areas in Jiangsu, Anhui, Henan, Hubei, Sichuan, Zhejiang and Shanghai have seriously occurred. It causes dead trees and poses a great threat to apple production. The diseased branches and dry xylem turn brown, with the development of the disease, the color deepens, and the diseased tissue is dry and fishy. Before flowering, the diseased leaves became ill, first lead, then silvery white, with brown spots in summer, small diseased leaves, crisp leaves and reduced chlorophyll. Symptoms of diseased leaves near the base of new branches are obvious. Three years after the symptoms of silver leaves appeared, the tree died. The diseased fruit is slightly flat and some varieties have fruit rust on the surface.

The symptom of silver leaf is that the parasitic branches of pathogenic bacteria secrete cells to crush toxins (called CA toxins), which separates the intercellular spaces of leaf epidermal cells and has air between them. After being refracted by sunlight, the diseased leaves are silvery white, and there is no pathogen in the diseased leaves themselves.

The cause of disease

The pathogen is chondromycetes, which belong to basidiomycetes and are not clumped. Sick trees and branches grow fruiting bodies after death. The fruiting body is imbricate, purple, nearly round, then turned gray, with light edge color and strong fishy smell. Procumbent fruiting body, sometimes spreading in pieces. The fruiting body with inverted edge has fluff on it and smooth bottom. Frontal villi are grayish brown, grow longitudinally and have wheel stripes. The seed layer is mixed with pear-shaped vesicles. Basidiospore unit cell, D-shaped, colorless, thin-walled, with one end pointed and one side flat. The fruiting body cultured indoors is white to yellowish, not purple.

The host range of silver leaf pathogen is very wide, but it is limited to broad-leaved trees, such as pears, peaches, apricots, plums, cherries, kiwis, poplars and willows. In spring, this tree is rich in carbohydrates, which makes it easy to get sick. After pruning, the wound is not protected and the xylem is exposed. When it rains, the basidiospores in the orchard fly away, which is the easiest to induce diseases. From July to August, the carbohydrate in the tree decreased and the resistance increased. The old fruit area in the north is dry in spring. After pruning for several months, there are many saprophytic colonies on the surface of the big wound, which affects the infection of bacteria and will not cause silver leaf disease. There was much rain in April and May in the Jianghuai Valley, and germs invaded unprotected new wounds. Tree conditions and environmental conditions are suitable for pathogen infection, and silver leaf disease is prone to occur.

Infection process and disease cycle

The pathogen overwinters in xylem with mycelium and forms fruiting bodies in rainy spring and summer of the following year. The temperature reached 10.2 ~ 15℃, and the rainfall was more than 7. 1 mm for two consecutive days. New fruiting bodies appear and become the primary source of infection. According to the data of Siyang Apple Orchard in Jiangsu Province, the appearance of new fruiting bodies varies from early April to mid-June due to the rainfall. The basidiospores released by the fruiting body invade the xylem transportation system from the wound, and then spread up and down, up to 2-3 years old branches and down to the root system. After inoculation with mycelium, symptoms appeared 88 days later, and the leaves near the wound first showed symptoms of silver leaves.

disease control

Before the apple trees germinate, clear the dead trees and branches with silver leaves in the orchard and burn them to reduce the source of overwintering bacteria; Check the willows near the orchard in spring, find the fruiting bodies, cut them off with a knife, and disinfect them with Pomei 5 degree stone sulfur mixture. Poplar stumps and willow trunks are the key inspection objects, and fruiting bodies may appear in these parts; After pruning in winter, burn the cut branches, and don't use them as fences in orchards or houses, because these diseased branches may appear fruiting bodies after the spring rain; Wound protection is an important measure to prevent and treat this disease. Apply systemic bactericide or residue of sulfur mixture such as thiophanate to the wound to prevent infection. The diseased tree was effectively treated with octahydroxyquinine sulfate. Strengthen fertilizer and water management in cultivation management to make plants grow healthily and improve disease resistance.

