| Dioscorea opposita Thunb, which is the traditional medicinal and edible plants in China, has been well-known for its blood-depressed and the immune system-strengthened activities. In recent years, root rot seriously occurred in Yam cultivation district of Ya’an City, Sichuan Province, as the time of planting increases. The outbreak of this disease led to a serious impact on the yield and quality of the yam. Currently, almost no systemic paper was reported about the disease. The dissertation included the symptom characteristies, the identification of pathogens, biological characteristics and the fungicides screening in laboratory. All results were reported as followed:Two Fusarium sp. were isolated from diseased root of Dioscorea opposita Thunb. in nursery of Ya’an country and were verificated the pathogens of Yam root rot after Koch’s rule. According to morphological observation, the colony diameter of pathogen F1on PSA was4cm after72h cultured at25℃. Colony central slightly white, and the back of the colony turned brick-red, and hyphe were cotton wool. The conidia was sickle-shaped,3to5septas. Chlamydospore was spherical, which were apical or lateral. The back of the F2colony turned yellow after5days on PSA, and two type’s conidia were produced on aerial hypha. The macroconidia were typical mild sickle-shaped curve. Microconidia were oval or elliptical, and at most one septa. According to molecular Identification, F1showed99%of identity with Fusarium chlamydosporum, and F2showed100%of identity with Fusarium solani. Based on the above, the pathogen Fl was identified as Fusarium chlamydosporum and F2was identified as Fusarium solani.Biological characteristic of F. solani indicated that the range of temperature for mycelia growth, conidia produce and conidia germination was15-35℃, and30℃was the optimum temperature for mycelia growth and conidia germination. All light condition was the most suitable for the growth of mycelia and faciliatated the germination of microconidia. The favorable pH value for mycelia growth and produce spores was4-10. Macro-and micro-conidias could not germinat at pH3. The range of pH value for the germination of conidia was4-10, and had no significant difference. F. solani could utilize the tested carbon and nitrogen sources, and glactose and sucrose were the most favorable carbon sources for mycelia growth and the conidia produced. Soluble starch and sucrose were best for macroconidia germination. Lactose was the most favorable for microconidia germination. Peptone was the best nitrogen source for mycelia growth and conidia produce. Ammonium nitrate was the least. The lethal temperatures for mycelia and conidia of F. solani were at55℃,10min and60℃,10min, respectively.Biological characteristic of F. chlamydosporum indicated that30℃was the optimum temperature for conidia germination and mycelia growth. The optimal pH value for mycelia growth and produce spores was4-10. Conidia could not germinate at pH3.0. Full illumination was the better condition for the growth of mycelia and faciliatated the germination of conidia than12h light and dark alternating and full darkness conditions, but had no significance difference on conidia germination. Glactose and glucose were the most favorable carbon source for mycelia growth and conidia produce. Soluble starch and sucrose were the most favorable for conidia germination. Urea was the best nitrate source for mycelia growth and conidia produced. The lethal temperature for mycelia and conidia of F. chlamydosporum were at60℃,10min and65℃,10min, respectively.The toxicities of eight fungicides on F. solani and F. chlamydosporum were assayed and results indicated that the toxicities of imazalilip and uniconazole.on targets strains were the strongest with EC50values of1.40μg/mL,11.13μg/mL and0.17μg/mL,3.73μg/mL respectively and the imazalil had the better pot experiment effect, the effectiveness of field trial was worth further investigations. |
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