Sweet potato stem nematode disease is caused by sweet potato stem nematode and occurs inSweet potatoDisease.The disease can harm not only tubers, but also vines. The internal tissues of the affected tubers are black and white, and loose ladles.[1]
Sweet potato stem nematode disease is more serious in shandong and hebei provinces in china.The disease mainly damages the tubers, leading to the pityriasis of tubers, followed by the tuber seedlings and the base of the tuber vines. Generally, the yield is reduced by 15%. In severe cases, the yield can be reduced by 60%, or even cut off.Generally, it is wet, loose, ventilated and drained sandy soil, thin ridge "white dry soil", which is seriously affected;There are obvious differences in disease resistance among varieties. Some varieties have serious disease of vine, and some varieties have serious disease of vine and tuber.[1-2]
It is difficult to control the damage of sweet potato stem nematode because of its wide transmission route, many damage parts, long time and long survival years in the soil.However, in production, because its main transmission way is seedling transfer, which causes widespread spread hazards, as long as we strengthen quarantine, prevent the transfer of diseased seedlings, strictly implement high pruning in field planting, seriously establish disease-free seed reserve, set up a system to cut off the source of diseased seedlings, and adhere to it for years, we can effectively reduce and control the damage.[2]
The pathogen of sweet potato stem nematode disease is sweet potato stem nematode (scientific name:Ditylenchus dipsaci(Kuhn) Filip.），genusLinear Fauna, Lepidoptera, LepidopteraStem nematode。Both male and female are slender, with slightly pointed ends.There are 6 mastoid protuberances at the mouth, 3 spherical protuberances at the base of the proboscis like nails, and the esophagus is slender and straight. There is an enlarged esophageal bulb in the center. There are developed digestive organs in the body, which are characterized by tail sharpening.The female is not very fat, straight, and more active. The vulva is 4/5 of the body length, and the male has a short and thick lead band,Copulatory spikeThe swelling part of,Copulate umbrellaDeveloped but not at the end.The female is slightly thicker than the male, the size of the male is (0.9-1.6) mm × (0.03-0.04) mm, the length of the snout is 11-13 μ m, the length of the mating thorn is 25 μ m, and the length of the band is 10-12 μ m.The size of the female is (0.9-1.86) mm × (0.04-0.06) mm, the length of the proboscis is 11-13 μ m, and the size of the egg is (58-65) mm × (17-19) μ m. The size may be slightly different in different regions.The egg is oval, (60-66) μ m × (19-29) μ m in size, colorless, and the newly hatched larva is similar to the adult, but only 1/10 of the adult.[2]
The sweet potato stem nematode can survive for 5-7 years in the field soil, and is resistant to low temperature. It stops at - 15 ℃, but does not die. It can die after 7 minutes at - 25 ℃.The resistance to high temperature is very weak, and 98% of those buried on the surface of potato seedlings can die in 48-49 ℃ warm water for 10 minutes.It can withstand extreme dryness and can survive for about one year under extreme dry conditions.When the moisture content of dried potato was 12.7%, the mortality rate was only 24%, and most of them could still survive.The mortality of stem nematode of dried potato stored for one, two and three years was 24%, 48% and 97.5% respectively.The survival rate of stem nematode of diseased potato vines stored for 7 months after drying and soaked in water for 24 hours was 98%.[2]
Harmful symptoms
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Sweet potato stem nematode disease
The sweet potato stem nematode mainly damages the tubers, followed by the tuber seedlings, the base of the tuber vines and the thick roots, and does not damage the leaves and fine roots.After being injured, the skin cracked and the internal bran rotted.In general, at the beginning and middle stages of the disease, there is no significant impact on the elongation of the vine and the development of the root tuber. Only in the middle and late stages of the disease, the root tuber bran splits, the vine is short and deformed, or even withers.[2]
root tuber
Symptoms vary depending on the source of infection.[2]
one
Bran core type:It is infected by diseased seedlings.It invades the top of the root tuber from the inside of the seedling stem, from top to bottom, from inside to outside.At the initial stage, the longitudinal section of the seedling base and the root tuber had intermittent white powdery interstices connected to the root tuber top. Some of them became brown white or black brown with chaff rot due to the infection of other miscellaneous bacteria.In the later stage, it gradually diffuses to the lower part and around, so that all the brown and white husks in the potato block are decayed. Sometimes the inside is empty, but the appearance has no obvious change, just the weight is reduced.[2]
two
Split skin type:It is soil borne.The nematode directly breaks the outer epidermis and invades the potato block with its snout needle, and damages from the outside to the inside and from the bottom to the top.At the initial stage, it is not easy to see with the naked eye. The skin fades first, then turns green, slightly concave or has small cracks, and the subcutaneous tissue turns brown and dry.Later, when infected with miscellaneous bacteria, the invasion site appeared dark brown, and due to cell division disorder, small cracks gradually emerged.Under the epidermis, there are powdery or white and brown powdery voids, and the first invasion site presents brown and white bran rot.In the later stage, as the root tuber grows up, it damages from the periphery to the center. The interior is brown and white with chaff rot, and the outer skin forms large cracks and dark brown halos or edema.[2]
