Research Progress of Diseases on Atractylodes lancea

Ruiling LU, Shi CHEN, Baosheng DAI, Siqi XU, Jie WANG, Shuang AN, Qian ZHAO, Zitong ZHAI

1. College of Biology and Agricultural Resources, Huanggang Normal University/Hubei Key Laboratory of Economic Forest Germplasm Improvement and Resources Comprehensive Utilization/Hubei Collaborative Innovation Center for the Characteristic Resources Exploitation of Dabie Mountain, Huanggang 438000, China; 2. Huanggang Academy of Agricultural Sciences, Huanggang 438000, China

Abstract According to the current situation of diseases on Atractylodes lancea, the etiology, pathogenesis, symptoms and control methods of root diseases, leaf diseases and other diseases of A. lancea are analyzed, in order to provide a reference for the diagnosis and control of diseases on A. lancea.

Key words Atractylodes lancea; Disease; Control

1 Introduction

Atractylodeslancea(Thunb.) DC., a perennial herb of Compositae, is one of the most commonly used bulk medicinal materials, mainly distributed in Northeast, Northwest and North China. The dried roots and stems are used medically, which have high medicinal and economic value, such as drying dampness and invigorating spleen, removing wind and dampness[1]. Modern medical research has found thatA.lanceahas pharmacological activities such as immune regulation, antibacterial, anti-osteoporosis and anti-tumor, and has great potential in the development of new drugs[2].Atractylodesplants are mainly composed of three branches:A.carlinoides,A.macrocephalaandAtractylodescomplex (A.japonica,A.coreana,A.lancea,A.lanceasubsp.luotianensis,A.chinensis,etc.)[3].

In recent years, with the development of traditional Chinese medicine industry,A.Lanceahas become a popular medicinal plant in China. However, due to the deterioration of ecological environment and artificial excessive mining, current wild resources can hardly match the market demand. At present,A.lanceahas been artificially cultivated intensively in large scale, but there are many problems such as high morbidity and heavy damage in production. Disease is a major problem restrictingA.lanceacultivation. Among the existing researches, there are many researches on individual diseases ofA.lancea, but few systematic researches on diseases ofA.lancea. Therefore, it is necessary to investigate the research progress of diseases onA.lancea, so as to facilitate the diagnosis and control of diseases in the field.

2 Root diseases

2.1 Southern blightSouthern blight ofA.lanceais caused bySclerotiwmrolfsii[4]. Huang Junbinetal.[4]put forward that southern blight can occur throughout the growth period ofA.lancea, which mainly infects the rhizome ofA.lancea. In the initial stage of incidence, there are no obvious symptoms in the aerial part of plants. As the disease worsens, the diseased part of plants will turn brown and rot into rotting hemp, eventually leaving only fiber bundle, but no odor, while the leaves are gradually atrophied and dead, but not easy to fall off. When the humidity in the environment is high, the mycelium will penetrate the surface of the soil, grow in the base of plants and surrounding soil and leaf litters, forming rapeseed-like beige to brown sclerotia.

Southern blight ofA.lanceapeaks from early June to middle August. The fungus survives the winter as sclerotia in soil, seedlings or debris. The fungal mycelium can proliferate in soil crevices and soil surface, and will further infect other plants under water flow and artificially mediated cases[4].

2.2 Root rotAccording to the studies of Huo Jiahuanetal.[5], Tang Guitingetal.[6], Zang Shaoxianetal.[7]and Cai Linetal.[8], root rot ofA.lanceamay be caused by different types of pathogenic fungi due to the difference of origin, which makes the pathogens causing root rot more complex. Based on the existing researches on root rot ofA.lancea, it is found that root rot is mainly caused by complex infection of multiple pathogens, among whichFusariumoxysporumandMacrophominaphaseolinaare the main causes.

According to the research of Liu Fan[9], root rot can occur throughout the growth period ofA.lancea. In the initial stage of incidence, there are no obvious symptoms in the aerial part of plants, while some taproroots and fibrous roots turn brown and decay, and plants will develop restorable wilt in the afternoon. In the late stage of incidence, the lesions on taproot will expand, and the diseased parts spread from root to stem, with lesions and rots on the stem. The plant vascular bundle system is atrophied and dried up, which makes the plant wilt and even die due to lack of water.

