What is root-knot nematodes?

Liao Jinling and Feng Zhixin

A sedentary parasitic nematode that causes the root of the host plant to form nodules and has a double uterus (or ovary). It belongs to the root knot family of Lepidoptera and is an important parasitic nematode in plants.

morphological character

Androgyny. The female insect is pear-shaped, oval or lemon-shaped. Tail degeneration. The anus and vulva are located at the end of the worm. The cuticular membrane is thin and annular. The horny membrane around the anal yin forms a special perineal pattern. The lip area is slightly hat-shaped with six lips. The oral needle is developed, generally about 12 ~ 15 micron long, with obvious basal bulb, and the opening of the esophageal dorsal gland tube is behind the basal bulb. The esophageal body is cylindrical, the middle esophagus is spherical, muscular and the valve is clear. Esophageal glands cover the sides of the abdomen and intestines. The drainage hole is located in front of the middle esophageal bulb. The vulva is slit-shaped and located at or near the end of the worm. There are two ovaries, long and curly, almost full of worms, oocytes arranged in a row, and spermatic sac. Eggs are usually produced in colloidal oocysts in vitro. The male worm is cylindrical, with a body length of 1000 ~ 2000 microns. The ring pattern on the body surface is clear, with four lateral lines, the lip area is slightly prominent, and there is no constriction mark. The length of the oral needle 18 ~ 26 microns, and the base ball is obvious. The esophageal body is cylindrical, and the middle esophageal bulb is spindle-shaped. The isthmus is very short. The esophageal gland covers the ventral surface of the intestine in the shape of long leaves, covering about 4 body widths. The drainage hole is located at the back of the nerve ring. There are 1 ~ 2 testis, and the intersecting spines are slender, about 25 ~ 33 microns. The lead-in zone is trough-shaped and about 7 ~ 1 1 micron long. No hugs. The tail is short, blunt and round, with fingers. The second instar larvae are linear with 1 ~ 4 thick rings in the lip area. There are obvious labial discs, slightly developed labial skeleton and wide lateral lips. The oral needle is slender, less than 20 microns, generally 12 ~ 15 microns. The drainage hole is located behind the lunate bone. The middle esophageal bulb has a large oval valve. There is obvious transparent area at the tail, narrow tip and irregular appearance (Figure 1).

Biological properties

Including life history, pathogenicity and ecological characteristics.

biography

Eggs are produced in colloidal medium, and the colloid gathers eggs in egg blocks or oocysts. Female insects (usually single cells) begin to develop several hours after laying eggs, and gradually divide into 2, 4 and 8 cells, and so on, and then go through the blastocyst stage, gastrula stage and mesoderm formation stage in turn until they form a first-instar larva, and there is obvious mouth needle curl in the egg shell. After molting for the first time, it becomes a second instar larva. Larvae constantly pierce the end of eggshell with oral needle and break out. Then, it enters the soil and keeps moving, waiting for the opportunity to infect the host. After the second instar larvae enter the roots of plants to parasitize, the width of the worms increases and the esophageal glands expand obviously. Differentiation and growth of germ cells. In female larvae, the gonads extend forward from both ends, showing a V-shaped appearance; However, in male larvae, a single gonad extends forward. Due to the continuous feeding of nematodes, the second instar larvae gradually expanded into pods. With the second and third molting, the third and fourth ages are formed. During these two periods, the epidermis of the worm often falls off, and the oral needle and the middle esophageal bulb disappear. After the fourth molting, the oral needle and the middle esophageal bulb are clearly visible, the gonads tend to mature, the uterus and vagina are formed, and obvious perineal patterns can be seen. With the development of nematodes, females are nearly spherical or slightly slender with necks, and their gonads are fully developed, highly differentiated and curled, occupying most body cavities, and finally mature and lay eggs. The shape of male worms does not change much during development, and they are all linear. The time required for root-knot nematodes to develop from single-celled eggs to mature females to lay eggs varies from species to species, generally about 25 ~ 30 days (at 27℃).

Fig. 1 morphological diagram of root-knot nematodes.

