| The kinds of alfalfa disease was investigated in this studies, which was occurred in north of China. The classic disease was sampled, identified and purified, and the species and pathogenicity of pathogen were identified and determined in vitro. The pathogenicity and biological characteristics of the strain of Fusarium sporotrichioide BYE27-2-5 were determined, which was isolated from alfalfa root rot in Chifeng. Meanwhile, thirty alfalfa varieties were used to determine or identify it resistance to the pathogen of Fusarium sporotrichioide BYE27-2-5, and one of six varieties were used to determine it defense enzyme activity. Also, it toxicity, pot and field control experiments were determined in vitro and field. The main results were as follows:(1) The species of fungal pathogens, incidence and severity of alfalfa fungal diseases were investigated in Langfang, Cangzhou, the forage base of Zhangjiakou(Hebei Province), Shunyi(Beijing) and Arhorchin Banner of Inner Mongolia alfalfa base. The species of main diseases and dynamic change regularity of alfalfa root rot disease were defined in this experiments.(2) The optimal temperature for mycelium growth, spores production of Fusarium sporotrichioide were 25℃, 30℃ and 28℃, respectively. The mycelium can growth at p H from 5.0 to 11.0, and the optimum p H for sporulation and spore germination were 8.0 and 7.0, respectively. The mycelium was grew better when treated at alternative light, and the best conditions for spore production and spore germination was complete light. The spore was germinated when treated with relative humidity was more than 95%, but it was not germinated when the relative humidity was lower than 75%. The best medium for mycelium growth and spore germination were dextrose peptone medium, and the best medium for spore production was PSA. The best carbon sources for mycelium growth and spore germination was glucose, while the best carbon sources for pore production was sucrose. The best beneficial nitrogen source for mycelium growth was peptone, while the best beneficial nitrogen source for spore germination and sporulation was yeast extract, respectively. The lethal temperature of mycelium and spore was 54 ℃(10 min) and 48 ℃(10 min), respectively.(3) The test evaluated resistance of 30 alfalfa varieties to Fusarium sporotrichioide with seedling rot in greenhouse. The results showed that Jinnan, Xunlu, PG Saite, Sulian No. 2 are four endured resistant varieties,with the frequency of 13.3%. The high sensitive varieties included Xinjiangdaye, Zhongmu No.1, Longzhong, Beijiang, Huangguan, Gansu and Salansi,with the frequency of 23.3%. The rest are all sensitive varieties, with the frequency of 63.4%. There were no resistance and immune varieties. The assay of enzyme activity showed that, for the endured resistance and high sensitive varieties, inoculated or not, there were great variation of CAT, SOD, PAL activity among different varieties. The activity in inoculated plant was higher than that of normal plant. Enzyme activities of endured resistance varieties were stronger than that of susceptible varieties. After inoculated 4-8d the enzymea ctivity showed rising trend, while 8-16 d it drops. CAT activity of inoculation plants increased significantly than control, while SOD, PAL increased smaller.(4) The results showed that the fungicides of 98% fludioxonil and 98% tebuconazole had significant inhibitory effect on Fusarium sporotrichioide growth, and optimum concentration was 1.25 μg/m L, and its inhibitory effect were 90.11% and 83.68%, respectively. However, the fungicides of 98% azoxystrobin and 97% hymexazol had lower inhibitory effect. Pot experiments indicated that the fungicides of 98% fludioxonil had significant effect on Fusarium sporotrichioide, and it EC50 was 2.06 μg/m L. All the compound fungicides had synergy effect except the combinations 4, 8, 9 and 10. Field experiments indicated that the optimum concentrations of 50% fludioxonil and 43% tebuconazole to inhibit Fusarium sporotrichioide growth was 250 g/hm2, which had higher control effect(69.42% and 66.78%) in field. While the combination of 50% fludioxonil(125g/hm2) and 43% tebuconazole(125g/hm2) had synergistic effect and better control effect, and the average control efficacy was 71.39%. |
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