Root rot ofA.lanceausually starts in middle May, peaks in June and July, and stops spreading in September. Climatic condition is one of the important factors determining the occurrence of root rot. High temperature, high humidity and poor soil drainage are conducive to the occurrence of root rot, and the wounds of plant roots and other parts are more conducive to the infection of the fungus.

2.3 Sclerotinia rotSclerotinia rot ofA.lanceais caused by the fungusSclerotinianivalis[10]. According to the studies of Zhou Rujunetal.[10]and Xu Haijiaoetal.[11], sclerotinia rot mainly harms the root and stem base ofA.lancea. In the initial stage of incidence, the roots and stem bases appear brown to black brown plaques and rot, and cortical decay is prone to expose fibrous tissue, while there is no significant difference at the junction of healthy and diseased part. In the late stage of incidence, when the humidity is heavy, mycelia will grow in roots and nearby soil to form black sclerotia. The old mature leaves at the bottom of infected plant will begin to turn yellow and wilt, and then gradually spread upward, eventually causing the death of the plant.

Sclerotiniarot ofA.lanceagenerally starts to occur in early and middle April in Liaoning, and enters the peak occurrence period from late April to May[11]. Because sclerotinia rot can still grow normally at a low temperature, it often occurs in early spring when the temperature is lower. Rainfall, humidity and root wounds are all conducive to the infection ofS.nivalis.

2.4FusariumwiltFusariumwilt ofA.lanceais mainly caused byFusariumsolaniandF.equiseti[12-13]. According to the studies of Xu Youguietal.[12]and Wei Mengdi[13], it is found that in the early stage of incidence, the lower leaves are chlorotic, and the symptom spreads from bottom to top. The infected leaves turn yellow and die, but do not fall. In the late stage of incidence, the vascular bundles of plants will turn brown, and flocculent white mycelia can be seen on the surface of lesion.

The first infection ofFusariumwilt ofA.lanceagenerally occurs in May and lasts till late September[14], and the fungi generally survive the winter in soil and debris. Wind, rain and plant wounds are conducive to the infection ofFusariumsp., and they also easily invade from plant wounds or roots.

2.5 Sheath blightSheath blight ofA.lanceais caused byRhizoctoniasolani[15-17]. The studies of Zhang Jiaxingetal.[15], Chen Yueetal.[16], Oliul Hassanetal.[17]and Wu Yunetal.[18]show that sheath blight mainly occurs in the seedling stage and mainly affects the rhizome ofA.lancea. In the initial stage of incidence, yellow spots appear at the base of stem. As the disease progresses, brown lesions form up and down the vascular bundle along the stem, and branches and leaves are partially withered. In the late stage of incidence, lesions gradually spread and merge with each other around the stem, resulting in total wilting of aboveground part of the plant, and the diseased plant is easily broken from lesions.

Sheath blight ofA.lanceabegins from late March to early April, peaks from late April to early May, and gradually decreases after June. The fungus generally survives the winter in soil. Wind and rain, humidity, soil quality and plant condition will affect the infection ofR.solani.

2.6 Soft rotSoft rot ofA.lanceais caused byErwiniacarotovorpv.caratovora[19], and it is the only bacterial disease reported inA.lancea[20]. According to the studies of Zheng Lietal.[19]and Xu Xiaobinetal.[20], it is found that in the early stage of incidence, the aboveground part has no obvious manifestations, and its root hairs become brown and decay. As the disease progresses, the diseased part gradually spread from root to taproot and aboveground part. In the late stage of incidence, the vascular bundle of infected plants become brown and lose the function of water transport, and the leaves gradually wither and die. The root rot of infected plants presents paste or bean curd residue, accompanied by sour odor[12].

Soft rot ofA.lanceagenerally begins in June and gradually weakens by middle October. The bacterium survives the winter mainly in soil and debris. If there are abundant precipitations during the growth season ofA.lancea, with the average temperature around 27 ℃ and the relative humidity of 90%, the disease will occur severely.