1. Male worm; 2. The front of the male worm; 3. The front of female insects; 4. Second instar larvae; 5. The back of the male worm; 6. Female insects (imitating A.L. Taylor and J.N. Sass)

pathogenicity

The host range of root-knot nematodes is wide. Taking the second instar larvae as infected larvae, it harms the root tissue. It invades from above the root cap, moves between root cells without any differentiation, and finally settles in the stele and cortex. Nematode needle constantly pierces the cell wall, secretes saliva, expands the vessel molecules and accelerates the cell division around it. Giant cell (also known as polyploid) is formed due to cell enlargement (abnormal hypertrophy), which leads to cell wall decomposition, abnormal nucleus and changes in cytoplasmic composition. At the same time, the cells around the head of the nematode proliferate (hyperproliferation). With the expansion of roots, obvious nodules are formed. Due to the infection of nematodes, substances such as carbohydrates, pectin, cellulose and lignin in root tissue decreased, while substances such as protein, free amino acids, RNA and DNA increased, and the transportation of gibberellin and cytokinin weakened. The transportation structure is destroyed and deformed, and the normal transportation of water and nutrients is greatly reduced.

Ecosystem characterization

The survival and reproduction of root-knot nematodes are related to many ecological factors. ① Soil temperature. Temperature mainly affects the survival of eggs and larvae, which is the most important factor to determine the survival of nematodes. Different species of root-knot nematodes have different requirements for soil temperature. At 0℃, 4 1% of Meloidogyne incognita eggs can survive in the soil for 90 days, and they are contagious when inoculated, while Meloidogyne incognita and Meloidogyne javanica are not contagious at 0℃ 1 1 days later. Meloidogyne incognita larvae can survive 16 days at 0℃ and are infectious, while Meloidogyne incognita larvae are not infectious for 7 days. The optimum temperature of root-knot nematodes in northern China is 15 ~ 20℃, and the optimum temperature for growth and reproduction is 20 ~ 25℃. The corresponding temperature required for root-knot nematodes in Java is about 5℃ higher. ② Soil moisture. When the water content is low, the hatching of eggs is inhibited by water loss, and the activity of larvae is more difficult. In very humid soil, hatching is hindered and the activities of larvae are slowed down due to lack of oxygen. ③ Soil structure. Root-knot nematodes are more serious in sandy soil and less serious in clay. In addition, soil osmotic pressure, pH value, soil oxygen content, root exudates and other factors also have a certain impact on the survival and reproduction of root-knot nematodes.

classify

There are more than 70 species of root-knot nematodes reported in the world. There are 65,438+06 species reported in China, including 9 new species: pea root-knot nematodes, Fujian root-knot nematodes, hole root-knot nematodes, forest root-knot nematodes, Jinan root-knot nematodes, Jianyang root-knot nematodes, Donghai root-knot nematodes, citrus root-knot nematodes and Curvularia root-knot nematodes.

There are two schools of classification of root-knot nematodes, namely traditional morphological classification and modern classification. The former classification is mainly based on female body shape, perineal pattern, position of excretory orifice, oral needle, hood and head area; Male insect's body length, oral needle, lateral area, cross-thorn and guide belt; The body length, oral needle, head area and tail shape of the second instar larva, especially the shape of perineal pattern, whether there is obvious lateral line in the lateral area, the height of dorsal arch, the thickness, density and smoothness of the pattern, etc. Modern classification system is based on traditional morphological identification, using the characteristics of nematode identification host, biochemical and genetic response. Identification of host reaction refers to the parasitic reaction of root-knot nematodes in tobacco (NC95), cotton (Deltapine 16), pepper (California Wonder), watermelon (Charleston Grey), peanut (Florrunner) and tomato (Rutgers). Biochemistry mainly observed the activity band RF of female insect esterase in gel electrophoresis; The genetic reaction mainly observes the number, morphology and reproductive mode of female insects. The modern classification system proposed by J.N.Sasser, an international cooperative group of root-knot nematodes, has been gradually accepted by people.

