| Two sweet potato varieties (Xiangshu—disease resistant, Shenglibaihao—disease sensitive) were used to be material for studying the Salicylic-Acid (SA)-induced effect of disease-resistance to Ralstonia solanacearum and its physiological and biochemical mechanisms. The effects of SA treatment on leaf properties were examined as well. The results were summarized as follows:1,Sweet potatoes sprayed with different concentrations of SA for 3 days before inoculated with R. solanacearum could develop resistance to diseases caused by R. solanacearum and the higher the concentration the more effective. The effective concentrations of SA ranged from 1 to 7 mmol/ L with the optimal concentation reaching 5 mmol/L.But SA higher than 5 mmol/L might inhibit the growth of young sweet potatoes. After treated with SA, the contents of chlorophyll and indole acetic acid (IAA) and activities of Superoxide dismutase (SOD), Catalase (CAT) and Peroxidase (POD) in the leaves increased. While contents of Malonadehyde (MDA) and Hydrogen peroxide(H2O2) and activities of indole acetic acid oxidase (IAAO) decreased. All results indicated that SA could lower the level of lipid peroxidation and induce disease-resistance to R. solanacearum.2,After infection, some photosynthetic properties of sweet potato leaves changed. As for the disease resistant Xiangshu, the structure of its chloroplast remained intact. So did cell membranes. Its membrane permeability was small while the activity of photosynthesis was strong. The content of its ABA remained at a low level. In the case of Shenglibaihao, which cell membranes were damaged and cell deformed with organelles dispersing unregularly in cells. Cell space as well as membrane permeability were on the rise. The content of ABA sharply increased, the photosynthetic rate dropped. But when treated with SA before inoculation, leave cells could firmly line together, maintaining their normal structures. The membrane permeability was relatively small. So was the level of ABA. the photosynthetic rate, compared with that without SA treatment, was higher.3,The results indicated that the activity of PAL and the contents of total phenolics, flavonoids and proline of Jinshan 75-55 were high while the content of H2O2 were low. After inoculation, they did not experience enormous change, causing high resistance to R. solanacearum. The situation in Shenglibaihao was in the opposite, which severely weakened its ability to resist. Through SA induction, the contents of H2O2, PAL, total phenolics, flavonoids and proline were all on the increase, hence enhancing capability of resistance in sweetpotatoes.4,The results also indicated that the nutrient element of sweetpotato leaves was improved by SA treatment ,reduced the amount of nitrates and nitrites and at the same time maintaining the high level of Vc. |
