The Physiological And Biochemical Mechanism Of Grafted Pepper In Improvement Of Bacterial Wilt Resistance

Changes of disease incidence and disease index of bacterial wilt in different rootstock varieties of pepper were investigated by manual inoculation, with'xinfeng 2'as control. The purpose is to screen a rootstock variety which has higher resistance to bacterial wilt. The effect of grafted on bacterial wilt resistance in pepper and its mechanism were studied, with the higher resistance to bacterial wilt of pepper as rootstock, and the own-root plant as control. The results were as follows.1.'Weishi'was diseased in later days, and showed the lowest disease incidence and disease index, therefore represent the highest disease resistance among the four rootstock varieties, secondly were'Buyeding'and'Weizhuangbeier', and'Graft'had the lowest resistance.2. The effect of grafted bacterial wilt resistance of pepper were investigated, with'Xinfeng 2'scion grafted onto'Weishi'rootstock. The own-root plants were as act as the control. The result show that grafted plants showed remarkable lower disease incidence and disease index than control plants, but higher than rootstock plants. This indicates that rootstock and scion were interfered in each other.3. Rootstock and grafted pepper showed higher root weight, total length, volume, surface area, ntips, forks, root activity and absorption area, compared with the control. This indicates that grafted plants had stronger root and higher absorption activity, therefore increase the disease resistance.4. The bacterium population, actinomyces population and ratio, activities of peroxidase and catalase in rhizosphere soil of rootstock and grafted peppers increased significantly compared with those of the control before inoculation. After been inoculated, rootstock and grafted plants had significant higher quantities of bacterium and actinomyces, actinomyces ratio, and soil enzymes'activity, in comparison with control. The observed increase in quantitiy of microoganism, ratio of actinomyces, and enzymes'activity in rhizosphere soil of grafted peppers are important reasons of enhancement of bacterial wilt resistance.5. Before inoculation, rootstock and grafted plants showed higher bound water/free water, but lower water content, water potential and osmotic potential in roots and leaves, compared with the control. Soluble sugar and proline content in roots of rootstock and grafted plants were higher than those of the control. The water content, water potential and osmotic potential in roots and leaves of rootstock and grafted plants decreased gradually after inoculation, but bound water/free water increased, the soluble sugar and proline contents increased at early stage, but decreased 4～8 d later. Compared with control plants, rootstock and grafted peppers showed less decreasing rates in water content, water potential and osmotic potential, and less increasing rate in bound water/free water. Soluble sugar and proline contents in leaves and roots of rootstock and grafted peppers were significantly higher than those of control plants. This data indicate that graft significantly increased the bacterial wilt resistance in pepper, and is closely related to the osmoregulation.6. Similar categories of phenolic acid were isolated in roots of graft plants and control plants before inoculation. Higher content of salicylic acid was detected in grafted plants, but didn't been isolated in control plants. No significant difference was observed in lignin content between greafted and control plants before inoculation. After inoculation, most of the phenolic acids increased in roots of grafted plants, while those in control plants decreased. Lignin contents in grafted and control plants all increased at early stage, but decreased at latter. The grafted plants showed higher contents of vanillin, salicylic acid and lignin than the control plants in all days.7. Grafted plants showed lower PAL acticity in leaves, higher in roots, and lower PPO activity in leaves and root compared with the control plants before inoculation. After inoculation, the PAL activity of grafted and own-root peppers increased at first, but decreased at latter stage. The PPO activity of grafed plants increased gradually, however, that of control plants elevated in the initial stage, decreased in the latter stage. Grafted plant showed an increase in activities of PAL and PPO in leaves and roots compared with the control.8. The H₂O₂ content in leaves and roots of pepper plants increased rapidly in the initial of inoculation. 4 days latter, the increasing amplitude of H₂O₂ content in grafted plants declined, while that the control increase continuously, therefore the H₂O₂ content in grafted plants was significant lower than that in control plants in the later stage. Grafted plants showed an decrease in ZT, GA and 6-BA contents in leaves before inoculation compared with the control, and no significant differences were found in IAA and ABA contents between grafted and control plants. After inoculation, most of the endogenous hormones in leaves of grafted plants were higher than those in control plants.