Important pathogenic nematodes

The most common and important species of root-knot nematodes that harm crops are root-knot nematodes in southern China, root-knot nematodes in Java, root-knot nematodes in peanuts and root-knot nematodes in northern China, and the perineal patterns of each species are obviously different (Figure 2). The crop losses caused by these four nematodes account for more than 90% of the damage losses of the whole root-knot nematodes.

Meloidogyne incognita

Chitin from Taxus chinensis var. mairei (Kofoid & white)

The perineal pattern of female insects has obvious high back arch, which is composed of smooth to wavy lines, and some of them diverge on the side, but there is no obvious lateral line. There are often some lines that bend to the vulva. The second instar larvae are 346 ~ 463 microns long (average 405 microns). There are two types of chromosomes, 2n = 32 ~ 36 and 3n = 40 ~ 46. The active band value of female insect esterase in gel electrophoresis is RF = 0.47. This species has four races. Root-knot nematodes in southern China are more widely distributed than other species, covering tropical and temperate zones, with an annual average temperature of 18 ~ 30℃. The optimum temperature is 27℃. The host range of this species is very wide. According to the statistics of V.W.Saka in Malawi and C.C. Carter in the United States (1987), its host is 1300.

Fig. 2 Morphology of perineal patterns of four common root-knot nematodes.

1. Meloidogyne incognita; 2. Peanut root-knot nematode disease; 3. Meloidogyne javanica; 4. Meloidogyne incognita (imitating J.D. Eisenbeck, etc. )

Meloidogyne javanica

The perineum pattern of female psylla javanica is a round and flat back arch. The lateral area has obvious lateral lines. The lateral line divides the line into obvious back and abdomen. There is little or no wire passing through the side line. Some lines bend towards the vulva. The second instar larvae are 402 ~ 560 microns long (average 488 microns). Chromosome number 3n = 43 ~ 48, female esterase RF = 0.47, 0.55 and 0.59. No host differentiation was found in this species. Its distribution range is narrower than that of southern root-knot nematodes, including temperate and tropical regions, from 33 north latitude to 33 south latitude. This species may be the dominant species in arid areas with monthly rainfall less than 5 mm for more than three months. The host range is wide.

Peanut root-knot nematode

Ariana (Neil) Chiwood

The perineum pattern of female insects is round to oval. The back arch is flat to round. The lines on the bow diverge slightly at the lateral line, often forming shoulder-like protrusions on the bow. The lines of the back and abdomen often intersect at the lateral line to form an angle. The line near the line is bifurcated, short and irregular. The lines are smooth and wavy, and some may bend in the direction of vulva. The pattern can also have some lines extending to the side to form one or two wings. The body length of the second instar larvae is 398 ~ 605 microns (average 52 1 micron). There are two types of chromosomes, 3n = 50 ~ 56 and 2n = 34 ~ 37, and female esterase RF = 0.54, 0.57 and RF = 0.50. This species is divided into two races. The distribution of peanut root-knot nematode is similar to that of southern root-knot nematode, and it also has a wide range of hosts.

Meloidogyne incognita

May Placci Wood

The perineum pattern of female insects is nearly round hexagon to slightly flat ellipse. The back arch is usually flat. The lines of the back and abdomen intersect at a certain angle or change irregularly. But the lateral lines are not obvious, and some lines can extend to the side to form one or two wings, and the lines are smooth and wavy. The tail end area is often carved. The body length of the second instar larvae is 357 ~ 5 17 micron. There are three types of chromosomes: haploid n = 17 (or 16, 15, 14), diploid 2n = 30 ~ 3 1, and triploid 3n = 43 ~ 48. Female insect esterase RF = 0.50, which can be divided into race A and race B according to the number of chromosomes. The host specificity of meloidogyne incognita is stronger than other three common nematodes. Mainly distributed in cold and tropical or subtropical high altitude areas (1000 meters above).

Harm and control

Root-knot nematodes are widely distributed, with more than 2000 host plants, causing diseases of many crops all over the world. Causing huge economic losses. According to statistics, the annual coffee loss caused by root-knot nematodes in South America is estimated to be 600-700 million dollars, of which Brazil lost 6,543.8+0.8 million tons of coffee in 654.38+0.983 ~ 654.38+0.984, accounting for more than 654.38+0.5% of the national output. In addition, field plant root-knot nematodes often coexist with fungi and bacteria, and interact with each other to form a compound infection.

