| Dry rot caused by Fusarium spp. is one of the most important diseases of post-harvest potato. At present, chemical fungicides have been used widely to control dry rot in potato. However, their applications are decreased gradually due to many problems such as environmental pollutions, fungicide residues, drug resistances. In this study, potato tubers (Strain of breed: Atlantic) were selected as experimental materials. These tissues were divided into two groups. One group was treated by 30, 45 and 60 mmol/L citric acid, respectively. The other group was treated by malic acid ranging from 50 mmol/L to 125 mmol/L. The respective inhibiting effects of citric acid and malic acid treatment on dry rot of wounded-inoculated potato caused by F. sulphureum have been studied in this work. The results showed that:1. Diameter of lesions of wounded-inoculated potato tubers caused by Fusarium sulphureum decreased effectively by different concentrations of citric acid immersion treatment. The best effect was observed in 45 mmol/L citric acid treatment for 48 h. To some extent, differences between treated group and the control were noticed as well, when treated by other concentrations of citric acid and other treatment periods. Noticeably, higher concentrations of citric acid and longer treatment periods could not enhance the inhibiting effects, and do no harm to fruits, actually.2. The inhibiting effects to diameters of lesions were different when wounded-inoculated potato tubers caused by F. sulphureum were treated by different concentrations of malic acid. The best effect was observed in 100 mmol/L malic acid treatment for 72 h. However, neither in 50 mmol/L treatment, nor in 75 mmol/L treatment, could obvious differences between treated group and the control be observed. With the increase of concentrations of malic acid, slight drug toxicity to potato tubers was observed in 125 mmol/L treatment, perhaps because malic acid with high concentration would inhibit respiration and other metabolisms of post-harvest potato tubers. 3. On the other hand, the results of further study showed that activities of POD and PPO and contents of H2O2 and O2- in potato tubers could enhance significantly by 45 mmol/L citric acid treatment, besides, activities of GLU, PAL and flavonoid and total phenolic compounds contents increased to some extent. On the contrary, activities of SOD, CAT and APX were induced to decrease. However, no obvious differences in activity of MDA of potato tubers were observed between treated group and the control when they were both treated by 45 mmol/L citric acid. Maybe this was resulted from an unappropriate determination method to potato was used in this study.4. The results showed that activities of POD, PPO, GLU and PAL and contents of H2O2 and O2- in potato tubers could increase effectively by 100 mmol/L malic acid treatment, as well. Besides, contents of flavonoid and total phenolic compounds were determined to increase to some extent. On the contrary, activities of SOD, CAT and APX, were induced to decrease. However, no obvious differences in activity of MDA of potato tubers were observed between treated group and the control when they were both treated by 100 mmol/L malic acid. Maybe this was resulted from an unappropriate determination method to potato was used in this study, as well.In conclusion, it was indicated that both of citric acid and malic acid could directly inhibit growth of F. sulphureum by interfering or affecting its metabolisms, and activate biochemical anti-disease factors in potato to inhibit extension of diameter of lesions of wound-inoculated potato tubers. The results could play important roles in providing theoretical and practical guidances for lowering diseases occurrence in potato tubers, and decreasing dosage of chemical fungicides used in post-harvest control of potato diseases.
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