Rong SONG,Kai DENG,Xiaoqi ZHU,Jiamin ZHOU,Liang CAO

Institute of Agricultural Biological Resources Utilization,Hunan Academy of Agricultural Sciences,Changsha 410125,PRC

Atractylodes macrocephalais a genus ofAtractylodesin the family of Compositae,whose roots perform excellently in invigorating spleen and supplementing qi,dispelling dampness and promoting diuresis, miscarriage prevention,hidroschesis,and treat spleen and stomach qi deficiency,vomiting,diarrhoea,threatened abortion,edema of pregnancy and leucopenia,well[1-3].

Atractylodes macrocephalaprefers cool,dry,and shady places.Pingjiang County,Hunan Province is cool in summer and warm in winter,characterized by mountain microclimate and plate-shale soil structure.Hence,it is a place suitable forAtractylodes macrocephalato grow.According to historical data,artificial cultivation of the plant has a history of 400 y and the major producing areas include Longmen,Sanyang,Anding,Jiayi,Changshou,and Zhongdong.In accordance with Compendium of Materia Medica,it is said that the thin and yellowAtractylodes macrocephalais just from Mufu Mountains.

Modern medicine has demonstrated that roots ofAtractylodes macrocephalaare abundant with atractylon,atractylenolide,and vitamin A,and volatile oils ofAtractylodes macrocephalain Pingjiang County is as high as 1.32%,so thatAtractylodes macrocephalais famous as“Southern ginseng”.Due to excellent quality,Atractylodes macrocephalain Pingjiang County is exported to Southeast Asia,America,and Japan,besides domestic markets.It is obvious thatAtractylodes macrocephalaindustry has become an important way for farmers to increase incomes.Nevertheless,during planting process,because of successive cropping obstacle,both of yield and quality ofAtractylodes macrocephalaare declining,which dramatically discourage farmers.In the research,therefore,on basis ofAtractylodes macrocephalaplanting in Pingjiang County,causes and damages of successive cropping obstacle were analyzed in order to provide ref-erences for overcoming the obstacles and promoting sustainable development ofAtractylodes macrocephalaindustry in Pingjiang County.

Definition of Successive Cropping Obstacle

In a narrow sense,successive cropping obstacle means to plant the same crop in the same space successively and in a broad sense,it means to plant the same crop or the crop infected with the same pathogenic bacteria or nematode.When the same crop or relative crop is planted successively,some problems occur,such as diseases’or insects’damages,deteriorating growth,declined quality and yield,under normal management,which is called successive cropping obstacle.

Damages of Successive Cropping Obstacle on Atractylodes macrocephala

Serious damages on growth and development

It is researched that succession planting prevents plants from growing and developing,especially for roots,reduces leaf area index and chlorophyll content,resulting in decrease of waterand nutrients absorbed by plants,and of photosynthetic rate[4-5].

Xuet al.[6]explored succession cropping ofAtractylodes macrocephalaand maize and the results showed that seedling mortality rate reached 79.33%in the treatment with succession cropping,but the rate was just 15.33%in the treatment with succession cropping,supplemented by irrigation and mulching.Furthermore,plant height in the treatment was 51.04 cm in the treatment guided by crop rotation,and 33.19 cm in the treatment by succession planting;crown diameter in the treatment was 35.47 cm in the treatment guided by crop rotation,and 20.82 cm in the treatment by succession planting;fresh weight per plant was 3.7 times in the treatment guided by crop rotation as high as that by succession planting.It can be concluded that succession planting ofAtractylodes macrocephalaadversely affects growth and development,biomassand yield ofAtractylodesmacrocephala.

Frequent diseasing of Atractylodes macrocephala

Southern blight,root rot,damping off,rust disease,black spot,mosaic disease,and bacterial wilt are common diseases occurring during growth period ofAtractylodes macrocephala,of which damping off in seedling stage and southern blight and root rot in adult-plant stage dominate[7].

Specifically,damping off is a disease caused by a number of different pathogens that kill or weaken seeds or seedlings before or after germination.It is most prevalent in wet and cool conditions.In early spring,Atractylodesmacrocephalaseedlings are prone to diseasing,when seedlings grow slowly.What’s more,succession planting with a long history or preceding crop provides a suitable condition forAtractylodes macrocephalato be diseased[8].

Southern blight is a fungal disease caused by the plant pathogen Sclerotium rolfsii of deuteromycotina,affecting plant roots and stems.It is most prevalent in wet and hot conditions.It is notable that sclerotium overwinters mainly on soils or plant residues,and the infestation maintains 5-6 y on soils.Hence,the diseased plant residues at succession planting would accumulate much pathogeny,deteriorating plant disease[9].

Root rot is a soilborne disease mainly affecting vascular bundles.It is caused byFusarium oxysporumof deuteromycotina,and mycelium would overwinterthrough seedlings,soils and diseased plant residues,becoming primary source of infection in following year.The germs would propagate by wind,rain,underground insects and agricultural activities,invading vascular bundle through lacerations made by insects and mechanical injuries,and then vascular bundles may brown and decay.Finally,only residual wood fiber and chippings are left.It is notable that more rainfalls and high relative humidity are major causes of root rot.