3 Leaf diseases

3.1 Black spotBlack spot ofA.lanceais caused byAlternariaNees[21]. According to the studies of Wang Yixunetal.[21]and Wang Junbinetal.[22], black spot mainly harms the leaves ofA.lancea. In the initial stage of incidence, the disease starts from the leaves at the base of stem, and then spreads upward gradually with the development of the disease. The disease spots generally occur from leaf tip or leaf margin, showing dark brown round or irregular shape. In the late stage of incidence, lesions spread contiguously, and the leaves are grayish brown or black brown, and finally die and fall off.

Black spot ofA.lanceagenerally starts from middle and late May, and climate factor is a major factor leading to black spot[22]. When the average temperature is about 26 ℃ and the relative humidity is above 90%, the incidence is severe, so it is more likely to cause black spot in the plum rain season.

3.2 Grey spotGrey spot ofA.lanceais caused byCercosporaatractylidis[23]. According to the research of Fu Junfan[23], grey spot mainly harms the leaves ofA.lancea. In the incidence stage, round spots, about 2-4 mm in diameter, are formed in the leaves of infected plants. The lesion is grayish white in the middle and dark brown in the margin, attached with black grey mold layer.

Grey spot ofA.lanceagenerally survives the winter in debris and weeds in the field, and overwintering fungi will produce conidia in the next year to cause primary infection. The fungus will infect plants with the help of wind, rain, water flow and other factors[23].

3.3 Rot spotRot spot ofA.lanceais caused byPanaxexigua[24]. According to the study of Zhang Jiaxingetal.[24], in the initial stage of incidence, approximately round brown spots of different sizes will be produced on leaves, and chlorosis will occur at the edge of spot. The vein can limit the spread of spots, and there is a narrow yellow halo at the junction of healthy and diseased part, which is gray white in the center and brown in the margin. In the late stage of incidence, the leaves will dry up and fall, and as the disease gradually worsens, the leaves of the whole plant will dry up and fall.

Rot spot ofA.lanceagenerally starts from late April to early May, peaks from June to August, and gradually decreases after September. The factors affecting rot spot ofA.lanceaare mainly related to temperature and humidity, and if the affected field is not properly cleaned and disinfected, there will be a higher incidence.

3.4 Ring spotRing spot ofA.lanceais caused byAscochytasp.[12]. Xu Youguietal.[12]put forward that ring spot mainly infectsA.lanceaseedlings. In the initial stage of incidence, there will be attached small black spots on both sides of veins. In the late stage of incidence, the lesions gradually spread and form yellow brown wheel-shaped plaques. Eventually, the plaques attach to each other, causing dried leaves, but the leaves do not fall off.

Ring spot ofA.lanceagenerally starts in late May and peaks from June to August. When the average temperature is about 28 ℃ and the relative humidity is 90%, the incidence of ring spot is the most serious.

3.5 AnthracnoseAnthracnose ofA.lanceais caused byColletotrichumatractylicola[25-26]. According to the study of Xu Haijiaoetal.[11, 25], anthracnose mainly harms leaves and can also damage calyx. In the initial stage of incidence, round or irregular brown plaques are formed, with obvious boundary between healthy and diseased part. As the disease progresses, the lesions spread, merge, and become slightly concave, presenting dark brown color. Acervulus appears on the surface of mature lesions, and a large number of red clay masses, namely conidial masses, appear on the lesions under high humidity. In the late stage of incidence, the leaves become yellow, wilt and fall off. The young leaves and calyx at the top ofA.lanceacan also be infected.

Anthracnose ofA.lanceapeaks from August to September. Temperature and humidity are the main environmental factors that significantly affectC.atractylicola. When the optimum temperature is 28 ℃ and the relative humidity is 100%, it is more conducive to spore germination, appressorium formation and lesion spread.

3.6 Leaf spotLeaf spot ofA.lanceais caused byParaphomachrysanthemicola[11, 27-28]. According to the studies of Ge Xinxinetal.[28], Zhang Yingyingetal.[29]and Fan Huiyanetal.[30], leaf spot mainly harms leaves, and a few can also harm petiole and stem. In the initial stage of incidence, round or irregular dark brown lesions with an off-white center are formed. As the disease progresses, the lesion spread and merge, with scattered small black spots on both sides of the leaf. In the late stage of incidence, the leaves are dry and the stems are necrotic, with lesions on stem and petiole.

