Effects Of Rhizoshphere Bacteria On Growth And Anti-herbivore Resistance Of Tomato

Plants subjected to herbivore attack will release volatiles to attract natural enemies to control pests.This plant-insect pest-natural enemy tritrophic interaction is one of hot research areas in chemical ecology.However,whether plants whose above-ground parts suffer from insect herbivore damage can recruit the underground beneficial rhizosphere microorganisms to induce plant systemic defense is unknown.In this study the soils were collected from different places,the effects of soil microbes on growth and anti-herbivore defense of tomato plants(Lycopersicon esculentum Mill.)were evaluated.The changes in rhizosphere bacteria were compared in rhizospheres between uninfested plants and plants infested by the caterpillar Spodoptera litura(Fabricius).The Plant GrowthPromoting Rhizobacteria(PGPR)were isolated from the rhizosphere of tomato plants infested by S.litura.The effects of insect herbivory on tomato root exudates were examined.The main results are as follows:(1)Soil samples were collected from Fuqing,Putian,Minhou and Nongda campus in Fujian Province.The microbes in the soils were extracted by water leaching,and the tomato plants were treated with their soil extracts leached from the above soil samples.The sterilized extracts acted as control.After 30 days of tomato growth,leachates from soil samples of Fuqing,Nongda and Minhou promoted tomato growth compared with the control.(2)Meanwhile,the leachates from soil samples of Fuqing,Putian and Minhou especially Fuqing soil extracts increased insect resistance of tomato plants against S.litura.Weight gain of S.litura were increased by 211% in the control group,while it was increased by only 97% in the PGPR-treated plants.There was no significant change in insect weight after Minhou soil extracts treatment compared to the control.(3)Fuqing soil extract(Fuqing soil bacteria)was added to the disinfected soil,and then tomato was planted.The tomato was treated with insects and an insects-free control group was set up.The total DNA was extracted from the rhizosphere soil and subjected to 16 S rDNA sequencing,and then the samples were subjected to OTUs cluster analysis.After distinguishing the microbial group,the plant rhizosphere bacteria were isolated and identified.The results showed that: the Phylum Firmicutes,Bacillus Cohn as well as Actinomycetes,Micrococcaceae were increased in both root surface soil and the rhizosphere soil,while the Bacteroidetes,sphingobacterium was decreased.It indicated that the insect attack may increase the colonization of PGPR in the tomato soil to prime systemresistance against insect herbivore.(4)The bacterial communities in the rhizosphere soil of tomato,which was cultured in Fuqing soil bacteria,were isolated and identified by LB,TSA and NA medium respectively.We found that 76 strains of rhizosphere bacteria were obtained,including 25 strains of Phylum Firmicutes,24 strains of Actinomycetes,24 strains of Proteobacteria,3 strains of Bacteroides,and 33 strains of different species bacteria.(5)The defense enzyme of peroxidase(POD)and polyphenol oxidase(PPO),protease inhibitor(P)levels increased by 2.4-,1.4-and 1.7-fold at 24 h in T8-4/T6-4 strains treated plants after insect infestation relative to control treatment,respectively.The transcript levels of protease inhibitor gene(PI-II),allene oxide cyclase gene(AOC),lipoxygenase gene(LOXD)and allene oxide synthase gene(AOS)were significantly increased by 1.4-,2.2-,2.7-and 1.7-fold relative to control treatment 6 h after the insect attack in T8-4/T6-4 strains treated plants.These results indicate that isolated and identified PGPR can induce tomato systemic resistance and improve tomato resistance.(6)Effects of PGPR inoculation of T1-10,F2-6,F4-1,T1-4,T-2 and T2-4 on tomato growth were evaluated.Compared with the control,both T1-10 and F4-1 promoted the growth of tomato roots,but had no significant effect on the plant height and branch length of tomato,while F2-6 and F4-1 increased the aboveground biomass of tomato.T1-4 promotes the growth of tomato plants,the plant height and branch length were significantly different from the control,while the T-8-4/T6-4 mixed bacteria strains had no influence on plant height and branch length.(7)The GC-MS analysis showed that there were significant differences in the peak period of 15-27 min,indicating that the root exudates was changed in PGPR plants after insect infestation.It indicated that insect feeding may cause changes in tomato root exudates.This study is important for elucidating co-evolution relation among rhizobacteria,host plants and herbivorous insects,and it will lay a good foundation for use of rhizobacteria for pest management in agriculture.