Sutdy On Chemical Compounds Screening And Control Technologies Against The Citrus Huanglongbing In Plantation Field

Citrus Huanglongbing (Citrus Huanglongbing, HLB) is a devastating citrus diseasewidely distributed among citrus-producing countries and included in the major plantquarantine objects. In recent years, with an increasingly wide range of citrusHuanglongbing disease transimission, the harm be more intensive and difficult toeradicate. Citrus Huanglongbing pathogen Asian species (Candidatus Liberibacterasiaticus, Las) is a parasitic limited to sieve organsim, Gram-negative bacteria, andspread through Diaphorina citri. At present, the Huanglongbing pathogen still can notbe a successfully cultured in vitro, thus chemicals screening progress remains slow.Lackof effective chemicals and disease-resistant varieties, controlling psyllids, excavatiingdiseased trees and planting disease-free citrus seedlings are currently three coremeasures of HLB disease management. Chemical creening and contol technologiesagainst HLB has been going on in order to obtain the effective management.In order to screening chemicals and accessing to potential techniques againstplanation citrus Huanglongbing disease by effect control evaluation, real-timequantitative PCR was carried out to obtain long-term dynamic pathogen bacterial titerschanges after treatment HLB-infected citrus tress with chemicals or heat byphloem-injection, foliar spraying, trunk or branches paster, and heat treatmenttechnology. The main results and conclusions are as follows:Control effect evaluation system was established via a long-term of real-timequantitative PCR to dynamic monitor the changes of bacterial titers. The control trailwere set up for evaluation of control effect. In view of the control effect evaluation onlya preliminary assessment whether a treatment effectivly suppressing Huanglongbing,disease symptoms should be also observed after application including plant growth.Chemical compounds were screened via phloem-injection into the base of the trunkor branch of a tree. DNA of leaf midrib samples was extracted and quantified by usingquantitative PCR continuous dectected for eight months after initial treatment.2,2-Dibromo-3-Nitrilopropionamide(DBNPA), ampicillin, and isothiazolin-ketonecontrol effect were achieved89.75%,87.27%, and83.72%at a1g/L dosage, respective.The best prevention and treatment term is in May to August.For1g/L ZnSO4and CuSO4injection treatment, eight months after initial treatment,ZnSO4treatment was dectected the bacteria titers dropped by70%, while the CuSO4 group was less than30%. The control effecancy analysis showed that ZnSO4group hada control effect of56.62%, and CuSO4shows no obvious efficency. The results showedthat nutritional therapy can play a certain extent in enhancing trees vigor to reduce theincidence of the Huanglongbing.Foliar spraying with0.6g/L thiazole-zinc and0.5g/L busic chloride, the formerbacterial titers were almost no change while the latter decreased by15%. A controleffect achieved51.60%and49.53%, respective, with a certain ease of Huanglongbingsymptoms.The branches/trunk paste applicator test results showed that the paste treatmentprevent the huanglongbing down from expansion; overall the chemical via paste wasexpanding more slowly than that via both phloem injection and foliar.A plastic shield for short-term heat treatment maintained the upper space of thehood at a temperature of44°C to48°C for6hours twice every months. After threetimes treatment with a367.5°C effective accumulated temperature(EAT), bacterialtiters in vivo were detected a decline of99%, as well as the control efficiency up to99%.The hood temperature must not exceed50°C, or the heat will easy to hurt the treecrown. For adult fruit trees,heat treatment is a more effective prevention and controlmeasures.The ultilization of HLB-contol measures depends on the age of citrus trees andplantation conditions. Saplings and grafted seedlings less than3years old can beconsidered to carried out a short-time thermal treatment, while Huanglongbing adulttrees can be taken the the trunk/phloem injecton or long-term thermal treatment. NewlyHLB-infected trees were recommended lower-branches paste to blocking diseasesdownward extension. But, old symptomatic tress with no economic value should beremoved. Both of these technologies are not effective for citrus groves in the onset ofstrain rate of more than30%.This study screened several Huanglongbing chemical compounds as well asachieved ancillary application methods, which provide a reference for theHLB-prevention and control technology. The planation Huanglongbing control andintegrated management are of great significance in controling the expansion of thedisease and reducing the loss of diseases.