The control of root-knot nematodes depends on different crop varieties and different nematodes. Using the resistance of crop varieties is very effective and has been adopted by many countries. In recent years, the United States and other countries have cultivated excellent varieties of soybean, tobacco, cotton and other crops resistant to root-knot nematodes. For crops with high economic value, nematicides can be selected for control, such as Fenaphosphate, rugby, Mocap, Basamid, Wan Qiang and Mi Le. Crops with low economic value can be controlled by agricultural measures such as soil improvement, crop rotation and soil turning. In addition, Paecilomyces lilacinus has been successfully used to control root-knot nematode disease. The Philippines used this strain to make the preparation "Biocon" (trade name), which was widely used in practice and achieved remarkable results.

philology

Taylor, A.L. and J.N.Sasser, Biology: Identification and Control of Root-knot Nematodes, Cartography of North Carolina State University, USA, 1978.

Sasser J.N and Carter, C.C., Advanced Papers on Root-knot Nematodes, Volume I: Biology and Control, Cartography of North Carolina Lina State University, USA, 1985.

Barker, K.R., C.C.Carter and J.N.Sasser, Advanced Thesis on Root-knot Nematodes Volume II: Methodology, Cartography of North Carolina State University, USA, 1985.

* * * Homoantigen

Common antigen

Xuejun Zhang

Serologically identical or similar protein compounds between plants and microorganisms. Also known as cross-reactive antigen. There are * * * identical antigens between obligate parasitic bacteria, facultative parasite and plant pathogenic nematodes and their corresponding susceptible host plants.

When the interaction between stripe rust and its host flax varieties is an affinity reaction, there are many * * * identical antigens between them, and the titer of the globular protein antiserum of the pathogenic race of stripe rust to the globular protein of the susceptible flax near-isogenic line is as high as 1: 160 or1:320; When the interaction is incompatible, there are few identical antigens between them, and the titer is only 1: 20 or1:40; A rust race can only make flax strains containing the same antigen sick. There is a * * * antigen between maize head smut and susceptible maize, which is 80s ribosome. Its 40s and 60s subunits have immune cross-reaction with maize, but not with disease-resistant barley. The 1 diploid strain of this strain can infect oats germinated for 3 days with the same antigen. When oats grow for 6 days, the same antigen disappears and diploid strains can no longer be infected. The antiserum of Meloidogyne incognita eggs has cross-reaction with the antigen preparations of its host cotton and soybean root tips, and the antiserum of cotton and soybean root tips has cross-reaction with the antigens of Meloidogyne incognita eggs and larvae. In the affinity combinations between cotton leaves and cotton angular leaf spot, potato and cancer pathogen, sweet potato and black spot pathogen, kidney bean and leaf spot pathogen, wheat and black glume pathogen, leguminous plants and rhizobia, there are specific homologous antigens between host and pathogen. In these gene-to-gene disease systems, * * * homologous antigens are related to the interaction affinity between host species and pathogen strains (races). When there are the same antigens, they act as affinity for each other; When there is no * * antigen or only a small amount of * * antigen, the interaction is incompatible. The antigen of the pathogen depends on the similarity with the host antigen, and the less likely it is to be recognized as a foreign molecule after invading the host, the plant's defense response cannot be triggered, thus maintaining an affinity relationship with the host.

Four cotton varieties with different resistance have the same antigenic determinants as pathogenic or non-pathogenic (wild strains or avirulent mutant) strains of Verticillium dahliae, cotton fusarium wilt and Fusarium solani. However, there is no * * same antigen between cotton and non-self pathogen Fusarium moniliforme, and between cotton wilt and verticillium wilt and non-host plants. Wheat take-all bacteria can react with the antiserum of wheat and oat roots regardless of pathogenicity, and produce precipitation bands in agar double diffusion test, while other fungi can not form precipitation bands with the antiserum of wheat and oat. In these diseases that do not conform to the gene-to-gene relationship, the homologous antigen between host and pathogen is related to the compatibility of plant-microorganism interaction at the level of plant species (genus)-pathogen species (specialized type). When there is the same antigen between plants and microorganisms, it is the host of the microorganisms, and the microorganisms are the pathogens of plants; Without the same antigen, it is a non-host or non-self pathogen.

