Sweet potato root rot is caused by a variety of Fusarium sppSweet potatoDisease.It mainly occurs in the field stage. The disease starts from the tip or middle of the fibrous root, becoming black and necrotic locally, and then extends to the whole root, becoming black and decaying, and spreading to the underground stem, forming brown concave longitudinal crack spots, and the subcutaneous tissue is loose.The internode of aboveground seedling vine is shortened and dwarfed, and the leaves are yellow.The surface of the diseased tubers is rough, covered with dark brown disease spots of different sizes, cracked in the middle and late stages, and the subcutaneous tissue became black.[1-2]
Sweet potato root rot is a serious disease in Shandong, Hebei, Henan, Jiangsu, Anhui, Hunan, Hubei, Shaanxi and other provinces in China.The disease has a great impact on the yield and quality of sweet potato, resulting in yield reduction and quality decline. After the disease is felt, the root and stem of sweet potato become black and rot, and can not form tubers or tubers are few and small. In the light cases, the yield is reduced by 10-20%, in the serious cases, the yield is reduced by 40-50%, or even death in pieces, resulting in no harvest.[1][3]
The practice has proved that comprehensive control measures focusing on breeding disease resistant varieties can effectively control the damage of sweet potato root rot.[2]
Chinese name
Root rot of sweet potato
Foreign name
Sweet potato root rot
Alias
Root rot of sweet potato、Flowering rot、Chicken paw root、Ginger twig disease、Root rot of sweet potato
Sweet potato root rot is caused by many Fusarium species.ChinaPlant Protection Institute of Shandong Academy of Agricultural SciencesIt was identified that the asexual stage of sweet potato root rot pathogen was the specialized type of Fusarium putrescens (scientific name:Fusarium solani(Mart.) Sacc. f. sp.batatasMcclure）。In the natural development cycle, the reproductive organ of the pathogen isConidia。On the artificial culture medium, the mycelium is gray white, in the form of thin fluff to dense fluff or flocculent, and has circular whorls;The culture base is light yellow to bluish green or bluish brown.The small conidia are ovoid, short rod shaped, and most of them are unicellular, with the size of (5.5-9.9) μ m × (1.7-2.8) μ m, and a few have a partition, with the size of (13.2-17.6) μ m × (2.8-4.6) μ m, which are aggregated into a false head, and are born on a bottle shaped peduncle.The small conidiophores are long, (24-31.2) μ m × (2.9-3.6) μ m in size, with few branches.At the top of each branch, there are one to several bottle shaped small stems with slightly narrow top, which are (43.2-52.8) μ m × (1.9-2.6) μ m;Large conidiophores are short, (15.6-21.6) μ m × (2.4-2.9) μ m, with lateral bottle shaped small stems（Sporogenous cell）, the size is (25.2-31.2) μ m × (1.9-2.4) μ m.MegaconidiumSpindle shaped, the second and third cells in the upper part are the widest, with thick walls and obvious separation. The apical cells are round or beaklike, with 3-8 separations, mainly 5 separations, which are generally (48.4-59.4) μ m × (4.4-5.6) μ m.Myxospores are light beige, cheese yellow or dark blue-green.ChlamydosporeIt grows on lateral hyphae or large conidia, and is solitary or twin, spherical or oblate.There are two types of chlamydospores, one is smooth surface, with a diameter of 7.1-11 μ m;The other has warty projections on its surface, with a diameter of 9.1-12 μ m.sclerotiumIt is grayish brown to grayish purple, flat spherical, with a diameter of 0.5-1 mm. It is born on the medium of steamed rice or potato tubers, and has no smell.[2]
The sexual stage is (scientific name:Nectria haematococcaBerk. et Br.）。The role of sexual generation in the infection cycle is unclear.According to the experiment and investigation of Shandong Academy of Agricultural Sciences, under the natural conditions in the field, the disease has not been found on the plantAscus shellHowever, artificial induction can produce a lot.It was proved to have strong pathogenicity by root and soil inoculation.The ascus shell is irregularly spherical, beginning with light orange, the surface of the shell is smooth, gradually turning red to brown, and the surface produces verrucous protrusions, and finally turns light brown.There is light yellow jelly on the surface of the ascus. The diameter of the top orifice is 59.8-82.8 μ m, with stripes, light color, transparent, slightly protruding. The ascus is generally (289.8-349.6) μ m × (276-303.6) μ m.The ascus is stick shaped, (62.4-72) μ m × (7.2-8.4) μ m, 8 endogenousAscospore。The ascospore is oval, (12-14.4) μ m × (4.8-6.0) μ m, with a partition in the center, slightly constricted at the septum, transparent, then light brown, with longitudinal stripes.[2]
Harmful symptoms
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Seedbed stage
The diseased potato seedlings have light yellow leaves, slow growth, and dark brown spots on the tip and middle of fibrous roots.The emergence rate was significantly reduced due to late emergence.[2]
Field stage
root system, tubers, stems and leaves have obvious symptoms.[2]
one
root system:The root system is the main infection site of the bacteria, and it begins to form dark brown spots from the absorption root, root tip or middle part, and then most of the roots become black and rotten.The underground stem is also infected, forming black spots, most of the epidermis of the diseased part is split, and the subcutaneous tissue is black and loose.The roots of the seriously diseased plants are all rotten;If the disease is mild, new roots can still grow from the underground stems near the soil surface, but most of them form firewood roots and do not form tubers.Some diseased plants even have tubers, but the tubers are few and small.[2]
two
