| In recent years, astragalus root rot is widespread in the genuine producing aera. The root rot pathogens from A. membranaceus planted Weiyuan county were studied in this paper. The results show as follows:1. Isolation, identification and pathogenicity tests of the pathogens from A. membranaceus root rot in Weiyuan county were conducted. The result showed that 6 kinds of fungus were isolated from the biennial root rot plants. The major pathogens were F. oxysporum Schiecht. and F. solani (Mart.) Sacc., which could be isolated in different stages of growth by 15.8%-38.1% and 25.0%-42.1%, respectively. The root rot incidence after inoculating pathogens by goring radicles was significantly higher than that by non-goring. The F. oxysporum showed strongly nosopoietic ability. The root rot spots would not develop under culture conditions and the health seedlings always grow well without spots. All above reveals that the climate, environment factors and the seedlings are the major factors causing root rot and the wound is helpful for the pathogens to infect. It suggests that it should ensure the seedling quality, prevent the wound in the standardization operation and integrate stubble change with medicament early application so as to synthetically control the root rot.2. Biological characteristics study showed that LT of F. oxysporum is 60℃. The mycelia growed well under continuous light at 15℃-30℃, with the optimum temperature of 25℃and optimum pH=6. The best carbon and nitrogen sources were sucrose and sodium nitrate. The sporulation produced higher in the dark under 25℃-35℃and pH=5, especially using sucrose and glucose as carbon source. The best nitrogen source for the sporulation is sodium nitrate. The LT of Fusarium was 65℃and the mycelia are suitable under light at 20℃-30℃with the optimum temperature of 25℃and pH=8. The best carbon and nitrogen sources were sucrose and ammonium nitrate. The spores were highly yielded in the dark under 20℃-35℃and pH=7, using ammonium nitrate as nitrogen source. All these reveal that the growth characteristics of pathogens are quite different.3. Toxic pharmaceutical test showed that 1.25 mg/mL of thiophanate methyl had significantly inhibitory effect on F. oxysporum and Fusarium fungi with 1.8 cm and 1.9 cm in colony diameter and 85.3% and 84.4% of the inhibition rates. The inhibitory effect of 2.00 mg/mL metalaxyl mancozeb was the second. The EC50 of Metalaxyl mancozeb, thiophanate methyl, carbendazim and Kangdileide for F. oxysporum were 0.9623 mg/mL, 0.6599 mg/mL,2.4997 mg/mL and 3.2462 mg/mL, respectively. The EC50 for Fusarium were 0.6161mg/mL,0.5643 mg/mL,2.3442 mg/mL and 3.6828mg/mL. Toxicity of the two pathogens were ranged in thiophanate-methyl> metalaxyl mancozeb> carbendazim> Kangdileide.4. Field medicament selection showed that after 20 d following inoculation when transplant and spray application when growed for 10 days, the aerial parts of astragalus showed some wilting even yellow leaves falling off, however, these symptoms were not happened in the non-inoculated plants. Under inoculation, The root rot incidence ranged from 63.3% to 90.0% and disease index ranged from 30% to 44.2%, but the control effect varied in 11.5%-15.4%.800 dilution of thiophanate-methyl was the most effective in prevention and treatment,500 dilution of Kangdileide followed. However, under non-inoculation, the fissure incidence ranged from 20.0% to 66.7%, disease index ranged from 13.3% to 31% , but the control effect varied from 46.2.5% to 73.1% ,800 dilution of thiophanate methyl and 500 dilution of mancozeb metalaxyl had excellent control effect on carbendazim, and the effect of 400 dilution followed. It shows severity incidence of root rot after pathogen inoculation as compared with the control. |