Lycium barbarum anthracnose

Lycium barbarum anthracnose

Gong Hao

A fungal disease caused by Sclerotinia sclerotiorum, which mainly harms fruits and causes black rot.

Distribution and harm

Ningxia Lycium barbarum is a precious Chinese herbal medicine, which is widely introduced and cultivated in various places. Since 1970, anthracnose (also known as black rot) has widely occurred in Hebei, Shandong, Henan, Shaanxi and other places, and the yield has been reduced by about 50% due to illness, reaching more than 80%. It mainly harms olives, flowers and buds. When the olive is damaged, small dots with large brown needles are produced on the fruit grains in the early stage, and there are radial black-brown pearl stalks on the fruit surface. After that, the lesion was soft and concave, and the surface was scattered with small black spots. In rainy days, orange microspore clusters gushed out, and diseased spots spread all over the fruit in 2 ~ 3 days, and the diseased fruit turned into hard black fruit in the later stage. In severe cases, the fruit particles on the branches are covered with black spots, and the buds and petals appear black spots, resulting in black buds and unable to blossom and bear fruit. In early spring, shoots, leaf tips or leaf edges are occasionally killed, leading to brown spot or wet rot.

The cause of disease

The pathogen belongs to Glomerella cingulat a (stonem. )Spauld。 Et schrenk, belonging to Ascomycetes, has not been found in the wild. The asexual state is Colletotrichum gloeosporioides. It is a kind of semi-unknown bacteria, black discospora. Apetalous particle size 195 ~ 325 microns; Conidiophore; The conidia are oval, colorless, with oil globules 1 ~ 3, and the size is 7.8 ~ 17.2× 4. 1 ~ 4.9 (micron). Conidia pile is orange-red with bristles in the later stage. The host range is wide, including apples, pears, sand fruits, grapes, peaches, cucumbers, sweet peppers, tomatoes, zucchini and so on. The fruit of Cornus officinalis was also seriously damaged. Several cultivated varieties of Lycium barbarum, such as hemp leaves and hemp leaves, have no obvious difference in resistance to anthracnose, and belong to highly susceptible varieties.

The climatic conditions of the disease are high temperature, high humidity and rainy. The conidia can germinate at 8 ~ 33℃, and the germination rate is 94.65438 0% at 28℃ for 6 hours. Spore formation, reproduction and germination invasion can only be carried out under high humidity and rainfall conditions, and field diseases are directly related to rainfall. Lycium barbarum can be harmed from the early fruit-bearing stage in early May to the late fruit-bearing stage in mid-June. Due to different years, regions and meteorological conditions, the onset time and severity vary from place to place. For example, the growth and decline of anthrax in Ningjin County, Shandong Province: from May to June, the average daily temperature was above 65,438 07℃ and the relative humidity was about 60%. It rained for 2-3 days in ten days, and the disease could occur in the field; From July to September, the daily average temperature 17.8 ~ 28.5℃, the rain lasted for more than 4 days, and the relative humidity was over 80%, which led to a sharp increase in field diseases. From June 65438+ 10 to the end of the first frost, the average daily temperature is 9.2 ~ 14.6℃. If there is rain, the disease can continue. Temperature has a certain influence on the disease. The incubation period at 26 ~ 30℃ is only 3 days, and 2 1 ~ 26℃ takes 5 days. The humidity and rainfall during the flowering and fruiting period of Lycium barbarum played a leading role in the spread of diseases, and the temperature increased.

