Soybean cyst nematode disease, also known as soybean root nematode disease, chlorosis, commonly known as "Fire Dragonfly", is an important nematode disease in soybean production in the world, mainly in cold regions.
Distribution and hazards are mainly distributed in the two major soybean producing areas in the northeast and Huang-Huai-Hai in China, especially in the drought-prone and sand-alkali-old soybean areas in the Northeast where the crop is continuously planted for many years. It is second only to soybean mosaic virus disease. Major diseases. After soybeans are harmed, the lighter ones will reduce production by 20% to 30%, seriously reach 70% to 80%, and each year will have large-scale land plots.
Symptomatic cyst nematode disease can occur during the entire period of soybean growth. Cysticercosis is parasitic on soybean roots and directly harms the roots. In the seedling stage, the growth of the plants was delayed, the cotyledons and the true leaves turned yellow, and the severely infected seedlings stopped growing and eventually died. After being parasitized by nematodes, the roots are dwarfed, the flower buds are clustered, the internodes are shortened, the flowering period is delayed, and the leaves are not yellow or knot and the leaves are yellow. The large plots are yellow and resemble a fire, so they are also called “Fire Dragonâ€. ". After being parasitized by nematodes, the main roots and lateral roots were stunted, and the fibrous roots increased. The entire root system showed hairy fibrous roots. The sessile roots are white to yellow-white and slightly larger than the tip of the needle, and the size is about 0.5 mm, which is the cyst of the nematode. No root nodule or no nodules. The above-ground part of the plant is obviously short and short, the internodes are short, the leaves are yellow, and the top of the petioles and stems are also light yellow, with few junctions.
The pathogenic soybean cyst nematode disease is caused by the infection of Heterodera glycines Ichinohe (SCN).
1. Morphological characteristics The cyst is lemon-shaped, initially white, gradually yellow, and finally brown, 0.6 mm long. There are markings on the surface. Eggs are oval or barrel-shaped, with a size of 50 to 111 microns and 39 to 43 microns, and are hidden in cysts. The larvae were divided into 4 stages. The male and female were similar before the 2nd instar, and the male and female were divided after the 3rd instar. The mature male is lemon-shaped and has a size of 0.85 mm (0.51 mm), white to yellow-white, and the body is full of oocysts. The thickening of the body's stratum corneum can be directly converted into a lemon-shaped skin (or cyst), which is resistant to adverse effects. The role of the environment, eggs can survive in cysts more than 10 years.
2. The host range of soybean cyst nematode hosts a wide range. The host plants of SCN in China include soybeans, kidney beans, red beans, rice beans, wild soybeans, semi-wild soybeans, rehmannia, peas, Paulownia, and others.
3. The occurrence and distribution of physiological races of soybean cyst nematode The SCNs among different groups were divided into different physiological races because of different virulence. There are 8 races such as 1, 2, 3, 4, 5, 6, 7, 14 in the SCN race in China. No. 1 races are mainly distributed in Liaoning, Jilin, Shandong and Jiangsu; races Nos. 2 and 7 are distributed in Shandong; races No. 3 are mainly distributed in Heilongjiang, Jilin, Inner Mongolia and other places; No. 4 races are mainly distributed in Shanxi, Soybean production areas in Henan, Jiangsu, Shandong, Anhui, Hebei, and Beijing; No. 5 races distributed in major soybean producing areas and counties in Anhui, Jilin, Inner Mongolia, and other places; No. 6 and 14 races are distributed in a few counties in Heilongjiang Province. . The physiological races of soybean cyst nematode in China occurred in the 3rd and 4th races, and the damage was serious.
Infection cycle and conditions
1. Infection cycle The soybean cyst nematode sheds winter eggs in the cyst. When the temperature is above 16°C in spring, the eggs hatch into first-instar larvae, fold into the egg shells, become second-instar larvae after molting, and use the oral acupuncture to invade host cells to parasitize parasite life. After the second molting, it became a 3rd instar larvae, and the body expanded into a pod shape. After the third molting, it became a 4th instar larvae, and the 4th instar larvae became adults after the last molting. The male adults break through the root bark into the soil to find the mating of female adults. The eggs in the cysts became the source of re-dip in the year and the source of infestation at the beginning of the year. In the absence of the host, the eggs in the cyst remain viable for up to 10 years, and can be hatched in batches year by year, becoming a source of diffusing for many years.
2. Disease conditions The severity of soybean cyst nematode disease is related to many factors such as farming system, soil type, soil texture and soil temperature and humidity.
