Phytophthora root rot is one of the most devastating diseases on soybeans. First discovered in 1948 in Indiana, USA, it has occurred in many soybean producing countries. In 1995, China was identified as a domestic phytosanitary object. At present, Phytophthora root rot occurs in soybean producing areas in more than 20 countries in Asia, Africa, Europe, North and South America and Oceania, and the annual global soybean production losses exceed US$1 billion. In recent years, with the increase in soybean imports from the above areas in China, the pests of Phytophthora sojae have also been found in some parts of our country. The host's scope, hazard characteristics, typical symptoms, transmission route and conditions, quarantine and prevention of the disease are described as follows:
First, the host range and hazard characteristics The pathogenic parasitism is more specialized and it mainly infects soybeans. In addition, it can also be harmful to lupins, beans, peas, flower lentils, safflower, parsley, beets, spinach, carrots, potatoes, tomatoes, sugar cane, sweet clover, and the like.
Soybeans can infect throughout the growing season, causing rot before seedling emergence and tripling of post-emergence seedlings, yellowing of the lower leaves of plantlets at the adult planting stage, and large dark brown disease classes on near-ground stems, browning and necrosis of vascular bundles. Withered to death.
Second, the typical symptoms of Phytophthora sojae germination symptoms: Hydatid and root water stains, initially red, gradually turned brown, contracture, and finally into a dark brown, cotyledons do not open. When it is serious, it loses its vitality and rots before it is unearthed.
Symptoms at the seedling stage: Water stains on the roots, gradually turning brown to dark brown, and finally rot; after the emergence of the true leaves until the appearance of the compound leaves, the germinal lesions appear on the hypocotyls, initially red, gradually Turns brown, curled, and eventually turns dark brown; germs invade the stem, spotting watery brown spots at the stem nodes, expanding upwards and downwards, circumventing the diseased part, eventually turning into dark brown, diseased and healthy borders Obviously; causing the diseased parts and above parts of the leaves wilting, drooping, top tip down bend, the final whole plant withered, the leaves do not fall off.
Symptoms of adulthood: Root symptoms: The diseased part appears water-stained and gradually turns brown to dark brown, and finally rots, the root system is not vigorous and gradually declines; the plants are caused to grow slowly, obviously dwarfed, and when severe, the entire plant leaves from below At the beginning, wilting began, the petiole slowly drooped, and the stalk formed a figure eight shape. The top growth point dangled and bent down, eventually withered and died, and the leaves did not fall off.
Branches and stems symptoms: Water-stained brown spots appear at the middle and upper stem nodes and gradually expand upwards and downwards. The sick and healthy junctions are clearly visible. If the disease progresses, the disease department expands further and eventually turns dark brown, otherwise, the disease The Department turned reddish-brown and did not spread; when the condition is serious, the leaves of the diseased part and above are wilted, the petioles slowly droop, and the culm is shaped into a figure eight, and the top tip is bent down. As the disease progresses further, the whole plant eventually becomes Gradually withered and died, the leaves did not fall off, otherwise it would not have a great impact on the plants.
Symptoms of the leaves: Generally, they do not invade the leaves of soybeans, but occasionally the pathogens are splashed on young leaves due to heavy rain. This causes yellowing and withering of the leaves; when the humidity is high, the disease can spread to the petioles and stems; the base of the petioles and stems After the connection is infested, brown lesions appear, shrink, petiole sagging; leaves wilting, dry, but do not fall off; if infected at the end of the petiole and leaves, brown spots, shrinkage, but petiole Not drooping; also cause leaves wilting, dry, leaves do not fall off. Symptoms of pods: Young pods will blight and yellow after being infested and eventually fall off. The watery spotted brown spot on the skin of the crust has gradually sunk into the skin, and it has gradually expanded into irregular spots. The sick and healthy junctions are obvious, and the grains are stunted. Finally, clams and pods are formed. Seed Symptoms: Infested seeds are dry and not full.
