| Efficacy and mechanism of systemic acquired resistance to Verticillium wiltin eggplant induced by seven chemical inducers were studied systemically. Theresearch gave the following results:(1)Measurement of colony diameter and dryweight of Verticillium dahliae culture showed that within certain concentrationsthese chemicals had no significant influence on mycelial growth of thepathogen.These inducer candidates were safe to eggplant. Several of them greatlyreduced the disease caused by Verticillium dahliae Kleb and could be goodinducers.(2)Function of defense enzymes such as PPO, POD, PAL ,SOD andCAT in SAR was made clear.(3) Ca2+, H2O2 and SA were most probable thesignals of systemic acquired resistance to Verticillium wilt ineggplant.(4)Chemical inducers promoted root activity of eggplant and hadsignificant effect on microbe population and dynamics(of bacteria, fungi andactinomycetes) in rhizosphere of treated eggplants.(5)Temperature, relativeactivity and pH values of soil were important factors for efficacy of chemicalinducers; each inducer has its optimum environment requirement. Efficacy ofinducers was also different in eggplant cultivars of different resistancebackground. Efficacy in resistant cultivars are more stable and less affected byenvironmental factors, and was best in partially resistant cultivar. (6) Magnitudeof disease reduction depended on inducer concentration and mode of application.Combined use of different inducers or applying the same more than once showedbetter effect than applying an inducer just once.This research found that at low concentrations trifluralin(<3μL.L-1),peracetic acid(<100μL.L-1), hydrogen peroxide(<100μL.L-1),oxalic acid(<10mmol.L-1), potassium oxalate(<40mmol.L-1), di-potassium hydrogen phosphate((<100mmol.L-1), and salicylic acid(<5mmol.L-1) didn't inhibit growth of the pathogen, and seed germination or seedling growth was not stunted. All of the seven inducers have disease control effect to some extent. Di-potassium hydrogen phosphate was least efficient. Trifluralin, peracetic acid, oxalic acid, potassium oxalate and salicylic acid showed high efficiency in control of Verticillium wilt, seed soaking with them individually reduced disease severity by 60-90% and eggplants could be protected for over 22 days.Root activity of plants treated with inducers increased slightly,which was helpful for enhancing eggplant resistance. Population of rhizospherial microorganisms was exposed to complicated factors among which root secretion was the most vital. Rhizospherial microorganisms of inducer-treated plants differed significantly from that of control. Fungi were most rich during early and middle stage of growth season, population of rhizospherial fungi of induced plants was much richer than the nontreated in most of the time. Rhizospherial bacteria and actinomycetes were rich in middle growth season.In the later period of investigation amounts of fungi,bacteria and actinomycetes in rhizosphere of peratic acid and trifluralin treated plants were much greater than the nontreated, but that of oxalic acid and hydrogen peroxide treatment were poorer.Change of total and soluble calcium concentrations pre- and post inoculation suggested that Ca2+ signal system was important in systemic induced resistance to Verticillium wilt in eggplant. Relative activity of catalase increased greatly soon after peratic acid treatment in leaves of different ages, but after challenge inoculation the activity was lower than the nontreated. The fluctuation of catalase indicates that reactive oxygen species(ROS) and ROS burst may be the pioneer of resistance signal transduction. H2O2 and SA could be important signal of SAR.Defence enzymes PAL,PPO,POD and SOD played important roles in induced resistance to Verticillium wilt. Peratic acid treatment dramatically increased relative activity of these enzymes. The activity of some of them(eg. POD , SOD) increased transiently soon afte... |
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