Occurrence Of Fungal Disease In Tendril And Root Of Continuous Cropping Melon Plants And Its Management By Biocontrol Actinomycetes

Fungal diseases of the tendril and root of continuous cropping melon plants are themajor limiting factors of the development of melon protected cultivation and specializedplanting base. Finding effective disease control approaches is the first priority to solve theseproblems. The current measures for controlling melon fungal diseases at home and abroadmainly include chemical pesticides, grafting, resistant varieties screening and so on. Thesemeasures show little effect, while have their own shortcomings and drawbacks, such asenvironment pollution, pesticide residue, pathogens variation and drug resistance. With thedevelopment of green agriculture and organic fruit and vegetables, the new environment-friendly measures such as biocontrol methods attract widespread attention, and will be themain trend in current and future. The biocontrol idea ‘to prevent and cure fungal diseases byantagonistic microorganisms’ was a new way to solve these problems. Actinomycetes werewidely used in medicine for their inhibition effect on animal pathogens, human and livestockdiseases via antibiotics production. The agricultural antibiotics also played an important partin agricultural production, while the applications of live actinomycetes preparations on plantsfungal diseases control were somewhat slow, their action mechanisms and effects remainedunclear. There were still few researches about the biocontrol potential of live actinomycetespreparations on fungal diseases of melon tendril and root.In this paper, the author systematically studied the microecology mechnism of theoccurrence of melon fungal diseases, screening and identification of antagonisticactinomycetes, biocontrol and growth promotion effect of actinomycetes, biocontrolmechnism as well as the interaction mechnism among pathogenic fungi, biocontrolactinomycetes and melon plants. Biocontrol actinomycetes with high efficiency and stabilitywere obtained for controlling melon fungal diseases and overcoming melon continuouscropping obstacles. The related studies about biocontrol mechanisms provided solid scientific basis for the commercially production and practical application of the biocontrol preparationsin the near future. The main contributions of this research were summarized as follows:(1) Microecology mechnism of fungal diseases occurrence in tendril and root ofcontinuous cropping melon plantsVarious fungi were obtained from the infected melon plants and their rhizosphere soils,when the fungal diseases of tendril and root of continuous cropping melon plants occurred,which including direct pathogenic fungi, indirect pathogenic fungi but with infection andtoxin action, as well as indirect pathogenic fungi. From the infected melon plants and theirrhizosphere soils,13fungi isolates were collected and further attributed to4genus and8species, according to morphological characters and rDNA-ITS sequence analysis. Thesuperior fungi mainly included Didymella bryoniae, Fusarium equiseti, Fusariumproliferatum, Fusarium solani, Botryosphaeria dothidea, Alternaria alternata, Fusariumtricinctum and Fusarium chlamydosporum. Among which, D. bryoniae was the pathogencaused melon gummy stem blight, F. equiseti and F. proliferatum showed melon root andstem infection ability in vitro. Other fungi isolates had no pathogenicity to melon plants, theirtoxin production ability were unknown.(2) Disease biocontrol and growth promotion effect of antagonistic actinomycetesActinomycetes A12, C28, C13, C27and their sterile culture filtrates showed favorableantagonistic effect against D. bryoniae in Petri dish. Sterile culture filtrates of actinomycetesA12and C28expressed significant reduction effect on the disease severity (DS) and AUDPCvalue of melon plants; solid-state fermentation preparations of actinomycetes C13and C27also showed obvious biocontrol effect on melon gummy stem blight. The four actinomycetesdisplayed definite growth promotion effect and substantial survival ability (105～106cfu·g-1dry soil) in the rhizosphere and on the rhizoplane of melon plants in pots. Actinomycetes A1,A11and A12showed evident mycelia inhibition effect on F. equiseti. The hypocotyl, radiclelength, and simple vigor index of melon seeds were all increased by their sterile culturefiltrates. Compared with the control or F. equiseti single inoculation, the chlorophyll contentsand PPO activity of melon leaves, root weights and activities were all improved, when F.equiseti were inoculated with the3antagonistic actinomycetes.(3) Identification of the biocontrol actinomycetesActinomycetes A12, C28, C13and C27, with biocontrol effect on melon gummy stemblight, were subsequently identified as Streptomyces pactum, Streptomyces globisporus subsp.globisporus, Streptomyces celluloflavus and Streptomyces flavotricini. Actinomycetes A1andA11, with obvious antagonistic effect against F. equiseti, were identified as Streptomycescalifornicus and Streptomyces carnosus, respectively. (4) Biocontrol mechnisms of the actinomycetesThe biocontrol actinomycetes showed good repair effect on the continuous croppingobstacle of melon plants from the following5action mechnisms: fungal mycelia growthinhibition effect via antimicrobial active substances; extracellular enzymes production andfungal mycelia degradation effect through these enzymes; growth and yield promotion, fruitquality improvement, as well as plant physiological and biochemical metabolism regulationby means of hormone-like substances; plant systematic disease resistance induction effect viaprotective enzymes improvement; rhizosphere soil microecosystem repair and regulation.Biocontrol actinomycetes A12, C28, C13and C27showed favorable growth and yieldpromotion effect on melon plants in greenhouse. Fruit quality such as soluble protein, vitaminC, soluble sugar and solids contents were improved in the presence of these actinomycetes.The net photosynthetic rate was also increased by A12and C28treatments, which waspropitious to the accumulation of photosynthetic product. The root absorption ability ofnutrient elements N, P, K was improved by actinomycete C13treatment.Two biocontrol preparations C28and Kangzhao showed obvious growth promotioneffect on melon plants in field. The induced enzymes activities and soluble protein contentsof melon plants were improved, and MDA contents were decreased by biocontrolpreparations treatments. With the enhanced disease resistance and decreased lipidperoxidation, melon plants have formed a protective barrier to resist disease attack. Themicroelements admixture of zine, manganese and titanium displayed significantly growthpromotion effect on melon plants, when biocontrol preparations C28and Kangzhao wereapplied. Application of microelements admixture with biocontrol preparations showed littledistinct variety even negative effect on the disease resistance of melon plants.There was an upward trend about the soil bacteria and actinomycetes amounts in therhizosphere and on the rhizoplane soil of melon plants after treated by biocontrolactinomycetes A12, C28, C13and C27. The pathogenic fungi quantities in the rhizospheresoil of melon plants were decreased by A12and C28treatments. Microorganisms in the rootdomain soil of melon plants were transited from “fungal-type” to “bacteria-type”, whichmeant the biocontrol actinomycetes displayed a positive effect on the regulation of soilmicroecosystem.(5) Interaction mechnism among pathogenic fungi, biocontrol actinomycetes and melonplantsMycelia preparation of the pathogenic fungi (MPPF) of cucurbit plants showedsynchronous induction effect on extracellular enzymes produced by antagonisitcactinomycetes, fungal mycelia degadation and inhibition were the combined action of these enzymes. The MPPF served as good carbon source to enhance cellulase activities, especiallythose from F. proliferatum. The MPPF from F. equiseti obviously improved chitinaseactivities of actinomycetes A12and C28.Indirect pathogenic fungi with infection ability showed double allelopathic effect onmelon plants via toxin production. F. equiseti and F. proliferatum showed obvious inhibitioneffect on seeds germination and the growth of melon plants. The MDA, soluble proteincontents and cell membrane permeability of melon roots were increased in the presence ofFusarium toxins. The induced protective enzymes of melon roots were improved whentreated by the toxins at stated dilutions, which strengthened the disease resistance of melonplants.