Grape white rot

Grape white rot

Li Zhixing

Fungal diseases of grape fruit, ear axis, leaves and new shoots caused by white rot shield. It was first discovered in Italy on 1878 and first reported in China on 1899.

Distribution and harm

Globally, hail-prone areas in Europe suffer the greatest losses. At present, it is a serious disease in grape producing areas in northern China, which can make fruits rot and fall off in clusters. The old course of the Yellow River often occurs in North China, Shaanxi Guanzhong and other places. If it is not prevented, the loss can reach 60%.

Ear injury is the most typical symptom. Before the ear ripens, the diseased fruit is slightly yellow and the appearance is not full. Conidia of pathogenic bacteria raised the epidermis of the host, but did not break, and the diseased fruit was pale. Mature conidia are grayish white, and diseased fruit grains eventually fall off. In the environment of high temperature and high humidity, germs spread from diseased grains through fruit stalks to ear axes, damaging the ear. At first, the disease of the fruit stalk is blue-brown long and small spots. If the temperature and humidity are suitable, the spots will spread all over the fruit stalk. The ear shaft was sick, and the ear under the diseased spot soon dried up. If the grain is dry before infection, conidia will not form. Unlignified buds are damaged to form ulcer spots, and ulcer buds are easy to break when encountering strong wind. When the leaves are damaged, light brown large lesions are often produced at the edge of the leaves, and the wheel lines are not obvious, and gray spots are scattered locally on the lesions. Later, the diseased tissue dried up and cracked, and the diseased leaves were damaged.

The cause of disease

The pathogen is scutella. )saee。 It belongs to Ascomycetes, Ascomycetes, and has not been found in China. The asexual state is white rot cospora, which belongs to Hemiptera and cocci. Conidia grow from the substrate under the stratum corneum, brown, spherical, with small holes, and the sporogenous area at the bottom is cushion-shaped, generally without conidiophore. Sporogenous cells are bottle handles, conidia are olive brown or olive-colored, single-celled, ovoid, with a blunt top and a flat bottom.

Infection process and disease cycle

The life history of bacteria in soil includes parasitic period (short) and dormant period (long). In the late growing season, diseased fruit grains, ear axes and new shoots fall off, and the bacteria enter a dormant period in the soil. A large number of conidia released by conidia apparatus can survive for 2 ~ 3 years. Dry conidia can still release live conidia after 15 years. Most pathogens are distributed in the soil layer within the depth of 1 m, and the most are from the surface layer to 20 cm, accounting for about 80% of the total number of bacteria. When it rains in summer, soil particles with bacteria splash on the ear of fruit, causing initial infection, and hail and orchard operation also play a similar role. Pathogens do not infect undamaged ear, and damage caused by hail is the most likely to cause infection, but pathogens can directly invade ear axis and fruit stalk. Conidia can germinate and start to infect in the juice of broken fruit or the raindrops infiltrated by fruit secretions after several hours (24 ~ 27℃). Infection is slow below 15℃, and the incidence is slight above 34℃. The incubation period is 3 ~ 8 days, and it takes a long time for new buds to be infected. Continuous high humidity, relative humidity above 95% and high temperature of 24 ~ 28℃ after heavy rain in summer are the main factors of disease epidemic. In case of hail, a large number of wound diseases are particularly serious. In orchards in northern China, the rainy season in July and August is usually the period when diseases occur. In other countries, there is more rain in the early stage of plant growth, less rain in the later stage, and the disease is lighter. The young fruit particles have stronger disease resistance than the later fruit particles.

disease control

The main measures to control white rot are: spraying triamcinolone acetonide, thiram, chlorothalonil or captan in time after high temperature, rainy weather or hail in summer; Remove the earliest diseased ear in time to reduce the reinfection of germs; Because the initial infection source comes from the soil, the fruiting part should be raised properly during pruning to make the ear not close to the ground and reduce the infection opportunity of germs; Clean the garden immediately after harvesting, defoliation and pruning; Weeding, tying vines and picking secondary buds in time make the branches ventilated and transparent, which is not conducive to the spread of germs and is conducive to spraying protection.