Infection process and disease cycle

It is the first infection of the disease that the pathogen overwinters on the residual trees and dead fruits. Dry branches do not carry bacteria. In the second year, when the weather turned warmer, conidia piles were scattered by rain or dew, flowed along branches or splashed on fruits and buds by wind and rain. After germination, it invades directly through the bud tube or from the wound (wind friction, insect injury, etc.). ). Every year, the first diseased fruit (that is, diseased heart) in the field is near the stiff fruit on the branch or under the tree, and then it continues to cause reinfection, and the disease further expands and spreads.

disease control

Mainly to clean the countryside, strengthen cultivation management, and cooperate with chemical defense. ① Garden cleaning: Prune in winter to completely remove diseased fruits, and prune the garden again before germination of Lycium barbarum in early spring. It's best to spray a mixture of stone and sulfur when cleaning the garden. ② Strengthen cultivation management: according to meteorological characteristics, control fruiting period and avoid rainy season. For example, Hebei, Shandong and other places, spring drought, the annual rain concentrated in July and August, the implementation of light pruning in winter and spring, heavy pruning in summer, in order to ensure the spring and autumn fruits, give up Xia Guo. There is a lot of autumn rain in Guanzhong area of Shaanxi Province. In order to protect the spring fruit, strive for Xia Guo, give up the autumn fruit and cut it thoroughly, and accumulate nutrients to promote the early spring fruit harvest next year. ③ Spray protection: spray for the first time before it rains from May to June, once every half month, and once every 7 ~ 10 day during the peak period from July to August; After spraying, spray it again in case it rains. 1: 1: 100 bordeaux mixture, 50% bactericide, anthrax thiram, etc. Various chemicals should be used alternately. In addition, non-pathogenic kenaf anthracnose can be sprayed in the field, or branches with bacteria can be hung to make Lycium barbarum immune to anthracnose.

melon powdery mildew

Powdery mildew of melon

Gu Xixin

Powdery mildew attacks the fungal diseases of melon. Cucumber, zucchini, pumpkin, bitter gourd and melon can all be killed. It was first discovered in 1800.

Distribution and harm

The worldwide diseases occurred in melon growing areas in China. Cucumber, zucchini, melon and pumpkin are more serious in the north, which is harmful to cucumber in open spring, greenhouse and greenhouse. Cucumber and bitter gourd are more serious in the south, and they are more harmful in spring and autumn. It mainly harms leaves. The lesions on the front and back of leaves are small and round, and white powdery mildew (hyphae, conidia and conidia) grows on them, which gradually expands and merges. In severe cases, the whole leaf is covered with white powder, which turns yellow-brown and dry, and the white powdery mildew turns gray. In some areas, black particles (bacterial capsules) are produced on the mold layer or between mold layers at the later stage of the disease.

The cause of disease

Pathogens are powdery mildew of gourd and powdery mildew of gourd. ) z.y. zhao, belonging to Ascomycetes and Powdery Mildew. It has parasitic harm to cucurbitaceae plants. The mycelia of both powdery mildew are supergene, and the haustorium extends into the host cell to absorb nutrients. Conidia of powdery mildew in Cucurbitaceae are grouped into two basic types, and there are many capsules in the closed capsule shell, which are hyphal and about 300 microns long. The conidia of melon single capsule shell are clustered in the basic type, the single capsule is closed, and the accessory filaments are colorless or only the lower part is light brown. The conidia of the two bacteria can still germinate and invade when the relative humidity is lower than 25%, and absorb too much water in the water droplets, and the cell wall is broken due to the increase of swelling pressure, which is not conducive to spore germination. The optimum temperature for spore germination is 20 ~ 25℃, which should not be lower than 10℃ or higher than 40℃. Cucumber varieties resistant to downy mildew are often resistant to powdery mildew, while Jin Yan, Dalian 8 162, Xu Jing, Tangshan Qiugua and Jinza series varieties are resistant to diseases. Usually, 45% ~ 75% air humidity causes disease quickly, and more than 95% is obviously inhibited. The incidence rate is higher in years with less rainfall. Poor ventilation and drainage plots, excessive or insufficient nitrogen fertilizer, water shortage and poor growth all aggravate the disease.

