Studies On Conditions And Control Of Tomato Bacterial Wilt In Hydroponics

Ralstonia solanacearum can cause serious harm to crops spreading through soil. The bacteria may infect nearly 300 varieties of plants in over 44 families so far. This bacterial disease is difficult to control, which is related to several factors, including plant species, soil management, cultivation and management, fertilization conditions and climate variability. Therefore, integrated control is needed, rather than single way.At present, biocontrol is an promising way to control tomato disease in many methods of disease-contronl. The studies were carried out on hydroponic tomato as a media of R. solanacearum. Three aspects were designed to systematic and deep studied, including the activities of defense enzymes, biocontrol and nutrition elements. The main research results were as follows:1. The highly pathogenic R.solanacearum was obtained by the methods of dilution and bacterial pus separation, and the latter was favorite, which is benefit to obtain pathogenic strains with a shorter time, fewer purification, and much longer pathogenic maintaining. The initial infected tomato was the best source of R.solanacearum.2. The conditions of break-out of tomato bacterial wilt were investigated through Single-factor experiments and Uniform Design in hydroponics. The optimal conditions were at 32℃, pH6.4, EC(electricity conductance) 2.2ms/cm, in 80% relative humidity, by root-wounding method, on tomato seedling in 4 or 5 leaf stages and with inoculation concentration of 6.3×10⁸ cfu/mL.3. 4 strains of antagonistic bacteria, namely S59, S8, S57, S43, were obtained from the rhizosphere soil of healthy tomatos by the antagonize experiment, taking LuxAB and streptomycin, tetracycline as markers. By antagonistic experiment, germination test and disease-control experiment, the results showed that S59 strain could restrain germination of tomato seed, and control plant disease effectively. The colonization study of S59 strain indicated that it could not only colonizate but also maitain a unsiderably population on tomato roots-surface, stems. 4. The incidence of tomato bacterial wilt was studied by the combination of Ca²⁺ or K⁺ in nutrient and S59. The results showed that the integrated application of S59 and K⁺ is beneficial to raising tomato resistance and enhancing the ability of disease prevention. At the same time, the incidence of bacterial wilt decreased along with the increase of K⁺ concentration, decreased from 40.1% to 32.4%, under the same concentration of S59 strain, compared with the control lower 52.0%, the controlling efficiency increased 9.1%. The increase of Ca²⁺ concentration is detrimental to the prevention of tomato bacterial wilt in hydroponics. When Ca²⁺ concentration increased from 3.5 mmol/L to 9.5 mmol/L, the incidence of tomato increased from 39.5% to 48.7% and the controlling efficiency declined 11.5%.5. The results of the physiological and biochemical analysis on tomato showed that the activities of phenylalanine (PAL), peroxidase (PPO) and polyphenol oxidase (POD) activities has been significantly improved by the treatment of different concentration of K⁺ and S59 strain, proportional to the concentration of K⁺. The combination of Ca²⁺ and S59 showed no any regularity on above three enzymes. The activity of superoxide dismutase (SOD) would be increased with the increase of Ca²⁺ concentration, but SOD activity showed no significant changes after the treatment of K⁺ and S59 strain. Judged from the dynamic curves of the four defense enzyme activities in tomato seedlings, the peak activity would be delayed after the entry of antagonistic bacteria S59.All above research results have important theoretical and practical significances on the sustainability control of tomato bacterial wilt, the development of new anti-microbial agent, tomato cultivation and management, fertilizer management, and also have very important reference value to other plants on soil-borne diseases.