Leaf spot ofA.lanceadevelops in early June, peaks from middle July to middle August, and gradually decreases after middle October.P.chrysanthemicolasurvives the winter in debris or on soil surface, and spreads mainly relying on wind and rain. Higher relative humidity and temperature are more conducive to the occurrence of the disease.

3.7 Spot blightSpot blight ofA.lancea, also known as leaf blight, is commonly known as "iron scorched leaf"[18, 31]. According to the studies of Wu Yunetal.[18]and Huang Ligangetal.[31], spot blight mainly infect the leaves ofA.lancea, and can also infect stem and flower bud. In the initial stage of incidence, yellow or brown round or irregular lesions appear on leaves. The disease starts from the lower leaves ofA.lancea. In the late stage of incidence, the lesions are grayish white in the center, with a large number of black dots. The lesions will spread and merge, resulting in iron black leaves, and similar brown lesions are also produced in stem and bract.

Spot blight ofA.lanceastarts in late April, and reaches the peak from June to August untilA.lanceaharvest. The pathogen mainly survives the winter in debris, and spread rapidly under suitable temperature and humidity. Rain and farming activities are also conducive to the spread of the pathogen.

3.8PhytophthorablightPhytophthorablight ofA.lanceais caused byPhytophthoradrechsleriandP.cryptogea[32-33]. According to the study of Kimetal.[32], it is found that in the early stage of incidence, the plants show external characteristics such as yellow appearance and slow growth. The stems of infected plants are dark brown or black and gradually become soften and rot as the disease progresses. In the late stage of incidence, dark brown to black lesions are observed in rhizomes, petioles and lower leaves, and finally make the plants wither and die[33].

Phytophthorablight ofA.lanceareaches the peak occurrence from early May to September. The pathogens can spread rapidly under suitable temperature and humidity. Heavy rainfall and high humidity in the field will lead to increased incidence of infected fields.

4 Other diseases

4.1 Root-knot nematodeRoot-knot nematode ofA.lanceais caused byMeloidogyneincognita[34]. In the early stage of incidence, nodules of different sizes appear on the fibrous root of seedlings, including eggs in brown female worms. After the fibrous roots are damaged, sarcomas show brown rot cavities[34]. In the late stage of incidence, the fibrous roots gradually decay and fall off, and rhizome spores are in a dwarf state[34]. The seedlings are in abnormal growth stage, showing slow growth, deformity, or yellow withered leaves, atrophied and dead plants in severe cases. The infected adult plants are characterized by dwarf plants, small leaves, abnormal development of flower buds, shriveled or unable to bear seeds normally. In severe cases, the lower leaves of the plant drop and the flower buds wilt[34-35].

Root-knot nematode ofA.lanceadevelops in middle and late April after the eggs are hatched, and gradually decreases in July and August when the soil temperature increases. Southern root-knot nematode mainly survives the winter as eggs or female worms in soil or debris. When the temperature is about 13 ℃, the eggs will hatch, and the females will drill into fibrous roots ofA.lancea, forming nodules. When the soil temperature is high and the soil water content is lower than 10%, root-knot nematode significantly decreases. Moreover, nematodes have a small range of activity and limited transmission routes.

4.2 Virus diseaseA.lanceavirus disease is mainly caused by complex infection of BBWV2 and CMV[36]. Virus disease is mainly manifested as whole-plant mosaic disease[36]. The infected plants generally have lesions of the same shade of green, and the leaf veins are wrinkled and deformed, leading to uneven leaves. The overall plant shows the symptoms of slow growth, dwarf plants and increased branching[36].

A.lanceavirus disease is transmitted mainly by insects such as aphids that feed with piercing-sucking mouthparts. It can also be transmitted by rubbing of diseased leaves of infected plants against healthy leaves. Plants are also more susceptible to virus disease when there are small wounds on the leaves.

5 Disease control

5.1 Agricultural controlFor agricultural control,A.lanceashould be cultivated on sloping land as far as possible, rather than hot, strong light and damp land. Before cultivatingA.lancea, soil also needs to be properly treated in advance. Adjustment of appropriate soil pH and other factors is conducive to the growth ofA.lanceaand prevention and control of diseases.

