| Tomato is widely cultivated in China,but in recent years,soil-borne diseases such as bacterial wilt have intensified,which has become one of the biggest obstacles to the development of tomato industry.Root exudates are one of the important mediators of Plant-Soil interaction,and play an important role in regulating rhizosphere microbial composition and plant disease resistance.'Fanzhen No.1','Qiezhen No.21'and cherry tomato'Fenbeibei'were used as rootstocks and scion,respectively.There were five grafted combinations,namely scion-rootstock grafted combinations(Fb/No.1,Fb/No.21),rootstock own-rooted grafted combinations(No.1/No.1,No.21/No.21),and scion own-rooted grafted combination(Fb/Fb,CK).Rhizospheric microorganisms of different grafted combinations were separated by dilution plate method.Under phytotron inoculation of Ralstonia solanacearum(R.solanacearum),the effects of rootstock-grafting on resistance to bacterial wilt,rhizospheric culturable microorganisms qunantities and diversity were studied.Root exudates were collected by continuous hydroponics at budding stage of all grafted plants,and their different organic components were analyzed by gas chromatography-mass spectrometry(GC-MS).Selection of specific substances that may be related to disease resistance was based on the changes of substance composition and content of root exudates.Through allelopathic validation test,the effects of active substances in root exudates on resistance to bacterial wilt of tomato were studied.The aim of this study is to further reveal the mechanism of disease-resistant rootstocks grafting to improve the resistance of tomato to bacterial wilt,and to provide'a scientific theoretical basis for using root exudates of disease-resistant rootstocks to control bacterial wilt.The main results were showed below:1.The resistance of grafted combinations to bacterial wilt was identified by the combination of inoculation in artificial climate chamber and cultivation in natural disease nursery.The results showed that:scion-rootstock grafted combinations and rootstock self-rooted grafted combinations showed high resistance level(HR)or resistance level(R),but CK showed high susceptible level(HS).Therefore,grafting with disease-resistant rootstocks significantly improved tomato disease resistance,reduced the incidence and disease index,and delayed the progression of disease.After inoculating R.solanacearum with root injury perfusion method at seedling stage,the time of onset process was cleared according to the change of incidence rate and disease index of grafted plants:5-10 d after inoculation was the early stage,10-25 d was the peak stage,and 25 d later was the end stage.2.R.solanacearum showed a dynamic change in the process of plant infection,which quantity decreased gradually from root to shoot.The quantity of R.solanacearum in rhizospheric matrix and root of scion-rootstock grafted plants and rootstock self-rooted grafted plants decreased.At the end stage,the quantity of R.solanacearum was controlled at 3.03×105 CFU·g-1 and below,which was significantly lower than CK(21.21×105CFU·g-1).It is concluded that grafting with disease-resistant rootstocks can effectively prevent bacterial wilt from infecting roots and shoots,and inhibit the proliferation of R.solanacearum3.After inoculation,the quanantities of bacteria,fungi and actinomycetes in rhizospheric matrix of all grafted combinations increased first and then decreased with the progression of disease.Grafting with disease-resistant rootstocks increased the total quantity of rhizospheric microorganisms,bacteria and actinomycetes,and decreased the quantity of fungi.The richness of rhizosphere bacterial population was increased,and the diversity of fungi and community was reduced.Meanwhile,the relative abundance of beneficial microorganisms was increased,and the proliferation of harmful microorganisms including pathogenic bacteria was inhibited.The results showed that,grafting with disease-resistant rootstocks could improve the rhizospheric microenvironment and play an important role in improving the resistance of tomato to bacterial wilt4.The root exudates of each grafted combinations were collected.The pathogen inoculation test and plate bacteriostasis test showed that the disease incidence and disease index of tomato bacterial wilt were reduced by 4.44%-7.78%and 5.59%-12.49%respectively by root exudates of rootstock self-rooted grafted plants and scion-rootstock grafted plants,compared with CK.The growth of R.solanacearum was also inhibited significantly,and the relative inhibition rate was 7.69%-18.63%.The results showed that there were active substances in root exudates of grafted plants with disease-resistant rootstocks that could inhibit bacteria and improve disease resistance.5.The root exudates of different grafted combinations before and after inoculation were analyzed by GC-MS.The results showed that there were some differences in the composition of root exudates among different grafted combinations.The composition and relative content of root exudates changed after inoculation.Among them,the relative content of Dibutyl phthalate(DBP),Diisooctyl phthalate(DIOP)and 2,4-di-tert-butylphenol(2,4-DTBP)in the root exudates of grafted rootstocks were generally increased after inoculation,which in CK were decreased.This indicated that these three substances may be related to resistance to bacterial wilt.6.Allelopathic tests of three simulated active substances with different concentrations showed that DBP,DIOP and 2,4-DTBP could inhibit the proliferation of pathogenic bacteria,and the relative inhibition rate was 34.65%-51.32%.And 2,4-DTBP at 1.0 mL·L-1 showed the best inhibiting effect to R.solanacearum.The inoculation test showed that the incidence and disease index of tomato bacterial wilt could be significantly reduced by root irrigation with different concentrations of three substances,and DBP at 1.0 mL·L-1 showed the best resistance to bacterial wilt,47.78%and 57.28%lower than sterile water treatment,respectively.7.Seeds and seedlings of tomato were treated with three simulated active substances of different concentration.The results showed that DBP at 0.05-1.0 mL·L-1,DIOP and 2,4-DTBP at higher concentration(0.5-1.0 mL·L-1)could inhibit the germination of tomato seeds,and the inhibiting effect enhanced with the increase of treatment concentration.DIOP and 2,4-DTBP at lower concentration(0.05-0.2 mL·L-1)could promote seed germination.The best effect was DIOP with 0.2 mL·L-1 and the average germination rate was 4.00%higher than that of sterile water treatment.Three simulated active substances were used to irrigate tomato seedlings.Both of them could promote the growth of plant height and stem diameter of tomato seedlings and increase the fresh weight of shoots and roots,but had no significant effect on dry weight. |
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