| The tomato root knot nematode disease caused by continuous cropping is common,which results in the decrease of soil quality,the imbalance of soil microbial community structure,and the decrease of tomato Yield and quality.Microbial control is currently the mainly research direction of prevention and control of plant root knot nematode,screening of microorganisms which could resist root knot nematode,and exploring its ecological mechanism is the basis for using microbiological methods to control the root knot nematode disease.The study explored the inducing effect of sick soil to tomato root-knot disease and the micro ecological mechanism of continuous cropping obstacle,and we used Caenorhabditis elegansas a model organism to screen microbes that can resist C.elegans from more than and 100 strains of antagonistic microbes.Pot experiments were then conducted to assess the effects of the agent made of antagonistic microbes.We quantified endophytes in tomato roots,as well as microbes and nematodes in root zone soil with or without inoculationof the agent.Additionally,we measured the plant biomass and physiobiochemical traits of tomato at different growth stages.The main results are as follows:(1)The Streptomyces rochei D74 had disease resist and growth promote effect on the continuous cropping tomato:(i)The survival rate of diseased tomato plant was 92% after D74 treatment,which was significantly increased 15% comparing CK(P<0.05).The stem diameter significantly increased 10% compare to CK(P<0.05).(ii)After D74 treatment,the rotting rate of tomato root decreased by 14%,and the morbidity rate decreased by 61%,comparing with CK.The fresh quality of fibrous root,with absorption function,significantly increased by 102% compare to CK(P<0.05).(iii)The total number of bacteria in tomato root zone soil increased by 5%.A dominant bacteria Bacillus amyloliquefaciens thatcould help tomato resist disease and promote its growth increased by 53%;Cupriavidus taiwanensis decreased by 67% and Bacillus pumilus increased by 50%.The total number of fungi significantly decreased by 5%(P<0.05).Plant pathogenic fungus Fusarium oxysporum significantly decreased 131%(P<0.05).Cladosporium tenuissimuand Aspergillus niger respectively increased 120% and 58%.The total number of actinomycetes decreased 44%.B/F increased 11%,while A/F decreased 58%.(2)T4 could resist disease and promote growth of tomato:(i)After the treatment of T4,the mortality of diseased plant was 0,which decreased by 100% comparing to CK.The plant height significantly increased 9.6%(P<0.05).Stem diameter significantly increased 20%(P<0.05).(ii)The rotting rate of tomato root decreased by 41%;Morbidity decreased by 45%;Fresh quality of fibrous root which had absorption function significantly increased 76%(P<0.05).(iii)The seed vigor of tomato increased by 113%,and the seed vigor of maize increased by 14%,compare to CK.The differences were all significant(P<0.05).(iv)The total number of bacteria in tomato root zone soil increased by 14.A dominant bacteria Bacillus amyloliquefaciens,which could resist disease and promote growth of tomato,decreased by 35%;Cupriavidus taiwanensisand Bacillus pumilus respectively increased by 17% and 100%,compared to CK.The total number of fungi significantly decreased by 16%(P<0.05).The plant pathogenic fungus Fusarium oxysporumsignificantly decrease by 38% compared to CK(P<0.05);The total number of actinomycetes has no significant difference between the treatments,but the dominant actinomycete Streptomyces griseuswas only detected in the root zone soil after the treatment of T4.(v)T4 was identified to be Streptomyces albidoflavus.It was proved having the ability to produce IAA and siderophore.The output of IAA was 20.26±0.4mg·L-1.24 h killing activity to C.elegans was 95.4%.(3)Pot experiments were conducted to assess the effects of a Streptomyces agent(1:1 mixture of S.pactum and S.Rochei)for biocontrol of RKN disease in tomato.We quantified endophytes in tomato roots,as well as microbes and nematodes in root zone soil with or without inoculationof Streptomyces.Additionally,we measured the plant biomass and physiobiochemical traits of tomato at different growth stages.The results showed that after inoculation of Streptomyces:(i)The RKN disease index of tomato plants decreased by 37%.The quantity of bacterial-feeding nematodes decreased by 14% in root zone soil,while the quantity of fungal-feeding and plant parasitic nematodes increased by 10% and 137%,respectively.(ii)The fresh weight of shoot and root increased by 14% and 35%,respectively.Meanwhile,the polyphenol oxidase activity of leaves increased by 33% at the seedling stage.(iii)The total number of culturable bacteria decreased by 49% in root knots.Regarding the total number of culturable microbes in root zone soil,bacteria and actinomycetes also decreased by 18% and 10%,respectively,whereas fungi increased by 20%.Moreover,the quantity of both plant growth-promoting bacteria and nematicidal bacteria increased,while the quantity of plant-pathogenic bacteria decreased.In conclusion,the Streptomyces agent could reduce RKN disease in tomato by activating the systemic resistance and defensive mechanism against nematode infection.This agent triggered complex interactions between plants,microbes,and nematodes in the micro-ecosystem of root zone soil,resulting in decreased RKN infection ability and/or enhanced tomato disease resistance.(4)Compared with the healthy soil,the sick soil resulted in a series of changes:(i)At seedling stage,the root knot nematodes began to infect the roots and there were root knots on tomato root systems.Soil nematode abundance increased by 390.4% compared with the healthy soil.At maturity stage,the infection rate of root knots was 62.7%,and the disease index was 80.0%.(ii)The growth of tomato was restrained,and the activity of defense enzyme was reduced.The blossom and fruit date were delayed.The fresh biomass of shoot and root at maturity stage significantly decreased by 50.2% and 33.1% respectively,and the quantity and fresh mass of fruit were significantly(P<0.05)decreased by 59.7% and 68.2% respectively.The PPO activity of seedling leaves significantly(P<0.05)decreased by 15.8%,and the POD activity significantly(P<0.05)increased by 24.0%compared with healthy soil.(iii)The tomato roots became easier to be infected by harmful bacteria(Pseudomonas brassicacearum).The quantity of pathogenic bacteria P.brassicacearum in tomato roots was 463 times more than healthy soil treatment.The total quantity of bacteria,fungi and actinomycetes in root zone soil increased by 46.3%,94.5% and 134.0%,respectively.(iv)The abundance of soil nematodes increased nearly 3 times,among them,the abundance of fungi-feeding nematodes,bacteria-feedingin nematodes and plant parasitic nematodes increased by 1.6,3.3 and 7.3 times,respectively.The abundance and diversity of plant parasitic nematodes largely increased,of which root knot nematode accounted for 95.6% of the total. |
PDF Full Text Request