Microecological Mechanism Of Healthy Plant Growth In Continuous Cropping Potato Fields And Biocontrol Microorganisms Of Soil-borne Fungal Diseases

The increasing severity of soil-borne diseases is one of the important forms ofContinuous cropping obstacles. In recent years, soil-borne fungal diseases of potato seriouslyimpacted the yeild and quality of potato, and restricted the development of potato industry.The diseases caused by Rhizoctonia solani, Fusarium spp. and Verticillium dahliae are threemain soil-borne fungal diseases of potato which have serious harm on potato plant. Themeaning of finding effective ways to control potato soil-borne fungal diseases is significant.Currently, improving cultivation measures and using chemicals were two main methods tocontrol potato soil-borne fungal diseases both in domestic and overseases areases. However,the control efficiency of these two methods are not ideal and both have many drawbacks.Using antagonistic microorganisms to control the growth and reproduction of fungalpathogens in rhizosphere soil of plants is an effective way which accords withmicroecological principle. Until now, researches about biocontrol actinomycetes of potatosoil-borne fungal diseases were relatively few, and the study about biocontrol fungi wasmainly focus on Trichoderma. Moreover, there is no study on the reasons of healthy potatoplant’s keeping healthy in continuous potato field. This study used potato rhizosphere soilsamples which were collected from two-year and four-year continuous potato fields in DingxiGansu Province as materials, analysed the microecological mechanism of healthy plant’skeeping healthy in continuous potato fields on the basis of soil available nutrients, theabundance of rhizosphere soil actinomycetes and the ratio of antagoniatic actinomycetes.Antagonistic actinomycetes against four potato soil-borne fungal pathogens R. solani,Fusarium solani, Fusarium sulphureum and V. dahliae were screened out from both obtainedactinomycete isolated from the above continuous potato fields and our libratory long-termpreserved actinomycetes which have good antagonism against many pathogens. This studyalso examined the growth promoting, stress resistance of potato plant and rhizosphere soilmicroflora associated with the selected high effective biocontrol actinomycetes. What’s more,this study still examined the antagonism of Penicillium griseofulvum CF3against foursoil-borne fungal pathogens of potato (i.e., R. solani, F. solani, F. sulphureum, and V. dahliae) and its growth promoting. This study is aimed at offering high effeciency biocontrol bacterialstrains against potato soil-borne diseases caused by above four fungal pathogens andproviding basis for the production of biocontrol bacterial strains in factories. The main resultsof this study were summarized as follows:(1) In the four-year continuous potato field: Available soil P and K contents in therhizosphere of diseased plants were respectively29.9%and12.5%lower than those in therhizosphere of healthy plants, whereas soil NH4+-N content in the rhizosphere of diseasedplant was24.1%higher than that in the rhizosphere of healthy plant. Compared to those fromthe rhizosphere of healthy plants, the numbers of soil actinomycetes from the rhizosphere ofdiseased plants with the Gause1medium and Humic Acid medium decreased by51.1%and46.0%, respectively. The soil actinomycete antagonistic potentiality (SAAP) of actinomyceteswith antagonistic effects on the four fungal pathogens of potato were lower in the rhizosphereof diseased plants than in the rhizosphere of healthy plants. Streptomyces. gancidicus, whichhave antagonism against four potato soil-borne fungal pathogens, and Streptomyces. galilaeus,which was the pathogen of potato common scab, were found dominant in the rhizosphere ofhealthy and diseased plants, respectively.