Symptoms of soybean diseases and other diseases distinguish root rot caused by other pathogens: After the plants are infected, the main root grows slowly, which is weaker than the main root of healthy plants. The difference between the main root and the fibrous root is not obvious, but the disease does not cause diseases in the roots. The symptoms of plaque and rot are therefore distinguishable from Phytophthora root rot.
Sclerotinia: When the plants are infected, the vascular bundles are hollow and dry. There are no sclerotia in the vascular bundles. The white mold layer is rarely seen in the stem and can be distinguished from Phytophthora sojae.
Flooding and flooding: Since soybean diseases generally occur in low-lying lands, inland areas, and over-water lands, flooded plants also appear as sagging leaves, so they are often confused with flooded plants. At this point to check whether there are no spots on the main stem, if the growing point is wilting and sagging arc, the most critical is whether the vascular bundle color is pink or reddish-brown, if the above symptoms are Phytophthora sojae root rot .
Third, transmission routes and pathogenic conditions The ooze spore survival in the soil as the initial source of infection in the winter, zoospores in the crop growing season is the main mode of transmission of disease, relying on rain to spread. The soil with pathogenic bacteria is caused by wind and rain or splashed on soybeans to cause initial infestation. After the zoospores in the aquatic soil meet the soybean roots, they first form quiescent spores, then germinate and invade, and the mycelium spreads between the host cells. The formation of spherical or finger sucker nutrition, but also the formation of a large number of oospores. Oocyspores can live for many years in the soil or on sick and sick bodies. The oospore germinates after 30 days of dormancy. High humidity or rain, heavy soil, easy to disease. Repeatedly to the disease.
Soybean resistance to P. sojae is race-specific resistance. There is a clear difference in resistance between soybean varieties. The susceptibility of the variety is also one of the main conditions that cause the occurrence of Phytophthora root rot.
IV. Quarantine and Prevention
1. To strengthen the quarantine prohibition of the transfer of soybean seeds to the soybean disease-prone areas. If it is really necessary to transport the soybean seed, it must undergo strict quarantine and be transported after being qualified. It is forbidden to collect seeds in the fields where soybean diseases occur, and it is forbidden to transfer seeds to the areas where no diseases have occurred.
2. Selection of resistant and disease-resistant varieties It is known that different varieties of soybean have very different resistance to soybean diseases. In the disease-prone areas, the use of resistant and disease-resistant varieties is widely promoted to avoid the use of susceptible varieties.
3. Agricultural control and crop rotation Rotation is carried out in areas where the root rot of Phytophthora infestans is severe, such as soybean and paddy crop rotations, to avoid continuous cropping as much as possible.
Strengthen water pipes to avoid planting in low-lying, poorly drained or heavy clay lands, strengthen cultivation, prevent soil compaction, increase water permeability, eliminate water accumulation in the field after rain, avoid string irrigation and soaking for a long time.
Remove the diseased plants found during planting to remove the disease in a timely manner, clearing the field sickness. After harvesting, the plants cannot be discarded everywhere and must be burned in time.
4. Chemical Control Seed Treatment The seeds for field use must be rigorously screened to ensure that there are no pathogens and no self-retained species in the ward. Before sowing, use 50% Anke WP, 25% Metalaxyl WP or 60% WP WP for seed dressing. The dosage is 0.2% of the seed weight, up to no more than 0.4% of the seed weight. Avoid white areas; 35% metalaxyl WP is seeded at a seed weight of 0.3.
Chemical control According to the field monitoring situation, once the Phytophthora root rot disease strain was found, it was immediately treated with selective fungicides. Recommended pesticides: 50% Anke WP 1500x, 25% Metalaxyl WP 600x or 60% WP 1500x Spray Control, 7d Spray 1x, Spray 3 Times; 25% metalaxyl WP 800 times, 58% metalaxyl MnZn wettable powder 600 times, 64% antitoxic WP 500 times, 72% Glucosamine or 72% Cream Urea MnZn Wettable powder 700 times, or 69% ank manganese zinc wettable powder 900 times spray control. The drug was stopped 3 days before harvest.
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