seedling stage
It is not easy to distinguish between the light and healthy seedlings. The heavy seedlings are thin and dwarf yellow, mainly due to the white part of the base.The severely injured seedlings rose from the end of the seedlings to about 3 inches (1 inch is about 3.33 cm, the same below), and the seriously ill old seedlings can reach 4-5 inches.As the invasion site is accompanied by mixed bacteria, it turns dark brown, white rhizome varieties show blue and black patches, and pink rhizome varieties turn purple red, and erode when the water is too wet.In the middle stage, there are brown voids inside, and there is little or no white pulp after shearing.The amount of nematodes was large in the late stage, and the invading part of the old seedlings of the last crop was cracked, and the pith was brown bran rot.[2]
Stem vine
Generally, when planting summer potatoes, they only damage the main vine about 2.5-3 inches above the ground, and the side vine is 1.5 inches long.The inside is white, then brown, dry rot;It can damage more than 2 feet on the seedling vine of susceptible varieties, even reaching the top.As a result, the stems and vines are not long and yellow, and even die.Sometimes it can penetrate through the phloem, and the skin is yellow and brown, wrinkled and cracked, and it is easy to break when climbing.[2]
Distribution range
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Sweet potato stem nematode disease has occurred in Beijing, Tianjin, Shandong, Hebei, Henan, Jiangsu, Fujian, Liaoning, Gansu and other provinces (cities) in China;Shandong and Hebei provinces are more serious.[3]
Infection cycle
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Because sweet potato stem nematode is an egg, larva and adult worm, it can infect seedlings, vines, vine blocks and thick roots almost everywhere at any time during seedling raising, tuber formation and storage, as long as the temperature conditions are suitable.However, the concentrated damage part is the potato block, and the peak damage period is about the last month of the potato block growth stage. At this time, there are often 300000 to 500000 nematodes in a potato block.There are thousands of nematodes in the vines about 1 foot near the ground.[2]
After raising seedlings on the kang with seed potatoes with stem nematodes, because the temperature of seedling raising is just suitable for the propagation of stem nematodes, nematodes invade from the attachment point of seed potato buds, move upward along the pith or cortex, and live as parasites in the camp.When the diseased seedlings are planted in the field, the stem nematode can spread into the soil along with them, but it mainly moves in the seedling vine.It moves along the vine (root base) to the top of the potato block, develops deeply into the potato block, and moves up along the stem. Generally, it is less than half a foot in the lateral vine in the early stage, but it varies according to the height of the branch point.If disease-free seedlings are planted in diseased soil, stem nematodes can invade most of them directly from the white root at the end of the seedlings or the natural orifice of the newly formed small potato piece epidermis by the snout needle hole about 12 hours after planting.If the seedlings are tender and the roots or small potatoes have wounds, it is more conducive to invasion.[2]
The vine cut from the spring potato has a hard epidermal tissue. The climate is suitable when planting, and the cutting mouth heals quickly, so the invasion is slow. But after the invasion, it will continue to spawn and breed at a suitable temperature.Each female lays 1-3 eggs each time, and can produce 100-200 eggs in her lifetime. It will take 20-30 days to complete a generation from self laying and hatching to adult.Due to overlapping generations, eggs, larvae and adults often exist at the same time, and the insect state is very irregular, without obvious boundaries of egg stage, larval stage and adult stage.About a month before the spring potatoes are going to be harvested, the insect population has multiplied, the nutrients in the potatoes are the most abundant, and the damage is becoming more and more serious.On summer tubers, due to the lack of infectious sources, late planting period and late onset of disease, adults, larvae and eggs will survive in the damaged spring and summer tubers and in the stems and callipers when harvesting and planing.However, during a period of storage before cellaring or processing for food, it can continue to harm, reproduce and even spread.[2]
The stem nematode left in the soil overwinters in the soil as an adult and can survive in the soil until the next year, or invades when planting sweet potatoes later.[2]
Epidemic law