Stem and leaf:The stems and tendrils of the diseased plants elongate more slowly than those of the healthy plants, with many branches and wilting when exposed to sunlight.When the temperature drops in autumn, the stems and vines can continue to grow, but buds can blossom in the axils of each leaf.The internode of the seriously diseased plant is shortened, from the bottom leaf to the top, the leaves turn pale and yellow in turn, the leaves shrink, thicken and roll back.In case of drought, the edges of the leaves are often scorched and fall off early, leaving only two or three young leaves on the top of the vine until the whole plant dies, forming large dead seedlings.[2]
three
Potato chunks:After being infected, abnormal potato blocks such as large intestine type and gourd type were formed.There are brown to dark brown spots of different sizes on the surface, which are mostly round and slightly sunken. The epidermis does not break at the initial stage, but it cracks vertically and horizontally in the middle and later stages, and is easy to fall off. The subcutaneous tissue becomes black and loose. A new layer of epidermis can be formed at the junction between the bottom and the healthy tissue.The disease spot does not expand during storage.Sick potatoes do not harden the heart, and there is no odor when cooked.[2]
Root rot of sweet potato
Infection cycle
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Root rot is a soil borne disease, and the infected soil is the main source of initial infection in the next year.The survival years and bacterial forms of pathogens in soil are still lack of in-depth research. It is speculated that a considerable part of pathogens can survive in soil for at least 4 years from the situation that the plots can continue to suffer from disease after 3-4 years of rotation.In the soil, the vertical distribution of pathogenic bacteria can reach 100 cm of soil layer, but the density of cultivated soil is the highest.[4]
The diseased seed tubers are the primary source of infection of potato seedlings in the seedbed and field in the sweet potato nursery areas in northern China and the fields where the egg is laid on the muskmelon directly planted with seed tubers.The diseased seed tuber not only carries bacteria in the tissue, but also the pathogenic effect of the bacteria carrying soil attached to its surface is very important.In the seedling stage, diseased soil as a bed and diseased fertilizer as a brew can lead to disease of seedlings.Due to the growing commercialization of seed potatoes and seedlings, diseased seed potatoes and diseased seedlings are the main media for long-distance transmission.The sewage from diseased soil washer, diseased residue and pickled sweet potato dry enters into manure and organic fertilizer, which can make these fertilizers become an important source of initial infection.In one area, a few fields often expand rapidly to other fields after the disease, which is closely related to the spread of fertilizer borne bacteria.[4]
A large number of experiments have proved that the dried sweet potato in the disease area is infected with bacteria.Because the root of sweet potato can be infected, the potato chips cut into pieces and dried in the sun are naturally infected. In addition, most farmers cut in situ and dry in the sun when harvesting, and the surface is also contaminated with diseased soil, becoming a state of both internal and external bacteria.Dried potatoes must be pickled before being eaten, and sewage with fungus can enter the field through contaminated fertilizers and other channels.Potato is an important commodity grain in sweet potato producing areas. With large market exchange volume and long-distance transportation, it is one of the important transmission channels.[4]
Epidemic law
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The root rot of sweet potato is serious under high temperature and drought conditions.The susceptible variety Shengli 100 was more serious than other varieties;Summer potato is more important than sweet potato, and continuous cropping land is more important than rotation land;Late planting is more important than early planting;Sandy barren land is heavier than loam fertile land.[2]
Relationship between temperature and humidity and pathogenesis:The onset period of sweet potato root rot disease in Shandong Province of China is about 20 days after planting of spring potatoes and 10 days after planting of summer potatoes. The peak period of the disease is from late June to August. After the middle of September, the disease is alleviated with the decline of air and temperature.The onset temperature is 21-30 ℃, and the appropriate temperature is about 27 ℃.The soil moisture content below 10% is favorable for the disease;On the contrary, if the rain is harmonious or the soil is wet, the disease will be alleviated.[2]
Relationship between variety and disease:No immune varieties have been found for root rot of sweet potato, but there are obvious differences in resistance among different varieties.The root susceptibility index of Nanjing 92 was 10, and the fresh potato yield per mu was 1700kg;The disease susceptibility index of a litter of red roots is 7.5, and the yield of fresh potatoes per mu is 1932.5 kg;The root susceptibility index of Shengli 100 was 76.3, and the fresh potato yield per mu was only 146.25kg.In the same severely diseased area, the yield difference is 10.6-12.5 times due to different disease resistance of varieties.[2]
Relationship between continuous cropping and morbidity:The disease of rotation is light, and the disease of continuous cropping is serious. The longer the continuous cropping years, the more the tax burden of disease and disability in the soil, the higher the amount of bacteria in the soil, and the more serious the disease.[2]