Healthy and disease-freeA.lanceaseedlings should be selected before cultivation, which should be properly disinfected before transplanting. In the cultivation process ofA.lancea, it is necessary to keep the field clean without weeds as far as possible, and ensure rational use of fertilizer and appropriate application of phosphate potassium fertilizer, so as to improve the resistance ofA.lancea. Timely irrigation and drainage is conducted to promote normal and healthy growth of plants. Meantime, debris and infected plants must be concentrated and burned.

Soil microorganisms and insect communities are also important factors affecting the growth ofA.lancea. WhenA.lanceais continuously cropping, the incidence of plants will increase significantly, and these causes can be attributed to replanting diseases. Because continuous planting will lead to changes in soil microorganisms and insect communities, resulting in reduced diversity and richness of bacteria, reduced richness and increased diversity of fungi, and also promote the proliferation of some insects[37-40]. Therefore, reasonable crop rotation and improvement of soil microbial structure are conducive to increasing soil nutrients, thus promoting the absorption of nutrients by plants[41]. Moreover, whenA.lanceais intercropped reasonably, it can inhibit the proliferation of pathogenic fungi in soil, significantly increase the number of bacteria in soil, especially the number of gram-negative bacteria, which not only reduces the accumulation of phenols in the rhizosphere ofA.lancea, but also has great potential for inhibiting fungal diseases[42-43].

Reasonable selection of cultivation site, screening ofA.lanceaseedlings, and reasonable management, crop rotation or intercropping during cultivation can effectively prevent the occurrence of diseases and insect pests.

5.2 Chemical controlThe application against leaf diseases ofA.lanceais more flexible. Spraying thiophanate methyl or carbendazim at seedling stage can effectively prevent diseases onA.lancea. If it is necessary to deal with diseases that are insensitive to traditional drugs, such as black spot, 500 g/L iprodione SC 1 000 times dilution can be used in the initial stage of incidence, which can effectively control the incidence rate[20].

Drugs with low toxicity and low residue must be used to control root diseases ofA.lancea, so as not to affect the quality ofA.lancea. For common root diseases, thiophanate methyl can be used, which has better control effect[20]. Carbendazim can also be used to treat common root diseases.

For root-knot nematode, the fibrous roots ofA.lanceacan be treated before cultivation to remove the gall on fibrous roots, and soaking in fosthiazate can also play a preventive role.

At present, the plant protection policy of "prevention first and comprehensive control and prevention" is advocated in the prevention and control of diseases and insect pests. The use of chemical agent inA.lancea, as a medicinal plant, should be very cautious if chemical control is adopted, so as not to affect the quality ofA.lancea. As a new control means, proper biological control method can better ensure the quality ofA.lancea.

5.3 Biological controlBiological control refers to the use of beneficial microorganisms and their metabolites or plant active ingredients to control the occurrence of diseases[44]. As medicinal materials, the quality and quality of Chinese medicinal materials are particularly important, so it is necessary to take many aspects into account in the process of disease and insect pest control. Biological control is safe and effective, so it is an excellent choice for Chinese medicinal materials to control insect pests and diseases.

People pay more and more attention to the research and application of microbial fungicides. The microorganisms used vary with different microbial fungicides, which can be divided into three categories: biocontrol bacteria, biocontrol fungi and biocontrol actinomyces.

The action mechanisms of biocontrol bacteria against root rot mainly include antagonism, competition, induction of plant resistance and promotion of plant growth[45]. In the current application of biocontrol bacteria, the most widely used bacteria areBacillusandPseudomonas. Because of strong stress resistance and reproduction ability, as well as stable morphological structure and environment-friendly characteristics,Bacillushas incomparable advantages over other biocontrol bacteria in the field of biological control[46]. In terms of biocontrol fungi, the fungi that have been developed into biocontrol pesticides includeConithyriumminitans,Streptomycetaceae,Gliodadium,F.oxysporum,Trichoderma,etc.[47].Trichodermais often used in daily agricultural production to control soil-borne diseases of medicinal plants or to improve soil varieties. For example,Trichodermabrevicompactumis used to regulate soil microbial communities and inhibit pathogenic bacteria to control root rot ofA.lancea[48-49]. At present,Streptomycesis the most common biocontrol actinomyces. The use of actinomyces in Chinese herbal medicine can be traced back to 1978, earlier than biocontrol bacteria and fungi, and it is also a good biocontrol pesticide.