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Generally, it is wet, loose, ventilated and drained sandy soil, thin ridge "white dry soil", which is seriously affected;Clay, lots with much organic matter, extremely wet and extremely dry soil, light disease.In the soil, nematodes are mostly concentrated at the junction of dry and wet soil layers, where the soil moisture is good (within 10 cm soil layer), the amount of insects accounts for 99%, and there are few dry topsoil layers.In extreme drought,Waterlogged depressionSerious disease, 14% of which occurred at high altitude,low-lying62%, and more concentrated damage to the underground part, resulting in a particularly serious disease of potato lumps.When there is a lot of rain, the damage will rise in the main vine of susceptible varieties, and the damage will be high, even to the top of the vine.[2]
There are obvious differences in disease resistance among varieties. Some varieties have serious disease of vine, and some varieties have serious disease of vine and tuber.[2]
Prevention and control methods
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Agricultural control
one
Select disease resistant varieties:Screening disease resistant varieties is an effective way with small investment, quick effect and the most acceptable to the masses, and is the main body of integrated control.Fresh sweet potato varieties suitable for planting in Lulong County with disease resistance and high yield can be selectedLongshu No.9, Jizishu 70-47Beijing 553, Xinxiang, Anping No. 1, etc.[4]
two
Strengthen quarantine:The seedlings transferred in and out shall be strictly quarantined and shall not be transferred or purchased from the epidemic area with stem nematode disease.[5]
three
Thoroughly deal with the disease residues and reduce the pathogenic nematodes:Stem nematode is mainly spread by diseased potatoes and vines.In the whole diseased plant, the stem nematode in diseased potato blocks is the most. Although it has been frozen in winter and spring, it can survive.Therefore, in the spring seedling raising period, transplanting period and harvesting and planing period in the affected area, do not leave diseased potatoes, diseased seedlings and vines in the fields or randomly discard them in the ridges, roads, houses, livestock sheds and other places.Clean the countryside in time, collect the diseased and disabled bodies thoroughly, dry them in the sun and burn them or bury them deeply to prevent stem nematodes from entering the soil.In addition, the slurry water after the processing of lightly diseased potatoes should not flow everywhere, but should be concentrated in a fixed slurry pool. The land polluted by diseased slurry water cannot be used as enclosure soil, nor can it be used for seedling beds or planted in fields.[6]
four
Establish disease-free seed reserve land and cultivate disease-free and strong seedlings:Breeding disease-free seed potatoes and cultivating disease-free seedlings are effective measures to control sweet potato stem nematode disease.Choose the place that has not planted sweet potatoes or dried potatoes for more than 3 years as the seed reserve.Replace the seedbed with a new one, and raise seedlings without diseased soil and fertilizer.Select the seed potatoes before going to bed, remove the diseased potatoes (the potatoes with purple or cracked skins and wounds), and then go to bed, and use high cutting seedlings or spring potato vine seedlings.[6]
five
Implement rotation or system reform:Crop rotation for more than 5 years in severely ill areasWheat、Corn、cotton、sesameAnd other crops, but cannot be replantedsoybean、Potato、peanutAnd rice rotation is better in places with water sources.The seriously diseased field of spring potato that cannot be rotated should be changed into wheat sweet potato in summer, or the seed harvest time should be adjusted. The planting of spring potato should be postponed to the middle of May, and the harvest should be advanced to the end of September or the beginning of October to avoid the peak period of stem nematode damage, so as to reduce the disease.[6]
six
Plastic film covering:The optimum temperature for nematode disease development is 25-30 ℃. The cultivation of sweet potato covered with plastic film can raise the temperature. After plastic film covering, it will grow early and prosperously. The number of leaves and the height of the main stem of the seedlings 30 days after planting will enhance the disease resistance of the seedlings.[4]
chemical control
one
Soak seedlings in liquid medicine:Use 50%PhoximEmulsion or 40% methyl isocarbophos emulsion 100-150 times liquid, about 10 cm of the base of the seedlings cut off for planting can be immersed in the liquid for 10 minutes before planting.[6]
two
Poisonous soil acupoint application:5% Ganxianling Granule or 5% Shennongdan Granule of 1-2 kg can be used, and 30 kg of fine dry soil can be added to mix well to make toxic soil. When planting seedlings, 10 g of toxic soil can be applied to each hole, and then irrigation, seedling planting and soil covering can be carried out;3% Miler granules can also be used for acupoint application or soil treatment 10-15 days before planting.[6]
three
Solution irrigation:40%Isophos methylThe emulsion is 0.3-0.5kg, and the water is 1500kg. Before planting, pour 0.5kg diluted liquid into each hole, and then plant seedlings and cover soil.For severely ill areas, the method of soaking seedlings with liquid medicine and irrigating acupoints with liquid medicine can be adopted to achieve better control effect.A new nematicidal drug with high efficiency and low toxicity - sweet potato treasure microcapsule can also be used. The effect on sweet potato stem nematode disease can reach more than 90%, and the toxicity is greatly reduced. It has the advantages of labor saving and simple application.[6]