“Longye” is a common disease caused by Septoria atractylodis of deuteromycotina,affecting leaf,and stem,which would reduceAtractylodes macrocephalayield.The germs overwinter on plant residuals or petioles in the forms of pycnidium and mycelium,becoming a primary infection source in following year.It is notable that the disease usually lasts longer and is most prevalent in rainy days.

Deteriorating quality of Atractylodes macrocephala

The quality of traditional Chinese medicinal materials is a deciding factor of clinical effects and it is researched that succession planting of medicinal plants would reduce polysaccharide and saponin in plants,resulting in declining of plant quality[10-11].In processing process ofAtractylodes macrocephala,because of succession planting,plant growth would be affected,including reduction of biomass and insufficient nutrient supply,resulting in decreases of lactone,atractylon,and polysaccharide ofAtractylodes macrocephala.

Causes of Successive Cropping Obstacle

Much more reports are available on causes of successive cropping obstacle.It is earliest believed that there was a kind of toxin producing from cropsecondarymetabolism,which would prevent the crop from growing.Later,the phenomenon was termed mutual promotion and restraint between the five elements.In 1983,a Japanese expert proposed that successive cropping obstacle resulted from five factors,including insufficiency of soil nutrient,abnormal soil reaction,deteriorating of soil physical and chemicalproperties,harmful substances of plants and changes of edaphon[12].Based on information above,the research concluded some causes of successive cropping obstacle ofAtractylodes macrocephalain Pingjiang County.

Changes of soil properties

According to researches,different crops have specific demands on mineral nutrients.For example,to grow the same crop in a farmland for a long term would definitely lead to deficiency of one or some mineral elements.With mineral elements accumulated and other elements insufficient,the crop would be diseased by nutrient defi-ciency symptom,preventing the crop from growing[13].

With a long growth period ofAtractylodes macrocephala,inbalance of mineral substances happens in soils after long term succession planting.Consequently,constituents of organic matter would be confined,granular structure would be destroyed,the proportion of inactive pore would decline,and soil hardening would be much common,with poor air permeability and permeability.In addition,with succession planting,lots of inorganic fertilizer would increase salts of soils,resulting in secondary salinization.Hence,plants would lose more water and the growth would be affected,accordingly.Meanwhile,long-term succession planting would reduce soil pH significantly,and lead to soil acidification.In general,due to long-term succession planting,the growth environment ofAtractylodes macrocephalawould go deteriorating,so that nutrient supply would become insufficient,and the growth would be hindered,leading to degrading of crop yield and quality.

Deterioration of environment of soil microorganism

Soils generally contain diversified microorganismsand beneficialmicroorganisms are usually more for crops.Then,mutualistic symbiosis of beneficial microorganisms and plants would decompose humus,and provide nutrients for plants,promoting plant growth and development.Nevertheless,long-term succession planting actually destroys soil structure and mineral substance balance,so that original eco-environment is gradually unsuitable for microorganism growth,especially for beneficial microorganism.With decrease of soil microorganisms,original balance of microorganism would be broken,and the inhibited harmfulmicroorganisms would increase,leading to deteriorating of soilborne diseases,influence on plant growth and yield declining.It is researched that the number of soil microorganism is of positive correlation with biomass ofAtractylodes macrocephala,which is also true between the number of microflora and extractum ofAtractylodes macrocephala[14].

Enzyme,one of soil components,is a polymeric catalyst,as well as an important biological index indicating soil quality[15-17].Specifically,enzymes increase the rate of decompositions of humus,animals,plants and microorganisms,advancing transformation of organic and inorganic matters and releasing nutrient elements into soils,such as N,P and K[18].Furthermore,the growth of enzyme activity would promote soil metabolism,change soil nutrients and structures,enhance soil fertility,which is conductive to plant growth[19].However,with increase of succession planting year,enzyme activity would undergo changes.For instances,acid phosphatase,invertase and urease activities are decreasing,but catalase activities are growing,which are adverse for crop growth[20].

Allelopathic autotoxicity

The process that plants produce and release secondary metabolites by volatilizing,leaching,secreting,and decomposing during metabolism,affecting growth of associated plants,is called allelopathy.Furthermore,the inhibition effect of allelochemicals released by plants on growth of the same crops(species or family)in the same season or following crop is termed allelopathic autotoxicity.

During metabolism process,plants would secrete some organic or inorganic matters to rhizosphere soils,and the secreta contain beneficial and harmful substances for plants.For example,some organic acids and phenols would accumulate in soils,seriously affecting plant growth[22-24].During the process of succession planting,harmful substances from stems and leaves,under influence of rainwash and microorganism effects,would accumulate in soils,change soil microflora,prevent root growth,and reduce root activity,leading to declining of yield and quality[25-26].