Infection process and disease cycle

Cucumber or other melon crops are planted all the year round in the warm areas of southern China, and powdery mildew occurs all the year round. There is no overwintering problem for germs. In the north, pathogenic bacteria overwinter on the ground with closed capsules and ascospores. In winter, pathogens in protected areas overwinter in greenhouses or greenhouses with conidia and hyphae, and continue to infect. Conidia are mainly spread by airflow. Under suitable environmental conditions, the incubation period is short and reinfection is frequent. When the temperature rises to 14℃, the disease begins to occur, and it occurs rapidly in the continuous cloudy and sultry weather.

disease control

Selecting disease-resistant varieties and planting melon crops in ventilated and light-transmitting plots; Apply more phosphorus and potassium base fertilizer and avoid applying more nitrogen fertilizer during the growth period; Spraying triamcinolone acetonide, mirex and wettable sulfur powder during the onset period.

Gourd virus disease

Gourd virus disease

Cucurbitacin is a plant-wide disease caused by many viruses infecting melons.

Distribution and harm

This happens all over the world. Symptoms vary with viruses and different melons, such as flowering leaves, yellowing, shrinkage, green spots, necrosis and so on. The symptoms of mixed infection of several viruses are complex and serious. Mosaic type: the diseased plant is a systematic mosaic, the upper leaves appear first, showing uneven dark green mosaic and mottling, the diseased plant is slightly short, the stems and internodes become shorter and the growth is poor; The fruit surface appears faded, mottled and deformed seriously, such as mosaic disease of cucumber, melon and towel gourd. Atrophic type: the newly grown leaves appear thick green ridges and wrinkles along the veins, or fern leaves, lobes and leaves become smaller, sometimes die along the veins, and the fruit surface appears mottled or tuberous protrusions of different sizes, and the melon is small and deformed. In severe cases, the diseased plant dies, which is more common in zucchini, pumpkin and watermelon. Green spot type: the new leaves produce small macula, which gradually turns pale yellow and mottled, and the green part is tumor-like; The fruit produces thick green spots and tumors, is deformed, and the watermelon pulp is uneven in color or becomes soft and stuffy. Yellowing type: the leaves change from yellow-green to yellow, the veins remain green, and some of them produce waterlogging spots between veins in the early stage of the disease, and the diseased leaves harden and curl to the back of the leaves, mainly on cucumbers.

The cause of disease

The main pathogens are: ① cucumber mosaic virus, spherical particle (icosahedron), 30 nm, lethal temperature 60 ~ 75℃, dilution end point 10-3 ~ 10-5, and in vitro survival period of 3 ~ 7 days; Myzus persicae, Aphis gossypii, Aphis brassicae, etc. It belongs to non-persistent infection, and beetles can also be infected when they contact juice; Cucumber, pumpkin and melon seeds may be poisonous; The host range is wide, which can infect nearly 800 kinds of plants, causing systematic mosaic or yellowing shrinkage on melons. ② Pumpkin mosaic virus (SqMV), spherical particle (icosahedron), 30 nm, lethal temperature 75℃, dilution end point 10-5 ~ 10-6, in vitro survival time of 42 days, virus vector beetle, juice contact can also infect, and seeds can also infect; In pumpkins and zucchini, it can cause verrucous processes on chicken feet, dwarf plants and fruits. ③ Watermelon mosaic virus -2 (WMV-2), with linear particle size of 15×7 10 (nanometer), lethal temperature of 45 ~ 50℃, dilution end point of 10-2 ~ 10-5, survived in vitro. In addition, there are tobacco spot virus (TRSV), tobacco brown spot virus (TNV) and cucumber green mottle mosaic virus (CGMMV). Cucumber Necrosis Virus (CNV), Cucumber Vein Virus (CVYV), Cucumber Latent Virus (CLV), Cucumber Dwarf Mottle Virus (CSMV), Wild Cucumber Mosaic Virus (WCMV), Melon Vein Necrosis Virus (MVNV), Cucumber Mosaic Virus (OPMV) and Zucchini Yellow Mosaic Virus (ZYMV). Watermelon mosaic virus -l 1 (WMV- 1) and other varieties have different disease resistance. Disease-resistant varieties: cucumber Jin Yan 7 and Lv Wan, zucchini Hanxihu and Tianjin 25. High temperature, drought and strong sunshine are beneficial to the spread of virus vectors and viruses in plants.