(2) In Dingxi Gansu Province, small quantities of antagonistic actinomycetes which hadstrong antagonism against four soil-borne fungal pathogens of potato were screened out bothfrom rhizosphere and out-rhizosphere soil of healthy and diseased plants in two-year andfour-year continuous potato fields. Three high activity antagonistic actinomycetes werescreened out and both strain G5and strain G43are Streptomyces rochei, strain G108isStreptomyces sindenensis through identification. Compare with control, the fresh weight ofpotato plant aboveground part increased by19.0%and7.5%, the stem height in growth periodincreased by7.3%and9.5%, the diameter of base stem increased by10.7%and4.1%,wherease the content of malonaldehyde (MDA) decreased by11.6%and25.2%associatedwith soil inoculation and seed coating of S. rochei G5spore powder, respectively.(3) The number of antagonistic actinomycetes against F. solani, F. sulphureum and R.solani were25,24and17strains, respectively among the tested26our libratory long-termpreserved antagonistic actinomycetes. Three strains of antagonistic actinomycetes,Streptomyces polychromogenes.1, Streptomyces globisporus subsp. Globisporus andStreptomyces rubiginosohelvolus, which had good antagonism against three above soil-bornefungal pathogens of potato were screened, and the inhibition rates of the above threeantagonistic actinomycetes culture filtrate against F. solani, F. sulphureum and R. solani were45.1%~100.0%. Both Streptomyces globisporus subsp. Globisporus and Streptomycesrubiginosohelvolus culture filtrate disintegrated F. solani and F. sulphureum. Compared with control, the length of melon seed radicle and plumular axis increased26.7%-67.0%and62.1%-104.5%, respectively by soaking in the above screened antagonistic actinomycetesculture filtrate.(4) The stem height were11.2%and10.2%higher; the soil plant analysis development(SPAD) were10.7%and7.6%higher; the fresh weight of potato aboveground part, total freshweight of potato were15.4%and0.6%,13.2%and1.5%higher; whereas the correspondingMDA content were respectively23.09%and4.82%lower in the soil inoculanting with“Kangzhao” inoculant and G5spore powder treatments than those in the control.(5) The numbers of soil actinomycetes from the rhizosphere soil were44.1%and4.1%higher, whereas the number of fungi were17.9%and45.8%lower associated with soilinoculation of “Kangzhao” inoculant and G5spore powder than those in the control,respectively. The ratio between actinomycetes and fungi (A/F) were75.4%and92.4%higher,whereas the ratio between bacteria and actinomycetes (B/A) were51.9%and30.8%lowerassociated with soil inoculation of “Kangzhao” powder and G5spore powder than those in thecontrol, respectively. The numbers of isolated Streptomyces carnosus (Act11) plusStreptomyces pactum (Act12) and S.rochei (G5) were taken34.4%and45.9%parts of thetotal isolated actinomycetes, respectively.(6) The inhibition rate of sterile CF3culture filtrate against mycelial growth of the foursoil-borne fungal pathogens of potato (i.e., R. solani, F. solani, F. sulphureum, and V. dahliae)and microsclerotia formation of R. solani were53.0%-72.1%and36.8%-100.0%, respectively.Pre-treatment of melon seeds by soaking in CF3culture filtrate significantly promoted thegrowth of radicle and plumular axis. The fresh weight of potato plant aboveground parts andthe polyphenol oxidase (PPO) activity of potato leaves associated with soil inoculation of CF3spore powder were respectively38.3%and9.0%higher than those in the control, whereas thecorresponding MDA content was28.8%lower than that in the control.In conclusion, the microecology of rhizosphere soil that supports healthy plant growth incontinuous potato field is mainly characterized with: available nutrient combination ofabundant P and K with relatively poor N contents; and a larger number of soil actinomycetesand a larger SAAP of antagonistic actinomycetes than that of diseased plants, with thenumerically dominant actinomycetes showing beneficial antagonistic effect on severalcommon soil-borne fungal pathogens. Six antagonistic actinomycetes, S. rochei (G5and G43),S. sindenensis, S. polychromogenes, S. globisporus subsp. Globisporus and S.rubiginosohelvolus, which had biocontrol potential in controling common potato soil-bornefungal diseases, were screened out in this study.“Kangzhao” inoculant and G5spore powderpromoted growth of potato plant and improved rhizosphere soil microflora. Moreover, P. griseofulvum (CF3) is a strain of biocontrol fungus which had good antagonism againstcommon potato soil-borne fungal pathogens.