Atractylodesmacrocephalain Pingjiang County is popular due to high content of volatile oil,and root secreta are relatively more.Therefore,long-term succession planting would cause high content of root exudate,which would inhibitAtractylodes macrocephalafrom growing.What’s worse,harmful root exudates might irritate growth of pathogenic microorganism,promoting proliferation and deteriorating diseases.Researches available suggest that in the process of succession planting,stem,leaf,and root residues are left on fields and would produce harmful chemical substances after decomposition,which prevents growth of radicle and germ,and even leads to seedling death[27].

The Ways in Removing Successive Cropping Obstacle

To select the variety with high resistance

During production ofAtractylodes macrocephala,diseases always happen in succession planting,which constitutes the largest obstacle.It is researched that disease resistance tends to be volatile uponAtractylodes macrocephalavarietiesand variety degradation and resistance decline might occur for the same variety.Hence,it is effective for overcoming successive cropping obstacle to cultivate excellent varieties with high resistance according to crop characters.Additionally,withAtractylodes macrocephalacultivated as per vegetative propagation,some pathogens would parasitize plants and cause diseases,which can be concluded that to cultivate virus-free germchit is also an effective way to control soilborne diseases and overcome successive cropping obstacle.

Rational crop rotation and succession planting

Currently,crop rotation is the simplest and the most effective way to resolve the issue of successive cropping obstacle,and there are two methods,asfollows:paddy-upland crop rotation refers to the rotation ofAtractylodes macrocephalaand rice,which would kill may harmful microorganisms by water logging,and constitutes effective in control successive cropping obstacle.Upland-upland crop rotation refers to the rotation ofAtractylodes macrocephalaand maize.By changing crops,some allelochemicals would be regrouped by allelopathy,increasing soil nutrients and fertility.Furthermore, propagation of pathogenic bacteria would be inhibited on basis of biological characters of different crops,decreasing soilborne diseases and enhancing crop yields and quality.

Intercropping is a practice involving growing two or more crops in proximity in the same farmland.A rational arrangement of intercropping would improve soil use rate,make full use of sunlight and plant characters,promoting plant growth and increase yield.For example,for intercropping ofAtractylodesmacrocephalaandTrichosanthes kirilowii,the former prefers cool conditions,and grows faster upon temperature (below 30℃),but confronts growth inhibition with temperature over 30℃.Roots and stems are suitable in the range of 26-28℃;the period of March-July is a seedling stage and the period of July-November is the growth stage of root and stem.In contrast,Trichosanthes kirilowii is a climbing herbaceous plant,with vine length of 5 m.It is generally sown from March to April,and grows fast in June-July.The term of July-August is a flowering phase and the period of September-November is a fruit stage.The south of China usually undergoes a hot season from June,and it proves effective for growingAtractylodes macrocephalaunderTrichosanthes kirilowiito improve use rates of soil and sunlight.Meanwhile,the practice saves production costs,and increases farmers’incomes,which is conductive to the goal of establishing stereo cultivation.

Rational fertilization and soil sterilization

During production process,overuse of chemical fertilizer easily causes soil acidification and salinization,destroys soil structure and leads to soil hardening.Therefore,it is necessary to control the amount of chemical fertilizer,increase organic fertilizer,improve soil structure,enhance plant resistance and soil fertility.At present,organic fertilizeris dominated by farmyard manure,with multiple fertilizer sources and diversified varieties.However, the farmyard manures should be fermented and fully decomposed before fertilization.In general,fermentation lasts for 30 d,and microorganisms can be added to accelerate decomposition.It is notable that soil sterilization can be achieved with temperature over 65℃.At the sametime,inorganic fertilizer can be added upon soil fertility.

It is surveyed that soil sterilization with limes will reduce adverse effects of successive cropping obstacle.For instance,quick lime,chemical agent and irrigation are available for soil sterilization.On sterilized soils,Atractylodes macrocephalagrows well and diseases were not so serious,so that both of yield and quality improve.

Introduction of antagonistic bacteria to remove autotoxicity

It is obvious that allelopathic autotoxicity is much significant in succession planting,which can be removed by introducing antagonistic bacteria and bio-organic fertilizer.Specifically,the cultivated antagonistic bacteria can be applied to soils grown withAtractylodes macrocephalato reduce the density of soil pathogenic bacteria and prevent activities of pathogenic bacteria,to further reduce diseases.It is notable thatinoculation ofbeneficial microbial community and use of bio-organic fertilizercontaining beneficial microbial population will create a kind of biological barrier, preventing pathogenic bacteria in soils and decomposing autotoxins.Still,the application of bio-organic fertilizer containing AM and organic amendment in soils would improve soil eco-environment,and adjust soil enzyme activity,which is suitable forAtractylodes macrocephalagrowth.

Conclusions

With development of modern traditionalChinese medicine,medical components ofAtractylodes macrocephalaare increasingly known by people,andmarketdemandsare growing,so thatplanting area is widening.Nevertheless,successive cropping obstacle considerably discourages farmers and affectsAtractylodes macrocephaladevelopment.The researches available ofAtractylodesmacrocephalaare moston medical aspects,and few attention is paid to successive cropping obstacle.What’s more,such obstacle is a result of multiple factors,requiring further exploration.

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