The relationship between soil quality, soil fertility and disease:According to the survey, the disease is more serious in dry and thin hilly land and barren sandy land, while the disease is less serious in fertile plain soil.Increase fertilizer application, improve soil fertility, and strengthen field management. The disease of field managers is relatively alleviated.[2]
Relationship between different seedling planting stages and disease incidence:The incidence of spring potato is light when planted early, but heavy when planted late.In the central Shandong area of China,grain rainBefore and after planting seedlings, the disease was light and the yield was high;Beginning of summerAlthough the disease of planting is mild, it affects the yield,grain fulltoAwn seedThe disease is serious and the yield is low.Because the temperature of early planting is low, it is not conducive to the infection of pathogens, but is beneficial to the early rooting and early returning of sweet potatoes.When the temperature gradually rises, the root system of sweet potato has basically formed and is less affected by further damage.The late planted potato seedlings immediately encountered high temperature, and the root system was infected by the pathogen just after it was extended, which also caused heavy damage.The incidence of summer tubers is more serious than that of spring tubers, which is also related to temperature.[2]
Prevention and control methods
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one
Select disease resistant varieties:Select disease-free tubers as seed potatoes.High yield and disease resistant varieties mainly includeShangshu 19、Xushu 18Yushu 13, Xiaoshu 3Lushu No.3、Lushu No.4、Lushu No.7, short vine sweet potato, Wan84-559, etc.The disease resistance of varieties tends to weaken with the extension of planting years. Therefore, attention should be paid to the purification and rejuvenation every year, and species and seedlings with shorter service life should be selected.[3]
two
Increase application of organic fertilizer and potassium fertilizer:Plant early at the right time, plant disease-free seedlings, deeply renovate the soil, apply more organic fertilizer and potassium fertilizer, and water at the right time.At the same time, strengthen field management to improve the disease resistance of plants.[3]
three
Crop rotation:Avoid continuous cropping or continuous cropping with tomato, pepper, potato and other crops.The longer the continuous cropping years, the more bacteria in the soil, and the more serious the disease.The rotation of sweet potato, peanut, cotton, sesame, corn, sorghum, etc. has a better effect of disease prevention and production assurance.The number of years of rotation depends on the degree of disease.According to the experiment, there are still different degrees of disease in the diseased areas with 3 years of rotation.Therefore, the rotation years of seriously ill plots should be appropriately extended.[3]
four
Clean the countryside and eliminate fecal diseases:Usually, the diseased plants in the field will be collected on the spot and buried or burned.When harvesting, the diseased potatoes and seedlings and vines in diseased areas shall be properly treated.It is strictly prohibited to throw diseased potatoes or compost them everywhere.[3]
five
Establish "three no seed" land to prevent seedling disease transmission:Establish disease-free seedbeds (use disease-free soil, apply bacteria free fertilizer, select disease-free, injury free, and freeze free seed potatoes), and soak seeds and seedlings in combination with the prevention and control of sweet potato black spot;Select disease-free plots to establish disease-free nursery and disease-free reserved seed fields (select disease-free plots and plant disease-free seedlings) to cultivate disease-free seed potatoes.[3]
six
Chemical control:① Seed potato disinfection: 50%CarbendazimSoak seed potatoes in 500 times liquid of wettable powder or 600 times liquid of 70% thiophanate methyl for 3-5 minutes, soak 10 tons of seed potatoes in 1 kg liquid, and dry them in the cellar. ②Disinfection by medicament soaking: 70%Thiophanate methyl600 times solution or 50% carbendazim 250-300 times solution, dip in the base of the potato seedlings 6-10 cm deep for 2-3 minutes. ③Root irrigation: 96%OxamylinRoot irrigation and soil treatment with 3000 times liquid medicineBlack spot of sweet potatoThe control effect is good.[3]
Grading standard
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Grading standard of sweet potato root rot
Grade
Overground
Underground
Illustration
Level 0
No symptoms
The tubers are normal and disease-free
Grading standard
Level 1
Leaf color is slightly yellow, others are normal
Individual roots turn black (the number of diseased roots accounts for less than 10% of the total number of roots), the underground stem has no disease, and has no obvious effect on tuber formation
Level 2
The branches are few and short, the leaves are significantly yellow, and sometimes buds or flowers appear
A few roots turn black (the number of diseased roots accounts for 10-25% of the total number of roots), underground stems and tubers have individual disease spots, which has a slight impact on tuber formation
Level 3
Plant growth stagnates, significantly dwarfs, does not branch, and old leaves fall off from bottom to top
Nearly half of the roots turn black (the number of diseased roots accounts for 25-50% of the total number of roots). There are many diseased spots on the underground stems and tubers, which have a significant impact on the tuber formation, including firewood roots
Level 4
Whole plant death
Most roots turn black (the number of diseased roots accounts for more than 50% of the total number of roots), and the underground stems have many and large disease spots, no tubers, or even die