(1) Relationship with temperature and humidity Temperature is high, soil moisture is moderate, ventilation is good, and nematodes develop rapidly. The optimum development and activity temperature is 18°C～25°C. Below 10°C, the larvae stop their activities. The most suitable soil is Humidity is 60% to 80%. Insufficient moisture and oxygen can easily cause nematodes to die.
(2) Relationship with soil types In well-ventilated soils, such as alluvial soils, light soils, sandy soils, meadow brown soils, and other coarse-grained soils and mature pods, sandy lands, sloping lands, etc., cyst density, nematodes The disease occurred early and heavier, with a large reduction in output. In the alkaline soil and white earth, nematode disease is also heavy.
(3) Relationship with the farming system The soybean cyst nematode is vertically distributed in the soybean layer in the soil. Therefore, the number of nematodes in soil has increased year after year in continuous cropping, and the damage has also increased year by year. Taking a reasonable rotation with non-host plants, the soil nematodes will be reduced year by year and the damage will be reduced accordingly.
Prevention
1. Seed test The adherence of the line insects, such as mud face insects on the seeds of soybeans, mixed contaminated soil particles between seeds, soil containing nematodes on agricultural implements, and seed transport are the main ways of causing long-distance transmission. Therefore, we must do a good job in the inspection of seeds to prevent the seeds of nematodes from entering the disease-free zone.
2. The agricultural technology rotation is currently the most effective measure to control soybean cyst nematodes. Rotation of soybeans and grasses such as wheat, corn and millet can effectively prevent and control the rotation. In general, two years of non-host plant rotations allowed the planting of susceptible soybean varieties. If the density of nematode larvae is extremely high, then rotation of crops for another year without the host plant will achieve better control effects. Disease-resistant varieties can also sometimes replace non-host crops. Insects with very low density of insect populations or severe fungal parasitic nematodes, or non-host crops for 1 year, are sufficient to control soybean cyst nematodes. Applying base fertilizer to increase soil fertility can enhance plant resistance to disease. Field machinery operations should pay attention to the removal of residual grass and soil, and must first work in a disease-free field and then go to sick fields.
3. Disease-resistant Breeding Different varieties of soybean have different degrees of resistance to soybean cyst nematodes. Planting resistance (resistant) varieties such as Fufeng No. 1, Kangxian No. 1, Kangxian No. 2, Liaodou 13 and so on are available. It can avoid the reduction of production caused by nematode damage, and it can greatly reduce the density of nematode in soil and shorten the rotation period. However, most field nematodes are mixed types of different genotypes. Since the resistant varieties affect the applied selection force, the ratio of the gene of the nematode larvae changes. Continuous or regular use of disease-resistant varieties will lead to changes in physiological races, resulting in an increase in vicious physiologic races, such as the long-term use of anti-line No. 1 disease-resistant varieties in the Anda region in Heilongjiang Province, making the original weak pathogenicity The No. 3 dominant race became a virulent No. 14 race. Therefore, in the future, disease-resistant breeding should select rotation planting of multiple resistance gene varieties and rotation planting of disease-resistant and disease-resistant varieties and common varieties, which can effectively avoid the occurrence of virulent physiological races.
4. The treatment of the severely diseased plots throughout the year is recommended to use pesticides to treat the soil. The nematicides that have been used, such as DDT, carbofuran, aldicarb (iron and gem), are all highly toxic drugs, and they are expensive, costly, use in large amounts, and cause serious pollution. They are highly toxic to humans and animals. Gradually disable or restrict use.
5. Biological control Biological control is the use of natural enemies of soybean cyst nematode to control the population of insect populations and limit nematode-induced losses.
(1) Insecta insects Some insects can ingest cysts. In the Petri dish, some collembola can greedily eat the cysts of the soybean cyst nematode. A large number of worms can be found in greenhouse pots with soybean cyst nematodes. However, if they are used in production, they need to be further research.
(2) Bacterial nematodes Pastoruapenetrans Sayre & Astarr has been found to infect Heterodera glycines in Japan, Korea and the United States. The bacteria have high infection efficiency and are resistant to adverse environmental conditions, but it cannot grow on artificial medium, which limits the application of this parasitic nematode parasite.
(3) Fungal Nematodes
1 Predatory Fungal Predatory fungi produce predatory organs such as cohesive nets, sticky balls, sticky branches and shrink rings from vegetative hyphae to prey on moving nematodes in the soil.
2 Parasitic fungi 3 important obligate endoparasitic fungi have been found on cyst nematodes: Catenaria auxiliaris and Nematophthora gynophila and Laginidiaceous. There are many parasitic fungi that are gradually found.
The combined use of predatory and non-predatory parasitic fungi is more effective than applying one of them alone. Ideally, parasitic fungi can parasitize eggs and females of soybean cyst nematode, while predatory fungi can kill active nematode larvae.
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